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Title: Zoonomia; Or, the Laws of Organic Life, Vol. I

Author: Erasmus Darwin

Release date: April 25, 2005 [eBook #15707]
                Most recently updated: December 14, 2020

Language: English

Credits: Produced by Greg Alethoup, Robert Shimmin, Keith Edkins and the
        Online Distributed Proofreading Team.


*** START OF THE PROJECT GUTENBERG EBOOK ZOONOMIA; OR, THE LAWS OF ORGANIC LIFE, VOL. I ***




Produced by Greg Alethoup, Robert Shimmin, Keith Edkins and the
Online Distributed Proofreading Team.





ZOONOMIA;

OR,

THE LAWS

OF

ORGANIC LIFE.

VOL. I.

_By ERASMUS DARWIN, M.D. F.R.S._

AUTHOR OF THE BOTANIC GARDEN.

       *       *       *       *       *

  Principiò coelum, ac terras, camposque liquentes,
  Lucentemque globum lunæ, titaniaque astra,
  Spiritus intùs alit, totamque infusa per artus
  Mens agitat molem, et magno se corpore miscet.--VIRG. Æn. vi.

  Earth, on whose lap a thousand nations tread,
  And Ocean, brooding his prolific bed,
  Night's changeful orb, blue pole, and silvery zones,
  Where other worlds encircle other suns,
  One Mind inhabits, one diffusive Soul
  Wields the large limbs, and mingles with the whole.

       *       *       *       *       *

_THE SECOND EDITION, CORRECTED._

       *       *       *       *       *

LONDON:
PRINTED FOR. J. JOHNSON, IN ST. PAUL'S CHURCH-YARD.
1796.

Entered at Stationers' Hall.

       *       *       *       *       *

DEDICATION.

To the candid and ingenious Members of the College of Physicians, of the
Royal Philosophical Society, of the Two Universities, and to all those, who
study the Operations of the Mind as a Science, or who practice Medicine as
a Profession, the subsequent Work is, with great respect, inscribed by the
Author,

DERBY, May 1, 1794.

CONTENTS.

            _Preface._
  SECT. I.  _Of Motion._
       II.  _Explanations and Definitions._
      III.  _The Motions of the Retina demonstrated by Experiments._
       IV.  _Laws of Animal Causation._
        V.  _Of the four Faculties or Motions of the Sensorium._
       VI.  _Of the four Classes of Fibrous Motions._
      VII.  _Of Irritative Motions._
     VIII.  _Of Sensitive Motions._
       IX.  _Of Voluntary Motions._
        X.  _Of Associate Motions._
       XI.  _Additional Observations on the Sensorial Powers._
      XII.  _Of Stimulus, Sensorial Exertion, and Fibrous Contraction._
     XIII.  _Of Vegetable Animation._
      XIV.  _Of the Production of Ideas._
       XV.  _Of the Classes of Ideas._
      XVI.  _Of Instinct._
     XVII.  _The Catenation of Animal Motions._
    XVIII.  _Of Sleep._
      XIX.  _Of Reverie._
       XX.  _Of Vertigo._
      XXI.  _Of Drunkenness._
     XXII.  _Of Propensity to Motion. Repetition. Imitation._
    XXIII.  _Of the Circulatory System._
     XXIV.  _Of the Secretion of Saliva, and of Tears. And of the
            Lacrymal Sack._
      XXV.  _Of the Stomach and Intestines._
     XXVI.  _Of the Capillary Glands, and of the Membranes._
    XXVII.  _Of Hemorrhages._
   XXVIII.  _The Paralysis of the Lacteals._
     XXIX.  _The Retrograde Motions of the Absorbent Vessels._
      XXX.  _The Paralysis of the Liver._
     XXXI.  _Of Temperaments._
    XXXII.  _Diseases of Irritation._
   XXXIII.  ---- _of Sensation._
    XXXIV.  ---- _of Volition._
     XXXV.  ---- _of Relation._
    XXXVI.  _The Periods of Diseases._
   XXXVII.  _Of Digestion, Secretion, Nutrition._
  XXXVIII.  _Of the Oxygenation of the Blood in the Lungs and Placenta._
    XXXIX.  _Of Generation._
       XL.  _Of Ocular Spectra._

       *       *       *       *       *

TO

ERASMUS DARWIN,

ON HIS WORK INTITLED

ZOONOMIA,

_By DEWHURST BILSBORROW._

       *       *       *       *       *

  HAIL TO THE BARD! who sung, from Chaos hurl'd
  How suns and planets form'd the whirling world;
  How sphere on sphere Earth's hidden strata bend,
  And caves of rock her central fires defend;
  Where gems new-born their twinkling eyes unfold,               5
  And young ores shoot in arborescent gold.
    How the fair Flower, by Zephyr woo'd, unfurls
  Its panting leaves, and waves its azure curls;
  Or spreads in gay undress its lucid form
  To meet the sun, and shuts it to the storm;                   10
  While in green veins impassion'd eddies move,
  And Beauty kindles into life and love.
    How the first embryon-fibre, sphere, or cube,
  Lives in new forms,--a line,--a ring,--a tube;
  Closed in the womb with limbs unfinish'd laves,               15
  Sips with rude mouth the salutary waves;
  Seeks round its cell the sanguine streams, that pass,
  And drinks with crimson gills the vital gas;
  Weaves with soft threads the blue meandering vein,
  The heart's red concave, and the silver brain;                20
  Leads the long nerve, expands the impatient sense,
  And clothes in silken skin the nascent Ens.
    Erewhile, emerging from its liquid bed,
  It lifts in gelid air its nodding head;
  The lights first dawn with trembling eyelid hails,            25
  With lungs untaught arrests the balmy gales;
  Tries its new tongue in tones unknown, and hears
  The strange vibrations with unpractised ears;
  Seeks with spread hands the bosom's velvet orbs.
  With closing lips the milky fount absorbs;                    30
  And, as compress'd the dulcet streams distil,
  Drinks warmth and fragrance from the living rill;--
  Eyes with mute rapture every waving line,
  Prints with adoring kiss the Paphian shrine,
  And learns erelong, the perfect form confess'd,               35
  Ideal Beauty from its mother's breast.
    Now in strong lines, with bolder tints design'd,
  You sketch ideas, and portray the mind;
  Teach how fine atoms of impinging light
  To ceaseless change the visual sense excite;                  40
  While the bright lens collects the rays, that swerve,
  And bends their focus on the moving nerve.
  How thoughts to thoughts are link'd with viewless chains,
  Tribes leading tribes, and trains pursuing trains;
  With shadowy trident how Volition guides,                     45
  Surge after surge, his intellectual tides;
  Or, Queen of Sleep, Imagination roves
  With frantic Sorrows, or delirious Loves.
    Go on, O FRIEND! explore with eagle-eye;
  Where wrapp'd in night retiring Causes lie:                   50
  Trace their slight bands, their secret haunts betray,
  And give new wonders to the beam of day;
  Till, link by link with step aspiring trod,
  You climb from NATURE to the throne of GOD.
  --So saw the Patriarch with admiring eyes                     55
  From earth to heaven a golden ladder rise;
  Involv'd in clouds the mystic scale ascends,
  And brutes and angels crowd the distant ends.

TRIN. COL. CAMBRIDGE, _Jan._ 1, 1794.

       *       *       *       *       *

REFERENCES TO THE WORK.

          _Botanic Garden._ Part I.

  Line 1.  Canto I.  l. 105.
  ---- 3.  ---- IV.  l. 402.
  ---- 4.  ---- I.  l. 140.
  ---- 5.  ---- III.  l. 401.
  ---- 8.  ---- IV.  l. 452.
  ---- 9.  ---- I.  l. 14.


          _Zoonomia._

  ---- 12.  Sect. XIII.
  ---- 13.  ---- XXXIX. 4. 1.
  ---- 18.  ---- XVI. 2. and XXXVIII.
  ---- 26.  ---- XVI. 4.
  ---- 30.  ---- XVI. 4.
  ---- 36.  ---- XVI. 6.
  ---- 38.  ---- III. and VII.
  ---- 43.  ---- X.
  ---- 44.  ---- XVIII. 17.
  ---- 45.  ---- XVII. 3. 7.
  ---- 47.  ---- XVIII. 8.
  ---- 50.  ---- XXXIX. 4. 8.
  ---- 51.  ---- XXXIX the Motto.
  ---- 54.  ---- XXXIX. 8.

       *       *       *       *       *

PREFACE.

       *       *       *       *       *

The purport of the following pages is an endeavour to reduce the facts
belonging to ANIMAL LIFE into classes, orders, genera, and species; and, by
comparing them with each other, to unravel the theory of diseases. It
happened, perhaps unfortunately for the inquirers into the knowledge of
diseases, that other sciences had received improvement previous to their
own; whence, instead of comparing the properties belonging to animated
nature with each other, they, idly ingenious, busied themselves in
attempting to explain the laws of life by those of mechanism and chemistry;
they considered the body as an hydraulic machine, and the fluids as passing
through a series of chemical changes, forgetting that animation was its
essential characteristic.

The great CREATOR of all things has infinitely diversified the works of his
hands, but has at the same time stamped a certain similitude on the
features of nature, that demonstrates to us, that _the whole is one family
of one parent_. On this similitude is founded all rational analogy; which,
so long as it is concerned in comparing the essential properties of bodies,
leads us to many and important discoveries; but when with licentious
activity it links together objects, otherwise discordant, by some fanciful
similitude; it may indeed collect ornaments for wit and poetry, but
philosophy and truth recoil from its combinations.

The want of a theory, deduced from such strict analogy, to conduct the
practice of medicine is lamented by its professors; for, as a great number
of unconnected facts are difficult to be acquired, and to be reasoned from,
the art of medicine is in many instances less efficacious under the
direction of its wisest practitioners; and by that busy crowd, who either
boldly wade in darkness, or are led into endless error by the glare of
false theory, it is daily practised to the destruction of thousands; add to
this the unceasing injury which accrues to the public by the perpetual
advertisements of pretended nostrums; the minds of the indolent become
superstitiously fearful of diseases, which they do not labour under; and
thus become the daily prey of some crafty empyric.

A theory founded upon nature, that should bind together the scattered facts
of medical knowledge, and converge into one point of view the laws of
organic life, would thus on many accounts contribute to the interest of
society. It would capacitate men of moderate abilities to practise the art
of healing with real advantage to the public; it would enable every one of
literary acquirements to distinguish the genuine disciples of medicine from
those of boastful effrontery, or of wily address; and would teach mankind
in some important situations the _knowledge of themselves_.

There are some modern practitioners, who declaim against medical theory in
general, not considering that to think is to theorize; and that no one can
direct a method of cure to a person labouring under disease without
thinking, that is, without theorizing; and happy therefore is the patient,
whose physician possesses the best theory.

The words idea, perception, sensation, recollection, suggestion, and
association, are each of them used in this treatise in a more limited sense
than in the writers of metaphysic. The author was in doubt, whether he
should rather have substituted new words instead of them; but was at length
of opinion, that new definitions of words already in use would be less
burthensome to the memory of the reader.

A great part of this work has lain by the writer above twenty years, as
some of his friends can testify: he had hoped by frequent revision to have
made it more worthy the acceptance of the public; this however his other
perpetual occupations have in part prevented, and may continue to prevent,
as long as he may be capable of revising it; he therefore begs of the
candid reader to accept of it in its present state, and to excuse any
inaccuracies of expression, or of conclusion, into which the intricacy of
his subject, the general imperfection of language, or the frailty he has in
common with other men, may have betrayed him; and from which he has not the
vanity to believe this treatise to be exempt.

       *       *       *       *       *

ZOONOMIA.

       *       *       *       *       *

SECT. I.

OF MOTION.

The whole of nature may be supposed to consist of two essences or
substances; one of which may be termed spirit, and the other matter. The
former of these possesses the power to commence or produce motion, and the
latter to receive and communicate it. So that motion, considered as a
cause, immediately precedes every effect; and, considered as an effect, it
immediately succeeds every cause.

The MOTIONS OF MATTER may be divided into two kinds, primary and secondary.
The secondary motions are those, which are given to or received from other
matter in motion. Their laws have been successfully investigated by
philosophers in their treatises on mechanic powers. These motions are
distinguished by this circumstance, that the velocity multiplied into the
quantity of matter of the body acted upon is equal to the velocity
multiplied into the quantity of matter of the acting body.

The primary motions of matter may be divided into three classes, those
belonging to gravitation, to chemistry, and to life; and each class has its
peculiar laws. Though these three classes include the motions of solid,
liquid, and aerial bodies; there is nevertheless a fourth division of
motions; I mean those of the supposed ethereal fluids of magnetism,
electricity, heat, and light; whose properties are not so well investigated
as to be classed with sufficient accuracy.

_1st._ The gravitating motions include the annual and diurnal rotation of
the earth and planets, the flux and reflux of the ocean, the descent of
heavy bodies, and other phænomena of gravitation. The unparalleled sagacity
of the great NEWTON has deduced the laws of this class of motions from the
simple principle of the general attraction of matter. These motions are
distinguished by their tendency to or from the centers of the sun or
planets.

_2d._ The chemical class of motions includes all the various appearances of
chemistry. Many of the facts, which belong to these branches of science,
are nicely ascertained, and elegantly classed; but their laws have not yet
been developed from such simple principles as those above-mentioned; though
it is probable, that they depend on the specific attractions belonging to
the particles of bodies, or to the difference of the quantity of attraction
belonging to the sides and angles of those particles. The chemical motions
are distinguished by their being generally attended with an evident
decomposition or new combination of the active materials.

_3d._ The third class includes all the motions of the animal and vegetable
world; as well those of the vessels, which circulate their juices, and of
the muscles, which perform their locomotion, as those of the organs of
sense, which constitute their ideas.

This last class of motion is the subject of the following pages; which,
though conscious of their many imperfections, I hope may give some pleasure
to the patient reader, and contribute something to the knowledge and to the
cure of diseases.

       *       *       *       *       *

SECT. II.

EXPLANATIONS AND DEFINITIONS.

    I. _Outline of the animal economy._--II. 1. _Of the sensorium._ 2. _Of
    the brain and nervous medulla._ 3. _A nerve._ 4. _A muscular fibre._ 5.
    _The immediate organs of sense._ 6. _The external organs of sense._ 7.
    _An idea or sensual motion._ 8. _Perception._ 9. _Sensation._ 10.
    _Recollection and suggestion._ 11. _Habit, causation, association,
    catenation._ 12. _Reflex ideas._ 13. _Stimulus defined._

       *       *       *       *       *

    As some explanations and definitions will be necessary in the
    prosecution of the work, the reader is troubled with them in this
    place, and is intreated to keep them in his mind as he proceeds, and to
    take them for granted, till an apt opportunity occurs to evince their
    truth; to which I shall premise a very short outline of the animal
    economy.

       *       *       *       *       *

I.--1. The nervous system has its origin from the brain, and is distributed
to every part of the body. Those nerves, which serve the senses,
principally arise from that part of the brain, which is lodged in the head;
and those, which serve the purposes of muscular motion, principally arise
from that part of the brain, which is lodged in the neck and back, and
which is erroneously called the spinal marrow. The ultimate fibrils of
these nerves terminate in the immediate organs of sense and muscular
fibres, and if a ligature be put on any part of their passage from the head
or spine, all motion and perception cease in the parts beneath the
ligature.

2. The longitudinal muscular fibres compose the locomotive muscles, whose
contractions move the bones of the limbs and trunk, to which their
extremities are attached. The annular or spiral muscular fibres compose the
vascular muscles, which constitute the intestinal canal, the arteries,
veins, glands, and absorbent vessels.

3. The immediate organs of sense, as the retina of the eye, probably
consist of moving fibrils, with a power of contraction similar to that of
the larger muscles above described.

4. The cellular membrane consists of cells, which resemble those of a
sponge, communicating with each other, and connecting together all the
other parts of the body.

5. The arterial system consists of the aortal and the pulmonary artery,
which are attended through their whole course with their correspondent
veins. The pulmonary artery receives the blood from the right chamber of
the heart, and carries it to the minute extensive ramifications of the
lungs, where it is exposed to the action of the air on a surface equal to
that of the whole external skin, through the thin moist coats of those
vessels, which are spread on the air-cells, which constitute the minute
terminal ramifications of the wind-pipe. Here the blood changes its colour
from a dark red to a bright scarlet. It is then collected by the branches
of the pulmonary vein, and conveyed to the left chamber of the heart.

6. The aorta is another large artery, which receives the blood from the
left chamber of the heart, after it has been thus aerated in the lungs, and
conveys it by ascending and descending branches to every other part of the
system; the extremities of this artery terminate either in glands, as the
salivary glands, lacrymal glands, &c. or in capillary vessels, which are
probably less involuted glands; in these some fluid, as saliva, tears,
perspiration, are separated from the blood; and the remainder of the blood
is absorbed or drank up by branches of veins correspondent to the branches
of the artery; which are furnished with valves to prevent its return; and
is thus carried back, after having again changed its colour to a dark red,
to the right chamber of the heart. The circulation of the blood in the
liver differs from this general system; for the veins which drink up the
refluent blood from those arteries, which are spread on the bowels and
mesentery, unite into a trunk in the liver, and form a kind of artery,
which is branched into the whole substance of the liver, and is called the
vena portarum; and from which the bile is separated by the numerous hepatic
glands, which constitute that viscus.

7. The glands may be divided into three systems, the convoluted glands,
such as those above described, which separate bile, tears, saliva, &c.
Secondly, the glands without convolution, as the capillary vessels, which
unite the terminations of the arteries and veins; and separate both the
mucus, which lubricates the cellular membrane, and the perspirable matter,
which preserves the skin moist and flexible. And thirdly, the whole
absorbent system, consisting of the lacteals, which open their mouths into
the stomach and intestines, and of the lymphatics, which open their mouths
on the external surface of the body, and on the internal linings of all the
cells of the cellular membrane, and other cavities of the body.

These lacteal and lymphatic vessels are furnished with numerous valves to
prevent the return of the fluids, which they absorb, and terminate in
glands, called lymphatic glands, and may hence be considered as long necks
or mouths belonging to these glands. To these they convey the chyle and
mucus, with a part of the perspirable matter, and atmospheric moisture; all
which, after having passed through these glands, and having suffered some
change in them, are carried forward into the blood, and supply perpetual
nourishment to the system, or replace its hourly waste.

8. The stomach and intestinal canal have a constant vermicular motion,
which carries forwards their contents, after the lacteals have drank up the
chyle from them; and which is excited into action by the stimulus of the
aliment we swallow, but which becomes occasionally inverted or retrograde,
as in vomiting, and in the iliac passion.

II. 1. The word _sensorium_ in the following pages is designed to express
not only the medullary part of the brain, spinal marrow, nerves, organs of
sense, and of the muscles; but also at the same time that living principle,
or spirit of animation, which resides throughout the body, without being
cognizable to our senses, except by its effects. The changes which
occasionally take place in the sensorium, as during the exertions of
volition, or the sensations of pleasure or pain, are termed _sensorial
motions_.

2. The similarity of the texture of the brain to that of the pancreas, and
some other glands of the body, has induced the inquirers into this subject
to believe, that a fluid, perhaps much more subtile than the electric aura,
is separated from the blood by that organ for the purposes of motion and
sensation. When we recollect, that the electric fluid itself is actually
accumulated and given out voluntarily by the torpedo and the gymnotus
electricus, that an electric shock will frequently stimulate into motion a
paralytic limb, and lastly that it needs no perceptible tubes to convey it,
this opinion seems not without probability; and the singular figure of the
brain and nervous system seems well adapted to distribute it over every
part of the body.

For the medullary substance of the brain not only occupies the cavities of
the head and spine, but passes along the innumerable ramifications of the
nerves to the various muscles and organs of sense. In these it lays aside
its coverings, and is intermixed with the slender fibres, which constitute
those muscles and organs of sense. Thus all these distant ramifications of
the sensorium are united at one of their extremities, that is, in the head
and spine; and thus these central parts of the sensorium constitute a
communication between all the organs of sense and muscles.

3. A _nerve_ is a continuation of the medullary substance of the brain from
the head or spine towards the other parts of the body, wrapped in its
proper membrane.

4. The _muscular fibres_ are moving organs intermixed with that medullary
substance, which is continued along the nerves, as mentioned above. They
are indued with the power of contraction, and are again elongated either by
antagonist muscles, by circulating fluids, or by elastic ligaments. So the
muscles on one side of the forearm bend the fingers by means of their
tendons, and those on the other side of the fore-arm extend them again. The
arteries are distended by the circulating blood; and in the necks of
quadrupeds there is a strong elastic ligament, which assists the muscles,
which elevate the head, to keep it in its horizontal position, and to raise
it after it has been depressed.

5. The _immediate organs of sense_ consist in like manner of moving fibres
enveloped in the medullary substance above mentioned; and are erroneously
supposed to be simply an expansion of the nervous medulla, as the retina of
the eye, and the rete mucosum of the skin, which are the immediate organs
of vision, and of touch. Hence when we speak of the contractions of the
fibrous parts of the body, we shall mean both the contractions of the
muscles, and those of the immediate organs of sense. These _fibrous
motions_ are thus distinguished from the _sensorial motions_ above
mentioned.

6. The _external organs_ of sense are the coverings of the immediate organs
of sense, and are mechanically adapted for the reception or transmission of
peculiar bodies, or of their qualities, as the cornea and humours of the
eye, the tympanum of the ear, the cuticle of the fingers and tongue.

7. The word _idea_ has various meanings in the writers of metaphysic: it is
here used simply for those notions of external things, which our organs of
sense bring us acquainted with originally; and is defined a contraction, or
motion, or configuration, of the fibres, which constitute the immediate
organ of sense; which will be explained at large in another part of the
work. Synonymous with the word idea, we shall sometimes use the words
_sensual motion_ in contradistinction to _muscular motion_.

8. The word _perception_ includes both the action of the organ of sense in
consequence of the impact of external objects, and our attention to that
action; that is, it expresses both the motion of the organ of sense, or
idea, and the pain or pleasure that succeeds or accompanies it.

9. The pleasure or pain which necessarily accompanies all those perceptions
or ideas which we attend to, either gradually subsides, or is succeeded by
other fibrous motions. In the latter case it is termed _sensation_, as
explained in Sect. V. 2, and VI. 2.--The reader is intreated to keep this
in his mind, that through all this treatise the word sensation is used to
express pleasure or pain only in its active state, by whatever means it is
introduced into the system, without any reference to the stimulation of
external objects.

10. The vulgar use of the word _memory_ is too unlimited for our purpose:
those ideas which we voluntarily recall are here termed ideas of
_recollection_, as when we will to repeat the alphabet backwards. And those
ideas which are suggested to us by preceding ideas are here termed ideas of
_suggestion_, as whilst we repeat the alphabet in the usual order; when by
habits previously acquired B is suggested by A, and C by B, without any
effort of deliberation.

11. The word _association_ properly signifies a society or convention of
things in some respects similar to each other. We never say in common
language, that the effect is associated with the cause, though they
necessarily accompany or succeed each other. Thus the contractions of our
muscles and organs of sense may be said to be associated together, but
cannot with propriety be said to be associated with irritations, or with
volition, or with sensation; because they are caused by them, as mentioned
in Sect. IV. When fibrous contractions succeed other fibrous contractions,
the connection is termed _association_; when fibrous contractions succeed
sensorial motions, the connection is termed _causation_; when fibrous and
sensorial motions reciprocally introduce each other in progressive trains
or tribes, it is termed _catenation_ of animal motions. All these
connections are said to be produced by _habit_; that is, by frequent
repetition.

12. It may be proper to observe, that by the unavoidable idiom of our
language the ideas of perception, of recollection, or of imagination, in
the plural number signify the ideas belonging to perception, to
recollection, or to imagination; whilst the idea of perception, of
recollection, or of imagination, in the singular number is used for what is
termed "a reflex idea of any of those operations of the sensorium."

13. By the word _stimulus_ is not only meant the application of external
bodies to our organs of sense and muscular fibres, which excites into
action the sensorial power termed irritation; but also pleasure or pain,
when they excite into action the sensorial power termed sensation; and
desire or aversion, when they excite into action the power of volition; and
lastly, the fibrous contractions which precede association; as is further
explained in Sect. XII. 2. 1.

       *       *       *       *       *

SECT. III.

THE MOTIONS OF THE RETINA DEMONSTRATED BY EXPERIMENTS.

    I. _Of animal motions and of ideas._ II. _The fibrous structure of the
    retina._ III. _The activity of the retina in vision._ 1. _Rays of light
    have no momentum._ 2. _Objects long viewed become fainter._ 3. _Spectra
    of black objects become luminous._ 4. _Varying spectra from gyration._
    5. _From long inspection of various colours._ IV. _Motions of the
    organs of sense constitute ideas._ 1. _Light from pressing the
    eye-ball, and sound from the pulsation of the carotid artery._ 2.
    _Ideas in sleep mistaken for perceptions._ 3. _Ideas of imagination
    produce pain and sickness like sensations._ 4. _When the organ of sense
    is destroyed, the ideas belonging to that sense perish._ V. _Analogy
    between muscular motions and sensual motions, or ideas._ 1. _They are
    both originally excited by irritations._ 2. _And associated together in
    the same manner._ 3. _Both act in nearly the same times._ 4. _Are alike
    strengthened or fatigued by exercise._ 5. _Are alike painful from
    inflammation._ 6. _Are alike benumbed by compression._ 7. _Are alike
    liable to paralysis._ 8. _To convulsion._ 9. _To the influence of old
    age._--VI. _Objections answered._ 1. _Why we cannot invent new ideas._
    2. _If ideas resemble external objects._ 3. _Of the imagined sensation
    in an amputated limb._ 4. _Abstract ideas._--VII. _What are ideas, if
    they are not animal motions?_

Before the great variety of animal motions can be duly arranged into
natural classes and orders, it is necessary to smooth the way to this yet
unconquered field of science, by removing some obstacles which thwart our
passage. I. To demonstrate that the retina and other immediate organs of
sense possess a power of motion, and that these motions constitute our
ideas, according to the fifth and seventh of the preceding assertions,
claims our first attention.

Animal motions are distinguished from the communicated motions, mentioned
in the first section, as they have no mechanical proportion to their cause;
for the goad of a spur on the skin of a horse shall induce him to move a
load of hay. They differ from the gravitating motions there mentioned as
they are exerted with equal facility in all directions, and they differ
from the chemical class of motions, because no apparent decompositions or
new combinations are produced in the moving materials.

Hence, when we say animal motion is excited by irritation, we do not mean
that the motion bears any proportion to the mechanical impulse of the
stimulus; nor that it is affected by the general gravitation of the two
bodies; nor by their chemical properties, but solely that certain animal
fibres are excited into action by something external to the moving organ.

In this sense the stimulus of the blood produces the contractions of the
heart; and the substances we take into our stomach and bowels stimulate
them to perform their necessary functions. The rays of light excite the
retina into animal motion by their stimulus; at the same time that those
rays of light themselves are physically converged to a focus by the
inactive humours of the eye. The vibrations of the air stimulate the
auditory nerve into animal action; while it is probable that the tympanum
of the ear at the same time undergoes a mechanical vibration.

To render this circumstance more easy to be comprehended, _motion may be
defined to be a variation of figure_; for the whole universe may be
considered as one thing possessing a certain figure; the motions of any of
its parts are a variation of this figure of the whole: this definition of
motion will be further explained in Section XIV. 2. 2. on the production of
ideas.

Now the motions of an organ of sense are a succession of configurations of
that organ; these configurations succeed each other quicker or slower; and
whatever configuration of this organ of sense, that is, whatever portion of
the motion of it is, or has usually been, attended to, constitutes an idea.
Hence the configuration is not to be considered as an effect of the motion
of the organ, but rather as a part or temporary termination of it; and
that, whether a pause succeeds it, or a new configuration immediately takes
place. Thus when a succession of moving objects are presented to our view,
the ideas of trumpets, horns, lords and ladies, trains and canopies, are
configurations, that is, parts or links of the successive motions of the
organ of vision.

[Illustration: Plate I.]

These motions or configurations of the organs of sense differ from the
sensorial motions to be described hereafter, as they appear to be simply
contractions of the fibrous extremities of those organs, and in that
respect exactly resemble the motions or contractions of the larger muscles,
as appears from the following experiment. Place a circular piece of red
silk about an inch in diameter on a sheet of white paper in a strong light,
as in Plate I.--look for a minute on this area, or till the eye becomes
somewhat fatigued, and then, gently closing your eyes, and shading them
with your hand, a circular green area of the same apparent diameter becomes
visible in the closed eye. This green area is the colour reverse to the red
area, which had been previously inspected, as explained in the experiments
on ocular spectra at the end of the work, and in Botanical Garden, P. 1.
additional note, No. 1. Hence it appears, that a part of the retina, which
had been fatigued by contraction in one direction, relieves itself by
exerting the antagonist fibres, and producing a contraction in an opposite
direction, as is common in the exertions of our muscles. Thus when we are
tired with long action of our arms in one direction, as in holding a bridle
on a journey, we occasionally throw them into an opposite position to
relieve the fatigued muscles.

Mr. Locke has defined an idea to be "whatever is present to the mind;" but
this would include the exertions of volition, and the sensations of
pleasure and pain, as well as those operations of our system, which
acquaint us with external objects; and is therefore too unlimited for our
purpose. Mr. Lock seems to have fallen into a further error, by conceiving,
that the mind could form a general or abstract idea by its own operation,
which was the copy of no particular perception; as of a triangle in
general, that was neither acute, obtuse, nor right angled. The ingenious
Dr. Berkley and Mr. Hume have demonstrated, that such general ideas have no
existence in nature, not even in the mind of their celebrated inventor. We
shall therefore take for granted at present, that our recollection or
imagination of external objects consists of a partial repetition of the
perceptions, which were excited by those external objects, at the time we
became acquainted with them; and that our reflex ideas of the operations of
our minds are partial repetitions of those operations.

II. The following article evinces that the organ of vision consists of a
fibrous part as well as of the nervous medulla, like other white muscles;
and hence, as it resembles the muscular parts of the body in its structure,
we may conclude, that it must resemble them in possessing a power of being
excited into animal motion.--The subsequent experiments on the optic nerve,
and on the colours remaining in the eye, are copied from a paper on ocular
spectra published in the seventy-sixth volume of the Philos. Trans. by Dr.
R. Darwin of Shrewsbury; which, as I shall have frequent occasion to refer
to, is reprinted in this work, Sect. XL. The retina of an ox's eye was
suspended in a glass of warm water, and forcibly torn in a few places; the
edges of these parts appeared jagged and hairy, and did not contract and
become smooth like simple mucus, when it is distended till it breaks; which
evinced that it consisted of fibres. This fibrous construction became still
more distinct to the light by adding some caustic alcali to the water; as
the adhering mucus was first eroded, and the hair-like fibres remained
floating in the vessel. Nor does the degree of transparency of the retina
invalidate this evidence of its fibrous structure, since Leeuwenhoek has
shewn, that the crystalline humour itself consists of fibres. Arc. Nat. V.
I. 70.

Hence it appears, that as the muscles consist of larger fibres intermixed
with a smaller quantity of nervous medulla, the organ of vision consists of
a greater quantity of nervous medulla intermixed with smaller fibres. It is
probable that the locomotive muscles of microscopic animals may have
greater tenuity than these of the retina; and there is reason to conclude
from analogy, that the other immediate organs of sense, as the portio
mollis of the auditory nerve, and the rete mucosum of the skin, possess a
similarity of structure with the retina, and a similar power of being
excited into animal motion.

III. The subsequent articles shew, that neither mechanical impressions, nor
chemical combinations of light, but that the animal activity of the retina
constitutes vision.

1. Much has been conjectured by philosophers about the momentum of the rays
of light; to subject this to experiment a very light horizontal balance was
constructed by Mr. Michel, with about an inch square of thin leaf-copper
suspended at each end of it, as described in Dr. Priestley's History of
Light and Colours. The focus of a very large convex mirror was thrown by
Dr. Powel, in his lectures on experimental philosophy, in my presence, on
one wing of this delicate balance, and it receded from the light; thrown on
the other wing, it approached towards the light, and this repeatedly; so
that no sensible impulse could be observed, but what might well be ascribed
to the ascent of heated air.

Whence it is reasonable to conclude, that the light of the day must be much
too weak in its dilute state to make any mechanical impression on so
tenacious a substance as the retina of the eye.--Add to this, that as the
retina is nearly transparent, it could therefore make less resistance to
the mechanical impulse of light; which, according, to the observations
related by Mr. Melvil in the Edinburgh Literary Essays, only communicates
heat, and should therefore only communicate momentum, where it is
obstructed, reflected, or refracted.--From whence also may be collected the
final cause of this degree of transparency of the retina, viz. left by the
focus of stronger lights, heat and pain should have been produced in the
retina, instead of that stimulus which excites it into animal motion.

2. On looking long on an area of scarlet silk of about an inch in diameter
laid on white paper, as in Plate I. the scarlet colour becomes fainter,
till at length it entirely vanishes, though the eye is kept uniformly and
steadily upon it. Now if the change or motion of the retina was a
mechanical impression, or a chemical tinge of coloured light, the
perception would every minute become stronger and stronger,--whereas in
this experiment it becomes every instant weaker and weaker. The same
circumstance obtains in the continued application of sound, or of sapid
bodies, or of odorous ones, or of tangible ones, to their adapted organs of
sense.

[Illustration: Plate II.]

Thus when a circular coin, as a shilling, is pressed on the palm of the
hand, the sense of touch is mechanically compressed; but it is the stimulus
of this pressure that excites the organ of touch into animal action, which
constitutes the perception of hardness and of figure; for in some minutes
the perception ceases, though the mechanical pressure of the object
remains.

3. Make with ink on white paper a very black spot about half an inch in
diameter, with a tail about an inch in length, so as to resemble a tadpole,
as in Plate II.; look steadfastly for a minute on the center of this spot,
and, on moving the eye a little, the figure of the tadpole will be seen on
the white part of the paper; which figure of the tadpole will appear more
luminous than the other part of the white paper; which can only be
explained by supposing that a part of the retina, on which the tadpole was
delineated, to have become more sensible to light than the other parts of
it, which were exposed to the white paper; and not from any idea of
mechanical impression or chemical combination of light with the retina.

4. When any one turns round rapidly, till he becomes dizzy, and falls upon
the ground, the spectra of the ambient objects continue to present
themselves in rotation, and he seems to behold the objects still in motion.
Now if these spectra were impressions on a passive organ, they either must
continue as they were received last, or not continue at all.

5. Place a piece of red silk about an inch in diameter on a sheet of white
paper in a strong light, as in Plate I; look steadily upon it from the
distance of about half a yard for a minute; then closing your eye-lids,
cover them with your hands and handkerchief, and a green spectrum will be
seen in your eyes resembling in form the piece of red silk. After some
seconds of time the spectrum will disappear, and in a few more seconds will
reappear; and thus alternately three or four times, if the experiment be
well made, till at length it vanishes entirely.

[Illustration: Plate III.]

6. Place a circular piece of white paper, about four inches in diameter, in
the sunshine, cover the center of this with a circular piece of black silk,
about three inches in diameter; and the center of the black silk with a
circle of pink silk, about two inches in diameter; and the center of the
pink silk with a circle of yellow silk, about one inch in diameter; and the
center of this with a circle of blue silk, about half an inch in diameter;
make a small spot with ink in the center of the blue silk, as in Plate
III.; look steadily for a minute on this central spot, and then closing
your eyes, and applying your hand at about an inch distance before them, so
as to prevent too much or too little light from passing through the
eye-lids, and you will see the most beautiful circles of colours that
imagination can conceive; which are most resembled by the colours
occasioned by pouring a drop or two of oil on a still lake in a bright day.
But these circular irises of colours are not only different from the
colours of the silks above mentioned, but are at the same time perpetually
changing as long as they exist.

From all these experiments it appears, that these spectra in the eye are
not owing to the mechanical impulse of light impressed on the retina; nor
to its chemical combination with that organ; nor to the absorption and
emission of light, as is supposed, perhaps erroneously, to take place in
calcined shells and other phosphorescent bodies, after having been exposed
to the light: for in all these cases the spectra in the eye should either
remain of the same colour, or gradually decay, when the object is
withdrawn; and neither their evanescence during the presence of their
object, as in the second experiment, nor their change from dark to
luminous, as in the third experiment, nor their rotation, as in the fourth
experiment, nor the alternate presence and evanescence of them, as in the
fifth experiment, nor the perpetual change of colours of them, as in the
last experiment, could exist.

IV. The subsequent articles shew, that these animal motions or
configurations of our organs of sense constitute our ideas.

1. If any one in the dark presses the ball of his eye, by applying his
finger to the external corner of it, a luminous appearance is observed; and
by a smart stroke on the eye great slashes of fire are perceived. (Newton's
Optics.) So that when the arteries, that are near the auditory nerve, make
stronger pulsations than usual, as in some fevers, an undulating sound is
excited in the ears. Hence it is not the presence of the light and sound,
but the motions of the organ, that are immediately necessary to constitute
the perception or idea of light and sound.

2. During the time of sleep, or in delirium, the ideas of imagination are
mistaken for the perceptions of external objects; whence it appears, that
these ideas of imagination, are no other than a reiteration of those
motions of the organs of sense, which were originally excited by the
stimulus of external objects: and in our waking hours the simple ideas,
that we call up by recollection or by imagination, as the colour of red, or
the smell of a rose, are exact resemblances of the same simple ideas from
perception; and in consequence must be a repetition of those very motions.

3. The disagreeable sensation called the tooth-edge is originally excited
by the painful jarring of the teeth in biting the edge of the glass, or
porcelain cup, in which our food was given us in our infancy, as is further
explained in the Section XVI. 10, on Instinct.--This disagreeable sensation
is afterwards excitable not only by a repetition of the sound, that was
then produced, but by imagination alone, as I have myself frequently
experienced; in this case the idea of biting a china cup, when I imagine it
very distinctly, or when I see another person bite a cup or glass, excites
an actual pain in the nerves of my teeth. So that this idea and pain seem
to be nothing more than the reiterated motions of those nerves, that were
formerly so disagreeably affected.

Other ideas that are excited by imagination or recollection in many
instances produce similar effects on the constitution, as our perceptions
had formerly produced, and are therefore undoubtedly a repetition of the
same motions. A story which the celebrated Baron Van Swieton relates of
himself is to this purpose. He was present when the putrid carcase of a
dead dog exploded with prodigious stench; and some years afterwards,
accidentally riding along the same road, he was thrown into the same
sickness and vomiting by the idea of the stench, as he had before
experienced from the perception of it.

4. Where the organ of sense is totally destroyed, the ideas which were
received by that organ seem to perish along with it, as well as the power
of perception. Of this a satisfactory instance has fallen under my
observation. A gentleman about sixty years of age had been totally deaf for
near thirty years: he appeared to be a man of good understanding, and
amused himself with reading, and by conversing either by the use of the
pen, or by signs made with his fingers, to represent letters. I observed
that he had so far forgot the pronunciation of the language, that when he
attempted to speak, none of his words had distinct articulation, though his
relations could sometimes understand his meaning. But, which is much to the
point, he assured me, that in his dreams he always imagined that people
conversed with him by signs or writing, and never that he heard any one
speak to him. From hence it appears, that with the perceptions of sounds he
has also lost the ideas of them; though the organs of speech still retain
somewhat of their usual habits of articulation.

This observation may throw some light on the medical treatment of deaf
people; as it may be learnt from their dreams whether the auditory nerve be
paralytic, or their deafness be owing to some defect of the external organ.

It rarely happens that the immediate organ of vision is perfectly
destroyed. The most frequent causes of blindness are occasioned by defects
of the external organ, as in cataracts and obfuscations of the cornea. But
I have had the opportunity of conversing with two men, who had been some
years blind; one of them had a complete gutta serena, and the other had
lost the whole substance of his eyes. They both told me that they did not
remember to have ever dreamt of visible objects, since the total loss of
their sight.

V. Another method of discovering that our ideas are animal motions of the
organs of sense, is from considering the great analogy they bear to the
motions of the larger muscles of the body. In the following articles it
will appear that they are originally excited into action by the irritation
of external objects like our muscles; are associated together like our
muscular motions; act in similar time with them; are fatigued by continued
exertion like them; and that the organs of sense are subject to
inflammation, numbness, palsy, convulsion, and the defects of old age, in
the same manner as the muscular fibres.

1. All our perceptions or ideas of external objects are universally allowed
to have been originally excited by the stimulus of those external objects;
and it will be shewn in a succeeding section, that it is probable that all
our muscular motions, as well those that are become voluntary as those of
the heart and glandular system, were originally in like manner excited by
the stimulus of something external to the organ of motion.

2. Our ideas are also associated together after their production precisely
in the same manner as our muscular motions; which will likewise be fully
explained in the succeeding section.

3. The time taken up in performing an idea is likewise much the same as
that taken up in performing a muscular motion. A musician can press the
keys of an harpsichord with his fingers in the order of a tune he has been
accustomed to play, in as little time as he can run over those notes in his
mind. So we many times in an hour cover our eye-balls with our eye-lids
without perceiving that we are in the dark; hence the perception or idea of
light is not changed for that of darkness in so small a time as the
twinkling of an eye; so that in this case the muscular motion of the
eye-lid is performed quicker than the perception of light can be changed
for that of darkness.--So if a fire-stick be whirled round in the dark, a
luminous circle appears to the observer; if it be whirled somewhat slower,
this circle becomes interrupted in one part; and then the time taken up in
such a revolution of the stick is the same that the observer uses in
changing his ideas: thus the [Greek: dolikoskoton enkos] of Homer, the long
shadow of the flying javelin, is elegantly designed to give us an idea of
its velocity, and not of its length.

4. The fatigue that follows a continued attention of the mind to one object
is relieved by changing the subject of our thoughts; as the continued
movement of one limb is relieved by moving another in its stead. Whereas a
due exercise of the faculties of the mind strengthens and improves those
faculties, whether of imagination or recollection; as the exercise of our
limbs in dancing or fencing increases the strength and agility of the
muscles thus employed.

5. If the muscles of any limb are inflamed, they do not move without pain;
so when the retina is inflamed, its motions also are painful. Hence light
is as intolerable in this kind of ophthalmia, as pressure is to the finger
in the paronychia. In this disease the patients frequently dream of having
their eyes painfully dazzled; hence the idea of strong light is painful as
well as the reality. The first of these facts evinces that our perceptions
are motions of the organs of sense; and the latter, that our imaginations
are also motions of the same organs.

6. The organs of sense, like the moving muscles, are liable to become
benumbed, or less sensible, from compression. Thus, if any person on a
light day looks on a white wall, he may perceive the ramifications of the
optic artery, at every pulsation of it, represented by darker branches on
the white wall; which is evidently owing to its compressing the retina
during the diastole of the artery. Savage Nosolog.

7. The organs of sense and the moving muscles are alike liable to be
affected with palsy, as in the gutta serena, and in some cases of deafness;
and one side of the face has sometimes lost its power of sensation, but
retained its power of motion; other parts of the body have lost their
motions but retained their sensation, as in the common hemiplagia; and in
other instances both these powers have perished together.

8. In some convulsive diseases a delirium or insanity supervenes, and the
convulsions cease; and conversely the convulsions shall supervene, and the
delirium cease. Of this I have been a witness many times in a day in the
paroxysms of violent epilepsies; which evinces that one kind of delirium is
a convulsion of the organs of sense, and that our ideas are the motions of
these organs: the subsequent cases will illustrate this observation.

Miss G----, a fair young lady, with light eyes and hair, was seized with
most violent convulsions of her limbs, with outrageous hiccough, and most
vehement efforts to vomit: after near an hour was elapsed this tragedy
ceased, and a calm talkative delirium supervened for about another hour;
and these relieved each other at intervals during the greatest part of
three or four days. After having carefully considered this disease, I
thought the convulsions of her ideas less dangerous than those of her
muscles; and having in vain attempted to make any opiate continue in her
stomach, an ounce of laudanum was rubbed along the spine of her back, and a
dram of it was used as an enema; by this medicine a kind of drunken
delirium was continued many hours; and when it ceased the convulsions did
not return; and the lady continued well many years, except some lighter
relapses, which were relieved in the same manner.

Miss H----, an accomplished young lady, with light eyes and hair, was
seized with convulsions of her limbs, with hiccough, and efforts to vomit,
more violent than words can express; these continued near an hour, and were
succeeded with a cataleptic spasm of one arm, with the hand applied to her
head; and after about twenty minutes these spasms ceased, and a talkative
reverie supervened for near an other hour, from which no violence, which it
was proper to use, could awaken her. These periods of convulsions, first of
the muscles, and then of the ideas, returned twice a day for several weeks;
and were at length removed by great doses of opium, after a great variety
of other medicines and applications had been in vain experienced. This lady
was subject to frequent relapses, once or twice a year for many years, and
was as frequently relieved by the same method.

Miss W----, an elegant young lady, with black eyes and hair, had sometimes
a violent pain of her side, at other times a most painful strangury, which
were every day succeeded by delirium; which gave a temporary relief to the
painful spasms. After the vain exhibition of variety of medicines and
applications by different physicians, for more than a twelvemonth, she was
directed to take some doses of opium, which were gradually increased, by
which a drunken delirium was kept up for a day or two, and the pains
prevented from returning. A flesh diet, with a little wine or beer, instead
of the low regimen she had previously used, in a few weeks completely
established her health; which, except a few relapses, has continued for
many years.

9. Lastly, as we advance in life all the parts of the body become more
rigid, and are rendered less susceptible of new habits of motion, though
they retain those that were before established. This is sensibly observed
by those who apply themselves late in life to music, fencing, or any of the
mechanic arts. In the same manner many elderly people retain the ideas they
had learned early in life, but find great difficulty in acquiring new
trains of memory; insomuch that in extreme old age we frequently see a
forgetfulness of the business of yesterday, and at the same time a
circumstantial remembrance of the amusements of their youth; till at length
the ideas of recollection and activity of the body gradually cease
together,--such is the condition of humanity!--and nothing remains but the
vital motions and sensations.

VI. 1. In opposition to this doctrine of the production of our ideas, it
may be asked, if some of our ideas, like other animal motions, are
voluntary, why can we not invent new ones, that have not been received by
perception? The answer will be better understood after having perused the
succeeding section, where it will be explained, that the muscular motions
likewise are originally excited by the stimulus of bodies external to the
moving organ; and that the will has only the power of repeating the motions
thus excited.

2. Another objector may ask, Can the motion of an organ of sense resemble
an odour or a colour? To which I can only answer, that it has not been
demonstrated that any of our ideas resemble the objects that excite them;
it has generally been believed that they do not; but this shall be
discussed at large in Sect. XIV.

3. There is another objection that at first view would seem less easy to
surmount. After the amputation, of a foot or a finger, it has frequently
happened, that an injury being offered to the stump of the amputated limb,
whether from cold air, too great pressure, or other accidents, the patient
has complained, of a sensation of pain in the foot or finger, that was cut
off. Does not this evince that all our ideas are excited in the brain, and
not in the organs of sense? This objection is answered, by observing that
our ideas of the shape, place, and solidity of our limbs, are acquired by
our organs of touch and of sight, which are situated in our fingers and
eyes, and not by any sensations in the limb itself.

In this case the pain or sensation, which formerly has arisen in the foot
or toes, and been propagated along the nerves to the central part of the
sensorium, was at the same time accompanied with a visible idea of the
shape and place, and with a tangible idea of the solidity of the affected
limb: now when these nerves are afterwards affected by any injury done to
the remaining stump with a similar degree or kind of pain, the ideas of the
shape, place, or solidity of the lost limb, return by association; as these
ideas belong to the organs of sight and touch, on which they were first
excited.

4. If you wonder what organs of sense can be excited into motion, when you
call up the ideas of wisdom or benevolence, which Mr. Locke has termed
abstracted ideas; I ask you by what organs of sense you first became
acquainted with these ideas? And the answer will be reciprocal; for it is
certain that all our ideas were originally acquired by our organs of sense;
for whatever excites our perception must be external to the organ that
perceives it, and we have no other inlets to knowledge but by our
perceptions: as will be further explained in Section XIV. and XV. on the
Productions and Classes of Ideas.

VII. If our recollection or imagination be not a repetition of animal
movements, I ask, in my turn, What is it? You tell me it consists of images
or pictures of things. Where is this extensive canvas hung up? or where are
the numerous receptacles in which those are deposited? or to what else in
the animal system have they any similitude?

That pleasing picture of objects, represented in miniature on the retina of
the eye, seems to have given rise to this illusive oratory! It was forgot
that this representation belongs rather to the laws of light, than to those
of life; and may with equal elegance be seen in the camera obscura as in
the eye; and that the picture vanishes for ever, when the object is
withdrawn.

       *       *       *       *       *

SECT. IV.

LAWS OF ANIMAL CAUSATION.

I. The fibres, which constitute the muscles and organs of sense, possess a
power of contraction. The circumstances attending the exertion of this
power of CONTRACTION constitute the laws of animal motion, as the
circumstances attending the exertion of the power of ATTRACTION constitute
the laws of motion of inanimate matter.

II. The spirit of animation is the immediate cause of the contraction of
animal fibres, it resides in the brain and nerves, and is liable to general
or partial diminution or accumulation.

III. The stimulus of bodies external to the moving organ is the remote
cause of the original contractions of animal fibres.

IV. A certain quantity of stimulus produces irritation, which is an
exertion of the spirit of animation exciting the fibres into contraction.

V. A certain quantity of contraction of animal fibres, if it be perceived
at all, produces pleasure; a greater or less quantity of contraction, if it
be perceived at all, produces pain; these constitute sensation.

VI. A certain quantity of sensation produces desire or aversion; these
constitute volition.

VII. All animal motions which have occurred at the same time, or in
immediate succession, become so connected, that when one of them is
reproduced, the other has a tendency to accompany or succeed it. When
fibrous contractions succeed or accompany other fibrous contractions, the
connection is termed association; when fibrous contractions succeed
sensorial motions, the connexion is termed causation; when fibrous and
sensorial motions reciprocally introduce each other, it is termed
catenation of animal motions. All these connections are said to be produced
by habit, that is, by frequent repetition. These laws of animal causation
will be evinced by numerous facts, which occur in our daily exertions; and
will afterwards be employed to explain the more recondite phænomena of the
production, growth, diseases, and decay of the animal system.

       *       *       *       *       *

SECT. V.

OF THE FOUR FACULTIES OR MOTIONS OF THE SENSORIUM.

    1. _Four sensorial powers._ 2. _Irritation, sensation, volition,
    association defined._ 3. _Sensorial motions distinguished from fibrous
    motions._

1. The spirit of animation has four different modes of action, or in other
words the animal sensorium possesses four different faculties, which are
occasionally exerted, and cause all the contractions of the fibrous parts
of the body. These are the faculty of causing fibrous contractions in
consequence of the irritations excited by external bodies, in consequence
of the sensations of pleasure or pain, in consequence of volition, and in
consequence of the associations of fibrous contractions with other fibrous
contractions, which precede or accompany them.

These four faculties of the sensorium during their inactive state are
termed irritability, sensibility, voluntarity, and associability; in their
active state they are termed as above, irritation, sensation, volition,
association.

2. IRRITATION is an exertion or change of some extreme part of the
sensorium residing in the muscles or organs of sense, in consequence of the
appulses of external bodies.

SENSATION is an exertion or change of the central parts of the sensorium,
or of the whole of it, _beginning_ at some of those extreme parts of it,
which reside in the muscles or organs of sense.

VOLITION is an exertion or change of the central parts of the sensorium, or
of the whole of it, _terminating_ in some of those extreme parts of it,
which reside in the muscles or organs of sense.

ASSOCIATION is an exertion or change of some extreme part of the sensorium
residing in the muscles or organs of sense, in consequence of some
antecedent or attendant fibrous contractions.

3. These four faculties of the animal sensorium may at the time of their
exertions be termed motions without impropriety of language; for we cannot
pass from a state of insensibility or inaction to a state of sensibility or
of exertion without some change of the sensorium, and every change includes
motion. We shall therefore sometimes term the above described faculties
_sensorial motions_ to distinguish them from _fibrous motions_; which
latter expression includes the motions of the muscles and organs of sense.

The active motions of the fibres, whether those of the muscles or organs of
sense, are probably simple contractions; the fibres being again elongated
by antagonist muscles, by circulating fluids, or sometimes by elastic
ligaments, as in the necks of quadrupeds. The sensorial motions, which
constitute the sensations of pleasure or pain, and which constitute
volition, and which cause the fibrous contractions in consequence of
irritation or of association, are not here supposed to be fluctuations or
refluctuations of the spirit of animation; nor are they supposed to be
vibrations or revibrations, nor condensations or equilibrations of it; but
to be changes or motions of it peculiar to life.

       *       *       *       *       *

SECT. VI.

OF THE FOUR CLASSES OF FIBROUS MOTIONS.

    I. _Origin of fibrous contractions._ II. _Distribution of them into
    four classes, irritative motions, sensitive motions, voluntary motions,
    and associate motions, defined._

I. All the fibrous contractions of animal bodies originate from the
sensorium, and resolve themselves into four classes, correspondent with the
four powers or motions of the sensorium above described, and from which
they have their causation.

1. These fibrous contractions were originally caused by the irritations
excited by objects, which are external to the moving organ. As the
pulsations of the heart are owing to the irritations excited by the
stimulus of the blood; and the ideas of perception are owing to the
irritations excited by external bodies.

2. But as painful or pleasurable sensations frequently accompanied those
irritations, by habit these fibrous contractions became causeable by the
sensations, and the irritations ceased to be necessary to their production.
As the secretion of tears in grief is caused by the sensation of pain; and
the ideas of imagination, as in dreams or delirium, are excited by the
pleasure or pain, with which they were formerly accompanied.

3. But as the efforts of the will frequently accompanied these painful or
pleasureable sensations, by habit the fibrous contractions became causable
by volition; and both the irritations and sensations ceased to be necessary
to their production. As the deliberate locomotions of the body, and the
ideas of recollection, as when we will to repeat the alphabet backwards.

4. But as many of these fibrous contractions frequently accompanied other
fibrous contractions, by habit they became causable by their associations
with them; and the irritations, sensations, and volition, ceased to be
necessary to their production. As the actions of the muscles of the lower
limbs in fencing are associated with those of the arms; and the ideas of
suggestion are associated with other ideas, which precede or accompany
them; as in repeating carelessly the alphabet in its usual order after
having began it.

II. We shall give the following names to these four classes of fibrous
motions, and subjoin their definitions.

1. Irritative motions. That exertion or change of the sensorium, which is
caused by the appulses of external bodies, either simply subsides, or is
succeeded by sensation, or it produces fibrous motions; it is termed
irritation, and irritative motions are those contractions of the muscular
fibres, or of the organs of sense, that are immediately consequent to this
exertion or change of the sensorium.

2. Sensitive motions. That exertion or change of the sensorium, which
constitutes pleasure or pain, either simply subsides, or is succeeded by
volition, or it produces fibrous motions; it is termed sensation, and the
sensitive motions are those contractions of the muscular fibres, or of the
organs of sense, that are immediately consequent to this exertion or change
of the sensorium.

3. Voluntary motions. That exertion or change of the sensorium, which
constitutes desire or aversion, either simply subsides, or is succeeded by
fibrous motions; it is then termed volition, and voluntary motions are
those contractions of the muscular fibres, or of the organs of sense, that
are immediately consequent to this exertion or change of the sensorium.

4. Associate motions. That exertion or change of the sensorium, which
accompanies fibrous motions, either simply subsides, or is succeeded by
sensation or volition, or it produces other fibrous motions; it is then
termed association, and the associate motions are those contractions of the
muscular fibres, or of the organs of sense, that are immediately consequent
to this exertion or change of the sensorium.

       *       *       *       *       *

SECT. VII.

OF IRRITATIVE MOTIONS.

    I. 1. _Some muscular motions are excited by perpetual irritations._ 2.
    _Others more frequently by sensations._ 3. _Others by volition. Case of
    involuntary stretchings in paralytic limbs._ 4. _Some sensual motions
    are excited by perpetual irritations._ 5. _Others more frequently by
    sensation or volition._

    II. 1. _Muscular motions excited by perpetual irritations occasionally
    become obedient sensation and to volition._ 2. _And the sensual
    motions._

    III. 1. _Other muscular motions are associated with the irritative
    ones._ 2. _And other ideas with irritative ones. Of letters, language,
    hieroglyphics. Irritative ideas exist without our attention to them._

I. 1. Many of our muscular motions are excited by perpetual irritations, as
those of the heart and arterial system by the circumfluent blood. Many
other of them are excited by intermitted irritations, as those of the
stomach and bowels by the aliment we swallow; of the bile-ducts by the
bile; of the kidneys, pancreas, and many other glands, by the peculiar
fluids they separate from the blood; and those of the lacteal and other
absorbent vessels by the chyle, lymph, and moisture of the atmosphere.
These motions are accelerated or retarded, as their correspondent
irritations are increased or diminished, without our attention or
consciousness, in the same manner as the various secretions of fruit, gum,
resin, wax, and, honey, are produced in the vegetable world, and as the
juices of the earth and the moisture of the atmosphere are absorbed by
their roots and foliage.

2. Other muscular motions, that are most frequently connected with our
sensations, as those of the sphincters of the bladder and anus, and the
musculi erectores penis, were originally excited into motion by irritation,
for young children make water, and have other evacuations without attention
to these circumstances; "et primis etiam ab incunabulis tenduntur sæpius
puerorum penes, amore nondum expergefacto." So the nipples of young women
are liable to become turgid by irritation, long before they are in a
situation to be excited by the pleasure of giving milk to the lips of a
child.

3. The contractions of the larger muscles of our bodies, that are most
frequently connected with volition, were originally excited into action by
internal irritations: as appears from the stretching or yawning of all
animals after long sleep. In the beginning of some fevers this irritation
of the muscles produces perpetual stretching and yawning; in other periods
of fever an universal restlessness arises from the same cause, the patient
changing the attitude of his body every minute. The repeated struggles of
the foetus in the uterus must be owing to this internal irritation: for the
foetus can have no other inducement to move its limbs but the tædium or
irksomeness of a continued posture.

The following case evinces, that the motions of stretching the limbs after
a continued attitude are not always owing to the power of the will. Mr.
Dean, a mason, of Austry in Leicestershire, had the spine of the third
vertebra of the back enlarged; in some weeks his lower extremities became
feeble, and at length quite paralytic: neither the pain of blisters, the
heat of fomentations, nor the utmost efforts of the will could produce the
least motion in these limbs; yet twice or thrice a day for many months his
feet, legs, and thighs, were affected for many minutes with forceable
stretchings, attended with the sensation of fatigue; and he at length
recovered the use of his limbs, though the spine continued protuberant. The
same circumstance is frequently seen in a less degree in the common
hemiplagia; and when this happens, I have believed repeated and strong
shocks of electricity to have been of great advantage.

4. In like manner the various organs of sense are originally excited into
motion by various external stimuli adapted to this purpose, which motions
are termed perceptions or ideas; and many of these motions during our
waking hours are excited by perpetual irritation, as those of the organs of
hearing and of touch. The former by the constant low indistinct noises that
murmur around us, and the latter by the weight of our bodies on the parts
which support them; and by the unceasing variations of the heat, moisture,
and pressure of the atmosphere; and these sensual motions, precisely as the
muscular ones above mentioned, obey their correspondent irritations without
our attention or consciousness.

5. Other classes of our ideas are more frequently excited by our sensations
of pleasure or pain, and others by volition: but that these have all been
originally excited by stimuli from external objects, and only vary in their
combinations or reparations, has been fully evinced by Mr. Locke: and are
by him termed the ideas of perception in contradistinction to those, which
he calls the ideas of reflection.

II. 1. These muscular motions, that are excited by perpetual irritation,
are nevertheless occasionally excitable by the sensations of pleasure or
pain, or by volition; as appears by the palpitation of the heart from fear,
the increased secretion of saliva at the sight of agreeable food, and the
glow on the skin of those who are ashamed. There is an instance told in the
Philosophical Transactions of a man, who could for a time stop the motion
of his heart when he pleased; and Mr. D. has often told me, be could so far
increase the peristaltic motion of his bowels by voluntary efforts, as to
produce an evacuation by stool at any time in half an hour.

2. In like manner the sensual motions, or ideas, that are excited by
perpetual irritation, are nevertheless occasionally excited by sensation or
volition; as in the night, when we listen under the influence of fear, or
from voluntary attention, the motions excited in the organ of hearing by
the whispering of the air in our room, the pulsation of our own arteries,
or the faint beating of a distant watch, become objects of perception.

III. 1. Innumerable trains or tribes of other motions are associated with
these muscular motions which are excited by irritation; as by the stimulus
of the blood in the right chamber of the heart, the lungs are induced to
expand themselves; and the pectoral and intercostal muscles, and the
diaphragm, act at the same time by their associations with them. And when
the pharinx is irritated by agreeable food, the muscles of deglutition are
brought into action by association. Thus when a greater light falls on the
eye, the iris is brought into action without our attention; and the ciliary
process, when the focus is formed before or behind the retina, by their
associations with the increased irritative motions of the organ of vision.
Many common actions of life are produced in a similar manner. If a fly
settle on my forehead, whilst I am intent on my present occupation, I
dislodge it with my finger, without exciting my attention or breaking the
train of my ideas.

2. In like manner the irritative ideas suggest to us many other trains or
tribes of ideas that are associated with them. On this kind of connection,
language, letters, hieroglyphics, and every kind of symbol, depend. The
symbols themselves produce irritative ideas, or sensual motions, which we
do not attend to; and other ideas, that are succeeded by sensation, are
excited by their association with them. And as these irritative ideas make
up a part of the chain of our waking thoughts, introducing other ideas that
engage our attention, though themselves are unattended to, we find it very
difficult to investigate by what steps many of our hourly trains of ideas
gain their admittance.

It may appear paradoxical, that ideas can exist, and not be attended to;
but all our perceptions are ideas excited by irritation, and succeeded by
sensation. Now when these ideas excited by irritation give us neither
pleasure nor pain, we cease to attend to them. Thus whilst I am walking
through that grove before my window, I do not run against the trees or the
benches, though my thoughts are strenuously exerted on some other object.
This leads us to a distinct knowledge of irritative ideas, for the idea of
the tree or bench, which I avoid, exists on my retina, and induces by
association the action of certain locomotive muscles; though neither itself
nor the actions of those muscles engage my attention.

Thus whilst we are conversing on this subject, the tone, note, and
articulation of every individual word forms its correspondent irritative
idea on the organ of hearing; but we only attend to the associated ideas,
that are attached by habit to these irritative ones, and are succeeded by
sensation; thus when we read the words "PRINTING-PRESS" we do not attend to
the shape, size, or existence of the letters which compose these words,
though each of them excites a correspondent irritative motion of our organ
of vision, but they introduce by association our idea of the most useful of
modern inventions; the capacious reservoir of human knowledge, whose
branching streams diffuse sciences, arts, and morality, through all nations
and all ages.

       *       *       *       *       *

SECT. VIII.

OF SENSITIVE MOTIONS.

    I. 1. _Sensitive muscular motions were originally excited into action
    by irritation._ 2. _And sensitive sensual motions, ideas of
    imagination, dreams._ II. 1. _Sensitive muscular motions are
    occasionally obedient to volition._ 2. _And sensitive sensual motions._
    III. 1. _Other muscular motions are associated with the sensitive
    ones._ 2. _And other sensual motions._

I. 1. Many of the motions of our muscles, that are excited into action by
irritation, are at the same time accompanied with painful or pleasurable
sensations; and at length become by habit causable by the sensations. Thus
the motions of the sphincters of the bladder and anus were originally
excited into action by irritation; for young children give no attention to
these evacuations; but as soon as they become sensible of the inconvenience
of obeying these irritations, they suffer the water or excrement to
accumulate, till it disagreeably affects them; and the action of those
sphincters is then in consequence of this disagreeable sensation. So the
secretion of saliva, which in young children is copiously produced by
irritation, and drops from their mouths, is frequently attended with the
agreeable sensation produced by the mastication of tasteful food;, till at
length the sight of such food to a hungry person excites into action these
salival glands; as is seen in the slavering of hungry dogs.

The motions of those muscles, which are affected by lascivious ideas, and
those which are exerted in smiling, weeping, starting from fear, and
winking at the approach of danger to the eye, and at times the actions of
every large muscle of the body become causable by our sensations. And all
these motions are performed with strength and velocity in proportion to the
energy of the sensation that excites them, and the quantity of sensorial
power.

2. Many of the motions of our organs of sense, or ideas, that were
originally excited into action by irritation, become in like manner more
frequently causable by our sensations of pleasure or pain. These motions
are then termed the ideas of imagination, and make up all the scenery and
transactions of our dreams. Thus when any painful or pleasurable sensations
possess us, as of love, anger, fear; whether in our sleep or waking hours,
the ideas, that have been formerly excited by the objects of these
sensations, now vividly recur before us by their connection with these
sensations themselves. So the fair smiling virgin, that excited your love
by her presence, whenever that sensation recurs, rises before you in
imagination; and that with all the pleasing circumstances, that had before
engaged your attention. And in sleep, when you dream under the influence of
fear, all the robbers, fires, and precipices, that you formerly have seen
or heard of, arise before you with terrible vivacity. All these sensual
motions, like the muscular ones above mentioned, are performed with
strength and velocity in proportion to the energy of the sensation of
pleasure or pain, which excites them, and the quantity of sensorial power.

II. 1. Many of these muscular motions above described, that are most
frequently excited by our sensations, are nevertheless occasionally
causable by volition; for we can smile or frown spontaneously, can make
water before the quantity or acrimony of the urine produces a disagreeable
sensation, and can voluntarily masticate a nauseous drug, or swallow a
bitter draught, though our sensation would strongly dissuade us.

2. In like manner the sensual motions, or ideas, that are most frequently
excited by our sensations, are nevertheless occasionally causeable by
volition, as we can spontaneously call up our last night's dream before us,
tracing it industriously step by step through all its variety of scenery
and transaction; or can voluntarily examine or repeat the ideas, that have
been excited by out disgust or admiration.

III. 1. Innumerable trains or tribes of motions are associated with these
sensitive muscular motions above mentioned; as when a drop of water falling
into the wind-pipe disagreeably affects the air-vessels of the lungs, they
are excited into violent action; and with these sensitive motions are
associated the actions of the pectoral and intercostal muscles, and the
diaphragm; till by their united and repeated succussions the drop is
returned through the larinx. The same occurs when any thing disagreeably
affects the nostrils, or the stomach, or the uterus; variety of muscles are
excited by association into forcible action, not to be suppressed by the
utmost efforts of the will; as in sneezing, vomiting, and parturition.

2. In like manner with these sensitive sensual motions, or ideas of
imagination, are associated many other trains or tribes of ideas, which by
some writers of metaphysics have been classed under the terms of
resemblance, causation, and contiguity; and will be more fully treated of
hereafter.

       *       *       *       *       *

SECT. IX.

OF VOLUNTARY MOTIONS.

    I. 1. _Voluntary muscular motions are originally excited by
    irritations._ 2. _And voluntary ideas. Of reason._ II. 1. _Voluntary
    muscular motions are occasionally causable by sensations._ 2. _And
    voluntary ideas._ III. 1. _Voluntary muscular motions are occasionally
    obedient to irritations._ 2. _And voluntary ideas._ IV. 1. _Voluntary
    muscular motions are associated with other muscular motions._ 2. _And
    voluntary ideas._

When pleasure or pain affect the animal system, many of its motions both
muscular and sensual are brought into action; as was shewn in the preceding
section, and were called sensitive motions. The general tendency of these
motions is to arrest and to possess the pleasure, or to dislodge or avoid
the pain: but if this cannot immediately be accomplished, desire or
aversion are produced, and the motions in consequence of this new faculty
of the sensorium are called voluntary.

I. 1. Those muscles of the body that are attached to bones, have in general
their principal connections with volition, as I move my pen or raise my
body. These motions were originally excited by irritation, as was explained
in the section on that subject, afterwards the sensations of pleasure or
pain, that accompanied the motions thus excited, induced a repetition of
them; and at length many of them were voluntarily practised in succession
or in combination for the common purposes of life, as in learning to walk,
or to speak; and are performed with strength and velocity in proportion to
the energy of the volition, that excites them, and the quantity of
sensorial power.

2. Another great class of voluntary motions consists of the ideas of
recollection. We will to repeat a certain train of ideas, as of the
alphabet backwards; and if any ideas, that do not belong to this intended
train, intrude themselves by other connections, we will to reject them, and
voluntarily persist in the determined train. So at my approach to a house
which I have but once visited, and that at the distance of many months, I
will to recollect the names of the numerous family I expect to see there,
and I do recollect them.

On this voluntary recollection of ideas our faculty of reason depends, as
it enables us to acquire an idea of the dissimilitude of any two ideas.
Thus if you voluntarily produce the idea of a right-angled triangle, and
then of a square; and after having excited these ideas repeatedly, you
excite the idea of their difference, which is that of another right-angled
triangle inverted over the former; you are said to reason upon this
subject, or to compare your ideas.

These ideas of recollection, like the muscular motions above mentioned,
were originally excited by the irritation of external bodies, and were
termed ideas of perception: afterwards the pleasure or pain, that
accompanied these motions, induced a repetition of them in the absence of
the external body, by which they were first excited; and then they were
termed ideas of imagination. At length they become voluntarily practised in
succession or in combination for the common purposes of life; as when we
make ourselves masters of the history of mankind, or of the sciences they
have investigated; and are then called ideas of recollection; and are
performed with strength and velocity in proportion to the energy of the
volition that excites them, and the quantity of sensorial power.

II. 1. The muscular motions above described, that are most frequently
obedient to the will are nevertheless occasionally causable by painful or
pleasurable sensation, as in the starting from fear, and the contraction of
the calf of the leg in the cramp.

2. In like manner the sensual motions, or ideas, that are most frequently
connected with volition, are nevertheless occasionally causable by painful
or pleasurable sensation. As the histories of men, or the description of
places, which we have voluntarily taken pains to remember, sometimes occur
to us in our dreams.

III. 1. The muscular motions that are generally subservient to volition,
are also occasionally causable by irritation, as in stretching the limbs
after sleep, and yawning. In this manner a contraction of the arm is
produced by passing the electric fluid from the Leyden phial along its
muscles; and that even though the limb is paralytic. The sudden motion of
the arm produces a disagreeable sensation in the joint, but the muscles
seem to be brought into action simply by irritation.

2. The ideas, that are generally subservient to the will, are in like
manner occasionally excited by irritation; as when we view again an object,
we have before well studied, and often recollected.

IV. 1. Innumerable trains or tribes of motions are associated with these
voluntary muscular motions above mentioned; as when I will to extend my arm
to a distant object, some other muscles are brought into action, and
preserve the balance of my body. And when I wish to perform any steady
exertion, as in threading a needle, or chopping with an ax, the pectoral
muscles are at the same time brought into action to preserve the trunk of
the body motionless, and we cease to respire for a time.

2. In like manner the voluntary sensual motions, or ideas of recollection,
are associated with many other trains or tribes of ideas. As when I
voluntarily recollect a gothic window, that I saw some time ago, the whole
front of the cathedral occurs to me at the same time.

       *       *       *       *       *

SECT. X.

OF ASSOCIATE MOTIONS.

    I. 1. _Many muscular motions excited by irritations in trains or tribes
    become associated._ 2. _And many ideas._ II. 1. _Many sensitive
    muscular motions become associated._ 2. _And many sensitive ideas._
    III. 1. _Many voluntary muscular motions become associated._ 2. _And
    then become obedient to sensation or irritation._ 3. _And many
    voluntary ideas become associated._

All the fibrous motions, whether muscular or sensual, which are frequently
brought into action together, either in combined tribes, or in successive
trains, become so connected by habit, that when one of them is reproduced
the others have a tendency to succeed or accompany it.

I. 1. Many of our muscular motions were originally excited in successive
trains, as the contractions of the auricles and of the ventricles of the
heart; and others in combined tribes, as the various divisions of the
muscles which compose the calf of the leg, which were originally irritated
into synchronous action by the tædium or irksomeness of a continued
posture. By frequent repetitions these motions acquire associations, which
continue during our lives, and even after the destruction of the greatest
part of the sensorium; for the heart of a viper or frog will continue to
pulsate long after it is taken from the body; and when it has entirely
ceased to move, if any part of it is goaded with a pin, the whole heart
will again renew its pulsations. This kind of connection we shall term
irritative association, to distinguish it from sensitive and voluntary
associations.

2. In like manner many of our ideas are originally excited in tribes; as
all the objects of sight, after we become so well acquainted with the laws
of vision, as to distinguish figure and distance as well as colour; or in
trains, as while we pass along the objects that surround us. The tribes
thus received by irritation become associated by habit, and have been
termed complex ideas by the writers of metaphysics, as this book, or that
orange. The trains have received no particular name, but these are alike
associations of ideas, and frequently continue during our lives. So the
taste of a pine-apple, though we eat it blindfold, recalls the colour and
shape of it; and we can scarcely think on solidity without figure.

II. 1. By the various efforts of our sensations to acquire or avoid their
objects, many muscles are daily brought into successive or synchronous
actions; these become associated by habit, and are then excited together
with great facility, and in many instances gain indissoluble connections.
So the play of puppies and kittens is a representation of their mode of
fighting or of taking their prey; and the motions of the muscles necessary
for those purposes become associated by habit, and gain a great adroitness
of action by these early repetitions: so the motions of the abdominal
muscles, which were originally brought into concurrent action, with the
protrusive motion of the rectum or bladder by sensation, become so
conjoined with them by habit, that they not only easily obey these
sensations occasioned by the stimulus of the excrement and urine, but are
brought into violent and unrestrainable action in the strangury and
tenesmus. This kind of connection we shall term sensitive association.

2. So many of our ideas, that have been excited together or in succession
by our sensations, gain synchronous or successive associations, that are
sometimes indissoluble but with life. Hence the idea of an inhuman or
dishonourable action perpetually calls up before us the idea of the wretch
that was guilty of it. And hence those unconquerable antipathies are
formed, which some people have to the sight of peculiar kinds of food, of
which in their infancy they have eaten to excess or by constraint.

III. 1. In learning any mechanic art, as music, dancing, or the use of the
sword, we teach many of our muscles to act together or in succession by
repeated voluntary efforts; which by habit become formed into tribes or
trains of association, and serve all our purposes with great facility, and
in some instances acquire an indissoluble union. These motions are
gradually formed into a habit of acting together by a multitude of
repetitions, whilst they are yet separately causable by the will, as is
evident from the long time that is taken up by children in learning to walk
and to speak; and is experienced by every one, when he first attempts to
skate upon the ice or to swim: these we shall term voluntary associations.

2. All these muscular movements, when they are thus associated into tribes
or trains, become afterwards not only obedient to volition, but to the
sensations and irritations; and the same movement composes a part of many
different tribes or trains of motion. Thus a single muscle, when it acts in
consort with its neighbours on one side, assists to move the limb in one
direction; and in another, when, it acts with those in its neighbourhood on
the other side; and in other directions, when it acts separately or jointly
with those that lie immediately under or above it; and all these with equal
facility after their associations have been well established.

The facility, with which each muscle changes from one associated tribe to
another, and that either backwards or forwards, is well observable in the
muscles of the arm in moving the windlass of an air-pump; and the slowness
of those muscular movements, that have not been associated by habit, may be
experienced by any one, who shall attempt to saw the air quick
perpendicularly with one hand, and horizontally with the other at the same
time.

3. In learning every kind of science we voluntarily associate many tribes
and trains of ideas, which afterwards are ready for all the purposes either
of volition, sensation, or irritation; and in some instances acquire
indissoluble habits of acting together, so as to affect our reasoning, and
influence our actions. Hence the necessity of a good education.

These associate ideas are gradually formed into habits of acting together
by frequent repetition, while they are yet separately obedient to the will;
as is evident from the difficulty we experience in gaining so exact an idea
of the front of St. Paul's church, as to be able to delineate it with
accuracy, or in recollecting a poem of a few pages.

And these ideas, thus associated into tribes, not only make up the parts of
the trains of volition, sensation, and irritation; but the same idea
composes a part of many different tribes and trains of ideas. So the simple
idea of whiteness composes a part of the complex idea of snow, milk, ivory;
and the complex idea of the letter A composes a part of the several
associated trains of ideas that make up the variety of words, in which this
letter enters.

The numerous trains of these associated ideas are divided by Mr. Hume into
three classes, which he has termed contiguity, causation, and resemblance.
Nor should we wonder to find them thus connected together, since it is the
business of our lives to dispose them into those three classes; and we
become valuable to ourselves and our friends, as we succeed in it. Those
who have combined an extensive class of ideas by the contiguity of time or
place, are men learned in the history of mankind, and of the sciences they
have cultivated. Those who have connected a great class of ideas of
resemblances, possess the source of the ornaments of poetry and oratory,
and of all rational analogy. While those who have connected great classes
of ideas of causation, are furnished with the powers of producing effects.
These are the men of active wisdom, who lead armies to victory, and
kingdoms to prosperity; or discover and improve the sciences, which
meliorate and adorn the condition of humanity.

       *       *       *       *       *

SECT. XI.

ADDITIONAL OBSERVATIONS ON THE SENSORIAL POWERS.

    I. _Stimulation is of various kinds adapted to the organs of sense, to
    the muscles, to hollow membranes, and glands. Some objects irritate our
    senses by repeated impulses._ II. 1. _Sensation and volition frequently
    affect the whole sensorium._ 2. _Emotions, passions, appetites._ 3.
    _Origin of desire and aversion. Criterion of voluntary actions,
    difference of brutes and men._ 4. _Sensibility and voluntarity._ III.
    _Associations formed before nativity, irritative motions mistaken for
    officiated ones._

_Irritation._

I. The various organs of sense require various kinds of stimulation to
excite them into action; the particles of light penetrate the cornea and
humours of the eye, and then irritate the naked retina; rapid particles,
dissolved or diffused in water or saliva, and odorous ones, mixed or
combined with the air, irritate the extremities of the nerves of taste and
smell; which either penetrate, or are expanded on the membranes of the
tongue and nostrils; the auditory nerves are stimulated by the vibrations
of the atmosphere communicated by means of the tympanum and of the fluid,
whether of air or of water, behind it; and the nerves of touch by the
hardness of surrounding bodies, though the cuticle is interposed between
these bodies and the medulla of the nerve.

As the nerves of the senses have each their appropriated objects, which
stimulate them into activity; so the muscular fibres, which are the
terminations of other sets of nerves, have their peculiar objects, which
excite them into action; the longitudinal muscles are stimulated into
contraction by extension, whence the stretching or pandiculation after a
long continued posture, during which they have been kept in a state of
extension; and the hollow muscles are excited into action by distention, as
those of the rectum and bladder are induced to protrude their contents from
their sense of the distention rather than of the acrimony of those
contents.

There are other objects adapted to stimulate the nerves, which terminate in
variety of membranes, and those especially which form the terminations of
canals; thus the preparations of mercury particularly affect the salivary
glands, ipecacuanha the stomach, aloe the sphincter of the anus,
cantharides that of the bladder, and lastly every gland of the body appears
to be indued with a kind of taste, by which it selects or forms each its
peculiar fluid from the blood; and by which it is irritated into activity.

Many of these external properties of bodies, which stimulate our organs of
sense, do not seem to effect this by a single impulse, but by repeated
impulses; as the nerve of the ear is probably not excitable by a single
vibration of air, nor the optic nerve by a single particle of light; which
circumstance produces some analogy between those two senses, at the same
time the solidity of bodies is perceived by a single application of a solid
body to the nerves of touch, and that even through the cuticle; and we are
probably possessed of a peculiar sense to distinguish the nice degrees of
heat and cold.

The senses of touch and of hearing acquaint us with the mechanical impact
and vibration of bodies, those of smell and taste seem to acquaint us with
some of their chemical properties, while the sense of vision and of heat
acquaint us with the existence of their peculiar fluids.

_Sensation and Volition._

II. Many motions are produced by pleasure or pain, and that even in
contradiction to the power of volition, as in laughing, or in the
strangury; but as no name has been given to pleasure or pain, at the time
it is exerted so as to cause fibrous motions, we have used the term
sensation for this purpose; and mean it to bear the same analogy to
pleasure and pain, that the word volition does to desire and aversion.

1. It was mentioned in the fifth Section, that, what we have termed
sensation is a motion of the central parts, or of the whole sensorium,
_beginning_ at some of the extremities of it. This appears first, because
our pains and pleasures are always caused by our ideas or muscular motions,
which are the motions of the extremities of the sensorium. And, secondly,
because the sensation of pleasure or pain frequently continues some time
after the ideas or muscular motions which excited it have ceased: for we
often feel a glow of pleasure from an agreeable reverie, for many minutes
after the ideas, that were the subject of it, have escaped our memory; and
frequently experience a dejection of spirits without being able to assign
the cause of it but by much recollection.

When the sensorial faculty of desire or aversion is exerted so as to cause
fibrous motions, it is termed volition; which is said in Sect. V. to be a
motion of the central parts, or of the whole sensorium, _terminating_ in
some of the extremities of it. This appears, first, because our desires and
aversions always terminate in recollecting and comparing our ideas, or in
exerting our muscles; which are the motions of the extremities of the
sensorium. And, secondly, because desire or aversion begins, and frequently
continues for a time in the central parts of the sensorium, before it is
peculiarly exerted at the extremities of it; for we sometimes feel desire
or aversion without immediately knowing their objects, and in consequence
without immediately exerting any of our muscular or sensual motions to
attain them: as in the beginning of the passion of love, and perhaps of
hunger, or in the ennui of indolent people.

Though sensation and volition begin or terminate at the extremities or
central parts of the sensorium, yet the whole of it is frequently
influenced by the exertion of these faculties, as appears from their
effects on the external habit: for the whole skin is reddened by shame, and
an universal trembling is produced by fear: and every muscle of the body is
agitated in angry people by the desire of revenge.

There is another very curious circumstance, which shews that sensation and
volition are movements of the sensorium in contrary directions; that is,
that volition begins at the central parts of it, and proceeds to the
extremities; and that sensation begins at the extremities, and proceeds to
the central parts: I mean that these two sensorial faculties cannot be
strongly exerted at the same time; for when we exert our volition strongly,
we do not attend to pleasure or pain; and conversely, when we are strongly
affected with the sensation of pleasure or pain, we use no volition. As
will be further explained in Section XVIII. on sleep, and Section XXXIV. on
volition.

2. All our emotions and passions seem to arise out of the exertions of
these two faculties of the animal sensorium. Pride, hope, joy, are the
names of particular pleasures: shame, despair, sorrow, are the names of
peculiar pains: and love, ambition, avarice, of particular desires: hatred,
disgust, fear, anxiety, of particular aversions. Whilst the passion of
anger includes the pain from a recent injury, and the aversion to the
adversary that occasioned it. And compassion is the pain we experience at
the sight of misery, and the desire of relieving it.

There is another tribe of desires, which are commonly termed appetites, and
are the immediate consequences of the absence of some irritative motions.
Those, which arise from defect of internal irritations, have proper names
conferred upon them, as hunger, thirst, lust, and the desire of air, when
our respiration is impaired by noxious vapours; and of warmth, when we are
exposed to too great a degree of cold. But those, whose stimuli are
external to the body, are named from the objects, which are by nature
constituted to excite them; these desires originate from our past
experience of the pleasurable sensations they occasion, as the smell of an
hyacinth, or the taste of a pine-apple.

Whence it appears, that our pleasures and pains are at least as various and
as numerous as our irritations; and that our desires and aversions must be
as numerous as our pleasures and pains. And that as sensation is here used
as a general term for our numerous pleasures and pains, when they produce
the contractions of our fibres; so volition is the general name for our
desires and aversions, when they produce fibrous contractions. Thus when a
motion of the central parts, or of the whole sensorium, terminates in the
exertion of our muscles, it is generally called voluntary action; when it
terminates in the exertion of our ideas, it is termed recollection,
reasoning, determining.

3. As the sensations of pleasure and pain are originally introduced by the
irritations of external objects: so our desires and aversions are
originally introduced by those sensations; for when the objects of our
pleasures or pains are at a distance, and we cannot instantaneously possess
the one, or avoid the other, then desire or aversion is produced, and a
voluntary exertion of our ideas or muscles succeeds.

The pain of hunger excites you to look out for food, the tree, that shades
you, presents its odoriferous fruit before your eyes, you approach, pluck,
and eat.

The various movements of walking to the tree, gathering the fruit, and
masticating it, are associated motions introduced by their connection with
sensation; but if from the uncommon height of the tree, the fruit be
inaccessible, and you are prevented from quickly possessing the intended
pleasure, desire is produced. The consequence of this desire is, first, a
deliberation about the means to gain the object of pleasure in process of
time, as it cannot be procured immediately; and, secondly, the muscular
action necessary for this purpose.

You voluntarily call up all your ideas of causation, that are related to
the effect you desire, and voluntarily examine and compare them, and at
length determine whether to ascend the tree, or to gather stones from the
neighbouring brook, is easier to practise, or more promising of success;
and, finally, you gather the stones, and repeatedly fling them to dislodge
the fruit.

Hence then we gain a criterion to distinguish voluntary acts or thoughts
from those caused by sensation. As the former are always employed about the
_means_ to acquire pleasurable objects, or the _means_ to avoid painful
ones; while the latter are employed in the possession of those, which are
already in our power.

Hence the activity of this power of volition produces the great difference
between the human and the brute creation. The ideas and the actions of
brutes are almost perpetually employed about their present pleasures, or
their present pains; and, except in the few instances which are mentioned
in Section XVI, on instinct, they seldom busy themselves about the means of
procuring future bliss, or of avoiding future misery; so that the acquiring
of languages, the making of tools, and labouring for money, which are all
only the means to procure pleasures; and the praying to the Deity, as
another means to procure happiness, are characteristic of human nature.

4. As there are many diseases produced by the quantity of the sensation of
pain or pleasure being too great or too little; so are there diseases
produced by the susceptibility of the constitution to motions causable by
these sensations being too dull or too vivid. This susceptibility of the
system to sensitive motions is termed sensibility, to distinguish it from
sensation, which is the actual existence or exertion of pain or pleasure.

Other classes of diseases are owing to the excessive promptitude, or
sluggishness of the constitution to voluntary exertions, as well as to the
quantity of desire or of aversion. This susceptibility of the system to
voluntary motions is termed voluntarity, to distinguish it from volition,
which is the exertion of desire or aversion; these diseases will be treated
of at length in the progress of the work.

_Association._

III. 1. It is not easy to assign a cause, why those animal movements, that
have once occurred in succession, or in combination, should afterwards have
a tendency to succeed or accompany each other. It is a property of
animation, and distinguishes this order of being from the other productions
of nature.

When a child first wrote the word man, it was distinguished in his mind
into three letters, and those letters into many parts of letters; but by
repeated use the word man becomes to his hand in writing it, as to his
organs of speech in pronouncing it, but one movement without any
deliberation, or sensation, or irritation, interposed between the parts of
it. And as many separate motions of our muscles thus become united, and
form, as it were, one motion; so each separate motion before such union may
be conceived to consist of many parts or spaces moved through; and perhaps
even the individual fibres of our muscles have thus gradually been brought
to act in concert, which habits began to be acquired as early as the very
formation of the moving organs, long before the nativity of the animal; as
explained in the Section XVI. 2. on instinct.

2. There are many motions of the body, belonging to the irritative class,
which might by a hasty observer be mistaken for associated ones; as the
peristaltic motion of the stomach and intestines, and the contractions of
the heart and arteries, might be supposed to be associated with the
irritative motions of their nerves of sense, rather than to be excited by
the irritation of their muscular fibres by the distention, acrimony, or
momentum of the blood. So the distention or elongation of muscles by
objects external to them irritates them into contraction, though the
cuticle or other parts may intervene between the stimulating body and the
contracting muscle. Thus a horse voids his excrement when its weight or
bulk irritates the rectum or sphincter ani. These muscles act from the
irritation of distention, when he excludes his excrement, but the muscles
of the abdomen and diaphragm are brought into motion by association with
those of the sphincter and rectum.

       *       *       *       *       *

SECT. XII.

OF STIMULUS, SENSORIAL EXERTION, AND FIBROUS CONTRACTION.

    I. Of fibrous contraction. 1. _Two particles of a fibre cannot approach
    without the intervention of something, as in magnetism, electricity,
    elasticity. Spirit of life is not electric ether. Galvani's
    experiments._ 2. _Contraction of a fibre._ 3. _Relaxation succeeds._ 4.
    _Successive contractions, with intervals. Quick pulse from debility,
    from paucity of blood. Weak contractions performed in less time, and
    with shorter intervals._ 5. _Last situation of the fibres continues
    after contraction._ 6. _Contraction greater than usual induces pleasure
    or pain._ 7. _Mobility of the fibres uniform. Quantity of sensorial
    power fluctuates. Constitutes excitability._ II. Of sensorial exertion.
    1. _Animal motion includes stimulus, sensorial power, and contractile
    fibres. The sensorial faculties act separately or conjointly. Stimulus
    of four kinds. Strength and weakness defined. Sensorial power
    perpetually exhausted and renewed. Weakness from defect of stimulus.
    From defect of sensorial power, the direct and indirect debility of Dr.
    Brown. Why we become warm in Buxton bath after a time, and see well
    after a time in a darkish room. Fibres may act violently, or with their
    whole force, and yet feebly. Great exertion in inflammation explained.
    Great muscular force of some insane people._ 2. _Occasional
    accumulation of sensorial power in muscles subject to constant
    stimulus. In animals sleeping in winter. In eggs, seeds, schirrous
    tumours, tendons, bones._ 3. _Great exertion introduces pleasure or
    pain. Inflammation. Libration of the system between torpor and
    activity. Fever-fits._ 4. _Desire and aversion introduced. Excess of
    volition cures fevers._ III. Of repeated stimulus. 1. _A stimulus
    repeated too frequently looses effect. As opium, wine, grief. Hence old
    age. Opium and aloes in small doses._ 2. _A stimulus not repeated too
    frequently does not lose effect. Perpetual movement of the vital
    organs._ 3. _A stimulus repeated at uniform times produces greater
    effect. Irritation combined with association._ 4. _A stimulus repeated
    frequently and uniformly may be withdrawn, and the action of the organ
    will continue. Hence the bark cures agues, and strengthens weak
    constitutions._ 5. _Defect of stimulus repeated at certain intervals
    causes fever-fits._ 6. _Stimulus long applied ceases to act a second
    time._ 7. _If a stimulus excites sensation in an organ not usually
    excited into sensation, inflammation is produced._ IV. Of stimulus
    greater than natural. 1. _A stimulus greater than natural diminishes
    the quantity of sensorial power in general._ 2. _In particular organs._
    3. _Induces the organ into spasmodic actions._ 4. _Induces the
    antagonist fibres into action._ 5. _Induces the organ into convulsive
    or fixed spasms._ 6. _Produces paralysis of the organ._ V. Of stimulus
    less than natural. 1. _Stimulus less than natural occasions
    accumulation of sensorial power in general._ 2. _In particular organs,
    flushing of the face in a frosty morning. In fibres subject to
    perpetual stimulus only. Quantity of sensorial power inversely as the
    stimulus._ 3. _Induces pain. As of cold, hunger, head-ach._ 4. _Induces
    more feeble and frequent contraction. As in low fevers. Which are
    frequently owing to deficiency of sensorial power rather than to
    deficiency of stimulus._ 5. _Inverts successive trains of motion.
    Inverts ideas._ 6. _Induces paralysis and death._ VI. Cure of increased
    exertion. 1. _Natural cure of exhaustion of sensorial power._ 2.
    _Decrease the irritations. Venesection. Cold. Abstinence._ 3. _Prevent
    the previous cold fit. Opium. Bark. Warmth. Anger. Surprise._ 4.
    _Excite some other part of the system. Opium and warm bath relieve
    pains both from defect and from excess of stimulus._ 5. _First increase
    the stimulus above, and then decrease it beneath the natural quantity._
    VII. Cure of decreased exertion. 1. _Natural cure by accumulation of
    sensorial power. Ague-fits. Syncope._ 2. _Increase the stimulation, by
    wine, opium, given so as not to intoxicate. Cheerful ideas._ 3. _Change
    the kinds of stimulus._ 4. _Stimulate the associated organs. Blisters
    of use in heart-burn, and cold extremities._ 5. _Decrease the
    stimulation for a time, cold bath._ 6. _Decrease the stimulation below
    natural, and then increase it above natural. Bark after emetics. Opium
    after venesection. Practice of Sydenham in chlorosis._ 7. _Prevent
    unnecessary expenditure of sensorial power. Decumbent posture, silence,
    darkness. Pulse quickened by rising out of bed._ 8. _To the greatest
    degree of quiescence apply the least stimulus. Otherwise paralysis or
    inflammation of the organ ensues. Gin, wine, blisters, destroy by too
    great stimulation in fevers with debility. Intoxication in the
    slightest degree succeeded by debility. Golden rule for determining the
    best degree of stimulus in low fevers. Another golden rule for
    determining the quantity of spirit which those, who are debilitated by
    drinking it, may safely omit._

I. _Of fibrous contraction._

1. If two particles of iron lie near each other without motion, and
afterwards approach each other; it is reasonable to conclude that something
besides the iron particles is the cause of their approximation; this
invisible something is termed magnetism. In the same manner, if the
particles, which compose an animal muscle, do not touch each other in the
relaxed state of the muscle, and are brought into contact during the
contraction of the muscle, it is reasonable to conclude, that some other
agent is the cause of this new approximation. For nothing can act, where it
does not exist; for to act includes to exist; and therefore the particles
of the muscular fibre (which in its state of relaxation are supposed not to
touch) cannot affect each other without the influence of some intermediate
agent; this agent is here termed the spirit of animation, or sensorial
power, but may with equal propriety be termed the power, which causes
contraction; or may be called by any other name, which the reader may
choose to affix to it.

The contraction of a muscular fibre may be compared to the following
electric experiment, which is here mentioned not as a philosophical
analogy, but as an illustration or simile to facilitate the conception of a
difficult subject. Let twenty very small Leyden phials properly coated be
hung in a row by fine silk threads at a small distance from each other; let
the internal charge of one phial be positive, and of the other negative
alternately, if a communication be made from the internal surface of the
first to the external surface of the last in the row, they will all of them
instantly approach each other, and thus shorten a line that might connect
them like a muscular fibre. See Botanic Garden, p. 1. Canto I. 1. 202, note
on Gymnotus.

The attractions of electricity or of magnetism do not apply philosophically
to the illustration of the contraction of animal fibres, since the force of
those attractions increases in some proportion inversely as the distance,
but in muscular motion there appears no difference in velocity or strength
during the beginning or end of the contraction, but what may be clearly
ascribed to the varying mechanic advantage in the approximation of one bone
to another. Nor can muscular motion be assimilated with greater
plausibility to the attraction of cohesion or elasticity; for in bending a
steel spring, as a small sword, a less force is required to bend it the
first inch than the second; and the second than the third; the particles of
steel on the convex side of the bent spring endeavouring to restore
themselves more powerfully the further they are drawn from each other. See
Botanic Garden, P. I. addit. Note XVIII.

I am aware that this may be explained another way, by supposing the
elasticity of the spring to depend more on the compression of the particles
on the concave side than on the extension of them on the convex side; and
by supposing the elasticity of the elastic gum to depend more on the
resistance to the lateral compression of its particles than to the
longitudinal extension of them. Nevertheless in muscular contraction, as
above observed, there appears no difference in the velocity or force of it
at its commencement or at its termination; from whence we must conclude
that animal contraction is governed by laws of its own, and not by those of
mechanics, chemistry, magnetism, or electricity.

On these accounts I do not think the experiments conclusive, which were
lately published by Galvani, Volta, and others, to shew a similitude
between the spirit of animation, which contracts the muscular fibres, and
the electric fluid. Since the electric fluid may act only as a more potent
stimulus exciting the muscular fibres into action, and not by supplying
them with a new quantity of the spirit of life. Thus in a recent hemiplegia
I have frequently observed, when the patient yawned and stretched himself,
that the paralytic limbs moved also, though they were totally disobedient
to the will. And when he was electrified by passing shocks from the
affected hand to the affected foot, a motion of the paralytic limbs was
also produced. Now as in the act of yawning the muscles of the paralytic
limbs were excited into action by the stimulus of the irksomeness of a
continued posture, and not by any additional quantity of the spirit of
life; so we may conclude, that the passage of the electric fluid, which
produced a similar effect, acted only as a stimulus, and not by supplying
any addition of sensorial power.

If nevertheless this theory should ever become established, a stimulus must
be called an eductor of vital ether; which stimulus may consist of
sensation or volition, as in the electric eel, as well as in the appulses
of external bodies; and by drawing off the charges of vital fluid may
occasion the contraction or motions of the muscular fibres, and organs of
sense.

2. The immediate effect of the action of the spirit of animation or
sensorial power on the fibrous parts of the body, whether it acts in the
mode of irritation, sensation, volition, or association, is a contraction
of the animal fibre, according to the second law of animal causation. Sect.
IV. Thus the stimulus of the blood induces the contraction of the heart;
the agreeable taste of a strawberry produces the contraction of the muscles
of deglutition; the effort of the will contracts the muscles, which move
the limbs in walking; and by association other muscles of the trunk are
brought into contraction to preserve the balance of the body. The fibrous
extremities of the organs of sense have been shewn, by the ocular spectra
in Sect. III. to suffer similar contraction by each of the above modes of
excitation; and by their configurations to constitute our ideas.

3. After animal fibres have for some time been excited into contraction, a
relaxation succeeds, even though the exciting cause continues to act. In
respect to the irritative motions this is exemplified in the peristaltic
contractions of the bowels; which cease and are renewed alternately, though
the stimulus of the aliment continues to be uniformly applied; in the
sensitive motions, as in strangury, tenesmus, and parturition, the
alternate contractions and relaxations of the muscles exist, though the
stimulus is perpetual. In our voluntary exertions it is experienced, as no
one can hang long by the hands, however vehemently he wills so to do; and
in the associate motions the constant change of our attitudes evinces the
necessity of relaxation to those muscles, which have been long in action.

This relaxation of a muscle after its contraction, even though the stimulus
continues to be applied, appears to arise from the expenditure or
diminution of the spirit of animation previously resident in the muscle,
according to the second law of animal causation in Sect. IV. In those
constitutions, which are termed weak, the spirit of animation becomes
sooner exhausted, and tremulous motions are produced, as in the hands of
infirm people, when they lift a cup to their mouths. This quicker
exhaustion of the spirit of animation is probably owing to a less quantity
of it residing in the acting fibres, which therefore more frequently
require a supply from the nerves, which belong to them.

4. If the sensorial power continues to act, whether it acts in the mode of
irritation, sensation, volition, or association, a new contraction of the
animal fibre succeeds after a certain interval; which interval is of
shorter continuance in weak people than in strong ones. This is exemplified
in the shaking of the hands of weak people, when they attempt to write. In
a manuscript epistle of one of my correspondents, which is written in a
small hand, I observed from four to six zigzags in the perpendicular stroke
of every letter, which shews that both the contractions of the fingers, and
intervals between them, must have been performed in very short periods of
time.

The times of contraction of the muscles of enfeebled people being less, and
the intervals between those contractions being less also, accounts for the
quick pulse in fevers with debility, and in dying animals. The shortness of
the intervals between one contraction and another in weak constitutions, is
probably owing to the general deficiency of the quantity of the spirit of
animation, and that therefore there is a less quantity of it to be received
at each interval of the activity of the fibres. Hence in repeated motions,
as of the fingers in performing on the harpsichord, it would at first sight
appear, that swiftness and strength were incompatible; nevertheless the
single contraction of a muscle is performed with greater velocity as well
as with greater force by vigorous constitutions, as in throwing a javelin.

There is however another circumstance, which may often contribute to cause
the quickness of the pulse in nervous fevers, as in animals bleeding to
death in the slaughter-house; which is the deficient quantity of blood;
whence the heart is but half distended, and in consequence sooner
contracts. See Sect. XXXII. 2. 1.

For we must not confound frequency of repetition with quickness of motion,
or the number of pulsations with the velocity, with which the fibres, which
constitute the coats of the arteries, contract themselves. For where the
frequency of the pulsations is but seventy-five in a minute, as in health;
the contracting fibres, which constitute the sides of the arteries, may
move through a greater space in a given time, than where the frequency of
pulsation is one hundred and fifty in a minute, as in some fevers with
great debility. For if in those fevers the arteries do not expand
themselves in their diastole to more than half the usual diameter of their
diastole in health, the fibres which constitute their coats, will move
through a less space in a minute than in health, though they make two
pulsations for one.

Suppose the diameter of the artery during its systole to be one line, and
that the diameter of the same artery during its diastole is in health is
four lines, and in a fever with, great debility only two lines. It follows,
that the arterial fibres contract in health from a circle of twelve lines
in circumference to a circle of three lines in circumference, that is they
move through a space of nine lines in length. While the arterial fibres in
the fever with debility would twice contract from a circle of six lines to
a circle of three lines; that is while they move through a space equal to
six lines. Hence though the frequency of pulsation in fever be greater as
two to one, yet the velocity of contraction in health is greater as nine to
six, or as three to two.

On the contrary in inflammatory diseases with strength, as in the pleurisy,
the velocity of the contracting sides of the arteries is much greater than
in health, for if we suppose the number of pulsations in a pleurisy to be
half as much more than in health, that is as one hundred and twenty to
eighty, (which is about what generally happens in inflammatory diseases)
and if the diameter of the artery in diastole be one third greater than in
health, which I believe is near the truth, the result will be, that the
velocity of the contractile sides of the arteries will be in a pleurisy as
two and a half to one, compared to the velocity of their contraction in a
state of health, for if the circumference of the systole of the artery be
three lines, and the diastole in health be twelve lines in circumference,
and in a pleurisy eighteen lines; and secondly, if the artery pulsates
thrice in the diseased state for twice in the healthy one, it follows, that
the velocity of contraction in the diseased state to that in the healthy
state will be forty-five to eighteen, or as two and a half to one.

From hence it would appear, that if we had a criterion to determine the
velocity of the arterial contractions, it would at the same time give us
their strength, and thus be of more service in distinguishing diseases,
than the knowledge of their frequency. As such a criterion cannot be had,
the frequency of pulsation, the age of the patient being allowed for, will
in some measure assist us to distinguish arterial strength from arterial
debility, since in inflammatory diseases with strength the frequency seldom
exceeds one hundred and eighteen or one hundred and twenty pulsations in a
minute; unless under peculiar circumstance, as the great additional stimuli
of wine or of external heat.

5. After a muscle or organ of sense has been excited into contraction, and
the sensorial power ceases to act, the last situation or configuration of
it continues; unless it be disturbed by the action of some antagonist
fibres, or other extraneous power. Thus in weak or languid people, wherever
they throw their limbs on their bed or sofa, there they lie, till another
exertion changes their attitude; hence one kind of ocular spectra seems to
be produced after looking at bright objects; thus when a fire-stick is
whirled round in the night, there appears in the eye a complete circle of
fire; the action or configuration of one part of the retina not ceasing
before the return of the whirling fire.

Thus if any one looks at the setting sun for a short time, and then covers
his closed eyes with his hand, he will for many seconds of time perceive
the image of the sun on his retina. A similar image of all other bodies
would remain some time in the eye, but is effaced by the eternal change of
the motions of the extremity of this nerve in our attention to other
objects. See Sect. XVIII. 5. on Sleep. Hence the dark spots, and other
ocular spectra, are more frequently attended to, and remain longer in the
eyes of weak people, as after violent exercise, intoxication, or want of
sleep.

6. A contraction of the fibres somewhat greater than usual introduces
pleasurable sensation into the system, according to the fourth law of
animal causation. Hence the pleasure in the beginning of drunkenness is
owing to the increased action of the system from the stimulus of vinous
spirit or of opium. If the contractions be still greater in energy or
duration, painful sensations are introduced, as in consequence of great
heat, or caustic applications, or fatigue.

If any part of the system, which is used to perpetual activity, as the
stomach, or heart, or the fine vessels of the skin, acts for a time with
less energy, another kind of painful sensation ensues, which is called
hunger, or faintness, or cold. This occurs in a less degree in the
locomotive muscles, and is called wearysomeness. In the two former kinds of
sensation there is an expenditure of sensorial power, in these latter there
is an accumulation of it.

7. We have used the words exertion of sensorial power as a general term to
express either irritation, sensation, volition, or association; that is, to
express the activity or motion of the spirit of animation, at the time it
produces the contractions of the fibrous parts of the system. It may be
supposed that there may exist a greater or less mobility of the fibrous
parts of our system, or a propensity to be stimulated into contraction by
the greater or less quantity or energy of the spirit of animation; and that
hence if the exertion of the sensorial power be in its natural state, and
the mobility of the fibres be increased, the same quantity of fibrous
contraction will be caused, as if the mobility of the fibres continues in
its natural state, and the sensorial exertion be increased.

Thus it may be conceived, that in diseases accompanied with strength, as in
inflammatory fevers with arterial strength, that the cause of greater
fibrous contraction, may exist in the increased mobility of the fibres,
whose contractions are thence both more forceable and more frequent. And
that in diseases attended with debility, as in nervous fevers, where the
fibrous contractions are weaker, and more frequent, it may be conceived
that the cause consists in a decrease of mobility of the fibres; and that
those weak constitutions, which are attended with cold extremities and
large pupils of the eyes, may possess less mobility of the contractile
fibres, as well as less quantity of exertion of the spirit of animation.

In answer to this mode of reasoning it may be sufficient to observe, that
the contractile fibres consist of inert matter, and when the sensorial
power is withdrawn, as in death, they possess no power of motion at all,
but remain in their last state, whether of contraction or relaxation, and
must thence derive the whole of this property from the spirit of animation.
At the same time it is not improbable, that the moving fibres of strong
people may possess a capability of receiving or containing a greater
quantity of the spirit of animation than those of weak people.

In every contraction of a fibre there is an expenditure of the sensorial
power, or spirit of animation; and where the exertion of this sensorial
power has been for some time increased, and the muscles or organs of sense
have in consequence acted with greater energy, its propensity to activity
is proportionally lessened; which is to be ascribed to the exhaustion or
diminution of its quantity. On the contrary, where there has been less
fibrous contraction than usual for a certain time, the sensorial power or
spirit of animation becomes accumulated in the inactive part of the system.
Hence vigour succeeds rest, and hence the propensity to action of all our
organs of sense and muscles is in a state of perpetual fluctuation. The
irritability for instance of the retina, that is, its quantity of sensorial
power, varies every moment according to the brightness or obscurity of the
object last beheld compared with the present one. The same occurs to our
sense of heat, and to every part of our system, which is capable of being
excited into action.

When this variation of the exertion of the sensorial power becomes much and
permanently above or beneath the natural quantity, it becomes a disease. If
the irritative motions be too great or too little, it shews that the
stimulus of external things affect this sensorial power too violently or
too inertly. If the sensitive motions be too great or too little, the cause
arises from the deficient or exuberant quantity of sensation produced in
consequence of the motions of the muscular fibres or organs of sense; if
the voluntary actions are diseased the cause is to be looked for in the
quantity of volition produced in consequence of the desire or aversion
occasioned by the painful or pleasurable sensations above mentioned. And
the diseases of associations probably depend on the greater or less
quantity of the other three sensorial powers by which they were formed.

From whence it appears that the propensity to action, whether it be called
irritability, sensibility, voluntarity, or associability, is only another
mode of expression for the quantity of sensorial power residing in the
organ to be excited. And that on the contrary the words inirritability and
insensibility, together with inaptitude to voluntary and associate motions,
are synonymous with deficiency of the quantity of sensorial power, or of
the spirit of animation, residing in the organs to be excited.

II. _Of sensorial Exertion._

1. There are three circumstances to be attended to in the production of
animal motions, 1st. The stimulus. 2d. The sensorial power. 3d. The
contractile fibre. 1st. A stimulus, external to the organ, originally
induces into action the sensorial faculty termed irritation; this produces
the contraction of the fibres, which, if it be perceived at all, introduces
pleasure or pain; which in their active state are termed sensation; which
is another sensorial faculty, and occasionally produces contraction of the
fibres; this pleasure or pain is therefore to be considered as another
stimulus, which may either act alone or in conjunction with the former
faculty of the sensorium termed irritation.

This new stimulus of pleasure or pain either induces into action the
sensorial faculty termed sensation, which then produces the contraction of
the fibres; or it introduces desire or aversion, which excite into action
another sensorial faculty, termed volition, and may therefore be considered
as another stimulus, which either alone or in conjunction with one or both
of the two former faculties of the sensorium produces the contraction of
animal fibres. There is another sensorial power, that of association, which
perpetually, in conjunction with one or more of the above, and frequently
singly, produces the contraction of animal fibres, and which is itself
excited into action by the previous motions of contracting fibres.

Now as the sensorial power, termed irritation, residing in any particular
fibres, is excited into exertion by the stimulus of external bodies acting
on those fibres; the sensorial power, termed sensation, residing in any
particular fibres is excited into exertion by the stimulus of pleasure or
pain acting on those fibres; the sensorial power, termed volition, residing
in any particular fibres is excited into exertion by the stimulus of desire
or aversion; and the sensorial power, termed association, residing in any
particular fibres, is excited into action by the stimulus of other fibrous
motions, which had frequently preceded them. The word stimulus may
therefore be used without impropriety of language, for any of these four
causes, which excite the four sensorial powers into exertion. For though
the immediate cause of volition has generally been termed _a motive_; and
that of irritation only has generally obtained the name of _stimulus_; yet
as the immediate cause, which excites the sensorial powers of sensation, or
of association into exertion, have obtained no general name, we shall use
the word stimulus for them all.

Hence the quantity of motion produced in any particular part of the animal
system will be as the quantity of stimulus and the quantity of sensorial
power, or spirit of animation, residing in the contracting fibres. Where
both these quantities are great, _strength_ is produced, when that word is
applied to the motions of animal bodies. Where either of them is deficient,
_weakness_ is produced, as applied to the motions of animal bodies.

Now as the sensorial power, or spirit of animation, is perpetually
exhausted by the expenditure of it in fibrous contractions, and is
perpetually renewed by the secretion or production of it in the brain and
spinal marrow, the quantity of animal strength must be in a perpetual state
of fluctuation on this account; and if to this be added the unceasing
variation of all the four kinds of stimulus above described, which produce
the exertions of the sensorial powers, the ceaseless vicissitude of animal
strength becomes easily comprehended.

If the quantity of sensorial power remains the same, and the quantity of
stimulus be lessened, a weakness of the fibrous contractions ensues, which
may be denominated _debility from defect of stimulus_. If the quantity of
stimulus remains the same, and the quantity of sensorial power be lessened,
another kind of weakness ensues, which may be termed _debility from defect
of sensorial power_; the former of these is called by Dr. Brown, in his
Elements of Medicine, direct debility, and the latter indirect debility.
The coincidence of some parts of this work with correspondent deductions in
the Brunonian Elementa Medicina, a work (with some exceptions) of great
genius, must be considered as confirmations of the truth of the theory, as
they were probably arrived at by different trains of reasoning.

Thus in those who have been exposed to cold and hunger there is a
deficiency of stimulus. While in nervous fever there is a deficiency of
sensorial power. And in habitual drunkards, in a morning before their usual
potation, there is a deficiency both of stimulus and of sensorial power.
While, on the other hand, in the beginning of intoxication there is an
excess of stimulus; in the hot-ach, after the hands have been immersed in
snow, there is a redundancy of sensorial power; and in inflammatory
diseases with arterial strength, there is an excess of both.

Hence if the sensorial power be lessened, while the quantity of stimulus
remains the same as in nervous fever, the frequency of repetition of the
arterial contractions may continue, but their force in respect to removing
obstacles, as in promoting the circulation of the blood, or the velocity of
each contraction, will be diminished, that is, the animal strength will be
lessened. And secondly, if the quantity of sensorial power be lessened, and
the stimulus be increased to a certain degree, as in giving opium in
nervous fevers, the arterial contractions may be performed more frequently
than natural, yet with less strength.

And thirdly, if the sensorial power continues the same in respect to
quantity, and the stimulus be somewhat diminished, as in going into a
darkish room, or into a coldish bath, suppose of about eighty degrees of
heat, as Buxton-bath, a temporary weakness of the affected fibres is
induced, till an accumulation of sensorial power gradually succeeds, and
counterbalances the deficiency of stimulus, and then the bath ceases to
feel cold, and the room ceases to appear dark; because the fibres of the
subcutaneous vessels, or of the organs of sense, act with their usual
energy.

A set of muscular fibres may thus be stimulated into violent exertion, that
is, they may act frequently, and with their whole sensorial power, but may
nevertheless not act strongly; because the quantity of their sensorial
power was originally small, or was previously exhausted. Hence a stimulus
may be great, and the irritation in consequence act with its full force, as
in the hot paroxysms of nervous fever; but if the sensorial power, termed
irritation, be small in quantity, the force of the fibrous contractions,
and the times of their continuance in their contracted state, will be
proportionally small.

In the same manner in the hot paroxysm of putrid fevers, which are shewn in
Sect. XXXIII. to be inflammatory fevers with arterial debility, the
sensorial power termed sensation is exerted with great activity, yet the
fibrous contractions, which produce the circulation of the blood, are
performed without strength, because the quantity of sensorial power then
residing in that part of the system is small.

Thus in irritative fever with arterial strength, that is, with excess of
spirit of animation, the quantity of exertion during the hot part of the
paroxysm is to be estimated from the quantity of stimulus, and the quantity
of sensorial power. While in sensitive (or inflammatory) fever with
arterial strength, that is, with excess of spirit of animation, the violent
and forcible actions of the vascular system during the hot part of the
paroxysm are induced by the exertions of two sensorial powers, which are
excited by two kinds of stimulus. These are the sensorial power of
irritation excited by the stimulus of bodies external to the moving fibres,
and the sensorial power of sensation excited by the pain in consequence of
the increased contractions of those moving fibres.

And in insane people in some cases the force of their muscular actions will
be in proportion to the quantity of sensorial power, which they possess,
and the quantity of the stimulus of desire or aversion, which excites their
volition into action. At the same time in other cases the stimulus of pain
or pleasure, and the stimulus of external bodies, may excite into action
the sensorial powers of sensation and irritation, and thus add greater
force to their muscular actions.

2. The application of the stimulus, whether that stimulus be some quality
of external bodies, or pleasure or pain, or desire or aversion, or a link
of association, excites the correspondent sensorial power into action, and
this causes the contraction of the fibre. On the contraction of the fibre a
part of the spirit of animation becomes expended, and the fibre ceases to
contract, though the stimulus continues to be applied; till in a certain
time the fibre having received a supply of sensorial power is ready to
contract again, if the stimulus continues to be applied. If the stimulus on
the contrary be withdrawn, the same quantity of quiescent sensorial power
becomes resident in the fibre as before its contraction; as appears from
the readiness for action of the large locomotive muscles of the body in a
short time after common exertion.

But in those muscular fibres, which are subject to constant stimulus, as
the arteries, glands, and capillary vessels, another phenomenon occurs, if
their accustomed stimulus be withdrawn; which is, that the sensorial power
becomes accumulated in the contractile fibres, owing to the want of its
being perpetually expended, or carried away, by their usual unremitted
contractions. And on this account those muscular fibres become afterwards
excitable into their natural actions by a much weaker stimulus; or into
unnatural violence of action by their accustomed stimulus, as is seen in
the hot fits of intermittent fevers, which are in consequence of the
previous cold ones. Thus the minute vessels of the skin are constantly
stimulated by the fluid matter of heat; if the quantity of this stimulus of
heat be a while diminished, as in covering the hands with snow, the vessels
cease to act, as appears from the paleness of the skin; if this cold
application of snow be continued but a short time, the sensorial power,
which had habitually been supplied to the fibres, becomes now accumulated
in them, owing to the want of its being expended by their accustomed
contractions. And thence a less stimulus of heat will now excite them into
violent contractions.

If the quiescence of fibres, which had previously been subject to perpetual
stimulus, continues a longer time; or their accustomed stimulus be more
completely withdrawn; the accumulation of sensorial power becomes still
greater, as in those exposed to cold and hunger; pain is produced, and the
organ gradually dies from the chemical changes, which take place in it; or
it is at a great distance of time restored to action by stimulus applied
with great caution in small quantity, as happens to some larger animals and
to many insects, which during the winter months lie benumbed with cold, and
are said to sleep, and to persons apparently drowned, or apparently frozen
to death. Snails have been said to revive by throwing them into water after
having been many years shut up in the cabinets of the curious; and eggs and
seeds in general are restored to life after many months of torpor by the
stimulus of warmth and moisture.

The inflammation of schirrous tumours, which have long existed in a state
of inaction, is a process of this kind; as well as the sensibility acquired
by inflamed tendons and bones, which had at their formation a similar
sensibility, which had so long lain dormant in their uninflamed state.

3. If after long quiescence from defect of stimulus the fibres, which had
previously been habituated to perpetual stimulus, are again exposed to but
their usual quantity of it; as in those who have suffered the extremes of
cold or hunger; a violent exertion of the affected organ commences, owing,
as above explained, to the great accumulation of sensorial power. This
violent exertion not only diminishes the accumulated spirit of animation,
but at the same time induces pleasure or pain into the system, which,
whether it be succeeded by inflammation or not, becomes an additional
stimulus, and acting along with the former one, produces still greater
exertions; and thus reduces the sensorial power in the contracting fibres
beneath its natural quantity.

When the spirit of animation is thus exhausted by useless exertions, the
organ becomes torpid or unexcitable into action, and a second fit of
quiescence succeeds that of abundant activity. During this second fit of
quiescence the sensorial power becomes again accumulated, and another fit
of exertion follows in train. These vicissitudes of exertion and inertion
of the arterial system constitute the paroxysms of remittent fevers; or
intermittent ones, when there is an interval of the natural action of the
arteries between the exacerbations.

In these paroxysms of fevers, which consist of the libration of the
arterial system between the extremes of exertion and quiescence, either the
fits become less and less violent from the contractile fibres becoming
coming less excitable to the stimulus by habit, that is, by becoming
accustomed to it, as explained below XII. 3. 1. or the whole sensorial
power becomes exhausted, and the arteries cease to beat, and the patient
dies in the cold part of the paroxysm. Or secondly, so much pain is
introduced into the system by the violent contractions of the fibres, that
inflammation arises, which prevents future cold fits by expending a part of
the sensorial power in the extension of old vessels or the production of
new ones; and thus preventing the too great accumulation or exertion of it
in other parts of the system; or which by the great increase of stimulus
excites into great action the whole glandular system as well as the
arterial, and thence a greater quantity of sensorial power is produced in
the brain, and thus its exhaustion in any peculiar part of the system
ceases to be affected.

4. Or thirdly, in consequence of the painful or pleasurable sensation above
mentioned, desire and aversion are introduced, and inordinate volition
succeeds; which by its own exertions expends so much of the spirit of
animation, that the two other sensorial faculties, or irritation and
sensation, act so much more feebly; that the paroxysms of fever, or that
libration between the extremes of exertion and inactivity of the arterial
system, gradually subsides. On this account a temporary insanity is a
favourable sign in fevers, as I have had some opportunities of observing.

III. _Of repeated Stimulus._

1. When a stimulus is repeated more frequently than the expenditure of
sensorial power can be renewed in the acting organ, the effect of the
stimulus becomes gradually diminished. Thus if two grains of opium be
swallowed by a person unused to so strong a stimulus, all the vascular
systems in the body act with greater energy, all the secretions and the
absorption from those secreted fluids are increased in quantity; and
pleasure or pain are introduced into the system, which adds an additional
stimulus to that already too great. After some hours the sensorial power
becomes diminished in quantity, expended by the great activity of the
system; and thence, when the stimulus of the opium is withdrawn, the fibres
will not obey their usual degree of natural stimulus, and a consequent
torpor or quiescence succeeds, as is experienced by drunkards, who on the
day after a great excess of spirituous potation feel indigestion, head-ach,
and general debility.

In this fit of torpor or quiescence of a part or of the whole of the
system, an accumulation of the sensorial power in the affected fibres is
formed, and occasions a second paroxysm of exertion by the application only
of the natural stimulus, and thus a libration of the sensorial exertion
between one excess and the other continues for two or three days, where the
stimulus was violent in degree; and for weeks in some fevers, from the
stimulus of contagious matter.

But if a second dose of opium be exhibited before the fibres have regained
their natural quantity of sensorial power, its effect will be much less
than the former, because the spirit of animation or sensorial power is in
part exhausted by the previous excess of exertion. Hence all medicines
repeated too frequently gradually lose their effect, as opium and wine.
Many things of disagreeable taste at first cease to be disagreeable by
frequent repetition, as tobacco; grief and pain gradually diminish, and at
length cease altogether, and hence life itself becomes tolerable.

Besides the temporary diminution of the spirit of animation or sensorial
power, which is naturally stationary or resident in every living fibre, by
a single exhibition of a powerful stimulus, the contractile fibres
themselves, by the perpetual application of a new quantity of stimulus,
before they have regained their natural quantity of sensorial power, appear
to suffer in their capability of receiving so much as the natural quantity
of sensorial power; and hence a permanent deficiency of spirit of animation
takes place, however long the stimulus may have been withdrawn. On this
cause depends the permanent debility of those, who have been addicted to
intoxication, the general weakness of old age, and the natural debility or
inirritability of those, who have pale skins and large pupils of their
eyes.

There is a curious phenomenon belongs to this place, which has always
appeared difficult of solution; and that is, that opium or aloes may be
exhibited in small doses at first, and gradually increased to very large
ones without producing stupor or diarrhoea. In this case, though the opium
and aloes are given in such small doses as not to produce intoxication or
catharsis, yet they are exhibited in quantities sufficient in some degree
to exhaust the sensorial power, and hence a stronger and a stronger dose is
required; otherwise the medicine would soon cease to act at all.

On the contrary, if the opium or aloes be exhibited in a large dose at
first, so as to produce intoxication or diarrhoea; after a few repetitions
the quantity of either of them may be diminished, and they will still
produce this effect. For the more powerful stimulus dissevers the
progressive catenations of animal motions, described in Sect. XVII. and
introduces a new link between them; whence every repetition strengthens
this new association or catenation, and the stimulus may be gradually
decreased, or be nearly withdrawn, and yet the effect shall continue;
because the sensorial power of association or catenation being united with
the stimulus, increases in energy with every repetition of the catenated
circle; and it is by these means that all the irritative associations of
motions are originally produced.

2. When a stimulus is repeated at such distant intervals of time, that the
natural quantity of sensorial power becomes completely restored in the
acting fibres, it will act with the same energy as when first applied.
Hence those who have lately accustomed themselves to large doses of opium
by beginning with small ones, and gradually increasing them, and repeating
them frequently, as mentioned in the preceding paragraph; if they intermit
the use of it for a few days only, must begin again with as small doses as
they took at first, otherwise they will experience the inconveniences of
intoxication.

On this circumstance depend the constant unfailing effects of the various
kinds of stimulus, which excite into action all the vascular systems in the
body; the arterial, venous, absorbent, and glandular vessels, are brought
into perpetual unwearied action by the fluids, which are adapted to
stimulate them; but these have the sensorial power of association added to
that of irritation, and even in some degree that of sensation, and even of
volition, as will be spoken of in their places; and life itself is thus
carried on by the production of sensorial power being equal to its waste or
expenditure in the perpetual movement of the vascular organization.

3. When a stimulus is repeated at uniform intervals of time with such
distances between them, that the expenditure of sensorial power in the
acting fibres becomes completely renewed, the effect is produced with
greater facility or energy. For the sensorial power of association is
combined with the sensorial power of irritation, or, in common language,
the acquired habit assists the power of the stimulus.

This circumstance not only obtains in the annual and diurnal catenations of
animal motions explained in Sect. XXXVI. but in every less circle of
actions or ideas, as in the burthen of a song, or the iterations of a
dance; and constitutes the pleasure we receive from repetition and
imitation; as treated of in Sect. XXII. 2.

4. When a stimulus has been many times repeated at uniform intervals, so as
to produce the complete action of the organ, it may then be gradually
diminished, or totally withdrawn, and the action of the organ will
continue. For the sensorial power of association becomes united with that
of irritation, and by frequent repetition becomes at length of sufficient
energy to carry on the new link in the circle of actions, without the
irritation which at first introduced it.

Hence, when the bark is given at stated intervals for the cure of
intermittent fevers, if sixty grains of it be given every three hours for
the twenty-four hours preceding the expected paroxysm, so as to stimulate
the defective part of the system into action, and by that means to prevent
the torpor or quiescence of the fibres, which constitutes the cold fit;
much less than half the quantity, given before the time at which another
paroxysm of quiescence would have taken place, will be sufficient to
prevent it; because now the sensorial power, termed association, acts in a
twofold manner. First, in respect to the period of the catenation in which
the cold fit was produced, which is now dissevered by the stronger stimulus
of the first doses of the bark; and, secondly, because each dose of bark
being repeated at periodical times, has its effect increased by the
sensorial faculty of association being combined with that of irritation.

Now, when sixty grains of Peruvian bark are taken twice a day, suppose at
ten o'clock and at six, for a fortnight, the irritation excited by this
additional stimulus becomes a part of the diurnal circle of actions, and
will at length carry on the increased action of the system without the
assistance of the stimulus of the bark. On this theory the bitter
medicines, chalybeates, and opiates in appropriated doses, exhibited for a
fortnight, give permanent strength to pale feeble children, and other weak
constitutions.

5. When a defect of stimulus, as of heat, recurs at certain diurnal
intervals, which induces some torpor or quiescence of a part of the system,
the diurnal catenation of actions becomes disordered, and a new association
with this link of torpid action is formed; on the next period the quantity
of quiescence will be increased, suppose the same defect of stimulus to
recur, because now the new association conspires with the defective
irritation in introducing the torpid action of this part of the diurnal
catenation. In this manner many fever-fits commence, where the patient is
for some days indisposed at certain hours, before the cold paroxysm of
fever is completely formed. See Sect. XVII. 3. 3. on Catenation of Animal
Motions.

6. If a stimulus, which at first excited the affected organ into so great
exertion as to produce sensation, be continued for a certain time, it will
cease to produce sensation both then and when repeated, though the
irritative motions in consequence of it may continue or be re-excited.

Many catenations of irritative motions were at first succeeded by
sensation, as the apparent motions of objects when we walk past them, and
probably the vital motions themselves in the early state of our existence.
But as those sensations were followed by no movements of the system in
consequence of them, they gradually ceased to be produced, not being joined
to any succeeding link of catenation. Hence contagious matter, which has
for some weeks stimulated the system into great and permanent sensation,
ceases afterwards to produce general sensation, or inflammation, though it
may still induce topical irritations. See Sect. XXXIII. 2. 8. XIX. 9.

Our absorbent system then seems to receive those contagious matters, which
it has before experienced, in the same manner as it imbibes common moisture
or other fluids; that is, without being thrown into so violent action as to
produce sensation; the consequence of which is an increase of daily energy
or activity, till inflammation and its consequences succeed.

7. If a stimulus excites an organ into such violent contractions as to
produce sensation, the motions of which organ had not usually produced
sensation, this new sensorial power, added to the irritation occasioned by
the stimulus, increases the activity of the organ. And if this activity be
catenated with the diurnal circle of actions, an increasing inflammation is
produced; as in the evening paroxysms of small-pox, and other fevers with
inflammation. And hence schirrous tumours, tendons and membranes, and
probably the arteries themselves become inflamed, when they are strongly
stimulated.

IV. _Of Stimulus greater than natural._

1. A quantity of stimulus greater than natural, producing an increased
exertion of sensorial power, whether that exertion be in the mode of
irritation, sensation, volition, or association, diminishes the general
quantity of it. This fact is observable in the progress of intoxication, as
the increased quantity or energy of the irritative motions, owing to the
stimulus of vinous spirit, introduces much pleasurable sensation into the
system, and much exertion of muscular or sensual motions in consequence of
this increased sensation; the voluntary motions, and even the associate
ones, become much impaired or diminished; and delirium and staggering
succeed. See Sect. XXI. on Drunkenness. And hence the great prostration of
the strength of the locomotive muscles in some fevers, is owing to the
exhaustion of sensorial power by the increased action of the arterial
system.

In like manner a stimulus greater than natural, applied to a part of the
system, increases the exertion of sensorial power in that part, and
diminishes it in some other part. As in the commencement of scarlet fever,
it is usual to see great redness and heat on the faces and breasts of
children, while at the same time their feet are colder than natural;
partial heats are observable in other fevers with debility, and are
generally attended with torpor or quiescence of some other part of the
system. But these partial exertions of sensorial power are sometimes
attended with increased partial exertions in other parts of the system,
which sympathize with them, as the flushing of the face after a full meal.
Both these therefore are to be ascribed to sympathetic associations,
explained in Sect. XXXV. and not to general exhaustion or accumulation of
sensorial power.

2. A quantity of stimulus greater than natural, producing an increased
exertion of sensorial power in any particular organ, diminishes the
quantity of it in that organ. This appears from the contractions of animal
fibres being not so easily excited by a less stimulus after the organ has
been subjected to a greater. Thus after looking at any luminous object of a
small size, as at the setting sun, for a short time, so as not much to
fatigue the eye, this part of the retina becomes less sensible to smaller
quantities of light; hence when the eyes are turned on other less luminous
parts of the sky, a dark spot is seen resembling the shape of the sun, or
other luminous object which we last behold. See Sect. XL. No. 2.

Thus we are some time before we can distinguish objects in an obscure room
after coming from bright day-light, though the iris presently contracts
itself. We are not able to hear weak sounds after loud ones. And the
stomachs of those who have been much habituated to the stronger stimulus of
fermented or spirituous liquors, are not excited into due action by weaker
ones.

3. A quantity of stimulus something greater than the last mentioned, or
longer continued, induces the organ into spasmodic action, which ceases and
recurs alternately. Thus on looking for a time on the setting sun, so as
not greatly to fatigue the sight, a yellow spectrum is seen when the eyes
are closed and covered, which continues for a time, and then disappears and
recurs repeatedly before it entirely vanishes. See Sect. XL. No. 5. Thus
the action of vomiting ceases and is renewed by intervals, although the
emetic drug is thrown up with the first effort. A tenesmus continues by
intervals some time after the exclusion of acrid excrement; and the
pulsations of the heart of a viper are said to continue some time after it
is cleared from its blood.

In these cases the violent contractions of the fibres produce pain
according to law 4; and this pain constitutes an additional kind or
quantity of excitement, which again induces the fibres into contraction,
and which painful excitement is again renewed, and again induces
contractions of the fibres with gradually diminishing effect.

4. A quantity of stimulus greater than that last mentioned, or longer
continued, induces the antagonist muscles into spasmodic action. This is
beautifully illustrated by the ocular spectra described in Sect. XL. No. 6.
to which the reader is referred. From those experiments there is reason to
conclude that the fatigued part of the retina throws itself into a contrary
mode of action like oscitation or pandiculation, as soon as the stimulus,
which has fatigued it, is withdrawn; but that it still remains liable to be
excited into action by any other colours except the colour with which it
has been fatigued. Thus the yawning and stretching the limbs after a
continued action or attitude seems occasioned by the antagonist muscles
being stimulated by their extension during the contractions of those in
action, or in the situation in which that action last left them.

5. A quantity of stimulus greater than the last, or longer continued,
induces variety of convulsions or fixed spasms either of the affected organ
or of the moving fibres in the other parts of the body. In respect to the
spectra in the eye, this is well illustrated in No. 7 and 8, of Sect. XL.
Epileptic convulsions, as the emprosthotonos and opisthotonos, with the
cramp of the calf of the leg, locked jaw, and other cataleptic fits, appear
to originate from pain, as some of these patients scream aloud before the
convulsion takes place; which seems at first to be an effort to relieve
painful sensation, and afterwards an effort to prevent it.

In these cases the violent contractions of the fibres produce so much pain,
as to constitute a perpetual excitement; and that in so great a degree as
to allow but small intervals of relaxation of the contracting fibres as in
convulsions, or no intervals at all as in fixed spasms.

6. A quantity of stimulus greater than the last, or longer continued,
produces a paralysis of the organ. In many cases this paralysis is only a
temporary effect, as on looking long on a small area of bright red silk
placed on a sheet of white paper on the floor in a strong light, the red
silk gradually becomes paler, and at length disappears; which evinces that
a part of the retina, by being violently excited, becomes for a time
unaffected by the stimulus of that colour. Thus cathartic medicines,
opiates, poisons, contagious matter, cease to influence our system after it
has been habituated to the use of them, except by the exhibition of
increased quantities of them; our fibres not only become unaffected by
stimuli, by which they have previously been violently irritated, as by the
matter of the small-pox or measles; but they also become unaffected by
sensation, where the violent exertions, which disabled them, were in
consequence of too great quantity of sensation. And lastly the fibres,
which become disobedient to volition, are probably disabled by their too
violent exertions in consequence of too great a quantity of volition.

After every exertion of our fibres a temporary paralysis succeeds, whence
the intervals of all muscular contractions, as mentioned in No. 3 and 4 of
this Section; the immediate cause of these more permanent kinds of
paralysis is probably owing in the same manner to the too great exhaustion
of the spirit of animation in the affected part; so that a stronger
stimulus is required, or one of a different kind from that, which
occasioned those too violent contractions, to again excite the affected
organ into activity; and if a stronger stimulus could be applied, it must
again induce paralysis.

For these powerful stimuli excite pain at the same time, that they produce
irritation; and this pain not only excites fibrous motions by its stimulus,
but it also produces volition; and thus all these stimuli acting at the
same time, and sometimes with the addition of their associations, produce
so great exertion as to expend the whole of the sensorial power in the
affected fibres.

V. _Of Stimulus less than natural._

1. A quantity of stimulus less than natural, producing a decreased exertion
of sensorial power, occasions an accumulation of the general quantity of
it. This circumstance is observable in the hemiplagia, in which the
patients are perpetually moving the muscles, which are unaffected. On this
account we awake with greater vigour after sleep, because during so many
hours, the great usual expenditure of sensorial power in the performance of
voluntary actions, and in the exertions of our organs of sense, in
consequence of the irritations occasioned by external objects had been
suspended, and a consequent accumulation had taken place.

In like manner the exertion of the sensorial power less than natural in one
part of the system, is liable to produce an increase of the exertion of it
in some other part. Thus by the action of vomiting, in which the natural
exertion of the motions of the stomach are destroyed or diminished, an
increased absorption of the pulmonary and cellular lymphatics is produced,
as is known by the increased absorption of the fluid deposited in them in
dropsical cases. But these partial quiescences of sensorial power are also
sometimes attended with other partial quiescences, which sympathize with
them, as cold and pale extremities from hunger. These therefore are to be
ascribed to the associations of sympathy explained in Sect. XXXV. and not
to the general accumulation of sensorial power.

2. A quantity of stimulus less than natural, applied to fibres previously
accustomed to perpetual stimulus, is succeeded by accumulation of sensorial
power in the affected organ. The truth of this proposition is evinced,
because a stimulus less than natural, if it be somewhat greater than that
above mentioned, will excite the organ so circumstanced into violent
activity. Thus on a frosty day with wind, the face of a person exposed to
the wind is at first pale and shrunk; but on turning the face from the
wind, it becomes soon of a glow with warmth and flushing. The glow of the
skin in emerging from the cold-bath is owing to the same cause.

It does not appear, that an accumulation of sensorial power above the
natural quantity is acquired by those muscles, which are not subject to
perpetual stimulus, as the locomotive muscles: these, after the greatest
fatigue, only acquire by rest their usual aptitude to motion; whereas the
vascular system, as the heart and arteries, after a short quiescence, are
thrown into violent action by their natural quantity of stimulus.

Nevertheless by this accumulation of sensorial power during the application
of decreased stimulus, and by the exhaustion of it during the action of
increased stimulus, it is wisely provided, that the actions of the vascular
muscles and organs of sense are not much deranged by small variations of
stimulus; as the quantity of sensorial power becomes in some measure
inversely as the quantity of stimulus.

3. A quantity of stimulus less than that mentioned above, and continued for
some time, induces pain in the affected organ, as the pain of cold in the
hands, when they are immersed in snow, is owing to a deficiency of the
stimulation of heat. Hunger is a pain from the deficiency of the
stimulation of food. Pain in the back at the commencement of ague-fits, and
the head-achs which attend feeble people, are pains from defect of
stimulus, and are hence relieved by opium, essential oils, spirit of wine.

As the pains, which originate from defect of stimulus, only occur in those
parts of the system, which have been previously subjected to perpetual
stimulus; and as an accumulation of sensorial power is produced in the
quiescent organ along with the pain, as in cold or hunger, there is reason
to believe, that the pain is owing to the accumulation of sensorial power.
For, in the locomotive muscles, in the retina of the eye, and other organs
of senses, no pain occurs from the absence of stimulus, nor any great
accumulation of sensorial power beyond their natural quantity, since these
organs have not been used to a perpetual supply of it. There is indeed a
greater accumulation occurs in the organ of vision after its quiescence,
because it is subject to more constant stimulus.

4. A certain quantity of stimulus less than natural induces the moving
organ into feebler and more frequent contractions, as mentioned in No. I.
4. of this Section. For each contraction moving through a less space, or
with less force, that is, with less expenditure of the spirit of animation,
is sooner relaxed, and the spirit of animation derived at each interval
into the acting fibres being less, these intervals likewise become shorter.
Hence the tremours of the hands of people accustomed to vinous spirit, till
they take their usual stimulus; hence the quick pulse in fevers attended
with debility, which is greater than in fevers attended with strength; in
the latter the pulse seldom beats above 120 times in a minute, in the
former it frequently exceeds 140.

It must be observed, that in this and the two following articles the
decreased action of the system is probably more frequently occasioned by
deficiency in the quantity of sensorial power, than in the quantity of
stimulus. Thus those feeble constitutions which have large pupils of their
eyes, and all who labour under nervous fevers, seem to owe their want of
natural quantity of activity in the system to the deficiency of sensorial
power; since, as far as can be seen, they frequently possess the natural
quantity of stimulus.

5. A certain quantity of stimulus, less than that above mentioned, inverts
the order of successive fibrous contractions; as in vomiting the vermicular
motions of the stomach and duodenum are inverted, and their contents
ejected, which is probably owing to the exhaustion of the spirit of
animation in the acting muscles by a previous excessive stimulus, as by the
root of ipecacuanha, and the consequent defect of sensorial power. The same
retrograde motions affect the whole intestinal canal in ileus; and the
oesophagus in globus hystericus. See this further explained in Sect. XXIX.
No. 11. on Retrograde Motions.

I must observe, also, that something similar happens in the production of
our ideas, or sensual motions, when they are too weakly excited; when any
one is thinking intensely about one thing, and carelessly conversing about
another, he is liable to use the word of a contrary meaning to that which
he designed, as cold weather for hot weather, summer for winter.

6. A certain quantity of stimulus, less than that above mentioned, is
succeeded by paralysis, first of the voluntary and sensitive motions, and
afterwards of those of irritation, and of association, which constitutes
death.

VI. _Cure of increased Exertion._

1. The cure, which nature has provided for the increased exertion of any
part of the system, consists in the consequent expenditure of the sensorial
power. But as a greater torpor follows this exhaustion of sensorial power,
as explained in the next paragraph, and a greater exertion succeeds this
torpor, the constitution frequently sinks under these increasing librations
between exertion and quiescence; till at length complete quiescence, that
is, death, closes the scene.

For, during the great exertion of the system in the hot fit of fever, an
increase of stimulus is produced from the greater momentum of the blood,
the greater distention of the heart and arteries, and the increased
production of heat, by the violent actions of the system occasioned by this
augmentation of stimulus, the sensorial power becomes diminished in a few
hours much beneath its natural quantity, the vessels at length cease to
obey even these great degrees of stimulus, as shewn in Sect. XL. 9. 1. and
a torpor of the whole or of a part of the system ensues.

Now as this second cold fit commences with a greater deficiency of
sensorial power, it is also attended with a greater deficiency of stimulus
than in the preceding cold fit, that is, with less momentum of blood, less
distention of the heart. On this account the second cold fit becomes more
violent and of longer duration than the first; and as a greater
accumulation of sensorial power must be produced before the system of
vessels will again obey the diminished stimulus, it follows, that the
second hot fit of fever will be more violent than the former one. And that
unless some other causes counteract either the violent exertions in the hot
fit, or the great torpor in the cold fit, life will at length be
extinguished by the expenditure of the whole of the sensorial power. And
from hence it appears, that the true means of curing fevers must be such as
decrease the action of the system in the hot fit, and increase it in the
cold fit; that is, such as prevent the too great diminution of sensorial
power in the hot fit, and the too great accumulation of it in the cold one.

2. Where the exertion of the sensorial powers is much increased, as in the
hot fits of fever or inflammation, the following are the usual means of
relieving it. Decrease the irritations by blood-letting, and other
evacuations; by cold water taken into the stomach, or injected as an enema,
or used externally; by cold air breathed into the lungs, and diffused over
the skin; with food of less stimulus than the patient has been accustomed
to.

3. As a cold fit, or paroxysm of inactivity of some parts of the system,
generally precedes the hot fit, or paroxysm of exertion, by which the
sensorial power becomes accumulated, this cold paroxysm should be prevented
by stimulant medicines and diet, as wine, opium, bark, warmth,
cheerfulness, anger, surprise.

4. Excite into greater action some other part of the system, by which means
the spirit of animation may be in part expended, and thence the inordinate
actions of the diseased part may be lessened. Hence when a part of the skin
acts violently, as of the face in the eruption of the small-pox, if the
feet be cold they should be covered. Hence the use of a blister applied
near a topical inflammation. Hence opium and warm bath relieve pains both
from excess and defect of stimulus.

5. First increase the general stimulation above its natural quantity, which
may in some degree exhaust the spirit of animation, and then decrease the
stimulation beneath its natural quantity. Hence after sudorific medicines
and warm air, the application of refrigerants may have greater effect, if
they could be administered without danger of producing too great torpor of
some part of the system; as frequently happens to people in health from
coming out of a warm room into the cold air, by which a topical
inflammation in consequence of torpor of the mucous membrane of the nostril
is produced, and is termed a cold in the head.

VII. _Cure of decreased Exertion._

1. Where the exertion of the sensorial powers is much decreased, as in the
cold fits of fever, a gradual accumulation of the spirit of animation takes
place; as occurs in all cases where inactivity or torpor of a part of the
system exists; this accumulation of sensorial power increases, till stimuli
less than natural are sufficient to throw it into action, then the cold fit
ceases; and from the action of the natural stimuli a hot one succeeds with
increased activity of the whole system.

So in fainting fits, or syncope, there is a temporary deficiency of
sensorial exertion, and a consequent quiescence of a great part of the
system. This quiescence continues, till the sensorial power becomes again
accumulated in the torpid organs; and then the usual diurnal stimuli excite
the revivescent parts again into action; but as this kind of quiescence
continues but a short time compared to the cold paroxysm of an ague, and
less affects the circulatory system, a less superabundancy of exertion
succeeds in the organs previously torpid, and a less excess of arterial
activity. See Sect. XXXIV. 1. 6.

2. In the diseases occasioned by a defect of sensorial exertion, as in cold
fits of ague, hysteric complaint, and nervous fever, the following means
are those commonly used. 1. Increase the stimulation above its natural
quantity for some weeks, till a new habit of more energetic contraction of
the fibres is established. This is to be done by wine, opium, bark, steel,
given at exact periods, and in appropriate quantities; for if these
medicines be given in such quantity, as to induce the least degree of
intoxication, a debility succeeds from the useless exhaustion of spirit of
animation in consequence of too great exertion of the muscles or organs of
sense. To these irritative stimuli should be added the sensitive ones of
cheerful ideas, hope, affection.

3. Change the kinds of stimulus. The habits acquired by the constitution
depend on such nice circumstances, that when one kind of stimulus ceases to
excite the sensorial power into the quantity of exertion necessary to
health, it is often sufficient to change the stimulus for another
apparently similar in quantity and quality. Thus when wine ceases to
stimulate the constitution, opium in appropriate doses supplies the defect;
and the contrary. This is also observed in the effects of cathartic
medicines, when one loses its power, another, apparently less efficacious,
will succeed. Hence a change of diet, drink, and stimulating medicines, is
often advantageous in diseases of debility.

4. Stimulate the organs, whose motions are associated with the torpid parts
of the system. The actions of the minute vessels of the various parts of
the external skin are not only associated with each other, but are strongly
associated with those of some of the internal membranes, and particularly
of the stomach. Hence when the exertion of the stomach is less than
natural, and indigestion and heartburn succeed, nothing so certainly
removes these symptoms as the stimulus of a blister on the back. The
coldness of the extremities, as of the nose, ears, or fingers, are hence
the best indication for the successful application of blisters.

5. Decrease the stimulus for a time. By lessening the quantity of heat for
a minute or two by going into the cold bath, a great accumulation of
sensorial power is produced; for not only the minute vessels of the whole
external skin for a time become inactive, as appears by their paleness; but
the minute vessels of the lungs lose much of their activity also by concert
with those of the skin, as appears from the difficulty of breathing at
first going into cold water. On emerging from the bath the sensorial power
is thrown into great exertion by the stimulus of the common degree of the
warmth of the atmosphere, and a great production of animal heat is the
consequence. The longer a person continues in the cold bath the greater
must be the present inertion of a great part of the system, and in
consequence a greater accumulation of sensorial power. Whence M. Pomè
recommends some melancholy patients to be kept from two to six hours in
spring-water, and in baths still colder.

6. Decrease the stimulus for a time below the natural, and then increase it
above natural. The effect of this process, improperly used, is seen in
giving much food, or applying much warmth, to those who have been
previously exposed to great hunger, or to great cold. The accumulated
sensorial power is thrown into so violent exertion, that inflammations and
mortifications supervene, and death closes the catastrophe. In many
diseases this method is the most successful; hence the bark in agues
produces more certain effect after the previous exhibition of emetics. In
diseases attended with violent pain, opium has double the effect, if
venesection and a cathartic have been previously used. On this seems to
have been founded the successful practice of Sydenham, who used venesection
and a cathartic in chlorosis before the exhibition of the bark, steel, and
opiates.

7. Prevent any unnecessary expenditure of sensorial power. Hence in fevers
with debility, a decumbent posture is preferred, with silence, little
light, and such a quantity of heat as may prevent any chill sensation, or
any coldness of the extremities. The pulse of patients in fevers with
debility increases in frequency above ten pulsations in a minute on their
rising out of bed. For the expenditure of sensorial power to preserve an
erect posture of the body adds to the general deficiency of it, and thus
affects the circulation.

8. The longer in time and the greater in degree the quiescence or inertion
of an organ has been, so that it still retains life or excitability, the
less stimulus should at first be applied to it. The quantity of stimulation
is a matter of great nicety to determine, where the torpor or quiescence of
the fibres has been experienced in a great degree, or for a considerable
time, as in cold fits of the ague, in continued fevers with great debility,
or in people famished at sea, or perishing with cold. In the two last
cases, very minute quantities of food should be first supplied, and very
few additional degrees of heat. In the two former cases, but little
stimulus of wine or medicine, above what they had been lately accustomed
to, should be exhibited, and this at frequent and stated intervals, so that
the effect of one quantity may be observed before the exhibition of
another.

If these circumstances are not attended to, as the sensorial power becomes
accumulated in the quiescent fibres, an inordinate exertion takes place by
the increase of stimulus acting on the accumulated quantity of sensorial
power, and either the paralysis, or death of the contractile fibres ensues,
from the total expenditure of the sensorial power in the affected organ,
owing to this increase of exertion, like the debility after intoxication.
Or, secondly, the violent exertions above mentioned produce painful
sensation, which becomes a new stimulus, and by thus producing
inflammation, and increasing the activity of the fibres already too great,
sooner exhausts the whole of the sensorial power in the acting organ, and
mortification, that is, the death of the part, supervenes.

Hence there have been many instances of people, whose limbs have been long
benumbed by exposure to cold, who have lost them by mortification on their
being too hastily brought to the fire; and of others, who were nearly
famished at sea, who have died soon after having taken not more than an
usual meal of food. I have heard of two well-attested instances of patients
in the cold fit of ague, who have died from the exhibition of gin and
vinegar, by the inflammation which ensued. And in many fevers attended with
debility, the unlimited use of wine, and the wanton application of
blisters, I believe, has destroyed numbers by the debility consequent to
too great stimulation, that is, by the exhaustion of the sensorial power by
its inordinate exertion.

Wherever the least degree of intoxication exists, a proportional debility
is the consequence; but there is a golden rule by which the necessary and
useful quantity of stimulus in fevers with debility may be ascertained.
When wine or beer are exhibited either alone or diluted with water, if the
pulse becomes slower the stimulus is of a proper quantity; and should be
repeated every two or three hours, or when the pulse again becomes quicker.

In the chronical debility brought on by drinking spirituous or fermented
liquors, there is another golden rule by which I have successfully directed
the quantity of spirit which they may safely lessen, for there is no other
means by which they can recover their health. It should be premised, that
where the power of digestion in these patients is totally destroyed, there
is not much reason to expect a return to healthful vigour.

I have directed several of these patients to omit one fourth part of the
quantity of vinous spirit they have been lately accustomed to, and if in a
fortnight their appetite increases, they are advised to omit another fourth
part; but if they perceive that their digestion becomes impaired from the
want of this quantity of spirituous potation, they are advised to continue
as they are, and rather bear the ills they have, than risk the encounter of
greater. At the same time flesh-meat with or without spice is recommended,
with Peruvian bark and steel in small quantities between their meals, and
half a grain of opium or a grain, with five or eight grains of rhubarb at
night.

       *       *       *       *       *

SECT. XIII.

OF VEGETABLE ANIMATION.

    I. 1. _Vegetables are irritable; mimosa, dionæa muscipula. Vegetable
    secretions._ 2. _Vegetable buds are inferior animals, are liable to
    greater or less irritability._ II. _Stamens and pistils of plants shew
    marks of sensibility._ III. _Vegetables possess some degree of
    volition._ IV. _Motions of plants are associated like those of
    animals._ V. 1. _Vegetable structure like that of animals, their
    anthers and stigmas are living creatures. Male-flowers of Vallisneria._
    2. _Whether vegetables, possess ideas? They have organs of sense as of
    touch and smell, and ideas of external things?_

I. 1. The fibres of the vegetable world, as well as those of the animal,
are excitable into a variety of motion by irritations of external objects.
This appears particularly in the mimosa or sensitive plant, whose leaves
contract on the slightest injury; the dionæa muscipula, which was lately
brought over from the marshes of America, presents us with another curious
instance of vegetable irritability; its leaves are armed with spines on
their upper edge, and are spread on the ground around the stem; when an
insect creeps on any of them in its passage to the flower or seed, the leaf
shuts up like a steel rat-trap, and destroys its enemy. See Botanic Garden,
Part II. note on Silene.

The various secretions of vegetables, as of odour, fruit, gum, resin, wax,
honey, seem brought about in the same manner as in the glands of animals;
the tasteless moisture of the earth is converted by the hop-plant into a
bitter juice; as by the caterpillar in the nut-shell the sweet kernel is
converted into a bitter powder. While the power of absorption in the roots
and barks of vegetables is excited into action by the fluids applied to
their mouths like the lacteals and lymphatics of animals.

2. The individuals of the vegetable world may be considered as inferior or
less perfect animals; a tree is a congeries of many living buds, and in
this respect resembles the branches of coralline, which are a congeries of
a multitude of animals. Each of these buds of a tree has its proper leaves
or petals for lungs, produces its viviparous or its oviparous offspring in
buds or seeds; has its own roots, which extending down the stem of the tree
are interwoven with the roots of the other buds, and form the bark, which
is the only living part of the stem, is annually renewed, and is
superinduced upon the former bark, which then dies, and with its stagnated
juices gradually hardening into wood forms the concentric circles, which we
see in blocks of timber.

The following circumstances evince the individuality of the buds of trees.
First, there are many trees, whose whole internal wood is perished, and yet
the branches are vegete and healthy. Secondly, the fibres of the barks of
trees are chiefly longitudinal, resembling roots, as is beautifully seen in
those prepared barks, that were lately brought from Otaheita. Thirdly, in
horizontal wounds of the bark of trees, the fibres of the upper lip are
always elongated downwards like roots, but those of the lower lip do not
approach to meet them. Fourthly, if you wrap wet moss round any joint of a
vine, or cover it with moist earth, roots will shoot out from it. Fifthly,
by the inoculation or engrafting of trees many fruits are produced from one
stem. Sixthly, a new tree is produced from a branch plucked from an old
one, and set in the ground. Whence it appears that the buds of deciduous
trees are so many annual plants, that the bark is a contexture of the roots
of each individual bud; and that the internal wood is of no other use but
to support them in the air, and that thus they resemble the animal world in
their individuality.

The irritability of plants, like that of animals, appears liable to be
increased or decreased by habit; for those trees or shrubs, which are
brought from a colder climate to a warmer, put out their leaves and
blossoms a fortnight sooner than the indigenous ones.

Professor Kalm, in his Travels in New York, observes that the apple-trees
brought from England blossom a fortnight sooner than the native ones. In
our country the shrubs, that are brought a degree or two from the north,
are observed to flourish better than those, which come from the south. The
Siberian barley and cabbage are said to grow larger in this climate than
the similar more southern vegetables. And our hoards of roots, as of
potatoes and onions, germinate with less heat in spring, after they have
been accustomed to the winter's cold, than in autumn after the summer's
heat.

II. The stamens and pistils of flowers shew evident marks of sensibility,
not only from many of the stamens and some pistils approaching towards each
other at the season of impregnation, but from many of them closing their
petals and calyxes during the cold parts of the day. For this cannot be
ascribed to irritation, because cold means a defect of the stimulus of
heat; but as the want of accustomed stimuli produces pain, as in coldness,
hunger, and thirst of animals, these motions of vegetables in closing up
their flowers must be ascribed to the disgreeable sensation, and not to the
irritation of cold. Others close up their leaves during darkness, which,
like the former, cannot be owing to irritation, as the irritating material
is withdrawn.

The approach of the anthers in many flowers to the stigmas, and of the
pistils of some flowers to the anthers, must be ascribed to the passion of
love, and hence belongs to sensation, not to irritation.

III. That the vegetable world possesses some degree of voluntary powers,
appears from their necessity to sleep, which we have shewn in Sect. XVIII.
to consist in the temporary abolition of voluntary power. This voluntary
power seems to be exerted in the circular movement of the tendrils of
vines, and other climbing vegetables; or in the efforts to turn the upper
surface of their leaves, or their flowers to the light.

IV. The associations of fibrous motions are observable in the vegetable
world, as well as in the animal. The divisions of the leaves of the
sensitive plant have been accustomed to contract at the same time from the
absence of light; hence if by any other circumstance, as a slight stroke or
injury, one division is irritated into contraction, the neighbouring ones
contract also, from their motions being associated with those of the
irritated part. So the various stamina of the class of syngenesia have been
accustomed to contract together in the evening, and thence if you stimulate
one of them with a pin, according to the experiment of M. Colvolo, they all
contract from their acquired associations.

To evince that the collapsing of the sensitive plant is not owing to any
mechanical vibrations propagated along the whole branch, when a single leaf
is struck with the finger, a leaf of it was slit with sharp scissors, and
some seconds of time passed before the plant seemed sensible of the injury;
and then the whole branch collapsed as far as the principal stem: this
experiment was repeated several times with the least possible impulse to
the plant.

V. 1. For the numerous circumstances in which vegetable buds are analogous
to animals, the reader is referred to the additional notes at the end of
the Botanic Garden, Part I. It is there shewn, that the roots of vegetables
resemble the lacteal system of animals; the sap-vessels in the early
spring, before their leaves expand, are analogous to the placental vessels
of the foetus; that the leaves of land-plants resemble lungs, and those of
aquatic plants the gills of fish; that there are other systems of vessels
resembling the vena portarum of quadrupeds, or the aorta of fish; that the
digestive power of vegetables is similar to that of animals converting the
fluids, which they absorb, into sugar; that their seeds resemble the eggs
of animals, and their buds and bulbs their viviparous offspring. And,
lastly, that the anthers and stigmas are real animals, attached indeed to
their parent tree like polypi or coral insects, but capable of spontaneous
motion; that they are affected with the passion of love, and furnished with
powers of reproducing their species, and are fed with honey like the moths
and butterflies, which plunder their nectaries. See Botanic Garden, Part I.
add. note XXXIX.

The male flowers of vallisneria approach still nearer to apparent
animality, as they detach themselves from the parent plant, and float on
the surface of the water to the female ones. Botanic Garden, Part II. Art.
Vallisneria. Other flowers of the classes of monecia and diecia, and
polygamia, discharge the fecundating farina, which floating in the air is
carried to the stigma of the female flowers, and that at considerable
distances. Can this be effected by any specific attraction? or, like the
diffusion of the odorous particles of flowers, is it left to the currents
of winds, and the accidental miscarriages of it counteracted by the
quantity of its production?

2. This leads us to a curious enquiry, whether vegetables have ideas of
external things? As all our ideas are originally received by our senses,
the question may be changed to, whether vegetables possess any organs of
sense? Certain it is, that they possess a sense of heat and cold, another
of moisture and dryness, and another of light and darkness; for they close
their petals occasionally from the presence of cold, moisture, or darkness.
And it has been already shewn, that these actions cannot be performed
simply from irritation, because cold and darkness are negative quantities,
and on that account sensation or volition are implied, and in consequence a
sensorium or union of their nerves. So when we go into the light, we
contract the iris; not from any stimulus of the light on the fine muscles
of the iris, but from its motions being associated with the sensation of
too much light on the retina: which could not take place without a
sensorium or center of union of the nerves of the iris with those of
vision. See Botanic Garden, Part I. Canto 3. l. 440. note.

Besides these organs of sense, which distinguish cold, moisture, and
darkness, the leaves of mimosa, and of dionæa, and of drosera, and the
stamens of many flowers, as of the berbery, and the numerous class of
syngenesia, are sensible to mechanic impact, that is, they possess a sense
of touch, as well as a common sensorium; by the medium of which their
muscles are excited into action. Lastly, in many flowers the anthers, when
mature, approach the stigma, in others the female organ approaches to the
male. In a plant of collinsonia, a branch of which is now before me, the
two yellow stamens are about three eights of an inch high, and diverge from
each other, at an angle of about fifteen degrees, the purple style is half
an inch high, and in some flowers is now applied to the stamen on the right
hand, and in others to that of the left; and will, I suppose, change place
to-morrow in those, where the anthers have not yet effused their powder.

I ask, by what means are the anthers in many flowers, and stigmas in other
flowers, directed to find their paramours? How do either of them know, that
the other exists in their vicinity? Is this curious kind of storge produced
by mechanic attraction, or by the sensation of love? The latter opinion is
supported by the strongest analogy, because a reproduction of the species
is the consequence; and then another organ of sense must be wanted to
direct these vegetable amourettes to find each other, one probably
analogous to our sense of smell, which in the animal world directs the
new-born infant to its source of nourishment, and they may thus possess a
faculty of perceiving as well as of producing odours.

Thus, besides a kind of taste at the extremities of their roots, similar to
that of the extremities of our lacteal vessels, for the purpose of
selecting their proper food: and besides different kinds of irritability
residing in the various glands, which separate honey, wax, resin, and other
juices from their blood; vegetable life seems to possess an organ of sense
to distinguish the variations of heat, another to distinguish the varying
degrees of moisture, another of light, another of touch, and probably
another analogous to our sense of smell. To these must be added the
indubitable evidence of their passion of love, and I think we may truly
conclude, that they are furnished with a common sensorium belonging to each
bud and that they must occasionally repeat those perceptions either in
their dreams or waking hours, and consequently possess ideas of so many of
the properties of the external world, and of their own existence.

       *       *       *       *       *

SECT. XIV.

OF THE PRODUCTION OF IDEAS.

    I. _Of material and immaterial beings. Doctrine of St. Paul._ II. 1.
    _Of the sense of touch. Of solidity._ 2. _Of figure. Motion. Time.
    Place. Space. Number._ 3. _Of the penetrability of matter._ 4. _Spirit
    of animation possesses solidity, figure, visibility, &c. Of Spirits and
    angels._ 5. _The existence of external things._ III. _Of vision._ IV.
    _Of hearing._ V. _Of smell and taste._ VI. _Of the organ of sense by
    which we perceive heat and cold, not by the sense of touch._ VII. _Of
    the sense of extension, the whole of the locomotive muscles may be
    considered as one organ of sense._ VIII. _Of the senses of hunger,
    thirst, want of fresh air, suckling children, and lust._ IX. _Of many
    other organs of sense belonging to the glands. Of painful sensations
    from the excess of light, pressure, heat, itching, caustics, and
    electricity._

I. Philosophers have been much perplexed to understand, in what manner we
become acquainted with the external world; insomuch that Dr. Berkly even
doubted its existence, from having observed (as he thought) that none of
our ideas resemble their correspondent objects. Mr. Hume asserts, that our
belief depends on the greater distinctness or energy of our ideas from
perception; and Mr. Reid has lately contended, that our belief of external
objects is an innate principle necessarily joined with our perceptions.

So true is the observation of the famous Malbranch, "that our senses are
not given us to discover the essences of things, but to acquaint us with
the means of preserving our existence," (L. I. ch. v.) a melancholy
reflection to philosophers!

Some philosophers have divided all created beings into material and
immaterial: the former including all that part of being, which obeys the
mechanic laws of action and reaction, but which can begin no motion of
itself; the other is the cause of all motion, and is either termed the
power of gravity, or of specific attraction, or the spirit of animation.
This immaterial agent is supposed to exist in or with matter, but to be
quite distinct from it, and to be equally capable of existence, after the
matter, which now possesses it, is decomposed.

Nor is this theory ill supported by analogy, since heat, electricity, and
magnetism, can be given to or taken from a piece of iron; and must
therefore exist, whether separated from the metal, or combined with it.
From a parity of reasoning, the spirit of animation, would appear to be
capable of existing as well separately from the body as with it.

I beg to be understood, that I do not wish to dispute about words, and am
ready to allow, that the powers of gravity, specific attraction,
electricity, magnetism, and even the spirit of animation, may consist of
matter of a finer kind; and to believe, with St. Paul and Malbranch, that
the ultimate cause only of all motion is immaterial, that is God. St. Paul
says, "in him we live and move, and have our being;" and, in the 15th
chapter to the Corinthians, distinguishes between the psyche or living
spirit, and the pneuma or reviving spirit. By the words spirit of animation
or sensorial power, I mean only that animal life, which mankind possesses
in common with brutes, and in some degree even with vegetables, and leave
the consideration of the immortal part of us, which is the object of
religion, to those who treat of revelation.

II. 1. _Of the Sense of Touch._

The first idea we become acquainted with, are those of the sense of touch;
for the foetus must experience some varieties of agitation, and exert some
muscular action, in the womb; and may with great probability be supposed
thus to gain some ideas of its own figure, of that of the uterus, and of
the tenacity of the fluid, that surrounds it, (as appears from the facts
mentioned in the succeeding Section upon Instinct.)

Many of the organs of sense are confined to a small part of the body, as
the nostrils, ear, or eye, whilst the sense of touch is diffused over the
whole skin, but exists with a more exquisite degree of delicacy at the
extremities of the fingers and thumbs, and in the lips. The sense of touch
is thus very commodiously disposed for the purpose of encompassing smaller
bodies, and for adapting itself to the inequalities of larger ones. The
figure of small bodies seems to be learnt by children by their lips as much
as by their fingers; on which account they put every new object to their
mouths, when they are satiated with food, as well as when they are hungry.
And puppies seem to learn their ideas of figure principally by the lips in
their mode of play.

We acquire our tangible ideas of objects either by the simple pressure of
this organ of touch against a solid body, or by moving our organ of touch
along the surface of it. In the former case we learn the length and breadth
of the object by the quantity of our organ of touch, that is impressed by
it: in the latter case we learn the length and breadth of objects by the
continuance of their pressure on our moving organ of touch.

It is hence, that we are very slow in acquiring our tangible ideas, and
very slow in recollecting them; for if I now think of the tangible idea of
a cube, that is, if I think of its figure, and of the solidity of every
part of that figure, I must conceive myself as passing my fingers over it,
and seem in some measure to feel the idea, as I formerly did the
impression, at the ends of them, and am thus very slow in distinctly
recollecting it.

When a body compresses any part of our sense of touch, what happens? First,
this part of our sensorium undergoes a mechanical compression, which is
termed a stimulus; secondly, an idea, or contraction of a part of the organ
of sense is excited; thirdly, a motion of the central parts, or of the
whole sensorium, which is termed sensation, is produced; and these three
constitute the perception of solidity.

2. _Of Figure, Motion, Time, Place, Space, Number._

No one will deny, that the medulla of the brain and nerves has a certain
figure; which, as it is diffused through nearly the whole of the body, must
have nearly the figure of that body. Now it follows, that the spirit of
animation, or living principle, as it occupies this medulla, and no other
part, (which is evinced by a great variety of cruel experiments on living
animals,) it follows, that this spirit of animation has also the same
figure as the medulla above described. I appeal to common sense! the spirit
of animation acts, Where does it act? It acts wherever there is the medulla
above mentioned; and that whether the limb is yet joined to a living
animal, or whether it be recently detached from it; as the heart of a viper
or frog will renew its contractions, when pricked with a pin, for many
minutes of time after its exsection from the body.--Does it act any where
else?--No; then it certainly exists in this part of space, and no where
else; that is, it hath figure; namely, the figure of the nervous system,
which is nearly the figure of the body. When the idea of solidity is
excited, as above explained, a part of the extensive organ of touch is
compressed by some external body, and this part of the sensorium so
compressed exactly resembles _in figure_ the figure of the body that
compressed it. Hence, when we acquire the idea of solidity, we acquire at
the same time the idea of FIGURE; and this idea of figure, or motion of _a
part_ of the organ of touch, exactly resembles _in its figure_ the figure
of the body that occasions it; and thus exactly acquaints us with this
property of the external world.

Now, as the whole universe with all its parts possesses a certain form or
figure, if any part of it moves, that form or figure of the whole is
varied: hence, as MOTION is no other than a perpetual variation of figure,
our idea of motion is also a real resemblance of the motion that produced
it.

It may be said in objection to this definition of motion, that an ivory
globe may revolve on its axis, and that here will be a motion without
change of figure. But the figure of the particle _x_ on one side of this
globe is not the _same_ figure as the figure of _y_ on the other side, any
more than the particles themselves are the same, though they are _similar_
figures; and hence they cannot change place with each other without
disturbing or changing the figure of the whole.

Our idea of TIME is from the same source, but is more abstracted, as it
includes only the comparative velocities of these variations of figure;
hence if it be asked, How long was this book in printing? it may be
answered, Whilst the sun was passing through Aries.

Our idea of PLACE includes only the figure of a group of bodies, not the
figures of the bodies themselves. If it be asked where is Nottinghamshire,
the answer is, it is surrounded by Derbyshire, Lincolnshire and
Leicestershire; hence place is our idea of the figure of one body
surrounded by the figures of other bodies.

The idea of SPACE is a more abstracted idea of place excluding the group of
bodies.

The idea of NUMBER includes only the particular arrangements, or
distributions of a group of bodies, and is therefore only a more abstracted
idea of the parts of the figure of the group of bodies; thus when I say
England is divided into forty counties, I only speak of certain divisions
of its figure.

Hence arises the certainty of the mathematical sciences, as they explain
these properties of bodies, which are exactly resembled by our ideas of
them, whilst we are obliged to collect almost all our other knowledge from
experiment; that is, by observing the effects exerted by one body upon
another.

3. _Of the Penetrability of Matter._

The impossibility of two bodies existing together in the same space cannot
be deduced from our idea of solidity, or of figure. As soon as we perceive
the motions of objects that surround us, and learn that we possess a power
to move our own bodies, we experience, that those objects, which excite in
us the idea of solidity and of figure, oppose this voluntary movement of
our own organs; as whilst I endeavour to compress between my hands an ivory
ball into a spheroid. And we are hence taught by experience, that our own
body and those, which we touch, cannot exist in the same part of space.

But this by no means demonstrates, that no two bodies can exist together in
the same part of space. Galilæo in the preface to his works seems to be of
opinion, that matter is not impenetrable; Mr. Michel, and Mr. Boscowich in
his Theoria. Philos. Natur. have espoused this hypothesis: which has been
lately published by Dr. Priestley, to whom the world is much indebted for
so many important discoveries in science. (Hist. of Light and Colours, p.
391.) The uninterrupted passage of light through transparent bodies, of the
electric æther through metallic and aqueous bodies, and of the magnetic
effluvia through all bodies, would seem to give some probability to this
opinion. Hence it appears, that beings may exist without possessing the
property of solidity, as well as they can exist without possessing the
properties, which excite our smell or taste, and can thence occupy space
without detruding other bodies from it; but we cannot become acquainted
with such beings by our sense of touch, any more than we can with odours or
flavours without our senses of smell and taste.

But that any being can exist without existing in space, is to my ideas
utterly incomprehensible. My appeal is to common sense. _To be_ implies a
when and a where; the one is comparing it with the motions of other beings,
and the other with their situations.

If there was but one object, as the whole creation may be considered as one
object, then I cannot ask where it exists? for there are no other objects
to compare its situation with. Hence if any one denies, that a being exists
in space, he denies, that there are any other beings but that one; for to
answer the question, "Where does it exist?" is only to mention the
situation of the objects that surround it.

In the same manner if it be asked--"When does a being exist?" The answer
only specifies the successive motions either of itself, or of other bodies;
hence to say, a body exists not in time, is to say, that there is, or was,
no motion in the world.

4. _Of the Spirit of Animation._

But though there may exist beings in the universe, that have not the
property of solidity; that is, which can possess any part of space, at the
same time that it is occupied by other bodies; yet there may be other
beings, that can assume this property of solidity, or disrobe themselves of
it occasionally, as we are taught of spirits, and of angels; and it would
seem, that THE SPIRIT OF ANIMATION must be endued with this property,
otherwise how could it occasionally give motion to the limbs of
animals?--or be itself stimulated into motion by the obtrusions of
surrounding bodies, as of light, or odour?

If the spirit of animation was always necessarily penetrable, it could not
influence or be influenced by the solidity of common matter; they would
exist together, but could not detrude each other from the part of space,
where they exist; that is, they could not communicate motion to each other.
_No two things can influence or affect each other, which have not some
property common to both of them_; for to influence or affect another body
is to give or communicate some property to it, that it had not before; but
how can one body give that to another, which it does not possess
itself?--The words imply, that they must agree in having the power or
faculty of possessing some common property. Thus if one body removes
another from the part of space, that it possesses, it must have the power
of occupying that space itself: and if one body communicates heat or motion
to another, it follows, that they have alike the property of possessing
heat or motion.

Hence the spirit of animation at the time it communicates or receives
motion from solid bodies, must itself possess some property of solidity.
And in consequence at the time it receives other kinds of motion from
light, it must possess that property, which light possesses, to communicate
that kind of motion; and for which no language has a name, unless it may be
termed Visibility. And at the time it is stimulated into other kinds of
animal motion by the particles of sapid and odorous bodies affecting the
senses of taste and smell, it must resemble these particles of flavour, and
of odour, in possessing some similar or correspondent property; and for
which language has no name, unless we may use the words Saporosity and
Odorosity for those common properties, which are possessed by our organs of
taste and smell, and by the particles of sapid and odorous bodies; as the
words Tangibility and Audibility may express the common property possessed
by our organs of touch, and of hearing, and by the solid bodies, or their
vibrations, which affect those organs.

5. Finally, though the figures of bodies are in truth resembled by the
figure of the part of the organ of touch, which is stimulated into motion;
and that organ resembles the solid body, which stimulates it, in its
property of solidity; and though the sense of hearing resembles the
vibrations of external bodies in its capability of being stimulated into
motion by those vibrations; and though our other organs of sense resemble
the bodies, that stimulate them, in their capability of being stimulated by
them; and we hence become acquainted with these properties of the external
world; yet as we can repeat all these motions of our organs of sense by the
efforts of volition, or in consequence of the sensation of pleasure or
pain, or by their association with other fibrous motions, as happens in our
reveries or in sleep, there would still appear to be some difficulty in
demonstrating the existence of any thing external to us.

In our dreams we cannot determine this circumstance, because our power of
volition is suspended, and the stimuli of external objects are excluded;
but in our waking hours we can compare our ideas belonging to one sense
with those belonging to another, and can thus distinguish the ideas
occasioned by irritation from those excited by sensation, volition, or
association. Thus if the idea of the sweetness of sugar should be excited
in our dreams, the whiteness and hardness of it occur at the same time by
association; and we believe a material lump of sugar present before us. But
if, in our waking hours, the idea of the sweetness of sugar occurs to us,
the stimuli of surrounding objects, as the edge of the table, on which we
press, or green colour of the grass, on which we tread, prevent the other
ideas of the hardness and whiteness of the sugar from being exerted by
association. Or if they should occur, we voluntarily compare them with the
irritative ideas of the table or grass above mentioned, and detect their
fallacy. We can thus distinguish the ideas caused by the stimuli of
external objects from those, which are introduced by association,
sensation, or volition; and during our waking hours can thus acquire a
knowledge of the external world. Which nevertheless we cannot do in our
dreams, because we have neither perceptions of external bodies, nor the
power of volition to enable us to compare them with the ideas of
imagination.

III. _Of Vision._

Our eyes observe a difference of colour, or of shade, in the prominences
and depressions of objects, and that those shades uniformly vary, when the
sense of touch observes any variation. Hence when the retina becomes
stimulated by colours or shades of light in a certain form, as in a
circular spot; we know by experience, that this is a sign, that a tangible
body is before us; and that its figure is resembled by the miniature figure
of the part of the organ of vision, that is thus stimulated.

Here whilst the stimulated part of the retina resembles exactly the visible
figure of the whole in miniature, the various kinds of stimuli from
different colours mark the visible figures of the minuter parts; and by
habit we instantly recall the tangible figures.

Thus when a tree is the object of sight, a part of the retina resembling a
flat branching figure is stimulated by various shades of colours; but it is
by suggestion, that the gibbosity of the tree, and the moss, that fringes
its trunk, appear before us. These are ideas of suggestion, which we feel
or attend to, associated with the motions of the retina, or irritative
ideas, which we do not attend to.

So that though our visible ideas resemble in miniature the outline of the
figure of coloured bodies, in other respects they serve only as a language,
which by acquired associations introduce the tangible ideas of bodies.
Hence it is, that this sense is so readily deceived by the art of the
painter to our amusement and instruction. The reader will find much very
curious knowledge on this subject in Bishop Berkley's Essay on Vision, a
work of great ingenuity.

The immediate object however of the sense of vision is light; this fluid,
though its velocity is so great, appears to have no perceptible mechanical
impulse, as was mentioned in the third Section, but seems to stimulate the
retina into animal motion by its transmission through this part of the
sensorium: for though the eyes of cats or other animals appear luminous in
obscure places; yet it is probable, that none of the light, which falls on
the retina, is reflected from it, but adheres to or enters into combination
with the choroide coat behind it.

The combination of the particles of light with opake bodies, and therefore
with the choroide coat of the eye, is evinced from the heat, which is given
out, as in other chemical combinations. For the sunbeams communicate no
heat in their passage through transparent bodies, with which they do not
combine, as the air continues cool even in the focus of the largest
burning-glasses, which in a moment vitrifies a particle of opaque matter.

IV. _Of the Organ of Hearing._

It is generally believed, that the tympanum of the ear vibrates
mechanically, when exposed to audible sounds, like the strings of one
musical instrument, when the same notes are struck upon another. Nor is
this opinion improbable, as the muscles and cartilages of the larynx are
employed in producing variety of tones by mechanical vibration: so the
muscles and bones of the ear seem adapted to increase or diminish the
tension of the tympanum for the purposes of similar mechanical vibrations.

But it appears from dissection, that the tympanum is not the immediate
organ of hearing, but that like the humours and cornea of the eye, it is
only of use to prepare the object for the immediate organ. For the portio
mollis of the auditory nerve is not spread upon the tympanum, but upon the
vestibulum, and cochlea, and semicircular canals of the ear; while between
the tympanum and the expansion of the auditory nerve the cavity is said by
Dr. Cotunnus and Dr. Meckel to be filled with water; as they had frequently
observed by freezing the heads of dead animals before they dissected them;
and water being a more dense fluid than air is much better adapted to the
propagation of vibrations. We may add, that even the external opening of
the ear is not absolutely necessary for the perception of sound: for some
people, who from these defects would have been completely deaf, have
distinguished acute or grave sounds by the tremours of a stick held between
their teeth propagated along the bones of the head, (Haller. Phys. T. V. p.
295).

Hence it appears, that the immediate organ of hearing is not affected by
the particles of the air themselves, but is stimulated into animal motion
by the vibrations of them. And it is probable from the loose bones, which
are found in the heads of some fishes, that the vibrations of water are
sensible to the inhabitants of that element by a similar organ.

The motions of the atmosphere, which we become acquainted with by the sense
of touch, are combined with its solidity, weight, or vis intertiæ; whereas
those, that are perceived by this organ, depend alone on its elasticity.
But though the vibration of the air is the immediate object of the sense of
hearing, yet the ideas, we receive by this sense, like those received from
light, are only as a language, which by acquired associations acquaints us
with those motions of tangible bodies, which depend on their elasticity;
and which we had before learned by our sense of touch.

V. _Of Smell and of Taste._

The objects of smell are dissolved in the fluid atmosphere, and those of
taste in the saliva, or other aqueous fluid, for the better diffusing them
on their respective organs, which seem to be stimulated into animal motion
perhaps by the chemical affinities of these particles, which constitute the
sapidity and odorosity of bodies with the nerves of sense, which perceive
them.

Mr. Volta has lately observed a curious circumstance relative to our sense
of taste. If a bit of clean lead and a bit of clean silver be separately
applied to the tongue and palate no taste is perceived; but by applying
them in contact in respect to the parts out of the mouth, and nearly so in
respect to the parts, which are immediately applied to the tongue and
palate, a saline or acidulous taste is perceived, as of a fluid like a
stream of electricity passing from one of them to the other. This new
application of the sense of taste deserves further investigation, as it may
acquaint us with new properties of matter.

From the experiments above mentioned of Galvani, Volta, Fowler, and others,
it appears, that a plate of zinc and a plate of silver have greater effect
than lead and silver. If one edge of a plate of silver about the size of
half a crown-piece be placed upon the tongue, and one edge of a plate of
zinc about the same size beneath the tongue, and if their opposite edges
are then brought into contact before the point of the tongue, a taste is
perceived at the moment of their coming into contact; secondly, if one of
the above plates be put between the upper lip and the gum of the
fore-teeth, and the other be placed under the tongue, and their exterior
edges be then brought into contact in a darkish room, a flash of light is
perceived in the eyes.

These effects I imagine only shew the sensibility of our nerves of sense to
very small quantities of the electric fluid, as it passes through them; for
I suppose these sensations are occasioned by slight electric shocks
produced in the following manner. By the experiments published by Mr.
Bennet, with his ingenious doubler of electricity, which is the greatest
discovery made in that science since the coated jar, and the eduction of
lightning from the skies, it appears that zinc was always found minus, and
silver was always found plus, when both of them were in their separate
state. Hence, when they are placed in the manner above described, as soon
as their exterior edges come nearly into contact, so near as to have an
extremely thin plate of air between them, that plate of air becomes charged
in the same manner as a plate of coated glass; and is at the same instant
discharged through the nerves of taste or of sight, and gives the
sensations, as above described, of light or of saporocity; and only shews
the great sensibility of these organs of sense to the stimulus of the
electric fluid in suddenly passing through them.

VI. _Of the Sense of Heat._

There are many experiments in chemical writers, that evince the existence
of heat as a fluid element, which covers and pervades all bodies, and is
attracted by the solutions of some of them, and is detruded from the
combination of others. Thus from the combinations of metals with acids, and
from those combinations of animal fluids, which are termed secretions, this
fluid matter of heat is given out amongst the neighbouring bodies; and in
the solutions of salts in water, or of water in air, it is absorbed from
the bodies, that surround them; whilst in its facility in passing through
metallic bodies, and its difficulty in pervading resins and glass, it
resembles the properties of the electric aura; and is like that excited by
friction, and seems like that to gravitate amongst other bodies in its
uncombined state, and to find its equilibrium.

There is no circumstance of more consequence in the animal economy than a
due proportion of this fluid of heat; for the digestion of our nutriment in
the stomach and bowels, and the proper qualities of all our secreted
fluids, as they are produced or prepared partly by animal and partly by
chemical processes, depend much on the quantity of heat; the excess of
which, or its deficiency, alike gives us pain, and induces us to avoid the
circumstances that occasion them. And in this the perception of heat
essentially differs from the perceptions of the sense of touch, as we
receive pain from too great pressure of solid bodies, but none from the
absence of it. It is hence probable, that nature has provided us with a set
of nerves for the perception of this fluid, which anatomists have not yet
attended to.

There may be some difficulty in the proof of this assertion; if we look at
a hot fire, we experience no pain of the optic nerve, though the heat along
with the light must be concentrated upon it. Nor does warm water or warm
oil poured into the ear give pain to the organ of hearing; and hence as
these organs of sense do not perceive small excesses or deficiences of
heat; and as heat has no greater analogy to the solidity or to the figures
of bodies, than it has to their colours or vibrations; there seems no
sufficient reason for our ascribing the perception of heat and cold to the
sense of touch; to which it has generally been attributed, either because
it is diffused beneath the whole skin like the sense of touch, or owing to
the inaccuracy of our observations, or the defect of our languages.

There is another circumstance would induce us to believe, that the
perceptions of heat and cold do not belong to the organ of touch; since the
teeth, which are the least adapted for the perceptions of solidity or
figure, are the most sensible to heat or cold; whence we are forewarned
from swallowing those materials, whose degree of coldness or of heat would
injure our stomachs.

The following is an extract from a letter of Dr. R.W. Darwin, of
Shrewsbury, when he was a student at Edinburgh. "I made an experiment
yesterday in our hospital, which much favours your opinion, that the
sensation of heat and of touch depend on different sets of nerves. A man
who had lately recovered from a fever, and was still weak, was seized with
violent cramps in his legs and feet; which were removed by opiates, except
that one of his feet remained insensible. Mr. Ewart pricked him with a pin
in five or six places, and the patient declared he did not feel it in the
least, nor was he sensible of a very smart pinch. I then held a red-hot
poker at some distance, and brought it gradually nearer till it came within
three inches, when he asserted that he felt it quite distinctly. I suppose
some violent irritation on the nerves of touch had caused the cramps, and
had left them paralytic; while the nerves of heat, having suffered no
increased stimulus, retained their irritability."

Add to this, that the lungs, though easily stimulated into inflammation,
are not sensible to heat. See Class. III. 1. 1. 10.

VII. _Of the Sense of Extension._

The organ of touch is properly the sense of pressure, but the muscular
fibres themselves constitute the organ of sense, that feels extension. The
sense of pressure is always attended with the ideas of the figure and
solidity of the object, neither of which accompany our perception of
extension. The whole set of muscles, whether they are hollow ones, as the
heart, arteries, and intestines, or longitudinal ones attached to bones,
contract themselves, whenever they are stimulated by forcible elongation;
and it is observable, that the white muscles, which constitute the arterial
system, seem to be excited into contraction from no other kinds of
stimulus, according to the experiments of Haller. And hence the violent
pain in some inflammations, as in the paronychia, obtains immediate relief
by cutting the membrane, that was stretched by the tumour of the subjacent
parts.

Hence the whole muscular system may be considered as one organ of sense,
and the various attitudes of the body, as ideas belonging to this organ, of
many of which we are hourly conscious, while many others, like the
irritative ideas of the other senses, are performed without our attention.

When the muscles of the heart cease to act, the refluent blood again
distends or elongates them; and thus irritated they contract as before. The
same happens to the arterial system, and I suppose to the capillaries,
intestines, and various glands of the body.

When the quantity of urine, or of excrement, distends the bladder, or
rectum, those parts contract, and exclude their contents, and many other
muscles by association act along with them; but if these evacuations are
not soon complied with, pain is produced by a little further extension of
the muscular fibres: a similar pain is caused in the muscles, when a limb
is much extended for the reduction of dislocated bones; and in the
punishment of the rack: and in the painful cramps of the calf of the leg,
or of other muscles, for a greater degree of contraction of a muscle, than
the movement of the two bones, to which its ends are affixed, will admit
of, must give similar pain to that, which is produced by extending it
beyond its due length. And the pain from punctures or incisions arises from
the distention of the fibres, as the knife passes through them; for it
nearly ceases as soon as the division is completed.

All these motions of the muscles, that are thus naturally excited by the
stimulus of distending bodies, are also liable to be called into strong
action by their catenation, with the irritations or sensations produced by
the momentum of the progressive particles of blood in the arteries, as in
inflammatory fevers, or by acrid substances on other sensible organs, as in
the strangury, or tenesmus, or cholera.

We shall conclude this account of the sense of extension by observing, that
the want of its object is attended with a disagreeable sensation, as well
as the excess of it. In those hollow muscles, which have been accustomed to
it, this disagreeable sensation is called faintness, emptiness, and
sinking; and, when it arises to a certain degree, is attended with syncope,
or a total quiescence of all motions, but the internal irritative ones, as
happens from sudden loss of blood, or in the operation of tapping in the
dropsy.

VIII. _Of the Appetites of Hunger, Thirst, Heat, Extension, the want of
fresh Air, animal Love, and the Suckling of Children._

Hunger is most probably perceived by those numerous ramifications of nerves
that are seen about the upper opening of the stomach; and thirst by the
nerves about the fauces, and the top of the gula. The ideas of these senses
are few in the generality of mankind, but are more numerous in those, who
by disease, or indulgence, desire particular kinds of foods or liquids.

A sense of heat has already been spoken of, which may with propriety be
called an appetite, as we painfully desire it, when it is deficient in
quantity.

The sense of extension may be ranked amongst these appetites, since the
deficiency of its object gives disagreeable sensation; when this happens in
the arterial system, it is called faintness, and seems to bear some analogy
to hunger and to cold; which like it are attended with emptiness of a part
of the vascular system.

The sense of want of fresh air has not been attended to, but is as distinct
as the others, and the first perhaps that we experience after our nativity;
from the want of the object of this sense many diseases are produced, as
the jail-fever, plague, and other epidemic maladies. Animal love is another
appetite, which occurs later in life, and the females of lactiferous
animals have another natural inlet of pleasure or pain from the suckling
their offspring. The want of which either owing to the death of their
progeny, or to the fashion of their country, has been fatal to many of the
sex. The males have also pectoral glands, which are frequently turgid with
a thin milk at their nativity, and are furnished with nipples, which erect
on titillation like those of the female; but which seem now to be of no
further use, owing perhaps to some change which these animals have
undergone in the gradual progression of the formation of the earth, and of
all that it inhabit.

These seven last mentioned senses may properly be termed appetites, as they
differ from those of touch, sight, hearing, taste, and smell, in this
respect; that they are affected with pain as well by the defect of their
objects as by the excess of them, which is not so in the latter. Thus cold
and hunger give us pain, as well as an excess of heat or satiety; but it is
not so with darkness and silence.

IX. Before we conclude this Section on the organs of sense, we must
observe, that, as far as we know, there are many more senses, than have
been here mentioned, as every gland seems to be influenced to separate from
the blood, or to absorb from the cavities of the body, or from the
atmosphere, its appropriated fluid, by the stimulus of that fluid on the
living gland; and not by mechanical capillary absorption, nor by chemical
affinity. Hence it appears, that each of these glands must have a peculiar
organ to perceive these irritations, but as these irritations are not
succeeded by sensation, they have not acquired the names of senses.

However when these glands are excited into motions stronger than usual,
either by the acrimony of their fluids, or by their own irritability being
much increased, then the sensation of pain is produced in them as in all
the other senses of the body; and these pains are all of different kinds,
and hence the glands at this time really become each a different organ of
sense, though these different kinds of pain have acquired no names.

Thus a great excess of light does not give the idea of light but of pain;
as in forcibly opening the eye when it is much inflamed. The great excess
of pressure or distention, as when the point of a pin is pressed upon our
skin, produces pain, (and when this pain of the sense of distention is
slighter, it is termed itching, or tickling), without any idea of solidity
or of figure: an excess of heat produces smarting, of cold another kind of
pain; it is probable by this sense of heat the pain produced by caustic
bodies is perceived, and of electricity, as all these are fluids, that
permeate, distend, or decompose the parts that feel them.

       *       *       *       *       *

SECT. XV.

OF THE CLASSES OF IDEAS.

    I. 1. _Ideas received in tribes._ 2. _We combine them further, or
    abstract from these tribes._ 3. _Complex ideas._ 4. _Compounded ideas._
    5. _Simple ideas, modes, substances, relations, general ideas._ 6.
    _Ideas of reflexion._ 7. _Memory and imagination imperfectly defined.
    Ideal presence. Memorandum-rings._ II. 1. _Irritative ideas.
    Perception._ 2. _Sensitive ideas, imagination._ 3. _Voluntary ideas,
    recollection._ 4. _Associated ideas, suggestion._ III. 1. _Definitions
    of perception, memory._ 2. _Reasoning, judgment, doubting,
    distinguishing, comparing._ 3. _Invention._ 4. _Consciousness._ 5.
    _Identity._ 6. _Lapse of time._ 7. _Free-will._

I. 1. As the constituent elements of the material world are only
perceptible to our organs of sense in a state of combination; it follows,
that the ideas or sensual motions excited by them, are never received
singly, but ever with a greater or less degree of combination. So the
colours of bodies or their hardnesses occur with their figures: every smell
and taste has its degree of pungency as well as its peculiar flavour: and
each note in music is combined with the tone of some instrument. It appears
from hence, that we can be sensible of a number of ideas at the same time,
such as the whiteness, hardness, and coldness, of a snow-ball, and can
experience at the same time many irritative ideas of surrounding bodies,
which we do not attend to, as mentioned in Section VII. 3. 2. But those
ideas which belong to the same sense, seem to be more easily combined into
synchronous tribes, than those which were not received by the same sense,
as we can more easily think of the whiteness and figure of a lump of sugar
at the same time, than the whiteness and sweetness of it.

2. As these ideas, or sensual motions, are thus excited with greater or
less degrees of combination; so we have a power, when we repeat them either
by our volition or sensation, to increase or diminish this degree of
combination, that is, to form compounded ideas from those, which were more
simple; and abstract ones from those, which were more complex, when they
were first excited; that is, we can repeat a part or the whole of those
sensual motions, which did constitute our ideas of perception; and the
repetition of which now constitutes our ideas of recollection, or of
imagination.

3. Those ideas, which we repeat without change of the quantity of that
combination, with which we first received them, are called complex ideas,
as when you recollect Westminster Abbey, or the planet Saturn: but it must
be observed, that these complex ideas, thus re-excited by volition,
sensation, or association, are seldom perfect copies of their correspondent
perceptions, except in our dreams, where other external objects do not
detract our attention.

4. Those ideas, which are more complex than the natural objects that first
excited them, have been called compounded ideas, as when we think of a
sphinx, or griffin.

5. And those that are less complex than the correspondent natural objects,
have been termed abstracted ideas: thus sweetness, and whiteness, and
solidity, are received at the same time from a lump of sugar, yet I can
recollect any of these qualities without thinking of the others, that were
excited along with them.

When ideas are so far abstracted as in the above example, they have been
termed simple by the writers of metaphysics, and seem indeed to be more
complete repetitions of the ideas or sensual motions, originally excited by
external objects.

Other classes of these ideas, where the abstraction has not been so great,
have been termed, by Mr. Locke, modes, substances, and relations, but they
seem only to differ in their degree of abstraction from the complex ideas
that were at first excited; for as these complex or natural ideas are
themselves imperfect copies of their correspondent perceptions, so these
abstract or general ideas are only still more imperfect copies of the same
perceptions. Thus when I have seen an object but once, as a rhinoceros, my
abstract idea of this animal is the same as my complex one. I may think
more or less distinctly of a rhinoceros, but it is the very rhinoceros that
I saw, or some part or property of him, which recurs to my mind.

But when any class of complex objects becomes the subject of conversation,
of which I have seen many individuals, as a castle or an army, some
property or circumstance belonging to it is peculiarly alluded to; and then
I feel in my own mind, that my abstract idea of this complex object is only
an idea of that part, property, or attitude of it, that employs the present
conversation, and varies with every sentence that is spoken concerning it.
So if any one should say, "one may sit upon a horse safer than on a camel,"
my abstract idea of the two animals includes only an outline of the level
back of the one, and the gibbosity on the back of the other. What noise is
that in the street?--Some horses trotting over the pavement. Here my idea
of the horses includes principally the shape and motion of their legs. So
also the abstract ideas of goodness and courage are still more imperfect
representations of the objects they were received from; for here we
abstract the material parts, and recollect only the qualities.

Thus we abstract so much from some of our complex ideas, that at length it
becomes difficult to determine of what perception they partake; and in many
instances our idea seems to be no other than of the sound or letters of the
word, that stands for the collective tribe, of which we are said to have an
abstracted idea, as noun, verb, chimæra, apparition.

6. Ideas have been divided into those of perception and those of
reflection, but as whatever is perceived must be external to the organ that
perceives it, all our ideas must originally be ideas of perception.

7. Others have divided our ideas into those of memory, and those of
imagination; they have said that a recollection of ideas in the order they
were received constitutes memory, and without that order imagination; but
all the ideas of imagination, excepting the few that are termed simple
ideas, are parts of trains or tribes in the order they were received; as if
I think of a sphinx, or a griffin, the fair face, bosom, wings, claws,
tail, are all complex ideas in the order they were received: and it behoves
the writers, who adhere to this definition, to determine, how small the
trains must be, that shall be called imagination; and how great those, that
shall be called memory.

Others have thought that the ideas of memory have a greater vivacity than
those of imagination: but the ideas of a person in sleep, or in a waking
reverie, where the trains connected with sensation are uninterrupted, are
more vivid and distinct than those of memory, so that they cannot be
distinguished by this criterion.

The very ingenious author of the Elements of Criticism has described what
he conceives to be a species of memory, and calls it ideal presence; but
the instances he produces are the reveries of sensation, and are therefore
in truth connections of the imagination, though they are recalled in the
order they were received.

The ideas connected by association are in common discourse attributed to
memory, as we talk of memorandum-rings, and tie a knot on our handkerchiefs
to bring something into our minds at a distance of time. And a school-boy,
who can repeat a thousand unmeaning lines in Lilly's Grammar, is said to
have a good memory. But these have been already shewn to belong to the
class of association; and are termed ideas of suggestion.

II. Lastly, the method already explained of classing ideas into those
excited by irritation, sensation, volition, or association, we hope will be
found more convenient both for explaining the operations of the mind, and
for comparing them with those of the body; and for the illustration and the
cure of the diseases of both, and which we shall here recapitulate.

1. Irritative ideas are those, which are preceded by irritation, which is
excited by objects external to the organs of sense: as the idea of that
tree, which either I attend to, or which I shun in walking near it without
attention. In the former case it is termed perception, in the latter it is
termed simply an irritative idea.

2. Sensitive ideas are those, which are preceded by the sensation of
pleasure or pain; as the ideas, which constitute our dreams or reveries,
this is called imagination.

3. Voluntary ideas are those, which are preceded by voluntary exertion, as
when I repeat the alphabet backwards: this is called recollection.

4. Associate ideas are those, which are preceded by other ideas or muscular
motions, as when we think over or repeat the alphabet by rote in its usual
order; or sing a tune we are accustomed to; this is called suggestion.

III. 1. Perceptions signify those ideas, which are preceded by irritation
and succeeded by the sensation of pleasure or pain, for whatever excites
our attention interests us; that is, it is accompanied with, pleasure or
pain; however slight may be the degree or quantity of either of them.

The word memory includes two classes of ideas, either those which, are
preceded by voluntary exertion, or those which are suggested by their
associations with other ideas.

2. Reasoning is that operation of the sensorium, by which we excite two or
many tribes of ideas; and then re-excite the ideas, in which they differ,
or correspond. If we determine this difference, it is called judgment; if
we in vain endeavour to determine it, it is called doubting.

If we re-excited the ideas, in which they differ, it is called
distinguishing. If we re-excite those in which they correspond, it is
called comparing.

3. Invention is an operation of the sensorium, by which we voluntarily
continue to excite one train of ideas, suppose the design of raising water
by a machine; and at the same time attend to all other ideas, which are
connected with this by every kind of catenation; and combine or separate
them voluntarily for the purpose of obtaining some end.

For we can create nothing new, we can only combine or separate the ideas,
which we have already received by our perceptions: thus if I wish to
represent a monster, I call to my mind the ideas of every thing
disagreeable and horrible, and combine the nastiness and gluttony of a hog,
the stupidity and obstinacy of an ass, with the fur and awkwardness of a
bear, and call the new combination Caliban. Yet such a monster may exist in
nature, as all his attributes are parts of nature. So when I wish to
represent every thing, that is excellent, and amiable; when I combine
benevolence with cheerfulness, wisdom, knowledge, taste, wit, beauty of
person, and elegance of manners, and associate them in one lady as a
pattern to the world, it is called invention; yet such a person may
exist,--such a person does exist!--It is ---- ----, who is as much a
monster as Caliban.

4. In respect to consciousness, we are only conscious of our existence,
when we think about it; as we only perceive the lapse of time, when we
attend to it; when we are busied about other objects, neither the lapse of
time nor the consciousness of our own existence can occupy our attention.
Hence, when we think of our own existence, we only excite abstracted or
reflex ideas (as they are termed), of our principal pleasures or pains, of
our desires or aversions, or of the figure, solidity, colour, or other
properties of our bodies, and call that act of the sensorium a
consciousness of our existence. Some philosopher, I believe it is Des
Cartes, has said, "I think, therefore I exist." But this is not right
reasoning, because thinking is a mode of existence; and it is thence only
saying, "I exist, therefore I exist." For there are three modes of
existence, or in the language of grammarians three kinds of verbs. First,
simply I am, or exist. Secondly, I am acting, or exist in a state of
activity, as I move. Thirdly, I am suffering, or exist in a state of being
acted upon, as I am moved. The when, and the where, as applicable to this
existence, depends on the successive motions of our own or of other bodies;
and on their respective situations, as spoken of Sect. XIV. 2. 5.

5. Our identity is known by our acquired habits or catenated trains of
ideas and muscular motions; and perhaps, when we compare infancy with old
age, in those alone can our identity be supposed to exist. For what else is
there of similitude between the first speck of living entity and the mature
man?--every deduction of reasoning, every sentiment or passion, with every
fibre of the corporeal part of our system, has been subject almost to
annual mutation; while some catenations alone of our ideas and muscular
actions have continued in part unchanged.

By the facility, with which we can in our waking hours voluntarily produce
certain successive trains of ideas, we know by experience, that we have
before reproduced them; that is, we are conscious of a time of our
existence previous to the present time; that is, of our identity now and
heretofore. It is these habits of action, these catenations of ideas and
muscular motions, which begin with life, and only terminate with it; and
which we can in some measure deliver to our posterity; as explained in
Sect. XXXIX.

6. When the progressive motions of external bodies make a part of our
present catenation of ideas, we attend to the lapse of time; which appears
the longer, the more frequently we thus attend to it; as when we expect
something at a certain hour, which much interests us, whether it be an
agreeable or disagreeable event; or when we count the passing seconds on a
stop-watch.

When an idea of our own person, or a reflex idea of our pleasures and
pains, desires and aversions, makes a part of this catenation, it is termed
consciousness; and if this idea of consciousness makes a part of a
catenation, which we excite by recollection, and know by the facility with
which we excite it, that we have before experienced it, it is called
identity, as explained above.

7. In respect to freewill, it is certain, that we cannot will to think of a
new train of ideas, without previously thinking of the first link of it; as
I cannot will to think of a black swan, without previously thinking of a
black swan. But if I now think of a tail, I can voluntarily recollect all
animals, which have tails; my will is so far free, that I can pursue the
ideas linked to this idea of tail, as far as my knowledge of the subject
extends; but to will without motive is to will without desire or aversion;
which is as absurd as to feel without pleasure or pain; they are both
solecisms in the terms. So far are we governed by the catenations of
motions, which affect both the body and the mind of man, and which begin
with our irritability, and end with it.

       *       *       *       *       *

SECT. XVI.

OF INSTINCT.

  Haud equidem credo, quia sit divinitus illis
  Ingenium, aut rerum fato prudentia major.--Virg. Georg. L. I. 415.

    I. _Instinctive actions defined. Of connate passions._ II. _Of the
    sensations and motions of the foetus in the womb._ III. _Some animals
    are more perfectly formed than others before nativity. Of learning to
    walk._ IV. _Of the swallowing, breathing, sucking, pecking, and lapping
    of young animals._ V. _Of the sense of smell, and its uses to animals.
    Why cats do not eat their kittens._ VI. _Of the accuracy of sight in
    mankind, and their sense of beauty. Of the sense of touch in elephants,
    monkies, beavers, men._ VII. _Of natural language._ VIII. _The origin
    of natural language;_ 1. _the language of fear;_ 2. _of grief;_ 3. _of
    tender pleasure;_ 4. _of serene pleasure;_ 5. _of anger;_ 6. _of
    attention._ IX. _Artificial language of turkies, hens, ducklings,
    wagtails, cuckoos, rabbits, dogs, and nightingales._ X. _Of music; of
    tooth-edge; of a good ear; of architecture._ XI. _Of acquired
    knowledge; of foxes, rooks, fieldfares, lapwings, dogs, cats, horses,
    crows, and pelicans._ XII. _Of birds of passage, dormice, snakes, bats,
    swallows, quails, ringdoves, stare, chaffinch, hoopoe, chatterer,
    hawfinch, crossbill, rails and cranes._ XIII. _Of birds nests; of the
    cuckoo; of swallows nests; of the taylor bird._ XIV. _Of the old
    soldier; of haddocks, cods, and dog fish; of the remora; of crabs,
    herrings, and salmon._ XV. _Of spiders, caterpillars, ants, and the
    ichneumon._ XVI. 1. _Of locusts, gnats;_ 2. _bees;_ 3. _dormice, flies,
    worms, ants, and wasps._ XVII. _Of the faculty that distinguishes man
    from the brutes._

I. All those internal motions of animal bodies, which contribute to digest
their aliment, produce their secretions, repair their injuries, or increase
their growth, are performed without our attention or consciousness. They
exist as well in our sleep, as in our waking hours, as well in the foetus
during the time of gestation, as in the infant after nativity, and proceed
with equal regularity in the vegetable as in the animal system. These
motions have been shewn in a former part of this work to depend on the
irritations of peculiar fluids, and as they have never been classed amongst
the instinctive actions of animals, are precluded from our present
disquisition.

But all those actions of men or animals, that are attended with
consciousness, and seem neither to have been directed by their appetites,
taught by their experience, nor deduced from observation or tradition, have
been referred to the power of instinct. And this power has been explained
to be a _divine something_, a kind of inspiration; whilst the poor animal,
that possesses it, has been thought little better than _a machine_!

The _irksomeness_, that attends a continued attitude of the body, or the
_pains_, that we receive from heat, cold, hunger, or other injurious
circumstances, excite us to _general locomotion_: and our senses are so
formed and constituted by the hand of nature, that certain objects present
us with pleasure, others with pain, and we are induced to approach and
embrace these, to avoid and abhor those, as such sensations direct us.

Thus the palates of some animals are gratefully affected by the mastication
of fruits, others of grains, and others of flesh; and they are thence
instigated to attain, and to consume those materials; and are furnished
with powers of muscular motion, and of digestion proper for such purposes.

These _sensations_ and _desires_ constitute a part of our system, as our
_muscles_ and _bones_ constitute another part: and hence they may alike be
termed _natural_ or _connate_; but neither of them can properly be termed
_instinctive_: as the word instinct in its usual acceptation refers only to
the _actions_ of animals, as above explained: the origin of these _actions_
is the subject of our present enquiry.

The reader is intreated carefully to attend to this definition of
_instinctive actions_, lest by using the word instinct without adjoining
any accurate idea to it, he may not only include the natural desires of
love and hunger, and the natural sensations of pain or pleasure, but the
figure and contexture of the body, and the faculty of reason itself under
this general term.

II. We experience some sensations, and perform some actions before our
nativity; the sensations of cold and warmth, agitation and rest, fulness
and inanition, are instances of the former; and the repeated struggles of
the limbs of the foetus, which begin about the middle of gestation, and
those motions by which it frequently wraps the umbilical chord around its
neck or body, and even sometimes ties it on a knot; are instances of the
latter. Smellie's Midwifery, (Vol. I. p. 182.)

By a due attention to these circumstances many of the actions of young
animals, which at first sight seemed only referable to an inexplicable
instinct, will appear to have been acquired like all other animal actions,
that are attended with consciousness, _by the repeated efforts of our
muscles under the conduct of our sensations or desires_.

The chick in the shell begins to move its feet and legs on the sixth day of
incubation (Mattreican, p. 138); or on the seventh day, (Langley);
afterwards they are seen to move themselves gently in the liquid that
surrounds them, and to open and shut their mouths, (Harvei, de Generat. p.
62, and 197. Form de Poulet. ii. p. 129). Puppies before the membranes are
broken, that involve them, are seen to move themselves, to put out their
tongues, and to open and shut their mouths, (Harvey, Gipson, Riolan,
Haller). And calves lick themselves and swallow many of their hairs before
their nativity: which however puppies do not, (Swammerden, p. 319. Flemyng
Phil. Trans. Ann. 1755. 42). And towards the end of gestation, the foetus
of all animals are proved to drink part of the liquid in which they swim,
(Haller. Physiol. T. 8. 204). The white of egg is found in the mouth and
gizzard of the chick, and is nearly or quite consumed before it is hatched,
(Harvie de Generat. 58). And the liquor amnii is found in the mouth and
stomach of the human foetus, and of calves; and how else should that
excrement be produced in the intestines of all animals, which is voided in
great quantity soon after their birth; (Gipson, Med. Essays, Edinb. V. i.
13. Halleri Physiolog. T. 3. p. 318. and T. 8). In the stomach of a calf
the quantity of this liquid amounted to about three pints, and the hairs
amongst it were of the same colour with those on its skin, (Blasii Anat.
Animal, p.m. 122). These facts are attested by many other writers of
credit, besides those above mentioned.

III. It has been deemed a surprising instance of instinct, that calves and
chickens should be able to walk by a few efforts almost immediately after
their nativity: whilst the human infant in those countries where he is not
incumbered with clothes, as in India, is five or six months, and in our
climate almost a twelvemonth, before he can safely stand upon his feet.

The struggles of all animals in the womb must resemble their mode of
swimming, as by this kind of motion they can best change their attitude in
water. But the swimming of the calf and chicken resembles their manner of
walking, which they have thus in part acquired before their nativity, and
hence accomplish it afterwards with very few efforts, whilst the swimming
of the human creature resembles that of the frog, and totally differs from
his mode of walking.

There is another circumstance to be attended to in this affair, that not
only the growth of those peculiar parts of animals, which are first wanted
to secure their subsistence, are in general furthest advanced before their
nativity: but some animals come into the world more completely formed
throughout their whole system than others: and are thence much forwarder in
all their habits of motion. Thus the colt, and the lamb, are much more
perfect animals than the blind puppy, and the naked rabbit; and the chick
of the pheasant, and the partridge, has more perfect plumage, and more
perfect eyes, as well as greater aptitude to locomotion, than the callow
nestlings of the dove, and of the wren. The parents of the former only find
it necessary to shew them their food, and to teach them to take it up;
whilst those of the latter are obliged for many days to obtrude it into
their gaping mouths.

IV. From the facts mentioned in No. 2. of this Section, it is evinced that
the foetus learns to swallow before its nativity; for it is seen to open
its mouth, and its stomach is found filled with the liquid that surrounds
it. It opens its mouth, either instigated by hunger, or by the irksomeness
of a continued attitude of the muscles of its face; the liquor amnii, in
which it swims, is agreeable to its palate, as it consists of a nourishing
material, (Haller Phys. T. 8. p. 204). It is tempted to experience its
taste further in the mouth, and by a few efforts learns to swallow, in the
same manner as we learn all other animal actions, which are attended with
consciousness, _by the repeated efforts of our muscles under the conduct of
our sensations or volitions_.

The inspiration of air into the lungs is so totally different from that of
swallowing a fluid in which we are immersed, that it cannot be acquired
before our nativity. But at this time, when the circulation of the blood is
no longer continued through the placenta, that suffocating sensation, which
we feel about the precordia, when we are in want of fresh air, disagreeably
affects the infant: and all the muscles of the body are excited into action
to relieve this oppression; those of the breast, ribs, and diaphragm are
found to answer this purpose, and thus respiration is discovered, and is
continued throughout our lives, as often as the oppression begins to recur.
Many infants, both of the human creature, and of quadrupeds, struggle for a
minute after they are born before they begin to breathe, (Haller Phys. T.
8. p. 400. ib pt. 2. p. 1). Mr. Buffon thinks the action of the dry air
upon the nerves of smell of new-born animals, by producing an endeavour to
sneeze, may contribute to induce this first inspiration, and that the
rarefaction of the air by the warmth of the lungs contributes to induce
expiration, (Hist. Nat. Tom. 4. p. 174). Which latter it may effect by
producing a disagreeable sensation by its delay, and a consequent effort to
relieve it. Many children sneeze before they respire, but not all, as far
as I have observed, or can learn from others.

At length, by the direction of its sense of smell, or by the officious care
of its mother, the young animal approaches the odoriferous rill of its
future nourishment, already experienced to swallow. But in the act of
swallowing, it is necessary nearly to close the mouth, whether the creature
be immersed in the fluid it is about to drink, or not: hence, when the
child first attempts to suck, it does not slightly compress the nipple
between its lips, and suck as an adult person would do, by absorbing the
milk; but it takes the whole nipple into its mouth for this purpose,
compresses it between its gums, and thus repeatedly chewing (as it were)
the nipple, presses out the milk, exactly in the same manner as it is drawn
from the teats of cows by the hands of the milkmaid. The celebrated Harvey
observes, that the foetus in the womb must have sucked in a part of its
nourishment, because it knows how to suck the minute it is born, as any one
may experience by putting a finger between its lips, and because in a few
days it forgets this art of sucking, and cannot without some difficulty
again acquire it, (Exercit. de Gener. Anim. 48). The same observation is
made by Hippocrates.

A little further experience teaches the young animal to suck by absorption,
as well as by compression; that is, to open the chest as in the beginning
of respiration, and thus to rarefy the air in the mouth, that the pressure
of the denser external atmosphere may contribute to force out the milk.

The chick yet in the shell has learnt to drink by swallowing a part of the
white of the egg for its food; but not having experienced how to take up
and swallow solid seeds, or grains, is either taught by the felicitous
industry of its mother; or by many repeated attempts is enabled at length
to distinguish and to swallow this kind of nutriment.

And puppies, though they know how to suck like other animals from their
previous experience in swallowing, and in respiration; yet are they long in
acquiring the art of lapping with their tongues, which from the flaccidity
of their cheeks, and length of their mouths, is afterwards a more
convenient way for them to take in water.

V. The senses of smell and taste in many other animals greatly excel those
of mankind, for in civilized society, as our victuals are generally
prepared by others, and are adulterated with salt, spice, oil, and
empyreuma, we do not hesitate about eating whatever is set before us, and
neglect to cultivate these senses: whereas other animals try every morsel
by the smell, before they take it into their mouths, and by the taste
before they swallow it: and are led not only each to his proper nourishment
by this organ of sense, but it also at a maturer age directs them in the
gratification of their appetite of love. Which may be further understood by
considering the sympathies of these parts described in Class IV. 2. 1. 7.
While the human animal is directed to the object of his love by his sense
of beauty, as mentioned in No. VI. of this Section. Thus Virgil. Georg.
III. 250.

  Nonne vides, ut tota tremor pertentat equorum
  Corpora, si tantum notas odor attulit auras?
  Nonne canis nidum veneris nasutus odore
  Quærit, et erranti trahitur sublambere linguâ?
  Respuit at gustum cupidus, labiisque retractis
  Elevat os, trepidansque novis impellitur æstris
  Inserit et vivum felici vomere semen.--
  Quam tenui filo cæcos adnectit amores
  Docta Venus, vitæque monet renovare favillam!--ANON.

The following curious experiment is related by Galen. "On dissecting a goat
great with young I found a brisk embryon, and having detached it from the
matrix, and snatching it away before it saw its dam, I brought it into a
certain room, where there were many vessels, some filled with wine, others
with oil, some with honey, others with milk, or some other liquor; and in
others were grains and fruits; we first observed the young animal get upon
its feet, and walk; then it shook itself, and afterwards scratched its side
with one of its feet: then we saw it smelling to every one of these things,
that were set in the room; and when it had smelt to them all, it drank up
the milk." L. 6. de locis. cap. 6.

Parturient quadrupeds, as cats, and bitches, and sows, are led by their
sense of smell to eat the placenta as other common food; why then do they
not devour their whole progeny, as is represented in an antient emblem of
TIME? This is said sometimes to happen in the unnatural state in which we
confine sows; and indeed nature would seem to have endangered her offspring
in this nice circumstance! But at this time the stimulus of the milk in the
tumid teats of the mother excites her to look out for, and to desire some
unknown circumstance to relieve her. At the same time the smell of the milk
attracts the exertions of the young animals towards its source, and thus
the delighted mother discovers a new appetite, as mentioned in Sect. XIV.
8. and her little progeny are led to receive and to communicate pleasure by
this most beautiful contrivance.

VI. But though the human species in some of their sensations are much
inferior to other animals, yet the accuracy of the sense of touch, which
they possess in so eminent a degree, gives them a great superiority of
understanding; as is well observed by the ingenious Mr. Buffon. The
extremities of other animals terminate in horns, and hoofs, and claws, very
unfit for the sensation of touch; whilst the human hand is finely adapted
to encompass its object with this organ of sense.

The elephant is indeed endued with a fine sense of feeling at the extremity
of his proboscis, and hence has acquired much more accurate ideas of touch
and of sight than most other creatures. The two following instances of the
sagacity of these animals may entertain the reader, as they were told me by
some gentlemen of distinct observation, and undoubted veracity, who had
been much conversant with our eastern settlements. First, the elephants
that are used to carry the baggage of our armies, are put each under the
care of one of the natives of Indostan, and whilst himself and his wife go
into the woods to collect leaves and branches of trees for his food, they
fix him to the ground by a length of chain, and frequently leave a child
yet unable to walk, under his protection: and the intelligent animal not
only defends it, but as it creeps about, when it arrives near the extremity
of his chain, he wraps his trunk gently round its body, and brings it again
into the centre of his circle. Secondly, the traitor elephants are taught
to walk on a narrow path between two pit-falls, which are covered with
turf, and then to go into the woods, and to seduce the wild elephants to
come that way, who fall into these wells, whilst he passes safe between
them: and it is universally observed, that those wild elephants that escape
the snare, pursue the traitor with the utmost vehemence, and if they can
overtake him, which sometimes happens, they always beat him to death.

The monkey has a hand well enough adapted for the sense of touch, which
contributes to his great facility of imitation; but in taking objects with
his hands, as a stick or an apple, he puts his thumb on the same side of
them with his fingers, instead of counteracting the pressure of his fingers
with it: from this neglect he is much slower in acquiring the figures of
objects, as he is less able to determine the distances or diameters of
their parts, or to distinguish their vis inertiæ from their hardness.
Helvetius adds, that the shortness of his life, his being fugitive before
mankind, and his not inhabiting all climates, combine to prevent his
improvement. (De l'Esprit. T. 1. p.) There is however at this time an old
monkey shewn in Exeter Change, London, who having lost his teeth, when nuts
are given him, takes a stone into his hand, and cracks them with it one by
one; thus using tools to effect his purpose like mankind.

The beaver is another animal that makes much use of his hands, and if we
may credit the reports of travellers, is possessed of amazing ingenuity.
This however, M. Buffon affirms, is only where they exist in large numbers,
and in countries thinly peopled with men; while in France in their solitary
state they shew no uncommon ingenuity.

Indeed all the quadrupeds, that have collar-bones, (claviculæ) use their
fore-limbs in some measure as we use our hands, as the cat, squirrel,
tyger, bear and lion; and as they exercise the sense of touch more
universally than other animals, so are they more sagacious in watching and
surprising their prey. All those birds, that use their claws for hands, as
the hawk, parrot, and cuckoo, appear to be more docile and intelligent;
though the gregarious tribes of birds have more acquired knowledge.

Now as the images, that are painted on the retina of the eye, are no other
than signs, which recall to our imaginations the objects we had before
examined by the organ of touch, as is fully demonstrated by Dr. Berkley in
his treatise on vision; it follows that the human creature has greatly more
accurate and distinct sense of vision than that of any other animal. Whence
as he advances to maturity he gradually acquires a sense of female beauty,
which at this time directs him to the object of his new passion.

Sentimental love, as distinguished from the animal passion of that name,
with which it is frequently accompanied, consists in the desire or
sensation of beholding, embracing, and saluting a beautiful object.

The characteristic of beauty therefore is that it is the object of love;
and though many other objects are in common language called beautiful, yet
they are only called so metaphorically, and ought to be termed agreeable. A
Grecian temple may give us the pleasurable idea of sublimity, a Gothic
temple may give us the pleasurable idea of variety, and a modern house the
pleasurable idea of utility; music and poetry may inspire our love by
association of ideas; but none of these, except metaphorically, can be
termed beautiful; as we have no wish to embrace or salute them.

Our perception of beauty consists in our recognition by the sense of vision
of those objects, first, which have before inspired our love by the
pleasure, which they have afforded to many of our senses: as to our sense
of warmth, of touch, of smell, of taste, hunger and thirst; and, secondly,
which bear any analogy of form to such objects.

When the babe, soon after it is born into this cold world, is applied to
its mother's bosom; its sense of perceiving warmth is first agreeably
affected; next its sense of smell is delighted with the odour of her milk;
then its taste is gratified by the flavour of it: afterwards the appetites
of hunger and of thirst afford pleasure by the possession of their objects,
and by the subsequent digestion of the aliment; and, lastly, the sense of
touch is delighted by the softness and smoothness of the milky fountain,
the source of such variety of happiness.

All these various kinds of pleasure at length become associated with the
form of the mother's breast; which the infant embraces with its hands,
presses with its lips, and watches with its eyes; and thus acquires more
accurate ideas of the form of its mother's bosom, than of the odour and
flavour or warmth, which it perceives by its other senses. And hence at our
maturer years, when any object of vision is presented to us, which by its
waving or spiral lines bears any similitude to the form of the female
bosom, whether it be found in a landscape with soft gradations of rising
and descending surface, or in the forms of some antique vases, or in other
works of the pencil or the chissel, we feel a general glow of delight,
which seems to influence all our senses; and, if the object be not too
large, we experience an attraction to embrace it with our arms, and to
salute it with our lips, as we did in our early infancy the bosom of our
mother. And thus we find, according to the ingenious idea of Hogarth, that
the waving lines of beauty were originally taken from the temple of Venus.

This animal attraction is love; which is a sensation, when the object is
present; and a desire, when it is absent. Which constitutes the purest
source of human felicity, the cordial drop in the otherwise vapid cup of
life, and which overpays mankind for the care and labour, which are
attached to the pre-eminence of his situation above other animals.

It should have been observed, that colour as well as form sometimes enters
into our idea of a beautiful object, as a good complexion for instance,
because a fine or fair colour is in general a sign of health, and conveys
to us an idea of the warmth of the object; and a pale countenance on the
contrary gives an idea of its being cold to the touch.

It was before remarked, that young animals use their lips to distinguish
the forms of things, as well as their fingers, and hence we learn the
origin of our inclination to salute beautiful objects with our lips. For a
definition of Grace, see Class III. 1. 2. 4.

VII. There are two ways by which we become acquainted with the passions of
others: first, by having observed the effects of them, as of fear or anger,
on our own bodies, we know at sight when others are under the influence of
these affections. So when two cocks are preparing to fight, each feels the
feathers rise round his own neck, and knows from the same sign the
disposition of his adversary: and children long before they can speak, or
understand the language of their parents, may be frightened by an angry
countenance, or soothed by smiles and blandishments.

Secondly, when we put ourselves into the attitude that any passion
naturally occasions, we soon in some degree acquire that passion; hence
when those that scold indulge themselves in loud oaths, and violent actions
of the arms, they increase their anger by the mode of expressing
themselves: and on the contrary the counterfeited smile of pleasure in
disagreeable company soon brings along with it a portion of the reality, as
is well illustrated by Mr. Burke. (Essay on the Sublime and Beautiful.)

This latter method of entering into the passions of others is rendered of
very extensive use by the pleasure we take in imitation, which is every day
presented before our eyes, in the actions of children, and indeed in all
the customs and fashions of the world. From this our aptitude to imitation,
arises what is generally understood by the word sympathy so well explained
by Dr. Smith of Glasgow. Thus the appearance of a cheerful countenance
gives us pleasure, and of a melancholy one makes us sorrowful. Yawning and
sometimes vomiting are thus propagated by sympathy, and some people of
delicate fibres, at the presence of a spectacle of misery, have felt pain
in the same parts of their own bodies, that were diseased or mangled in the
other. Amongst the writers of antiquity Aristotle thought this aptitude to
imitation an essential property of the human species, and calls man an
imitative animal. [Greek: To zôon mimômenon].

These then are the natural signs by which we understand each other, and on
this slender basis is built all human language. For without some natural
signs, no artificial ones could have been invented or understood, as is
very ingeniously observed by Dr. Reid. (Inquiry into the Human Mind.)

VIII. The origin of this universal language is a subject of the highest
curiosity, the knowledge of which has always been thought utterly
inaccessible. A part of which we shall however here attempt.

Light, sound, and odours, are unknown to the foetus in the womb, which,
except the few sensations and motions already mentioned, sleeps away its
time insensible of the busy world. But the moment he arrives into day, he
begins to experience many vivid pains and pleasures; these are at the same
time attended with certain muscular motions, and from this their early, and
individual association, they acquire habits of occurring together, that are
afterwards indissoluble.

1. _Of Fear._

As soon as the young animal is born, the first important sensations, that
occur to him, are occasioned by the oppression about his precordia for want
of respiration, and by his sudden transition from ninety-eight degrees of
heat into so cold a climate.--He trembles, that is, he exerts alternately
all the muscles of his body, to enfranchise himself from the oppression
about his bosom, and begins to breathe with frequent and short
respirations; at the same time the cold contracts his red skin, gradually
turning it pale; the contents of the bladder and of the bowels are
evacuated: and from the experience of these first disagreeable sensations
the passion of fear is excited, which is no other than the expectation of
disagreeable sensations. This early association of motions and sensations
persists throughout life; the passion of fear produces a cold and pale
skin, with tremblings, quick respiration, and an evacuation of the bladder
and bowels, and thus constitutes the natural or universal language of this
passion.

On observing a Canary bird this morning, January 28, 1772, at the house of
Mr. Harvey, near Tutbury, in Derbyshire, I was told it always fainted away,
when its cage was cleaned, and desired to see the experiment. The cage
being taken from the ceiling, and its bottom drawn out, the bird began to
tremble, and turned quite white about the root of his bill: he then opened
his mouth as if for breath, and respired quick, stood straighter up on his
perch, hung his wings, spread his tail, closed his eyes, and appeared quite
stiff and cataleptic for near half an hour, and at length with much
trembling and deep respirations came gradually to himself.

2. _Of Grief._

That the internal membrane of the nostrils may be kept always moist, for
the better perception of odours, there are two canals, that conduct the
tears after they have done their office in moistening and cleaning the ball
of the eye into a sack, which is called the lacrymal sack; and from which
there is a duct, that opens into the nostrils: the aperture of this duct is
formed of exquisite sensibility, and when it is stimulated by odorous
particles, or by the dryness or coldness of the air, the sack contracts
itself, and pours more of its contained moisture on the organ of smell. By
this contrivance the organ is rendered more fit for perceiving such odours,
and is preserved from being injured by those that are more strong or
corrosive. Many other receptacles of peculiar fluids disgorge their
contents, when the ends of their ducts are stimulated; as the gall bladder,
when the contents of the duodenum stimulate the extremity of the common
bile duct: and the salivary glands, when the termination of their ducts in
the mouth are excited by the stimulus of the food we masticate. Atque
vesiculæ seminales suum exprimunt fluidum glande penis fricatâ.

The coldness and dryness of the atmosphere, compared with the warmth and
moisture, which the new-born infant had just before experienced,
disagreeably affects the aperture of this lacrymal sack: the tears, that
are contained in this sack, are poured into the nostrils, and a further
supply is secreted by the lacrymal glands, and diffused upon the eye-balls;
as is very visible in the eyes and nostrils of children soon after their
nativity. The same happens to us at our maturer age, for in severe frosty
weather, snivelling and tears are produced by the coldness and dryness of
the air.

But the lacrymal glands, which separate the tears from the blood, are
situated on the upper external part of the globes of each eye; and, when a
greater quantity of tears are wanted, we contract the forehead, and bring
down the eye-brows, and use many other distortions of the face, to compress
these glands.

Now as the suffocating sensation, that produces respiration, is removed
almost as soon as perceived, and does not recur again: this disagreeable
irritation of the lacrymal ducts, as it must frequently recur, till the
tender organ becomes used to variety of odours, is one of the first pains
that is repeatedly attended to: and hence throughout our infancy, and in
many people throughout their lives, all disagreeable sensations are
attended with snivelling at the nose, a profusion of tears, and some
peculiar distortions of countenance: according to the laws of early
association before mentioned, which constitutes the natural or universal
language of grief.

You may assure yourself of the truth of this observation, if you will
attend to what passes, when you read a distressful tale alone; before the
tears overflow your eyes, you will invariably feel a titillation at that
extremity of the lacrymal duct, which terminates in the nostril, then the
compression of the eyes succeeds, and the profusion of tears.

Linnæus asserts, that the female bear sheds tears in grief; the same has
been said of the hind, and some other animals.

3. _Of Tender Pleasure._

The first most lively impression of pleasure, that the infant enjoys after
its nativity, is excited by the odour of its mother's milk. The organ of
smell is irritated by this perfume, and the lacrymal sack empties itself
into the nostrils, as before explained, and an increase of tears is poured
into the eyes. Any one may observe this, when very young infants are about
to suck; for at those early periods of life, the sensation affects the
organ of smell, much more powerfully, than after the repeated habits of
smelling has inured it to odours of common strength: and in our adult
years, the stronger smells, though they are at the same time agreeable to
us, as of volatile spirits, continue to produce an increased secretion of
tears.

This pleasing sensation of smell is followed by the early affection of the
infant to the mother that suckles it, and hence the tender feelings of
gratitude and love, as well as of hopeless grief, are ever after joined
with the titillation of the extremity of the lacrymal ducts, and a
profusion of tears.

Nor is it singular, that the lacrymal sack should be influenced by pleasing
ideas, as the sight of agreeable food produces the same effect on the
salivary glands. Ac dum vidimus insomniis lascivæ puellæ simulacrum
tenditur penis.

Lambs shake or wriggle their tails, at the time when they first suck, to
get free of the hard excrement, which had been long lodged in their bowels.
Hence this becomes afterwards a mark of pleasure in them, and in dogs, and
other tailed animals. But cats gently extend and contract their paws when
they are pleased, and purr by drawing in their breath, both which resemble
their manner of sucking, and thus become their language of pleasure, for
these animals having collar-bones use their paws like hands when they suck,
which dogs and sheep do not.

4. _Of Serene Pleasure._

In the action of sucking, the lips of the infant are closed around the
nipple of its mother, till he has filled his stomach, and the pleasure
occasioned by the stimulus of this grateful food succeeds. Then the
sphincter of the mouth, fatigued by the continued action of sucking, is
relaxed; and the antagonist muscles of the face gently acting, produce the
smile of pleasure: as cannot but be seen by all who are conversant with
children.

Hence this smile during our lives is associated with gentle pleasure; it is
visible in kittens, and puppies, when they are played with, and tickled;
but more particularly marks the human features. For in children this
expression of pleasure is much encouraged, by their imitation of their
parents, or friends; who generally address them with a smiling countenance:
and hence some nations are more remarkable for the gaiety, and others for
the gravity of their looks.

5. _Of Anger._

The actions that constitute the mode of fighting, are the immediate
language of anger in all animals; and a preparation for these actions is
the natural language of threatening. Hence the human creature clenches his
fist, and sternly surveys his adversary, as if meditating where to make the
attack; the ram, and the bull, draws himself some steps backwards, and
levels his horns; and the horse, as he most frequently fights by striking
with his hinder feet, turns his heels to his foe, and bends back his ears,
to listen out the place of his adversary, that the threatened blow may not
be ineffectual.

6. _Of Attention._

The eye takes in at once but half our horizon, and that only in the day,
and our smell informs us of no very distant objects, hence we confide
principally in the organ of hearing to apprize us of danger: when we hear
any the smallest sound, that we cannot immediately account for, our fears
are alarmed, we suspend our steps, hold every muscle still, open our mouths
a little, erect our ears, and listen to gain further information: and this
by habit becomes the general language of attention to objects of sight, as
well as of hearing; and even to the successive trains of our ideas.

The natural language of violent pain, which is expressed by writhing the
body, grinning, and screaming; and that of tumultuous pleasure, expressed
in loud laughter; belong to Section XXXIV. on Diseases from Volition.

IX. It must have already appeared to the reader, that all other animals, as
well as man, are possessed of this natural language of the passions,
expressed in signs or tones; and we shall endeavour to evince, that those
animals, which have preserved themselves from being enslaved by mankind,
and are associated in flocks, are also possessed of some artificial
language, and of some traditional knowledge.

The mother-turkey, when she eyes a kite hovering high in air, has either
seen her own parents thrown into fear at his presence, or has by
observation been acquainted with his dangerous designs upon her young. She
becomes agitated with fear, and uses the natural language of that passion,
her young ones catch the fear by imitation, and in an instant conceal
themselves in the grass.

At the same time that she shews her fears by her gesture and deportment,
she uses a certain exclamation, Koe-ut, Koe-ut, and the young ones
afterwards know, when they hear this note, though they do not see their
dam, that the presence of their adversary is denounced, and hide themselves
as before.

The wild tribes of birds have very frequent opportunities of knowing their
enemies, by observing the destruction they make among their progeny, of
which every year but a small part escapes to maturity: but to our domestic
birds these opportunities so rarely occur, that their knowledge of their
distant enemies must frequently be delivered by tradition in the manner
above explained, through many generations.

This note of danger, as well as the other notes of the mother-turkey, when
she calls her flock to their food, or to sleep under her wings, appears to
be an artificial language, both as expressed by the mother, and as
understood by the progeny. For a hen teaches this language with equal ease
to the ducklings, she has hatched from suppositious eggs, and educates as
her own offspring: and the wagtails, or hedge-sparrows, learn it from the
young cuckoo their softer nursling, and supply him with food long after he
can fly about, whenever they hear his cuckooing, which Linnæus tells us, is
his call of hunger, (Syst. Nat.) And all our domestic animals are readily
taught to come to us for food, when we use one tone of voice, and to fly
from our anger, when we use another.

Rabbits, as they cannot easily articulate sounds, and are formed into
societies, that live under ground, have a very different method of giving
alarm. When danger is threatened, they thump on the ground with one of
their hinder feet, and produce a sound, that can be heard a great way by
animals near the surface of the earth, which would seem to be an artificial
sign both from its singularity and its aptness to the situation of the
animal.

The rabbits on the island of Sor, near Senegal, have white flesh, and are
well tasted, but do not burrow in the earth, so that we may suspect their
digging themselves houses in this cold climate is an acquired art, as well
as their note of alarm, (Adanson's Voyage to Senegal).

The barking of dogs is another curious note of alarm, and would seem to be
an acquired language, rather than a natural sign: for "in the island of
Juan Fernandes, the dogs did not attempt to bark, till some European dogs
were put among them, and then they gradually begun to imitate them, but in
a strange manner at first, as if they were learning a thing that was not
natural to them," (Voyage to South America by Don G. Juan, and Don Ant. de
Ulloa. B. 2. c. 4).

Linnæus also observes, that the dogs of South America do not bark at
strangers, (Syst. Nat.) And the European dogs, that have been carried to
Guinea, are said in three or four generations to cease to bark, and only
howl, like the dogs that are natives of that coast, (World Displayed, Vol.
XVII. p. 26.)

A circumstance not dissimilar to this, and equally curious, is mentioned by
Kircherus, de Musurgia, in his Chapter de Lusciniis, "That the young
nightingales, that are hatched under other birds, never sing till they are
instructed by the company of other nightingales." And Jonston affirms, that
the nightingales that visit Scotland, have not the same harmony as those of
Italy, (Pennant's Zoology, octavo, p. 255); which would lead us to suspect
that the singing of birds, like human music, is an artificial language
rather than a natural expression of passion.

X. Our music like our language, is perhaps entirely constituted of
artificial tones, which by habit suggest certain agreeable passions. For
the same combination of notes and tones do not excite devotion, love, or
poetic melancholy in a native of Indostan and of Europe. And "the
Highlander has the same warlike ideas annexed to the sound of a bagpipe (an
instrument which an Englishman derides), as the Englishman has to that of a
trumpet or fife," (Dr. Brown's Union of Poetry and Music, p. 58.) So "the
music of the Turks is very different from the Italian, and the people of
Fez and Morocco have again a different kind, which to us appears very rough
and horrid, but is highly pleasing to them," (L'Arte Armoniaca a Giorgio
Antoniotto). Hence we see why the Italian opera does not delight an
untutored Englishman; and why those, who are unaccustomed to music, are
more pleased with a tune, the second or third time they hear it, than the
first. For then the same melodious train of sounds excites the melancholy,
they had learned from the song; or the same vivid combination of them
recalls all the mirthful ideas of the dance and company.

Even the sounds, that were once disagreeable to us, may by habit be
associated with other ideas, so as to become agreeable. Father Lasitau, in
his account of the Iroquois, says "the music and dance of those Americans,
have something in them extremely barbarous, which at first disgusts. We
grow reconciled to them by degrees, and in the end partake of them with
pleasure, the savages themselves are fond of them to distraction," (Moeurs
des Savages, Tom. ii.)

There are indeed a few sounds, that we very generally associate with
agreeable ideas, as the whistling of birds, or purring of animals, that are
delighted; and some others, that we as generally associate with
disagreeable ideas, as the cries of animals in pain, the hiss of some of
them in anger, and the midnight howl of beasts of prey. Yet we receive no
terrible or sublime ideas from the lowing of a cow, or the braying of an
ass. Which evinces, that these emotions are owing to previous associations.
So if the rumbling of a carriage in the street be for a moment mistaken for
thunder, we receive a sublime sensation, which ceases as soon as we know it
is the noise of a coach and six.

There are other disagreeable sounds, that are said to set the teeth on
edge; which, as they have always been thought a necessary effect of certain
discordant notes, become a proper subject of our enquiry. Every one in his
childhood has repeatedly bit a part of the glass or earthen vessel, in
which his food has been given him, and has thence had a very disagreeable
sensation in the teeth, which sensation was designed by nature to prevent
us from exerting them on objects harder than themselves. The jarring sound
produced between the cup and the teeth is always attendant on this
disagreeable sensation: and ever after when such a sound is accidentally
produced by the conflict of two hard bodies, we feel by association of
ideas the concomitant disagreeable sensation in our teeth.

Others have in their infancy frequently held the corner of a silk
handkerchief in their mouth, or the end of the velvet cape of their coat,
whilst their companions in play have plucked it from them, and have given
another disagreeable sensation to their teeth, which has afterwards
recurred on touching those materials. And the sight of a knife drawn along
a china plate, though no sound is excited by it, and even the imagination
of such a knife and plate so scraped together, I know by repeated
experience will produce the same disagreeable sensation of the teeth.

These circumstances indisputably prove, that this sensation of the
tooth-edge is owing to associated ideas; as it is equally excitable by
sight, touch, hearing, or imagination.

In respect to the artificial proportions of sound excited by musical
instruments, those, who have early in life associated them with agreeable
ideas, and have nicely attended to distinguish them from each other, are
said to have a good ear, in that country where such proportions are in
fashion: and not from any superior perfection in the organ of hearing, or
any intuitive sympathy between certain sounds and passions.

I have observed a child to be exquisitely delighted with music, and who
could with great facility learn to sing any tune that he heard distinctly,
and yet whole organ of hearing was so imperfect, that it was necessary to
speak louder to him in common conversation than to others.

Our music, like our architecture, seems to have no foundation in nature,
they are both arts purely of human creation, as they imitate nothing. And
the professors of them have only classed those circumstances, that are most
agreeable to the accidental taste of their age, or country; and have called
it Proportion. But this proportion must always fluctuate, as it rests on
the caprices, that are introduced into our minds by our various modes of
education. And these fluctuations of taste must become more frequent in the
present age, where mankind have enfranchised themselves from the blind
obedience to the rules of antiquity in perhaps every science, but that of
architecture. See Sect. XII. 7. 3.

XI. There are many articles of knowledge, which the animals in cultivated
countries seem to learn very early in their lives, either from each other,
or from experience, or observation: one of the most general of these is to
avoid mankind. There is so great a resemblance in the natural language of
the passions of all animals, that we generally know, when they are in a
pacific, or in a malevolent humour, they have the same knowledge of us; and
hence we can scold them from us by some tones and gestures, and could
possibly attract them to us by others, if they were not already apprized of
our general malevolence towards them. Mr. Gmelin, Professor at Petersburg,
assures us, that in his journey into Siberia, undertaken by order of the
Empress of Russia, he saw foxes, that expressed no fear of himself or
companions, but permitted him to come quite near them, having never seen
the human creature before. And Mr. Bongainville relates, that at his
arrival at the Malouine, or Falkland's Islands, which were not inhabited by
men, all the animals came about himself and his people; the fowls settling
upon their heads and shoulders, and the quadrupeds running about their
feet. From the difficulty of acquiring the confidence of old animals, and
the ease of taming young ones, it appears that the fear, they all conceive
at the sight of mankind, is an acquired article of knowledge.

This knowledge is more nicely understood by rooks, who are formed into
societies, and build, as it were, cities over our heads; they evidently
distinguish, that the danger is greater when a man is armed with a gun.
Every one has seen this, who in the spring of the year has walked under a
rookery with a gun in his hand: the inhabitants of the trees rise on their
wings, and scream to the unfledged young to shrink into their nests from
the sight of the enemy. The vulgar observing this circumstance so uniformly
to occur, assert that rooks can smell gun-powder.

The fieldfares, (turdus pilarus) which breed in Norway, and come hither in
the cold season for our winter berries; as they are associated in flocks,
and are in a foreign country, have evident marks of keeping a kind of
watch, to remark and announce the appearance of danger. On approaching a
tree, that is covered with them, they continue fearless till one at the
extremity of the bush rising on his wings gives a loud and peculiar note of
alarm, when they all immediately fly, except one other, who continues till
you approach still nearer, to certify as it were the reality of the danger,
and then he also flies off repeating the note of alarm.

And in the woods about Senegal there is a bird called uett-uett by the
negroes, and squallers by the French, which, as soon as they see a man, set
up a loud scream, and keep flying round him, as if their intent was to warn
other birds, which upon hearing the cry immediately take wing. These birds
are the bane of sportsmen, and frequently put me into a passion, and
obliged me to shoot them, (Adanson's Voyage to Senegal, 78). For the same
intent the lesser birds of our climate seem to fly after a hawk, cuckoo, or
owl, and scream to prevent their companions from being surprised by the
general enemies of themselves, or of their eggs and progeny.

But the lapwing, (charadrius pluvialis Lin.) when her unfledged offspring
run about the marshes, where they were hatched, not only gives the note of
alarm at the approach of men or dogs, that her young may conceal
themselves; but flying and screaming near the adversary, she appears more
felicitous and impatient, as he recedes from her family, and thus
endeavours to mislead him, and frequently succeeds in her design. These
last instances are so apposite to the situation, rather than to the natures
of the creatures, that use them; and are so similar to the actions of men
in the same circumstances, that we cannot but believe, that they proceed
from a similar principle.

Miss M.E. Jacson acquainted me, that she witnessed this autumn an agreeable
instance of sagacity in a little bird, which seemed to use the means to
obtain an end; the bird repeatedly hopped upon a poppy-stem, and shook the
head with its bill, till many seeds were scattered, then it settled on the
ground, and eat the seeds, and again repeated the same management. Sept. 1,
1794.

On the northern coast of Ireland a friend of mine saw above a hundred crows
at once preying upon muscles; each crow took a muscle up into the air
twenty or forty yards high, and let it fall on the stones, and thus by
breaking the shell, got possession of the animal.--A certain philosopher (I
think it was Anaxagoras) walking along the sea-shore to gather shells, one
of these unlucky birds mistaking his bald head for a stone, dropped a
shell-fish upon it, and killed at once a philosopher and an oyster.

Our domestic animals, that have some liberty, are also possessed of some
peculiar traditional knowledge: dogs and cats have been forced into each
other's society, though naturally animals of a very different kind, and
have hence learned from each other to eat dog's grass (agrostis canina)
when they are sick, to promote vomiting. I have seen a cat mistake the
blade of barley for this grass, which evinces it is an acquired knowledge.
They have also learnt of each other to cover their excrement and
urine;--about a spoonful of water was spilt upon my hearth from the
tea-kettle, and I observed a kitten cover it with ashes. Hence this must
also be an acquired art, as the creature mistook the application of it.

To preserve their fur clean, and especially their whiskers, cats wash their
faces, and generally quite behind their ears, every time they eat. As they
cannot lick those places with their tongues, they first wet the inside of
the leg with saliva, and then repeatedly wash their faces with it, which
must originally be an effect of reasoning, because a means is used to
produce an effect; and seems afterwards to be taught or acquired by
imitation, like the greatest part of human arts.

These animals seem to possess something like an additional sense by means
of their whiskers; which have perhaps some analogy to the antennæ of moths
and butterflies. The whiskers of cats consist not only of the long hairs on
their upper lips, but they have also four or five long hairs standing up
from each eyebrow, and also two or three on each cheek; all which, when the
animal erects them, make with their points so many parts of the periphery
of a circle, of an extent at least equal to the circumference of any part
of their own bodies. With this instrument, I conceive, by a little
experience, they can at once determine, whether any aperture amongst hedges
or shrubs, in which animals of this genus live in their wild state, is
large enough to admit their bodies; which to them is a matter of the
greatest consequence, whether pursuing or pursued. They have likewise a
power of erecting and bringing forward the whiskers on their lips; which
probably is for the purpose of feeling, whether a dark hole be further
permeable.

The antennæ, or horns, of butterflies and moths, who have awkward wings,
the minute feathers of which are very liable to injury, serve, I suppose, a
similar purpose of measuring, as they fly or creep amongst the leaves of
plants and trees, whither their wings can pass without touching them.

Mr. Leonard, a very intelligent friend of mine, saw a cat catch a trout by
darting upon it in a deep clear water at the mill at Weaford, near
Lichfield. The cat belonged to Mr. Stanley, who had often seen her catch
fish in the same manner in summer, when the mill-pool was drawn so low,
that the fish could be seen. I have heard of other cats taking fish in
shallow water, as they stood on the bank. This seems a natural art of
taking their prey in cats, which their acquired delicacy by domestication
has in general prevented them from using, though their desire of eating
fish continues in its original strength.

Mr. White, in his ingenious History of Selbourn, was witness to a cat's
suckling a young hare, which followed her about the garden, and came
jumping to her call of affection. At Elford, near Lichfield, the Rev. Mr.
Sawley had taken the young ones out of a hare, which was shot; they were
alive, and the cat, who had just lost her own kittens, carried them away,
as it was supposed, to eat them; but it presently appeared, that it was
affection not hunger which incited her, as she suckled them, and brought
them up as their mother.

Other instances of the mistaken application of what has been termed
instinct may be observed in flies in the night, who mistaking a candle for
day-light, approach and perish in the flame. So the putrid smell of the
stapelia, or carrion-flower, allures the large flesh-fly to deposit its
young worms on its beautiful petals, which perish there for want of
nourishment. This therefore cannot be a necessary instinct, because the
creature mistakes the application of it.

Though in this country horses shew little vestiges of policy, yet in the
deserts of Tartary, and Siberia, when hunted by the Tartars they are seen
to form a kind of community, set watches to prevent their being surprised,
and have commanders, who direct, and hasten their flight, Origin of
Language, Vol. I. p. 212. In this country, where four or five horses travel
in a line, the first always points his ears forward, and the last points
his backward, while the intermediate ones seem quite careless in this
respect; which seems a part of policy to prevent surprise. As all animals
depend most on the ear to apprize them of the approach of danger, the eye
taking in only half the horizon at once, and horses possess a great nicety
of this sense; as appears from their mode of fighting mentioned No. 8. 5.
of this Section, as well as by common observation.

There are some parts of a horse, which he cannot conveniently rub, when
they itch, as about the shoulder, which he can neither bite with his teeth,
nor scratch with his hind foot; when this part itches, he goes to another
horse, and gently bites him in the part which he wishes to be bitten, which
is immediately done by his intelligent friend. I once observed a young foal
thus bite its large mother, who did not choose to drop the grass she had in
her mouth, and rubbed her nose against the foal's neck instead of biting
it; which evinces that she knew the design of her progeny, and was not
governed by a necessary instinct to bite where she was bitten.

Many of our shrubs, which would otherwise afford an agreeable food to
horses, are armed with thorns or prickles, which secure them from those
animals; as the holly, hawthorn, gooseberry, gorse. In the extensive
moorlands of Staffordshire, the horses have learnt to stamp upon a
gorse-bush with one of their fore-feet for a minute together, and when the
points are broken, they eat it without injury. The horses in the new forest
in Hampshire are affirmed to do the same by Mr. Gilpin. Forest Scenery, II.
251, and 112. Which is an art other horses in the fertile parts of the
country do not possess, and prick their mouths till they bleed, if they are
induced by hunger or caprice to attempt eating gorse.

Swine have a sense of touch as well as of smell at the end of their nose,
which they use as a hand, both to root up the soil, and to turn over and
examine objects of food, somewhat like the proboscis of an elephant. As
they require shelter from the cold in this climate, they have learnt to
collect straw in their mouths to make their nest, when the wind blows cold;
and to call their companions by repeated cries to assist in the work, and
add to their warmth by their numerous bedfellows. Hence these animals,
which are esteemed so unclean, have also learned never to befoul their
dens, where they have liberty, with their own excrement; an art, which cows
and horses, which have open hovels to run into, have never acquired. I have
observed great sagacity in swine; but the short lives we allow them, and
their general confinement, prevents their improvement, which might probably
be otherwise greater than that of dogs.

Instances of the sagacity and knowledge of animals are very numerous to
every observer, and their docility in learning various arts from mankind,
evinces that they may learn similar arts from their own species, and thus
be possessed of much acquired and traditional knowledge.

A dog whose natural prey is sheep, is taught by mankind, not only to leave
them unmolested, but to guard them; and to hunt, to set, or to destroy
other kinds of animals, as birds, or vermin; and in some countries to catch
fish, in others to find truffles, and to practise a great variety of
tricks; is it more surprising that the crows should teach each other, that
the hawk can catch less birds, by the superior swiftness of his wing, and
if two of them follow him, till he succeeds in his design, that they can by
force share a part of the capture? This I have formerly observed with
attention and astonishment.

There is one kind of pelican mentioned by Mr. Osbeck, one of Linnæus's
travelling pupils (the pelicanus aquilus), whose food is fish; and which it
takes from other birds, because it is not formed to catch them itself;
hence it is called by the English a Man-of-war-bird, Voyage to China, p.
88. There are many other interesting anecdotes of the pelican and
cormorant, collected from authors of the best authority, in a well-managed
Natural History for Children, published by Mr. Galton. Johnson. London.

And the following narration from the very accurate Mons. Adanson, in his
Voyage to Senegal, may gain credit with the reader: as his employment in
this country was solely to make observations in natural history. On the
river Niger, in his road to the island Griel, he saw a great number of
pelicans, or wide throats. "They moved with great state like swans upon the
water, and are the largest bird next to the ostrich; the bill of the one I
killed was upwards of a foot and half long, and the bag fastened underneath
it held two and twenty pints of water. They swim in flocks, and form a
large circle, which they contract afterwards, driving the fish before them
with their legs: when they see the fish in sufficient number confined in
this space, they plunge their bill wide open into the water, and shut it
again with great quickness. They thus get fish into their throat-bag, which
they eat afterwards on shore at their leisure." P. 247.

XII. The knowledge and language of those birds, that frequently change
their climate with the seasons, is still more extensive: as they perform
these migrations in large societies, and are less subject to the power of
man, than the resident tribes of birds. They are said to follow a leader
during the day, who is occasionally changed, and to keep a continual cry
during the night to keep themselves together. It is probable that these
emigrations were at first undertaken as accident directed, by the more
adventurous of their species, and learned from one another like the
discoveries of mankind in navigation. The following circumstances strongly
support this opinion.

1. Nature has provided these animals, in the climates where they are
produced, with another resource: when the season becomes too cold for their
constitutions, or the food they were supported with ceases to be supplied,
I mean that of sleeping. Dormice, snakes, and bats, have not the means of
changing their country; the two former from the want of wings, and the
latter from his being not able to bear the light of the day. Hence these
animals are obliged to make use of this resource, and sleep during the
winter. And those swallows that have been hatched too late in the year to
acquire their full strength of pinion, or that have been maimed by accident
or disease, have been frequently found in the hollows of rocks on the sea
coasts, and even under water in this torpid state, from which they have
been revived by the warmth of a fire. This torpid state of swallows is
testified by innumerable evidences both of antient and modern names.
Aristotle speaking of the swallows says, "They pass into warmer climates in
winter, if such places are at no great distance; if they are, they bury
themselves in the climates where they dwell," (8. Hist. c. 16. See also
Derham's Phys. Theol. v. ii. p. 177.)

Hence their emigrations cannot depend on a _necessary_ instinct, as the
emigrations themselves are not _necessary_.

2. When the weather becomes cold, the swallows in the neighbourhood
assemble in large flocks; that is, the unexperienced attend those that have
before experienced the journey they are about to undertake: they are then
seen some time to hover on the coast, till there is calm whether, or a
wind, that suits the direction of their flight. Other birds of passage have
been drowned by thousands in the sea, or have settled on ships quite
exhausted with fatigue. And others, either by mistaking their course, or by
distress of weather, have arrived in countries where they were never seen
before: and thus are evidently subject to the same hazards that the human
species undergo, in the execution of their artificial purposes.

3. The same birds are emigrant from some countries and not so from others:
the swallows were seen at Goree in January by an ingenious philosopher of
my acquaintance, and he was told that they continued there all the year; as
the warmth of the climate was at all seasons sufficient for their own
constitutions, and for the production of the flies that supply them with
nourishment. Herodotus says, that in Libya, about the springs of the Nile,
the swallows continue all the year. (L. 2.)

Quails (tetrao corturnix, Lin.) are birds of passage from the coast of
Barbary to Italy, and have frequently settled in large shoals on ships
fatigued with their flight. (Ray, Wisdom of God, p. 129. Derham. Physic.
Theol. v. ii. p. 178,) Dr. Ruffel, in his History of Aleppo, observes that
the swallows visit that country about the end of February, and having
hatched their young disappear about the end of July; and returning again
about the beginning of October, continue about a fortnight, and then again
disappear. (P. 70.)

When my late friend Dr. Chambres, of Derby, was on the island of Caprea in
the bay of Naples, he was informed that great flights of quails annually
settle on that island about the beginning of May, in their passage from
Africa to Europe. And that they always come when the south-east wind blows,
are fatigued when they rest on this island, and are taken in such amazing
quantities and sold to the Continent, that the inhabitants pay the bishop
his stipend out of the profits arising from the sale of them.

The flights of these birds across the Mediterranean are recorded near three
thousand years ago. "There went forth a wind from the Lord and brought
quails from the sea, and let them fall upon the camp, a day's journey round
about it, and they were two cubits above the earth," (Numbers, chap. ii.
ver. 31.)

In our country, Mr. Pennant informs us, that some quails migrate, and
others only remove from the internal parts of the island to the coasts,
(Zoology, octavo, 210.) Some of the ringdoves and stares breed here, others
migrate, (ibid. 510, ii.) And the slender billed small birds do not all
quit these kingdoms in the winter, though the difficulty of procuring the
worms and insects, that they feed on, supplies the same reason for
migration to them all, (ibid. 511.)

Linnæus has observed, that in Sweden the female chaffinches quit that
country in September, migrating into Holland, and leave their mates behind
till their return in spring. Hence he has called them Fringilla cælebs,
(Amæn. Acad. ii. 42. iv. 595.) Now in our climate both sexes of them are
perennial birds. And Mr. Pennant observes that the hoopoe, chatterer,
hawfinch, and crossbill, migrate into England so rarely, and at such
uncertain times, as not to deserve to be ranked among our birds of passage,
(ibid. 511.)

The water fowl, as geese and ducks, are better adapted for long migrations,
than the other tribes of birds, as, when the weather is calm, they can not
only rest themselves, or sleep upon the ocean, but possibly procure some
kind of food from it.

Hence in Siberia, as soon as the lakes are frozen, the water fowl, which
are very numerous, all disappear, and are supposed to fly to warmer
climates, except the rail, which, from its inability for long flights,
probably sleeps, like our bat, in their winter. The following account from
the Journey of Professor Gmelin, may entertain the reader. "In the
neighbourhood of Krasnoiark, amongst many other emigrant water fowls, we
observed a great number of rails, which when pursued never took flight, but
endeavoured to escape by running. We enquired how these birds, that could
not fly, could retire into other countries in the winter, and were told,
both by the Tartars and Assanians, that they well knew those birds could
not alone pass into other countries: but when the cranes (les grues) retire
in autumn, each one takes a rail (un rale) upon his back, and carries him
to a warmer climate."

_Recapitulation._

1. All birds of passage can exist in the climates, where they are produced.

2. They are subject in their migrations to the same accidents and
difficulties, that mankind are subject to in navigation.

3. The same species of birds migrate from some countries, and are resident
in others.

From all these circumstances it appears that the migrations of birds are
not produced by a necessary instinct, but are accidental improvements, like
the arts among mankind, taught by their cotemporaries, or delivered by
tradition from one generation of them to another.

XIII. In that season of the year which supplies the nourishment proper for
the expected brood, the birds enter into a contract of marriage, and with
joint labour construct a bed for the reception of their offspring. Their
choice of the proper season, their contracts of marriage, and the
regularity with which they construct their nests, have in all ages excited
the admiration of naturalists; and have always been attributed to the power
of instinct, which, like the occult qualities of the antient philosophers,
prevented all further enquiry. We shall consider them in their order.

_Their Choice of the Season._

Our domestic birds, that are plentifully supplied throughout the year with
their adapted food, and are covered with houses from the inclemency of the
weather, lay their eggs at any season: which evinces that the spring of the
year is not pointed out to them by a necessary instinct.

Whilst the wild tribes of birds choose this time of the year from their
acquired knowledge, that the mild temperature of the air is more convenient
for hatching their eggs, and is soon likely to supply that kind of
nourishment, that is wanted for their young.

If the genial warmth of the spring produced the passion of love, as it
expands the foliage of trees, all other animals should feel its influence
as well as birds: but, the viviparous creatures, as they suckle their
young, that is, as they previously digest the natural food, that it may
better suit the tender stomachs of their offspring, experience the
influence of this passion at all seasons of the year, as cats and bitches.
The graminivorous animals indeed generally produce their young about the
time when grass is supplied in the greatest plenty, but this is without any
degree of exactness, as appears from our cows, sheep, and hares, and may be
a part of the traditional knowledge, which they learn from the example of
their parents.

_Their Contracts of Marriage._

Their mutual passion, and the acquired knowledge, that their joint labour
is necessary to procure sustenance for their numerous family, induces the
wild birds to enter into a contract of marriage, which does not however
take place among the ducks, geese, and fowls, that are provided with their
daily food from our barns.

An ingenious philosopher has lately denied, that animals can enter into
contracts, and thinks this an essential difference between them and the
human creature:--but does not daily observation convince us, that they form
contracts of friendship with each other, and with mankind? When puppies and
kittens play together, is there not a tacit contract, that they will not
hurt each other? And does not your favorite dog expect you should give him
his daily food, for his services and attention to you? And thus barters his
love for your protection? In the same manner that all contracts are made
amongst men, that do not understand each others arbitrary language.

_Construction of their Nests._

1. They seem to be instructed how to build their nests from their
observation of that, in which they were educated, and from their knowledge
of those things, that are most agreeable to their touch in respect: to
warmth, cleanliness, and stability. They choose their situations from their
ideas of safety from their enemies, and of shelter from the weather. Nor is
the colour of their nests a circumstance unthought of; the finches, that
build in green hedges, cover their habitations with green moss; the swallow
or martin, that builds against rocks and houses, covers her's with clay,
whilst the lark chooses vegetable straw nearly of the colour of the ground
she inhabits: by this contrivance, they are all less liable to be
discovered by their adversaries.

2. Nor are the nests of the same species of birds constructed always of the
same materials, nor in the same form; which is another circumstance that
ascertains, that they are led by observation.

In the trees before Mr. Levet's house in Lichfield, there are annually
nests built by sparrows, a bird which usually builds under the tiles of
houses, or the thatch of barns. Not finding such convenient situations for
their nests, they build a covered nest bigger than a man's head, with an
opening like a mouth at the side, resembling that of a magpie, except that
it is built with straw and hay, and lined with feathers, and so nicely
managed as to be a defence against both wind and rain.

The following extract from a Letter of the Rev. Mr. J. Darwin, of Carleton
Scroop in Lincolnshire, authenticates a curious fact of this kind. "When I
mentioned to you the circumstance of crows or rooks building in the spire
of Welbourn church, you expressed a desire of being well informed of the
certainty of the fact. Welbourn is situated in the road from Grantham to
Lincoln on the Cliff row; I yesterday took a ride thither, and enquired of
the rector, Mr. Ridgehill, whether the report was true, that rooks built in
the spire of his church. He assured me it was true, and that they had done
so time immemorial, as his parishioners affirmed. There was a common
tradition, he said, that formerly a rookery in some high trees adjoined the
church yard, which being cut down (probably in the spring, the building
season), the rooks removed to the church, and built their nests on the
outside of the spire on the tops of windows, which by their projection a
little from the spire made them convenient room, but that they built also
on the inside. I saw two nests made with sticks on the outside, and in the
spires, and Mr. Ridgehill said there were always a great many.

"I spent the day with Mr. Wright, a clergyman, at Fulbeck, near Welbourn,
and in the afternoon Dr. Ellis of Headenham, about two miles from Welbourn,
drank tea at Mr. Wright's, who said he remembered, when Mr. Welby lived at
Welbourn, that he received a letter from an acquaintance in the west of
England, desiring an answer, whether the report of rooks building in
Welbourn church was true, as a wager was depending on that subject; to
which he returned an answer ascertaining the fact, and decided the wager."
Aug. 30, 1794.

So the jackdaw (corvus monedula) generally builds in church-steeples, or
under the roofs of high houses; but at Selbourn, in Southamptonshire, where
towers and steeples are not sufficiently numerous, these birds build in
forsaken rabbit burrows. See a curious account of these subterranean nests
in White's History of Selbourn, p. 59. Can the skilful change of
architecture in these birds and the sparrows above mentioned be governed by
instinct? Then they must have two instincts, one for common, and the other
for extraordinary occasions.

I have seen green worsted in a nest, which no where exists in nature: and
the down of thistles in those nests, that were by some accident constructed
later in the summer, which material could not be procured for the earlier
nests: in many different climates they cannot procure the same materials,
that they use in ours. And it is well known, that the canary birds, that
are propagated in this country, and the finches, that are kept tame, will
build their nests of any flexile materials, that are given them. Plutarch,
in his Book on Rivers, speaking of the Nile, says, "that the swallows
collect a material, when the waters recede, with which they form nests,
that are impervious to water." And in India there is a swallow that
collects a glutinous substance for this purpose, whose nest is esculent,
and esteemed a principal rarity amongst epicures, (Lin. Syst. Nat.) Both
these must be constructed of very different materials from those used by
the swallows of our country.

In India the birds exert more artifice in building their nests on account
of the monkeys and snakes: some form their pensile nests in the shape of a
purse, deep and open at top; others with a hole in the side; and others,
still more cautious, with an entrance at the very bottom, forming their
lodge near the summit. But the taylor-bird will not ever trust its nest to
the extremity of a tender twig, but makes one more advance to safety by
fixing it to the leaf itself. It picks up a dead leaf, and sews it to the
side of a living one, its slender bill being its needle, and its thread
some fine fibres; the lining consists of feathers, gossamer, and down; its
eggs are white, the colour of the bird light yellow, its length three
inches, its weight three sixteenths of an ounce; so that the materials of
the nest, and the weight of the bird, are not likely to draw down an
habitation so slightly suspended. A nest of this bird is preserved in the
British Museum, (Pennant's Indian Zoology). This calls to one's mind the
Mosaic account of the origin of mankind, the first dawning of art there
ascribed to them, is that of sewing leaves together. For many other curious
kinds of nests see Natural History for Children, by Mr. Galton. Johnson.
London. Part I. p. 47. Gen. Oriolus.

3. Those birds that are brought up by our care, and have had little
communication with others of their own species, are very defective in this
acquired knowledge; they are not only very awkward in the construction of
their nests, but generally scatter their eggs in various parts of the room
or cage, where they are confined, and seldom produce young ones, till, by
failing in their first attempt, they have learnt something from their own
observation.

4. During the time of incubation birds are said in general to turn their
eggs every day; some cover them, when they leave the nest, as ducks and
geese; in some the male is said to bring food to the female, that she may
have less occasion of absence, in others he is said to take her place, when
she goes in quest of food; and all of them are said to leave their eggs a
shorter time in cold weather than in warm. In Senegal the ostrich sits on
her eggs only during the night, leaving them in the day to the heat of the
sun; but at the Cape of Good Hope, where the heat is less, she sits on them
day and night.

If it should be asked, what induces a bird to sit weeks on its first eggs
unconscious that a brood of young ones will be the product? The answer must
be, that it is the same passion that induces the human mother to hold her
offspring whole nights and days in her fond arms, and press it to her
bosom, unconscious of its future growth to sense and manhood, till
observation or tradition have informed her.

5. And as many ladies are too refined to nurse their own children, and
deliver them to the care and provision of others; so is there one instance
of this vice in the feathered world. The cuckoo in some parts of England,
as I am well informed by a very distinct and ingenious gentleman, hatches
and educates her own young; whilst in other parts she builds no nest, but
uses that of some lesser bird, generally either of the wagtail, or hedge
sparrow, and depositing one egg in it, takes no further care of her
progeny.

As the Rev. Mr. Stafford was walking in Glosop Dale, in the Peak of
Derbyshire, he saw a cuckoo rise from its nest. The nest was on the stump
of a tree, that had been some time felled, among some chips that were in
part turned grey, so as much to resemble the colour of the bird, in this
nest were two young cuckoos: tying a string about the leg of one of them,
he pegged the other end of it to the ground, and very frequently for many
days beheld the old cuckoo feed these her young, as he stood very near
them.

The following extract of a Letter from the Rev. Mr. Wilmot, of Morley, near
Derby, strengthens the truth of the fact above mentioned, of the cuckoo
sometimes making a nest, and hatching her own young.

"In the beginning of July 1792, I was attending some labourers on my farm,
when one of them said to me, "There is a bird's nest upon one of the
Coal-slack Hills; the bird is now sitting, and is exactly like a cuckoo.
They say that cuckoo's never hatch their own eggs, otherwise I should have
sworn it was one." He took me to the spot, it was in an open fallow ground;
the bird was upon the nest, I stood and observed her some time, and was
perfectly satisfied it was a cuckoo; I then put my hand towards her, and
she almost let me touch her before she rose from the nest, which she
appeared to quit with great uneasiness, skimming over the ground in the
manner that a hen partridge does when disturbed from a new hatched brood,
and went only to a thicket about forty or fifty yards from the nest; and
continued there as long as I staid to observe her, which was not many
minutes. In the nest, which was barely a hole scratched out of the
coal-slack in the manner of a plover's nest, I observed three eggs, but did
not touch them. As I had labourers constantly at work in that field, I went
thither every day, and always looked to see if the bird was there, but did
not disturb her for seven or eight days, when I was tempted to drive her
from the nest, and found _two_ young ones, that appeared to have been
hatched some days, but there was no appearance of the third egg. I then
mentioned this extraordinary circumstance (for such I thought it) to Mr.
and Mrs. Holyoak of Bidford Grange, Warwickshire, and to Miss M. Willes,
who were on a visit at my house, and who all went to see it. Very lately I
reminded Mr. Holyoak of it, who told me he had a perfect recollection of
the whole, and that, considering it a curiosity, he walked to look at it
several times, was perfectly satisfied as to its being a cuckoo, and
thought her more attentive to her young, than any other bird he ever
observed, having always found her brooding her young. In about a week after
I first saw the young ones, one of them was missing, and I rather suspected
my plough-boys having taken it; though it might possibly have been taken by
a hawk, some time when the old one was seeking food. I never found her off
her nest but once, and that was the last time I saw the remaining young
one, when it was almost full feathered. I then went from home for two or
three days, and, when I returned, the young one was gone, which I take for
granted had flown. Though during this time I frequently saw cuckoos in the
thicket I mention, I never observed any one, that I supposed to be the
cock-bird, paired with this hen."

Nor is this a new observation, though it is entirely overlooked by the
modern naturalists, for Aristotle speaking of the cuckoo, asserts that she
sometimes builds her nest among broken rocks, and on high mountains, (L. 6.
H. c. 1.) but adds in another place that she generally possesses the nest
of another bird, (L. 6. H. c. 7.) And Niphus says that cuckoos rarely build
for themselves, most frequently laying their eggs in the nests of other
birds, (Gesner, L. 3. de Cuculo.)

The Philosopher who is acquainted with these facts concerning the cuckoo,
would seem to have very little _reason_ himself, if he could imagine this
neglect of her young to be a necessary _instinct_!

XIV. The deep recesses of the ocean are inaccessible to mankind, which
prevents us from having much knowledge of the arts and government of its
inhabitants.

1. One of the baits used by the fisherman is an animal called an Old
Soldier, his size and form are somewhat like the craw-fish, with this
difference, that his tail is covered with a tough membrane instead of a
shell; and to obviate this defect, he seeks out the uninhabited shell of
some dead fish, that is large enough to receive his tail, and carries it
about with him as part of his clothing or armour.

2. On the coasts about Scarborough, where the haddocks, cods, and dog-fish,
are in great abundance, the fishermen universally believe that the dog-fish
make a line, or semicircle, to encompass a shoal of haddocks and cod,
confining them within certain limits near the shore, and eating them as
occasion requires. For the haddocks and cod are always found near the shore
without any dog-fish among them, and the dog-fish further off without any
haddocks or cod; and yet the former are known to prey upon the latter, and
in some years devour such immense quantities as to render this fishery more
expensive than profitable.

3. The remora, when he wishes to remove his situation, as he is a very slow
swimmer, is content to take an outside place on whatever conveyance is
going his way; nor can the cunning animal be tempted to quit his hold of a
ship when she is sailing, not even for the lucre of a piece of pork, lest
it should endanger the loss of his passage: at other times he is easily
caught with the hook.

4. The crab-fish, like many other testaceous animals, annually changes its
shell; it is then in a soft state, covered only with a mucous membrane, and
conceals itself in holes in the sand or under weeds; at this place a hard
shelled crab always stands centinel, to prevent the sea insects from
injuring the other in its defenceless state; and the fishermen from his
appearance know where to find the soft ones, which they use for baits in
catching other fish.

And though the hard shelled crab, when he is on this duty, advances boldly
to meet the foe, and will with difficulty quit the field; yet at other
times he shews great timidity, and has a wonderful speed in attempting his
escape; and, if often interrupted, will pretend death like the spider, and
watch an opportunity to sink himself into the sand, keeping only his eyes
above. My ingenious friend Mr. Burdett, who favoured me with these accounts
at the time he was surveying the coasts, thinks the commerce between the
sexes takes place at this time, and inspires the courage of the creature.

5. The shoals of herrings, cods, haddocks, and other fish, which approach
our shores at certain seasons, and quit them at other seasons without
leaving one behind; and the salmon, that periodically frequent our rivers,
evince, that there are vagrant tribes of fish, that perform as regular
migrations as the birds of passage already mentioned.

6. There is a cataract on the river Liffey in Ireland about nineteen feet
high: here in the salmon season many of the inhabitants amuse themselves in
observing these fish leap up the torrent. They dart themselves quite out of
the water as they ascend, and frequently fall back many times before they
surmount it, and baskets made of twigs are placed near the edge of the
stream to catch them in their fall.

I have observed, as I have sat by a spout of water, which descends from a
stone trough about two feet into a stream below, at particular seasons of
the year, a great number of little fish called minums, or pinks, throw
themselves about twenty times their own length out of the water, expecting
to get into the trough above.

This evinces that the storgee, or attention of the dam to provide for the
offspring, is strongly exerted amongst the nations of fish, where it would
seem to be the most neglected; as these salmon cannot be supposed to
attempt so difficult and dangerous a task without being conscious of the
purpose or end of their endeavours.

It is further remarkable, that most of the old salmon return to the sea
before it is proper for the young shoals to attend them, yet that a few old
ones continue in the rivers so late, that they become perfectly emaciated
by the inconvenience of their situation, and this apparently to guide or to
protect the unexperienced brood.

Of the smaller water animals we have still less knowledge, who nevertheless
probably possess many superior arts; some of these are mentioned in Botanic
Garden, P. I. Add. Note XXVII. and XXVIII. The nympha of the water-moths of
our rivers, which cover themselves with cases of straw, gravel, and shell,
contrive to make their habitations, nearly in equilibrium with the water;
when too heavy, they add a bit of wood or straw; when too light, a bit of
gravel. Edinb. Trans.

All these circumstances bear a near resemblance to the deliberate actions
of human reason.

XV. We have a very imperfect acquaintance with the various tribes of
insects: their occupations, manner of life, and even the number of their
senses, differ from our own, and from each other; but there is reason to
imagine, that those which possess the sense of touch in the most exquisite
degree, and whole occupations require the most constant exertion of their
powers, are induced with a greater proportion or knowledge and ingenuity.

The spiders of this country manufacture nets of various forms, adapted to
various situations, to arrest the flies that are their food; and some of
them have a house or lodging-place in the middle of the net, well contrived
for warmth, security, or concealment. There is a large spider in South
America, who constructs nets of so strong a texture as to entangle small
birds, particularly the humming bird. And in Jamaica there is another
spider, who digs a hole in the earth obliquely downwards, about three
inches in length, and one inch in diameter, this cavity she lines with a
tough thick web, which when taken out resembles a leathern purse: but what
is most curious, this house has a door with hinges, like the operculum of
some sea shells; and herself and family, who tenant this nest, open and
shut the door, whenever they pass or repass. This history was told me, and
the nest with its operculum shewn me by the late Dr. Butt of Bath, who was
some years physician in Jamaica.

The production of these nets is indeed a part of the nature or conformation
of the animal, and their natural use is to supply the place of wings, when
she wishes to remove to another situation. But when she employs them to
entangle her prey, there are marks of evident design, for she adapts the
form of each net to its situation, and strengthens those lines, that
require it, by joining others to the middle of them, and attaching those
others to distant objects, with the same individual art, that is used by
mankind in supporting the masts and extending the sails of ships. This work
is executed with more mathematical exactness and ingenuity by the field
spiders, than by those in our houses, as their constructions are more
subjected to the injuries of dews and tempests.

Besides the ingenuity shewn by these little creatures in taking their prey,
the circumstance of their counterfeiting death, when they are put into
terror, is truly wonderful; and as soon as the object of terror is removed,
they recover and run away. Some beetles are also said to possess this piece
of hypocrisy.

The curious webs, or chords, constructed by some young caterpillars to
defend themselves from cold, or from insects of prey; and by silk-worms and
some other caterpillars, when they transmigrate into aureliæ or larvæ, have
deservedly excited the admiration of the inquisitive. But our ignorance of
their manner of life, and even of the number of their senses, totally
precludes us from understanding the means by which they acquire this
knowledge.

The care of the salmon in choosing a proper situation for her spawn, the
structure of the nests of birds, their patient incubation, and the art of
the cuckoo in depositing her egg in her neighbour's nursery, are instances
of great sagacity in those creatures: and yet they are much inferior to the
arts exerted by many of the insect tribes on similar occasions. The hairy
excrescences on briars, the oak apples, the blasted leaves of trees, and
the lumps on the backs of cows, are situations that are rather produced
than chosen by the mother insect for the convenience of her offspring. The
cells of bees, wasps, spiders, and of the various coralline insects,
equally astonish us, whether we attend to the materials or to the
architecture.

But the conduct of the ant, and of some species of the ichneumon fly in the
incubation of their eggs, is equal to any exertion of human science. The
ants many times in a day move their eggs nearer the surface of their
habitation, or deeper below it, as the heat of the weather varies; and in
colder days lie upon them in heaps for the purpose of incubation: if their
mansion is too dry, they carry them to places where there is moisture, and
you may distinctly see the little worms move and suck up the water. When
too much moisture approaches their nest, they convey their eggs deeper in
the earth, or to some other place of safety. (Swammerd. Epil. ad Hist.
Insects, p. 153. Phil. Trans. No. 23. Lowthrop. V. 2. p. 7.)

There is one species of ichneumon-fly, that digs a hole in the earth, and
carrying into it two or three living caterpillars, deposits her eggs, and
nicely closing up the nest leaves them there; partly doubtless to assist
the incubation, and partly to supply food to her future young, (Derham. B.
4, c. 13. Aristotle Hist. Animal, L. 5. c. 20.)

A friend of mine put about fifty large caterpillars collected from cabbages
on some bran and a few leaves into a box, and covered it with gauze to
prevent their escape. After a few days we saw, from more than three fourths
of them, about eight or ten little caterpillars of the ichneumon-fly come
out of their backs, and spin each a small cocoon of silk, and in a few days
the large caterpillars died. This small fly it seems lays its egg in the
back of the cabbage caterpillar, which when hatched preys upon the
material, which is produced there for the purpose of making silk for the
future nest of the cabbage caterpillar; of which being deprived, the
creature wanders about till it dies, and thus our gardens are preserved by
the ingenuity of this cruel fly. This curious property of producing a silk
thread, which is common to some sea animals, see Botanic Garden, Part I.
Note XXVII. and is designed for the purpose of their transformation as in
the silk-worm, is used for conveying themselves from higher branches to
lower ones of trees by some caterpillars, and to make themselves temporary
nests or tents, and by the spider for entangling his prey. Nor is it
strange that so much knowledge should be acquired by such small animals;
since there is reason to imagine, that these insects have the sense of
touch, either in their proboscis, or their antennæ, to a great degree of
perfection; and thence may possess, as far as their sphere extends, as
accurate knowledge, and as subtle invention, as the discoverers of human
arts.

XVI. 1. If we were better acquainted with the histories of those insects
that are formed into societies, as the bees, wasps, and ants, I make no
doubt but we should find, that their arts and improvements are not so
similar and uniform as they now appear to us, but that they arose in the
same manner from experience and tradition, as the arts of our own species;
though their reasoning is from fewer ideas, is busied about fewer objects,
and is exerted with less energy.

There are some kinds of insects that migrate like the birds before
mentioned. The locust of warmer climates has sometimes come over to
England; it is shaped like a grasshopper, with very large wings, and a body
above an inch in length. It is mentioned as coming into Egypt with an east
wind, "The lord brought an east wind upon the land all that day and night,
and in the morning the east wind brought the locusts, and covered the face
of the earth, so that the land was dark," Exod. x. 13. The migrations of
these insects are mentioned in another part of the scripture, "The locusts
have no king, yet go they forth all of them in bands," Prov. xxx. 27.

The accurate Mr. Adanson, near the river Gambia in Africa, was witness to
the migration of these insects. "About eight in the morning, in the month
of February, there suddenly arose over our heads a thick cloud, which
darkened the air, and deprived us of the rays of the sun. We found it was a
cloud of locusts raised about twenty or thirty fathoms from the ground, and
covering an extent of several leagues; at length a shower of these insects
descended, and after devouring every green herb, while they rested, again
resumed their flight. This cloud was brought by a strong east-wind, and was
all the morning in passing over the adjacent country." (Voyage to Senegal,
158.)

In this country the gnats are sometimes seen to migrate in clouds, like the
musketoes of warmer climates, and our swarms of bees frequently travel many
miles, and are said in North America always to fly towards the south. The
prophet Isaiah has a beautiful allusion to these migrations, "The Lord
shall call the fly from the rivers of Egypt, and shall hiss for the bee
that is in the land of Assyria," Isa. vii. 18. which has been lately
explained by Mr. Bruce, in his travels to discover the source of the Nile.

2. I am well informed that the bees that were carried into Barbadoes, and
other western islands, ceased to lay up any honey after the first year, as
they found it not useful to them: and are now become very troublesome to
the inhabitants of those islands by infesting their sugar houses; but those
in Jamaica continue to make honey, as the cold north winds, or rainy
seasons of that island, confine them at home for several weeks together.
And the bees of Senegal, which differ from those of Europe only in size,
make their honey not only superior to ours in delicacy of flavour, but it
has this singularity, that it never concretes, but remains liquid as syrup,
(Adanson). From some observations of Mr. Wildman, and of other people of
veracity, it appears, that during the severe part of the winter season for
weeks together the bees are quite benumbed and torpid from the cold, and do
not consume any of their provision. This state of sleep, like that of
swallows and bats, seems to be the natural resource of those creatures in
cold climates, and the making of honey to be an artificial improvement.

As the death of our hives of bees appears to be owning to their being kept
so warm, as to require food when their stock is exhausted; a very observing
gentleman at my request put two hives for many weeks into a dry cellar, and
observed, during all that time, they did not consume any of their
provision, for their weight did not decrease as it had done when they were
kept in the open air. The same observation is made in the Annual Register
for 1768, p. 113. And the Rev. Mr. White, in his Method of preserving Bees,
adds, that those on the north side of his house consumed less honey in the
winter than those on the south side.

There is another observation on bees well ascertained, that they at various
times, when the season begins to be cold, by a general motion of their legs
as they hang in clusters produce a degree of warmth, which is easily
perceptible by the hand. Hence by this ingenious exertion, they for a long
time prevent the torpid state they would naturally fall into.

According to the late observations of Mr. Hunter, it appears that the
bee's-wax is not made from the dust of the anthers of flowers, which they
bring home on their thighs, but that this makes what is termed bee-bread,
and is used for the purpose of feeding the bee-maggots; in the same manner
butterflies live on honey, but the previous caterpillar lives on vegetable
leaves, while the maggots of large flies require flesh for their food, and
those of the ichneumon fly require insects for their food. What induces the
bee who lives on honey to lay up vegetable powder for its young? What
induces the butterfly to lay its eggs on leaves, when itself feeds on
honey? What induces the other flies to seek a food for their progeny
different from what they consume themselves? If these are not deductions
from their own previous experience or observation, all the actions of
mankind must be resolved into instinct.

3. The dormouse consumes but little of its food during the rigour of the
season, for they roll themselves up, or sleep, or lie torpid the greatest
part of the time; but on warm sunny days experience a short revival, and
take a little food, and then relapse into their former state." (Pennant
Zoolog. p. 67.) Other animals, that sleep in winter without laying up any
provender, are observed to go into their winter beds fat and strong, but
return to day-light in the spring season very lean and feeble. The common
flies sleep during the winter without any provision for their nourishment,
and are daily revived by the warmth of the sun, or of our fires. These
whenever they see light endeavour to approach it, having observed, that by
its greater vicinity they get free from the degree of torpor, that the cold
produces; and are hence induced perpetually to burn themselves in our
candles: deceived, like mankind, by the misapplication of their knowledge.
Whilst many of the subterraneous insects, as the common worms, seem to
retreat so deep into the earth as not to be enlivened or awakened by the
difference of our winter days; and stop up their holes with leaves or
straws, to prevent the frosts from injuring them, or the centipes from
devouring them. The habits of peace, or the stratagems of war, of these
subterranean nations are covered from our view; but a friend of mine
prevailed on a distressed worm to enter the hole of another worm on a
bowling-green, and he presently returned much wounded about his head. And I
once saw a worm rise hastily out of the earth into the sunshine, and
observed a centipes hanging at its tail: the centipes nimbly quitted the
tail, and seizing the worm about its middle cut it in half with its
forceps, and preyed upon one part, while the other escaped. Which evinces
they have design in stopping the mouths of their habitations.

4. The wasp of this country fixes his habitation under ground, that he may
not be affected with the various changes of our climate; but in Jamaica he
hangs it on the bough of a tree, where the seasons are less severe. He
weaves a very curious paper of vegetable fibres to cover his nest, which is
constructed on the same principle with that of the bee, but with a
different material; but as his prey consists of flesh, fruits, and insects,
which are perishable commodities, he can lay up no provender for the
winter.

M. de la Loubiere, in his relation of Siam, says, "That in a part of that
kingdom, which lies open to great inundations, all the ants make their
settlements upon trees; no ants' nests are to be seen any where else."
Whereas in our country the ground is their only situation. From the
scriptual account of these insects, one might be led to suspect, that in
some climates they lay up a provision for the winter. Origen affirms the
same, (Cont. Cels. L. 4.) But it is generally believed that in this country
they do not, (Prov. vi. 6. xxx. 25.) The white ants of the coast of Africa
make themselves pyramids eight or ten feet high, on a base of about the
same width, with a smooth surface of rich clay, excessively hard and well
built, which appear at a distance like an assemblage of the huts of the
negroes, (Adanson). The history of these has been lately well described in
the Philosoph. Transactions, under the name of termes, or termites. These
differ very much from the nest of our large ant; but the real history of
this creature, as well as of the wasp, is yet very imperfectly known.

Wasps are said to catch large spiders, and to cut off their legs, and carry
their mutilated bodies to their young, Dict. Raison. Tom. I. p. 152.

One circumstance I shall relate which fell under my own eye, and shewed the
power or reason in a wasp, as it is exercised among men. A wasp, on a
gravel walk, had caught a fly nearly as large as himself; kneeling on the
ground I observed him separate the tail and the head from the body part, to
which the wings were attached. He then took the body part in his paws, and
rose about two feet from the ground with it; but a gentle breeze wafting
the wings of the fly turned him round in the air, and he settled again with
his prey upon the gravel. I then distinctly observed him cut off with his
mouth, first one of the wings, and then the other, after which he flew away
with it unmolested by the wind.

Go, thou sluggard, learn arts and industry from the bee, and from the ant!

Go, proud reasoner, and call the worm thy sister!

XVII. _Conclusion._

It was before observed how much the superior accuracy of our sense of touch
contributes to increase our knowledge; but it is the greater energy and
activity of the power of volition (as explained in the former Sections of
this work) that marks mankind, and has given him the empire of the world.

There is a criterion by which we may distinguish our voluntary acts or
thoughts from those that are excited by our sensations: "The former are
always employed about the _means_ to acquire pleasureable objects, or to
avoid painful ones: while the latter are employed about the _possession_ of
those that are already in our power."

If we turn our eyes upon the fabric of our fellow animals, we find they are
supported with bones, covered with skins, moved by muscles; that they
possess the same senses, acknowledge the same appetites, and are nourished
by the same aliment with ourselves; and we should hence conclude from the
strongest analogy, that their internal faculties were also in some measure
similar to our own.

Mr. Locke indeed published an opinion, that other animals possessed no
abstract or general ideas, and thought this circumstance was the barrier
between the brute and the human world. But these abstracted ideas have been
since demonstrated by Bishop Berkley, and allowed by Mr. Hume, to have no
existence in nature, not even in the mind of their inventor, and we are
hence necessitated to look for some other mark of distinction.

The ideas and actions of brutes, like those of children, are almost
perpetually produced by their present pleasures, or their present pains;
and, except in the few instances that have been mentioned in this Section,
they seldom busy themselves about the _means_ of procuring future bliss, or
of avoiding future misery.

Whilst the acquiring of languages, the making of tools, and the labouring
for money; which are all only the _means_ of procuring pleasure; and the
praying to the Deity, as another _means_ to procure happiness, are
characteristic of human nature.

       *       *       *       *       *

SECT. XVII.

THE CATENATION OF MOTIONS.

    I. 1. _Catenations of animal motion._ 2. _Are produced by irritations,
    by sensations, by volitions._ 3. _They continue some time after they
    have been excited. Cause of catenation._ 4. _We can then exert our
    attention on other objects._ 5. _Many catenations of motions go on
    together._ 6. _Some links of the catenations of motions may be left out
    without disuniting the chain._ 7. _Interrupted circles of motion
    continue confusedly till they come to the part of the circle, where
    they were disturbed._ 8. _Weaker catenations are dissevered by
    stronger._ 9. _Then new catenations take place._ 10. _Much effort
    prevents their reuniting. Impediment of speech._ 11. _Trains more
    easily dissevered than circles._ 12. _Sleep destroys volition and
    external stimulus._ II. _Instances of various catenations in a young
    lady playing on the harpsichord._ III. 1. _What catenations are the
    strongest._ 2. _Irritations joined with associations from strongest
    connexions. Vital motions._ 3. _New links with increased force, cold
    fits of fever produced._ 4. _New links with decreased force. Cold
    bath._ 5. _Irritation joined with sensation. Inflammatory fever. Why
    children cannot tickle themselves. 6. Volition joined with sensation.
    Irritative ideas of sound become sensible._ 7. _Ideas of imagination,
    dissevered by irritations, by volition, production of surprise._

I. 1. To investigate with precision the catenations of animal motions, it
would be well to attend to the manner of their production; but we cannot
begin this disquisition early enough for this purpose, as the catenations
of motion seem to begin with life, and are only extinguishable with it; We
have spoken of the power of irritation, of sensation, of volition, and of
association, as preceding the fibrous motions; we now step forwards, and
consider, that conversely they are in their turn preceded by those motions;
and that all the successive trains or circles of our actions are composed
of this twofold concatenation. Those we shall call trains of action, which
continue to proceed without any stated repetitions; and those circles of
action, when the parts of them return at certain periods, though the
trains, of which they consist, are not exactly similar. The reading an epic
poem is a train of actions; the reading a song with a chorus at equal
distances in the measure constitutes so many circles of action.

2. Some catenations of animal motion are produced by reiterated successive
irritations, as when we learn to repeat the alphabet in its order by
frequently reading the letters of it. Thus the vermicular motions of the
bowels were originally produced by the successive irritations of the
passing aliment; and the succession of actions of the auricles and
ventricles of the heart was originally formed by successive stimulus of the
blood, these afterwards become part of the diurnal circles of animal
actions, as appears by the periodical returns of hunger, and the quickened
pulse of weak people in the evening.

Other catenations of animal motion are gradually acquired by successive
agreeable sensations, as in learning a favourite song or dance; others by
disagreeable sensations, as in coughing or nictitation; these become
associated by frequent repetition, and afterwards compose parts of greater
circles of action like those above mentioned.

Other catenations of motions are gradually acquired by frequent voluntary
repetitions; as when we deliberately learn to march, read, fence, or any
mechanic art, the motions of many of our muscles become gradually linked
together in trains, tribes, or circles of action. Thus when any one at
first begins to use the tools in turning wood or metals in a lathe, he
wills the motions of his hand or fingers, till at length these actions
become so connected with the effect, that he seems only to will the point
of the chisel. These are caused by volition, connected by association like
those above described, and afterwards become parts of our diurnal trains or
circles of action.

3. All these catenations of animal motions, are liable to proceed some time
after they are excited, unless they are disturbed or impeded by other
irritations, sensations, or volitions; and in many instances in spite of
our endeavours to stop them; and this property of animal motions is
probably the cause of their catenation. Thus when a child revolves some
minute on one foot, the spectra of the ambient objects appear to circulate
round him some time after he falls upon the ground. Thus the palpitation of
the heart continues some time after the object of fear, which occasioned
it, is removed. The blush of shame, which is an excess of sensation, and
the glow of anger, which is an excess of volition, continue some time,
though the affected person finds, that those emotions were caused by
mistaken facts, and endeavours to extinguish their appearance. See Sect.
XII. 1. 5.

4. When a circle of motions becomes connected, by frequent repetitions as
above, we can exert our attention strongly on other objects, and the
concatenated circle of motions will nevertheless proceed in due order; as
whilst you are thinking on this subject, you use variety of muscles in
walking about your parlour, or in sitting at your writing-table.

5. Innumerable catenations of motions may proceed at the same time, without
incommoding each other. Of these are the motions of the heart and arteries;
those of digestion and glandular secretion; of the ideas, or sensual
motions; those of progression, and of speaking; the great annual circle of
actions so apparent in birds in their times of breeding and moulting; the
monthly circles of many female animals; and the diurnal circles of sleeping
and waking, of fulness and inanition.

6. Some links of successive trains or of synchronous tribes of action may
be left out without disjoining the whole. Such are our usual trains of
recollection; after having travelled through an entertaining country, and
viewed many delightful lawns, rolling rivers, and echoing rocks; in the
recollection of our journey we leave out the many districts, that we
crossed, which were marked with no peculiar pleasure. Such also are our
complex ideas, they are catenated tribes of ideas, which do not perfectly
resemble their correspondent perceptions, because some of the parts are
omitted.

7. If an interrupted circle of actions is not entirely dissevered, it will
continue to proceed confusedly, till it comes to the part of the circle,
where it was interrupted.

The vital motions in a fever from drunkenness, and in other periodical
diseases, are instances of this circumstance. The accidental inebriate does
not recover himself perfectly till about the same hour on the succeeding
day. The accustomed drunkard is disordered, if he has not his usual
potation of fermented liquor. So if a considerable part of a connected
tribe of action be disturbed, that whole tribe goes on with confusion, till
the part of the tribe affected regains its accustomed catenations. So
vertigo produces vomiting, and a great secretion of bile, as in
sea-sickness, all these being parts of the tribe of irritative catenations.

8. Weaker catenated trains may be dissevered by the sudden exertion of the
stronger. When a child first attempts to walk across a room, call to him,
and he instantly falls upon the ground. So while I am thinking over the
virtues of my friends, if the tea-kettle spurt out some hot water on my
stocking; the sudden pain breaks the weaker chain of ideas, and introduces
a new group of figures of its own. This circumstance is extended to some
unnatural trains of action, which have not been confirmed by long habit; as
the hiccough, or an ague-fit, which are frequently curable by surprise. A
young lady about eleven years old had for five days had a contraction of
one muscle in her fore arm, and another in her arm, which occurred four or
five times every minute; the muscles were seen to leap, but without bending
the arm. To counteract this new morbid habit, an issue was placed over the
convulsed muscle of her arm, and an adhesive plaster wrapped tight like a
bandage over the whole fore arm, by which the new motions were immediately
destroyed, but the means were continued some weeks to prevent a return.

9. If any circle of actions is dissevered, either by omission of some of
the links, as in sleep, or by insertion of other links, as in surprise, new
catenations take place in a greater or less degree. The last link of the
broken chain of actions becomes connected with the new motion which has
broken it, or with that which was nearest the link omitted; and these new
catenations proceed instead of the old ones. Hence the periodic returns of
ague-fits, and the chimeras of our dreams.

10. If a train of actions is dissevered, much effort of volition or
sensation will prevent its being restored. Thus in the common impediment of
speech, when the association of the motions of the muscles of enunciation
with the idea of the word to be spoken is disordered, the great voluntary
efforts, which distort the countenance, prevent the rejoining of the broken
associations. See No. II. 10. of this Section. It is thus likewise
observable in some inflammations of the bowels, the too strong efforts made
by the muscles to carry forwards the offending material fixes it more
firmly in its place, and prevents the cure. So in endeavouring to recal to
our memory some particular word of a sentence, if we exert ourselves too
strongly about it, we are less likely to regain it.

11. Catenated trains or tribes of action are easier dissevered than
catenated circles of action. Hence in epileptic fits the synchronous
connected tribes of action, which keep the body erect, are dissevered, but
the circle of vital motions continues undisturbed.

12. Sleep destroys the power of volition, and precludes the stimuli of
external objects, and thence dissevers the trains, of which these are a
part; which confirms the other catenations, as those of the vital motions,
secretions, and absorptions; and produces the new trains of ideas, which
constitute our dreams.

II. 1. All the preceding circumstances of the catenations of animal motions
will be more clearly understood by the following example of a person
learning music; and when we recollect the variety of mechanic arts, which
are performed by associated trains of muscular actions catenated with the
effects they produce, as in knitting, netting, weaving; and the greater
variety of associated trains of ideas caused or catenated by volitions or
sensations, as in our hourly modes of reasoning, or imagining, or
recollecting, we shall gain some idea of the innumerable catenated trains
and circles of action, which form the tenor of our lives, and which began,
and will only cease entirely with them.

2. When a young lady begins to learn music, she voluntarily applies herself
to the characters of her music-book, and by many repetitions endeavours to
catenate them with the proportions of sound, of which they are symbols. The
ideas excited by the musical characters are slowly connected with the keys
of the harpsichord, and much effort is necessary to produce every note with
the proper finger, and in its due place and time; till at length a train of
voluntary exertions becomes catenated with certain irritations. As the
various notes by frequent repetitions become connected in the order, in
which they are produced, a new catenation of sensitive exertions becomes
mixed with the voluntary ones above described; and not only the musical
symbols of crotchets and quavers, but the auditory notes and tones at the
same time, become so many successive or synchronous links in this circle of
catenated actions.

At length the motions of her fingers become catenated with the musical
characters; and these no sooner strike the eye, than the finger presses
down the key without any voluntary attention between them; the activity of
the hand being connected with the irritation of the figure or place of the
musical symbol on the retina; till at length by frequent repetitions of the
same tune the movements of her fingers in playing, and the muscles of the
larynx in singing, become associated with each other, and form part of
those intricate trains and circles of catenated motions, according with the
second article of the preceding propositions in No. 1. of this Section.

3. Besides the facility, which by habit attends the execution of this
musical performance, a curious circumstance occurs, which is, that when our
young musician has began a tune, she finds herself inclined to continue it;
and that even when she is carelessly singing alone without attending to her
own song; according with the third preceding article.

4. At the same time that our young performer continues to play with great
exactness this accustomed tune, she can bend her mind, and that intensely,
on some other object, according with the fourth article of the preceding
proportions.

The manuscript copy of this work was lent to many of my friends at
different times for the purpose of gaining their opinions and criticisms on
many parts of it, and I found the following anecdote written with a pencil
opposite to this page, but am not certain by whom. "I remember seeing the
pretty young actress, who succeeded Mrs. Arne in the performance of the
celebrated Padlock, rehearse the musical parts at her harpsichord under the
eye of her master with great taste and accuracy; though I observed her
countenance full of emotion, which I could not account for; at last she
suddenly burst into tears; for she had all this time been eyeing a beloved
canary bird, suffering great agonies, which at that instant fell dead from
its perch."

5. At the same time many other catenated circles of action are going on in
the person of our fair musician, as well as the motions of her fingers,
such as the vital motions, respiration, the movements of her eyes and
eyelids, and of the intricate muscles of vocality, according with the fifth
preceding article.

6. If by any strong impression on the mind of our fair musician she should
be interrupted for a very inconsiderable time, she can still continue her
performance, according to the sixth article.

7. If however this interruption be greater, though the chain of actions be
not dissevered, it proceeds confusedly, and our young performer continues
indeed to play, but in a hurry without accuracy and elegance, till she
begins the tune again, according to the seventh of the preceding articles.

8. But if this interruption be still greater, the circle of actions becomes
entirely dissevered, and she finds herself immediately under the necessity
to begin over again to recover the lost catenation, according to the eighth
preceding article.

9. Or in trying to recover it she will sing some dissonant notes, or strike
some improper keys, according to the ninth preceding article.

10. A very remarkable thing attends this breach of catenation, if the
performer has forgotten some word of her song, the more energy of mind she
uses about it, the more distant is she from regaining it; and artfully
employs her mind in part on some other object, or endeavours to dull its
perceptions, continuing to repeat, as it were inconsciously, the former
part of the song, that she remembers, in hopes to regain the lost
connexion.

For if the activity of the mind itself be more energetic, or takes its
attention more, than the connecting word, which is wanted; it will not
perceive the slighter link of this lost word; as who listens to a feeble
sound, must be very silent and motionless; so that in this case the very
vigour of the mind itself seems to prevent it from regaining the lost
catenation, as well as the too great exertion in endeavouring to regain it,
according to the tenth preceding article.

We frequently experience, when we are doubtful about the spelling of a
word, that the greater voluntary exertion we use, that is the more
intensely we think about it, the further are we from regaining the lost
association between the letters of it, but which readily recurs when we
have become careless about it. In the same manner, after having for an hour
laboured to recollect the name of some absent person, it shall seem,
particularly after sleep, to come into the mind as it were spontaneously;
that is the word we are in search of, was joined to the preceding one by
association; this association being dissevered, we endeavour to recover it
by volition; this very action of the mind strikes our attention more, than
the faint link of association, and we find it impossible by this means to
retrieve the lost word. After sleep, when volition is entirely suspended,
the mind becomes capable of perceiving the fainter link of association, and
the word is regained.

On this circumstance depends the impediment of speech before mentioned; the
first syllable of a word is causable by volition, but the remainder of it
is in common conversation introduced by its associations with this first
syllable acquired by long habit. Hence when the mind of the stammerer is
vehemently employed on some idea of ambition of shining, or fear of not
succeeding, the associations of the motions of the muscles of articulation
with each other become dissevered by this greater exertion, and he
endeavours in vain by voluntary efforts to rejoin the broken association.
For this purpose he continues to repeat the first syllable, which is
causable by volition, and strives in vain, by various distortions of
countenance, to produce the next links, which are subject to association.
See Class IV. 3. 1. 1.

11. After our accomplished musician has acquired great variety of tunes and
songs, so that some of them begin to cease to be easily recollected, she
finds progressive trains of musical notes more frequently forgotten, than
those which are composed of reiterated circles, according with the eleventh
preceding article.

12. To finish our example with the preceding articles we must at length
suppose, that our fair performer falls asleep over her harpsichord; and
thus by the suspension of volition, and the exclusion of external stimuli,
she dissevers the trains and circles of her musical exertions.

III. 1. Many of these circumstances of catenations of motions receive an
easy explanation from the four following consequences to the seventh law of
animal causation in Sect. IV. These are, first, that those successions or
combinations of animal motions, whether they were united by causation,
association, or catenation, which have been most frequently repeated,
acquire the strongest connection. Secondly, that of these, those, which
have been less frequently mixed with other trains or tribes of motion, have
the strongest connection. Thirdly, that of these, those, which were first
formed, have the strongest connection. Fourthly, that if an animal motion
be excited by more than one causation, association, or catenation, at the
same time, it will be performed with greater energy.

2. Hence also we understand, why the catenations of irritative motions are
more strongly connected than those of the other classes, where the quantity
of unmixed repetition has been equal; because they were first formed. Such
are those of the secerning and absorbent systems of vessels, where the
action of the gland produces a fluid, which stimulates the mouths of its
correspondent absorbents. The associated motions seem to be the next most
strongly united, from their frequent repetition; and where both these
circumstances unite, as in the vital motions, their catenations are
indissoluble but by the destruction of the animal.

3. Where a new link has been introduced into a circle of actions by some
accidental defect of stimulus; if that defect of stimulus be repeated at
the same part of the circle a second or a third time, the defective motions
thus produced, both by the repeated defect of stimulus and by their
catenation with the parts of the circle of actions, will be performed with
less and less energy. Thus if any person is exposed to cold at a certain
hour to-day, so long as to render some part of the system for a time
torpid; and is again exposed to it at the same hour to-morrow, and the next
day; he will be more and more affected by it, till at length a cold fit of
fever is completely formed, as happens at the beginning of many of those
fevers, which are called nervous or low fevers. Where the patient has
slight periodical shiverings and paleness for many days before the febrile
paroxysm is completely formed.

4. On the contrary, if the exposure to cold be for so short a time, as not
to induce any considerable degree of torpor or quiescence, and is repeated
daily as above mentioned, it loses its effect more and more at every
repetition, till the constitution can bear it without inconvenience, or
indeed without being conscious of it. As in walking into the cold air in
frosty weather. The same rule is applicable to increased stimulus, as of
heat, or of vinous spirit, within certain limits, as is applied in the two
last paragraphs to Deficient Stimulus; as is further explained in Sect.
XXXVI. on the Periods of Diseases.

5. Where irritation coincides with sensation to produce the same
catenations of motion, as in inflammatory fevers, they are excited with
still greater energy than by the irritation alone. So when children expect
to be tickled in play, by a feather lightly passed over the lips, or by
gently vellicating the soles of their feet, laughter is most vehemently
excited; though they can stimulate these parts with their own fingers
unmoved. Here the pleasureable idea of playfulness coincides with the
vellication; and there is no voluntary exertion used to diminish the
sensation, as there would be, if a child should endeavour to tickle
himself. See Sect. XXXIV. 1. 4.

6. And lastly, the motions excited by the junction of voluntary exertion
with irritation are performed with more energy, than those by irritation
singly; as when we listen to small noises, as to the ticking of a watch in
the night, we perceive the most weak sounds, that are at other times
unheeded. So when we attend to the irritative ideas of sound in our ears,
which are generally not attended to, we can hear them; and can see the
spectra of objects, which remain in the eye, whenever we please to exert
our voluntary power in aid of those weak actions of the retina, or of the
auditory nerve.

7. The temporary catenations of ideas, which are caused by the sensations
of pleasure or pain, are easily dissevered either by irritations, as when a
sudden noise disturbs a day-dream; or by the power of volition, as when we
awake from sleep. Hence in our waking hours, whenever an idea occurs, which
is incongruous to our former experience, we instantly dissever the train of
imagination by the power of volition, and compare the incongruous idea with
our previous knowledge of nature, and reject it. This operation of the mind
has not yet acquired a specific name, though it is exerted every minute of
our waking hours; unless it may be termed INTUITIVE ANALOGY. It is an act
of reasoning of which we are unconscious except from its effects in
preserving the congruity of our ideas, and bears the same relation to the
sensorial power of volition, that irritative ideas, of which we are
inconscious except by their effects, do to the sensorial power of
irritation; as the former is produced by volition without our attention to
it, and the latter by irritation without our attention to them.

If on the other hand a train of imagination or of voluntary ideas are
excited with great energy, and passing on with great vivacity, and become
dissevered by some violent stimulus, as the discharge of a pistol near
one's ear, another circumstance takes place, which is termed SURPRISE;
which by exciting violent irritation, and violent sensation, employs for a
time the whole sensorial energy, and thus dissevers the passing trains of
ideas, before the power of volition has time to compare them with the usual
phenomena of nature. In this case fear is generally the companion of
surprise, and adds to our embarrassment, as every one experiences in some
degree when he hears a noise in the dark, which he cannot instantly account
for. This catenation of fear with surprise is owing to our perpetual
experience of injuries from external bodies in motion, unless we are upon
our guard against them. See Sect. XVIII. 17. XIX. 2.

Many other examples of the catenations of animal motions are explained in
Sect. XXXVI. on the Periods of Diseases.

       *       *       *       *       *

SECT. XVIII.

OF SLEEP.

    1. _Volition is suspended in sleep._ 2. _Sensation continues. Dreams
    prevent delirium and inflammation._ 3. _Nightmare._ 4. _Ceaseless flow
    of ideas in dreams._ 5. _We seem to receive them by the senses. Optic
    nerve perfectly sensible in sleep. Eyes less dazzled after dreaming of
    visible objects._ 6. _Reverie, belief._ 7. _How we distinguish ideas
    from perceptions._ 8. _Variety of scenery in dreams, excellence of the
    sense of vision._ 9. _Novelty of combination in dreams._ 10.
    _Distinctness of imagery in dreams._ 11. _Rapidity of transaction in
    dreams._ 12. _Of measuring time. Of dramatic time and place. Why a dull
    play induces sleep, and an interesting one reverie._ 13. _Consciousness
    of our existence and identity in dreams._ 14. _How we awake sometimes
    suddenly, sometimes frequently._ 15. _Irritative motions continue in
    sleep, internal irritations are succeeded by sensation. Sensibility
    increases during sleep, and irritability. Morning dreams. Why
    epilepsies occur in sleep. Ecstacy of children. Case of convulsions in
    sleep. Cramp, why painful. Asthma. Morning sweats. Increase of heat.
    Increase of urine in sleep. Why more liable to take cold in sleep.
    Catarrh from thin night-caps. Why we feel chilly at the approach of
    sleep, and at waking in the open air._ 16. _Why the gout commences in
    sleep. Secretions are more copious in sleep, young animals and plants
    grow more in sleep._ 17. _Inconsistency of dreams. Absence of surprise
    in dreams._ 18. _Why we forget some dreams and not others._ 19.
    _Sleep-talkers awake with surprise._ 20. _Remote causes of sleep.
    Atmosphere with less oxygene. Compression of the brain in spina bifida.
    By whirling on an horizontal wheel. By cold._ 21. _Definition of
    sleep._

1. There are four situations of our system, which in their moderate degrees
are not usually termed diseases, and yet abound with many very curious and
instructive phenomena; these are sleep, reverie, vertigo, drunkenness.
These we shall previously consider, before we step forwards to develop the
causes and cures of diseases with the modes of the operation of medicines.

As all those trains and tribes of animal motion, which are subjected to
volition, were the last that were caused, their connection is weaker than
that of the other classes; and there is a peculiar circumstance attending
this causation, which is, that it is entirely suspended during sleep;
whilst the other classes of motion, which are more immediately necessary to
life, as those caused by internal stimuli, for instance the pulsations of
the heart and arteries, or those catenated with pleasurable sensation, as
the powers of digestion, continue to strengthen their habits without
interruption. Thus though man in his sleeping state is a much less perfect
animal, than in his waking hours; and though he consumes more than one
third of his life in this his irrational situation; yet is the wisdom of
the Author of nature manifest even in this seeming imperfection of his
work!

The truth of this assertion with respect to the large muscles of the body,
which are concerned in locomotion, is evident; as no one in perfect sanity
walks about in his sleep, or performs any domestic offices: and in respect
to the mind, we never exercise our reason or recollection in dreams; we may
sometimes seem distracted between contending passions, but we never compare
their objects, or deliberate about the acquisition of those objects, if our
sleep is perfect. And though many synchronous tribes or successive trains
of ideas may represent the houses or walks, which have real existence, yet
are they here introduced by their connection with our sensations, and are
in truth ideas of imagination, not of recollection.

2. For our sensations of pleasure and pain are experienced with great
vivacity in our dreams; and hence all that motley group of ideas, which are
caused by them, called the ideas of imagination, with their various
associated trains, are in a very vivid manner acted over in the sensorium;
and these sometimes call into action the larger muscles, which have been
much associated with them; as appears from the muttering sentences, which
some people utter in their dreams, and from the obscure barking of sleeping
dogs, and the motions of their feet and nostrils.

This perpetual flow of the trains of ideas, which constitute our dreams,
and which are caused by painful or pleasurable sensation, might at first
view be conceived to be an useless expenditure of sensorial power. But it
has been shewn, that those motions, which are perpetually excited, as those
of the arterial system by the stimulus of the blood, are attended by a
great accumulation of sensorial power, after they have been for a time
suspended; as the hot-fit of fever is the consequence of the cold one. Now
as these trains of ideas caused by sensation are perpetually excited during
our waking hours, if they were to be suspended in sleep like the voluntary
motions, (which are exerted only by intervals during our waking hours,) an
accumulation of sensorial power would follow; and on our awaking a delirium
would supervene, since these ideas caused by sensation would be produced
with such energy, that we should mistake the trains of imagination for
ideas excited by irritation; as perpetually happens to people debilitated
by fevers on their first awaking; for in these fevers with debility the
general quantity of irritation being diminished, that of sensation is
increased. In like manner if the actions of the stomach, intestines, and
various glands, which are perhaps in part at least caused by or catenated
with agreeable sensation, and which perpetually exist during our waking
hours, were like the voluntary motions suspended in our sleep; the great
accumulation of sensorial power, which would necessarily follow, would be
liable to excite inflammation in them.

3. When by our continued posture in sleep, some uneasy sensations are
produced, we either gradually awake by the exertion of volition, or the
muscles connected by habit with such sensations alter the position of the
body; but where the sleep is uncommonly profound, and those uneasy
sensations great, the disease called the incubus, or nightmare, is
produced. Here the desire of moving the body is painfully exerted, by the
power of moving it, or volition, is incapable of action, till we awake.
Many less disagreeable struggles in our dreams, as when we wish in vain to
fly from terrifying objects, constitute a slighter degree of this disease.
In awaking from the nightmare I have more than once observed, that there
was no disorder in my pulse; nor do I believe the respiration is laborious,
as some have affirmed. It occurs to people whose sleep is too profound, and
some disagreeable sensation exists, which at other times would have
awakened them, and have thence prevented the disease of nightmare; as after
great fatigue or hunger with too large a supper and wine, which occasion
our sleep to be uncommonly profound. See No. 14, of this Section.

4. As the larger muscles of the body are much more frequently excited by
volition than by sensation, they are but seldom brought into action in our
sleep: but the ideas of the mind are by habit much more frequently
connected with sensation than with volition; and hence the ceaseless flow
of our ideas in dreams. Every one's experience will teach him this truth,
for we all daily exert much voluntary muscular motion: but few of mankind
can bear the fatigue of much voluntary thinking.

5. A very curious circumstance attending these our sleeping imaginations
is, that we seem to receive them by the senses. The muscles, which are
subservient to the external organs of sense, are connected with volition,
and cease to act in sleep; hence the eyelids are closed, and the tympanum
of the ear relaxed; and it is probable a similarity of voluntary exertion
may be necessary for the perceptions of the other nerves of sense; for it
is observed that the papillæ of the tongue can be seen to become erected,
when we attempt to taste any thing extremely grateful. Hewson Exper.
Enquir. V. 2. 186. Albini Annot. Acad. L. i. c. 15. Add to this, that the
immediate organs of sense have no objects to excite them in the darkness
and silence of the night, but their nerves of sense nevertheless continue
to possess their perfect activity subservient to all their numerous
sensitive connections. This vivacity of our nerves of sense during the time
of sleep is evinced by a circumstance, which almost every one must at some
time or other have experienced; that is, if we sleep in the daylight, and
endeavour to see some object in our dream, the light is exceedingly painful
to our eyes; and after repeated struggles we lament in our sleep, that we
cannot see it. In this case I apprehend the eyelid is in some degree opened
by the vehemence of our sensations; and, the iris being dilated, the optic
nerve shews as great or greater sensibility than in our waking hours. See
No. 15. of this Section.

When we are forcibly waked at midnight from profound sleep, our eyes are
much dazzled with the light of the candle for a minute or two, after there
has been sufficient time allowed for the contraction of the iris; which is
owing to the accumulation of sensorial power in the organ of vision during
its state of less activity. But when we have dreamt much of visible
objects, this accumulation of sensorial power in the organ of vision is
lessened or prevented, and we awake in the morning without being dazzled
with the light, after the iris has had time to contract itself. This is a
matter of great curiosity, and may be thus tried by any one in the
day-light. Close your eyes, and cover them with your hat; think for a
minute on a tune, which you are accustomed to, and endeavour to sing it
with as little activity of mind as possible. Suddenly uncover and open your
eyes, and in one second of time the iris will contract itself, but you will
perceive the day more luminous for several seconds, owing to the
accumulation of sensorial power in the optic nerve.

Then again close and cover your eyes, and think intensely on a cube of
ivory two inches diameter, attending first to the north and south sides of
it, and then to the other four sides of it; then get a clear image in your
mind's eye of all the sides of the same cube coloured red; and then of it
coloured green; and then of it coloured blue; lastly, open your eyes as in
the former experiment, and after the first second of time allowed for the
contraction of the iris, you will not perceive any increase of the light of
the day, or dazzling; because now there is no accumulation of sensorial
power in the optic nerve; that having been expended by its action in
thinking over visible objects.

This experiment is not easy to be made at first, but by a few patient
trials the fact appears very certain; and shews clearly, that our ideas of
imagination are repetitions of the motions of the nerve, which were
originally occasioned by the stimulus of external bodies; because they
equally expend the sensorial power in the organ of sense. See Sect. III. 4.
which is analogous to our being as much fatigued by thinking as by labour.

6. Nor is it in our dreams alone, but even in our waking reveries, and in
great efforts of invention, so great is the vivacity of our ideas, that we
do not for a time distinguish them from the real presence of substantial
objects; though the external organs of sense are open, and surrounded with
their usual stimuli. Thus whilst I am thinking over the beautiful valley,
through which I yesterday travelled, I do not perceive the furniture of my
room: and there are some, whose waking imaginations are so apt to run into
perfect reverie, that in their common attention to a favourite idea they do
not hear the voice of the companion, who accosts them, unless it is
repeated with unusual energy.

This perpetual mistake in dreams and reveries, where our ideas of
imagination are attended with a belief of the presence of external objects,
evinces beyond a doubt, that all our ideas are repetitions of the motions
of the nerves of sense, by which they were acquired; and that this belief
is not, as some late philosophers contend, an instinct necessarily
connected only with our perceptions.

7. A curious question demands our attention in this place; as we do not
distinguish in our dreams and reveries between our perceptions of external
objects, and our ideas of them in their absence, how do we distinguish them
at any time? In a dream, if the sweetness of sugar occurs to my
imagination, the whiteness and hardness of it, which were ideas usually
connected with the sweetness, immediately follow in the train; and I
believe a material lump of sugar present before my senses: but in my waking
hours, if the sweetness occurs to my imagination, the stimulus of the table
to my hand, or of the window to my eye, prevents the other ideas of the
hardness and whiteness of the sugar from succeeding; and hence I perceive
the fallacy, and disbelieve the existence of objects correspondent to those
ideas, whose tribes or trains are broken by the stimulus of other objects.
And further in our waking hours, we frequently exert our volition in
comparing present appearances with such, as we have usually observed; and
thus correct the errors of one sense by our general knowledge of nature by
intuitive analogy. See Sect. XVII. 3. 7. Whereas in dreams the power of
volition is suspended, we can recollect and compare our present ideas with
none of our acquired knowledge, and are hence incapable of observing any
absurdities in them.

By this criterion we distinguish our waking from our sleeping hours, we can
voluntarily recollect our sleeping ideas, when we are awake, and compare
them with our waking ones; but we cannot in our sleep _voluntarily_
recollect our waking ideas at all.

8. The vast variety of scenery, novelty of combination, and distinctness of
imagery, are other curious circumstances of our sleeping imaginations. The
variety of scenery seems to arise from the superior activity and excellence
of our sense of vision; which in an instant unfolds to the mind extensive
fields of pleasurable ideas; while the other senses collect their objects
slowly, and with little combination; add to this, that the ideas, which
this organ presents us with, are more frequently connected with our
sensation than those of any other.

9. The great novelty of combination is owing to another circumstance; the
trains of ideas, which are carried on in our waking thoughts, are in our
dreams dissevered in a thousand places by the suspension of volition, and
the absence of irritative ideas, and are hence perpetually falling into new
catenations. As explained in Sect. XVII. 1. 9. For the power of volition is
perpetually exerted during our waking hours in comparing our passing trains
of ideas with our acquired knowledge of nature, and thus forms many
intermediate links in their catenation. And the irritative ideas excited by
the stimulus of the objects, with which we are surrounded, are every moment
intruded upon us, and form other links of our unceasing catenations of
ideas.

10. The absence of the stimuli of external bodies, and of volition, in our
dreams renders the organs of sense liable to be more strongly affected by
the powers of sensation, and of association. For our desires or aversions,
or the obtrusions of surrounding bodies, dissever the sensitive and
associate tribes of ideas in our waking hours by introducing those of
irritation and volition amongst them. Hence proceeds the superior
distinctness of pleasurable or painful imagery in our sleep; for we recal
the figure and the features of a long lost friend, whom we loved, in our
dreams with much more accuracy and vivacity than in our waking thoughts.
This circumstance contributes to prove, that our ideas of imagination are
reiterations of those motions of our organs of sense, which were excited by
external objects; because while we are exposed to the stimuli of present
objects, our ideas of absent objects cannot be so distinctly formed.

11. The rapidity of the succession of transactions in our dreams is almost
inconceivable; insomuch that, when we are accidentally awakened by the
jarring of a door, which is opened into our bed-chamber, we sometimes dream
a whole history of thieves or fire in the very instant of awaking.

During the suspension of volition we cannot compare our other ideas with
those of the parts of time in which they exist; that is, we cannot compare
the imaginary scene, which is before us, with those changes of it, which
precede or follow it: because this act of comparing requires recollection
or voluntary exertion. Whereas in our waking hours, we are perpetually
making this comparison, and by that means our waking ideas are kept
confident with each other by intuitive analogy; but this companion retards
the succession of them, by occasioning their repetition. Add to this, that
the transactions of our dreams consist chiefly of visible ideas, and that a
whole history of thieves and fire may be _beheld_ in an instant of time
like the figures in a picture.

12. From this incapacity of attending to the parts of time in our dreams,
arises our ignorance of the length of the night; which, but from our
constant experience to the contrary, we should conclude was but a few
minutes, when our sleep is perfect. The same happens in our reveries; thus
when we are possessed with vehement joy, grief, or anger, time appears
short, for we exert no volition to compare the present scenery with the
past or future; but when we are compelled to perform those exercises of
mind or body, which, are unmixed with passion, as in travelling over a
dreary country, time appears long; for our desire to finish our journey
occasions us more frequently to compare our present situation with the
parts of time or place, which are before and behind us.

So when we are enveloped in deep contemplation of any kind, or in reverie,
as in reading a very interesting play or romance, we measure time very
inaccurately; and hence, if a play greatly affects our passions, the
absurdities of passing over many days or years, and or perpetual changes of
place, are not perceived by the audience; as is experienced by every one,
who reads or sees some plays of the immortal Shakespear; but it is
necessary for inferior authors to observe those rules of the [Greek:
pithanon] and [Greek: prepon] inculcated by Aristotle, because their works
do not interest the passions sufficiently to produce complete reverie.

Those works, however, whether a romance or a sermon, which do not interest
us so much as to induce reverie, may nevertheless incline us to sleep. For
those pleasurable ideas, which are presented to us, and are too gentle to
excite laughter, (which is attended with interrupted voluntary exertions,
as explained Sect. XXXIV. 1. 4.) and which are not accompanied with any
other emotion, which usually excites some voluntary exertion, as anger, or
fear, are liable to produce sleep; which consists in a suspension of all
voluntary power. But if the ideas thus presented to us, and interest our
attention, are accompanied with so much pleasurable or painful sensation as
to excite our voluntary exertion at the same time, reverie is the
consequence. Hence an interesting play produces reverie, a tedious one
produces sleep: in the latter we become exhausted by attention, and are not
excited to any voluntary exertion, and therefore sleep; in the former we
are excited by some emotion, which prevents by its pain the suspension of
volition, and in as much as it interests us, induces reverie, as explained
in the next Section.

But when our sleep is imperfect, as when we have determined to rise in half
an hour, time appears longer to us than in most other situations. Here our
solicitude not to oversleep the determined time induces us in this
imperfect sleep to compare the quick changes of imagined scenery with the
parts of time or place, they would have taken up, had they real exigence;
and that more frequently than in our waking hours; and hence the time
appears longer to us: and I make no doubt, but the permitted time appears
long to a man going to the gallows, as the fear of its quick lapse will
make him think frequently about it.

13. As we gain our knowledge of time by comparing the present scenery with
the past and future, and of place by comparing the situations of objects
with each other; so we gain our idea of consciousness by comparing
ourselves with the scenery around us; and of identity by comparing our
present consciousness with our past consciousness: as we never think of
time or place, but when we make the companions above mentioned, so we never
think of consciousness, but when we compare our own existence with that of
other objects; nor of identity, but when we compare our present and our
past consciousness. Hence the consciousness of our own existence, and of
our identity, is owing to a voluntary exertion of our minds: and on that
account in our complete dreams we neither measure time, are surprised at
the sudden changes of place, nor attend to our own existence, or identity;
because our power of volition is suspended. But all these circumstances are
more or less observable in our incomplete ones; for then we attend a little
to the lapse of time, and the changes of place, and to our own existence;
and even to our identity of person; for a lady seldom dreams, that she is a
soldier; nor a man, that he is brought to bed.

14. As long as our sensations only excite their sensual motions, or ideas,
our sleep continues sound; but as soon as they excite desires or aversions,
our sleep becomes imperfect; and when that desire or aversion is so strong,
as to produce voluntary motions, we begin to awake; the larger muscles of
the body are brought into action to remove that irritation or sensation,
which a continued posture has caused; we stretch our limbs, and yawn, and
our sleep is thus broken by the accumulation of voluntary power.

Sometimes it happens, that the act of waking is suddenly produced, and this
soon after the commencement of sleep; which is occasioned by some sensation
so disagreeable, as instantaneously to excite the power of volition; and a
temporary action of all the voluntary motions suddenly succeeds, and we
start awake. This is sometimes accompanied with loud noise in the ears, and
with some degree of fear; and when it is in great excess, so as to produce
continued convulsive motions of those muscles, which are generally
subservient to volition, it becomes epilepsy: the fits of which in some
patients generally commence during sleep. This differs from the night-mare
described in No. 3. of this Section, because in that the disagreeable
sensation is not so great as to excite the power of volition into action;
for as soon as that happens, the disease ceases.

Another circumstance, which sometimes awakes people soon after the
commencement of their sleep, is where the voluntary power is already so
great in quantity as almost to prevent them from falling asleep, and then a
little accumulation of it soon again awakens them; this happens in cases of
insanity, or where the mind has been lately much agitated by fear or anger.
There is another circumstance in which sleep is likewise of short duration,
which arises from great debility, as after great over-fatigue, and in some
fevers, where the strength of the patient is greatly diminished, as in
these cases the pulse intermits or flutters, and the respiration is
previously affected, it seems to originate from the want of some voluntary
efforts to facilitate respiration, as when we are awake. And is further
treated of in Vol. II. Class I. 2. 1. 2. on the Diseases of the Voluntary
Power. Art. Somnus interruptus.

15. We come now to those motions which depend on irritation. The motions of
the arterial and glandular systems continue in our sleep, proceeding slower
indeed, but stronger and more uniformly, than in our waking hours, when
they are incommoded by external stimuli, or by the movements of volition;
the motions of the muscles subservient to respiration continue to be
stimulated into action, and the other internal senses of hunger, thirst,
and lust, are not only occasionally excited in our sleep, but their
irritative motions are succeeded by their usual sensations, and make a part
of the farrago of our dreams. These sensations of the want of air, of
hunger, thirst, and lust, in our dreams, contribute to prove, that the
nerves of the external senses are also alive and excitable in our sleep;
but as the stimuli of external objects are either excluded from them by the
darkness and silence of the night, or their access to them is prevented by
the suspension of volition, these nerves of sense fall more readily into
their connexions with sensation and with association; because much
sensorial power, which during the day was expended in moving the external
organs of sense in consequence of irritation from external stimuli, or in
consequence of volition, becomes now in some degree accumulated, and
renders the internal or immediate organs of sense more easily excitable by
the other sensorial powers. Thus in respect to the eye, the irritation from
external stimuli, and the power of volition during our waking hours,
elevate the eye-lids, adapt the aperture of the iris to the quantity of
light, the focus of the crystalline humour, and the angle of the optic
axises to the distance of the object, all which perpetual activity during
the day expends much sensorial power, which is saved during our sleep.

Hence it appears, that not only those parts of the system, which are always
excited by internal stimuli, as the stomach, intestinal canal, bile-ducts,
and the various glands, but the organs of sense also may be more violently
excited into action by the irritation from internal stimuli, or by
sensation, during our sleep than in our waking hours; because during the
suspension of volition, there is a greater quantity of the spirit of
animation to be expended by the other sensorial powers. On this account our
irritability to internal stimuli, and our sensibility to pain or pleasure,
is not only greater in sleep, but increases as our sleep is prolonged.
Whence digestion and secretion are performed better in sleep, than in our
waking hours, and our dreams in the morning have greater variety and
vivacity, as our sensibility increases, than at night when we first lie
down. And hence epileptic fits, which are always occasioned by some
disagreeable sensation, so frequently attack those, who are subject to
them, in their sleep; because at this time the system is more excitable by
painful sensation in consequence of internal stimuli; and the power of
volition is then suddenly exerted to relieve this pain, as explained Sect.
XXXIV. 1. 4.

There is a disease, which frequently affects children in the cradle, which
is termed ecstasy, and seems to consist in certain exertions to relieve
painful sensation, in which the voluntary power is not so far excited as
totally to awaken them, and yet is sufficient to remove the disagreeable
sensation, which excites it; in this case changing the posture of the child
frequently relieves it.

I have at this time under my care an elegant young man about twenty-two
years of age, who seldom sleeps more than an hour without experiencing a
convulsion fit; which ceases in about half a minute without any subsequent
stupor. Large doses of opium only prevented the paroxysms, so long as they
prevented him from sleeping by the intoxication, which they induced. Other
medicines had no effect on him. He was gently awakened every half hour for
one night, but without good effect, as he soon slept again, and the fit
returned at about the same periods of time, for the accumulated sensorial
power, which occasioned the increased sensibility to pain, was not thus
exhausted. This case evinces, that the sensibility of the system to
internal excitation increases, as our sleep is prolonged; till the pain
thus occasioned produces voluntary exertion; which, when it is in its usual
degree, only awakens us; but when it is more violent, it occasions
convulsions.

The cramp in the calf of the leg is another kind of convulsion, which
generally commences in sleep, occasioned by the continual increase of
irritability from internal stimuli, or of sensibility, during that state of
our existence. The cramp is a violent exertion to relieve pain, generally
either of the skin from cold, or of the bowels, as in some diarrhoeas, or
from the muscles having been previously overstretched, as in walking up or
down steep hills. But in these convulsions of the muscles, which form the
calf of the leg, the contraction is so violent as to occasion another pain
in consequence of their own too violent contraction; as soon as the
original pain, which caused the contraction, is removed. And hence the
cramp, or spasm, of these muscles is continued without intermission by this
new pain, unlike the alternate convulsions and remissions in epileptic
fits. The reason, that the contraction of these muscles of the calf of the
leg is more violent during their convulsion than that of others, depends on
the weakness of their antagonist muscles; for after these have been
contracted in their usual action, as at every step in walking, they are
again extended, not, as most other muscles are, by their antagonists, but
by the weight of the whole body on the balls of the toes; and that weight
applied to great mechanical advantage on the heel, that is, on the other
end of the bone of the foot, which thus acts as a lever.

Another disease, the periods of which generally commence during our sleep,
is the asthma. Whatever may be the remote cause of paroxysms of asthma, the
immediate cause of the convulsive respiration, whether in the common
asthma, or in what is termed the convulsive asthma, which are perhaps only
different degrees of the same disease, must be owing to violent voluntary
exertions to relieve pain, as in other convulsions; and the increase of
irritability to internal stimuli, or of sensibility, during sleep must
occasion them to commence at this time.

Debilitated people, who have been unfortunately accustomed to great
ingurgitation of spirituous potation, frequently part with a great quantity
of water during the night, but with not more than usual in the day-time.
This is owing to a beginning torpor of the absorbent system, and precedes
anasarca, which commences in the day, but is cured in the night by the
increase of the irritability of the absorbent system during sleep, which
thus imbibes from the cellular membrane the fluids, which had been
accumulated there during the day; though it is possible the horizontal
position of the body may contribute something to this purpose, and also the
greater irritability of some branches of the absorbent vessels, which open
their mouths in the cells of the cellular membrane, than that of other
branches.

As soon as a person begins to sleep, the irritability and sensibility of
the system begins to increase, owing to the suspension of volition and the
exclusion of external stimuli. Hence the actions of the vessels in
obedience to internal stimulation become stronger and more energetic,
though less frequent in respect to number. And as many of the secretions
are increased, so the heat of the system is gradually increased, and the
extremities of feeble people, which had been cold during the day, become
warm. Till towards morning many people become so warm, as to find it
necessary to throw off some of their bed-clothes, as soon as they awake;
and in others sweats are so liable to occur towards morning during their
sleep.

Thus those, who are not accustomed to sleep in the open air, are very
liable to take cold, if they happen to fall asleep on a garden bench, or in
a carriage with the window open. For as the system is warmer during sleep,
as above explained, if a current of cold air affects any part of the body,
a torpor of that part is more effectually produced, as when a cold blast of
air through a key-hole or casement falls upon a person in a warm room. In
those cases the affected part possesses less irritability in respect to
heat, from its having previously been exposed to a greater stimulus of
heat, as in the warm room, or during sleep; and hence, when the stimulus of
heat is diminished, a torpor is liable to ensue; that is, we take cold.
Hence people who sleep in the open air, generally feel chilly both at the
approach of sleep, and on their awaking; and hence many people are
perpetually subject to catarrhs if they sleep in a less warm head-dress,
than that which they wear in the day.

16. Not only the sensorial powers of irritation and of sensation, but that
of association also appear to act with greater vigour during the suspension
of volition in sleep. It will be shewn in another place, that the gout
generally first attacks the liver, and that afterwards an inflammation of
the ball of the great toe commences by association, and that of the liver
ceases. Now as this change or metastasis of the activity of the system
generally commences in sleep, it follows, that these associations of motion
exist with greater energy at that time; that is, that the sensorial faculty
of association, like those of irritation and of sensation, becomes in some
measure accumulated during the suspension of volition.

Other associate tribes and trains of motions, as well as the irritative and
sensitive ones, appear to be increased in their activity during the
suspension of volition in sleep. As those which contribute to circulate the
blood, and to perform the various secretions; as well as the associate
tribes and trains of ideas, which contribute to furnish the perpetual
dreams of our dreaming imaginations.

In sleep the secretions have generally been supposed to be diminished, as
the expectorated mucus in coughs, the fluids discharged in diarrhoeas, and
in salivation, except indeed the secretion of sweat, which is often visibly
increased. This error seems to have arisen from attention to the excretions
rather than to the secretions. For the secretions, except that of sweat,
are generally received into reservoirs, as the urine into the bladder, and
the mucus of the intestines and lungs into their respective cavities; but
these reservoirs do not exclude these fluids immediately by their stimulus,
but require at the same time some voluntary efforts, and therefore permit
them to remain during sleep. And as they thus continue longer in those
receptacles in our sleeping hours, a greater part is absorbed from them,
and the remainder becomes thicker, and sometimes in less quantity, though
at the time it was secreted the fluid was in greater quantity than in our
waking hours. Thus the urine is higher coloured after long sleep; which
shews that a greater quantity has been secreted, and that more of the
aqueous and saline part has been reabsorbed, and the earthy part left in
the bladder; hence thick urine in fevers shews only a greater action of the
vessels which secrete it in the kidneys, and of those which absorb it from
the bladder.

The same happens to the mucus expectorated in coughs, which is thus
thickened by absorption of its aqueous and saline parts; and the same of
the feces of the intestines. From hence it appears, and from what has been
said in No. 15. of this Section concerning the increase of irritability and
of sensibility during sleep, that the secretions are in general rather
increased than diminished during these hours of our existence; and it is
probable that nutrition is almost entirely performed in sleep; and that
young animals grow more at this time than in their waking hours, as young
plants have long since been observed to grow more in the night, which is
their time of sleep.

17. Two other remarkable circumstances of our dreaming ideas are their
inconsistency, and the total absence of surprise. Thus we seem to be
present at more extraordinary metamorphoses of animals or trees, than are
to be met with in the fables of antiquity; and appear to be transported
from place to place, which seas divide, as quickly as the changes of
scenery are performed in a play-house; and yet are not sensible of their
inconsistency, nor in the least degree affected with surprise.

We must consider this circumstance more minutely. In our waking trains of
ideas, those that are inconsistent with the usual order of nature, so
rarely have occurred to us, that their connexion is the slightest of all
others: hence, when a consistent train of ideas is exhausted, we attend to
the external stimuli, that usually surround us, rather than to any
inconsistent idea, which might otherwise present itself; and if an
inconsistent idea should intrude itself, we immediately compare it with the
preceding one, and voluntarily reject the train it would introduce; this
appears further in the Section on Reverie, in which state of the mind
external stimuli are not attended to, and yet the streams of ideas are kept
consistent by the efforts of volition. But as our faculty of volition is
suspended, and all external stimuli are excluded in sleep, this slighter
connexion of ideas takes place; and the train is said to be inconsistent;
that is, dissimilar to the usual order of nature.

But, when any consistent train of sensitive or voluntary ideas is flowing
along, if any external stimulus affects us so violently, as to intrude
irritative ideas forcibly into the mind, it disunites the former train of
ideas, and we are affected with surprise. These stimuli of unusual energy
or novelty not only disunite our common trains of ideas, but the trains of
muscular motions also, which have not been long established by habit, and
disturb those that have. Some people become motionless by great surprise,
the fits of hiccup and or ague have been often removed by it, and it even
affects the movements of the heart, and arteries; but in our sleep, all
external stimuli are excluded, and in consequence no surprise can exist.
See Section XVII. 3. 7.

18. We frequently awake with pleasure from a dream, which has delighted us,
without being able to recollect the transactions of it; unless perhaps at a
distance of time, some analogous idea may introduce afresh this forgotten
train: and in our waking reveries we sometimes in a moment lose the train
of thought, but continue to feel the glow of pleasure, or the depression of
spirits, it occasioned: whilst at other times we can retrace with ease
these histories of our reveries and dreams.

The above explanation of surprise throws light upon this subject. When we
are suddenly awaked by any violent stimulus, the surprise totally disunites
the trains of our sleeping ideas from these of our waking ones; but if we
gradually awake, this does not happen; and we readily unravel the preceding
trains of imagination.

19. There are various degrees of surprise; the more intent we are upon the
train of ideas, which we are employed about, the more violent must be the
stimulus that interrupts them, and the greater is the degree of surprise. I
have observed dogs, who have slept by the fire, and by their obscure
barking and struggling have appeared very intent on their prey, that shewed
great surprise for a few seconds after their awaking by looking eagerly
around them; which they did not do at other times of waking. And an
intelligent friend of mine has remarked, that his lady, who frequently
speaks much and articulately in her sleep, could never recollect her dreams
in the morning, when this happened to her: but that when she did not speak
in her sleep, she could always recollect them.

Hence, when our sensations act so strongly in sleep as to influence the
larger muscles, as in those, who talk or struggle in their dreams; or in
those, who are affected with complete reverie (as described in the next
Section), great surprise is produced, when they awake; and these as well as
those, who are completely drunk or delirious, totally forget afterwards
their imaginations at those times.

20. As the immediate cause of sleep consists in the suspension of volition,
it follows, that whatever diminishes the general quantity of sensorial
power, or derives it from the faculty of volition, will constitute a remote
cause of sleep; such as fatigue from muscular or mental exertion, which
diminishes the general quantity of sensorial power; or an increase of the
sensitive motions, as by attending to soft music, which diverts the
sensorial power from the faculty of volition; or lastly, by increase of the
irritative motions, as by wine, or food; or warmth; which not only by their
expenditure of sensorial power diminish the quantity of volition; but also
by their producing pleasureable sensations (which occasion other muscular
or sensual motions in consequence), doubly decrease the voluntary power,
and thus more forcibly produce sleep. See Sect. XXXIV. 1. 4.

Another method of inducing sleep is delivered in a very ingenious work
lately published by Dr. Beddoes. Who, after lamenting that opium frequently
occasions restlessness, thinks, "that in most cases it would be better to
induce sleep by the abstraction of stimuli, than by exhausting the
excitability;" and adds, "upon this principle we could not have a better
soporific than an atmosphere with a diminished proportion of oxygene air,
and that common air might be admitted after the patient was asleep."
(Observ. on Calculus, &c. by Dr. Beddoes, Murray.) If it should be found to
be true, that the excitability of the system depends on the quantity of
oxygene absorbed by the lungs in respiration according to the theory of Dr.
Beddoes, and of M. Girtanner, this idea of sleeping in an atmosphere with
less oxygene in its composition might be of great service in epileptic
cases, and in cramp, and even in fits of the asthma, where their periods
commence from the increase of irritability during sleep.

Sleep is likewise said to be induced by mechanic pressure on the brain in
the cases of spina bifida. Where there has been a defect of one of the
vertebræ of the back, a tumour is protruded in consequence; and, whenever
this tumour has been compressed by the hand, sleep is said to be induced,
because the whole of the brain both within the head and spine becomes
compressed by the retrocession of the fluid within the tumour. But by what
means a compression of the brain induces sleep has not been explained, but
probably by diminishing the secretion of sensorial power, and then the
voluntary motions become suspended previously to the irritative ones, as
occurs in most dying persons.

Another way of procuring sleep mechanically was related to me by Mr.
Brindley, the famous canal engineer, who was brought up to the business of
a mill-wright; he told me, that he had more than once seen the experiment
of a man extending himself across the large stone of a corn-mill, and that
by gradually letting the stone whirl, the man fell asleep, before the stone
had gained its full velocity, and he supposed would have died without pain
by the continuance or increase of the motion. In this case the centrifugal
motion of the head and feet must accumulate the blood in both those
extremities of the body, and thus compress the brain.

Lastly, we should mention the application of cold; which, when in a less
degree, produces watchfulness by the pain it occasions, and the tremulous
convulsions of the subcutaneous muscles; but when it is applied in great
degree, is said to produce sleep. To explain this effect it has been said,
that as the vessels of the skin and extremities become first torpid by the
want of the stimulus of heat, and as thence less blood is circulated
through them, as appears from their paleness, a greater quantity of blood
poured upon the brain produces sleep by its compression of that organ. But
I should rather imagine, that the sensorial power becomes exhausted by the
convulsive actions in consequence of the pain of cold, and of the voluntary
exercise previously used to prevent it, and that the sleep is only the
beginning to die, as the suspension of voluntary power in lingering deaths
precedes for many hours the extinction of the irritative motions.

21. The following are the characteristic circumstances attending perfect
sleep.

1. The power of volition is totally suspended.

2. The trains of ideas caused by sensation proceed with greater facility
and vivacity; but become inconsistent with the usual order of nature. The
muscular motions caused by sensation continue; as those concerned in our
evacuations during infancy, and afterwards in digestion, and in priapismus.

3. The irritative muscular motions continue, as those concerned in the
circulation, in secretion, in respiration. But the irritative sensual
motions, or ideas, are not excited; as the immediate organs of sense are
not stimulated into action by external objects, which are excluded by the
external organs of sense; which are not in sleep adapted to their reception
by the power of volition, as in our waking hours.

4. The associate motions continue; but their first link is not excited into
action by volition, or by external stimuli. In all respects, except those
above mentioned, the three last sensorial powers are somewhat increased in
energy during the suspension of volition, owing to the consequent
accumulation of the spirit of animation.

       *       *       *       *       *

SECT. XIX.

OF REVERIE.

    1. _Various degrees of reverie._ 2. _Sleep-walkers. Case of a young
    lady. Great surprise at awaking. And total forgetfulness of what passed
    in reverie._ 3. _No suspension of volition in reverie._ 4. _Sensitive
    motions continue, and are consistent._ 5. _Irritative motions continue,
    but are not succeeded by sensation._ 6. _Volition necessary for the
    perception of feeble impressions._ 7. _Associated motions continue._ 8.
    _Nerves of sense are irritable in sleep, but not in reverie._ 9.
    _Somnambuli are not asleep. Contagion received but once._ 10.
    _Definition of reverie._

1. When we are employed with great sensation of pleasure, or with great
efforts of volition, in the pursuit of some interesting train of ideas, we
cease to be conscious of our existence, are inattentive to time and place,
and do not distinguish this train of sensitive and voluntary ideas from the
irritative ones excited by the presence of external objects, though our
organs of sense are furnished with their accustomed stimuli, till at length
this interesting train of ideas becomes exhausted, or the appulses of
external objects are applied with unusual violence, and we return with
surprise, or with regret, into the common track of life. This is termed
reverie or studium.

In some constitutions these reveries continue a considerable time, and are
not to be removed without greater difficulty, but are experienced in a less
degree by us all; when we attend earnestly to the ideas excited by volition
or sensation, with their associated connexions, but are at the same time
conscious at intervals of the stimuli of surrounding bodies. Thus in being
present at a play, or in reading a romance, some persons are so totally
absorbed as to forget their usual time of sleep, and to neglect their
meals; while others are said to have been so involved in voluntary study as
not to have heard the discharge of artillery; and there is a story of an
Italian politician, who could think so intensely on other subjects, as to
be insensible to the torture of the rack.

From hence it appears, that these catenations of ideas and muscular
motions, which form the trains of reverie, are composed both of voluntary
and sensitive associations of them; and that these ideas differ from those
of delirium or of sleep, as they are kept consistent by the power of
volition; and they differ also from the trains of ideas belonging to
insanity, as they are as frequently excited by sensation as by volition.
But lastly, that the whole sensorial power is so employed on these trains
of complete reverie, that like the violent efforts of volition, as in
convulsions or insanity; or like the great activity of the irritative
motions in drunkenness; or of the sensitive motions in delirium; they
preclude all sensation consequent to external stimulus.

2. Those persons, who are said to walk in their sleep, are affected with
reverie to so great a degree, that it becomes a formidable disease; the
essence of which consists in the inaptitude of the mind to attend to
external stimuli. Many histories of this disease have been published by
medical writers; of which there is a very curious one in the Lausanne
Transactions. I shall here subjoin an account of such a case, with its
cure, for the better illustration of this subject.

A very ingenious and elegant young lady, with light eyes and hair, about
the age of seventeen, in other respects well, was suddenly seized soon
after her usual menstruation with this very wonderful malady. The disease
began with vehement convulsions of almost every muscle of her body, with
great but vain efforts to vomit, and the most violent hiccoughs, that can
be conceived: these were succeeded in about an hour with a fixed spasm; in
which one hand was applied to her head, and the other to support it: in
about half an hour these ceased, and the reverie began suddenly, and was at
first manifest by the look of her eyes and countenance, which seemed to
express attention. Then she conversed aloud with imaginary persons with her
eyes open, and could not for about an hour be brought to attend to the
stimulus of external objects by any kind of violence, which it was proper
to use; these symptoms returned in this order every day for five or six
weeks.

These conversations were quite consistent, and we could understand, what
she supposed her imaginary companions to answer, by the continuation of her
part of the discourse. Sometimes she was angry, at other times shewed much
wit and vivacity, but was most frequently inclined to melancholy. In these
reveries she sometimes sung over some music with accuracy, and repeated
whole pages from the English poets. In repeating some lines from Mr. Pope's
works she had forgot one word, and began again, endeavouring to recollect
it; when she came to the forgotten word, it was shouted aloud in her ear,
and this repeatedly, to no purpose; but by many trials she at length
regained it herself.

These paroxysms were terminated with the appearance of inexpressible
surprise, and great fear, from which she was some minutes in recovering
herself, calling on her sister with great agitation, and very frequently
underwent a repetition of convulsions, apparently from the pain of fear.
See Sect. XVII. 3. 7.

After having thus returned for about an hour every day for two or three
weeks, the reveries seemed to become less complete, and some of their
circumstances varied; so that she could walk about the room in them without
running against any of the furniture; though these motions were at first
very unsteady and tottering. And afterwards she once drank a dish of tea,
when the whole apparatus of the tea-table was set before her; and expressed
some suspicion, that a medicine was put into it, and once seemed to smell
of a tuberose, which was in flower in her chamber, and deliberated aloud
about breaking it from the stem, saying, "it would make her sister so
charmingly angry." At another time in her melancholy moments she heard the
sound of a passing bell, "I wish I was dead," she cried, listening to the
bell, and then taking off one of her shoes, as she sat upon the bed, "I
love the colour black," says she, "a little wider, and a little longer,
even this might make me a coffin!"--Yet it is evident, she was not sensible
at this time, any more than formerly, of seeing or hearing any person about
her; indeed when great light was thrown upon her by opening the shutters of
the window, her trains of ideas seemed less melancholy; and when I have
forcibly held her hands, or covered her eyes, she appeared to grow
impatient, and would say, she could not tell what to do, for she could
neither see nor move. In all these circumstances her pulse continued
unaffected as in health. And when the paroxysm was over, she could never
recollect a single idea of what had passed in it.

This astonishing disease, after the use of many other medicines and
applications in vain, was cured by very large doses of opium given about an
hour before the expected returns of the paroxysms; and after a few
relapses, at the intervals of three or four months, entirely disappeared.
But she continued at times to have other symptoms of epilepsy.

3. We shall only here consider, what happened during the time of her
reveries, as that is our present subject; the fits of convulsion belong to
another part of this treatise. Sect. XXXIV. 1. 4.

There seems to have been no suspension of volition during the fits of
reverie, because she endeavoured to regain the lost idea in repeating the
lines of poetry, and deliberated about breaking the tuberose, and suspected
the tea to have been medicated.

4. The ideas and muscular movements depending on sensation were exerted
with their usual vivacity, and were kept from being inconsistent by the
power of volition, as appeared from her whole conversation, and was
explained in Sect. XVII. 3. 7. and XVIII. 16.

5. The ideas and motions dependant on irritation during the first weeks of
her disease, whilst the reverie was complete, were never succeeded by the
sensation of pleasure or pain; as she neither saw, heard, nor felt any of
the surrounding objects. Nor was it certain that any irritative motions
succeeded the stimulus of external objects, till the reverie became less
complete, and then she could walk about the room without running against
the furniture of it. Afterwards, when the reverie became still less
complete from the use of opium, some few irritations were at times
succeeded by her attention to them. As when she smelt at a tuberose, and
drank a dish of tea, but this only when she seemed voluntarily to attend to
them.

6. In common life when we listen to distant sounds, or wish to distinguish
objects in the night, we are obliged strongly to exert our volition to
dispose the organs of sense to perceive them, and to suppress the other
trains of ideas, which might interrupt these feeble sensations. Hence in
the present history the strongest stimuli were not perceived, except when
the faculty of volition was exerted on the organ of sense; and then even
common stimuli were sometimes perceived: for her mind was so strenuously
employed in pursuing its own trains of voluntary or sensitive ideas, that
no common stimuli could so far excite her attention as to disunite them;
that is, the quantity of volition or of sensation already existing was
greater than any, which could be produced in consequence of common degrees
of stimulation. But the few stimuli of the tuberose, and of the tea, which
she did perceive, were such, as accidentally coincided with the trains of
thought, which were passing in her mind; and hence did not disunite those
trains, and create surprise. And their being perceived at all was owing to
the power of volition preceding or coinciding with that of irritation.

This explication is countenanced by a fact mentioned concerning a
somnambulist in the Lausanne Transactions, who sometimes opened his eyes
for a short time to examine, where he was, or where his ink-pot stood, and
then shut them again, dipping his pen into the pot every now and then, and
writing on, but never opening his eyes afterwards, although he wrote on
from line to line regularly, and corrected some errors of the pen, or in
spelling: so much easier was it to him to refer to his ideas of the
positions of things, than to his perceptions of them.

7. The associated motions persisted in their usual channel, as appeared by
the combinations of her ideas, and the use of her muscles, and the equality
of her pulse; for the natural motions of the arterial system, though
originally excited like other motions by stimulus, seem in part to continue
by their association with each other. As the heart of a viper pulsates long
after it is cut out of the body, and removed from the stimulus of the
blood.

8. In the section on sleep, it was observed that the nerves of sense are
equally alive and susceptible to irritation in that state, as when we are
awake; but that they are secluded from stimulating objects, or rendered
unfit to receive them: but in complete reverie the reverse happens, the
immediate organs of sense are exposed to their usual stimuli; but are
either not excited into action at all, or not into so great action, as to
produce attention or sensation.

The total forgetfulness of what passes in reveries; and the surprise on
recovering from them, are explained in Section XVIII. 19. and in Section
XVII. 3. 7.

9. It appears from hence, that reverie is a disease of the epileptic or
cataleptic kind, since the paroxysms of this young lady always began and
frequently terminated with convulsions; and though in its greatest degree
it has been called somnambulation, or sleep-walking, it is totally
different from sleep; because the essential character of sleep consists in
the total suspension of volition, which in reverie is not affected; and the
essential character of reverie consists not in the absence of those
irritative motions of our senses, which are occasioned by the stimulus of
external objects, but in their never being productive of sensation. So that
during a fit of reverie that strange event happens to the whole system of
nerves, which occurs only to some particular branches of them in those, who
are a second time exposed to the action of contagious matter. If the matter
of the small-pox be inserted into the arm of one, who has previously had
that disease, it will stimulate the wound, but the general sensation or
inflammation of the system does not follow, which constitutes the disease.
See Sect. XII. 3. 6. XXXIII. 2. 8.

10. The following is the definition or character of complete reverie. 1.
The irritative motions occasioned by internal stimuli continue, those from
the stimuli of external objects are either not produced at all, or are
never succeeded by sensation or attention, unless they are at the same time
excited by volition. 2. The sensitive motions continue, and are kept
consistent by the power of volition. 3. The voluntary motions continue
undisturbed. 4. The associate motions continue undisturbed.

Two other cases of reverie are related in Section XXXIV. 3. which further
evince, that reverie is an effort of the mind to relieve some painful
sensation, and is hence allied to convulsion, and to insanity. Another case
is related in Class III. 1. 2. 2.

       *       *       *       *       *

SECT. XX.

OF VERTIGO.

    1. _We determine our perpendicularity by the apparent motions of
    objects. A person hood-winked cannot walk in a straight line. Dizziness
    in looking from a tower, in a room stained with uniform lozenges, on
    riding over snow._ 2. _Dizziness from moving objects. A whirling-wheel.
    Fluctuations of a river. Experiment with a child._ 3. _Dizziness from
    our own motions and those of other objects._ 4. _Riding over a broad
    stream. Sea-sickness._ 5. _Of turning round on one foot. Dervises in
    Turkey. Attention of the mind prevents slight sea-sickness. After a
    voyage ideas of vibratory motions are still perceived on shore._ 6.
    _Ideas continue some time after they are excited. Circumstances of
    turning on one foot, standing on a tower, and walking in the dark,
    explained._ 7. _Irritative ideas of apparent motions. Irritative ideas
    of sounds. Battèment of the sound of bells and organ-pipes. Vertiginous
    noise in the head. Irritative motions of the stomach, intestines, and
    glands._ 8. _Symptoms that accompany vertigo. Why vomiting comes on in
    strokes of the palsy. By the motion of a ship. By injuries on the head.
    Why motion makes sick people vomit._ 9. _Why drunken people are
    vertiginous. Why a stone in the ureter, or bile-duct, produces
    vomiting._ 10. _Why after a voyage ideas of vibratory motions are
    perceived on shore._ 11. _Kinds of vertigo and their cure._ 12.
    _Definition of vertigo._

1. In learning to walk we judge of the distances of the objects, which we
approach, by the eye; and by observing their perpendicularity determine our
own. This circumstance not having been attended to by the writers on
vision, the disease called vertigo or dizziness has been little understood.

When any person loses the power of muscular action, whether he is erect or
in a sitting posture, he sinks down upon the ground; as is seen in fainting
fits, and other instances of great debility. Hence it follows, that some
exertion of muscular power is necessary to preserve our perpendicular
attitude. This is performed by proportionally exerting the antagonist
muscles of the trunk, neck, and limbs; and if at any time in our
locomotions we find ourselves inclining to one side, we either restore our
equilibrium by the efforts of the muscles on the other side, or by moving
one of our feet extend the base, which we rest upon, to the new center of
gravity.

But the most easy and habitual manner of determining our want of
perpendicularity, is by attending to the apparent motion of the objects
within the sphere of distinct vision; for this apparent motion of objects,
when we incline from our perpendicularity, or begin to fall, is as much
greater than the real motion of the eye, as the diameter of the sphere of
distinct vision is to our perpendicular height.

Hence no one, who is hood-winked, can walk in a straight line for a hundred
steps together; for he inclines so greatly, before he is warned of his want
of perpendicularity by the sense of touch, not having the apparent motions
of ambient objects to measure this inclination by, that he is necessitated
to move one of his feet outwards, to the right or to the left, to support
the new centre of gravity, and thus errs from the line he endeavours to
proceed in.

For the same reason many people become dizzy, when they look from the
summit of a tower, which is raised much above all other objects, as these
objects are out of the sphere of distinct vision, and they are obliged to
balance their bodies by the less accurate feelings of their muscles.

There is another curious phenomenon belonging to this place, if the
circumjacent visible objects are so small, that we do not distinguish their
minute parts; or so similar, that we do not know them from each other; we
cannot determine our perpendicularity by them. Thus in a room hung with a
paper, which is coloured over with similar small black lozenges or
rhomboids, many people become dizzy; for when they begin to fall, the next
and the next lozenge succeeds upon the eye; which they mistake for the
first, and are not aware, that they have any apparent motion. But if you
fix a sheet of paper, or draw any other figure, in the midst of these
lozenges, the charm ceases, and no dizziness is perceptible.--The same
occurs, when we ride over a plain covered with snow without trees or other
eminent objects.

2. But after having compared visible objects at rest with the sense of
touch, and learnt to distinguish their shapes and shades, and to measure
our want of perpendicularity by their apparent motions, we come to consider
them in real motion. Here a new difficulty occurs, and we require some
experience to learn the peculiar mode of motion of any moving objects,
before we can make use of them for the purposes of determining our
perpendicularity. Thus some people become dizzy at the sight of a whirling
wheel, or by gazing on the fluctuations of a river, if no steady objects
are at the same time within the sphere of their distinct vision; and when a
child first can stand erect upon his legs, if you gain his attention to a
white handkerchief steadily extended like a sail, and afterwards make it
undulate, he instantly loses his perpendicularity, and tumbles on the
ground.

3. A second difficulty we have to encounter is to distinguish our own real
movements from the apparent motions of objects. Our daily practice of
walking and riding on horseback soon instructs us with accuracy to discern
these modes of motion, and to ascribe the apparent motions of the ambient
objects to ourselves; but those, which we have not acquired by repeated
habit, continue to confound us. So as we ride on horseback the trees and
cottages, which occur to us, appear at rest; we can measure their distances
with our eye, and regulate our attitude by them; yet if we carelessly
attend to distant hills or woods through a thin hedge, which is near us, we
observe the jumping and progressive motions of them; as this is increased
by the paralax of these objects; which we have not habituated ourselves to
attend to. When first an European mounts an elephant sixteen feet high, and
whose mode of motion he is not accustomed to, the objects seem to undulate,
as he passes, and he frequently becomes sick and vertiginous, as I am well
informed. Any other unusual movement of our bodies has the same effect, as
riding backwards in a coach, swinging on a rope, turning round swiftly on
one leg, scating on the ice, and a thousand others. So after a patient has
been long confined to his bed, when he first attempts to walk, he finds
himself vertiginous, and is obliged by practice to learn again the
particular modes of the apparent motions of objects, as he walks by them.

4. A third difficulty, which occurs to us in learning to balance ourselves
by the eye, is, when both ourselves and the circumjacent objects are in
real motion. Here it is necessary, that we should be habituated to both
these modes of motion in order to preserve our perpendicularity. Thus on
horseback we accurately observe another person, whom we meet, trotting
towards us, without confounding his jumping and progressive motion with our
own, because we have been accustomed to them both; that is, to undergo the
one, and to see the other at the same time. But in riding over a broad and
fluctuating stream, though we are well experienced in the motions of our
horse, we are liable to become dizzy from our inexperience in that of the
water. And when first we go on ship-board, where the movements of
ourselves, and the movements of the large waves are both new to us, the
vertigo is almost unavoidable with the terrible sickness, which attends it.
And this I have been assured has happened to several from being removed
from a large ship into a small one; and again from a small one into a man
of war.

5. From the foregoing examples it is evident, that, when we are surrounded
with unusual motions, we lose our perpendicularity: but there are some
peculiar circumstances attending this effect of moving objects, which we
come now to mention, and shall hope from the recital of them to gain some
insight into the manner of their production.

When a child moves round quick upon one foot, the circumjacent objects
become quite indistinct, as their distance increases their apparent
motions; and this great velocity confounds both their forms, and their
colours, as is seen in whirling round a many coloured wheel; he then loses
his usual method of balancing himself by vision, and begins to stagger, and
attempts to recover himself by his muscular feelings. This staggering adds
to the instability of the visible objects by giving a vibratory motion
besides their rotatory one. The child then drops upon the ground, and the
neighbouring objects seem to continue for some seconds of time to circulate
around him, and the earth under him appears to librate like a balance. In
some seconds of time these sensations of a continuation of the motion of
objects vanish; but if he continues turning round somewhat longer, before
he falls, sickness and vomiting are very liable to succeed. But none of
these circumstances affect those who have habituated themselves to this
kind of motion, as the dervises in Turkey, amongst whom these swift
gyrations are a ceremony of religion.

In an open boat passing from Leith to Kinghorn in Scotland, a sudden change
of the wind shook the undistended sail, and stopt our boat; from this
unusual movement the passengers all vomited except myself. I observed, that
the undulation of the ship, and the instability of all visible objects,
inclined me strongly to be sick; and this continued or increased, when I
closed my eyes, but as often as I bent my attention with energy on the
management and mechanism of the ropes and sails, the sickness ceased; and
recurred again, as often as I relaxed this attention; and I am assured by a
gentleman of observation and veracity, that he has more than once observed,
when the vessel has been in immediate danger, that the sea-sickness of the
passengers has instantaneously ceased, and recurred again, when the danger
was over.

Those, who have been upon the water in a boat or ship so long, that they
have acquired the necessary habits of motion upon that unstable element, at
their return on land frequently think in their reveries, or between
sleeping and waking, that they observe the room, they sit in, or some of
its furniture, to librate like the motion of the vessel. This I have
experienced myself, and have been told, that after long voyages, it is some
time before these ideas entirely vanish. The same is observable in a less
degree after having travelled some days in a stage coach, and particularly
when we lie down in bed, and compose ourselves to sleep; in this case it is
observable, that the rattling noise of the coach, as well as the undulatory
motion, haunts us. The drunken vertigo, and the vulgar custom of rocking
children, will be considered in the next Section.

6. The motions, which are produced by the power of volition, may be
immediately stopped by the exertion of the same power on the antagonist
muscles; otherwise these with all the other classes of motion continue to
go on, some time after they are excited, as the palpitation of the heart
continues after the object of fear, which occasioned it, is removed. But
this circumstance is in no class of motions more remarkable than in those
dependent on irritation; thus if any one looks at the sun, and then covers
his eyes with his hand, he will for many seconds of time, perceive the
image of the sun marked on his retina: a similar image of all other visible
objects would remain some time formed on the retina, but is extinguished by
the perpetual change of the motions of this nerve in our attention to other
objects. To this must be added, that the longer time any movements have
continued to be excited without fatigue to the organ, the longer will they
continue spontaneously, after the excitement is withdrawn: as the taste of
tobacco in the mouth after a person has been smoaking it.

This taste remains so strong, that if a person continues to draw air
through a tobacco pipe in the dark, after having been smoking some time, he
cannot distinguish whether his pipe be lighted or not.

From these two considerations it appears, that the dizziness felt in the
head, after seeing objects in unusual motion, is no other than a
continuation of the motions of the optic nerve excited by those objects and
which engage our attention. Thus on turning round on one foot, the vertigo
continues for some seconds of time after the person is fallen on the
ground; and the longer he has continued to revolve, the longer will
continue these successive motions of the parts of the optic nerve.

    _Additional Observations on _VERTIGO.

    After revolving with your eyes open till you become vertiginous, as
    soon as you cease to revolve, not only the circum-ambient objects
    appear to circulate round you in a direction contrary to that, in which
    you have been turning, but you are liable to roll your eyes forwards
    and backwards; as is well observed, and ingeniously demonstrated by Dr.
    Wells in a late publication on vision. The same occurs, if you revolve
    with your eyes closed, and open them immediately at the time of your
    ceasing to turn; and even during the whole time of revolving, as may be
    felt by your hand pressed lightly on your closed eyelids. To these
    movements of the eyes, of which he supposes the observer to be
    inconscious, Dr. Wells ascribes the apparent circumgyration of objects
    on ceasing to revolve.

    The cause of thus turning our eyes forwards, and then back again, after
    our body is at rest, depends, I imagine, on the same circumstance,
    which induces us to follow the indistinct spectra, which are formed on
    one side of the center of the retina, when we observe them apparently
    on clouds, as described in Sect. XL. 2. 2.; and then not being able to
    gain a more distinct vision of them, we turn our eyes back, and again
    and again pursue the flying shade.

    But this rolling of the eyes, after revolving till we become
    vertiginous, cannot cause the apparent circumgyration of objects, in a
    direction contrary to that in which we have been revolving, for the
    following reasons. 1. Because in pursuing a spectrum in the sky, or on
    the ground, as above mentioned, we perceive no retrograde motions of
    objects. 2. Because the apparent retrograde motions of objects, when we
    have revolved till we are vertiginous, continues much longer than the
    rolling of the eyes above described.

    3. When we have revolved from right to left, the apparent motion of
    objects, when we stop, is from left to right; and when we have revolved
    from left to right, the apparent circulation of objects is from right
    to left; yet in both these cases the eyes of the revolver are seen
    equally to roll forwards and backwards.

    4. Because this rolling of the eyes backwards and forwards takes place
    during our revolving, as may be perceived by the hand lightly pressed
    on the closed eyelids, and therefore exists before the effect ascribed
    to it.

    And fifthly, I now come to relate an experiment, in which the rolling
    of the eyes does not take place at all after revolving, and yet the
    vertigo is more distressing than in the situations above mentioned. If
    any one looks steadily at a spot in the ceiling over his head, or
    indeed at his own finger held up high over his head, and in that
    situation turns round till he becomes giddy; and then stops, and looks
    horizontally; he now finds, that the apparent rotation of objects is
    from above downwards, or from below upwards; that is, that the apparent
    circulation of objects is now vertical instead of horizontal, making
    part of a circle round the axis of his _eye_; and this without any
    rolling of his eyeballs. The reason of there being no rolling of the
    eyeballs, perceived after this experiment, is, because the images of
    objects are formed in rotation round the axis of the eye, and not from
    one side to the other of the axis of it; so that, as the eyeball has
    not power to turn in its socket round its own axis, it cannot follow
    the apparent motions of these evanescent spectra, either before or
    after the body is at rest. From all which arguments it is manifest,
    that these apparent retrograde gyrations of objects are not caused by
    the rolling of the eyeballs; first, because no apparent retrogression
    of objects is observed in other rollings of the eyes: secondly, because
    the apparent retrogression of objects continues many seconds after the
    rolling of the eyeballs ceases. Thirdly, because the apparent
    retrogression of objects is sometimes one way, and sometimes another,
    yet the rolling of the eyeballs is the same. Fourthly, because the
    rolling of the eyeballs exists before the apparent retrograde motions
    of objects is observed; that is, before the revolving person stops. And
    fifthly, because the apparent retrograde gyration of objects is
    produced, when there is no rolling of the eyeballs at all.

    Doctor Wells imagines, that no spectra can be gained in the eye, if a
    person revolves with his eyelids closed, and thinks this a sufficient
    argument against the opinion, that the apparent progression of the
    spectra of light or colours in the eye can cause the apparent
    retrogression of objects in the vertigo above described; but it is
    certain, when any person revolves in a light room with his eyes closed,
    that he nevertheless perceives differences of light both in quantity
    and colour through his eyelids, as he turns round; and readily gains
    spectra of those differences. And these spectra are not very different
    except in vivacity from those, which he acquires, when he revolves with
    unclosed eyes, since if he then revolves very rapidly the colours and
    forms of surrounding objects are as it were mixed together in his eye;.
    as when, the prismatic colours are painted on a wheel, they appear
    white as they revolve. The truth of this is evinced by the staggering
    or vertigo of men perfectly blind, when they turn round; which is not
    attended with apparent circulation of objects, but is a vertiginous
    disorder of the sense of touch. Blind men balance themselves by their
    sense of touch; which, being less adapted for perceiving small
    deviations from their perpendicular, occasions them to carry themselves
    more erect in walking. This method of balancing themselves by the
    direction of their pressure against the floor, becomes disordered by
    the unusual mode of action in turning round, and they begin to lose
    their perpendicularity, that is, they become vertiginous; but without
    any apparent circular motions of visible objects.

    It will appear from the following experiments, that the apparent
    progression of the ocular spectra of light or colours is the cause of
    the apparent retrogression of objects, after a person has revolved,
    till he is vertiginous.

    First, when a person turns round in a light room with his eyes open,
    but closes them before he stops, he will seem to be carried forwards in
    the direction he was turning for a short time after he stops. But if he
    opens his eyes again, the objects before him instantly appear to move
    in a retrograde direction, and he loses the sensation of being carried
    forwards. The same occurs if a person revolves in a light room with his
    eyes closed; when he stops, he seems to be for a time carried forwards,
    if his eyes are still closed; but the instant he opens them, the
    surrounding objects appear to move in retrograde gyration. From hence
    it may be concluded, that it is the sensation or imagination of our
    continuing to go forwards in the direction in which we were turning,
    that causes the apparent retrograde circulation of objects.

    Secondly, though there is an audible vertigo, as is known by the
    battement, or undulations of sound in the ears, which many vertiginous
    people experience; and though there is also a tangible vertigo, as when
    a blind person turns round, as mentioned above; yet as this
    circumgyration of objects is an hallucination or deception of the sense
    of sight, we are to look for the cause of our appearing to move
    forward, when we stop with our eyes closed after gyration, to some
    affection of this sense. Now, thirdly, if the spectra formed in the eye
    during our rotation, continue to change, when we stand still, like the
    spectra described in Sect. III. 3. 6. such changes must suggest to us
    the idea or sensation of our still continuing to turn round; as is the
    case, when we revolve in a light room, and close our eyes before we
    stop. And lastly, on opening our eyes in the situation above described,
    the objects we chance to view amid these changing spectra in the eye,
    must seem to move in a contrary direction; as the moon sometimes
    appears to move retrograde, when swift-gliding clouds are passing
    forwards so much nearer the eye of the beholder.

    To make observations on faint ocular spectra requires some degree of
    habit, and composure of mind, and even patience; some of those
    described in Sect. XL. were found difficult to see, by many, who tried
    them; now it happens, that the mind, during the confusion of vertigo,
    when all the other irritative tribes of motion, as well as those of
    vision, are in some degree disturbed, together with the fear of
    falling, is in a very unfit state for the contemplation of such weak
    sensations, as are occasioned by faint ocular spectra. Yet after
    frequently revolving, both with my eyes closed, and with them open, and
    attending to the spectra remaining in them, by shading the light from
    my eyelids more or less with my hand, I at length ceased to have the
    idea of going forward, after I stopped with my eyes closed; and saw
    changing spectra in my eyes, which seemed to move, as it were, over the
    field of vision; till at length, by repeated trials on sunny days, I
    persuaded myself, on opening my eyes, after revolving some time, on a
    shelf of gilded books in my library, that I could perceive the spectra
    in my eyes move forwards over one or two of the books, like the vapours
    in the air of a summer's day; and could so far undeceive myself, as to
    perceive the books to stand still. After more trials I sometimes
    brought myself to believe, that I saw changing spectra of lights and
    shades moving in my eyes, after turning round for some time, but did
    not imagine either the spectra or the objects to be in a state of
    gyration. I speak, however, with diffidence of these facts, as I could
    not always make the experiments succeed, when there was not a strong
    light in my room, or when my eyes were not in the most proper state for
    such observations.

    The ingenious and learned M. Sauvage has mentioned other theories to
    account for the apparent circumgyration of objects in vertiginous
    people. As the retrograde motions of the particles of blood in the
    optic arteries, by spasm, or by fear, as is seen in the tails of
    tadpoles, and membranes between the fingers of frogs. Another cause he
    thinks may be from the librations to one side, and to the other, of the
    crystalline lens in the eye, by means of involuntary actions of the
    muscles, which constitute the ciliary process. Both these theories lie
    under the same objection as that of Dr. Wells before mentioned; namely,
    that the apparent motions of objects, after the observer has revolved
    for some time, should appear to vibrate this way and that; and not to
    circulate uniformly in a direction contrary to that, in which the
    observer had revolved.

    M. Sauvage has, lastly, mentioned the theory of colours left in the
    eye, which he has termed impressions on the retina. He says,
    "Experience teaches us, that impressions made on the retina by a
    visible object remain some seconds after the object is removed; as
    appears from the circle of fire which we see, when a fire-stick is
    whirled round in the dark; therefore when we are carried round our own
    axis in a circle, we undergo a temporary vertigo, when we stop; because
    the impressions of the circumjacent objects remain for a time
    afterwards on the retina." Nosolog. Method. Clas. VIII. I. 1. We have
    before observed, that the changes of these colours remaining in the
    eye, evinces them to be motions of the fine terminations of the retina,
    and not impressions on it; as impressions on a passive substance must
    either remain, or cease intirely. See an additional note at the end of
    the second volume.

Any one, who stands alone on the top of a high tower, if he has not been
accustomed to balance himself by objects placed at such distances and with
such inclinations, begins to stagger, and endeavours to recover himself by
his muscular feelings. During this time the apparent motion of objects at a
distance below him is very great, and the spectra of these apparent motions
continue a little time after he has experienced them; and he is persuaded
to incline the contrary way to counteract their effects; and either
immediately falls, or applying his hands to the building, uses his muscular
feelings to preserve his perpendicular attitude, contrary to the erroneous
persuasions of his eyes. Whilst the person, who walks in the dark,
staggers, but without dizziness; for he neither has the sensation of moving
objects to take off his attention from his muscular feelings, nor has he
the spectra of those motions continued on his retina to add to his
confusion. It happens indeed sometimes to one landing on a tower, that the
idea of his not having room to extend his base by moving one of his feet
outwards, when he begins to incline, superadds fears to his other
inconveniences; which like surprise, joy, or any great degree of sensation,
enervates him in a moment, by employing the whole sensorial power, and by
thus breaking all the associated trains and tribes of motion.

7. The irritative ideas of objects, whilst we are awake, are perpetually
present to our sense of sight; as we view the furniture of our rooms, or
the ground, we tread upon, throughout the whole day without attending to
it. And as our bodies are never at perfect rest during our waking hours,
these irritative ideas of objects are attended perpetually with irritative
ideas of their apparent motions. The ideas of apparent motions are always
irritative ideas, because we never attend to them, whether we attend to the
objects themselves, or to their real motions, or to neither. Hence the
ideas of the apparent motions of objects are a complete circle of
irritative ideas, which continue throughout the day.

Also during all our waking hours, there is a perpetual confused sound of
various bodies, as of the wind in our rooms, the fire, distant
conversations, mechanic business; this continued buzz, as we are seldom
quite motionless, changes its loudness perpetually, like the sound of a
bell; which rises and falls as long as it continues, and seems to pulsate
on the ear. This any one may experience by turning himself round near a
waterfall; or by striking a glass bell, and then moving the direction of
its mouth towards the ears, or from them, as long as its vibrations
continue. Hence this undulation of indistinct sound makes another
concomitant circle of irritative ideas, which continues throughout the day.

We hear this undulating sound, when we are perfectly at rest ourselves,
from other sonorous bodies besides bells; as from two organ-pipes, which
are nearly but not quite in unison, when they are sounded together. When a
bell is struck, the circular form is changed into an eliptic one; the
longest axis of which, as the vibrations continue, moves round the
periphery of the bell; and when either axis of this elipse is pointed
towards our ears, the sound is louder; and less when the intermediate parts
of the elipse are opposite to us. The vibrations of the two organ-pipes may
be compared to Nonius's rule; the sound is louder, when they coincide, and
less at the intermediate times. But, as the sound of bells is the most
familiar of those sounds, which have a considerable battement, the
vertiginous patients, who attend to the irritative circles of sounds above
described, generally compare it to the noise of bells.

The peristaltic motions of our stomach and intestines, and the secretions
of the various glands, are other circles of irritative motions, some of
them more or less complete, according to our abstinence or satiety.

So that the irritative ideas of the apparent motions of objects, the
irritative battements of sounds, and the movements of our bowels and glands
compose a great circle of irritative tribes of motion: and when one
considerable part of this circle of motions becomes interrupted, the whole
proceeds in confusion, as described in Section XVII. 1. 7. on Catenation of
Motions.

8. Hence a violent vertigo, from whatever cause it happens, is generally
attended with undulating noise in the head, perversions of the motions of
the stomach and duodenum, unusual excretion of bile and gastric juice, with
much pale urine, sometimes with yellowness of the skin, and a disordered
secretion of almost every gland of the body, till at length the arterial
system is affected, and fever succeeds.

Thus bilious vomitings accompany the vertigo occasioned by the motion of a
ship; and when the brain is rendered vertiginous by a paralytic affection
of any part of the body, a vomiting generally ensues, and a great discharge
of bile: and hence great injuries of the head from external violence are
succeeded with bilious vomitings, and sometimes with abscesses of the
liver. And hence, when a patient is inclined to vomit from other causes, as
in some fevers, any motions of the attendants in his room, or of himself
when he is raised or turned in his bed, presently induces the vomiting by
superadding a degree of vertigo.

9. And conversely it is very usual with those, whose stomachs are affected
from internal causes, to be afflicted with vertigo, and noise in the head;
such is the vertigo of drunken people, which continues, when their eyes are
closed, and themselves in a recumbent posture, as well as when they are in
an erect posture, and have their eyes open. And thus the irritation of a
stone in the bile-duct, or in the ureter, or an inflammation of any of the
intestines, are accompanied with vomitings and vertigo.

In these cases the irritative motions of the stomach, which are in general
not attended to, become so changed by some unnatural stimulus, as to become
uneasy, and excite our sensation or attention. And thus the other
irritative trains of motions, which are associated with it, become
disordered by their sympathy. The same happens, when a piece of gravel
sticks in the ureter, or when some part of the intestinal canal becomes
inflamed. In these cases the irritative muscular motions are first
disturbed by unusual stimulus, and a disordered action of the sensual
motions, or dizziness ensues. While in sea-sickness the irritative sensual
motions, as vertigo, precedes; and the disordered irritative muscular
motions, as those of the stomach in vomiting, follow.

10. When these irritative motions are disturbed, if the degree be not very
great, the exertion of voluntary attention to any other object, or any
sudden sensation, will disjoin these new habits of motion. Thus some
drunken people have become sober immediately, when any accident has
strongly excited their attention; and sea-sickness has vanished, when the
ship has been in danger. Hence when our attention to other objects is most
relaxed, as just before we fall asleep, or between our reveries when awake,
these irritative ideas of motion and sound are most liable to be perceived;
as those, who have been at sea, or have travelled long in a coach, seem to
perceive the vibrations of the ship, or the rattling of the wheels, at
these intervals; which cease again, as soon as they exert their attention.
That is, at those intervals they attend to the apparent motions, and to the
battement of sounds of the bodies around them, and for a moment mistake
them for those real motions of the ship, and noise of wheels, which they
had lately been accustomed to: or at these intervals of reverie, or on the
approach of sleep, these supposed motions or sounds may be produced
entirely by imagination.

We may conclude from this account of vertigo, that sea-sickness is not an
effort of nature to relieve herself, but a necessary consequence of the
associations or catenations of animal motions. And may thence infer, that
the vomiting, which attends the gravel in the ureter, inflammations of the
bowels, and the commencement of some fevers, has a similar origin, and is
not always an effort of the vis medicatrix naturæ. But where the action of
the organ is the immediate consequence of the stimulating cause, it is
frequently exerted to dislodge that stimulus, as in vomiting up an emetic
drug; at other times, the action of an organ is a general effort to relieve
pain, as in convulsions of the locomotive muscles; other actions drink up
and carry on the fluids, as in absorption and secretion; all which may be
termed efforts of nature to relieve, or to preserve herself.

11. The cure of vertigo will frequently depend on our previously
investigating the cause of it, which from what has been delivered above may
originate from the disorder of any part of the great tribes of irritative
motions, and of the associate motions catenated with them.

Many people, when they arrive at fifty or sixty years of age, are affected
with slight vertigo; which is generally but wrongly ascribed to
indigestion, but in reality arises from a beginning defect of their sight;
as about this time they also find it necessary to begin to use spectacles,
when they read small prints, especially in winter, or by candle light, but
are yet able to read without them during the summer days, when the light is
stronger. These people do not see objects so distinctly as formerly, and by
exerting their eyes more than usual, they perceive the apparent motions of
objects, and confound them with the real motions of them; and therefore
cannot accurately balance themselves so as easily to preserve their
perpendicularity by them.

That is, the apparent motions of objects, which are at rest, as we move by
them, should only excite irritative ideas: but as these are now become less
distinct, owing to the beginning imperfection of our sight, we are induced
_voluntarily_ to attend to them; and then these apparent motions become
succeeded by sensation; and thus the other parts of the trains of
irritative ideas, or irritative muscular motions, become disordered, as
explained above. In these cases of slight vertigo I have always promised my
patients, that they would get free from it in two or three months, as they
should acquire the habit of balancing their bodies by less distinct
objects, and have seldom been mistaken in my prognostic.

There is an auditory vertigo, which is called a noise in the head,
explained in No. 7. of this section, which also is very liable to affect
people in the advance of life, and is owing to their hearing less perfectly
than before. This is sometimes called a ringing, and sometimes a singing,
or buzzing, in the ears, and is occasioned by our first experiencing a
disagreeable sensation from our not being able distinctly to hear the
sounds, we used formerly to hear distinctly. And this disagreeable
sensation excites desire and consequent volition; and when we voluntarily
attend to small indistinct sounds, even the whispering of the air in a
room, and the pulsations of the arteries of the ear are succeeded by
sensation; which minute sounds ought only to have produced irritative
sensual motions, or unperceived ideas. See Section XVII. 3. 6. These
patients after a while lose this auditory vertigo, by acquiring a new habit
of not attending voluntarily to these indistinct sounds, but contenting
themselves with the less accuracy of their sense of hearing.

Another kind of vertigo begins with the disordered action of some
irritative muscular motions, as those of the stomach from intoxication, or
from emetics; or those of the ureter, from the stimulus of a stone lodged
in it; and it is probable, that the disordered motions of some of the great
congeries of glands, as of those which form the liver, or of the intestinal
canal, may occasion vertigo in consequence of their motions being
associated or catenated with the great circles of irritative motions; and
from hence it appears, that the means of cure must be adapted to the cause.

To prevent sea-sickness it is probable, that the habit of swinging for a
week or two before going on shipboard might be of service. For the vertigo
from failure of sight, spectacles may be used. For the auditory vertigo,
æther may be dropt into the ear to stimulate the part, or to dissolve
ear-wax, if such be a part of the cause. For the vertigo arising from
indigestion, the peruvian bark and a blister are recommended. And for that
owing to a stone in the ureter, venesection, cathartics, opiates, sal soda
aerated.

12. Definition of vertigo. 1. Some of the irritative sensual, or muscular
motions, which were usually not succeeded by sensation, are in this disease
succeeded by sensation; and the trains or circles of motions, which were
usually catenated with them, are interrupted, or inverted, or proceed in
confusion. 2. The sensitive and voluntary motions continue undisturbed. 3.
The associate trains or circles of motions continue; but their catenations
with some of the irritative motions are disordered, or inverted, or
dissevered.

       *       *       *       *       *

SECT. XXI.

OF DRUNKENNESS.

    1. _Sleep from satiety of hunger. From rocking children. From uniform
    sounds._ 2. _Intoxication from common food after fatigue and
    inanition._ 3. _From wine or of opium. Chilness after meals. Vertigo.
    Why pleasure is produced by intoxication, and by swinging and rocking
    children. And why pain is relieved by it._ 4. _Why drunkards stagger
    and stammer, and are liable to weep._ 5. _And become delirious, sleepy,
    and stupid._ 6. _Or make pale urine and vomit._ 7. _Objects are seen
    double._ 8. _Attention of the mind diminishes drunkenness._ 9.
    _Disordered irritative motions of all the senses._ 10. _Diseases from
    drunkenness._ 11. _Definition of drunkenness._

1. In the state of nature when the sense of hunger is appeased by the
stimulus of agreeable food, the business of the day is over, and the human
savage is at peace with the world, he then exerts little attention to
external objects, pleasing reveries of imagination succeed, and at length
sleep is the result: till the nourishment which he has procured, is carried
over every part of the system to repair the injuries of action, and he
awakens with fresh vigour, and feels a renewal of his sense of hunger.

The juices of some bitter vegetables, as of the poppy and the laurocerasus,
and the ardent spirit produced in the fermentation of the sugar found in
vegetable juices, are so agreeable to the nerves of the stomach, that,
taken in a small quantity, they instantly pacify the sense of hunger; and
the inattention to external stimuli with the reveries of imagination, and
sleep, succeeds, in the same manner as when the stomach is filled with
other less intoxicating food.

This inattention to the irritative motions occasioned by external stimuli
is a very important circumstance in the approach of sleep, and is produced
in young children by rocking their cradles: during which all visible
objects become indistinct to them. An uniform soft repeated sound, as the
murmurs of a gentle current, or of bees, are said to produce the same
effect, by presenting indistinct ideas of inconsequential sounds, and by
thus stealing our attention from other objects, whilst by their continued
reiterations they become familiar themselves, and we cease gradually to
attend to any thing, and sleep ensues.

2. After great fatigue or inanition, when the stomach is suddenly filled
with flesh and vegetable food, the inattention to external stimuli, and the
reveries of imagination, become so conspicuous as to amount to a degree of
intoxication. The same is at any time produced by superadding a little wine
or opium to our common meals; or by taking these separately in considerable
quantity; and this more efficaciously after fatigue or inanition; because a
less quantity of any stimulating material will excite an organ into
energetic action, after it has lately been torpid from defect of stimulus;
as objects appear more luminous, after we have been in the dark; and
because the suspension of volition, which is the immediate cause of sleep,
is sooner induced, after a continued voluntary exertion has in part
exhausted the sensorial power of volition; in the same manner as we cannot
contract a single muscle long together without intervals of inaction.

3. In the beginning of intoxication we are inclined to sleep, as mentioned
above, but by the excitement of external circumstances, as of noise, light,
business, or by the exertion of volition, we prevent the approaches of it,
and continue to take into our stomach greater quantities of the inebriating
materials. By these means the irritative movements of the stomach are
excited into greater action than is natural; and in consequence all the
irritative tribes and trains of motion, which are catenated with them,
become susceptible of stronger action from their accustomed stimuli;
because these motions are excited both by their usual irritation, and by
their association with the increased actions of the stomach and lacteals.
Hence the skin glows, and the heat of the body is increased, by the more
energetic action of the whole glandular system; and pleasure is introduced
in consequence of these increased motions from internal stimulus. According
to Law 5. Sect. IV. on Animal Causation.

From this great increase of irritative motions from internal stimulus, and
the increased sensation introduced into the system in consequence; and
secondly, from the increased sensitive motions in consequence of this
additional quantity of sensation, so much sensorial power is expended, that
the voluntary power becomes feebly exerted, and the irritation from the
stimulus of external objects is less forcible; the external parts of the
eye are not therefore voluntarily adapted to the distances of objects,
whence the apparent motions of those objects either are seen double, or
become too indistinct for the purpose of balancing the body, and vertigo is
induced.

Hence we become acquainted with that very curious circumstance, why the
drunken vertigo is attended with an increase of pleasure; for the
irritative ideas and motions occasioned by internal stimulus, that were not
attended to in our sober hours, are now just so much increased as to be
succeeded by pleasurable sensation, in the same manner as the more violent
motions of our organs are succeeded by painful sensation. And hence a
greater quantity of pleasurable sensation is introduced into the
constitution; which is attended in some people with an increase of
benevolence and good humour.

If the apparent motions of objects is much increased, as when we revolve on
one foot, or are swung on a rope, the ideas of these apparent motions are
also attended to, and are succeeded with pleasureable sensation, till they
become familiar to us by frequent use. Hence children are at first
delighted with these kinds of exercise, and with riding, and failing, and
hence rocking young children inclines them to sleep. For though in the
vertigo from intoxication the irritative ideas of the apparent motions of
objects are indistinct from their decrease of energy: yet in the vertigo
occasioned by rocking or swinging the irritative ideas of the apparent
motions of objects are increased in energy, and hence they induce pleasure
into the system, but are equally indistinct, and in consequence equally
unfit to balance ourselves by. This addition of pleasure precludes desire
or aversion, and in consequence the voluntary power is feebly exerted, and
on this account rocking young children inclines them to sleep.

In what manner opium and wine act in relieving pain is another article,
that well deserves our attention. There are many pains that originate from
defect as well as from excess of stimulus; of these are those of the six
appetites of hunger, thirst, lust, the want of heat, of distention, and of
fresh air. Thus if our cutaneous capillaries cease to act from the
diminished stimulus of heat, when we are exposed to cold weather, or our
stomach is uneasy for want of food; these are both pains from defect of
stimulus, and in consequence opium, which stimulates all the moving system
into increased action, must relieve them. But this is not the case in those
pains, which arise from excess of stimulus, as in violent inflammations: in
these the exhibition of opium is frequently injurious by increasing the
action of the system already too great, as in inflammation of the bowels
mortification is often produced by the stimulus of opium. Where, however,
no such bad consequences follow; the stimulus of opium, by increasing all
the motions of the system, expends so much of the sensorial power, that the
actions of the whole system soon become feebler, and in consequence those
which produced the pain and inflammation.

4. When intoxication proceeds a little further, the quantity of pleasurable
sensation is so far increased, that all desire ceases, for there is no pain
in the system to excite it. Hence the voluntary exertions are diminished,
staggering and stammering succeed; and the trains of ideas become more and
more inconsistent from this defect of voluntary exertion, as explained in
the sections on sleep and reverie, whilst those passions which are unmixed
with volition are more vividly felt, and shewn with less reserve; hence
pining love, or superstitious fear, and the maudling tear dropped on the
remembrance of the most trifling distress.

5. At length all these circumstances are increased; the quantity of
pleasure introduced into the system by the increased irritative muscular
motions of the whole sanguiferous, and glandular, and absorbent systems,
becomes so great, that the organs of sense are more forcibly excited into
action by this internal pleasurable sensation, than by the irritation from
the stimulus of external objects. Hence the drunkard ceases to attend to
external stimuli, and as volition is now also suspended, the trains of his
ideas become totally inconsistent as in dreams, or delirium: and at length
a stupor succeeds from the great exhaustion of sensorial power, which
probably does not even admit of dreams, and in which, as in apoplexy, no
motions continue but those from internal stimuli, from sensation, and from
association.

6. In other people a paroxysm of drunkenness has another termination; the
inebriate, as soon as he begins to be vertiginous, makes pale urine in
great quantities and very frequently, and at length becomes sick, vomits
repeatedly, or purges, or has profuse sweats, and a temporary fever ensues
with a quick strong pulse. This in some hours is succeeded by sleep; but
the unfortunate bacchanalian does not perfectly recover himself till about
the same time of the succeeding day, when his course of inebriation began.
As shewn in Sect. XVII. 1. 7. on Catenation. The temporary fever with
strong pulse is owing to the same cause as the glow on the skin mentioned
in the third paragraph of this Section: the flow of urine and sickness
arises from the whole system of irritative motions being thrown into
confusion by their associations with each other; as in sea-sickness,
mentioned in Sect. XX. 4. on Vertigo; and which is more fully explained in
Section XXIX. on Diabetes.

7. In this vertigo from internal causes we see objects double, as two
candles instead of one, which is thus explained. Two lines drawn through
the axes of our two eyes meet at the object we attend to: this angle of the
optic axes increases or diminishes with the less or greater distances of
objects. All objects before or behind the place where this angle is formed,
appear double; as any one may observe by holding up a pen between his eyes
and the candle; when he looks attentively at a spot on the pen, and
carelessly at the candle, it will appear double; and the reverse when he
looks attentively at the candle and carelessly at the pen; so that in this
case the muscles of the eye, like those of the limbs, stagger and are
disobedient to the expiring efforts of volition. Numerous objects are
indeed sometimes seen by the inebriate, occasioned by the refractions made
by the tears, which stand upon his eye-lids.

8. This vertigo also continues, when the inebriate lies in his bed, in the
dark, or with his eyes closed; and this more powerfully than when he is
erect, and in the light. For the irritative ideas of the apparent motions
of objects are now excited by irritation from internal stimulus, or by
association with other irritative motions; and the inebriate, like one in a
dream, believes the objects of these irritative motions to be present, and
feels himself vertiginous. I have observed in this situation, so long as my
eyes and mind were intent upon a book, the sickness and vertigo ceased, and
were renewed again the moment I discontinued this attention; as was
explained in the preceding account of sea-sickness. Some drunken people
have been known to become sober instantly from some accident, that has
strongly excited their attention, as the pain of a broken bone, or the news
of their house being on fire.

9. Sometimes the vertigo from internal causes, as from intoxication, or at
the beginning of some fevers, becomes so universal, that the irritative
motions which belong to other organs of sense are succeeded by sensation or
attention, as well as those of the eye. The vertiginous noise in the ears
has been explained in Section XX. on Vertigo. The taste of the saliva,
which in general is not attended to, becomes perceptible, and the patients
complain of a bad taste in their mouth.

The common smells of the surrounding air sometimes excite the attention of
these patients, and bad smells are complained of, which to other people are
imperceptible. The irritative motions that belong to the sense of pressure,
or of touch, are attended to, and the patient conceives the bed to librate,
and is fearful of falling out of it. The irritative motions belonging to
the senses of distention, and of heat, like those above mentioned, become
attended to at this time: hence we feel the pulsation of our arteries all
over us, and complain of heat, or of cold, in parts of the body where there
is no accumulation or diminution of actual heat. All which are to be
explained, as in the last paragraph, by the irritative ideas belonging to
the various senses being now excited by internal stimuli, or by their
associations with other irritative motions. And that the inebriate, like
one in a dream, believes the external objects, which usually caused these
irritative ideas, to be now present.

10. The diseases in consequence of frequent inebriety, or of daily taking
much vinous spirit without inebriety, consist in the paralysis, which is
liable to succeed violent stimulation. Organs, whose actions are associated
with others, are frequently more affected than the organ, which is
stimulated into too violent action. See Sect. XXIV. 2. 8. Hence in drunken
people it generally happens, that the secretory vessels of the liver become
first paralytic, and a torpor with consequent gall-stones or schirrus of
this viscus is induced with concomitant jaundice; otherwise it becomes
inflamed in consequence of previous torpor, and this inflammation is
frequently transferred to a more sensible part, which is associated with
it, and produces the gout, or the rosy eruption of the face, or some other
leprous eruption on the head, or arms, or legs. Sometimes the stomach is
first affected, and paralysis of the lacteal system is induced: whence a
total abhorrence from flesh-food, and general emaciation. In others the
lymphatic system is affected with paralysis, and dropsy is the consequence.
In some inebriates the torpor of the liver produces pain without apparent
schirrus, or gall stones, or inflammation, or consequent gout, and in these
epilepsy or insanity are often the consequence. All which will be more
fully treated of in the course of the work.

I am well aware, that it is a common opinion, that the gout is as
frequently owing to gluttony in eating, as to intemperance in drinking
fermented or spirituous liquors. To this I answer, that I have seen no
person afflicted with the gout, who has not drank freely of fermented
liquor, as wine and water, or small beer; though as the disposition to all
the diseases, which have originated from intoxication, is in some degree
hereditary, a less quantity of spirituous potation will induce the gout in
those, who inherit the disposition from their parents. To which I must add,
that in young people the rheumatism is frequently mistaken for the gout.

Spice is seldom taken in such quantity as to do any material injury to the
system, flesh-meats as well as vegetables are the natural diet of mankind;
with these a glutton may be crammed up to the throat, and fed fat like a
stalled ox; but he will not be diseased, unless he adds spirituous or
fermented liquor to his food. This is well known in the distilleries, where
the swine, which are fattened by the spirituous sediments of barrels,
acquire diseased livers. But mark what happens to a man, who drinks a quart
of wine or of ale, if he has not been habituated to it. He loses the use
both of his limbs and of his understanding! He becomes a temporary idiot,
and has a temporary stroke of the palsy! And though he slowly recovers
after some hours, is it not reasonable to conclude, that a perpetual
repetition of so powerful a poison must at length permanently affect
him?--If a person accidentally becomes intoxicated by eating a few
mushrooms of a peculiar kind, a general alarm is excited, and he is said to
be poisoned, and emetics are exhibited; but so familiarised are we to the
intoxication from vinous spirit, that it occasions laughter rather than
alarm.

There is however considerable danger in too hastily discontinuing the use
of so strong a stimulus, lest the torpor of the system, or paralysis,
should sooner be induced by the omission than by the continuance of this
habit, when unfortunately acquired. A golden rule for determining the
quantity, which may with safety be discontinued, is delivered in Sect. XII.
7. 8.

11. Definition of drunkenness. Many of the irritative motions are much
increased in energy by internal stimulation.

2. A great additional quantity of pleasurable sensation is occasioned by
this increased exertion of the irritative motions. And many sensitive
motions are produced in consequence of this increased sensation.

3. The associated trains and tribes of motions, catenated with the
increased irritative and sensitive motions, are disturbed, and proceed in
confusion.

4. The faculty of volition is gradually impaired, whence proceeds the
instability of locomotion, inaccuracy of perception, and inconsistency of
ideas; and is at length totally suspended, and a temporary apoplexy
succeeds.

       *       *       *       *       *

SECT. XXII.

OF PROPENSITY TO MOTION, REPETITION AND IMITATION.

    I. _Accumulation of sensorial power in hemiplagia, in sleep, in cold
    fit of fever, in the locomotive muscles, in the organs of sense.
    Produces propensity to action._ II. _Repetition by three sensorial
    powers. In rhimes and alliterations, in music, dancing, architecture,
    landscape-painting, beauty._ III. 1. _Perception consists in imitation.
    Four kinds of imitation._ 2. _Voluntary. Dogs taught to dance._ 3.
    _Sensitive. Hence sympathy, and all our virtues. Contagious matter of
    venereal ulcers, of hydrophobia, of jail-fever, of small-pox, produced
    by imitation, and the sex of the embryon._ 4. _Irritative imitation._
    5. _Imitations resolvable into associations._

I. 1. In the hemiplagia, when the limbs on one side have lost their power
of voluntary motion, the patient is for many days perpetually employed in
moving those of the other. 2. When the voluntary power is suspended during
sleep, there commences a ceaseless flow of sensitive motions, or ideas of
imagination, which compose our dreams. 3. When in the cold fit of an
intermittent fever some parts of the system have for a time continued
torpid, and have thus expended less than their usual expenditure of
sensorial power; a hot fit succeeds, with violent action of those vessels,
which had previously been quiescent. All these are explained from an
accumulation of sensorial power during the inactivity of some part of the
system.

Besides the very great quantity of sensorial power perpetually produced and
expended in moving the arterial, venous, and glandular systems, with the
various organs or digestion, as described in Section XXXII. 3. 2. there is
also a constant expenditure of it by the action of our locomotive muscles
and organs of sense. Thus the thickness of the optic nerves, where they
enter the eye, and the great expansion of the nerves of touch beneath the
whole of the cuticle, evince the great consumption of sensorial power by
these senses. And our perpetual muscular actions in the common offices of
life, and in constantly preserving the perpendicularity of our bodies
during the day, evince a considerable expenditure of the spirit of
animation by our locomotive muscles. It follows, that if the exertion of
these organs of sense and muscles be for a while intermitted, that some
quantity of sensorial power must be accumulated, and a propensity to
activity of some kind ensue from the increased excitability of the system.
Whence proceeds the irksomeness of a continued attitude, and of an indolent
life.

However small this hourly accumulation of the spirit of animation may be,
it produces a propensity to some kind of action; but it nevertheless
requires either desire or aversion, either pleasure or pain, or some
external stimulus, or a previous link of association, to excite the system
into activity; thus it frequently happens, when the mind and body are so
unemployed as not to possess any of the three first kinds of stimuli, that
the last takes place, and consumes the small but perpetual accumulation of
sensorial power. Whence some indolent people repeat the same verse for
hours together, or hum the same tune. Thus the poet:

  Onward he trudged, not knowing what he sought,
  And whistled, as he went, for want of thought.

II. The repetitions of motions may be at first produced either by volition,
or by sensation, or by irritation, but they soon become easier to perform
than any other kinds of action, because they soon become associated
together, according to Law the seventh, Section IV. on Animal Causation.
And because their frequency of repetition, if as much sensorial power be
produced during every reiteration as is expended, adds to the facility of
their production.

If a stimulus be repeated at uniform intervals of time, as described in
Sect. XII. 3. 3. the action, whether of our muscles or organs of sense, is
produced with still greater facility or energy; because the sensorial power
of association, mentioned above, is combined with the sensorial power of
irritation; that is, in common language, the acquired habit assists the
power of the stimulus.

This not only obtains in the annual, lunar, and diurnal catenations of
animal motions, as explained in Sect. XXXVI. which are thus performed with
great facility and energy; but in every less circle of actions or ideas, as
in the burthen of a song, or the reiterations of a dance. To the facility
and distinctness, with which we hear sounds at repeated intervals, we owe
the pleasure, which we receive from musical time, and from poetic time; as
described in Botanic Garden, P. 2. Interlude 3. And to this the pleasure we
receive from the rhimes and alliterations of modern verification; the
source of which without this key would be difficult to discover. And to
this likewise should be ascribed the beauty of the duplicature in the
perfect tense of the Greek verbs, and of some Latin ones, as tango tetegi,
mordeo momordi.

There is no variety of notes referable to the gamut in the beating of the
drum, yet if it be performed in musical time, it is agreeable to our ears;
and therefore this pleasurable sensation must be owing to the repetition of
the divisions of the sounds at certain intervals of time, or musical bars.
Whether these times or bars are distinguished by a pause, or by an
emphasis, or accent, certain it is, that this distinction is perpetually
repeated; otherwise the ear could not determine instantly, whether the
successions of sound were in common or in triple time. In common time there
is a division between every two crotchets, or other notes of equivalent
time; though the bar in written music is put after every fourth crotchet,
or notes equivalent in time; in triple time the division or bar is after
every three crotchets, or notes equivalent; so that in common time the
repetition recurs more frequently than in triple time. The grave or heroic
verses of the Greek and Latin poets are written in common time; the French
heroic verses, and Mr. Anstie's humorous verses in his Bath Guide, are
written in the same time as the Greek and Latin verses, but are one bar
shorter. The English grave or heroic verses are measured by triple time, as
Mr. Pope's translation of Homer.

But besides these little circles of musical time, there are the greater
returning periods, and the still more distant choruses, which, like the
rhimes at the ends of verses, owe their beauty to repetition; that is, to
the facility and distinctness with which we perceive sounds, which we
expect to perceive, or have perceived before; or in the language of this
work, to the greater ease and energy with which our organ is excited by the
combined sensorial powers of association and irritation, than by the latter
singly.

A certain uniformity or repetition of parts enters the very composition of
harmony. Thus two octaves nearest to each other in the scale commence their
vibrations together after every second vibration of the higher one. And
where the first, third, and fifth compose a chord the vibrations concur or
coincide frequently, though less to than in the two octaves. It is probable
that these chords bear some analogy to a mixture of three alternate colours
in the sun's spectrum separated by a prism.

The pleasure we receive from a melodious succession of notes referable to
the gamut is derived from another source, viz. to the pandiculation or
counteraction of antagonist fibres. See Botanic Garden, P. 2. Interlude 3.
If to these be added our early associations of agreeable ideas with certain
proportions of sound, I suppose, from these three sources springs all the
delight of music, so celebrated by ancient authors, and so enthusiastically
cultivated at present. See Sect. XVI. No. 10. on Instinct.

This kind of pleasure arising from repetition, that is from the facility
and distinctness, with which we perceive and understand repeated
sensations, enters into all the agreeable arts; and when it is carried to
excess is termed formality. The art of dancing like that of music depends
for a great part of the pleasure, it affords, on repetition; architecture,
especially the Grecian, consists of one part being a repetition of another;
and hence the beauty of the pyramidal outline in landscape-painting; where
one side of the picture may be said in some measure to balance the other.
So universally does repetition contribute to our pleasure in the fine arts,
that beauty itself has been defined by some writers to consist in a due
combination of uniformity and variety. See Sect. XVI. 6.

III. 1. Man is termed by Aristotle an imitative animal; this propensity to
imitation not only appears in the actions of children, but in all the
customs and fashions of the world: many thousands tread in the beaten paths
of others, for one who traverses regions of his own discovery. The origin
of this propensity of imitation has not, that I recollect, been deduced
from any known principle; when any action presents itself to the view of a
child, as of whetting a knife, or threading a needle, the parts of this
action in respect of time, motion, figure, is imitated by a part of the
retina of his eye; to perform this action therefore with his hands is
easier to him than to invent any new action, because it consists in
repeating with another set of fibres, viz. with the moving muscles, what he
had just performed by some parts of the retina; just as in dancing we
transfer the times of motion from the actions of the auditory nerves to the
muscles of the limbs. Imitation therefore consists of repetition, which we
have shewn above to be the easiest kind of animal action, and which we
perpetually fall into, when we possess an accumulation of sensorial power,
which is not otherwise called into exertion.

It has been shewn, that our ideas are configurations of the organs of
sense, produced originally in consequence of the stimulus of external
bodies. And that these ideas, or configurations of the organs of sense,
referable in some property a correspondent property of external matter; as
the parts of the senses of light and of touch, which are excited into
action, resemble in figure the figure of the stimulating body; and probably
also the colour, and the quantity of density, which they perceive. As
explained in Sect. XIV. 2. 2. Hence it appears, that our perceptions
themselves are copies, that is, imitations of some properties of external
matter; and the propensity to imitation is thus interwoven with our
existence, as it is produced by the stimuli of external bodies, and is
afterwards repeated by our volitions and sensations, and thus constitutes
all the operations of our minds.

2. Imitations resolve themselves into four kinds, voluntary, sensitive,
irritative, and associate. The voluntary imitations are, when we imitate
deliberately the actions of others, either by mimicry, as in acting a play,
or in delineating a flower; or in the common actions of our lives, as in
our dress, cookery, language, manners, and even in our habits of thinking.

Not only the greatest part of mankind learn all the common arts of life by
imitating others, but brute animals seem capable of acquiring knowledge
with greater facility by imitating each other, than by any methods by which
we can teach them; as dogs and cats, when they are sick, learn of each
other to eat grass; and I suppose, that by making an artificial dog perform
certain tricks, as in dancing on his hinder legs, a living dog might be
easily induced to imitate them; and that the readiest way of instructing
dumb animals is by practising them with others of the same species, which
have already learned the arts we wish to teach them. The important use of
imitation in acquiring natural language is mentioned in Section XVI. 7. and
8. on Instinct.

3. The sensitive imitations are the immediate consequences of pleasure or
pain, and these are often produced even contrary to the efforts of the
will. Thus many young men on seeing cruel surgical operations become sick,
and some even feel pain in the parts of their own bodies, which they see
tortured or wounded in others; that is, they in some measure imitate by the
exertions of their own fibres the violent actions, which they witnessed in
those of others. In this case a double imitation takes place, first the
observer imitates with the extremities of the optic nerve the mangled
limbs, which are present before his eyes; then by a second imitation he
excites to violent action of the fibres of his own limbs as to produce pain
in those parts of his own body, which he saw wounded in another. In these
pains produced by imitation the effect has some similarity to the cause,
which distinguishes them from those produced by association; as the pains
of the teeth, called tooth-edge, which are produced by association with
disagreeable sounds, as explained in Sect. XVI. 10.

The effect of this powerful agent, imitation, in the moral world, is
mentioned in Sect. XVI. 7. as it is the foundation of all our intellectual
sympathies with the pains and pleasures of others, and is in consequence
the source of all our virtues. For in what consists our sympathy with the
miseries, or with the joys, of our fellow creatures, but in an involuntary
excitation of ideas in some measure similar or imitative of those, which we
believe to exist in the minds of the persons, whom we commiserate or
congratulate?

There are certain concurrent or successive actions of some of the glands,
or other parts of the body, which are possessed of sensation, which become
intelligible from this propensity to imitation. Of these are the production
of matter by the membranes of the fauces, or by the skin, in consequence of
the venereal disease previously affecting the parts of generation. Since as
no fever is excited, and as neither the blood of such patients, nor even
the matter from ulcers of the throat, or from cutaneous ulcers, will by
inoculation produce the venereal disease in others, as observed by Mr.
Hunter, there is reason to conclude, that no contagious matter is conveyed
thither by the blood-vessels, but that a milder matter is formed by the
actions of the fine vessels in those membranes imitating each other. See
Section XXXIII. 2. 9. In this disease the actions of these vessels
producing ulcers on the throat and skin are imperfect imitations of those
producing chanker, or gonorrhoea; since the matter produced by them is not
infectious, while the imitative actions in the hydrophobia appear to be
perfect resemblances, as they produce a material equally infectious with
the original one, which induced them.

The contagion from the bite of a mad dog differs from other contagious
materials, from its being communicable from other animals to mankind, and
from many animals to each other; the phenomena attending the hydrophobia
are in some degree explicable on the foregoing theory. The infectious
matter does not appear to enter the circulation, as it cannot be traced
along the course of the lymphatics from the wound, nor is there any
swelling of the lymphatic glands, nor does any fever attend, as occurs in
the small-pox, and in many other contagious diseases; yet by some unknown
process the disease is communicated from the wound to the throat, and that
many months after the injury, so as to produce pain and hydrophobia, with a
secretion of infectious saliva of the same kind, as that of the mad dog,
which inflicted the wound.

This subject is very intricate.--It would appear, that by certain morbid
actions of the salivary glands of the mad dog, a peculiar kind of saliva is
produced; which being instilled into a wound of another animal stimulates
the cutaneous or mucous glands into morbid actions, but which are
ineffectual in respect to the production of a similar contagious material;
but the salivary glands by irritative sympathy are thrown into similar
action, and produce an infectious saliva similar to that instilled into the
wound.

Though in many contagious fevers a material similar to that which produced
the disease, is thus generated by imitation; yet there are other infectious
materials, which do not thus propagate themselves, but which seem to act
like slow poisons. Of this kind was the contagious matter, which produced
the jail-fever at the assizes at Oxford about a century ago. Which, though
fatal to so many, was not communicated to their nurses or attendants. In
these cases, the imitations of the fine vessels, as above described, appear
to be imperfect, and do not therefore produce a matter similar to that,
which stimulates them; in this circumstance resembling the venereal matter
in ulcers of the throat or skin, according to the curious discovery of Mr.
Hunter above related, who found, by repeated inoculations, that it would
not infect. Hunter on Venereal Disease, Part vi. ch. 1.

Another example of morbid imitation is in the production of a great
quantity of contagious matter, as in the inoculated small-pox, from a small
quantity of it inserted into the arm, and probably diffused in the blood.
These particles of contagious matter stimulate the extremities of the fine
arteries of the skin, and cause them to imitate some properties of those
particles of contagious matter, so as to produce a thousandfold of a
similar material. See Sect. XXXIII. 2. 6. Other instances are mentioned in
the Section on Generation, which shew the probability that the extremities
of the seminal glands may imitate certain ideas of the mind, or actions of
the organs of sense, and thus occasion the male or female sex of the
embryon. See Sect. XXXIX. 6.

4. We come now to those imitations, which are not attended with sensation.
Of these are all the irritative ideas already explained, as when the retina
of the eye imitates by its action or configuration the tree or the bench,
which I shun in walking past without attending to them. Other examples of
these irritative imitations are daily observable in common life; thus one
yawning person shall set a whole company a yawning; and some have acquired
winking of the eyes or impediments of speech by imitating their companions
without being conscious of it.

5. Besides the three species of imitations above described there may be
some associate motions, which may imitate each other in the kind as well as
in the quantity of their action; but it is difficult to distinguish them
from the associations of motions treated of in Section XXXV. Where the
actions of other persons are imitated there can be no doubt, or where we
imitate a preconceived idea by exertion of our locomotive muscles, as in
painting a dragon; all these imitations may aptly be referred to the
sources above described of the propensity to activity, and the facility of
repetition; at the same time I do not affirm, that all those other apparent
sensitive and irritative imitations may not be resolvable into associations
of a peculiar kind, in which certain distant parts of similar irritability
or sensibility, and which have habitually acted together, may affect each
other exactly with the same kinds of motion; as many parts are known to
sympathise in the quantity of their motions. And that therefore they may be
ultimately resolvable into associations of action, as described in Sect.
XXXV.

       *       *       *       *       *

SECT. XXIII.

OF THE CIRCULATORY SYSTEM.

    I. _The heart and arteries have no antagonist muscles. Veins absorb the
    blood, propel it forwards, and distend the heart; contraction of the
    heart distends the arteries. Vena portarum._ II. _Glands which take
    their fluids from the blood. With long necks, with short necks._ III.
    _Absorbent system._ IV. _Heat given out from glandular secretions.
    Blood changes colour in the lungs and in the glands and capillaries._
    V. _Blood is absorbed by veins, as chyle by lacteal vessels, otherwise
    they could not join their streams._ VI. _Two kinds of stimulus,
    agreeable and disagreeable. Glandular appetency. Glands originally
    possessed sensation._

I. We now step forwards to illustrate some of the phenomena of diseases,
and to trace out their most efficacious methods of cure; and shall commence
this subject with a short description of the circulatory system.

As the nerves, whose extremities form our various organs of sense and
muscles, are all joined, or communicate, by means of the brain, for the
convenience perhaps of the distribution of a subtile ethereal fluid for the
purpose of motion; so all those vessels of the body, which carry the
grosser fluids for the purposes of nutrition, communicate with each other
by the heart.

The heart and arteries are hollow muscles, and are therefore indued with
power of contraction in consequence of stimulus, like all other muscular
fibres; but, as they have no antagonist muscles, the cavities of the
vessels, which they form, would remain for ever closed, after they have
contracted themselves, unless some extraneous power be applied to again
distend them. This extraneous power in respect to the heart is the current
of blood, which is perpetually absorbed by the veins from the various
glands and capillaries, and pushed into the heart by a power probably very
similar to that, which raises the sap in vegetables in the spring, which,
according to Dr. Hale's experiment on the stump of a vine, exerted a force
equal to a column of water above twenty feet high. This force of the
current of blood in the veins is partly produced by their absorbent power,
exerted at the beginning of every fine ramification; which may be conceived
to be a mouth absorbing blood, as the mouths of the lacteals and lymphatics
absorb chyle and lymph. And partly by their intermitted compression by the
pulsations of their generally concomitant arteries; by which the blood is
perpetually propelled towards the heart, as the valves in many veins, and
the absorbent mouths in them all, will not suffer it to return.

The blood, thus forcibly injected into the chambers of the heart, distends
this combination of hollow muscles; till by the stimulus of distention they
contract themselves; and, pushing forwards the blood into the arteries,
exert sufficient force to overcome in less than a second of time the vis
inertiæ, and perhaps some elasticity, of the very extensive ramifications
of the two great systems of the aortal and pulmonary arteries. The power
necessary to do this in so short a time must be considerable, and has been
variously estimated by different physiologists.

The muscular coats of the arterial system are then brought into action by
the stimulus of distention, and propel the blood to the mouths, or through
the convolutions, which precede the secretory apertures of the various
glands and capillaries.

In the vessels of the liver there is no intervention of the heart; but the
vena portarum, which does the office of an artery, is distended by the
blood poured into it from the mesenteric veins, and is by this distention
stimulated to contract itself, and propel the blood to the mouths of the
numerous glands, which compose that viscus.

II. The glandular system of vessels may be divided into those, which take
some fluid from the circulation; and those, which give something to it.
Those, which take their fluid from the circulation are the various glands,
by which the tears, bile, urine, perspiration, and many other secretions
are produced; these glands probably consist of a mouth to select, a belly
to digest, and an excretory aperture to emit their appropriated fluids; the
blood is conveyed by the power of the heart and arteries to the mouths of
these glands, it is there taken up by the living power of the gland, and
carried forwards to its belly, and excretory aperture, where a part is
separated, and the remainder absorbed by the veins for further purposes.

Some of these glands are furnished with long convoluted necks or tubes, as
the seminal ones, which are curiously seen when injected with quicksilver.
Others seem to consist of shorter tubes, as that great congeries of glands,
which constitute the liver, and those of the kidneys. Some have their
excretory apertures opening into reservoirs, as the urinary and
gall-bladders. And others on the external body, as those which secrete the
tears, and perspirable matter.

Another great system of glands, which have very short necks, are the
capillary vessels; by which the insensible perspiration is secreted on the
skin; and the mucus of various consistences, which lubricates the
interstices of the cellular membrane, of the muscular fibres, and of all
the larger cavities of the body. From the want of a long convolution of
vessels some have doubted, whether these capillaries should be considered
as glands, and have been led to conclude, that the perspirable matter
rather exuded than was secreted. But the fluid of perspiration is not
simple water, though that part of it, which exhales into the air may be
such; for there is another part of it, which in a state of health is
absorbed again; but which, when the absorbents are diseased, remains on the
surface of the skin, in the form of scurf, or indurated mucus. Another
thing, which shews their similitude to other glands, is their sensibility
to certain affections of the mind; as is seen in the deeper colour of the
skin in the blush of shame, or the greater paleness of it from fear.

III. Another series of glandular vessels is called the absorbent system;
these open their mouths into all the cavities, and upon all those surfaces
of the body, where the excretory apertures of the other glands pour out
their fluids. The mouths of the absorbent system drink up a part or the
whole of these fluids, and carry them forwards by their living power to
their respective glands, which are called conglobate glands. There these
fluids undergo some change, before they pass on into the circulation; but
if they are very acrid, the conglobate gland swells, and sometimes
suppurates, as in inoculation of the small-pox, in the plague, and in
venereal absorptions; at other times the fluid may perhaps continue there,
till it undergoes some chemical change, that renders it less noxious; or,
what is more likely, till it is regurgitated by the retrograde motion of
the gland in spontaneous sweats or diarrhoeas, as disagreeing food is
vomited from the stomach.

IV. As all the fluids, that pass through these glands, and capillary
vessels, undergo a chemical change, acquiring new combinations, the matter
of heat is at the same time given out; this is apparent, since whatever
increases insensible perspiration, increases the heat of the skin; and when
the action of these vessels is much increased but for a moment, as in
blushing, a vivid heat on the skin is the immediate consequence. So when
great bilious secretions, or those of any other gland, are produced, heat
is generated in the part in proportion to the quantity of the secretion.

The heat produced on the skin by blushing may be thought by some too sudden
to be pronounced a chemical effect, as the fermentations or new
combinations taking place in a fluid is in general a slower process. Yet
are there many chemical mixtures in which heat is given out as
instantaneously; as in solutions of metals in acids, or in mixtures of
essential oils and acids, as of oil of cloves and acid of nitre. So the
bruised parts of an unripe apple become almost instantaneously sweet; and
if the chemico-animal process of digestion be stopped for but a moment, as
by fear, or even by voluntary eructation, a great quantity of air is
generated, by the fermentation, which instantly succeeds the stop of
digestion. By the experiments of Dr. Hales it appears, that an apple during
fermentation gave up above six hundred times its bulk of air; and the
materials in the stomach are such, and in such a situation, as immediately
to run into fermentation, when digestion is impeded.

As the blood passes through the small vessels of the lungs, which connect
the pulmonary artery and vein, it undergoes a change of colour from a dark
to a light red; which may be termed a chemical change, as it is known to be
effected by an admixture of oxygene, or vital air; which, according to a
discovery of Dr. Priestley, passes through the moist membranes, which
constitute the sides of these vessels. As the blood passes through the
capillary vessels, and glands, which connect the aorta and its various
branches with their correspondent veins in the extremities of the body, it
again loses the bright red colour, and undergoes some new combinations in
the glands or capillaries, in which the matter of heat is given out from
the secreted fluids. This process therefore, as well as the process of
respiration, has some analogy to combustion, as the vital air or oxygene
seems to become united to some inflammable base, and the matter of heat
escapes from the new acid, which is thus produced.

V. After the blood has passed these glands and capillaries, and parted with
whatever they chose to take from it, the remainder is received by the
veins, which are a set of blood-absorbing vessels in general corresponding
with the ramifications of the arterial system. At the extremity of the fine
convolutions of the glands the arterial force ceases; this in respect to
the capillary vessels, which unite the extremities of the arteries with the
commencement of the veins, is evident to the eye, on viewing the tail of a
tadpole by means of a solar, or even by a common microscope, for globules
of blood are seen to endeavour to pass, and to return again and again,
before they become absorbed by the mouths of the veins; which returning of
these globules evinces, that the arterial force behind them has ceased. The
veins are furnished with valves like the lymphatic absorbents; and the
great trunks of the veins, and of the lacteals and lymphatics, join
together before the ingress of their fluids into the left chamber of the
heart; both which evince, that the blood in the veins, and the lymph and
chyle in the lacteals and lymphatics, are carried on by a similar force;
otherwise the stream, which was propelled with a less power, could not
enter the vessels, which contained the stream propelled with a greater
power. From whence it appears, that the veins are a system of vessels
absorbing blood, as the lacteals and lymphatics are a system of vessels
absorbing chyle and lymph. See Sect. XXVII. 1.

VI. The movements of their adapted fluids in the various vessels of the
body are carried forwards by the actions of those vessels in consequence of
two kinds of stimulus, one of which may be compared to a pleasurable
sensation or desire inducing the vessel to seize, and, as it were, to
swallow the particles thus selected from the blood; as is done by the
mouths of the various glands, veins, and other absorbents, which may be
called glandular appetency. The other kind of stimulus may be compared to
disagreeable sensation, or aversion, as when the heart has received the
blood, and is stimulated by it to push it forwards into the arteries; the
same again stimulates the arteries to contract, and carry forwards the
blood to their extremities, the glands and capillaries. Thus the mesenteric
veins absorb the blood from the intestines by glandular appetency, and
carry it forward to the vena portarum; which acting as an artery contracts
itself by disagreeable stimulus, and pushes it to its ramified extremities,
the various glands, which constitute the liver.

It seems probable, that at the beginning of the formation of these vessels
in the embryon, an agreeable sensation was in reality felt by the glands
during secretion, as is now felt in the act of swallowing palatable food;
and that a disagreeable sensation was originally felt by the heart from the
distention occasioned by the blood, or by its chemical stimulus; but that
by habit these are all become irritative motions; that is, such motions as
do not affect the whole system, except when the vessels are diseased by
inflammation.

       *       *       *       *       *

SECT. XXIV.

OF THE SECRETIONS OF SALIVA, AND OF TEARS, AND OF THE LACRYMAL SACK.

    I. _Secretion of saliva increased by mercury in the blood._ 1. _By the
    food in the mouth. Dryness of the mouth not from a deficiency of
    saliva._ 2. _By Sensitive ideas._ 3. _By volition._ 4. _By distasteful
    substances. It is secreted in a dilute and saline state. It then
    becomes more viscid._ 5. _By ideas of distasteful substances._ 6. _By
    nausea._ 7. _By aversion._ 8. _By catenation with stimulating
    substances in the ear._ II. 1. _Secretion of tears less in sleep. From
    stimulation of their excretory duct._ 2. _Lacrymal sack is a gland._ 3.
    _Its uses._ 4. _Tears are secreted, when the nasal duct is stimulated._
    5. _Or when it is excited by sensation._ 6. _Or by volition._ 7. _The
    lacrymal sack can regurgitate its contents into the eye._ 8. _More
    tears are secreted by association with the irritation of the nasal duct
    of the lacrymal sack, than the puncta lacrymalia can imbibe. Of the
    gout in the liver and stomach._

I. The salival glands drink up a certain fluid from the circumfluent blood,
and pour it into the mouth. They are sometimes stimulated into action by
the blood, that surrounds their origin, or by some part of that
heterogeneous fluid: for when mercurial salts, or oxydes, are mixed with
the blood, they stimulate these glands into unnatural exertions; and then
an unusual quantity of saliva is separated.

1. As the saliva secreted by these glands is most wanted during the
mastication of our food, it happens, when the terminations of their ducts
in the mouth are stimulated into action, the salival glands themselves are
brought into increased action at the same time by association, and separate
a greater quantity of their juices from the blood; in the same manner as
tears are produced in greater abundance during the stimulus of the vapour
of onions, or of any other acrid material in the eye.

The saliva is thus naturally poured into the mouth only during the stimulus
of our food in mastication; for when there is too great an exhalation of
the mucilaginous secretion from the membranes, which line the mouth, or too
great an absorption of it, the mouth becomes dry, though there is no
deficiency in the quantity of saliva; as in those who sleep with their
mouths open, and in some fevers.

2. Though during the mastication of our natural food the salival glands are
excited into action by the stimulus on their excretory ducts, and a due
quantity of saliva is separated from the blood, and poured into the mouth;
yet as this mastication of our food is always attended with a degree of
pleasure; and that pleasurable sensation is also connected with our ideas
of certain kinds of aliment; it follows, that when these ideas are
reproduced, the pleasurable sensation arises along with them, and the
salival glands are excited into action, and fill the mouth with saliva from
this sensitive association, as is frequently seen in dogs, who slaver at
the sight of food.

3. We have also a voluntary power over the action of these salival glands,
for we can at any time produce a flow of saliva into our mouth, and spit
out, or swallow it at will.

4. If any very acrid material be held in the mouth, as the root of
pyrethrum, or the leaves of tobacco, the salival glands are stimulated into
stronger action than is natural, and thence secrete a much larger quantity
of saliva; which is at the same time more viscid than in its natural state;
because the lymphatics, that open their mouths into the ducts of the
salival glands, and on the membranes, which line the mouth, are likewise
stimulated into stronger action, and absorb the more liquid parts of the
saliva with greater avidity; and the remainder is left both in greater
quantity and more viscid.

The increased absorption in the mouth by some stimulating substances, which
are called astringents, as crab juice, is evident from the instant dryness
produced in the mouth by a small quantity of them.

As the extremities of the glands are of exquisite tenuity, as appears by
their difficulty of injection, it was necessary for them to secrete their
fluids in a very dilute state; and, probably for the purpose of stimulating
them into action, a quantity of neutral salt is likewise secreted or formed
by the gland. This aqueous and saline part of all secreted fluids is again
reabsorbed into the habit. More than half of some secreted fluids is thus
imbibed from the reservoirs, into which they are poured; as in the urinary
bladder much more than half of what is secreted by the kidneys becomes
reabsorbed by the lymphatics, which are thickly dispersed around the neck
of the bladder. This seems to be the purpose of the urinary bladders of
fish, as otherwise such a receptacle for the urine could have been of no
use to an animal immersed in water.

5. The idea of substances disagreeably acrid will also produce a quantity
of saliva in the mouth; as when we smell very putrid vapours, we are
induced to spit out our saliva, as if something disagreeable was actually
upon our palates.

6. When disagreeable food in the stomach produces nausea, a flow of saliva
is excited in the mouth by association; as efforts to vomit are frequently
produced by disagreeable drugs in the mouth by the same kind of
association.

7. A preternatural flow of saliva is likewise sometimes occasioned by a
disease of the voluntary power; for if we think about our saliva, and
determine not to swallow it, or not to spit it out, an exertion is produced
by the will, and more saliva is secreted against our wish; that is, by our
aversion, which bears the same analogy to desire, as pain does to pleasure;
as they are only modifications of the same disposition of the sensorium.
See Class IV. 3. 2. 1.

8. The quantity of saliva may also be increased beyond what is natural, by
the catenation of the motions of these glands with other motions, or
sensations, as by an extraneous body in the ear; of which I have known an
instance; or by the application of stizolobium, siliqua hirsuta, cowhage,
to the seat of the parotis, as some writers have affirmed.

II. 1. The lacrymal gland drinks up a certain fluid from the circumfluent
blood, and pours it on the ball of the eye, on the upper part of the
external corner of the eyelids. Though it may perhaps be stimulated into
the performance of its natural action by the blood, which surrounds its
origin, or by some part of that heterogeneous fluid; yet as the tears
secreted by this gland are more wanted at some times than at others, its
secretion is variable, like that of the saliva above mentioned, and is
chiefly produced when its excretory duct is stimulated; for in our common
sleep there seems to be little or no secretion of tears; though they are
occasionally produced by our sensations in dreams.

Thus when any extraneous material on the eye-ball, or the dryness of the
external covering of it, or the coldness of the air, or the acrimony of
some vapours, as of onions, stimulates the excretory duct of the lacrymal
gland, it discharges its contents upon the ball; a quicker secretion takes
place in the gland, and abundant tears succeed, to moisten, clean, and
lubricate the eye. These by frequent nictitation are diffused over the
whole ball, and as the external angle of the eye in winking is closed
sooner than the internal angle, the tears are gradually driven forwards,
and downwards from the lacrymal gland to the puncta lacrymalia.

2. The lacrymal sack, with its puncta lacrymalia, and its nasal duct, is a
complete gland; and is singular in this respect, that it neither derives
its fluid from, nor disgorges it into the circulation. The simplicity of
the structure of this gland, and both the extremities of it being on the
surface of the body, makes it well worthy our minuter observation; as the
actions of more intricate and concealed glands may be better understood
from their analogy to this.

3. This simple gland consists of two absorbing mouths, a belly, and an
excretory duct. As the tears are brought to the internal angle of the eye,
these two mouths drink them up, being stimulated into action by this fluid,
which they absorb. The belly of the gland, or lacrymal sack, is thus
filled, in which the saline part of the tears is absorbed, and when the
other end of the gland, or nasal duct, is stimulated by the dryness, or
pained by the coldness of the air, or affected by any acrimonious dust or
vapour in the nostrils, it is excited into action together with the sack,
and the tears are disgorged upon the membrane, which lines the nostrils;
where they serve a second purpose to moisten, clean, and lubricate, the
organ of smell.

4. When the nasal duct of this gland is stimulated by any very acrid
material, as the powder of tobacco, or volatile spirits, it not only
disgorges the contents of its belly or receptacle (the lacrymal sack), and
absorbs hastily all the fluid, that is ready for it in the corner of the
eye; but by the association of its motions with those of the lacrymal
gland, it excites that also into increased action, and a large flow of
tears is poured into the eye.

5. This nasal duct is likewise excited into strong action by sensitive
ideas, as in grief, or joy, and then also by its associations with the
lacrymal gland it produces a great flow of tears without any external
stimulus; as is more fully explained in Sect. XVI. 8. on Instinct.

6. There are some, famous in the arts of exciting compassion, who are said
to have acquired a voluntary power of producing a flow of tears in the eye;
which, from what has been said in the section on Instinct above mentioned,
I should suspect, is performed by acquiring a voluntary power over the
action of this nasal duct.

7. There is another circumstance well worthy our attention, that when by
any accident this nasal duct is obstructed, the lacrymal sack, which is the
belly or receptacle of this gland, by slight pressure of the finger is
enabled to disgorge its contents again into the eye; perhaps the bile in
the same manner, when the biliary ducts are obstructed, is returned into
the blood by the vessels which secrete it?

8. A very important though minute occurrence must here be observed, that
though the lacrymal gland is only excited into action, when we weep at a
distressful tale, by its association with this nasal duct, as is more fully
explained in Sect. XVI. 8; yet the quantity of tears secreted at once is
more than the puncta lacrymalia can readily absorb; which shews _that the
motions occasioned by associations are frequently more energetic than the
original motions, by which they were occasioned_. Which we shall have
occasion to mention hereafter, to illustrate, why pains frequently exist in
a part distant from the cause of them, as in the other end of the urethra,
when a stone stimulates the neck of the bladder. And why inflammations
frequently arise in parts distant from their cause, as the gutta rosea of
drinking people, from an inflamed liver.

The inflammation of a part is generally preceded by a torpor or quiescence
of it; if this exists in any large congeries of glands, as in the liver, or
any membranous part, as the stomach, pain is produced and chilliness in
consequence of the torpor of the vessels. In this situation sometimes an
inflammation of the parts succeeds the torpor; at other times a distant
more sensible part becomes inflamed; whose actions have previously been
associated with it; and the torpor of the first part ceases. This I
apprehend happens, when the gout of the foot succeeds a pain of the biliary
duct, or of the stomach. Lastly, it sometimes happens, that the pain of
torpor exists without any consequent inflammation of the affected part, or
of any distant part associated with it, as in the membranes about the
temple and eye-brows in hemicrania, and in those pains, which occasion
convulsions; if this happens to gouty people, when it affects the liver, I
suppose epileptic fits are produced; and, when it affects the stomach,
death is the consequence. In these cases the pulse is weak, and the
extremities cold, and such medicines as stimulate the quiescent parts into
action, or which induce inflammation in them, or in any distant part, which
is associated with them, cures the present pain of torpor, and saves the
patient.

I have twice seen a gouty inflammation of the liver, attended with
jaundice; the patients after a few days were both of them affected with
cold fits, like ague-fits, and their feet became affected with gout, and
the inflammation of their livers ceased. It is probable, that the uneasy
sensations about the stomach, and indigestion, which precedes gouty
paroxysms, are generally owing to torpor or slight inflammation of the
liver, and biliary ducts; but where great pain with continued sickness,
with feeble pulse, and sensation of cold, affect the stomach in patients
debilitated by the gout, that it is a torpor of the stomach itself, and
destroys the patient from the great connexion of that viscus with the vital
organs. See Sect. XXV. 17.

       *       *       *       *       *

SECT. XXV.

OF THE STOMACH AND INTESTINES.

    1. _Of swallowing our food. Ruminating animals._ 2. _Action of the
    stomach._ 3. _Action of the intestines. Irritative motions connected
    with these._ 4. _Effects of repletion._ 5. _Stronger action of the
    stomach and intestines from more stimulating food._ 6. _Their action
    inverted by still greater stimuli. Or by disgustful ideas. Or by
    volition._ 7. _Other glands strengthen or invert their motions by
    sympathy._ 8. _Vomiting performed by intervals._ 9. _Inversion of the
    cutaneous absorbents._ 10. _Increased secretion of bile and pancreatic
    juice._ 11. _Inversion of the lacteals._ 12. _And of the bile-ducts._
    13. _Case of a cholera._ 14. _Further account of the inversion of
    lacteals._ 15. _Iliac passions. Valve of the colon._ 16. _Cure of the
    iliac passion._ 17. _Pain of gall-stone distinguished from pain of the
    stomach. Gout of the stomach from torpor, from inflammation.
    Intermitting pulse owing to indigestion. To overdose of foxglove. Weak
    pulse from emetics. Death from a blow on the stomach. From gout of the
    stomach._

1. The throat, stomach, and intestines, may be considered as one great
gland; which like the lacrymal sack above mentioned, neither begins nor
ends in the circulation. Though the act of masticating our aliment belongs
to the sensitive class of motions, for the pleasure of its taste induces
the muscles of the jaw into action; yet the deglutition of it when
masticated is generally, if not always, an irritative motion, occasioned by
the application of the food already masticated to the origin of the
pharinx; in the same manner as we often swallow our spittle without
attending to it.

The ruminating class of animals have the power to invert the motion of
their gullet, and of their first stomach, from the stimulus of this
aliment, when it is a little further prepared; as is their daily practice
in chewing the cud; and appears to the eye of any one, who attends to them,
whilst they are employed in this second mastication of their food.

2. When our natural aliment arrives into the stomach, this organ is
simulated into its proper vermicular action; which beginning at the upper
orifice of it, and terminating at the lower one, gradually mixes together
and pushes forwards the digesting materials into the intestine beneath it.

At the same time the glands, that supply the gastric juices, which are
necessary to promote the chemical part of the process of digestion, are
stimulated to discharge their contained fluids, and to separate a further
supply from the blood-vessels: and the lacteals or lymphatics, which open
their mouths into the stomach, are stimulated into action, and take up some
part of the digesting materials.

3. The remainder of these digesting materials is carried forwards into the
upper intestines, and stimulates them into their peristaltic motion similar
to that of the stomach; which continues gradually to mix the changing
materials, and pass them along through the valve of the colon to the
excretory end of this great gland, the sphincter ani.

The digesting materials produce a flow of bile, and of pancreatic juice, as
they pass along the duodenum, by stimulating the excretory ducts of the
liver and pancreas, which terminate in that intestine: and other branches
of the absorbent or lymphatic system, called lacteals, are excited to drink
up, as it passes, those parts of the digesting materials, that are proper
for their purpose, by its stimulus on their mouths.

4. When the stomach and intestines are thus filled with their proper food,
not only the motions of the gastric glands, the pancreas, liver, and
lacteal vessels, are excited into action; but at the same time the whole
tribe of irritative motions are exerted with greater energy, a greater
degree of warmth, colour, plumpness, and moisture, is given to the skin
from the increased action of those glands called capillary vessels;
pleasurable sensation is excited, the voluntary motions are less easily
exerted, and at length suspended; and sleep succeeds, unless it be
prevented by the stimulus of surrounding objects, or by voluntary exertion,
or by an acquired habit, which was originally produced by one or other of
these circumstances, as is explained in Sect. XXI. on Drunkenness.

At this time also, as the blood-vessels become replete with chyle, more
urine is separated into the bladder, and less of it is reabsorbed; more
mucus poured into the cellular membranes, and less of it reabsorbed; the
pulse becomes fuller, and softer, and in general quicker. The reason why
less urine and cellular mucus is absorbed after a full meal with sufficient
drink is owing to the blood-vessels being fuller: hence one means to
promote absorption is to decrease the resistance by emptying the vessels by
venesection. From this decreased absorption the urine becomes pale as well
as copious, and the skin appears plump as well as florid.

By daily repetition of these movements they all become connected together,
and make a diurnal circle of irritative action, and if one of this chain be
disturbed, the whole is liable to be put into disorder. See Sect. XX. on
Vertigo.

5. When the stomach and intestines receive a quantity of food, whose
stimulus is greater than usual, all their motions, and those of the glands
and lymphatics, are stimulated into stronger action than usual, and perform
their offices with greater vigour and in less time: such are the effects of
certain quantities of spice or of vinous spirit.

6. But if the quantity or duration of these stimuli are still further
increased, the stomach and throat are stimulated into a motion, whose
direction is contrary to the natural one above described; and they
regurgitate the materials, which they contain, instead of carrying them
forwards. This retrograde motion of the stomach may be compared to the
stretchings of wearied limbs the contrary way, and is well elucidated by
the following experiment. Look earnestly for a minute or two on an area an
inch square of pink silk, placed in a strong light, the eye becomes
fatigued, the colour becomes faint, and at length vanishes, for the
fatigued eye can no longer be stimulated into direct motions; then on
closing the eye a green spectrum will appear in it, which is a colour
directly contrary to pink, and which will appear and disappear repeatedly,
like the efforts in vomiting. See Section XXIX. 11.

Hence all those drugs, which by their bitter or astringent stimulus
increase the action of the stomach, as camomile and white vitriol, if their
quantity is increased above a certain dose become emetics.

These inverted motions of the stomach and throat are generally produced
from the stimulus of unnatural food, and are attended with the sensation of
nausea or sickness: but as this sensation is again connected with an idea
of the distasteful food, which induced it; so an idea of nauseous food will
also sometimes excite the action of nausea; and that give rise by
association to the inversion of the motions of the stomach and throat. As
some, who have had horse-flesh or dogs-flesh given them for beef or mutton,
are said to have vomited many hours afterwards, when they have been told of
the imposition.

I have been told of a person, who had gained a voluntary command over these
inverted motions of the stomach and throat, and supported himself by
exhibiting this curiosity to the public. At these exhibitions he swallowed
a pint of red rough gooseberries, and a pint of white smooth ones, brought
them up in small parcels into his mouth, and restored them separately to
the spectators, who called for red or white as they pleased, till the whole
were redelivered.

7. At the same time that these motions of the stomach and throat are
stimulated into inversion, some of the other irritative motions, that had
acquired more immediate connexions with the stomach, as those of the
gastric glands, are excited into stronger action by this association; and
some other of these motions, which are more easily excited, as those of the
gastric lymphatics, are inverted by their association with the retrograde
motions of the stomach, and regurgitate their contents, and thus a greater
quantity of mucus, and of lymph, or chyle, is poured into the stomach, and
thrown up along with its contents.

8. These inversions of the motion of the stomach in vomiting are performed
by intervals, for the same reason that many other motions are reciprocally
exerted and relaxed; for during the time of exertion the stimulus, or
sensation, which caused this exertion, is not perceived; but begins to be
perceived again, as soon as the exertion ceases, and is some time in again
producing its effect. As explained in Sect. XXXIV. on Volition, where it is
shewn, that the contractions of the fibres, and the sensation of pain,
which occasioned that exertion, cannot exist at the same time. The exertion
ceases from another cause also, which is the exhaustion of the sensorial
power of the part, and these two causes frequently operate together.

9. At the times of these inverted efforts of the stomach not only the
lymphatics, which open their mouths into the stomach, but those of the skin
also, are for a time inverted; for sweats are sometimes pushed out during
the efforts of vomiting without an increase of heat.

10. But if by a greater stimulus the motions of the stomach are inverted
still more violently or more permanently, the duodenum has its peristaltic
motions inverted at the same time by their association with those of the
stomach; and the bile and pancreatic juice, which it contains, are by the
inverted motions brought up into the stomach, and discharged along with its
contents; while a greater quantity of bile and pancreatic juice is poured
into this intestine; as the glands, that secrete them, are by their
association with the motions of the intestine excited into stronger action
than usual.

11. The other intestines are by association excited into more powerful
action, while the lymphatics, that open their mouths into them, suffer an
inversion of their motions corresponding with the lymphatics of the
stomach, and duodenum; which with a part of the abundant secretion of bile
is carried downwards, and contributes both to stimulate the bowels, and to
increase the quantity of the evacuations. This inversion of the motion of
the lymphatics appears from the quantity of chyle, which comes away by
stools; which is otherwise absorbed as soon as produced, and by the immense
quantity of thin fluid, which is evacuated along with it.

12. But if the stimulus, which inverts the stomach, be still more powerful,
or more permanent, it sometimes happens, that the motions of the biliary
glands, and of their excretory ducts, are at the same time inverted, and
regurgitate their contained bile into the blood-vessels, as appears by the
yellow colour of the skin, and of the urine; and it is probable the
pancreatic secretion may suffer an inversion at the same time, though we
have yet no mark by which this can be ascertained.

13. Mr. ---- eat two putrid pigeons out of a cold pigeon-pye, and drank
about a pint of beer and ale along with them, and immediately rode about
five miles. He was then seized with vomiting, which was after a few periods
succeeded by purging; these continued alternately for two hours; and the
purging continued by intervals for six or eight hours longer. During this
time he could not force himself to drink more than one pint in the whole;
this great inability to drink was owing to the nausea, or inverted motions
of the stomach, which the voluntary exertion of swallowing could seldom and
with difficulty overcome; yet he discharged in the whole at least six
quarts; whence came this quantity of liquid? First, the contents of the
stomach were emitted, then of the duodenum, gall-bladder, and pancreas, by
vomiting. After this the contents of the lower bowels, then the chyle, that
was in the lacteal vessels, and in the receptacle of chyle, was
regurgitated into the intestines by a retrograde motion of these vessels.
And afterwards the mucus deposited in the cellular membrane, and on the
surface of all the other membranes, seems to have been absorbed; and with
the fluid absorbed from the air to have been carried up their respective
lymphatic branches by the increased energy of their natural motions, and
down the visceral lymphatics, or lacteals, by the inversion of their
motions.

14. It may be difficult to invent experiments to demonstrate the truth of
this inversion of some branches of the absorbent system, and increased
absorption of others, but the analogy of these vessels to the intestinal
canal, and the symptoms of many diseases, render this opinion more probable
than many other received opinions of the animal oeconomy.

In the above instance, after the yellow excrement was voided, the fluid
ceased to have any smell, and appeared like curdled milk, and then a
thinner fluid, and some mucus, were evacuated; did not these seem to
partake of the chyle, of the mucous fluid from all the cells of the body,
and lastly, of the atmospheric moisture? All these facts may be easily
observed by any one, who takes a brisk purge.

15. Where the stimulus on the stomach, or on some other part of the
intestinal canal, is still more permanent, not only the lacteal vessels,
but the whole canal itself, becomes inverted from its associations: this is
the iliac passion, in which all the fluids mentioned above are thrown up by
the mouth. At this time the valve in the colon, from the inverted motions
of that bowel, and the inverted action of this living valve, does not
prevent the regurgitation of its contents.

The structure of this valve may be represented by a flexile leathern pipe
standing up from the bottom of a vessel of water: its sides collapse by the
pressure of the ambient fluid, as a small part of that fluid passes through
it; but if it has a living power, and by its inverted action keeps itself
open, it becomes like a rigid pipe, and will admit the whole liquid to
pass. See Sect. XXIX. 2. 5.

In this case the patient is averse to drink, from the constant inversion of
the motions of the stomach, and yet many quarts are daily ejected from the
stomach, which at length smell of excrement, and at last seem to be only a
thin mucilaginous or aqueous liquor.

From whence is it possible, that this great quantity of fluid for many
successive days can be supplied, after the cells of the body have given up
their fluids, but from the atmosphere? When the cutaneous branch of
absorbents acts with unnatural strength, it is probable the intestinal
branch has its motions inverted, and thus a fluid is supplied without
entering the arterial system. Could oiling or painting the skin give a
check to this disease?

So when the stomach has its motions inverted, the lymphatics of the
stomach, which are most strictly associated with it, invert their motions
at the same time. But the more distant branches of lymphatics, which are
less strictly associated with it, act with increased energy; as the
cutaneous lymphatics in the cholera, or iliac passion, above described. And
other irritative motions become decreased, as the pulsations of the
arteries, from the extra-derivation or exhaustion of the sensorial power.

Sometimes when stronger vomiting takes place the more distant branches of
the lymphatic system invert their motions with those of the stomach, and
loose stools are produced, and cold sweats.

So when the lacteals have their motions inverted, as during the operation
of strong purges, the urinary and cutaneous absorbents have their motions
increased to supply the want of fluid in the blood, as in great thirst; but
after a meal with sufficient potation the urine is pale, that is, the
urinary absorbents act weakly, no supply of water being wanted for the
blood. And when the intestinal absorbents act too violently, as when too
great quantities of fluid have been drank, the urinary absorbents invert
their motions to carry off the superfluity, which is a new circumstance of
association, and a temporary diabetes supervenes.

16. I have had the opportunity of seeing four patients in the iliac
passion, where the ejected material smelled and looked like excrement. Two
of these were so exhausted at the time I saw them, that more blood could
not be taken from them, and as their pain had ceased, and they continued to
vomit up every thing which they drank, I suspected that a mortification of
the bowel had already taken place, and as they were both women advanced in
life, and a mortification is produced with less preceding pain in old and
weak people, these both died. The other two, who were both young men, had
still pain and strength sufficient for further venesection, and they
neither of them had any appearance of hernia, both recovered by repeated
bleeding, and a scruple of calomel given to one, and half a dram to the
other, in very small pills: the usual means of clysters, and purges joined
with opiates, had been in vain attempted. I have thought an ounce or two of
crude mercury in less violent diseases of this kind has been of use, by
contributing to restore its natural motion to some part of the intestinal
canal, either by its weight or stimulus; and that hence the whole tube
recovered its usual associations of progressive peristaltic motion. I have
in three cases seen crude mercury given in small doses, as one or two
ounces twice a day, have great effect in stopping pertinacious vomitings.

17. Besides the affections above described, the stomach is liable, like
many other membranes of the body, to torpor without consequent
inflammation: as happens to the membranes about the head in some cases of
hemicrania, or in general head-ach. This torpor of the stomach is attended
with indigestion, and consequent flatulency, and with pain, which is
usually called the cramp of the stomach, and is relievable by aromatics,
essential oils, alcohol, or opium.

The intrusion of a gall-stone into the common bile-duct from the
gall-bladder is sometimes mistaken for a pain of the stomach, as neither of
them are attended with fever; but in the passage of a gall-stone, the pain
is confined to a less space, which is exactly where the common bile-duct
enters the duodenum, as explained in Section XXX. 1. 3. Whereas in this
gastrodynia the pain is diffused over the whole stomach; and, like other
diseases from torpor, the pulse is weaker, and the extremities colder, and
the general debility greater, than in the passage of a gall-stone; for in
the former the debility is the consequence of the pain, in the latter it is
the cause of it.

Though the first fits of the gout, I believe, commence with a torpor of the
liver; and the ball of the toe becomes inflamed instead of the membranes of
the liver in consequence of this torpor, as a coryza or catarrh frequently
succeeds a long exposure of the feet to cold, as in snow, or on a moist
brick-floor; yet in old or exhausted constitutions, which have been long
habituated to its attacks, it sometimes commences with a torpor of the
stomach, and is transferable to every membrane of the body. When the gout
begins with torpor of the stomach, a painful sensation of cold occurs,
which the patient compares to ice, with weak pulse, cold extremities, and
sickness; this in its slighter degree is relievable by spice, wine, or
opium; in its greater degree it is succeeded by sudden death, which is
owing to the sympathy of the stomach with the heart, as explained below.

If the stomach becomes inflamed in consequence of this gouty torpor of it,
or in consequence of its sympathy with some other part, the danger is less.
A sickness and vomiting continues many days, or even weeks, the stomach
rejecting every thing stimulant, even opium or alcohol, together with much
viscid mucus; till the inflammation at length ceases, as happens when other
membranes, as those of the joints, are the seat of gouty inflammation; as
observed in Sect. XXIV. 2. 8.

The sympathy, or association of motions, between those of the stomach and
those of the heart, are evinced in many diseases. First, many people are
occasionally affected with an intermission of their pulse for a few days,
which then ceases again. In this case there is a stop of the motion of the
heart, and at the same time a tendency to eructation from the stomach. As
soon as the patient feels a tendency to the intermission of the motion of
his heart, if he voluntarily brings up wind from his stomach, the stop of
the heart does not occur. From hence I conclude that the stop of digestion
is the primary disease; and that air is instantly generated from the
aliment, which begins to ferment, if the digestive process is impeded for a
moment, (see Sect. XXIII. 4.); and that the stop of the heart is in
consequence of the association of the motions of these viscera, as
explained in Sect. XXXV. 1. 4.; but if the little air, which is instantly
generated during the temporary torpor of the stomach, be evacuated, the
digestion recommences, and the temporary torpor of the heart does not
follow. One patient, whom I lately saw, and who had been five or six days
much troubled with this intermission of a pulsation of his heart, and who
had hemicrania with some fever, was immediately relieved from them all by
losing ten ounces of blood, which had what is termed an inflammatory crust
on it.

Another instance of this association between the motions of the stomach and
heart is evinced by the exhibition of an over dose of foxglove, which
induces an incessant vomiting, which is attended with very slow, and
sometimes intermitting pulse.--Which continues in spite of the exhibition
of wine and opium for two or three days. To the same association must be
ascribed the weak pulse, which constantly attends the exhibition of emetics
during their operation. And also the sudden deaths, which have been
occasioned in boxing by a blow on the stomach; and lastly, the sudden death
of those, who have been long debilitated by the gout, from the torpor of
the stomach. See Sect. XXXV. 1. 4.

       *       *       *       *       *

SECT. XXVI.

OF THE CAPILLARY GLANDS AND MEMBRANES.

    I. 1. _The capillary vessels are glands._ 2. _Their excretory ducts.
    Experiments on the mucus of the intestines, abdomen, cellular membrane,
    and on the humours of the eye._ 3. _Scurf on the head, cough, catarrh,
    diarrhoea, gonorrhoea._ 4. _Rheumatism. Gout. Leprosy._ II. 1. _The
    most minute membranes are unorganized._ 2. _Larger membranes are
    composed of the ducts of the capillaries, and the mouths of the
    absorbents._ 3. _Mucilaginous fluid is secreted on their surfaces._
    III. _Three kinds of rheumatism._

I. 1. The capillary-vessels are like all the other glands except the
absorbent system, inasmuch as they receive blood from the arteries,
separate a fluid from it, and return the remainder by the veins.

2. This series of glands is of the most extensive use, as their excretory
ducts open on the whole external skin forming its perspirative pores, and
on the internal surfaces of every cavity of the body. Their secretion on
the skin is termed insensible perspiration, which in health is in part
reabsorbed by the mouths of the lymphatics, and in part evaporated in the
air; the secretion on the membranes, which line the larger cavities of the
body, which have external openings, as the mouth and intestinal canal, is
termed mucus, but is not however coagulable by heat; and the secretion on
the membranes of those cavities of the body, which have no external
openings, is called lymph or water, as in the cavities of the cellular
membrane, and of the abdomen; this lymph however is coagulable by the heat
of boiling water. Some mucus nearly as viscid as the white of egg, which
was discharged by stool, did not coagulate, though I evaporated it to one
fourth of the quantity, nor did the aqueous and vitreous humours of a
sheep's eye coagulate by the like experiment: but the serosity from an
anasarcous leg, and that from the abdomen of a dropsical person, and the
crystalline humour of a sheep's eye, coagulated in the same heat.

3. When any of these capillary glands are stimulated into greater
irritative actions, than is natural, they secrete a more copious material;
and as the mouths of the absorbent system, which open in their vicinity,
are at the same time stimulated into greater action, the thinner and more
saline part of the secreted fluid is taken up again; and the remainder is
not only more copious but also more viscid than natural. This is more or
less troublesome or noxious according to the importance of the functions of
the part affected: on the skin and bronchiæ, where this secretion ought
naturally to evaporate, it becomes so viscid as to adhere to the membrane;
on the tongue it forms a pellicle, which can with difficulty be scraped
off; produces the scurf on the heads of many people; and the mucus, which
is spit up by others in coughing. On the nostrils and fauces, when the
secretion of these capillary glands is increased, it is termed simple
catarrh; when in the intestines, a mucous diarrhoea; and in the urethra, or
vagina, it has the name of gonorrhoea, or fluor albus.

4. When these capillary glands become inflamed, a still more viscid or even
cretaceous humour is produced upon the surfaces of the membranes, which is
the cause or the effect of rheumatism, gout, leprosy, and of hard tumours
of the legs, which are generally termed scorbutic; all which will be
treated of hereafter.

II. 1. The whole surface of the body, with all its cavities and contents,
are covered with membrane. It lines every vessel, forms every cell, and
binds together all the muscular and perhaps the osseous fibres of the body;
and is itself therefore probably a simpler substance than those fibres. And
as the containing vessels of the body from the largest to the least are
thus lined and connected with membranes, it follows that these membranes
themselves consisted of unorganized materials.

For however small we may conceive the diameters of the minutest vessels of
the body, which escape our eyes and glasses, yet these vessels must consist
of coats or sides, which are made up of an unorganized material, and which
are probably produced from a gluten, which hardens after its production,
like the silk or web of caterpillars and spiders. Of this material consist
the membranes, which line the shells of eggs, and the shell itself, both
which are unorganized, and are formed from mucus, which hardens after it is
formed, either by the absorption of its more fluid part, or by its uniting
with some part of the atmosphere. Such is also the production of the shells
of snails, and of shell-fish, and I suppose of the enamel of the teeth.

2. But though the membranes, that compose the sides of the most minute
vessels, are in truth unorganized materials, yet the larger membranes,
which are perceptible to the eye, seem to be composed of an intertexture of
the mouths of the absorbent system, and of the excretory ducts of the
capillaries, with their concomitant arteries, veins, and nerves: and from
this construction it is evident, that these membranes must possess great
irritability to peculiar stimuli, though they are incapable of any motions,
that are visible to the naked eye: and daily experience shews us, that in
their inflamed state they have the greatest sensibility to pain, as in the
pleurisy and paronychia.

3. On all these membranes a mucilaginous or aqueous fluid is secreted,
which moistens and lubricates their surfaces, as was explained in Section
XXIII. 2. Some have doubted, whether this mucus is separated from the blood
by an appropriated set of glands, or exudes through the membranes, or is an
abrasion or destruction of the surface of the membrane itself, which is
continually repaired on the other side of it, but the great analogy between
the capillary vessels, and the other glands, countenances the former
opinion; and evinces, that these capillaries are the glands, that secrete
it; to which we must add, that the blood in passing these capillary vessels
undergoes a change in its colour from florid to purple, and gives out a
quantity of heat; from whence, as in other glands, we must conclude that
something is secreted from it.

III. The seat of rheumatism is in the membranes, or upon them; but there
are three very distinct diseases, which commonly are confounded under this
name. First, when a membrane becomes affected with torpor, or inactivity of
the vessels which compose it, pain and coldness succeed, as in the
hemicrania, and other head-achs, which are generally termed nervous
rheumatism; they exist whether the part be at rest or in motion, and are
generally attended with other marks of debility.

Another rheumatism is said to exist, when inflammation and swelling, as
well as pain, affect some of the membranes of the joints, as of the ancles,
wrists, knees, elbows, and sometimes of the ribs. This is accompanied with
fever, is analogous to pleurisy and other inflammations, and is termed the
acute rheumatism.

A third disease is called chronic rheumatism, which is distinguished from
that first mentioned, as in this the pain only affects the patient during
the motion of the part, and from the second kind of rheumatism above
described, as it is not attended with quick pulse or inflammation. It is
generally believed to succeed the acute rheumatism of the same part, and
that some coagulable lymph, or cretaceous, or calculous material, has been
left on the membrane; which gives pain, when the muscles move over it, as
some extraneous body would do, which was too insoluble to be absorbed.
Hence there is an analogy between this chronic rheumatism and the diseases
which produce gravel or gout-stones; and it may perhaps receive relief from
the same remedies, such as aerated sal soda.

       *       *       *       *       *

SECT. XXVII.

OF HÆMORRHAGES.

    I. _The veins are absorbent vessels._ 1. _Hæmorrhages from
    inflammation. Case of hæmorrhage from the kidney cured by cold bathing.
    Case of hæmorrhage from the nose cured by cold immersion._ II.
    _Hæmorrhage from venous paralysis. Of Piles. Black stools. Petechiæ.
    Consumption. Scurvy of the lungs. Blackness of the face and eyes in
    epileptic fits. Cure of hæmorrhages from venous inability._

I. As the imbibing mouths of the absorbent system already described open on
the surface, and into the larger cavities of the body, so there is another
system of absorbent vessels, which are not commonly esteemed such, I mean
the veins, which take up the blood from the various glands and capillaries,
after their proper fluids or secretions have been separated from it.

The veins resemble the other absorbent vessels; as the progression of their
contents is carried on in the same manner in both, they alike absorb their
appropriated fluids, and have valves to prevent its regurgitation by the
accidents of mechanical violence. This appears first, because there is no
pulsation in the very beginnings of the veins, as is seen by microscopes;
which must happen, if the blood was carried into them by the actions of the
arteries. For though the concurrence of various venous streams of blood
from different distances must prevent any pulsation in the larger branches,
yet in the very beginnings of all these branches a pulsation must
unavoidably exist, if the circulation in them was owing to the intermitted
force of the arteries. Secondly, the venous absorption of blood from the
penis, and from the teats of female animals after their erection, is still
more similar to the lymphatic absorption, as it is previously poured into
cells, where all arterial impulse must cease.

There is an experiment, which seems to evince this venous absorption, which
consists in the external application of a stimulus to the lips, as of
vinegar, by which they become instantly pale; that is, the bibulous mouths
of the veins by this stimulus are excited to absorb the blood faster, than
it can be supplied by the usual arterial exertion. See Sect. XXIII. 5.

There are two kinds of hæmorrhages frequent in diseases, one is where the
glandular or capillary action is too powerfully exerted, and propels the
blood forwards more hastily, than the veins can absorb it; and the other
is, where the absorbent power of the veins is diminished, or a branch of
them is become totally paralytic.

1. The former of these cases is known by the heat of the part, and the
general fever or inflammation that accompanies the hæmorrhage. An
hæmorrhage from the nose or from the lungs is sometimes a crisis of
inflammatory diseases, as of the hepatitis and gout, and generally ceases
spontaneously, when the vessels are considerably emptied. Sometimes the
hæmorrhage recurs by daily periods accompanying the hot fits of fever, and
ceasing in the cold fits, or in the intermissions; this is to be cured by
removing the febrile paroxysms, which will be treated of in their place.
Otherwise it is cured by venesection, by the internal or external
preparations of lead, or by the application of cold, with an abstemious
diet, and diluting liquids, like other inflammations. Which by inducing a
quiescence on those glandular parts, that are affected, prevents a greater
quantity of blood from being protruded forwards, than the veins are capable
of absorbing.

Mr. B---- had an hæmorrhage from his kidney, and parted with not less than
a pint of blood a day (by conjecture) along with his urine for above a
fortnight: venesections, mucilages, balsams, preparations of lead, the
bark, alum, and dragon's blood, opiates, with a large blister on his loins,
were separately tried, in large doses, to no purpose. He was then directed
to bathe in a cold spring up to the middle of his body only, the upper part
being covered, and the hæmorrhage diminished at the first, and ceased at
the second immersion.

In this case the external capillaries were rendered quiescent by the
coldness of the water, and thence a less quantity of blood was circulated
through them; and the internal capillaries, or other glands, became
quiescent from their irritative associations with the external ones; and
the hæmorrhage was stopped a sufficient time for the ruptured vessels to
contract their apertures, or for the blood in those apertures to coagulate.

Mrs. K---- had a continued haemorrhage from her nose for some days; the
ruptured vessel was not to be reached by plugs up the nostrils, and the
sensibility of her fauces was such that nothing could be born behind the
uvula. After repeated venesection, and other common applications, she was
directed to immerse her whole head into a pail of water, which was made
colder by the addition of several handfuls of salt, and the hæmorrhage
immediately ceased, and returned no more; but her pulse continued hard, and
she was necessitated to lose blood from the arm on the succeeding day.

Query, might not the cold bath instantly stop hæmorrhages from the lungs in
inflammatory cases?--for the shortness of breath of those, who go suddenly
into cold water, is not owing to the accumulation of blood in the lungs,
but to the quiescence of the pulmonary capillaries from association, as
explained in Section XXXII. 3. 2.

II. The other kind of hæmorrhage is known from its being attended with a
weak pulse, and other symptoms of general debility, and very frequently
occurs in those, who have diseased livers, owing to intemperance in the use
of fermented liquors. These constitutions are shewn to be liable to
paralysis of the lymphatic absorbents, producing the various kinds of
dropsies in Section XXIX. 5. Now if any branch of the venous system loses
its power of absorption, the part swells, and at length bursts and
discharges the blood, which the capillaries or other glands circulate
through them.

It sometimes happens that the large external veins of the legs burst, and
effuse their blood; but this occurs most frequently in the veins of the
intestines, as the vena portarum is liable to suffer from a schirrus of the
liver opposing the progression of the blood, which is absorbed from the
intestines. Hence the piles are a symptom of hepatic obstruction, and hence
the copious discharges downwards or upwards of a black material, which has
been called melancholia, or black bile; but is no other than the blood,
which is probably discharged from the veins of the intestines.

J.F. Meckel, in his Experimenta de Finibus Vasorum, published at Berlin,
1772, mentions his discovery of a communication of a lymphatic vessel with
the gastric branch of the vena portarum. It is possible, that when the
motion of the lymphatic becomes retrograde in some diseases, that blood may
obtain a passage into it, where it anastomoses with the vein, and thus be
poured into the intestines. A discharge of blood with the urine sometimes
attends diabetes, and may have its source in the same manner.

Mr. A----, who had been a hard drinker, and had the gutta rosacea on his
face and breast, after a stroke of the palsy voided near a quart of a black
viscid material by stool: on diluting it with water it did not become
yellow, as it must have done if it had been inspissated bile, but continued
black like the grounds of coffee.

But any other part of the venous system may become quiescent or totally
paralytic as well as the veins of the intestines: all which occur more
frequently in those who have diseased livers, than in any others. Hence
troublesome bleedings of the nose, or from the lungs with a weak pulse;
hence hæmorrhages from the kidneys, too great menstruation; and hence the
oozing of blood from every part of the body, and the petechiæ in those
fevers, which are termed putrid, and which is erroneously ascribed to the
thinness of the blood: for the blood in inflammatory diseases is equally
fluid before it coagulates in the cold air.

Is not that hereditary consumption, which occurs chiefly in dark-eyed
people about the age of twenty, and commences with slight pulmonary
hæmorrhages without fever, a disease of this kind?--These hæmorrhages
frequently begin during sleep, when the irritability of the lungs is not
sufficient in these patients to carry on the circulation without the
assistance of volition; for in our waking hours, the motions of the lungs
are in part voluntary, especially if any difficulty of breathing renders
the efforts of volition necessary. See Class I. 2. 1. 3. and Class III. 2.
1. 12. Another species of pulmonary consumption which seems more certainly
of scrophulous origin is described in the next Section, No. 2.

I have seen two cases of women, of about forty years of age, both of whom
were seized with quick weak pulse, with difficult respiration, and who spit
up by coughing much viscid mucus mixed with dark coloured blood. They had
both large vibices on their limbs, and petechiæ; in one the feet were in
danger of mortification, in the other the legs were oedematous. To relieve
the difficult respiration, about six ounces of blood were taken from one of
them, which to my surprise was sizy, like inflamed blood: they had both
palpitations or unequal pulsations of the heart. They continued four or
five weeks with pale and bloated countenances, and did not cease spitting
phlegm mixed with black blood, and the pulse seldom slower than 130 or 135
in a minute. This blood, from its dark colour, and from the many vibices
and petechiæ, seems to have been venous blood; the quickness of the pulse,
and the irregularity of the motion of the heart, are to be ascribed to
debility of that part of the system; as the extravasation of blood
originated from the defect of venous absorption. The approximation of these
two cases to sea-scurvy is peculiar, and may allow them to be called
scorbutus pulmonalis. Had these been younger subjects, and the paralysis of
the veins had only affected the lungs, it is probable the disease would
have been a pulmonary consumption.

Last week I saw a gentleman of Birmingham, who had for ten days laboured
under great palpitation of his heart, which was so distinctly felt by the
hand, as to discountenance the idea of there being a fluid in the
pericardium. He frequently spit up mucus stained with dark coloured blood,
his pulse very unequal and very weak, with cold hands and nose. He could
not lie down at all, and for about ten days past could not sleep a minute
together, but waked perpetually with great uneasiness. Could those symptoms
be owing to very extensive adhesions of the lungs? or is this a scorbutus
pulmonalis? After a few days he suddenly got so much better as to be able
to sleep many hours at a time by the use of one grain of powder of foxglove
twice a day, and a grain of opium at night. After a few days longer, the
bark was exhibited, and the opium continued with some wine; and the
palpitations of his heart became much relieved, and he recovered his usual
degree of health, but died suddenly some months afterwards.

In epileptic fits the patients frequently become black in the face, from
the temporary paralysis of the venous system of this part. I have known two
instances where the blackness has continued many days. M. P----, who had
drank intemperately, was seized with the epilepsy when he was in his
fortieth year; in one of these fits the white part of his eyes was left
totally black with effused blood; which was attended with no pain or heat,
and was in a few weeks gradually absorbed, changing colour as is usual with
vibices from bruises.

The hæmorrhages produced from the inability of the veins to absorb the
refluent blood, is cured by opium, the preparations of steel, lead, the
bark, vitriolic acid, and blisters; but these have the effect with much
more certainty, if a venesection to a few ounces, and a moderate cathartic
with four or six grains of calomel be premised, where the patient is not
already too much debilitated; as one great means of promoting the
absorption of any fluid consists in previously emptying the vessels, which
are to receive it.

       *       *       *       *       *

SECT. XXVIII.

OF THE PARALYSIS OF THE ABSORBENT SYSTEM.

    I. _Paralysis of the lacteals, atrophy. Distaste to animal food._ II.
    _Cause of dropsy. Cause of herpes. Scrophula. Mesenteric consumption.
    Pulmonary consumption. Why ulcers in the lungs are so difficult to
    heal._

The term paralysis has generally been used to express the loss of voluntary
motion, as in the hemiplagia, but may with equal propriety be applied to
express the disobediency of the muscular fibres to the other kinds of
stimulus; as to those of irritation or sensation.

I. There is a species of atrophy, which has not been well understood; when
the absorbent vessels of the stomach and intestines have been long inured
to the stimulus of too much spirituous liquor, they at length, either by
the too sudden omission of fermented or spirituous potation, or from the
gradual decay of nature, become in a certain degree paralytic; now it is
observed in the larger muscles of the body, when one side is paralytic, the
other is more frequently in motion, owing to the less expenditure of
sensorial power in the paralytic limbs; so in this case the other part of
the absorbent system acts with greater force, or with greater perseverance,
in consequence of the paralysis of the lacteals; and the body becomes
greatly emaciated in a small time.

I have seen several patients in this disease, of which the following are
the circumstances. 1. They were men about fifty years of age, and had lived
freely in respect to fermented liquors. 2. They lost their appetite to
animal food. 3. They became suddenly emaciated to a great degree. 4. Their
skins were dry and rough. 5. They coughed and expectorated with difficulty
a viscid phlegm. 6. The membrane of the tongue was dry and red, and liable
to become ulcerous.

The inability to digest animal food, and the consequent distaste to it,
generally precedes the dropsy, and other diseases, which originate from
spirituous potation. I suppose when the stomach becomes inirritable, that
there is at the same time a deficiency of gastric acid; hence milk seldom
agrees with these patients, unless it be previously curdled, as they have
not sufficient gastric acid to curdle it; and hence vegetable food, which
is itself acescent, will agree with their stomachs longer than animal food,
which requires more of the gastric acid for its digestion.

In this disease the skin is dry from the increased absorption of the
cutaneous lymphatics, the fat is absorbed from the increased absorption of
the cellular lymphatics, the mucus of the lungs is too viscid to be easily
spit up by the increased absorption of the thinner parts of it, the
membrana sneideriana becomes dry, covered with hardened mucus, and at
length becomes inflamed and full of aphthæ, and either these sloughs, or
pulmonary ulcers, terminate the scene.

II. The immediate cause of dropsy is the paralysis of some other branches
of the absorbent system, which are called lymphatics, and which open into
the larger cavities of the body, or into the cells of the cellular
membrane; whence those cavities or cells become distended with the fluid,
which is hourly secreted into them for the purpose of lubricating their
surfaces. As is more fully explained in No. 5. of the next Section.

As those lymphatic vessels consist generally of a long neck or mouth, which
drinks up its appropriated fluid, and of a conglobate gland, in which this
fluid undergoes some change, it happens, that sometimes the mouth of the
lymphatic, and sometimes the belly or glandular part of it, becomes totally
or partially paralytic. In the former case, where the mouths of the
cutaneous lymphatics become torpid or quiescent, the fluid secreted on the
skin ceases to be absorbed, and erodes the skin by its saline acrimony, and
produces eruptions termed herpes, the discharge from which is as salt, as
the tears, which are secreted too fast to be reabsorbed, as in grief, or
when the puncta lacrymalia are obstructed, and which running down the cheek
redden and inflame the skin.

When the mouths of the lymphatics, which open on the mucous membrane of the
nostrils, become torpid, as on walking into the air in a frosty morning;
the mucus, which continues to be secreted, has not its aqueous and saline
part reabsorbed, which running over the upper lip inflames it, and has a
salt taste, if it falls on the tongue.

When the belly, or glandular part of these lymphatics, becomes torpid, the
fluid absorbed by its mouth stagnates, and forms a tumour in the gland.
This disease is called the scrophula. If these glands suppurate externally,
they gradually heal, as those of the neck; if they suppurate without an
opening on the external habit, as the mesenteric glands, a hectic fever
ensues, which destroys the patient; if they suppurate in the lungs, a
pulmonary consumption ensues, which is believed thus to differ from that
described in the preceding Section, in respect to its seat or proximate
cause.

It is remarkable, that matter produced by suppuration will lie concealed in
the body many weeks, or even months, without producing hectic fever; but as
soon as the wound is opened, so as to admit air to the surface of the
ulcer, a hectic fever supervenes, even in very few hours, which is probably
owing to the azotic part of the atmosphere rather than to the oxygene;
because those medicines, which contain much oxygene, as the calces or
oxydes of metals, externally applied, greatly contribute to heal ulcers, of
these are the solutions of lead and mercury, and copper in acids, or their
precipitates.

Hence when wounds are to be healed by the first intention, as it is called,
it is necessary carefully to exclude the air from them. Hence we have one
cause, which prevents pulmonary ulcers from healing, which is their being
perpetually exposed to the air.

Both the dark-eyed patients, which are affected with pulmonary ulcers from
deficient venous absorption, as described in Section. XXVII. 2. and the
light-eyed patients from deficient lymphatic absorption, which we are now
treating of, have generally large apertures of the iris; these large pupils
of the eyes are a common mark of want of irritability; and it generally
happens, that an increase of sensibility, that is, of motions in
consequence of sensation, attends these constitutions. See Sect. XXXI. 2.
Whence inflammations may occur in these from stagnated fluids more
frequently than in those constitutions, which possess more irritability and
less sensibility.

Great expectations in respect to the cure of consumptions, as well as of
many other diseases, are produced by the very ingenious exertions of DR.
BEDDOES; who has established an apparatus for breathing various mixtures of
airs or gasses, at the hot-wells near Bristol, which well deserves the
attention of the public.

DR. BEDDOES very ingeniously concludes, from the florid colour of the blood
of consumptive patients, that it abounds in oxygene; and that the redness
of their tongues, and lips, and the fine blush of their cheeks shew the
presence of the same principle, like flesh reddened by nitre. And adds,
that the circumstance of the consumptions of pregnant women being stopped
in their progress during pregnancy, at which time their blood may be
supposed to be in part deprived of its oxygene, by oxygenating the blood of
the foetus, is a forceable argument in favour of this theory; which must
soon be confirmed or confuted by his experiments. See Essay on Scurvy,
Consumption, &c. by Dr. Beddoes. Murray. London. Also Letter to Dr. Darwin,
by the same. Murray. London.

       *       *       *       *       *

SECT. XXIX.

ON THE RETROGRADE MOTIONS OF THE ABSORBENT SYSTEM.

    I. _Account of the absorbent system._ II. _The valves of the absorbent
    vessels may suffer their fluids to regurgitate in some diseases._ III.
    _Communication from the alimentary canal to the bladder by means of the
    absorbent vessels._ IV. _The phenomena of diabetes explained._ V. 1.
    _The phenomena of dropsies explained._ 2. _Cases of the use of
    foxglove._ VI. _Of cold sweats._ VII. _Translations of matter, of
    chyle, of milk, of urine, operation of purging drugs applied
    externally._ VIII. _Circumstances by which the fluids, that are effused
    by the retrograde motions of the absorbent vessels, are distinguished._
    IX. _Retrograde motions of vegetable juices._ X. _Objections answered._
    XI. _The causes, which induce the retrograde motions of animal vessels,
    and the medicines by which the natural motions are restored._

    _N.B. The following Section is a translation of a part of a Latin
    thesis written by the late Mr. Charles Darwin, which was printed with
    his prize-dissertation on a criterion between matter and mucus in 1780.
    Sold by Cadell, London._

I. _Account of the Absorbent System._

1. The absorbent system of vessels in animal bodies consists of several
branches, differing in respect to their situations, and to the fluids,
which they absorb.

The intestinal absorbents open their mouths on the internal surfaces of the
intestines; their office is to drink up the chyle and the other fluids from
the alimentary canal; and they are termed lacteals, to distinguish them
from the other absorbent vessels, which have been termed lymphatics.

Those, whose mouths are dispersed on the external skin, imbibe a great
quantity of water from the atmosphere, and a part of the perspirable
matter, which does not evaporate, and are termed cutaneous absorbents.

Those, which arise from the internal surface of the bronchia, and which
imbibe moisture from the atmosphere, and a part of the bronchial mucus, are
called pulmonary absorbents.

Those, which open their innumerable mouths into the cells of the whole
cellular membrane; and whose use is to take up the fluid, which is poured
into those cells, after it has done its office there; may be called
cellular absorbents.

Those, which arise from the internal surfaces of the membranes, which line
the larger cavities of the body, as the thorax, abdomen, scrotum,
pericardium, take up the mucus poured into those cavities; and are
distinguished by the names of their respective cavities.

Whilst those, which arise from the internal surfaces of the urinary
bladder, gall-bladder, salivary ducts, or other receptacles of secreted
fluids, may take their names from those fluids; the thinner parts of which
it is their office to absorb: as urinary, bilious, or salivary absorbents.

2. Many of these absorbent vessels, both lacteals and lymphatics, like some
of the veins, are replete with valves: which seem designed to assist the
progress of their fluids, or at least to prevent their regurgitation; where
they are subjected to the intermitted pressure of the muscular, or arterial
actions in their neighbourhood.

These valves do not however appear to be necessary to all the absorbents,
any more than to all the veins; since they are not found to exist in the
absorbent system of fish; according to the discoveries of the ingenious,
and much lamented Mr. Hewson. Philos. Trans. v. 59, Enquiries into the
Lymph. Syst. p. 94.

3. These absorbent vessels are also furnished with glands, which are called
conglobate glands; whose use is not at present sufficiently investigated;
but it is probable that they resemble the conglomerate glands both in
structure and in use, except that their absorbent mouths are for the
conveniency of situation placed at a greater distance from the body of the
gland. The conglomerate glands open their mouths immediately into the
sanguiferous vessels, which bring the blood, from whence they absorb their
respective fluids, quite up to the gland: but these conglobate glands
collect their adapted fluids from very distant membranes, or cysts, by
means of mouths furnished with long necks for this purpose; and which are
called lacteals, or lymphatics.

4. The fluids, thus collected from various parts of the body, pass by means
of the thoracic duct into the left subclavian near the jugular vein; except
indeed that those collected from the right side of the head and neck, and
from the right arm, are carried into the right subclavian vein: and
sometimes even the lymphatics from the right side of the lungs are inserted
into the right subclavian vein; whilst those of the left side of the head
open but just into the summit of the thoracic duct.

5. In the absorbent system there are many anastomoses of the vessels, which
seem of great consequence to the preservation of health. These anastomoses
are discovered by dissection to be very frequent between the intestinal and
urinary lymphatics, as mentioned by Mr. Hewson, (Phil. Trans. v. 58.)

6. Nor do all the intestinal absorbents seem to terminate in the thoracic
duct, as appears from some curious experiments of D. Munro, who gave madder
to some animals, having previously put a ligature on the thoracic duct, and
found their bones, and the serum of their blood, coloured red.

II. _The Valves of the Absorbent System may suffer their Fluids to
regurgitate in some Diseases._

1. The many valves, which occur in the progress of the lymphatic and
lacteal vessels, would seem insuperable obstacles to the regurgitation of
their contents. But as these valves are placed in vessels, which are indued
with life, and are themselves indued with life also; and are very irritable
into those natural motions, which absorb, or propel the fluids they
contain; it is possible, in some diseases, where these valves or vessels
are stimulated into unnatural exertions, or are become paralytic, that
during the diastole of the part of the vessel to which the valve is
attached, the valve may not so completely close, as to prevent the relapse
of the lymph or chyle. This is rendered more probable, by the experiments
of injecting mercury, or water, or suet, or by blowing air down these
vessels: all which pass the valves very easily, contrary to the natural
course of their fluids, when the vessels are thus a little forcibly
dilated, as mentioned by Dr. Haller, Elem. Physiol. t. iii. s. 4.

"The valves of the thoracic duct are few, some assert they are not more
than twelve, and that they do not very accurately perform their office, as
they do not close the whole area of the duct, and thence may permit chyle
to repass them downwards. In living animals, however, though not always,
yet more frequently than in the dead, they prevent the chyle from
returning. The principal of these valves is that, which presides over the
insertion of the thoracic duct, into the subclavian vein; many have
believed this also to perform the office of a valve, both to admit the
chyle into the vein, and to preclude the blood from entering the duct; but
in my opinion it is scarcely sufficient for this purpose." Haller, Elem.
Phys. t. vii. p. 226.

2. The mouths of the lymphatics seem to admit water to pass through them
after death, the inverted way, easier than the natural one; since an
inverted bladder readily lets out the water with which it is filled; whence
it may be inferred, that there is no obstacle at the mouths of these
vessels to prevent the regurgitation of their contained fluids.

I was induced to repeat this experiment, and having accurately tied the
ureters and neck of a fresh ox's bladder, I made an opening at the fundus
of it; and then, having turned it inside outwards, filled it half full with
water, and was surprised to see it empty itself so hastily. I thought the
experiment more apposite to my purpose by suspending the bladder with its
neck downwards, as the lymphatics are chiefly spread upon this part of it,
as shewn by Dr. Watson, Philos. Trans. v. 59. p. 392.

3. In some diseases, as in the diabetes and scrophula, it is probable the
valves themselves are diseased, and are thence incapable of preventing the
return of the fluids they should support. Thus the valves of the aorta
itself have frequently been found schirrous, according to the dissections
of Mons. Lieutaud, and have given rise to an interrupted pulse, and
laborious palpitations, by suffering a return of part of the blood into the
heart. Nor are any parts of the body so liable to schirrosity as the
lymphatic glands and vessels, insomuch that their schirrosities have
acquired a distinct name, and been termed scrophula.

4. There are valves in other parts of the body, analogous to those of the
absorbent system, and which are liable, when diseased, to regurgitate their
contents: thus the upper and lower orifices of the stomach are closed by
valves, which, when too great quantities of warm water have been drank with
a design to promote vomiting, have sometimes resisted the utmost efforts of
the abdominal muscles, and diaphragm: yet, at other times, the upper valve,
or cardia, easily permits the evacuation of the contents of the stomach;
whilst the inferior valve, or pylorus, permits the bile, and other contents
of the duodenum, to regurgitate into the stomach.

5. The valve of the colon is well adapted to prevent the retrograde motion
of the excrements; yet, as this valve is possessed of a living power, in
the iliac passion, either from spasm, or other unnatural exertions, it
keeps itself open, and either suffers or promotes the retrograde movements
of the contents of the intestines below; as in ruminating animals the mouth
of the first stomach seems to be so constructed, as to facilitate or assist
the regurgitation of the food; the rings of the oesophagus afterwards
contracting themselves in inverted order. De Haeu, by means of a syringe,
forced so much water into the rectum intestinum of a dog, that he vomited
it in a full stream from his mouth; and in the iliac passion above
mentioned, excrements and clyster are often evacuated by the mouth. See
Section XXV. 15.

6. The puncta lacrymalia, with the lacrymal sack and nasal duct, compose a
complete gland, and much resemble the intestinal canal: the puncta
lacrymalia are absorbent mouths, that take up the tears from the eye, when
they have done their office there, and convey them into the nostrils; but
when the nasal duct is obstructed, and the lacrymal sack distended with its
fluid, on pressure with the finger the mouths of this gland (puncta
lacrymalia) will readily disgorge the fluid, they had previously absorbed,
back into the eye.

7. As the capillary vessels receive blood from the arteries, and separating
the mucus, or perspirable matter from it, convey the remainder back by the
veins; these capillary vessels are a set of glands, in every respect
similar to the secretory vessels of the liver, or other large congeries of
glands. The beginnings of these capillary vessels have frequent anastomoses
into each other, in which circumstance they are resembled by the lacteals;
and like the mouths or beginnings of other glands, they are a set of
absorbent vessels, which drink up the blood which is brought to them by the
arteries, as the chyle is drank up by the lacteals: for the circulation of
the blood through the capillaries is proved to be independent of arterial
impulse; since in the blush of shame, and in partial inflammations, their
action is increased, without any increase of the motion of the heart.

8. Yet not only the mouths, or beginnings of these anastomosing capillaries
are frequently seen by microscopes, to regurgitate some particles of blood,
during the struggles of the animal; but retrograde motion of the blood, in
the veins of those animals, from the very heart of the extremity of the
limbs, is observable, by intervals, during the distresses of the dying
creature. Haller, Elem. Physiol. t. i. p. 216. Now, as the veins have
perhaps all of them a valve somewhere between their extremities and the
heart, here is ocular demonstration of the fluids in this diseased
condition of the animal, repassing through venous valves: and it is hence
highly probable, from the strictest analogy, that if the course of the
fluids, in the lymphatic vessels, could be subjected to microscopic
observation, they would also, in the diseased state of the animal, be seen
to repass the valves, and the mouths of those vessels, which had previously
absorbed them, or promoted their progression.

III. _Communication from the Alimentary Canal to the Bladder, by means of
the Absorbent Vessels._

Many medical philosophers, both ancient and modern, have suspected that
there was a nearer communication between the stomach and the urinary
bladder, than that of the circulation: they were led into this opinion from
the great expedition with which cold water, when drank to excess, passes
off by the bladder; and from the similarity of the urine, when produced in
this hasty manner, with the material that was drank.

The former of these circumstances happens perpetually to those who drink
abundance of cold water, when they are much heated by exercise, and to many
at the beginning of intoxication.

Of the latter, many instances are recorded by Etmuller, t. xi. p. 716.
where simple water, wine, and wine with sugar, and emulsions, were returned
by urine unchanged.

There are other experiments, that seem to demonstrate the existence of
another passage to the bladder, besides that through the kidneys. Thus Dr.
Kratzenstein put ligatures on the ureters of a dog, and then emptied the
bladder by a catheter; yet in a little time the dog drank greedily, and
made a quantity of water, (Disputat. Morbor. Halleri. t. iv. p. 63.) A
similar experiment is related in the Philosophical Transactions, with the
same event, (No. 65, 67, for the year 1670.)

Add to this, that in some morbid cases the urine has continued to pass,
after the suppuration or total destruction of the kidneys; of which many
instances are referred to in the Elem. Physiol. t. vii. p. 379. of Dr.
Haller.

From all which it must be concluded, that some fluids have passed from the
stomach or abdomen, without having gone through the sanguiferous
circulation: and as the bladder is supplied with many lymphatics, as
described by Dr. Watson, in the Philos. Trans. v. 59. p. 392. and as no
other vessels open into it besides these and the ureters, it seems evident,
that the unnatural urine, produced as above described, when the ureters
were tied, or the kidneys obliterated, was carried into the bladder by the
retrograde motions of the urinary branch of the lymphatic system.

The more certainly to ascertain the existence of another communication
between the stomach and bladder, besides that of the circulation, the
following experiment was made, to which I must beg your patient
attention:--A friend of mine (June 14, 1772) on drinking repeatedly of cold
small punch, till he began to be intoxicated, made a quantity of colourless
urine. He then drank about two drams of nitre dissolved in some of the
punch, and eat about twenty stalks of boiled asparagus: on continuing to
drink more of the punch, the next urine that he made was quite clear, and
without smell; but in a little time another quantity was made, which was
not quite so colourless, and had a strong smell of the asparagus: he then
lost about four ounces of blood from the arm.

The smell of asparagus was not at all perceptible in the blood, neither
when fresh taken, nor the next morning, as myself and two others accurately
attended to; yet this smell was strongly perceived in the urine, which was
made just before the blood was taken from his arm.

Some bibulous paper, moistened in the serum of this blood, and suffered to
dry, shewed no signs of nitre by its manner of burning. But some of the
same paper, moistened in the urine, and dried, on being ignited, evidently
shewed the presence of nitre. This blood and the urine stood some days
exposed to the sun in the open air, till they were evaporated to about a
fourth of their original quantity, and began to stink: the paper, which was
then moistened with the concentrated urine, shewed the presence of much
nitre by its manner of burning; whilst that moistened with the blood shewed
no such appearance at all.

Hence it appears, that certain fluids at the beginning of intoxication,
find another passage to the bladder besides the long course of the arterial
circulation; and as the intestinal absorbents are joined with the urinary
lymphatics by frequent anastomoses, as Hewson has demonstrated; and as
there is no other road, we may justly conclude, that these fluids pass into
the bladder by the urinary branch of the lymphatics, which has its motions
inverted during the diseased state of the animal.

A gentleman, who had been some weeks affected with jaundice, and whose
urine was in consequence of a very deep yellow, took some cold small punch,
in which was dissolved about a dram of nitre; he then took repeated
draughts of the punch, and kept himself in a cool room, till on the
approach of slight intoxication he made a large quantity of water; this
water had a slight yellow tinge, as might be expected from a small
admixture of bile secreted from the kidneys; but if the whole of it had
passed through the sanguiferous vessels, which were now replete with bile
(his whole skin being as yellow as gold) would not this urine also, as well
as that he had made for weeks before, have been of a deep yellow? Paper
dipped in this water, and dryed, and ignited, shewed evident marks of the
presence of nitre, when the flame was blown out.

IV. _The Phænomena of the Diabetes explained, and of some Diarrhoeas._

The phenomena of many diseases are only explicable from the retrograde
motions of some of the branches of the lymphatic system; as the great and
immediate flow of pale urine in the beginning of drunkenness; in hysteric
paroxysms; from being exposed to cold air; or to the influence of fear or
anxiety.

Before we endeavour to illustrate this doctrine, by describing the
phænomena of these diseases, we must premise one circumstance; that all the
branches of the lymphatic system have a certain sympathy with each other,
insomuch that when one branch is stimulated into unusual kinds or
quantities of motion, some other branch has its motions either increased,
or decreased, or inverted at the same time. This kind of sympathy can only
be proved by the concurrent testimony of numerous facts, which will be
related in the course of the work. I shall only add here, that it is
probable, that this sympathy does not depend on any communication of
nervous filaments, but on habit; owing to the various branches of this
system having frequently been stimulated into action at the same time.

There are a thousand instances of involuntary motions associated in this
manner; as in the act of vomiting, while the motions of the stomach and
oesophagus are inverted, the pulsations of the arterial system by a certain
sympathy become weaker; and when the bowels or kidneys are stimulated by
poison, a stone, or inflammation, into more violent action; the stomach and
oesophagus by sympathy invert their motions.

1. When any one drinks a moderate quantity of vinous spirit, the whole
system acts with more energy by consent with the stomach and intestines, as
is seen from the glow on the skin, and the increase of strength and
activity; but when a greater quantity of this inebriating material is
drank, at the same time that the lacteals are excited into greater action
to absorb it; it frequently happens, that the urinary branch of absorbents,
which is connected with the lacteals by many anastomoses, inverts its
motions, and a great quantity of pale unanimalized urine is discharged. By
this wise contrivance too much of an unnecessary fluid is prevented from
entering the circulation--This may be called the drunken diabetes, to
distinguish it from the other temporary diabetes, which occur in hysteric
diseases, and from continued fear or anxiety.

2. If this idle ingurgitation of too much vinous spirit be daily practised,
the urinary branch of absorbents at length gains an habit of inverting its
motions, whenever the lacteals are much stimulated; and the whole or a
great part of the chyle is thus daily carried to the bladder without
entering the circulation, and the body becomes emaciated. This is one kind
of chronic diabetes, and may be distinguished from the others by the taste
and appearance of the urine; which is sweet, and the colour of whey, and
may be termed the chyliferous diabetes.

3. Many children have a similar deposition of chyle in their urine, from
the irritation of worms in their intestines, which stimulating the mouths
of the lacteals into unnatural action, the urinary branch of the absorbents
becomes inverted, and carries part of the chyle to the bladder: part of the
chyle also has been carried to the iliac and lumbar glands, of which
instances are recorded by Haller, t. vii. 225. and which can be explained
on no other theory: but the dissections of the lymphatic system of the
human body, which have yet been published, are not sufficiently extensive
for our purpose; yet if we may reason from comparative anatomy, this
translation of chyle to the bladder is much illustrated by the account
given of this system of vessels in a turtle, by Mr. Hewson, who observed,
"That the lacteals near the root of the mesentery anastomose, so as to form
a net-work, from which several large branches go into some considerable
lymphatics lying near the spine; and which can be traced almost to the
anus, and particularly to the kidneys." Philos. Trans. v. 59. p.
199--Enquiries, p. 74.

4. At the same time that the urinary branch of absorbents, in the beginning
of diabetes, is excited into inverted action, the cellular branch is
excited by the sympathy above mentioned, into more energetic action; and
the fat, that was before deposited, is reabsorbed and thrown into the blood
vessels; where it floats, and was mistaken for chyle, till the late
experiments of the ingenious Mr. Hewson demonstrated it to be fat.

This appearance of what was mistaken for chyle in the blood, which was
drawn from these patients, and the obstructed liver, which very frequently
accompanies this disease, seems to have led Dr. Mead to suspect the
diabetes was owing to a defect of sanguification; and that the schirrosity
of the liver was the original cause of it: but as the schirrhus of the
liver is most frequently owing to the same causes, that produce the
diabetes and dropsies; namely, the great use of fermented liquors; there is
no wonder they should exist together, without being the consequence of each
other.

5. If the cutaneous branch of absorbents gains a habit of being excited
into stronger action, and imbibes greater quantities of moisture from the
atmosphere, at the same time that the urinary branch has its motions
inverted, another kind of diabetes is formed, which may be termed the
aqueous diabetes. In this diabetes the cutaneous absorbents frequently
imbibe an amazing quantity of atmospheric moisture; insomuch that there are
authentic histories, where many gallons a day, for many weeks together,
above the quantity that has been drank, have been discharged by urine.

Dr. Keil, in his Medicina Statica, found that he gained eighteen ounces
from the moist air of one night; and Dr. Percival affirms, that one of his
hands imbibed, after being well chafed, near an ounce and half of water, in
a quarter of an hour. (Transact. of the College, London, vol. ii. p. 102.)
Home's Medic. Facts, p. 2. sect. 3.

The pale urine in hysterical women, or which is produced by fear or
anxiety, is a temporary complaint of this kind; and it would in reality be
the same disease, if it was confirmed by habit.

6. The purging stools, and pale urine, occasioned by exposing the naked
body to cold air, or sprinkling it with cold water, originate from a
similar cause; for the mouths of the cutaneous lymphatics being suddenly
exposed to cold become torpid, and cease, or nearly cease, to act; whilst,
by the sympathy above described, not only the lymphatics of the bladder and
intestines cease also to absorb the more aqueous and saline part of the
fluids secreted into them; but it is probable that these lymphatics invert
their motions, and return the fluids, which were previously absorbed, into
the intestines and bladder. At the very instant that the body is exposed
naked to the cold air, an unusual movement is felt in the bowels; as is
experienced by boys going into the cold bath: this could not occur from an
obstruction of the perspirable matter, since there is not time, for that to
be returned to the bowels by the course of the circulation.

There is also a chronic aqueous diarrhoea, in which the atmospheric
moisture, drank up by the cutaneous and pulmonary lymphatics, is poured
into the intestines, by the retrograde motions of the lacteals. This
disease is most similar to the aqueous diabetes, and is frequently
exchanged for it: a distinct instance of this is recorded by Benningerus,
Cent. v. Obs. 98. in which an aqueous diarrhoea succeeded an aqueous
diabetes, and destroyed the patient. There is a curious example of this,
described by Sympson (De Re Medica)--"A young man (says he) was seized with
a fever, upon which a diarrhoea came on, with great stupor; and he refused
to drink any thing, though he was parched up with excessive heat: the
better to supply him with moisture, I directed his feet to be immersed in
cold water; immediately I observed a wonderful decrease of water in the
vessel, and then an impetuous stream of a fluid, scarcely coloured, was
discharged by stool, like a cataract."

7. There is another kind of diarrhoea, which has been called cæliaca; in
this disease the chyle, drank up by the lacteals of the small intestines,
is probably poured into the large intestines, by the retrograde motions of
their lacteals: as in the chyliferous diabetes, the chyle is poured into
the bladder, by the retrograde motions of the urinary branch of absorbents.

The chyliferous diabetes, like this chyliferous diarrhoea, produces sudden
atrophy; since the nourishment, which ought to supply the hourly waste of
the body, is expelled by the bladder, or rectum: whilst the aqueous
diabetes, and the aqueous diarrhoea produce excessive thirst; because the
moisture, which is obtained from the atmosphere, is not conveyed to the
thoracic receptacle, as it ought to be, but to the bladder, or lower
intestines; whence the chyle, blood, and whole system of glands, are robbed
of their proportion of humidity.

8. There is a third species of diabetes, in which the urine is
mucilaginous, and appears ropy in pouring it from one vessel into another;
and will sometimes coagulate over the fire. This disease appears by
intervals, and ceases again, and seems to be occasioned by a previous
dropsy in some part of the body. When such a collection is reabsorbed, it
is not always returned into the circulation; but the same irritation that
stimulates one lymphatic branch to reabsorb the deposited fluid, inverts
the urinary branch, and pours it into the bladder. Hence this mucilaginous
diabetes is a cure, or the consequence of a cure, of a worse disease,
rather than a disease itself.

Dr. Cotunnius gave half an ounce of cream of tartar, every morning, to a
patient, who had the anasarca; and he voided a great quantity of urine; a
part of which, put over the fire, coagulated, on the evaporation of half of
it, so as to look like the white of an egg. De Ischiade Nervos.

This kind of diabetes frequently precedes a dropsy; and has this remarkable
circumstance attending it, that it generally happens in the night; as
during the recumbent state of the body, the fluid, that was accumulated in
the cellular membrane, or in the lungs, is more readily absorbed, as it is
less impeded by its gravity. I have seen more than one instance of this
disease. Mr. D. a man in the decline of life, who had long accustomed
himself to spirituous liquor, had swelled legs, and other symptoms of
approaching anasarca; about once in a week, or ten days, for several
months, he was seized, on going to bed, with great general uneasiness,
which his attendants resembled to an hysteric fit; and which terminated in
a great discharge of viscid urine; his legs became less swelled, and he
continued in better health for some days afterwards. I had not the
opportunity to try if this urine would coagulate over the fire, when part
of it was evaporated, which I imagine would be the criterion of this kind
of diabetes; as the mucilaginous fluid deposited in the cells and cysts of
the body, which have no communication with the external air, seems to
acquire, by stagnation, this property of coagulation by heat, which the
secreted mucus of the intestines and bladder do not appear to possess; as I
have found by experiment: and if any one should suppose this coagulable
urine was separated from the blood by the kidneys, he may recollect, that
in the most inflammatory diseases, in which the blood is most replete or
most ready to part with the coagulable lymph, none of this appears in the
urine.

9. Different kinds of diabetes require different methods of cure. For the
first kind, or chyliferous diabetes, after clearing the stomach and
intestines, by ipecacuanha and rhubarb, to evacuate any acid material,
which may too powerfully stimulate the mouths of the lacteals, repeated and
large doses of tincture of cantharides have been much recommended. The
specific stimulus of this medicine, on the neck of the bladder, is likely
to excite the numerous absorbent vessels, which are spread on that part,
into stronger natural actions, and by that means prevent their retrograde
ones; till, by persisting in the use of the medicine, their natural habits
of motions might again be established. Another indication of cure, requires
such medicines, as by lining the intestines with mucilaginous substances,
or with such as consist of smooth particles, or which chemically destroy
the acrimony of their contents, may prevent the too great action of the
intestinal absorbents. For this purpose, I have found the earth
precipitated from a solution of alum, by means of fixed alcali, given in
the dose of half a dram every six hours, of great advantage, with a few
grains of rhubarb, so as to produce a daily evacuation.

The food should consist of materials that have the least stimulus, with
calcareous water, as of Bristol and Matlock; that the mouths of the
lacteals may be as little stimulated as is necessary for their proper
absorption; lest with their greater exertions, should be connected by
sympathy, the inverted motions of the urinary lymphatics.

The same method may be employed with equal advantage in the aqueous
diabetes, so great is the sympathy between the skin and the stomach. To
which, however, some application to the skin might be usefully added; as
rubbing the patient all over with oil, to prevent the too great action of
the cutaneous absorbents. I knew an experiment of this kind made upon one
patient with apparent advantage.

The mucilaginous diabetes will require the same treatment, which is most
efficacious in the dropsy, and will be described below. I must add, that
the diet and medicines above mentioned, are strongly recommended by various
authors, as by Morgan, Willis, Harris, and Etmuller; but more histories of
the successful treatment of these diseases are wanting to fully ascertain
the most efficacious methods of cure.

In a letter from Mr. Charles Darwin, dated April 24, 1778, Edinburgh, is
the subsequent passage:--"A man who had long laboured under a diabetes died
yesterday in the clinical ward. He had for some time drank four, and passed
twelve pounds of fluid daily; each pound of urine contained an ounce of
sugar. He took, without considerable relief, gum kino, sanguis diaconis
melted with alum, tincture of cantharides, isinglass, gum arabic, crabs
eyes, spirit of hartshorn, and eat ten or fifteen oysters thrice a day. Dr.
Home, having read my thesis, bled him, and found that neither the fresh
blood nor the serum tasted sweet. His body was opened this morning--every
viscus appeared in a sound and natural state, except that the left kidney
had a very small pelvis, and that there was a considerable enlargement of
most of the mesenteric lymphatic glands. I intend to insert this in my
thesis, as it coincides with the experiment, where some asparagus was eaten
at the beginning of intoxication, and its smell perceived in the urine,
though not in the blood."

The following case of chyliferous diabetes is extracted from some letters
of Mr. Hughes, to whose unremitted care the infirmary at Stafford for many
years was much indebted. Dated October 10, 1778.

Richard Davis, aged 33, a whitesmith by trade, had drank hard by intervals;
was much troubled with sweating of his hands, which incommoded him in his
occupation, but which ceased on his frequently dipping them in lime. About
seven months ago he began to make large quantities of water; his legs are
oedematous, his belly tense, and he complains of a rising in his throat,
like the globus hystericus: he eats twice as much as other people, drinks
about fourteen pints of small beer a day, besides a pint of ale, some
milk-porridge, and a bason of broth, and he makes about eighteen pints of
water a day.

He tried alum, dragon's blood, steel, blue vitriol, and cantharides in
large quantities, and duly repeated, under the care of Dr. Underhill, but
without any effect; except that on the day after he omitted the
cantharides, he made but twelve pints of water, but on the next day this
good effect ceased again.

November 21.--He made eighteen pints of water, and he now, at Dr. Darwin's
request, took a grain of opium every four hours, and five grains of aloes
at night; and had a flannel shirt given him.

22.--Made sixteen pints. 23.--Thirteen pints: drinks less.

24.--Increased the opium to a grain and quarter every four hours: he made
twelve pints.

25.--Increased the opium to a grain and half: he now makes ten pints; and
drinks eight pints in a day.

The opium was gradually increased during the next fortnight, till he took
three grains every four hours, but without any further diminution of his
water. During the use of the opium he sweat much in the nights, so as to
have large drops stand on his face and all over him. The quantity of opium
was then gradually decreased, but not totally omitted, as he continued to
take about a grain morning and evening.

January 17.--He makes fourteen pints of water a day. Dr. Underhill now
directed him two scruples of common rosin triturated with as much sugar,
every six hours; and three grains of opium every night.

19.--Makes fifteen pints of water: sweats at night.

21.--Makes seventeen pints of water; has twitchings of his limbs in a
morning, and pains of his legs: he now takes a dram of rosin for a dose,
and continues the opium.

23.--Water more coloured, and reduced to sixteen pints, and he thinks has a
brackish taste.

26.--Water reduced to fourteen pints.

28.--Water thirteen pints: he continues the opium, and takes four scruples
of the rosin for a dose.

February 1.--Water twelve pints.

4.--Water eleven pints: twitchings less; takes five scruples for a dose.

8.--Water ten pints: has had many stools.

12.--Appetite less: purges very much.

After this the rosin either purged him, or would not stay on his stomach;
and he gradually relapsed nearly to his former condition, and in a few
months sunk under the disease.

October 3, Mr. Hughes evaporated two quarts of the water, and obtained from
it four ounces and half of a hard and brittle saccharine mass, like treacle
which had been some time boiled. Four ounces of blood, which he took from
his arm with design to examine it, had the common appearances, except that
the serum resembled cheese-whey; and that on the evidence of four persons,
two of whom did not know what it was they tasted, _the serum had a saltish
taste_.

From hence it appears, that the saccharine matter, with which the urine of
these patients so much abounds, does not enter the blood-vessels like the
nitre and asparagus mentioned above; but that the process of digestion
resembles the process of the germination of vegetables, or of making barley
into malt; as the vast quantity of sugar found in the urine must be made
from the food which he took (which was double that taken by others), and
from the fourteen pints of small beer which he drank. And, secondly, as the
serum of the blood was not sweet, the chyle appears to have been conveyed
to the bladder without entering the circulation of the blood, since so
large a quantity of sugar, as was found in the urine, namely, twenty ounces
a day, could not have previously existed in the blood without being
perceptible to the taste.

November 1. Mr. Hughes dissolved two drams of nitre in a pint of a
decoction of the roots of asparagus, and added to it two ounces of tincture
of rhubarb: the patient took a fourth part of this mixture every five
minutes, till he had taken the whole.--In about half an hour he made
eighteen ounces of water, which was very manifestly tinged with the
rhubarb; the smell of asparagus was doubtful.

He then lost four ounces of blood, the serum of which was not so opake as
that drawn before, but of a yellowish cast, as the serum of the blood
usually appears.

Paper, dipped three or four times in the tinged urine and dried again, did
not scintillate when it was set on fire; but when the flame was blown out,
the fire ran along the paper for half an inch; which, when the same paper
was unimpregnated, it would not do; nor when the same paper was dipped in
urine made before he took the nitre, and dried in the same manner.

Paper, dipped in the serum of the blood and dried in the same manner as in
the urine, did not scintillate when the flame was blown out, but burnt
exactly in the same manner as the same paper dipped in the serum of blood
drawn from another person.

This experiment, which is copied from a letter of Mr. Hughes, as well as
the former, seems to evince the existence of another passage from the
intestines to the bladder, in this disease, besides that of the
sanguiferous system; and coincides with the curious experiment related in
section the third, except that the smell of the asparagus was not here
perceived, owing perhaps to the roots having been made use of instead of
the heads.

The rising in the throat of this patient, and the twitchings of his limbs,
seem to indicate some similarity between the diabetes and the hysteric
disease, besides the great flow of pale urine, which is common to them
both.

Perhaps if the mesenteric glands were nicely inspected in the dissections
of these patients; and if the thoracic duct, and the larger branches of the
lacteals, and if the lymphatics, which arise from the bladder, were well
examined by injection, or by the knife, the cause of diabetes might be more
certainly understood.

The opium alone, and the opium with the rosin, seem much to have served
this patient, and might probably have effected a cure, if the disease had
been slighter, or the medicine had been exhibited, before it had been
confirmed by habit during the seven months it had continued. The increase
of the quantity of water on beginning the large doses of rosin was probably
owing to his omitting the morning doses of opium.

V. _The Phænomena of Dropsies explained._

I. Some inebriates have their paroxysms of inebriety terminated by much
pale urine, or profuse sweats, or vomiting, or stools; others have their
paroxysms terminated by stupor, or sleep, without the above evacuations.

The former kind of these inebriates have been observed to be more liable to
diabetes and dropsy; and the latter to gout, gravel, and leprosy. Evoe!
attend ye bacchanalians! start at this dark train of evils, and, amid your
immodest jests, and idiot laughter, recollect,

  Quem Deus vult perdere, prius dementat.

In those who are subject to diabetes and dropsy, the absorbent vessels are
naturally more irritable than in the latter; and by being frequently
disturbed or inverted by violent stimulus, and by their too great sympathy
with each other, they become at length either entirely paralytic, or are
only susceptible of motion from the stimulus of very acrid materials; as
every part of the body, after having been used to great irritations,
becomes less affected by smaller ones. Thus we cannot distinguish objects
in the night, for some time after we come out of a strong light, though the
iris is presently dilated; and the air of a summer evening appears cold,
after we have been exposed to the heat of the day.

There are no cells in the body, where dropsy may not be produced, if the
lymphatics cease to absorb that mucilaginous fluid, which is perpetually
deposited in them, for the purpose of lubricating their surfaces.

If the lymphatic branch, which opens into the cellular membrane, either
does its office imperfectly, or not at all; these cells become replete with
a mucilaginous fluid, which, after it has stagnated some time in the cells,
will coagulate over the fire; and is erroneously called water. Wherever the
seat of this disease is, (unless in the lungs or other pendent viscera) the
mucilaginous liquid above mentioned will subside to the most depending
parts of the body, as the feet and legs, when those are lower than the head
and trunk; for all these cells have communications with each other.

When the cellular absorbents are become insensible to their usual
irritations, it most frequently happens, but not always, that the cutaneous
branch of absorbents, which is strictly associated with them, suffers the
like inability. And then, as no water is absorbed from the atmosphere, the
urine is not only less diluted at the time of its secretion, and
consequently in less quantity and higher coloured: but great thirst is at
the same time induced, for as no water is absorbed from the atmosphere to
dilute the chyle and blood, the lacteals and other absorbent vessels, which
have not lost their powers, are excited into more constant or more violent
action, to supply this deficiency; whence the urine becomes still less in
quantity, and of a deeper colour, and turbid like the yolk of an egg, owing
to a greater absorption of its thinner parts. From this stronger action of
those absorbents, which still retain their irritability, the fat is also
absorbed, and the whole body becomes emaciated. This increased exertion of
some branches of the lymphatics, while others are totally or partially
paralytic, is resembled by what constantly occurs in the hemiplagia; when
the patient has lost the use of the limbs on one side, he is incessantly
moving those of the other; for the moving power, not having access to the
paralytic limbs, becomes redundant in those which are not diseased.

The paucity of urine and thirst cannot be explained from a greater quantity
of mucilaginous fluid being deposited in the cellular membrane: for though
these symptoms have continued many weeks, or even months, this collection
frequently does not amount to more than very few pints. Hence also the
difficulty of promoting copious sweats in anasarca is accounted for, as
well as the great thirst, paucity of urine, and loss of fat; since, when
the cutaneous branch of absorbents is paralytic, or nearly so, there is
already too small a quantity of aqueous fluid in the blood: nor can these
torpid cutaneous lymphatics be readily excited into retrograde motions.

Hence likewise we understand, why in the ascites, and some other dropsies,
there is often no thirst, and no paucity of urine; in these cases the
cutaneous absorbents continue to do their office.

Some have believed, that dropsies were occasioned by the inability of the
kidneys, from having only observed the paucity of urine; and have thence
laboured much to obtain diuretic medicines; but it is daily observable,
that those who die of a total inability to make water, do not become
dropsical in consequence of it: Fernelius mentions one, who laboured under
a perfect suppression of urine during twenty days before his death, and yet
had no symptoms of dropsy. Pathol. 1. vi. c. 8. From the same idea many
physicians have restrained their patients from drinking, though their
thirst has been very urgent; and some cases have been published, where this
cruel regimen has been thought advantageous: but others of nicer
observation are of opinion, that it has always aggravated the distresses of
the patient; and though it has abated his swellings, yet by inducing a
fever it has hastened his dissolution. See Transactions of the College,
London, vol. ii. p. 235. Cases of Dropsy by Dr. G. Baker.

The cure of anasarca, so far as respects the evacuation of the accumulated
fluid, coincides with the idea of the retrograde action of the lymphatic
system. It is well known that vomits, and other drugs, which induce
sickness or nausea; at the same time that they evacuate the stomach,
produce a great absorption of the lymph accumulated in the cellular
membrane. In the operation of a vomit, not only the motions of the stomach
and duodenum become inverted, but also those of the lymphatics and
lacteals, which belong to them; whence a great quantity of chyle and lymph
is perpetually poured into the stomach and intestines, during the
operation, and evacuated by the mouth. Now at the same time, other branches
of the lymphatic system, viz. those which open on the cellular membrane,
are brought into more energetic action, by the sympathy above mentioned,
and an increase of their absorption is produced.

Hence repeated vomits, and cupreous salts, and small doses of squill or
foxglove, are so efficacious in this disease. And as drastic purges act
also by inverting the motions of the lacteals; and thence the other
branches of lymphatics are induced into more powerful natural action, by
sympathy, and drink up the fluids from all the cells of the body; and by
their anastomoses, pour them into the lacteal branches; which, by their
inverted actions, return them into the intestines; and they are thus
evacuated from the body:--these purges also are used with success in
discharging the accumulated fluid in anasarca.

II. The following cases are related with design to ascertain the particular
kinds of dropsy in which the digitalis purpurea, or common foxglove, is
preferable to squill, or other evacuants, and were first published in 1780,
in a pamphlet entitled Experiments on mucilaginous and purulent Matter, &c.
Cadell. London. Other cases of dropsy, treated with digitalis, were
afterwards published by Dr. Darwin in the Medical Transactions, vol. iii.
in which there is a mistake in respect to the dose of the powder of
foxglove, which should have been from five grains to one, instead of from
five grains to ten.

_Anasarca of the Lungs._

1. A lady, between forty and fifty years of age, had been indisposed some
time, was then seized with cough and fever, and afterwards expectorated
much digested mucus. This expectoration suddenly ceased, and a considerable
difficulty of breathing supervened, with a pulse very irregular both in
velocity and strength; she was much distressed at first lying down, and at
first rising; but after a minute or two bore either of those attitudes with
ease. She had no pain or numbness in her arms; she had no hectic fever, nor
any cold shiverings, and the urine was in due quantity, and of the natural
colour.

The difficulty of breathing was twice considerably relieved by small doses
of ipecacuanha, which operated upwards and downwards, but recurred in a few
days: she was then directed a decoction of foxglove, (digitalis purpurea)
prepared by boiling four ounces of the fresh leaves from two pints of water
to one pint; to which was added two ounces of vinous spirit: she took three
large spoonfuls of this mixture every two hours, till she had taken it four
times; a continued sickness supervened, with frequent vomiting, and a
copious flow of urine: these evacuations continued at intervals for two or
three days, and relieved the difficulty of breathing--She had some relapses
afterwards, which were again relieved by the repetition of the decoction of
foxglove.

2. A gentleman, about sixty years of age, who had been addicted to an
immoderate use of fermented liquors, and had been very corpulent, gradually
lost his strength and flesh, had great difficulty of breathing, with legs
somewhat swelled, and a very irregular pulse. He was very much distressed
at first lying down, and at first rising from his bed, yet in a minute or
two was easy in both those attitudes. He made straw-coloured urine in due
quantity, and had no pain or numbness of his arms.

He took a large spoonful of the decoction of foxglove, as above, every
hour, for ten or twelve successive hours, had incessant sickness for about
two days, and passed a large quantity of urine; upon which his breath
became quite easy, and the swelling of his legs subsided; but as his whole
constitution was already sinking from the previous intemperance of his
life, he did not survive more than three or four months.

_Hydrops Pericardii._

3. A gentleman of temperate life and sedulous application to business,
between thirty and forty years of age, had long been subject, at intervals,
to an irregular pulse: a few months ago he became weak, with difficulty of
breathing, and dry cough. In this situation a physician of eminence
directed him to abstain from all animal food and fermented liquor, during
which regimen all his complaints increased; he now became emaciated, and
totally lost his appetite; his pulse very irregular both in velocity and
strength; with great difficulty of breathing, and some swelling of his
legs; yet he could lie down horizontally in his bed, though he got little
sleep, and passed a due quantity of urine, and of the natural colour: no
fullness or hardness could be perceived about the region of the liver; and
he had no pain or numbness in his arms.

One night he had a most profuse sweat all over his body and limbs, which
quite deluged his bed, and for a day or two somewhat relieved his
difficulty of breathing, and his pulse became less irregular: this copious
sweat recurred three or four times at the intervals of five or six days,
and repeatedly alleviated his symptoms.

He was directed one large spoonful of the above decoction of foxglove every
hour, till it procured some considerable evacuation: after he had taken it
eleven successive hours he had a few liquid stools, attended with a great
flow of urine, which last had a dark tinge, as if mixed with a few drops of
blood: he continued sick at intervals for two days, but his breath became
quite easy, and his pulse quite regular, the swelling of his legs
disappeared, and his appetite and sleep returned.

He then took three grains of white vitriol twice a day, with some bitter
medicines, and a grain of opium with five grains of rhubarb every night;
was advised to eat flesh meat, and spice, as his stomach would bear it,
with small beer, and a few glasses of wine; and had issues made in his
thighs; and has suffered no relapse.

4. A lady, about fifty years of age, had for some weeks great difficulty of
breathing, with very irregular pulse, and considerable general debility:
she could lie down in bed, and the urine was in due quantity and of the
natural colour, and she had no pain or numbness of her arms.

She took one large spoonful of the above decoction of foxglove every hour,
for ten or twelve successive hours; was sick, and made a quantity of pale
urine for about two days, and was quite relieved both of the difficulty of
breathing, and the irregularity of her pulse. She then took a grain of
opium, and five grains of rhubarb, every night, night, for many weeks; with
some slight chalybeate and bitter medicines, and has suffered no relapse.

_Hydrops Thoracis._

5. A tradesman, about fifty years of age, became weak and short of breath,
especially on increase of motion, with pain in one arm, about the insertion
of the biceps muscle. He observed he sometimes in the night made an unusual
quantity of pale water. He took calomel, alum, and peruvian bark, and all
his symptoms increased: his legs began to swell considerably; his breath
became more difficult, and he could not lie down in bed; but all this time
he made a due quantity of straw-coloured water.

The decoction of foxglove was given as in the preceding cases, which
operated chiefly by purging, and seemed to relieve his breath for a day or
two; but also seemed to contribute to weaken him.--He became after some
weeks universally dropsical, and died comatous.

6. A young lady of delicate constitution, with light eyes and hair, and who
had perhaps lived too abstemiously both in respect to the quantity and
quality of what she eat and drank, was seized with great difficulty of
breathing, so as to threaten immediate death. Her extremities were quite
cold, and her breath felt cold to the back of one's hand. She had no sweat,
nor could be down for a single moment; and had previously, and at present,
complained of great weakness and pain and numbness of both her arms; had no
swelling of her legs, no thirst, water in due quantity and colour. Her
sister, about a year before, was afflicted with similar symptoms, was
repeatedly blooded, and died universally dropsical.

A grain of opium was given immediately, and repeated every six hours with
evident and amazing advantage; afterwards a blister, with chalybeates,
bitters, and essential oils, were exhibited, but nothing had such eminent
effect in relieving the difficulty of breathing and coldness of her
extremities as opium, by the use of which in a few weeks she perfectly
regained her health, and has suffered no relapse.

_Ascites._

7. A young lady of delicate constitution having been exposed to great fear,
cold, and fatigue, by the overturn of a chaise in the night, began with
pain and tumour in the right hypochondrium: in a few months a fluctuation
was felt throughout the whole abdomen, more distinctly perceptible indeed
about the region of the stomach; since the integuments of the lower part of
the abdomen generally become thickened in this disease by a degree of
anasarca. Her legs were not swelled, no thirst, water in due quantity and
colour.--She took the foxglove so as to induce sickness and stools, but
without abating the swelling, and was obliged at length to submit to the
operation of tapping.

8. A man about sixty-seven, who had long been accustomed to spirituous
potation, had some time laboured under ascites; his legs somewhat swelled;
his breath easy in all attitudes; no appetite; great thirst; urine in
exceedingly small quantity, very deep coloured, and turbid; pulse equal. He
took the foxglove in such quantity as vomited him, and induced sickness for
two days; but procured no flow of urine, or diminution of his swelling; but
was thought to leave him considerably weaker.

9. A corpulent man, accustomed to large potation of fermented liquors, had
vehement cough, difficult breathing, anasarca of his legs, thighs, and
hands, and considerable tumour, with evident fluctuation of his abdomen;
his pulse was equal; his urine in small quantity, of deep colour, and
turbid. These swellings had been twice considerably abated by drastic
cathartics. He took three ounces of a decoction of foxglove (made by
boiling one ounce of the fresh leaves in a pint of water) every three
hours, for two whole days; it then began to vomit and purge him violently,
and promoted a great flow of urine; he was by these evacuations completely
emptied in twelve hours. After two or three months all these symptoms
returned, and were again relieved by the use of the foxglove; and thus in
the space of about three years he was about ten times evacuated, and
continued all that time his usual potations: excepting at first, the
medicine operated only by urine, and did not appear considerably to weaken
him--The last time he took it, it had no effect; and a few weeks afterwards
he vomited a great quantity of blood, and expired.

QUERIES.

1. As the first six of these patients had a due discharge of urine, and of
the natural colour, was not the feat of the disease confined to some part
of the thorax, and the swelling of the legs rather a symptom of the
obstructed circulation of the blood, than of a paralysis of the cellular
lymphatics of those parts?

2. When the original disease is a general anasarca, do not the cutaneous
lymphatics always become paralytic at the same time with the cellular ones,
by their greater sympathy with each other? and hence the paucity of urine,
and the great thirst, distinguish this kind of dropsy?

3. In the anasarca of the lungs, when the disease is not very great, though
the patients have considerable difficulty of breathing at their first lying
down, yet after a minute or two their breath becomes easy again; and the
same occurs at their first rising. Is not this owing to the time necessary
for the fluid in the cells of the lungs to change its place, so as the
least to incommode respiration in the new attitude?

4. In the dropsy of the pericardium does not the patient bear the
horizontal or perpendicular attitude with equal ease? Does this
circumstance distinguish the dropsy of the pericardium from that of the
lungs and of the thorax?

5. Do the universal sweats distinguish the dropsy of the pericardium, or of
the thorax? and those, which cover the upper parts of the body only, the
anasarca of the lungs?

6. When in the dropsy of the thorax, the patient endeavours to lie down,
does not the extravasated fluid compress the upper parts of the bronchia,
and totally preclude the access of air to every part of the lungs; whilst
in the perpendicular attitude the inferior parts of the lungs only are
compressed? Does not something similar to this occur in the anasarca of the
lungs, when the disease is very great, and thus prevent those patients also
from lying down?

7. As a principal branch of the fourth cervical nerve of the left side,
after having joined a branch of the third and of the second cervical
nerves, descending between the subclavian vein and artery, is received in a
groove formed for it in the pericardium, and is obliged to make a
considerable turn outwards to go over the prominent part of it, where the
point of the heart is lodged, in its course to the diaphragm; and as the
other phrenic nerve of the right side has a straight course to the
diaphragm; and as many other considerable branches of this fourth pair of
cervical nerves are spread on the arms; does not a pain in the left arm
distinguish a disease of the pericardium, as in the angina pectoris, or in
the dropsy of the pericardium? and does not a pain or weakness in both arms
distinguish the dropsy of the thorax?

8. Do not the dropsies of the thorax and pericardium frequently exist
together, and thus add to the uncertainty and fatality of the disease?

9. Might not the foxglove be serviceable in hydrocephalus internus, in
hydrocele, and in white swellings of the joints?

VI. _Of cold Sweats._

There have been histories given of chronical immoderate sweatings, which
bear some analogy to the diabetes. Dr. Willis mentions a lady then living,
whose sweats where for many years so profuse, that all her bed-clothes were
not only moistened, but deluged with them every night; and that many
ounces, and sometimes pints, of this sweat, were received in vessels
properly placed, as it trickled down her body. He adds, that she had great
thirst, had taken many medicines, and submitted to various rules of life,
and changes of climate, but still continued to have these immoderate
sweats. Pharmac. ration. de sudore anglico.

Dr. Willis has also observed, that the sudor anglicanus which appeared in
England, in 1483, and continued till 1551, was in some respects similar to
the diabetes; and as Dr. Caius, who saw this disease, mentions the
viscidity, as well as the quantity of these sweats, and adds, that the
extremities were often cold, when the internal parts were burnt up with
heat and thirst, with great and speedy emaciation and debility: there is
great reason to believe, that the fluids were absorbed from the cells of
the body by the cellular and cystic branches of the lymphatics, and poured
on the skin by the retrograde motions of the cutaneous ones.

Sydenham has recorded, in the stationary fever of the year 1685, the viscid
sweats flowing from the head, which were probably from the same source as
those in the sweating plague above mentioned.

It is very common in dropsies of the chest or lungs to have the difficulty
of breathing relieved by copious sweats, flowing from the head and neck.
Mr. P. about 50 years of age, had for many weeks been afflicted with
anasarca of his legs and thighs, attended with difficulty of breathing; and
had repeatedly been relieved by squill, other bitters, and
chalybeates.--One night the difficulty of breathing became so great, that
it was thought he must have expired; but so copious a sweat came out of his
head and neck, that in a few hours some pints, by estimation, were wiped
off from those parts, and his breath was for a time relieved. This dyspnoea
and these sweats recurred at intervals, and after some weeks he ceased to
exist. The skin of his head and neck felt cold to the hand, and appeared
pale at the time these sweats flowed so abundantly; which is a proof, that
they were produced by an inverted motion of the absorbents of those parts:
for sweats, which are the consequence of an increased action of the
sanguiferous system, are always attended with a warmth of the skin, greater
than is natural, and a more florid colour; as the sweats from exercise, or
those that succeed the cold fits of agues. Can any one explain how these
partial sweats should relieve the difficulty of breathing in anasarca, but
by supposing that the pulmonary branch of absorbents drank up the fluid in
the cavity of the thorax, or in the cells of the lungs, and threw it on the
skin, by the retrograde motions of the cutaneous branch? for, if we could
suppose, that the increased action of the cutaneous glands or capillaries
poured upon the skin this fluid, previously absorbed from the lungs; why is
not the whole surface of the body covered with sweat? why is not the skin
warm? Add to this, that the sweats above mentioned were clammy or
glutinous, which the condensed perspirable matter is not; whence it would
seem to have been a different fluid from that of common perspiration.

Dr. Dobson, of Liverpool, has given a very ingenious explanation of the
acid sweats, which he observed in a diabetic patient--he thinks part of the
chyle is secreted by the skin, and afterwards undergoes an acetous
fermentation.--Can the chyle get thither, but by an inverted motion of the
cutaneous lymphatics? in the same manner as it is carried to the bladder,
by the inverted motions of the urinary lymphatics. Medic. Observat. and
Enq. London, vol. v.

Are not the cold sweats in some fainting fits, and in dying people, owing
to an inverted motion of the cutaneous lymphatics? for in these there can
be no increased arterial or glandular action.

Is the difficulty of breathing, arising from anasarca of the lungs,
relieved by sweats from the head and neck; whilst that difficulty of
breathing, which arises from a dropsy of the thorax, or pericardium, is
never attended with these sweats of the head? and thence can these diseases
be distinguished from each other? Do the periodic returns of nocturnal
asthma rise from a temporary dropsy of the lungs, collected during their
more torpid state in sound deep, and then re-absorbed by the vehement
efforts of the disordered organs of respiration, and carried off by the
copious sweats about the head and neck?

More extensive and accurate dissections of the lymphatic system are wanting
to enable us to unravel these knots of science.

VII. _Translations of Matter, of Chyle, of Milk, of Urine. Operation of
purging Drugs applied externally._

1. The translations of matter from one part of the body to another, can
only receive an explanation from the doctrine of the occasional retrograde
motions of some branches of the lymphatic system: for how can matter,
absorbed and mixed with the whole mass of blood, be so hastily collected
again in any one part? and is it not an immutable law, in animal bodies,
that each gland can secrete no other, but its own proper fluid? which is,
in part, fabricated in the very gland by an animal process, which it there
undergoes: of these purulent translations innumerable and very remarkable
instances are recorded.

2. The chyle, which is seen among the materials thrown up by violent
vomiting, or in purging stools, can only come thither by its having been
poured into the bowels by the inverted motions of the lacteals: for our
aliment is not converted into chyle in the stomach or intestines by a
chemical process, but is made in the very mouths of the lacteals; or in the
mesenteric glands; in the same manner as other secreted fluids are made by
an animal process in their adapted glands.

Here a curious phænomenon in the exhibition of mercury is worth
explaining:--If a moderate dose of calomel, as six or ten grains, be
swallowed, and within one or two days a cathartic is given, a salivation is
prevented: but after three or four days, a salivation having come on,
repeated purges every day, for a week or two, are required to eliminate the
mercury from the constitution. For this acrid metallic preparation, being
absorbed by the mouth of the lacteals, continues, for a time arrested by
the mesenteric glands, (as the variolous or venereal poisons swell the
subaxillar or inguinal glands): which, during the operation of a cathartic,
is returned into the intestines by the inverted action of the lacteals, and
thus carried out of the system.

Hence we understand the use of vomits or purges, to those who have
swallowed either contagious or poisonous materials, even though exhibited a
day or even two days after such accidents; namely, that by the retrograde
motions of the lacteals and lymphatics, the material still arrested in the
mesenteric, or other glands, may be eliminated from the body.

3. Many instances of milk and chyle found in ulcers are given by Haller,
El. Physiol. t. vii. p. 12, 23, which admit of no other explanation than by
supposing, that the chyle, imbibed by one branch of the absorbent system,
was carried to the ulcer, by the inverted motions of another branch of the
same system.

4. Mrs. P. on the second day after delivery, was seized with a violent
purging, in which, though opiates, mucilages, the bark, and testacea were
profusely used, continued many days, till at length she recovered. During
the time of this purging, no milk could be drawn from her breasts; but the
stools appeared like the curd of milk broken into small pieces. In this
case, was not the milk taken up from the follicles of the pectoral glands,
and thrown on the intestines, by a retrogression of the intestinal
absorbents? for how can we for a moment suspect that the mucous glands of
the intestines could separate pure milk from the blood? Doctor Smelly has
observed, that loose stools, mixed with milk, which is curdled in the
intestines, frequently relieves the turgescency of the breasts of those who
studiously repel their milk. Cases in Midwifery, 43, No. 2. 1.

5. J.F. Meckel observed in a patient, whose urine was in small quantity and
high coloured, that a copious sweat under the arm-pits, of a perfectly
urinous smell, stained the linen; which ceased again when the usual
quantity of urine was discharged by the urethra. Here we must believe from
analogy, that the urine was first secreted in the kidneys, then re-absorbed
by the increased action of the urinary lymphatics, and lastly carried to
the axillae by the retrograde motions of the lymphatic branches of those
parts. As in the jaundice it is necessary, that the bile should first be
secreted by the liver, and re-absorbed into the circulation, to produce the
yellowness of the skin; as was formerly demonstrated by the late Dr. Munro,
(Edin. Medical Essays) and if in this patient the urine had been
re-absorbed into the mass of blood, as the bile in the jaundice, why was it
not detected in other parts of the body, as well as in the arm-pits?

6. Cathartic and vermifuge medicines applied externally to the abdomen,
seem to be taken up by the cutaneous branch of lymphatics, and poured on
the intestines by the retrograde motions of the lacteals, without having
passed the circulation.

For when the drastic purges are taken by the mouth, they excite the
lacteals of the intestines into retrograde motions, as appears from the
chyle, which is found coagulated among the fæces, as was shewn above,
(sect. 2 and 4.) And as the cutaneous lymphatics are joined with the
lacteals of the intestines, by frequent anastomoses; it would be more
extraordinary, when a strong purging drug, absorbed by the skin, is carried
to the anastomosing branches of the lacteals unchanged, if it should not
excite them into retrograde action as efficaciously, as if it was taken by
the mouth, and mixed with the food of the stomach.

VIII. _Circumstances by which the Fluids, that are effused by the
retrograde Motions of the absorbent Vessels, are distinguished._

1. We frequently observe an unusual quantity of mucus or other fluids in
some diseases, although the action of the glands, by which those fluids are
separated from the blood, is not unusually increased; but when the power of
absorption alone is diminished. Thus the catarrhal humour from the nostrils
of some, who ride in frosty weather; and the tears, which run down the
cheeks of those, who have an obstruction of the puncta lacrymalia; and the
ichor of those phagedenic ulcers, which are not attended with inflammation,
are all instances of this circumstance.

These fluids however are easily distinguished from others by their
abounding in ammoniacal or muriatic salts; whence they inflame the
circumjacent skin: thus in the catarrh the upper lip becomes red and
swelled from the acrimony of the mucus, and patients complain of the
saltness of its taste. The eyes and cheeks are red with the corrosive
tears, and the ichor of some herpetic eruptions erodes far and wide the
contiguous parts, and is pungently salt to the taste, as some patients have
informed me.

Whilst, on the contrary, those fluids, which are effused by the retrograde
action of the lymphatics, are for the most part mild and innocent; as
water, chyle, and the natural mucus: or they take their properties from the
materials previously absorbed, as in the coloured or vinous urine, or that
scented with asparagus, described before.

2. Whenever the secretion of any fluid is increased, there is at the same
time an increased heat in the part; for the secreted fluid, as the bile,
did not previously exist in the mass of blood, but a new combination is
produced in the gland. Now as solutions are attended with cold, so
combinations are attended with heat; and it is probable the sum of the heat
given out by all the secreted fluids of animal bodies may be the cause of
their general heat above that of the atmosphere.

Hence the fluids derived from increased secretions are readily
distinguished from those originating from the retrograde motions of the
lymphatics: thus an increase of heat either in the diseased parts, or
diffused over the whole body, is perceptible, when copious bilious stools
are consequent to an inflamed liver; or a copious mucous salivation from
the inflammatory angina.

3. When any secreted fluid is produced in an unusual quantity, and at the
same time the power of absorption is increased in equal proportion, not
only the heat of the gland becomes more intense, but the secreted fluid
becomes thicker and milder, its thinner and saline parts being re-absorbed:
and these are distinguishable both by their greater consistence, and by
their heat, from the fluids, which are effused by the retrograde motions of
the lymphatics; as is observable towards the termination of gonorrhoea,
catarrh, chincough, and in those ulcers, which are said to abound with
laudable pus.

4. When chyle is observed in stools, or among the materials ejected by
vomit, we may be confident it must have been brought thither by the
retrograde motions of the lacteals; for chyle does not previously exist
amid the contents of the intestines, but is made in the very mouths of the
lacteals, as was before explained.

5. When chyle, milk, or other extraneous fluids are found in the urinary
bladder, or in any other excretory receptacle of a gland; no one can for a
moment believe, that these have been collected from the mass of blood by a
morbid secretion, as it contradicts all analogy.

                  ---- Aurea duræ
  Mala ferant quercus? Narcisco floreat alnus?
  Pinguia corticibus sudent electra myricæ?--VIRGIL.

IX. _Retrograde Motions of Vegetable juices._

There are besides some motions of the sap in vegetables, which bear analogy
to our present subject; and as the vegetable tribes are by many
philosophers held to be inferior animals, it may be a matter of curiosity
at least to observe, that their absorbent vessels seem evidently, at times,
to be capable of a retrograde motion. Mr. Perault cut off a forked branch
of a tree, with the leaves on; and inverting one of the forks into a vessel
of water, observed, that the leaves on the other branch continued green
much longer than those of a similar branch, cut off from the same tree;
which shews, that the water from the vessel was carried up one part of the
forked branch, by the retrograde motion of its vessels, and supplied
nutriment some time to the other part of the branch, which was out of the
water. And the celebrated Dr. Hales found, by numerous very accurate
experiments, that the sap of trees rose upwards during the warmer hours of
the day, and in part descended again during the cooler ones. Vegetable
Statics.

It is well known that the branches of willows, and of many other trees,
will either take root in the earth or engraft on other trees, so as to have
their natural direction inverted, and yet flourish with vigour.

Dr. Hope has also made this pleasing experiment, after the manner of
Hales--he has placed a forked branch, cut from one tree, erect between two
others; then cutting off a part of the bark from one fork applied it to a
similar branch of one of the trees in its vicinity; and the same of the
other fork; so that a tree is seen to grow suspended in the air, between
two other trees; which supply their softer friend with due nourishment.

  Miranturque novas frondes, et non sua poma.

All these experiments clearly evince, that the juices of vegetables can
occasionally pass either upwards or downwards in their absorbent system of
vessels.

X. _Objections answered._

The following experiment, at first view, would seem to invalidate this
opinion of the retrograde motions of the lymphatic vessels, in some
diseases.

About a gallon of milk having been giving to an hungry swine, he was
suffered to live about an hour, and was then killed by a stroke or two on
his head with an axe.--On opening his belly the lacteals were well seen
filled with chyle; on irritating many of the branches of them with a knife,
they did not appear to empty themselves hastily; but they did however carry
forwards their contents in a little time.

I then passed a ligature round several branches of lacteals, and irritated
them much with a knife beneath the ligature, but could not make them
regurgitate their contained fluid into the bowels.

I am not indeed certain, that the nerve was not at the same time included
in the ligature, and thus the lymphatic rendered unirritable or lifeless;
but this however is certain, that it is not any quantity of any stimulus,
which induces the vessels of animal bodies to revert their motions; but a
certain quantity of a certain stimulus, as appears from wounds in the
stomach, which do not produce vomiting; and wounds of the intestines, which
do not produce the cholera morbus.

At Nottingham, a few years ago, two shoemakers quarrelled, and one of them
with a knife, which they use in their occupation, stabbed his companion
about the region of the stomach. On opening the abdomen of the wounded man
after his death the food and medicines he had taken were in part found in
the cavity of the belly, on the outside of the bowels; and there was a
wound about half an inch long at the bottom of the stomach; which I suppose
was distended with liquor and food at the time of the accident; and thence
was more liable to be injured at its bottom: but during the whole time he
lived, which was about ten days, he had no efforts to vomit, nor ever even
complained of being sick at the stomach! Other cases similar to this are
mentioned in the philosophical transactions.

Thus, if you vellicate the throat with a feather, nausea is produced; if
you wound it with a penknife, pain is induced, but not sickness. So if the
soles of the feet of children or their armpits are tickled, convulsive
laughter is excited, which ceases the moment the hand is applied, so as to
rub them more forcibly.

The experiment therefore above related upon the lacteals of a dead pig,
which were included in a strict ligature, proves nothing; as it is not the
quantity, but the kind of stimulus, which excites the lymphatic vessels
into retrograde motion.

XI. _The Causes which induce the retrograde Motions of animal Vessels; and
the Medicines by which the natural Motions are restored._

1. Such is the construction of animal bodies, that all their parts, which
are subjected to less stimuli than nature designed, perform their functions
with less accuracy: thus, when too watery or too acescent food is taken
into the stomach, indigestion, and flatulency, and heartburn succeed.

2. Another law of irritation, connate with our existence, is, that all
those parts of the body, which have previously been exposed to too great a
quantity of such stimuli, as strongly affect them, become for some time
afterwards disobedient to the natural quantity of their adapted
stimuli.--Thus the eye is incapable of seeing objects in an obscure room,
though the iris is quite dilated, after having been exposed to the meridian
sun.

3. There is a third law of irritation, that all the parts of our bodies,
which have been lately subjected to less stimulus, than they have been
accustomed to, when they are exposed to their usual quantity of stimulus,
are excited into more energetic motions: thus when we come from a dusky
cavern into the glare of daylight, our eyes are dazzled; and after emerging
from the cold bath, the skin becomes warm and red.

4. There is a fourth law of irritation, that all the parts of our bodies,
which are subjected to still stronger stimuli for a length of time, become
torpid, and refuse to obey even these stronger stimuli; and thence do their
offices very imperfectly.--Thus, if any one looks earnestly for some
minutes on an area, an inch diameter, of red silk, placed on a sheet of
white paper, the image of the silk will gradually become pale, and at
length totally vanish.

5. Nor is it the nerves of sense alone, as the optic and auditory nerves,
that thus become torpid, when the stimulus is withdrawn or their
irritability decreased; but the motive muscles, when they are deprived of
their natural stimuli, or of their irritability, become torpid and
paralytic; as is seen in the tremulous hand of the drunkard in a morning;
and in the awkward step of age.

The hollow muscles also, of which the various vessels of the body are
constructed, when they are deprived of their natural stimuli, or of their
due degree of irritability, not only become tremulous, as the arterial
pulsations of dying people; but also frequently invert their motions, as in
vomiting, in hysteric suffocations, and diabetes above described.

I must beg your patient attention, for a few moments whilst I endeavour to
explain, how the retrograde actions of our hollow muscles are the
consequence of their debility; as the tremulous actions of the solid
muscles are the consequence of their debility. When, through fatigue, a
muscle can act no longer; the antagonist muscles, either by their inanimate
elasticity, or by their animal action, draw the limb into a contrary
direction: in the solid muscles, as those of locomotion, their actions are
associated in tribes, which have been accustomed to synchronous action
only; hence when they are fatigued, only a single contrary effort takes
place; which is either tremulous, when the fatigued muscles are again
immediately brought into action; or it is a pandiculation, or stretching,
where they are not immediately again brought into action.

Now the motions of the hollow muscles, as they in general propel a fluid
along their cavities, are associated in trains, which have been accustomed
to successive actions: hence when one ring of such a muscle is fatigued
from its too great debility, and is brought into retrograde action, the
next ring from its association falls successively into retrograde action;
and so on throughout the whole canal. See Sect. XXV. 6.

6. But as the retrograde motions of the stomach, oesophagus, and fauces in
vomiting are, as it were, apparent to the eye; we shall consider this
operation more minutely, that the similar operations in the more recondite
parts of our system may be easier understood.

From certain nauseous ideas of the mind, from an ungrateful taste in the
mouth, or from foetid smells, vomiting is sometimes instantly excited; or
even from a stroke on the head, or from the vibratory motions of a ship;
all which originate from association, or sympathy. See Sect. XX. on
Vertigo.

But when the stomach is subjected to a less stimulus than is natural,
according to the first law of irritation mentioned above, its motions
become disturbed, as in hunger; first pain is produced, then sickness, and
at length vain efforts to vomit, as many authors inform us.

But when a great quantity of wine, or of opium, is swallowed, the
retrograde motions of the stomach do not occur till after several minutes,
or even hours; for when the power of so strong a stimulus ceases, according
to the second law of irritation, mentioned above, the peristaltic motions
become tremulous, and at length retrograde; as is well known to the
drunkard, who on the next morning has sickness and vomitings.

When a still greater quantity of wine, or of opium, or when nauseous
vegetables, or strong bitters, or metallic salts, are taken into the
stomach, they quickly induce vomiting; though all these in less doses
excite the stomach into more energetic action, and strengthen the
digestion; as the flowers of chamomile, and the vitriol of zinc: for,
according to the fourth law of irritation, the stomach will not long be
obedient to a stimulus so much greater than is natural; but its action
becomes first tremulous and then retrograde.

7. When the motions of any vessels become retrograde, less heat of the body
is produced; for in paroxysms of vomiting, of hysteric affections, of
diabetes, of asthma, the extremities of the body are cold: hence we may
conclude, that these symptoms arise from the debility of the parts in
action; for an increase of muscular action is always attended with increase
of heat.

8. But as animal debility is owing to defect of stimulus, or to defect of
irritability, as shewn above, the method of cure is easily deduced: when
the vascular muscles are not excited into their due action by the natural
stimuli, we should exhibit those medicines, which possess a still greater
degree of stimulus; amongst these are the foetids, the volatiles,
aromatics, bitters, metallic salts, opiates, wine, which indeed should be
given in small doses, and frequently repeated. To these should be added
constant, but moderate exercise, cheerfulness of mind, and change of
country to a warmer climate; and perhaps occasionally the external stimulus
of blisters.

It is also frequently useful to diminish the quantity of natural stimulus
for a short time, by which afterwards the irritability of the system
becomes increased; according to the third law of irritation
above-mentioned, hence the use of baths somewhat colder than animal heat,
and of equitation in the open air.

_The catalogue of diseases owing to the retrograde motions of lymphatics is
here omitted, as it will appear in the second volume of this work. The
following is the conclusion to this thesis of_ Mr. CHARLES DARWIN.

Thus have I endeavoured in a concise manner to explain the numerous
diseases, which deduce their origin from the inverted motions of the hollow
muscles of our bodies: and it is probable, that Saint Vitus's dance, and
the stammering of speech, originate from a similar, inverted order of the
associated motions of some of the solid muscles; which, as it is foreign to
my present purpose, I shall not here discuss.

I beg, illustrious professors, and ingenious fellow-students, that you will
recollect how difficult a talk I have attempted, to evince the retrograde
motions of the lymphatic vessels, when the vessels themselves for so many
ages escaped the eyes and glasses of philosophers: and if you are not yet
convinced of the truth of this theory, hold, I entreat you, your minds in
suspense, till ANATOMY draws her sword with happier omens, cuts asunder the
knots, which entangle PHYSIOLOGY; and, like an augur inspecting the
immolated victim, announces to mankind the wisdom of HEAVEN.

       *       *       *       *       *

SECT. XXX.

PARALYSIS OF THE LIVER AND KIDNEYS.

    I. 1._Bile-ducts less irritable after having been stimulated much._ 2.
    _Jaundice from paralysis of the bile-ducts cured by electric shocks._
    3. _From bile-stones. Experiments on bile-stones. Oil vomit._ 4. _Palsy
    of the liver, two cases._ 5. _Schirrosity of the liver._ 6. _Large
    livers of geese._ II. _Paralysis of the kidneys._ III. _Story of
    Prometheus._

I. 1. From the ingurgitation of spirituous liquors into the stomach and
duodenum, the termination of the common bile-duct in that bowel becomes
stimulated into unnatural action, and a greater quantity of bile is
produced from all the secretory vessels of the liver, by the association of
their motions with those of their excretory ducts; as has been explained in
Section XXIV. and XXV. but as all parts of the body, that have been
affected with stronger stimuli for any length of time, become less
susceptible of motion, from their natural weaker stimuli, it follows, that
the motions of the secretory vessels, and in consequence the secretion of
bile, is less than is natural during the intervals of sobriety. 2. If this
ingurgitation of spirituous liquors has been daily continued in
considerable quantity, and is then suddenly intermitted, a languor or
paralysis of the common bile-duct is induced; the bile is prevented from
being poured into the intestines; and as the bilious absorbents are
stimulated into stronger action by its accumulation, and by the acrimony or
viscidity, which it acquires by delay, it is absorbed, and carried to the
receptacle of the chyle; or otherwise the secretory vessels of the liver,
by the above-mentioned stimulus, invert their motions, and regurgitate
their contents into the blood, as sometimes happens to the tears in the
lachrymal sack, see Sect. XXIV. 2. 7. and one kind of jaundice is brought
on.

There is reason to believe, that the bile is most frequently returned into
the circulation by the inverted motions of these hepatic glands, for the
bile does not seem liable to be absorbed by the lymphatics, for it soaks
through the gall-ducts, and is frequently found in the cellular membrane.
This kind of jaundice is not generally attended with pain, neither at the
extremity of the bile-duct, where it enters the duodenum, nor on the region
of the gall-bladder.

Mr. S. a gentleman between 40 and 50 years of age, had had the jaundice
about six weeks, without pain, sickness, or fever; and had taken emetics,
cathartics, mercurials, bitters, chalybeates, essential oil, and ether,
without apparent advantage. On a supposition that the obstruction of the
bile might be owing to the paralysis, or torpid action of the common
bile-duct, and the stimulants taken into the stomach seeming to have no
effect, I directed half a score smart electric shocks from a coated bottle,
which held about a quart, to be passed through the liver, and along the
course of the common gall-duct, as near as could be guessed, and on that
very day the stools became yellow; he continued the electric shocks a few
days more, and his skin gradually became clear.

3. The bilious vomiting and purging, that affects some people by intervals
of a few weeks, is a less degree of this disease; the bile-duct is less
irritable than natural, and hence the bile becomes accumulated in the
gall-bladder, and hepatic ducts, till by its quantity, acrimony or
viscidity, a greater degree of irritation is produced, and it is suddenly
evacuated, or lastly from the absorption of the more liquid parts of the
bile, the remainder becomes inspissated, and chrystallizes into masses too
large to pass, and forms another kind of jaundice, where the bile-duct is
not quite paralytic, or has regained its irritability.

This disease is attended with much pain, which at first is felt at the pit
of the stomach, exactly in the centre of the body, where the bile-duct
enters the duodenum; afterwards, when the size of the bile-stones increase,
it is also felt on the right side, where the gall-bladder is situated. The
former pain at the pit of the stomach recurs by intervals, as the
bile-stone is pushed against the neck of the duct; like the paroxysms of
the stone in the urinary bladder, the other is a more dull and constant
pain.

Where these bile-stones are too large to pass, and the bile-ducts possess
their sensibility, this becomes a very painful and hopeless disease. I made
the following experiments with a view to their chemical solution.

Some fragments of the same bile-stone were put into the weak spirit of
marine salt, which is sold in the shops, and into solution of mild alcali;
and into a solution of caustic alcali; and into oil of turpentine; without
their being dissolved. All these mixtures were after some time put into a
heat of boiling water, and then the oil of turpentine dissolved its
fragments of bile-stone, but no alteration was produced upon those in the
other liquids except some change of their colour.

Some fragments of the same bile-stone were put into vitriolic æther, and
were quickly dissolved without additional heat. Might not æther mixed with
yolk of egg or with honey be given advantageously in bilious concretions?

I have in two instances seen from 30 to 50 bile-stones come away by stool,
about the size of large peas, after having given six grains of calomel in
the evening, and four ounces of oil of almonds or olives on the succeeding
morning. I have also given half a pint of good olive or almond oil as an
emetic during the painful fit, and repeated it in half an hour, if the
first did not operate, with frequent good effect.

4. Another disease of the liver, which I have several times observed,
consists in the inability or paralysis of the secretory vessels. This
disease has generally the same cause as the preceding one, the too frequent
potation of spirituous liquors, or the too sudden omission of them, after
the habit is confined; and is greater or less in proportion, as the whole
or a part of the liver is affected, and as the inability or paralysis is
more or less complete.

This palsy of the liver is known from these symptoms, the patients have
generally passed the meridian of life, have drank fermented liquors daily,
but perhaps not been opprobrious drunkards; they lose their appetite, then
their flesh and strength diminish in consequence, there appears no bile in
their stools, nor in their urine, nor is any hardness or swelling
perceptible on the region of the liver. But what is peculiar to this
disease, and distinguishes it from all others at the first glance of the
eye, is the bombycinous colour of the skin, which, like that of full-grown
silkworms, has a degree of transparency with a yellow tint not greater than
is natural to the serum of the blood.

Mr. C. and Mr. B. both very strong men, between 50 and 60 years of age, who
had drank ale at their meals instead of small beer, but were not reputed
hard-drinkers, suddenly became weak, lost their appetite, flesh, and
strength, with all the symptoms above enumerated, and died in about two
months from the beginning of their malady. Mr. C. became anasarcous a few
days before his death, and Mr. B. had frequent and great hæmorrhages from
an issue, and some parts of his mouth, a few days before his death. In both
these cases calomel, bitters and chalybeates were repeatedly used without
effect.

One of the patients described above, Mr. C, was by trade a plumber; both of
them could digest no food, and died apparently for want of blood. Might not
the transfusion of blood be used in these cases with advantage?

5. When the paralysis of the hepatic glands is less complete, or less
universal, a schirrosity of some part of the liver is induced; for the
secretory vessels retaining some of their living power take up a fluid from
the circulation, without being sufficiently irritable to carry it forwards
to their excretory ducts; hence the body, or receptacle of each gland,
becomes inflated, and this distension increases, till by its very great
stimulus inflammation is produced, or till those parts of the viscus become
totally paralytic. This disease is distinguishable from the foregoing by
the palpable hardness or largeness of the liver; and as the hepatic glands
are not totally paralytic, or the whole liver not affected, some bile
continues to be made. The inflammations of this viscus, consequent to the
schirrosity of it, belong to the diseases of the sensitive motions, and
will be treated of hereafter.

6. The ancients are said to have possessed an art of increasing the livers
of geese to a size greater than the remainder of the goose. Martial. l. 13.
epig. 58.--This is said to have been done by fat and figs. Horace, l. 2.
sat. 8.--Juvenal sets these large livers before an epicure as a great
rarity. Sat. 5. l. 114; and Persius, sat. 6. l. 71. Pliny says these large
goose-livers were soaked in mulled milk, that is, I suppose, milk mixed
with honey and wine; and adds, "that it is uncertain whether Scipio
Metellus, of consular dignity, or M. Sestius, a Roman knight, was the great
discoverer of this excellent dish." A modern traveller, I believe Mr.
Brydone, asserts that the art of enlarging the livers of geese still exists
in Sicily; and it is to be lamented that he did not import it into his
native country, as some method of affecting the human liver might perhaps
have been collected from it; besides the honour he might have acquired in
improving our giblet pies.

Our wiser caupones, I am told, know how to fatten their fowls, as well as
their geese, for the London markets, by mixing gin instead of figs and fat
with their food; by which they are said to become sleepy, and to fatten
apace, and probably acquire enlarged livers; as the swine are asserted to
do, which are fed on the sediments of barrels in the distilleries; and
which so frequently obtains in those, who ingurgitate much ale, or wine, or
drams.

II. The irritative diseases of the kidneys, pancreas, spleen, and other
glands, are analogous to those of the liver above described, differing only
in the consequences attending their inability to action. For instance, when
the secretory vessels of the kidneys become disobedient to the stimulus of
the passing current of blood, no urine is separated or produced by them;
their excretory mouths become filled with concreted mucus, or calculus
matter, and in eight or ten days stupor and death supervenes in consequence
of the retention of the feculent part of the blood.

This disease in a slighter degree, or when only a part of the kidney is
affected, is succeeded by partial inflammation of the kidney in consequence
of previous torpor. In that case greater actions of the secretory vessels
occur, and the nucleus of gravel is formed by the inflamed mucous membranes
of the tubuli uriniferi, as farther explained in its place.

This torpor, or paralysis of the secretory vessels of the kidneys, like
that of the liver, owes its origin to their being previously habituated to
too great stimulus; which in this country is generally owing to the alcohol
contained in ale or wine; and hence must be registered amongst the diseases
owing to inebriety; though it may be caused by whatever occasionally
inflames the kidney; as too violent riding on horseback, or the cold from a
damp bed, or by sleeping on the cold ground; or perhaps by drinking in
general too little aqueous fluids.

III. I shall conclude this section on the diseases of the liver induced by
spirituous liquors, with the well known story of Prometheus, which seems
indeed to have been invented by physicians in those ancient times, when all
things were clothed in hieroglyphic, or in fable. Prometheus was painted as
stealing fire from heaven, which might well represent the inflammable
spirit produced by fermentation; which may be said to animate or enliven
the man of clay: whence the conquests of Bacchus, as well as the temporary
mirth and noise of his devotees. But the after punishment of those, who
steal this accursed fire, is a vulture gnawing the liver; and well
allegorises the poor inebriate lingering for years under painful hepatic
diseases. When the expediency of laying a further tax on the distillation
of spirituous liquors from grain was canvassed before the House of Commons
some years ago, it was said of the distillers, with great truth, "_They
take the bread from the people, and convert it into poison!_" Yet is this
manufactory of disease permitted to continue, as appears by its paying into
the treasury above 900,000l. near a million of money annually. And thus,
under the names of rum, brandy, gin, whisky, usquebaugh, wine, cyder, beer,
and porter, alcohol is become the bane of the Christian world, as opium of
the Mahometan.

          Evoe! parce, liber?
  Parce, gravi metuende thirso!--Hor.

       *       *       *       *       *

SECT. XXXI.

OF TEMPERAMENTS.

    I. _The temperament of decreased irritability known by weak pulse,
    large pupils of the eyes, cold extremities. Are generally supposed to
    be too irritable. Bear pain better than labour. Natives of
    North-America contrasted with those upon the coast of Africa. Narrow
    and broad shouldered people. Irritable constitutions bear labour better
    than pain._ II. _Temperament of increased sensibility. Liable to
    intoxication, to inflammation, hæmoptoe, gutta serena, enthusiasm,
    delirium, reverie. These constitutions are indolent to voluntary
    exertions, and dull to irritations. The natives of South-America, and
    brute animals of this temperament._ III. _Of increased voluntarity;
    these are subject to locked jaw, convulsions, epilepsy, mania. Are very
    active, bear cold, hunger, fatigue. Are suited to great exertions. This
    temperament distinguishes mankind from other animals._ IV. _Of
    increased association. These have great memories, are liable to quartan
    agues, and stronger sympathies of parts with each other._ V. _Change of
    temperaments into one another._

Antient writers have spoken much of temperaments, but without sufficient
precision. By temperament of the system should be meant a permanent
predisposition to certain classes of diseases: without this definition a
temporary predisposition to every distinct malady might be termed a
temperament. There are four kinds of constitution, which permanently
deviate from good health, and are perhaps sufficiently marked to be
distinguished from each other, and constitute the temperaments or
predispositions to the irritative, sensitive, voluntary, and associate
classes of diseases.

I. _The Temperament of decreased Irritability._

The diseases, which are caused by irritation, most frequently originate
from the defect of it; for those, which are immediately owing to the excess
of it, as the hot fits of fever, are generally occasioned by an
accumulation of sensorial power in consequence of a previous defect of
irritation, as in the preceding cold fits of fever. Whereas the diseases,
which are caused by sensation and volition, most frequently originate from
the excess of those sensorial powers, as will be explained below.

The temperament of decreased irritability appears from the following
circumstances, which shew that the muscular fibres or organs of sense are
liable to become torpid or quiescent from less defect of stimulation than
is productive of torpor or quiescence in other constitutions.

1. The first is the weak pulse, which in some constitutions is at the same
time quick. 2. The next most marked criterion of this temperament is the
largeness of the aperture of the iris, or pupil of the eye, which has been
reckoned by some a beautiful feature in the female countenance, as an
indication of delicacy, but to an experienced observer it is an indication
of debility, and is therefore a defect, not an excellence. The third most
marked circumstance in this constitution is, that the extremities, as the
hands and feet, or nose and ears, are liable to become cold and pale in
situations in respect to warmth, where those of greater strength are not
affected. Those of this temperament are subject to hysteric affections,
nervous fevers, hydrocephalus, scrophula, and consumption, and to all other
diseases of debility.

Those, who possess this kind of constitution, are popularly supposed to be
more irritable than is natural, but are in reality less so.

This mistake has arisen from their generally having a greater quickness of
pulse, as explained in Sect. XII. 1. 4. XII. 3. 3.; but this frequency of
pulse is not necessary to the temperament, like the debility of it.

Persons of this temperament are frequently found amongst the softer sex,
and amongst narrow-shouldered men; who are said to bear labour worse, and
pain better than others. This last circumstance is supposed to have
prevented the natives of North America from having been made slaves by the
Europeans. They are a narrow-shouldered race of people, and will rather
expire under the lash, than be made to labour. Some nations of Asia have
small hands, as may be seen by the handles of their scymetars; which with
their narrow shoulders shew, that they have not been accustomed to so great
labour with their hands and arms, as the European nations in agriculture,
and those on the coasts of Africa in swimming and rowing. Dr. Maningham, a
popular accoucheur in the beginning of this century, observes in his
aphorisms, that broad-shouldered men procreate broad-shouldered children.
Now as labour strengthens the muscles employed, and increases their bulk,
it would seem that a few generations of labour or of indolence may in this
respect change the form and temperament of the body.

On the contrary, those who are happily possessed of a great degree of
irritability, bear labour better than pain; and are strong, active, and
ingenious. But there is not properly a temperament of increased
irritability tending to disease, because an increased quantity of
irritative motions generally induces an increase of pleasure or pain, as in
intoxication, or inflammation; and then the new motions are the immediate
consequences of increased sensation, not of increased irritation; which
have hence been so perpetually confounded with each other.

II. _Temperament of Sensibility._

There is not properly a temperament, or predisposition to disease, from
decreased sensibility, since irritability and not sensibility is
immediately necessary to bodily health. Hence it is the excess of sensation
alone, as it is the defect of irritation, that most frequently produces
disease. This temperament of increased sensibility is known from the
increased activity of all those motions of the organs of sense and muscles,
which are exerted in consequence of pleasure or pain, as in the beginning
of drunkenness, and in inflammatory fever. Hence those of this constitution
are liable to inflammatory diseases, as hepatitis; and to that kind of
consumption which is hereditary, and commences with slight repeated
hæmoptoe. They have high-coloured lips, frequently dark hair and dark eyes
with large pupils, and are in that case subject to gutta serena. They are
liable to enthusiasm, delirium, and reverie. In this last circumstance they
are liable to start at the clapping of a door; because the more intent any
one is on the passing current of his ideas, the greater surprise he
experiences on their being dissevered by some external violence, as
explained in Sect. XIX. on reverie.

As in these constitutions more than the natural quantities of sensitive
motions are produced by the increased quantity of sensation existing in the
habit, it follows, that the irritative motions will be performed in some
degree with less energy, owing to the great expenditure of sensorial power
on the sensitive ones. Hence those of this temperament do not attend to
slight stimulations, as explained in Sect. XIX. But when a stimulus is so
great as to excite sensation, it produces greater sensitive actions of the
system than in others; such as delirium or inflammation. Hence they are
liable to be absent in company; sit or lie long in one posture; and in
winter have the skin of their legs burnt into various colours by the fire.
Hence also they are fearful of pain; covet music and sleep; and delight in
poetry and romance.

As the motions in consequence of sensation are more than natural, it also
happens from the greater expenditure of sensorial power on them, that the
voluntary motions are less easily exerted. Hence the subjects of this
temperament are indolent in respect to all voluntary exertions, whether of
mind or body.

A race of people of this description seems to have been found by the
Spaniards in the islands of America, where they first landed, ten of whom
are said not to have consumed more food than one Spaniard, nor to have been
capable of more than one tenth of the exertion of a Spaniard. Robertson's
History.--In a state similar to this the greatest part of the animal world
pass their lives, between sleep or inactive reverie, except when they are
excited by the call of hunger.

III. _The Temperament of increased Voluntarity._

Those of this constitution differ from both the last mentioned in this,
that the pain, which gradually subsides in the first, and is productive of
inflammation or delirium in the second, is in this succeeded by the
exertion of the muscles or ideas, which are most frequently connected with
volition; and they are thence subject to locked jaw, convulsions, epilepsy,
and mania, as explained in Sect. XXXIV. Those of this temperament attend to
the slightest irritations or sensations, and immediately exert themselves
to obtain or avoid the objects of them; they can at the same time bear cold
and hunger better than others, of which Charles the Twelfth of Sweden was
an instance. They are suited and generally prompted to all great exertions
of genius or labour, as their desires are more extensive and more vehement,
and their powers of attention and of labour greater. It is this facility of
voluntary exertion, which distinguishes men from brutes, and which has made
them lords of the creation.

IV. _The Temperament of increased Association._

This constitution consists in the too great facility, with which the
fibrous motions acquire habits of association, and by which these
associations become proportionably stronger than in those of the other
temperaments. Those of this temperament are slow in voluntary exertions, or
in those dependent on sensation, or on irritation. Hence great memories
have been said to be attended with less sense and less imagination from
Aristotle down to the present time; for by the word memory these writers
only understood the unmeaning repetition of words or numbers in the order
they were received, without any voluntary efforts of the mind.

In this temperament those associations of motions, which are commonly
termed sympathies, act with greater certainty and energy, as those between
disturbed vision and the inversion of the motion of the stomach, as in
sea-sickness; and the pains in the shoulder from hepatic inflammation. Add
to this, that the catenated circles of actions are of greater extent than
in the other constitutions. Thus if a strong vomit or cathartic be
exhibited in this temperament, a smaller quantity will produce as great an
effect, if it be given some weeks afterwards; whereas in other temperaments
this is only to be expected, if it be exhibited in a few days after the
first dose. Hence quartan agues are formed in those of this temperament, as
explained in Section XXXII. on diseases from irritation, and other
intermittents are liable to recur from slight causes many weeks after they
have been cured by the bark.

V. The first of these temperaments differs from the standard of health from
defect, and the others from excess of sensorial power; but it sometimes
happens that the same individual, from the changes introduced into his
habit by the different seasons of the year, modes or periods of life, or by
accidental diseases, passes from one of these temperaments to another. Thus
a long use of too much fermented liquor produces the temperament of
increased sensibility; great indolence and solitude that of decreased
irritability; and want of the necessaries of life that of increased
voluntarity.

       *       *       *       *       *

SECT. XXXII.

DISEASES OF IRRITATION.

    I. _Irritative fevers with strong pulse. With weak pulse. Symptoms of
    fever, Their source._ II. 1. _Quick pulse is owing to decreased
    irritability_. 2. _Not in sleep or in apoplexy._ 3. _From inanition.
    Owing to deficiency of sensorial power._ III. 1. _Causes of fever. From
    defect of heat. Heat from secretions. Pain of cold in the loins and
    forehead._ 2. _Great expense of sensorial power in the vital motions.
    Immersion in cold water. Succeeding glow of heat. Difficult respiration
    in cold bathing explained. Why the cold bath invigorates. Bracing and
    relaxation are mechanical terms._ 3. _Uses of cold bathing. Uses of
    cold air in fevers._ 4. _Ague fits from cold air. Whence their
    periodical returns._ IV. _Defect of distention a cause of fever.
    Deficiency of blood. Transfusion of blood._ V. 1. _Defect of momentum
    of the blood from mechanic stimuli. 2. Air injected into the
    blood-vessels._ 3. _Exercise increases the momentum of the blood._ 4.
    _Sometimes bleeding increases the momentum of it._ VI. _Influence of
    the sun and moon on diseases. The chemical stimulus of the blood.
    Menstruation obeys the lunations. Queries._ VII. _Quiesence of large
    glands a cause of fever. Swelling of the præcordia._ VIII. _Other
    causes of quiescence, as hunger, bad air, fear, anxiety._ IX. 1.
    _Symptoms of the cold fit._ 2. _Of the hot fit._ 3. _Second cold fit
    why._ 4. _Inflammation introduced, or delirium, or stupor._ X.
    _Recapitulation. Fever not an effort of nature to relieve herself.
    Doctrine of spasm._

I. When the contractile sides of the heart and arteries perform a greater
number of pulsations in a given time, and move through a greater area at
each pulsation, whether these motions are occasioned by the stimulus of the
acrimony or quantity of the blood, or by their association with other
irritative motions, or by the increased irritability of the arterial
system, that is, by an increased quantity of sensorial power, one kind of
fever is produced; which may be called Synocha irritativa, or Febris
irritativa pulsu forti, or irritative fever with strong pulse.

When the contractile sides of the heart and arteries perform a greater
number of pulsations in a given time, but move through a much less area at
each pulsation, whether these motions are occasioned by defect of their
natural stimuli, or by the defect of other irritative motions with which
they are associated, or from the inirritability of the arterial system,
that is, from a decreased quantity of sensorial power, another kind of
fever arises; which may be termed, Typhus irritativus, or Febris irritativa
pulsu debili, or irritative fever with weak pulse. The former of these
fevers is the synocha of nosologists, and the latter the typhus mitior, or
nervous fever. In the former there appears to be an increase of sensorial
power, in the latter a deficiency of it; which is shewn to be the immediate
cause of strength and weakness, as defined in Sect. XII. 1. 3.

It should be added, that a temporary quantity of strength or debility may
be induced by the defect or excess of stimulus above what is natural; and
that in the same fever _debility always exists during the cold fit, though
strength does not always exist during the hot fit._

These fevers are always connected with, and generally induced by, the
disordered irritative motions of the organs of sense, or of the intestinal
canal, or of the glandular system, or of the absorbent system; and hence
are always complicated with some or many of these disordered motions, which
are termed the symptoms of the fever, and which compose the great variety
in these diseases.

The irritative fevers both with strong and with weak pulse, as well as the
sensitive fevers with strong and with weak pulse, which are to be described
in the next section, are liable to periodical remissions, and then they
take the name of intermittent fevers, and are distinguished by the
periodical times of their access.

II. For the better illustration of the phenomena of irritative fevers we
must refer the reader to the circumstances of irritation explained in Sect.
XII. and shall commence this intricate subject by speaking of the quick
pulse, and proceed by considering many of the causes, which either
separately or in combination most frequently produce the cold fits of
fevers.

1. If the arteries are dilated but to half their usual diameters, though
they contract twice as frequently in a given time, they will circulate only
half their usual quantity of blood: for as they are cylinders, the blood
which they contain must be as the squares of their diameters. Hence when
the pulse becomes quicker and smaller in the same proportion, the heart and
arteries act with less energy than in their natural state. See Sect. XII.
1. 4.

That this quick small pulse is owing to want of irritability, appears,
first, because it attends other symptoms of want of irritability; and,
secondly, because on the application of a stimulus greater than usual, it
becomes slower and larger. Thus in cold fits of agues, in hysteric
palpitations of the heart, and when the body is much exhausted by
hæmorrhages, or by fatigue, as well as in nervous fevers, the pulse becomes
quick and small; and secondly, in all those cases if an increase of
stimulus be added, by giving a little wine or opium; the quick small pulse
becomes slower and larger, as any one may easily experience on himself, by
counting his pulse after drinking one or two glasses of wine, when he is
faint from hunger or fatigue.

Now nothing can so strongly evince that this quick small pulse is owing to
defect of irritability, than that an additional stimulus, above what is
natural, makes it become slower and larger immediately: for what is meant
by a defect of irritability, but that the arteries and heart are not
excited into their usual exertions by their usual quantity of stimulus? but
if you increase the quantity of stimulus, and they immediately act with
their usual energy, this proves their previous want of their natural degree
of irritability. Thus the trembling hands of drunkards in a morning become
steady, and acquire strength to perform their usual offices, by the
accustomed stimulus of a glass or two of brandy.

2. In sleep and in apoplexy the pulse becomes slower, which is not owing to
defect of irritability, for it is at the same time larger; and thence the
quantity of the circulation is rather increased than diminished. In these
cases the organs of sense are closed, and the voluntary power is suspended,
while the motions dependent on internal irritations, as those of digestion
and secretion, are carried on with more than their usual vigour; which has
led superficial observers to confound these cases with those arising from
want of irritability. Thus if you lift up the eyelid of an apoplectic
patient, who is not actually dying, the iris will, as usual, contract
itself, as this motion is associated with the stimulus of light; but it is
not so in the last stages of nervous fevers, where the pupil of the eye
continues expanded in the broad day-light: in the former case there is a
want of voluntary power, in the latter a want of irritability.

Hence also those constitutions which are deficient in quantity of
irritability, and which possess too great sensibility, as during the pain
of hunger, of hysteric spasms, or nervous headachs, are generally supposed
to have too much irritability; and opium, which in its due dose is a most
powerful stimulant, is erroneously called a sedative; because by increasing
the irritative motions it decreases the pains arising from defect of them.

Why the pulse should become quicker both from an increase of irritation, as
in the synocha irritativa, or irritative fever with strong pulse; and from
the decrease of it, as in the typhus irritativus, or irritative fever with
weak pulse; seems paradoxical. The former circumstance needs no
illustration; since if the stimulus of the blood, or the irritability of
the sanguiferous system be increased, and the strength of the patient not
diminished, it is plain that the motions must be performed quicker and
stronger.

In the latter circumstance the weakness of the muscular power of the heart
is soon over-balanced by the elasticity of the coats of the arteries, which
they possess besides a muscular power of contraction; and hence the
arteries are distended to less than their usual diameters. The heart being
thus stopped, when it is but half emptied, begins sooner to dilate again;
and the arteries being dilated to less than their usual diameters, begin so
much sooner to contract themselves; insomuch, that in the last stages of
fevers with weakness the frequency of pulsation of the heart and arteries
becomes doubled; which, however, is never the case in fevers with strength,
in which they seldom exceed 118 or 120 pulsations in a minute. It must be
added, that in these cases, while the pulse is very small and very quick,
the heart often feels large, and labouring to one's hand; which coincides
with the above explanation, shewing that it does not completely empty
itself.

3. In cases however of debility from paucity of blood, as in animals which
are bleeding to death in the slaughter-house, the quick pulsations of the
heart and arteries may be owing to their not being distended to more than
half their usual diastole; and in consequence they must contract sooner, or
more frequently, in a given time. As weak people are liable to a deficient
quantity of blood, this cause may occasionally contribute to quicken the
pulse in fevers with debility, which may be known by applying one's hand
upon the heart as above; but the principal cause I suppose to consist in
the diminution of sensorial power. When a muscle contains, or is supplied
with but little sensorial power, its contraction soon ceases, and in
consequence may soon recur, as is seen in the trembling hands of people
weakened by age or by drunkenness. See Sect. XII. 1. 4. XII. 3. 4.

It may nevertheless frequently happen, that both the deficiency of
stimulus, as where the quantity of blood is lessened (as described in No.
4. of this section), and the deficiency of sensorial power, as in those of
the temperament of irritability, described in Sect. XXXI. occur at the same
time; which will thus add to the quickness of the pulse and to the danger
of the disease.

III. 1. A certain degree of heat is necessary to muscular motion, and is,
in consequence, essential to life. This is observed in those animals and
insects which pass the cold season in a torpid state, and which revive on
being warmed by the fire. This necessary stimulus of heat has two sources;
one from the fluid atmosphere of heat, in which all things are immersed,
and the other from the internal combinations of the particles, which form
the various fluids, which are produced in the extensive systems of the
glands. When either the external heat, which surrounds us, or the internal
production of it, becomes lessened to a certain degree, the pain of cold is
perceived.

This pain of cold is experienced most sensibly by our teeth, when ice is
held in the mouth; or by our whole system after having been previously
accustomed to much warmth. It is probable, that this pain does not arise
from the mechanical or chemical effects of a deficiency of heat; but that,
like the organs of sense by which we perceive hunger and thirst, this sense
of heat suffers pain, when the stimulus of its object is wanting to excite
the irritative motions of the organ; that is, when the sensorial power
becomes too much accumulated in the quiescent fibres. See Sect. XII. 5. 3.
For as the peristaltic motions of the stomach are lessened, when the pain
of hunger is great, so the action of the cutaneous capillaries are lessened
during the pain of cold; as appears by the paleness of the skin, as
explained in Sect. XIV. 6. on the production of ideas.

The pain in the small of the back and forehead in the cold fits of the
ague, in nervous hemicrania, and in hysteric paroxysms, when all the
irritative motions are much impaired, seems to arise from this cause; the
vessels of these membranes or muscles become torpid by their irritative
associations with other parts of the body, and thence produce less of their
accustomed secretions, and in consequence less heat is evolved, and they
experience the pain of cold; which coldness may often be felt by the hand
applied upon the affected part.

2. The importance of a greater or less deduction of heat from the system
will be more easy to comprehend, if we first consider the great expense of
sensorial power used in carrying on the vital motions; that is, which
circulates, absorbs, secretes, aerates, and elaborates the whole mass of
fluids with unceasing assiduity. The sensorial power, or spirit of
animation, used in giving perpetual and strong motion to the heart, which
overcomes the elasticity and vis inertiæ of the whole arterial system; next
the expense of sensorial power in moving with great force and velocity the
innumerable trunks and ramifications of the arterial system; the expense of
sensorial power in circulating the whole mass of blood through the long and
intricate intortions of the very fine vessels, which compose the glands and
capillaries; then the expense of sensorial power in the exertions of the
absorbent extremities of all the lacteals, and of all the lymphatics, which
open their mouths on the external surface of the skin, and on the internal
surfaces of every cell or interstice of the body; then the expense of
sensorial power in the venous absorption, by which the blood is received
from the capillary vessels, or glands, where the arterial power ceases, and
is drank up, and returned to the heart; next the expense of sensorial power
used by the muscles of respiration in their office of perpetually expanding
the bronchia, or air-vessels, of the lungs; and lastly in the unceasing
peristaltic motions of the stomach and whole system of intestines, and in
all the secretions of bile, gastric juice, mucus, perspirable matter, and
the various excretions from the system. If we consider the ceaseless
expense of sensorial power thus perpetually employed, it will appear to be
much greater in a day than all the voluntary exertions of our muscles and
organs of sense consume in a week; and all this without any sensible
fatigue! Now, if but a part of these vital motions are impeded, or totally
stopped for but a short time, we gain an idea, that there must be a great
accumulation of sensorial power; as its production in these organs, which
are subject to perpetual activity, is continued during their quiescence,
and is in consequence accumulated.

While, on the contrary, where those vital organs act too forcibly by
increase of stimulus without a proportionally-increased production of
sensorial power in the brain, it is evident, that a great deficiency of
action, that is torpor, must soon follow, as in fevers; whereas the
locomotive muscles, which act only by intervals, are neither liable to so
great accumulation of sensorial power during their times of inactivity, nor
to so great an exhaustion of it during their times of action.

Thus, on going into a very cold bath, suppose at 33 degrees of heat on
Fahrenheit's scale, the action of the subcutaneous capillaries, or glands,
and of the mouths of the cutaneous absorbents is diminished, or ceases for
a time. Hence less or no blood passes these capillaries, and paleness
succeeds. But soon after emerging from the bath, a more florid colour and a
greater degree of heat is generated on the skin than was possessed before
immersion; for the capillary glands, after this quiescent state, occasioned
by the want of stimulus, become more irritable than usual to their natural
stimuli, owing to the accumulation of sensorial power, and hence a greater
quantity of blood is transmitted through them, and a greater secretion of
perspirable matter; and, in consequence, a greater degree of heat succeeds.
During the continuance in cold water the breath is cold, and the act of
respiration quick and laborious; which have generally been ascribed to the
obstruction of the circulating fluid by a spasm of the cutaneous vessels,
and by a consequent accumulation of blood in the lungs, occasioned by the
pressure as well as by the coldness of the water. This is not a
satisfactory account of this curious phænomenon, since at this time the
whole circulation is less, as appears from the smallness of the pulse and
coldness of the breath; which shew that less blood passes through the lungs
in a given time; the same laborious breathing immediately occurs when the
paleness of the skin is produced by fear, where no external cold or
pressure are applied.

The minute vessels of the bronchia, through which the blood passes from the
arterial to the venal system, and which correspond with the cutaneous
capillaries, have frequently been exposed to cold air, and become quiescent
along with those of the skin; and hence their motions are so associated
together, that when one is affected either with quiescence or exertion, the
other sympathizes with it, according to the laws of irritative association.
See Sect. XXVII. 1. on hæmorrhages.

Besides the quiescence of the minute vessels of the lungs, there are many
other systems of vessels which become torpid from their irritative
associations with those of the skin, as the absorbents of the bladder and
intestines; whence an evacuation of pale urine occurs, when the naked skin
is exposed only to the coldness of the atmosphere; and sprinkling the naked
body with cold water is known to remove even pertinacious constipation of
the bowels. From the quiescence of such extensive systems of vessels as the
glands and capillaries of the skin, and the minute vessels of the lungs,
with their various absorbent series of vessels, a great accumulation of
sensorial powers is occasioned; part of which is again expended in the
increased exertion of all these vessels, with an universal glow of heat in
consequence of this exertion, and the remainder of it adds vigour to both
the vital and voluntary exertions of the whole day.

If the activity of the subcutaneous vessels, and of those with which their
actions are associated, was too great before cold immersion, as in the hot
days of summer, and by that means the sensorial power was previously
diminished, we see the cause why the cold bath gives such present strength;
namely, by stopping the unnecessary activity of the subcutaneous vessels,
and thus preventing the too great exhaustion of sensorial power; which, in
metaphorical language, has been called _bracing_ the system: which is,
however, a mechanical term, only applicable to drums, or musical strings:
as on the contrary the word _relaxation_, when applied to living animal
bodies, can only mean too small a quantity of stimulus, or too small a
quantity of sensorial power; as explained in Sect. XII. 1.

3. This experiment of cold bathing presents us with a simple fever-fit; for
the pulse is weak, small, and quick during the cold immersion; and becomes
strong, full, and quick during the subsequent glow of heat; till in a few
minutes these symptoms subside, and the temporary fever ceases.

In those constitutions where the degree of inirritability, or of debility,
is greater than natural, the coldness and paleness of the skin with the
quick and weak pulse continue a long time after the patient leaves the
bath; and the subsequent heat approaches by unequal flushings, and he feels
himself disordered for many hours. Hence the bathing in a cold spring of
water, where the heat is but forty-eight degrees on Fahrenheit's
thermometer, much disagrees with those of weak or inirritable habits of
body; who possess so little sensorial power, that they cannot without
injury bear to have it diminished even for a short time; but who can
nevertheless bear the more temperate coldness of Buxton bath, which is
about eighty degrees of heat, and which strengthens them, and makes them by
habit less liable to great quiescence from small variations of cold, and
thence less liable to be disordered by the unavoidable accidents of life.
Hence it appears, why people of these inirritable constitutions, which is
another expression for sensorial deficiency, are often much injured by
bathing in a cold spring of water; and why they should continue but a very
short time in baths, which are colder than their bodies; and should
gradually increase both the degree of coldness of the water, and the time
of their continuance in it, if they would obtain salutary effects from cold
immersions. See Sect. XII. 2. 1.

On the other hand, in all cases where the heat of the external surface of
the body, or of the internal surface of the lungs, is greater than natural,
the use of exposure to cool air may be deduced. In fever-fits attended with
strength, that is with great quantity of sensorial power, it removes the
additional stimulus of heat from the surfaces above mentioned, and thus
prevents their excess of useless motion; and in fever-fits attended with
debility, that is with a deficiency of the quantity of sensorial power, it
prevents the great and dangerous waste of sensorial power expended in the
unnecessary increase of the actions of the glands and capillaries of the
skin and lungs.

4. In the same manner, when any one is long exposed to very cold air, a
quiescence is produced of the cutaneous and pulmonary capillaries and
absorbents, owing to the deficiency of their usual stimulus of heat; and
this quiescence of so great a quantity of vessels affects, by irritative
association, the whole absorbent and glandular system, which becomes in a
greater or less degree quiescent, and a cold fit of fever is produced.

If the deficiency of the stimulus of heat is very great, the quiescence
becomes so general as to extinguish life, as in those who are frozen to
death.

If the deficiency of heat be in less degree, but yet so great as in some
measure to disorder the system, and should occur the succeeding day, it
will induce a greater degree of quiescence than before, from its acting in
concurrence with the period of the diurnal circle of actions, explained in
Sect. XXXVI. Hence from a small beginning a greater and greater degree of
quiescence may be induced, till a complete fever-fit is formed; and which
will continue to recur at the periods by which it was produced. See Sect.
XVII. 3. 6.

If the degree of quiescence occasioned by defect of the stimulus of heat be
very great, it will recur a second time by a slighter cause, than that
which first induced it. If the cause, which induces the second fit of
quiescence, recurs the succeeding day, the quotidian fever is produced; if
not till the alternate day, the tertian fever; and if not till after
seventy-two hours from the first fit of quiescence, the quartan fever is
formed. This last kind of fever recurs less frequently than the other, as
it is a disease only of those of the temperament of associability, as
mentioned in Sect. XXXI.; for in other constitutions the capability of
forming a habit ceases, before the new cause of quiescence is again
applied, if that does not occur sooner than in seventy-two hours.

And hence those fevers, whose cause is from cold air of the night or
morning, are more liable to observe the solar day in their periods; while
those from other causes frequently observe the lunar day in their periods,
their paroxysms returning near an hour later every day, as explained in
Sect. XXXVI.

IV. Another frequent cause of the cold fits of fever is the defect of the
stimulus of distention. The whole arterial system would appear, by the
experiments of Haller, to be irritable by no other stimulus, and the
motions of the heart and alimentary canal are certainly in some measure
dependant on the same cause. See Sect. XIV. 7. Hence there can be no
wonder, that the diminution of distention should frequently induce the
quiescence, which constitutes the beginning of fever-fits.

Monsieur Leiutaud has judiciously mentioned the deficiency of the quantity
of blood amongst the causes of diseases, which he says is frequently
evident in dissections: fevers are hence brought on by great hæmorrhages,
diarrhoeas, or other evacuations; or from the continued use of diet, which
contains but little nourishment; or from the exhaustion occasioned by
violent fatigue, or by those chronic diseases in which the digestion is
much impaired; as where the stomach has been long affected with the gout or
schirrus; or in the paralysis of the liver, as described in Sect. XXX.
Hence a paroxysm of gout is liable to recur on bleeding or purging; as the
torpor of some viscus, which precedes the inflammation of the foot, is thus
induced by the want of the stimulus of distention. And hence the
extremities of the body, as the nose and fingers, are more liable to become
cold, when we have long abstained from food; and hence the pulse is
increased both in strength and velocity above the natural standard after a
full meal by the stimulus of distention.

However, this stimulus of distention, like the stimulus of heat above
described, though it contributes much to the due action not only of the
heart, arteries, and alimentary canal, but seems necessary to the proper
secretion of all the various glands; yet perhaps it is not the sole cause
of any of these numerous motions: for as the lacteals, cutaneous
absorbents, and the various glands appear to be stimulated into action by
the peculiar pungency of the fluids they absorb, so in the intestinal canal
the pungency of the digesting aliment, or the acrimony of the fæces, seem
to contribute, as well as their bulk, to promote the peristaltic motions;
and in the arterial system, the momentum of the particles of the
circulating blood, and their acrimony, stimulate the arteries, as well as
the distention occasioned by it. Where the pulse is small this defect of
distention is present, and contributes much to produce the febris
irritativa pulsu debili, or irritative fever with weak pulse, called by
modern writers nervous fever, as a predisponent cause. See Sect. XII. 1. 4.
Might not the transfusion of blood, suppose of four ounces daily from a
strong man, or other healthful animal, as a sheep or an ass, be used in the
early state of nervous or putrid fevers with great prospect of success?

V. 1. The defect of the momentum of the particles of the circulating blood
is another cause of the quiescence, with which the cold fits of fever
commence. This stimulus of the momentum of the progressive particles of the
blood does not act over the whole body like those of heat and distention
above described, but is confined to the arterial system; and differs from
the stimulus of the distention of the blood, as much as the vibration of
the air does from the currents of it. Thus are the different organs of our
bodies stimulated by four different mechanic properties of the external
world: the sense of touch by the pressure of solid bodies so as to
distinguish their figure; the muscular system by the distention, which they
occasion; the internal surface of the arteries, by the momentum of their
moving particles; and the auditory nerves, by the vibration of them: and
these four mechanic properties are as different from each other as the
various chemical ones, which are adapted to the numerous glands, and to the
other organs of sense.

2. The momentum of the progressive particles of blood is compounded of
their velocity and their quantity of matter: hence whatever circumstances
diminish either of these without proportionally increasing the other, and
without superadding either of the general stimuli of heat or distention,
will tend to produce a quiescence of the arterial system, and from thence
of all the other irritative motions, which are connected with it.

Hence in all those constitutions or diseases where the blood contains a
greater proportion of serum, which is the lightest part of its composition,
the pulsations of the arteries are weaker, as in nervous fevers, chlorosis,
and hysteric complaints; for in these cases the momentum of the progressive
particles of blood is less: and hence, where the denser parts of its
composition abound, as the red part of it, or the coagulable lymph, the
arterial pulsations are stronger; as in those of robust health, and in
inflammatory diseases.

That this stimulus of the momentum of the particles of the circulating
fluid is of the greatest consequence to the arterial action, appears from
the experiment of injecting air into the blood vessels, which seems to
destroy animal life from the want of this stimulus of momentum; for the
distention of the arteries is not diminished by it, it possesses no
corrosive acrimony, and is less liable to repass the valves than the blood
itself; since air-valves in all machinery require much less accuracy of
construction than those which are opposed to water.

3. One method of increasing the velocity of the blood, and in consequence
the momentum of its particles, is by the exercise of the body, or by the
friction of its surface: so, on the contrary, too great indolence
contributes to decrease this stimulus of the momentum of the particles of
the circulating blood, and thus tends to induce quiescence; as is seen in
hysteric cases, and chlorosis, and the other diseases of sedentary people.

4. The velocity of the particles of the blood in certain circumstances is
increased by venesection, which, by removing a part of it, diminishes the
resistance to the motion of the other part, and hence the momentum of the
particles of it is increased. This may be easily understood by considering
it in the extreme, since, if the resistance was greatly increased, so as to
overcome the propelling power, there could be no velocity, and in
consequence no momentum at all. From this circumstance arises that curious
phænomenon, the truth of which I have been more than once witness to, that
venesection will often instantaneously relieve those nervous pains, which
attend the cold periods of hysteric, asthmatic, or epileptic diseases; and
that even where large doses of opium have been in vain exhibited. In these
cases the pulse becomes stronger after the bleeding, and the extremities
regain their natural warmth; and an opiate then given acts with much more
certain effect.

VI. There is another cause, which seems occasionally to induce quiescence
into some part of our system, I mean the influence of the sun and moon; the
attraction of these luminaries, by decreasing the gravity of the particles
of the blood, cannot affect their momentum, as their vis inertiæ remains
the same; but it may nevertheless produce some chemical change in them,
because whatever affects the general attractions of the particles of matter
may be supposed from analogy to affect their specific attractions or
affinities: and thus the stimulus of the particles of blood may be
diminished, though not their momentum. As the tides of the sea obey the
southing and northing of the moon (allowing for the time necessary for
their motion, and the obstructions of the shores), it is probable, that
there are also atmospheric tides on both sides of the earth, which to the
inhabitants of another planet might so deflect the light as to resemble the
ring of Saturn. Now as these tides of water, or of air, are raised by the
diminution of their gravity, it follows, that their pressure on the surface
of the earth is no greater than the pressure of the other parts of the
ocean, or of the atmosphere, where no such tides exist; and therefore that
they cannot affect the mercury in the barometer. In the same manner, the
gravity of all other terrestrial bodies is diminished at the times of the
southing and northing of the moon, and that in a greater degree when this
coincides with the southing and northing of the sun, and this in a still
greater degree about the times of the equinoxes. This decrease of the
gravity of all bodies during the time the moon passes our zenith or nadir
might possibly be shewn by the slower vibrations of a pendulum, compared
with a spring clock, or with astronomical observation. Since a pendulum of
a certain length moves slower at the line than near the poles, because the
gravity being diminished and the vis inertiæ continuing the same, the
motive power is less, but the resistance to be overcome continues the same.
The combined powers of the lunar and solar attraction is estimated by Sir
Isaac Newton not to exceed one 7,868,850th part of the power of
gravitation, which seems indeed but a small circumstance to produce any
considerable effect on the weight of sublunary bodies, and yet this is
sufficient to raise the tides at the equator above ten feet high; and if it
be considered, what small impulses of other bodies produce their effects on
the organs of sense adapted to the perception of them, as of vibration on
the auditory nerves, we shall cease to to be surprised, that so minute a
diminution in the gravity of the particles of blood should so far affect
their chemical changes, or their stimulating quality, as, joined with other
causes, sometimes to produce the beginnings of diseases.

Add to this, that if the lunar influence produces a very small degree of
quiescence at first, and if that recurs at certain periods even with less
power to produce quiescence than at first, yet the quiescence will daily
increase by the acquired habit acting at the same time, till at length so
great a degree of quiescence is induced as to produce phrensy, canine
madness, epilepsy, hysteric pains or cold fits of fever, instances of many
of which are to be found in Dr. Mead's work on this subject. The solar
influence also appears daily in several diseases; but as darkness, silence,
sleep, and our periodical meals mark the parts of the solar circle of
actions, it is sometimes dubious to which of these the periodical returns
of these diseases are to be ascribed.

As far as I have been able to observe, the periods of inflammatory diseases
observe the solar day; as the gout and rheumatism have their greatest
quiescence about noon and midnight, and their exacerbations some hours
after; as they have more frequently their immediate cause from cold air,
inanition, or fatigue, than from the effects of lunations: whilst the cold
fits of hysteric patients, and those in nervous fevers, more frequently
occur twice a day, later by near half an hour each time, according to the
lunar day; whilst some fits of intermittents, which are undisturbed by
medicines, return at regular solar periods, and others at lunar ones; which
may, probably, be owing to the difference of the periods of those external
circumstances of cold, inanition, or lunation, which immediately caused
them.

We must, however, observe, that the periods of quiescence and exacerbation
in diseases do not always commence at the times of the syzygies or
quadratures of the moon and sun, or at the times of their passing the
zenith or nadir; but as it is probable, that the stimulus of the particles
of the circumfluent blood is gradually diminished from the time of the
quadratures to that of the syzygies, the quiescence may commence at any
hour, when co-operating with other causes of quiescence, it becomes great
enough to produce a disease: afterwards it will continue to recur at the
same period of the lunar or solar influence; the same cause operating
conjointly with the acquired habit, that is with the catenation of this new
motion with the dissevered links of the lunar or solar circles of animal
action.

In this manner the periods of menstruation obey the lunar month with great
exactness in healthy patients (and perhaps the venereal orgasm in brute
animals does the same), yet these periods do not commence either at the
syzygies or quadratures of the lunations, but at whatever time of the lunar
periods they begin, they observe the same in their returns till some
greater cause disturbs them.

Hence, though the best way to calculate the time of the expected returns of
the paroxysms of periodical diseases is to count the number of hours
between the commencement of the two preceding fits, yet the following
observations may be worth attending to, when we endeavour to prevent the
returns of maniacal or epileptic diseases; whose periods (at the beginning
of them especially) frequently observe the syzygies of the moon and sun,
and particularly about the equinox.

The greatest of the two tides happening in every revolution of the moon, is
that when the moon approaches nearest to the zenith or nadir; for this
reason, while the sun is in the northern signs, that is during the vernal
and summer months, the greater of the two diurnal tides in our latitude is
that, when the moon is above the horizon; and when the sun is in the
southern signs, or during the autumnal and winter months, the greater tide
is that, which arises when the moon is below the horizon: and as the sun
approaches somewhat nearer the earth in winter than in summer, the greatest
equinoctial tides are observed to be a little before the vernal equinox,
and a little after the autumnal one.

Do not the cold periods of lunar diseases commence a few hours before the
southing of the moon during the vernal and summer months, and before the
northing of the moon during the autumnal and winter months? Do not palsies
and apoplexies, which occur about the equinoxes, happen a few days before
the vernal equinoctial lunation, and after the autumnal one? Are not the
periods of those diurnal diseases more obstinate, that commence many hours
before the southing or northing of the moon, than of those which commence
at those times? Are not those palsies and apoplexies more dangerous which
commence many days before the syzygies of the moon, than those which happen
at those times? See Sect. XXXVI. on the periods of diseases.

VII. Another very frequent cause of the cold fit of fever is the quiescence
of some of those large congeries of glands, which compose the liver,
spleen, or pancreas; one or more of which are frequently so enlarged in the
autumnal intermittents as to be perceptible to the touch externally, and
are called by the vulgar ague-cakes. As these glands are stimulated into
action by the specific pungency of the fluids, which they absorb, the
general cause of their quiescence seems to be the too great insipidity of
the fluids of the body, co-operating perhaps at the same time with other
general causes of quiescence.

Hence, in marshy countries at cold seasons, which have succeeded hot ones,
and amongst those, who have lived on innutritious and unstimulating diet,
these agues are most frequent. The enlargement of these quiescent viscera,
and the swelling of the præcordia in many other fevers, is, most probably,
owing to the same cause; which may consist in a general deficiency of the
production of sensorial power, as well as in the diminished stimulation of
the fluids; and when the quiescence of so great a number of glands, as
constitute one of those large viscera, commences, all the other irritative
motions are affected by their connection with it, and the cold fit of fever
is produced.

VIII. There are many other causes, which produce quiescence of some part of
the animal system, as fatigue, hunger, thirst, bad diet, disappointed love,
unwholesome air, exhaustion from evacuations, and many others; but the last
cause, that we shall mention, as frequently productive of cold fits of
fever, is fear or anxiety of mind. The pains, which we are first and most
generally acquainted with, have been produced by defect of some stimulus;
thus, soon after our nativity we become acquainted with the pain from the
coldness of the air, from the want of respiration, and from the want of
food. Now all these pains occasioned by defect of stimulus are attended
with quiescence of the organ, and at the same time with a greater or less
degree of quiescence of other parts of the system: thus, if we even endure
the pain of hunger so as to miss one meal instead of our daily habit of
repletion, not only the peristaltic motions of the stomach and bowels are
diminished, but we are more liable to coldness of our extremities, as of
our noses, and ears, and feet, than at other times.

Now, as fear is originally excited by our having experienced pain, and is
itself a painful affection, the same quiescence of other fibrous motions
accompany it, as have been most frequently connected with this kind of
pain, as explained in Sect. XVI. 8. 1. as the coldness and paleness of the
skin, trembling, difficult respiration, indigestion, and other symptoms,
which contribute to form the cold fit of fevers. Anxiety is fear continued
through a longer time, and, by producing chronical torpor of the system,
extinguishes life slowly, by what is commonly termed a broken heart.

IX. 1. We now step forwards to consider the other symptoms in consequence
of the quiescence which begins the fits of fever. If by any of the
circumstances before described, or by two or more of them acting at the
same time, a great degree of quiescence is induced on any considerable part
of the circle of irritative motions, the whole class of them is more or
less disturbed by their irritative associations. If this torpor be
occasioned by a deficient supply of sensorial power, and happens to any of
those parts of the system, which are accustomed to perpetual activity, as
the vital motions, the torpor increases rapidly, because of the great
expenditure of sensorial power by the incessant activity of those parts of
the system, as shewn in No. 3. 2. of this Section. Hence a deficiency of
all the secretions succeeds, and as animal heat is produced in proportion
to the quantity of those secretions, the coldness of the skin is the first
circumstance, which is attended to. Dr. Martin asserts, that some parts of
his body were warmer than natural in the cold fit of fever; but it is
certain, that those, which are uncovered, as the fingers, and nose, and
ears, are much colder to the touch, and paler in appearance. It is
possible, that his experiments were made at the beginning of the subsequent
hot fits; which commence with partial distributions of heat, owing to some
parts of the body regaining their natural irritability sooner than others.

From the quiescence of the anastomosing capillaries a paleness of the skin
succeeds, and a less secretion of the perspirable matter; from the
quiescence of the pulmonary capillaries a difficulty of respiration arises;
and from the quiescence of the other glands less bile, less gastric and
pancreatic juice, are secreted into the stomach and intestines, and less
mucus and saliva are poured into the mouth; whence arises the dry tongue,
costiveness, dry ulcers, and paucity of urine. From the quiescence of the
absorbent system arises the great thirst, as less moisture is absorbed from
the atmosphere. The absorption from the atmosphere was observed by Dr.
Lyster to amount to eighteen ounces in one night, above what he had at the
same time insensibly perspired. See Langrish. On the same account the urine
is pale, though in small quantity, for the thinner part is not absorbed
from it; and when repeated ague-fits continue long, the legs swell from the
diminished absorption of the cellular absorbents.

From the quiescence of the intestinal canal a loss of appetite and
flatulencies proceed. From the partial quiescence of the glandular viscera
a swelling and tension about the præcordia becomes sensible to the touch;
which is occasioned by the delay of the fluids from the defect of venous or
lymphatic absorption. The pain of the forehead, and of the limbs, and of
the small of the back, arises from the quiescence of the membranous fascia,
or muscles of those parts, in the same manner as the skin becomes painful,
when the vessels, of which it is composed, become quiescent from cold. The
trembling in consequence of the pain of coldness, the restlessness, and the
yawning, and stretching of the limbs, together with the shuddering, or
rigours, are convulsive motions; and will be explained amongst the diseases
of volition; Sect. XXXIV.

Sickness and vomiting is a frequent symptom in the beginnings of
fever-fits, the muscular fibres of the stomach share the general torpor and
debility of the system; their motions become first lessened, and then stop,
and then become retrograde; for the act of vomiting, like the globus
hystericus and the borborigmi of hypochondriasis, is always a symptom of
debility, either from want of stimulus, as in hunger; or from want of
sensorial power, as after intoxication; or from sympathy with some other
torpid irritative motions, as in the cold fits of ague. See Sect. XII. 5.
5. XXIX. 11. and XXXV. 1. 3. where this act of vomiting is further
explained.

The small pulse, which is said by some writers to be slow at the
commencement of ague-fits, and which is frequently trembling and
intermittent, is owing to the quiescence of the heart and arterial system,
and to the resistance opposed to the circulating fluid from the inactivity
of all the glands and capillaries. The great weakness and inability to
voluntary motions, with the insensibility of the extremities, are owing to
the general quiescence of the whole moving system; or, perhaps, simply to
the deficient production of sensorial power.

If all these symptoms are further increased, the quiescence of all the
muscles, including the heart and arteries, becomes complete, and death
ensues. This is, most probably, the case of those who are starved to death
with cold, and of those who are said to die in Holland from long skaiting
on their frozen canals.

2. As soon as this general quiescence of the system ceases, either by the
diminution of the cause, or by the accumulation of sensorial power, (as in
syncope, Sect. XII. 7. 1.) which is the natural consequence of previous
quiescence, the hot fit commences. Every gland of the body is now
stimulated into stronger action than is natural, as its irritability is
increased by accumulation of sensorial power during its late quiescence, a
superabundance of all the secretions is produced, and an increase of heat
in consequence of the increase of these secretions. The skin becomes red,
and the perspiration great, owing to the increased action of the
capillaries during the hot part of the paroxysm. The secretion of
perspirable matter is perhaps greater during the hot fit than in the
sweating fit which follows; but as the absorption of it also is greater, it
does not stand on the skin in visible drops: add to this, that the
evaporation of it also is greater, from the increased heat of the skin. But
at the decline of the hot fit, as the mouths of the absorbents of the skin
are exposed to the cooler air, or bed-clothes, these vessels sooner lose
their increased activity, and cease to absorb more than their natural
quantity: but the secerning vessels for some time longer, being kept warm
by the circulating blood, continue to pour out an increased quantity of
perspirable matter, which now stands on the skin in large visible drops;
the exhalation of it also being lessened by the greater coolness of the
skin, as well as its absorption by the diminished action of the lymphatics.
See Class I. 1. 2. 3.

The increased secretion of bile and of other fluids poured into the
intestines frequently induce a purging at the decline of the hot fit; for
as the external absorbent vessels have their mouths exposed to the cold
air, as above mentioned, they cease to be excited into unnatural activity
sooner than the secretory vessels, whose mouths are exposed to the warmth
of the blood: now, as the internal absorbents sympathize with the external
ones, these also, which during the hot fit drank up the thinner part of the
bile, or of other secreted fluids, lose their increased activity before the
gland loses its increased activity, at the decline of the hot fit; and the
loose dejections are produced from the same cause, that the increased
perspiration stands on the surface of the skin, from the increased
absorption ceasing sooner than the increased secretion.

The urine during the cold fit is in small quantity and pale, both from a
deficiency of the secretion and a deficiency of the absorption.

During the hot fit it is in its usual quantity, but very high coloured and
turbid, because a greater quantity had been secreted by the increased
action of the kidnies, and also a greater quantity of its more aqueous part
had been absorbed from it in the bladder by the increased action of the
absorbents; and lastly, at the decline of the hot fit it is in large
quantity and less coloured, or turbid, because the absorbent vessels of the
bladder, as observed above, lose their increased action by sympathy with
the cutaneous ones sooner than the secretory vessels of the kidnies lose
their increased activity. Hence the quantity of the sediment, and the
colour of the urine, in fevers, depend much on the quantity secreted by the
kidnies, and the quantity absorbed from it again in the bladder: the kinds
of sediment, as the lateritious, purulent, mucous, or bloody sediments,
depend on other causes. It should be observed, that if the sweating be
increased by the heat of the room, or of the bed-clothes, that a paucity of
turbid urine will continue to be produced, as the absorbents of the bladder
will have their activity increased by their sympathy with the vessels of
the skin, for the purpose of supplying the fluid expended in perspiration.

The pulse becomes strong and full owing to the increased irritability of
the heart and arteries, from the accumulation of sensorial power during
their quiescence, and to the quickness of the return of the blood from the
various glands and capillaries. This increased action of all the secretory
vessels does not occur very suddenly, nor universally at the same time. The
heat seems to begin about the center, and to be diffused from thence
irregularly to the other parts of the system. This may be owing to the
situation of the parts which first became quiescent and caused the
fever-fit, especially when a hardness or tumour about the præcordia can be
felt by the hand; and hence this part, in whatever viscus it is seated,
might be the first to regain its natural or increased irritability.

3. It must be here noted, that, by the increased quantity of heat, and of
the impulse of the blood at the commencement of the hot fit, a great
increase of stimulus is induced, and is now added to the increased
irritability of the system, which was occasioned by its previous
quiescence. This additional stimulus of heat and momentum of the blood
augments the violence of the movements of the arterial and glandular system
in an increasing ratio. These violent exertions still producing more heat
and greater momentum of the moving fluids, till at length the sensoral
power becomes wasted by this great stimulus beneath its natural quantity,
and predisposes the system to a second cold fit.

At length all these unnatural exertions spontaneously subside with the
increased irritability that produced them; and which was itself produced by
the preceding quiescence, in the same manner as the eye, on coming from
darkness into day-light, in a little time ceases to be dazzled and pained,
and gradually recovers its natural degree of irritability.

4. But if the increase of irritability, and the consequent increase of the
stimulus of heat and momentum, produce more violent exertions than those
above described; great pain arises in some part of the moving system, as in
the membranes of the brain, pleura, or joints; and new motions of the
vessels are produced in consequence of this pain, which are called
inflammation; or delirium or stupor arises; as explained in Sect. XXI. and
XXXIII.: for the immediate effect is the same, whether the great energy of
the moving organs arises from an increase of stimulus or an increase of
irritability; though in the former case the waste of sensorial power leads
to debility, and in the latter to health.

_Recapitulation._

X. Those muscles, which are less frequently exerted, and whose actions are
interrupted by sleep, acquire less accumulation of sensorial power during
their quiescent state, as the muscles of locomotion. In these muscles after
great exertion, that is, after great exhaustion of sensorial power, the
pain of fatigue ensues; and during rest there is a renovation of the
natural quantity of sensorial power; but where the rest, or quiescence of
the muscle, is long continued, a quantity of sensorial power becomes
accumulated beyond what is necessary; as appears by the uneasiness
occasioned by want of exercise; and which in young animals is one cause
exciting them into action, as is seen in the play of puppies and kittens.

But when those muscles, which are habituated to perpetual actions, as those
of the stomach by the stimulus of food, those of the vessels of the skin by
the stimulus of heat, and those which constitute the arteries and glands by
the stimulus of the blood, become for a time quiescent, from the want of
their appropriated stimuli, or by their associations with other quiescent
parts of the system; a greater accumulation of sensorial power is acquired
during their quiescence, and a greater or quicker exhaustion of it is
produced during their increased action.

This accumulation of sensorial power from deficient action, if it happens
to the stomach from want of food, occasions the pain of hunger; if it
happens to the vessels of the skin from want of heat, it occasions the pain
of cold; and if to the arterial system from the want of its adapted
stimuli, many disagreeable sensations are occasioned, such as are
experienced in the cold fits of intermittent fevers, and are as various, as
there are glands or membranes in the system, and are generally termed
universal uneasiness.

When the quiescence of the arterial system is not owing to defect of
stimulus as above, but to the defective quantity of sensorial power, as in
the commencement of nervous fever, or irritative fever with weak pulse, a
great torpor of this system is quickly induced; because both the irritation
from the stimulus of the blood, and the association of the vascular motions
with each other, continue to excite the arteries into action, and thence
quickly exhaust the ill-supplied vascular muscles; for to rest is death;
and therefore those vascular muscles continue to proceed, though with
feebler action, to the extreme of weariness or faintness: while nothing
similar to this affects the locomotive muscles, whose actions are generally
caused by volition, and not much subject either to irritation or to other
kinds of associations besides the voluntary ones, except indeed when they
are excited by the lash of slavery.

In these vascular muscles, which are subject to perpetual action, and
thence liable to great accumulation of sensorial power during their
quiescence from want of stimulus, a great increase of activity occurs,
either from the renewal of their accustomed stimulus, or even from much
less quantities of stimulus than usual. This increase of action constitutes
the hot fit of fever, which is attended with various increased secretions,
with great concomitant heat, and general uneasiness. The uneasiness
attending this hot paroxysm of fever, or fit of exertion, is very different
from that, which attends the previous cold fit, or fit of quiescence, and
is frequently the cause of inflammation, as in pleurisy, which is treated
of in the next section.

A similar effect occurs after the quiescence of our organs of sense; those
which are not subject to perpetual action, as the taste and smell, are less
liable to an exuberant accumulation of sensorial power after their having
for a time been inactive; but the eye, which is in perpetual action during
the day, becomes dazzled, and liable to inflammation after a temporary
quiescence.

Where the previous quiescence has been owing to a defect of sensorial
power, and not to a defect of stimulus, as in the irritative fever with
weak pulse, a similar increase of activity of the arterial system succeeds,
either from the usual stimulus of the blood, or from a stimulus less than
usual; but as there is in general in these cases of fever with weak pulse a
deficiency of the quantity of the blood, the pulse in the hot fit is weaker
than in health, though it is stronger than in the cold fit, as explained in
No. 2. of this section. But at the same time in those fevers, where the
defect of irritation is owing to the defect of the quantity of sensorial
power, as well as to the defect of stimulus, another circumstance occurs;
which consists in the partial distribution of it, as appears in partial
flushings, as of the face or bosom, while the extremities are cold; and in
the increase of particular secretions, as of bile, saliva, insensible
perspiration, with great heat of the skin, or with partial sweats, or
diarrhoea.

There are also many uneasy sensations attending these increased actions,
which, like those belonging to the hot fit of fever with strong pulse, are
frequently followed by inflammation, as in scarlet fever; which
inflammation is nevertheless accompanied with a pulse weaker, though
quicker, than the pulse during the remission or intermission of the
paroxysms, though stronger than that of the previous cold fit.

From hence I conclude, that both the cold and hot fits of fever are
necessary consequences of the perpetual and incessant action of the
arterial and glandular system; since those muscular fibres and those organs
of sense, which are most frequently exerted, become necessarily most
affected both with defect and accumulation of sensorial power: and that
hence _fever-fits are not an effort of nature to relieve herself_, and that
therefore they should always be prevented or diminished as much as
possible, by any means which decrease the general or partial vascular
actions, when they are greater, or by increasing them when they are less
than in health, as described in Sect. XII. 6. 1.

Thus have I endeavoured to explain, and I hope to the satisfaction of the
candid and patient reader, the principal symptoms or circumstances of fever
without the introduction of the supernatural power of spasm. To the
arguments in favour of the doctrine of spasm it may be sufficient to reply,
that in the evolution of medical as well as of dramatic catastrophe,

  Nec Deus intersit, nisi dignus vindice nodus inciderit.--HOR.

       *       *       *       *       *

SECT. XXXIII.

DISEASES OF SENSATION.

    I. 1. _Motions excited by sensation. Digestion. Generation. Pleasure of
    existence. Hypochondriacism._ 2. _Pain introduced. Sensitive fevers of
    two kinds._ 3. _Two sensorial powers exerted in sensitive fevers. Size
    of the blood. Nervous fevers distinguished from putrid ones. The septic
    and antiseptic theory._ 4. _Two kinds of delirium._ 5. _Other animals
    are less liable to delirium, cannot receive our contagious diseases,
    and are less liable to madness._ II. 1. _Sensitive motions generated._
    2. _Inflammation explained._ 3. _Its remote causes from excess of
    irritation, or of irritability, not from those pains which are owing to
    defect of irritation. New vessels produced, and much heat._ 4.
    _Purulent matter secreted._ 5. _Contagion explained._ 6. _Received but
    once._ 7. _If common matter be contagious?_ 8. _Why some contagions are
    received but once._ 9. _Why others may be received frequently.
    Contagions of small-pox and measles do not act at the same times. Two
    cases of such patients._ 10. _The blood from patients in the small-pox
    will not infect others. Cases of children thus inoculated. The
    variolous contagion is not received into the blood. It acts by
    sensitive association between the stomach and skin._ III. 1.
    _Absorption of solids and fluids._ 2. _Art of healing ulcers._ 3.
    _Mortification attended with less pain in weak people._

I. 1. As many motions of the body are excited and continued by irritations,
so others require, either conjunctly with these, or separately, the
pleasurable or painful sensations, for the purpose of producing them with
due energy. Amongst these the business of digestion supplies us with an
instance: if the food, which we swallow, is not attended with agreeable
sensation, it digests less perfectly; and if very disagreeable sensation
accompanies it, such as a nauseous idea, or very disgustful taste, the
digestion becomes impeded; or retrograde motions of the stomach and
oesophagus succeed, and the food is ejected.

The business of generation depends so much on agreeable sensation, that,
where the object is disgustful, neither voluntary exertion nor irritation
can effect the purpose; which is also liable to be interrupted by the pain
of fear or bashfulness.

Besides the pleasure, which attends the irritations produced by the objects
of lust and hunger, there seems to be a sum of pleasurable affection
accompanying the various secretions of the numerous glands, which
constitute the pleasure of life, in contradistinction to the tedium vitæ.
This quantity or sum of pleasurable affection, seems to contribute to the
due or energetic performance of the whole moveable system, as well that of
the heart and arteries, as of digestion and of absorption; since without
the due quantity of pleasurable sensation, flatulency and hypochondriacism
affect the intestines, and a languor seizes the arterial pulsations and
secretions; as occurs in great and continued anxiety of the mind.

2. Besides the febrile motions occasioned by irritation, described in Sect.
XXXII. and termed irritative fever, it frequently happens that pain is
excited by the violence of the fibrous contractions; and other new motions
are then superadded, in consequence of sensation, which we shall term
febris sensitiva, or sensitive fever. It must be observed, that most
irritative fevers begin with a decreased exertion of irritation, owing to
defect of stimulus; but that on the contrary the sensitive fevers, or
inflammations, generally begin with the increased exertion of sensation, as
mentioned in Sect. XXXI. on temperaments: for though the cold fit, which
introduces inflammation, commences with decreased irritation, yet the
inflammation itself commences in the hot fit during the increase of
sensation. Thus a common pustule, or phlegmon, in a part of little
sensibility does not excite an inflammatory fever; but if the stomach,
intestines, or the tender substance beneath the nails, be injured, great
sensation is produced, and the whole system is thrown into that kind of
exertion, which constitutes inflammation.

These sensitive fevers, like the irritative ones, resolve themselves into
those with arterial strength, and those with arterial debility, that is
with excess or defect of sensorial power; these may be termed the febris
sensitiva pulsu forti, sensitive fever with strong pulse, which is the
synocha, or inflammatory fever; and the febris sensitiva pulsu debili,
sensitive fever with weak pulse, which is the typhus gravior, or putrid
fever of some writers.

3. The inflammatory fevers, which are here termed sensitive fevers with
strong pulse, are generally attended with some topical inflammation, as
pleurisy, peripneumony, or rheumatism, which distinguishes them from
irritative fevers with strong pulse. The pulse is strong, quick, and full;
for in this fever there is great irritation, as well as great sensation,
employed in moving the arterial system. The size, or coagulable lymph,
which appears on the blood, is probably an increased secretion from the
inflamed internal lining of the whole arterial system, the thinner part
being taken away by the increased absorption of the inflamed lymphatics.

The sensitive fevers with weak pulse, which are termed putrid or malignant
fevers, are distinguished from irritative fevers with weak pulse, called
nervous fevers, described in the last section, as the former consist of
inflammation joined with debility, and the latter of debility alone. Hence
there is greater heat and more florid colour of the skin in the former,
with petechiæ, or purple spots, and aphthæ, or sloughs in the throat, and
generally with previous contagion.

When animal matter dies, as a slough in the throat, or the mortified part
of a carbuncle, if it be kept moist and warm, as during its abhesion to a
living body, it will soon putrify. This, and the origin of contagion from
putrid animal substances, seem to have given rise to the septic and
antiseptic theory of these fevers.

The matter in pustules and ulcers is thus liable to become putrid, and to
produce microscopic animalcula; the urine, if too long retained, may also
gain a putrescent smell, as well as the alvine feces; but some writers have
gone so far as to believe, that the blood itself in these fevers has smelt
putrid, when drawn from the arm of the patient: but this seems not well
founded; since a single particle of putrid matter taken into the blood can
produce fever, how can we conceive that the whole mass could continue a
minute in a putrid state without destroying life? Add to this, that putrid
animal substances give up air, as in gangrenes; and that hence if the blood
was putrid, air should be given out, which in the blood-vessels is known to
occasion immediate death.

In these sensitive fevers with strong pulse (or inflammations) there are
two sensorial faculties concerned in producing the disease, viz. irritation
and sensation; and hence, as their combined action is more violent, the
general quantity of sensorial power becomes further exhausted during the
exacerbation, and the system more rapidly weakened than in irritative fever
with strong pulse; where the spirit of animation is weakened by but one
mode of its exertion: so that this febris sensitiva pulsu forti (or
inflammatory fever,) may be considered as the febris irritativa pulsu
forti, with the addition of inflammation; and the febris sensitiva pulsu
debili (or malignant fever) may be considered as the febris irritativa
pulsu debili (or nervous fever), with the addition of inflammation.

4. In these putrid or malignant fevers a deficiency of irritability
accompanies the increase of sensibility; and by this waste of sensorial
power by the excess of sensation, which was already too small, arises the
delirium and stupor which so perpetually attend these inflammatory fevers
with arterial debility. In these cases the voluntary power first ceases to
act from deficiency of sensorial spirit; and the stimuli from external
bodies have no effect on the exhausted sensorial power, and a delirium like
a dream is the consequence. At length the internal stimuli cease to excite
sufficient irritation, and the secretions are either not produced at all,
or too parsimonious in quantity. Amongst these the secretion of the brain,
or production of the sensorial power, becomes deficient, till at last all
sensorial power ceases, except what is just necessary to perform the vital
motions, and a stupor succeeds; which is thus owing to the same cause as
the preceding delirium exerted in a greater degree.

This kind of delirium is owing to a suspension of volition, and to the
disobedience of the senses to external stimuli, and is always occasioned by
great debility, or paucity of sensorial power; it is therefore a bad sign
at the end of inflammatory fevers, which had previous arterial strength, as
rheumatism, or pleurisy, as it shews the presence of great exhaustion of
sensorial power in a system, which having lately been exposed to great
excitement, is not so liable to be stimulated into its healthy action,
either by additional stimulus of food and medicines, or by the accumulation
of sensorial power during its present torpor. In inflammatory fevers with
debility, as those termed putrid fevers, delirium is sometimes, as well as
stupor, rather a favourable sign; as less sensorial power is wasted during
its continuance (see Class II. 1. 6. 8.), and the constitution not having
been previously exposed to excess of stimulation, is more liable to be
excited after previous quiescence.

When the sum of general pleasurable sensation becomes too great, another
kind of delirium supervenes, and the ideas thus excited are mistaken for
the irritations of external objects: such a delirium is produced for a time
by intoxicating drugs, as fermented liquors, or opium: a permanent delirium
of this kind is sometimes induced by the pleasures of inordinate vanity, or
by the enthusiastic hopes of heaven. In these cases the power of volition
is incapable of exertion, and in a great degree the external senses become
incapable of perceiving their adapted stimuli, because the whole sensorial
power is employed or expended on the ideas excited by pleasurable
sensation.

This kind of delirium is distinguished from that which attends the fevers
above mentioned from its not being accompanied with general debility, but
simply with excess of pleasurable sensation; and is therefore in some
measure allied to madness or to reverie; it differs from the delirium of
dreams, as in this the power of volition is not totally suspended, nor are
the senses precluded from external stimulation; there is therefore a degree
of consistency, in this kind of delirium, and a degree of attention to
external objects, neither of which exist in the delirium of fevers or in
dreams.

5. It would appear, that the vascular system of other animals are less
liable to be put into action by their general sum of pleasurable or painful
sensation; and that the trains of their ideas, and the muscular motions
usually associated with them, are less powerfully connected than in the
human system. For other animals neither weep, nor smile, nor laugh; and are
hence seldom subject to delirium, as treated of in Sect. XVI. on Instinct.
Now as our epidemic and contagious diseases are probably produced by
disagreeable sensation, and not simply by irritation; there appears a
reason, why brute animals are less liable to epidemic or contagious
diseases; and secondly, why none of our contagions, as the small-pox or
measles, can be communicated to them, though one of theirs, viz. the
hydrophobia, as well as many of their poisons, as those of snakes and of in
insects, communicate their deleterious or painful effects to mankind.

Where the quantity of general painful sensation is too great in the system,
inordinate voluntary exertions are produced either of our ideas, as in
melancholy and madness, or of our muscles, as in convulsion. From these
maladies also brute animals are much more exempt than mankind, owing to
their greater inaptitude to voluntary exertion, as mentioned in Sect. XVI.
on Instinct.

II. 1. When any moving organ is excited into such violent motions, that a
quantity of pleasurable or painful sensation is produced, it frequently
happens (but not always) that new motions of the affected organ are
generated in consequence of the pain or pleasure, which are termed
inflammation.

These new motions are of a peculiar kind, tending to distend the old, and
to produce new fibres, and thence to elongate the straight muscles, which
serve locomotion, and to form new vessels at the extremities or sides of
the vascular muscles.

2. Thus the pleasurable sensations produce an enlargement of the nipples of
nurses, of the papillæ of the tongue, of the penis, and probably produce
the growth of the body from its embryon state to its maturity; whilst the
new motions in consequence of painful sensation, with the growth of the
fibres or vessels, which they occasion, are termed inflammation.

Hence when the straight muscles are inflamed, part of their tendons at each
extremity gain new life and sensibility, and thus the muscle is for a time
elongated; and inflamed bones become soft, vascular, and sensible. Thus new
vessels shoot over the cornea of inflamed eyes, and into scirrhous tumours,
when they become inflamed; and hence all inflamed parts grow together by
intermixture, and inosculation of the new and old vessels.

The heat is occasioned from the increased secretions either of mucus, or of
the fibres, which produce or elongate the vessels. The red colour is owing
to the pellucidity of the newly formed vessels, and as the arterial parts
of them are probably formed before their correspondent venous parts.

3. These new motions are excited either from the increased quantity of
sensation in consequence of greater fibrous contractions, or from increased
sensibility, that is, from the increased quantity of sensorial power in the
moving organ. Hence they are induced by great external stimuli, as by
wounds, broken bones; and by acrid or infectious materials; or by common
stimuli on those organs, which have been some time quiescent; as the usual
light of the day inflames the eyes of those, who have been confined in
dungeons; and the warmth of a common fire inflames those, who have been
previously exposed to much cold.

But these new motions are never generated by that pain, which arises from
defect of stimulus, as from hunger, thirst, cold, or inanition, with all
those pains, which are termed nervous. Where these pains exist, the motions
of the affected part are lessened; and if inflammation succeeds, it is in
some distant parts; as coughs are caused by coldness and moisture being
long applied to the feet; or it is in consequence of the renewal of the
stimulus, as of heat or food, which excites our organs into stronger action
after their temporary quiescence; as kibed heels after walking in snow.

4. But when these new motions of the vascular muscles are exerted with
greater violence, and these vessels are either elongated too much or too
hastily, a new material is secreted from their extremities, which is of
various kinds according to the peculiar animal motions of this new kind of
gland, which secretes it; such is the pus laudabile or common matter, the
variolous matter, venereal matter, catarrhous matter, and many others.

5. These matters are the product of an animal process; they are secreted or
produced from the blood by certain diseased motions of the extremities of
the blood-vessels, and are on that account all of them contagious; for if a
portion of any of these matters is transmitted into the circulation, or
perhaps only inserted into the skin, or beneath the cuticle of an healthy
person, its stimulus in a certain time produces the same kind of morbid
motions, by which itself was produced; and hence a similar kind is
generated. See Sect. XXXIX. 6. 1.

6. It is remarkable, that many of these contagious matters are capable of
producing a similar disease but once; as the small-pox and measles; and I
suppose this is true of all those contagious diseases, which are
spontaneously cured by nature in a certain time; for if the body was
capable of receiving the disease a second time, the patient must
perpetually infect himself by the very matter, which he has himself
produced, and is lodged about him; and hence he could never become free
from the disease. Something similar to this is seen in the secondary fever
of the confluent small-pox; there is a great absorption of variolous
matter, a very minute part of which would give the genuine small-pox to
another person; but here it only stimulates the system into common fever;
like that which common puss, or any other acrid material might occasion.

7. In the pulmonary consumption, where common matter is daily absorbed, an
irritative fever only, without new inflammation, is generally produced;
which is terminated like other irritative fevers by sweats, or loose
stools. Hence it does not appear, that this absorbed matter always acts as
a contagious material producing fresh inflammation or new abscesses. Though
there is reason to believe, that the first time any common matter is
absorbed, it has this effect, but not the second time, like the variolous
matter above mentioned.

This accounts for the opinion, that the pulmonary consumption is sometimes
infectious, which opinion was held by the ancients, and continues in Italy
at present; and I have myself seen three or four instances, where a husband
and wife, who have slept together, and have thus much received each other's
breath, who have infected each other, and both died in consequence of the
original taint of only one of them. This also accounts for the abscesses in
various parts of the body, that are sometimes produced after the inoculated
small-pox is terminated; for this second absorption of variolous matter
acts like common matter, and produces only irritative fever in those
children, whose constitutions have already experienced the absorption of
common matter; and inflammation with a tendency to produce new abscesses in
those, whose constitutions have not experienced the absorptions of common
matter.

It is probable, that more certain proofs might have been found to shew,
that common matter is infectious the first time it is absorbed, tending to
produce similar abscesses, but not the second time of its absorption, if
this subject had been attended to.

8. These contagious diseases are very numerous, as the plague, small-pox,
chicken-pox, measles, scarlet-fever, pemphigus, catarrh, chincough,
venereal disease, itch, trichoma, tinea. The infectious material does not
seem to be dissolved by the air, but only mixed with it perhaps in fine
powder, which soon subsides; since many of these contagions can only be
received by actual contact; and others of them only at small distances from
the infected person; as is evident from many persons having been near
patients of the small-pox without acquiring the disease.

The reason, why many of these diseases are received but once, and others
repeatedly, is not well understood; it appears to me, that the constitution
becomes so accustomed to the stimuli of these infectious materials, by
having once experienced them, that though irritative motions, as hectic
fevers, may again be produced by them, yet no sensation, and in consequence
no general inflammation succeeds; as disagreeable smells or tastes by habit
cease to be perceived; they continue indeed to excite irritative ideas on
the organs of sense, but these are not succeeded by sensation.

There are many irritative motions, which were at first succeeded by
sensation, but which by frequent repetition cease to excite sensation, as
explained in Sect. XX. on Vertigo. And, that this circumstance exists in
respect to infectious matter appears from a known fact; that nurses, who
have had the small-pox, are liable to experience small ulcers on their arms
by the contact of variolous matter in lifting their patients; and that when
patients, who have formerly had the small-pox have been inoculated in the
arm, a phlegmon, or inflamed sore, has succeeded, but no subsequent fever.
Which shews, that the contagious matter of the small-pox has not lost its
power of stimulating the part it is applied to, but that the general system
is not affected in consequence. See Section XII. 7. 6. XIX. 9.

9. From the accounts of the plague, virulent catarrh, and putrid dysentery,
it seems uncertain, whether these diseases are experienced more than once;
but the venereal disease and itch are doubtless repeatedly infectious; and
as these diseases are never cured spontaneously, but require medicines,
which act without apparent operation, some have suspected, that the
contagious material produces similar matter rather by a chemical change of
the fluids, than by an animal process; and that the specific medicines
destroy their virus by chemically combining with it. This opinion is
successfully combated by Mr. Hunter, in his Treatise on Venereal Disease,
Part I. c. i.

But this opinion wants the support of analogy, as there is no known process
in animal bodies, which is purely chemical, not even digestion; nor can any
of these matters be produced by chemical processes. Add to this, that it is
probable, that the insects, observed in the pustules of the itch, and in
the stools of dysenteric patients, are the consequences, and not the causes
of these diseases. And that the specific medicines, which cure the itch and
lues venerea, as brimstone and mercury, act only by increasing the
absorption of the matter in the ulcuscles of those diseases, and thence
disposing them to heal; which would otherwise continue to spread.

Why the venereal disease, and itch, and tenia, or scald head, are
repeatedly contagious, while those contagions attended with fever can be
received but once, seems to depend on their being rather local diseases
than universal ones, and are hence not attended with fever, except the
purulent fever in their last stages, when the patient is destroyed by them.
On this account the whole of the system does not become habituated to these
morbid actions, so as to cease to be affected with sensation by a
repetition of the contagion. Thus the contagious matter of the venereal
disease, and of the tenia, affects the lymphatic glands, as the inquinal
glands, and those about the roots of the hair and neck, where it is
arrested, but does not seem to affect the blood-vessels, since no fever
ensues.

Hence it would appear, that these kinds of contagion are propagated not by
means of the circulation, but by sympathy of distant parts with each other;
since if a distant part, as the palate, should be excited by sensitive
association into the same kind of motions, as the parts originally affected
by the contact of infectious matter; that distant part will produce the
same kind of infectious matter; for every secretion from the blood is
formed from it by the peculiar motions of the fine extremities of the
gland, which secretes it; the various secreted fluids, as the bile, saliva,
gastric juice, not previously existing, as such, in the blood-vessels.

And this peculiar sympathy between the genitals and the throat, owing to
sensitive association, appears not only in the production of venereal
ulcers in the throat, but in variety of other instances, as in the mumps,
in the hydrophobia, some coughs, strangulation, the production of the
beard, change of voice at puberty. Which are further described in Class IV.
1. 2. 7.

To evince that the production of such large quantities of contagious
matter, as are seen in some variolous patients, so as to cover the whole
skin almost with pustules, does not arise from any chemical fermentation in
the blood, but that it is owing to morbid motions of the fine extremities
of the capillaries, or glands, whether these be ruptured or not, appears
from the quantity of this matter always corresponding with the quantity of
the fever; that is, with the violent exertions of those glands and
capillaries, which are the terminations of the arterial system.

The truth of this theory is evinced further by a circumstance observed by
Mr. J. Hunter, in his Treatise on Venereal Disease; that in a patient, who
was inoculated for the small-pox, and who appeared afterwards to have been
previously infested with the measles, the progress of the small-pox was
delayed till the measles had run their course, and that then the small-pox
went through its usual periods.

Two similar cases fell under my care, which I shall here relate, as it
confirms that of Mr. Hunter, and contributes to illustrate this part of the
theory of contagious diseases. I have transcribed the particulars from a
letter of Mr. Lightwood of Yoxal, the surgeon who daily attended them, and
at my request, after I had seen them, kept a kind of journal of their
cases.

Miss H. and Miss L. two sisters, the one about four and the other about
three years old, were inoculated Feb. 7, 1791. On the 10th there was a
redness on both arms discernible by a glass. On the 11th their arms were so
much inflamed as to leave no doubt of the infection having taken place. On
the 12th less appearance of inflammation on their arms. In the evening Miss
L. had an eruption, which resembled the measles. On the 12th the eruption
on Miss L. was very full on the face and breast, like the measles, with
considerable fever. It was now known, that the measles were in a farm house
in the neighbourhood. Miss H.'s arm less inflamed than yesterday. On the
14th Miss L.'s fever great, and the eruption universal. The arm appears to
be healed. Miss H.'s arm somewhat redder. They were now put into separate
rooms. On the 15th Miss L.'s arms as yesterday. Eruption continues. Miss
H.'s arms have varied but little. 16th, the eruptions on Miss L. are dying
away, her fever gone. Begins to have a little redness in one arm at the
place of inoculation. Miss H.'s arms get redder, but she has no appearance
of complaint. 20th, Miss L.'s arms have advanced slowly till this day, and
now a few pustules appear. Miss H.'s arm has made little progress from the
16th to this day, and now she has some fever. 21st, Miss L. as yesterday.
Miss H. has much inflammation, and an increase of the red circle on one arm
to the size of half a crown, and had much fever at night, with fetid
breath. 22d, Miss L.'s pustules continue advancing. Miss H.'s inflammation
of her arm and red circle increases. A few red spots appear in different
parts with some degree of fever this morning, 23d. Miss L. has a larger
crop of pustules. Miss H. has small pustules and great inflammation of her
arms, with but one pustule likely to suppurate. After this day they
gradually got well, and the pustules disappeared.

In one of these cases the measles went through their common course with
milder symptoms than usual, and in the other the measly contagion seemed
just sufficient to stop the progress of variolous contagion, but without
itself throwing the constitution into any disorder. At the same time both
the measles and small-pox seem to have been rendered milder. Does not this
give an idea, that if they were both inoculated at the same time, that
neither of them might affect the patient?

From these cases I contend, that the contagious matter of these diseases
does not affect the constitution by a fermentation, or chemical change of
the blood, because then they must have proceeded together, and have
produced a third something, not exactly similar to either of them: but that
they produce new motions of the cutaneous terminations of the
blood-vessels, which for a time proceed daily with increasing activity,
like some paroxysms of fever, till they at length secrete or form a similar
poison by these unnatural actions.

Now as in the measles one kind of unnatural motion takes place, and in the
small-pox another kind, it is easy to conceive, that these different kinds
of morbid motions cannot exist together; and therefore, that that which has
first begun will continue till the system becomes habituated to the
stimulus which occasions it, and has ceased to be thrown into action by it;
and then the other kind of stimulus will in its turn produce fever, and new
kinds of motions peculiar to itself.

10. On further considering the action of contagious matter, since the
former part of this work was sent to the press; where I have asserted, in
Sect. XXII. 3. 3. that it is probable, that the variolous matter is
diffused through the blood; I prevailed on my friend Mr. Power, surgeon at
Bosworth in Leicestershire to try, whether the small-pox could be
inoculated by using the blood of a variolous patient instead of the matter
from the pustules; as I thought such an experiment might throw some light
at least on this interesting subject. The following is an extract from his
letter:--

"March 11, 1793. I inoculated two children, who had not had the small-pox,
with blood; which was taken from a patient on the second day after the
eruption commenced, and before it was completed. And at the same time I
inoculated myself with blood from the same person, in order to compare the
appearances, which might arise in a person liable to receive the infection,
and in one not liable to receive it. On the same day I inoculated four
other children liable to receive the infection with blood taken from
another person on the fourth day after the commencement of the eruption.
The patients from whom the blood was taken had the disease mildly, but had
the most pustules of any I could select from twenty inoculated patients;
and as much of the blood was insinuated under the cuticle as I could
introduce by elevating the skin without drawing blood; and three or four
such punctures were made in each of their arms, and the blood was used in
its fluid state.

"As the appearances in all these patients, as well as in myself, were
similar, I shall only mention them in general terms. March 13. A slight
subcuticular discoloration, with rather a livid appearance, without
soreness or pain, was visible in them all, as well as in my own hand. 15.
The discoloration somewhat less, without pain or soreness. Some patients
inoculated on the same day with variolous matter have considerable
inflammation. 17. The discoloration is quite gone in them all, and from my
own hand, a dry mark only remaining. And they were all inoculated on the
18th, with variolous matter, which produced the disease in them all."

Mr. Power afterwards observes, that, as the patients from whom the blood
was taken had the disease mildly, it may be supposed, that though the
contagious matter might be mixed with the blood, it might still be in too
dilute a state to convey the infection; but adds at the same time, that he
has diluted recent matter with at least five times its quantity of water,
and which has still given the infection; though he has sometimes diluted it
so far as to fail.

The following experiments were instituted at my request by my friend Mr.
Hadley, surgeon in Derby, to ascertain whether the blood of a person in the
small-pox be capable of communicating the disease. "Experiment 1st. October
18th, 1793. I took some blood from a vein in the arm of a person who had
the small-pox, on the second day of the eruption, and introduced a small
quantity of it immediately with the point of a lancet between the scars and
true skin of the right arm of a boy nine years old in two or three
different places; the other arm was inoculated with variolous matter at the
same time.

"19th. The punctured parts of the right arm were surrounded with some
degree of subcuticular inflammation. 20th. The inflammation more
considerable, with a slight degree of itching, but no pain upon pressure.
21st. Upon examining the arm this day with a lens I found the inflammation
less extensive, and the redness changing to a deep yellow or orange-colour,
22d. Inflammation nearly gone. 23d. Nothing remained, except a slight
discoloration and a little scurfy appearance on the punctures. At the same
time the inflammation of the arm inoculated with variolous matter was
increasing fast, and he had the disease mildly at the usual time.

"Experiment 2d. I inoculated another child at the same time and in the same
manner, with blood taken on the first day of the eruption; but as the
appearance and effects were similar to those in the preceding experiment, I
shall not relate them minutely.

"Experiment 3d. October 20th. Blood was taken from a person who had the
small-pox, on the third day of the eruption, and on the sixth from the
commencement of the eruptive fever. I introduced some of it in its fluid
state into both arms of a boy seven years old.

21st. There appeared to be some inflammation under the cuticle, where the
punctures were made. 22d. Inflammation more considerable. 23d. On this day
the inflammation was somewhat greater, and the cuticle rather elevated.

"24th. Inflammation much less, and only a brown or orange-colour remained.
25th. Scarcely any discoloration left. On this day he was inoculated with
variolous matter, the progress of the infection went on in the usual way,
and he had the small-pox very favourably.

"At this time I was requested to inoculate a young person, who was thought
to have had the small-pox, but his parents were not quite certain; in one
arm I introduced variolous matter, and in the other blood, taken as in
experiment 3d. On the second day after the operation, the punctured parts
were inflamed, though I think the arm in which I had inserted variolous
matter was rather more so than the other. On the third the inflammation was
increased, and looked much the same as in the preceding experiment. 4th.
The inflammation was much diminished, and on the 5th almost gone. He was
exposed at the same time to the natural infection, but has continued
perfectly well.

"I have frequently observed (and believe most practitioners have done the
same), that if variolous matter be inserted in the arm of a person who has
previously had the small-pox, that the inflammation on the second or third
days is much greater, than if they had not had the disease, but on the
fourth or fifth it disappears.

"On the 23d I introduced blood into the arms of three more children, taken
on the third and fourth days of the eruption. The appearances were much the
same as mentioned in experiments first and third. They were afterwards
inoculated with variolous matter, and had the disease in the regular way.

"The above experiments were made with blood taken from a small vein in the
hand or foot of three or four different patients, whom I had at that time
under inoculation. They were selected from 160, as having the greatest
number of pustules. The part was washed with warm water before the blood
was taken, to prevent the possibility of any matter being mixed with it
from the surface."

Shall we conclude from hence, that the variolous matter never enters the
blood-vessels? but that the morbid motions of the vessels of the skin
around the insertion of it continue to increase in a larger and larger
circle for six or seven days; that then their quantity of morbid action
becomes great enough to produce a fever-fit, and to affect the stomach by
association of motions? and finally, that a second association of motions
is produced between the stomach and the other parts of the skin, inducing
them into morbid actions similar to those of the circle round the insertion
of the variolous matter? Many more experiments and observations are
required before this important question can be satisfactorily answered.

It may be adduced, that as the matter inserted into the skin of the arm
frequently swells the lymphatic in the axilla, that in that circumstance it
seems to be there arrested in its progress, and cannot be imagined to enter
the blood by that lymphatic gland till the swelling of it subsides. Some
other phænomena of the disease are more easily reconcileable to this theory
of sympathetic motions than to that of absorption; as the time taken up
between the insertion of the matter, and the operation of it on the system,
as mentioned above. For the circle around the insertion is seen to
increase, and to inflame; and I believe, undergoes a kind of diurnal
paroxysm of torpor and paleness with a succeeding increase of action and
colour, like a topical fever-fit. Whereas if the matter is conceived to
circulate for six or seven days with the blood, without producing disorder,
it ought to be rendered milder, or the blood-vessels more familiarized to
its acrimony.

It is much easier to conceive from this doctrine of associated or
sympathetic motions of distant parts of the system, how it happens, that
the variolous infection can be received but once, as before explained; than
by supposing, that a change is effected in the mass of blood by any kind of
fermentative process.

The curious circumstance of the two contagions of small-pox and measles not
acting at the same time, but one of them resting or suspending its action
till that of the other ceases, may be much easier explained from
sympathetic or associated actions of the infected part with other parts of
the system, than it can from supposing the two contagions to enter the
circulation.

The skin of the face is subject to more frequent vicissitudes of heat and
cold, from its exposure to the open air, and is in consequence more liable
to sensitive association with the stomach than any other part of the
surface of the body, because their actions have been more frequently thus
associated. Thus in a surfeit from drinking cold water, when a person is
very hot and fatigued, an eruption is liable to appear on the face in
consequence of this sympathy. In the same manner the rosy eruption on the
faces of drunkards more probably arises from the sympathy of the face with
the stomach, rather than between the face and the liver, as is generally
supposed.

This sympathy between the stomach and the skin of the face is apparent in
the eruption of the small-pox; since, where the disease is in considerable
quantity, the eruption on the face first succeeds the sickness of the
stomach. In the natural disease the stomach seems to be frequently
primarily affected, either alone or along with the tonsils, as the matter
seems to be only diffused in the air, and by being mixed with the saliva,
or mucus of the tonsils, to be swallowed into the stomach.

After some days the irritative circles of motions become disordered by this
new stimulus, which acts upon the mucus lining of the stomach; and
sickness, vertigo, and a diurnal fever succeed. These disordered irritative
motions become daily increased for two or three days, and then by their
increased action certain sensitive motions, or inflammation, is produced,
and at the next cold fit of fever, when the stomach recovers from its
torpor, an inflammation of the external skin is formed in points (which
afterwards suppurate), by sensitive association, in the same manner as a
cough is produced in consequence of exposing the feet to cold, as described
in Sect. XXV. 17. and Class IV. 2. I. 7. If the inoculated skin of the arm,
as far as it appears inflamed, was to be cut out, or destroyed by caustic,
before the fever commenced, as suppose on the fourth day after inoculation,
would this prevent the disease? as it is supposed to prevent the
hydrophobia.

III. 1. Where the new vessels, and enlarged old ones, which constitute
inflammation, are not so hastily distended as to burst, and form a new kind
of gland for the secretion of matter, as above mentioned; if such
circumstances happen as diminish the painful sensation, the tendency to
growth ceases, and by and by an absorption commences, not only of the
superabundant quantity of fluids deposited in the inflamed part, but of the
solids likewise, and this even of the hardest kind.

Thus during the growth of the second set of teeth in children, the roots of
the first set are totally absorbed, till at length nothing of them remains
but the crown; though a few weeks before, if they are drawn immaturely,
their roots are found complete. Similar to this Mr. Hunter has observed,
that where a dead piece of bone is to exfoliate, or to separate from a
living one, that the dead part does not putrify, but remains perfectly
sound, while the surface of the living part of the bone, which is in
contact with the dead part, becomes absorbed, and thus effects its
separation. Med. Comment. Edinb. V. 1. 425. In the same manner the
calcareous matter of gouty concretions, the coagulable lymph deposited on
inflamed membranes in rheumatism and extravasated blood become absorbed;
which are all as solid and as indissoluble materials as the new vessels
produced in inflammation.

This absorption of the new vessels and deposited fluids of inflamed parts
is called resolution: it is produced by first using such internal means as
decrease the pain of the part, and in consequence its new motions, as
repeated bleeding, cathartics, diluent potations, and warm bath.

After the vessels are thus emptied, and the absorption of the new vessels
and deposited fluids is evidently begun, it is much promoted by stimulating
the part externally by solutions of lead, or other metals, and internally
by the bark, and small doses of opium. Hence when an ophthalmy begins to
become paler, any acrid eye-water, as a solution of six grains of white
vitriol in an ounce of water, hastens the absorption, and clears the eye in
a very short time. But the same application used a few days sooner would
have increased the inflammation. Hence after evacuation opium in small
doses may contribute to promote the absorption of fluids deposited on the
brain, as observed by Mr. Bromfield in his treatise of surgery.

2. Where an abscess is formed by the rupture of these new vessels, the
violence of inflammation ceases, and a new gland separates a material
called pus: at the same time a less degree of inflammation produces new
vessels called vulgarly proud flesh; which, if no bandage confines its
growth, nor any other circumstance promotes absorption in the wound, would
rise to a great height above the usual size of the part.

Hence the art of healing ulcers consists in producing a tendency to
absorption in the wound greater than the deposition. Thus when an
ill-conditioned ulcer separates a copious and thin discharge, by the use of
any stimulus, as of salts of lead, or mercury, or copper externally
applied, the discharge becomes diminished in quantity, and becomes thicker,
as the thinner parts are first absorbed.

But nothing so much contributes to increase the absorption in a wound as
covering the whole limb above the sore with a bandage, which should be
spread with some plaster, as with emplastrum de minio, to prevent it from
slipping. By this artificial tightness of the skin, the arterial pulsations
act with double their usual power in promoting the ascending current of the
fluid in the valvular lymphatics.

Internally the absorption from ulcers should be promoted first by
evacuation, then by opium, bark, mercury, steel.

3. Where the inflammation proceeds with greater violence or rapidity, that
is, when by the painful sensation a more inordinate activity of the organ
is produced, and by this great activity an additional quantity of painful
sensation follows in an increasing ratio, till the whole of the sensorial
power, or spirit of animation, in the part becomes exhausted, a
mortification ensues, as in a carbuncle, in inflammations of the bowels, in
the extremities of old people, or in the limbs of those who are brought
near a fire after having been much benumbed with cold. And from hence it
appears, why weak people are more subject to mortification than strong
ones, and why in weak persons less pain will produce mortification, namely,
because the sensorial power is sooner exhausted by any excess of activity.
I remember seeing a gentleman who had the preceding day travelled two
stages in a chaise with what he termed a bearable pain in his bowels; which
when I saw him had ceased rather suddenly, and without a passage through
him; his pulse was then weak, though not very quick; but as nothing which
he swallowed would continue in his stomach many minutes, I concluded that
the bowel was mortified; he died on the next day. It is usual for patients
sinking under the small-pox with mortified pustules, and with purple spots
intermixed, to complain of no pain, but to say they are pretty well to the
last moment.

_Recapitulation._

IV. When the motions of any part of the system, in consequence of previous
torpor, are performed with more energy than in the irritative fevers, a
disagreeable sensation is produced, and new actions of some part of the
system commence in consequence of this sensation conjointly with the
irritation: which motions constitute inflammation. If the fever be attended
with a strong pulse, as in pleurisy, or rheumatism, it is termed synocha
sensitiva, or sensitive fever with strong pulse; which is usually termed
inflammatory fever. If it be attended with weak pulse, it is termed typhus
sensitivus, or sensitive fever with weak pulse, or typhus gravior, or
putrid malignant fever.

The synocha sensitiva, or sensitive fever with strong pulse, is generally
attended with some topical inflammation, as in peripneumony, hepatitis, and
is accompanied with much coagulable lymph, or size; which rises to the
surface of the blood, when taken into a bason, as it cools; and which is
believed to be the increased mucous secretion from the coats of the
arteries, inspissated by a greater absorption of its aqueous and saline
part, and perhaps changed by its delay in the circulation.

The typhus sensitivus, or sensitive fever with weak pulse, is frequently
attended with delirium, which is caused by the deficiency of the quantity
of sensorial power, and with variety of cutaneous eruptions.

Inflammation is caused by the pains occasioned by excess of action, and not
by those pains which are occasioned by defect of action. These morbid
actions, which are thus produced by two sensorial powers, viz. by
irritation and sensation, secrete new living fibres, which elongate the old
vessels, or form new ones, and at the same time much heat is evolved from
these combinations. By the rupture of these vessels, or by a new
construction of their apertures, purulent matters are secreted of various
kinds; which are infectious the first time they are applied to the skin
beneath the cuticle, or swallowed with the saliva into the stomach. This
contagion acts not by its being absorbed into the circulation, but by the
sympathies, or associated actions, between the part first stimulated by the
contagious matter and the other parts of the system. Thus in the natural
small-pox the contagion is swallowed with the saliva, and by its stimulus
inflames the stomach; this variolous inflammation of the stomach increases
every day, like the circle round the puncture of an inoculated arm, till it
becomes great enough to disorder the circles of irritative and sensitive
motions, and thus produces fever-fits, with sickness and vomiting. Lastly,
after the cold paroxysm, or fit of torpor, of the stomach has increased for
two or three successive days, an inflammation of the skin commences in
points; which generally first appear upon the face, as the associated
actions between the skin of the face and that of the stomach have been more
frequently exerted together than those of any other parts of the external
surface.

Contagious matters, as those of the measles and small-pox, do not act upon
the system at the same time; but the progress of that which was last
received is delayed, till the action of the former infection ceases. All
kinds of matter, even that from common ulcers, are probably contagious the
first time they are inserted beneath the cuticle or swallowed into the
stomach; that is, as they were formed by certain morbid actions of the
extremities of the vessels, they have the power to excite similar morbid
actions in the extremities of other vessels, to which they are applied; and
these by sympathy, or associations of motion, excite similar morbid actions
in distant parts of the system, without entering the circulation; and hence
the blood of a patient in the small-pox will not give that disease by
inoculation to others.

When the new fibres or vessels become again absorbed into the circulation,
the inflammation ceases; which is promoted, after sufficient evacuations,
by external stimulants and bandages: but where the action of the vessels is
very great, a mortification of the part is liable to ensue, owing to the
exhaustion of sensorial power; which however occurs in weak people without
much pain, and without very violent previous inflammation; and, like
partial paralysis, may be esteemed one mode of natural death of old people,
a part dying before the whole.

       *       *       *       *       *

SECT. XXXIV.

DISEASES OF VOLITION.

    I. 1. _Volition defined. Motions termed involuntary are caused by
    volition. Desires opposed to each other. Deliberation. Ass between two
    hay-cocks. Saliva swallowed against one's desire. Voluntary motions
    distinguished from those associated with sensitive motions._ 2. _Pains
    from excess, and from defect of motion. No pain is felt during vehement
    voluntary exertion; as in cold fits of ague, labour-pains, strangury,
    tenesmus, vomiting, restlessness in fevers, convulsion of a wounded
    muscle._ 3. _Of holding the breath and screaming in pain; why swine and
    dogs cry out in pain, and not sheep and horses. Of grinning and biting
    in pain; why mad animals bite others._ 4. _Epileptic convulsions
    explained, why the fits begin with quivering of the under jaw, biting
    the tongue, and setting the teeth; why the convulsive motions are
    alternately relaxed. The phenomenon of laughter explained. Why children
    cannot tickle themselves. How some have died from immoderate laughter._
    5. _Of cataleptic spasms, of the locked jaw, of painful cramps._ 6.
    _Syncope explained. Why no external objects are perceived in syncope._
    7. _Of palsy and apoplexy from violent exertions. Case of Mrs. Scot.
    From dancing, scating, swimming. Case of Mr. Nairn. Why palsies are not
    always immediately preceded by violent exertions. Palsy and epilepsy
    from diseased livers. Why the right arm more frequently paralytic than
    the left. How paralytic limbs regain their motions._ II. _Diseases of
    the sensual motions from excess or defect of voluntary exertion._ 1.
    _Madness._ 2. _Distinguished from delirium._ 3. _Why mankind more
    liable to insanity than brutes._ 4. _Suspicion. Want of shame, and of
    cleanliness._ 5. _They bear cold, hunger, and fatigue. Charles XII. of
    Sweden._ 6. _Pleasureable delirium, and insanity. Child riding on a
    stick. Pains of martyrdom not felt._ 7. _Dropsy._ 8. _Inflammation
    cured by insanity._ III. 1. _Pain relieved by reverie. Reverie is an
    exertion of voluntary and sensitive motions._ 2. _Case of reverie._ 3.
    _Lady supposed to have two souls._ 4. _Methods of relieving pain._

I. 1. Before we commence this Section on Diseased Voluntary Motions, it may
be necessary to premise, that the word volition is not used in this work
exactly in its common acceptation. Volition is said in Section V. to bear
the same analogy to desire and aversion, which sensation does to pleasure
and pain. And hence that, when desire or aversion produces any action of
the muscular fibres, or of the organs of sense, they are termed volition;
and the actions produced in consequence are termed voluntary actions.
Whence it appears, that motions of our muscles or ideas may be produced in
consequence of desire or aversion without our having the power to prevent
them, and yet these motions may be termed voluntary, according to our
definition of the word; though in common language they would be called
involuntary.

The objects of desire and aversion are generally at a distance, whereas
those of pleasure and pain are immediately acting upon our organs. Hence,
before desire or aversion are exerted, so as to cause any actions, there is
generally time for deliberation; which consists in discovering the means to
obtain the object of desire, or to avoid the object of aversion; or in
examining the good or bad consequences, which may result from them. In this
case it is evident, that we have a power to delay the proposed action, or
to perform it; and this power of choosing, whether we shall act or not, is
in common language expressed by the word volition, or will. Whereas in this
work the word volition means simply the active state of the sensorial
faculty in producing motion in consequence of desire or aversion: whether
we have the power of restraining that action, or not; that is, whether we
exert any actions in consequence of opposite desires or aversions, or not.

For if the objects of desire or aversion are present, there is no necessity
to investigate or compare the _means_ of obtaining them, nor do we always
deliberate about their consequences; that is, no deliberation necessarily
intervenes, and in consequence the power of choosing to act or not is not
exerted. It is probable, that this twofold use of the word volition in all
languages has confounded the metaphysicians, who have disputed about free
will and necessity. Whereas from the above analysis it would appear, that
during our sleep, we use no voluntary exertions at all; and in our waking
hours, that they are the consequence of desire or aversion.

To will is to act in consequence of desire; but to desire means to desire
something, even if that something be only to become free from the pain,
which causes the desire; for to desire nothing is not to desire; the word
desire, therefore, includes both the action and the object or motive; for
the object and motive of desire are the same thing. Hence to desire without
an object, that is, without a motive, is a solecism in language. As if one
should ask, if you could eat without food, or breathe without air.

From this account of volition it appears, that convulsions of the muscles,
as in epileptic fits, may in the common sense of that word be termed
involuntary; because no deliberation is interposed between the desire or
aversion and the consequent action; but in the sense of the word, as above
defined, they belong to the class of voluntary motions, as delivered in
Vol. II. Class III. If this use of the word be discordant to the ear of the
reader, the term morbid voluntary motions, or motions in consequence of
aversion, may be substituted in its stead.

If a person has a desire to be cured of the ague, and has at the same time
an aversion (or contrary desire) to swallowing an ounce of Peruvian bark;
he balances desire against desire, or aversion against aversion; and thus
he acquires the power of choosing, which is the common acceptation of the
word _willing_. But in the cold fit of ague, after having discovered that
the act of shuddering, or exerting the subcutaneous muscles, relieves the
pain of cold; he immediately exerts this act of volition, and shudders, as
soon as the pain and consequent aversion return, without any deliberation
intervening; yet is this act, as well as that of swallowing an ounce of the
bark, caused by volition; and that even though he endeavours in vain to
prevent it by a weaker contrary volition. This recalls to our minds the
story of the hungry ass between two hay-stacks, where the two desires are
supposed so exactly to counteract each other, that he goes to neither of
the stacks, but perishes by want. Now as two equal and opposite desires are
thus supposed to balance each other, and prevent all action, it follows,
that if one of these hay-stacks was suddenly removed, that the ass would
irresistibly be hurried to the other, which in the common use of the word
might be called an involuntary act; but which, in our acceptation of it,
would be classed amongst voluntary actions, as above explained.

Hence to deliberate is to compare opposing desires or aversions, and that
which is the most interesting at length prevails, and produces action.
Similar to this, where two pains oppose each other, the stronger or more
interesting one produces action; as in pleurisy the pain from suffocation
would produce expansion of the lungs, but the pain occasioned by extending
the inflamed membrane, which lines the chest, opposes this expansion, and
one or the other alternately prevails.

When any one moves his hand quickly near another person's eyes, the
eye-lids instantly close; this act in common language is termed
involuntary, as we have not time to deliberate or to exert any contrary
desire or aversion, but in this work it would be termed a voluntary act,
because it is caused by the faculty of volition, and after a few trials the
nictitation can be prevented by a contrary or opposing volition.

The power of opposing volitions is best exemplified in the story of Mutius
Scævola, who is said to have thrust his hand into the fire before Porcenna,
and to have suffered it to be consumed for having failed him in his attempt
on the life of that general. Here the aversion for the loss of same, or the
unsatisfied desire to serve his country, the two prevalent enthusiasms at
that time, were more powerful than the desire of withdrawing his hand,
which must be occasioned by the pain of combustion; of these opposing
volitions

  Vincit amor patriæ, laudumque immensa cupido.

If any one is told not to swallow his saliva for a minute, he soon swallows
it contrary to his will, in the common sense of that word; but this also is
a voluntary action, as it is performed by the faculty of volition, and is
thus to be understood. When the power of volition is exerted on any of our
senses, they become more acute, as in our attempts to hear small noises in
the night. As explained in Section XIX. 6. Hence by our attention to the
fauces from our desire not to swallow our saliva; the fauces become more
sensible; and the stimulus of the saliva is followed by greater sensation,
and consequent desire of swallowing it. So that the desire or volition in
consequence of the increased sensation of the saliva is more powerful, than
the previous desire not to swallow it. See Vol. II. Deglutitio invita. In
the same manner if a modest man wishes not to want to make water, when he
is confined with ladies in a coach or an assembly-room; that very act of
volition induces the circumstance, which he wishes to avoid, as above
explained; insomuch that I once saw a partial insanity, which might be
called a voluntary diabetes, which was occasioned by the fear (and
consequent aversion) of not being able to make water at all.

It is further necessary to observe here, to prevent any confusion of
voluntary, with sensitive, or associate motions, that in all the instances
of violent efforts to relieve pain, those efforts are at first voluntary
exertions; but after they have been frequently repeated for the purpose of
relieving certain pains, they become associated with those pains, and cease
at those times to be subservient to the will; as in coughing, sneezing, and
strangury. Of these motions those which contribute to remove or dislodge
the offending cause, as the actions of the abdominal muscles in parturition
or in vomiting, though they were originally excited by volition, are in
this work termed sensitive motions; but those actions of the muscles or
organs of sense, which do not contribute to remove the offending cause, as
in general convulsions or in madness, are in this work termed voluntary
motions, or motions in consequence of aversion, though in common language
they are called involuntary ones. Those sensitive unrestrainable actions,
which contribute to remove the cause of pain are uniformly and invariably
exerted, as in coughing or sneezing; but those motions which are exerted in
consequence of aversion without contributing to remove the painful cause,
but only to prevent the sensation of it, as in epileptic, or cataleptic
fits, are not uniformly and invariably exerted, but change from one set of
muscles to another, as will be further explained; and may by this criterion
also be distinguished from the former.

At the same time those motions, which are excited by perpetual stimulus, or
by association with each other, or immediately by pleasureable or painful
sensation, may properly be termed involuntary motions, as those of the
heart and arteries; as the faculty of volition seldom affects those, except
when it exists in unnatural quantity, as in maniacal people.

2. It was observed in Section XIV. on the Production of Ideas, that those
parts of the system, which are usually termed the organs of sense, are
liable to be excited into pain by the excess of the stimulus of those
objects, which are by nature adapted to affect them; as of too great light,
sound, or pressure. But that these organs receive no pain from the defect
or absence of these stimuli, as in darkness or silence. But that our other
organs of perception, which have generally been called appetites, as of
hunger, thirst, want of heat, want of fresh air, are liable to be affected
with pain by the defect, as well as by the excess of their appropriated
stimuli.

This excess or defect of stimulus is however to be considered only as the
remote cause of the pain, the immediate cause being the excess or defect of
the natural action of the affected part, according to Sect. IV. 5. Hence
all the pains of the body may be divided into those from excess of motion,
and those from defect of motion; which distinction is of great importance
in the knowledge and the cure of many diseases. For as the pains from
excess of motion either gradually subside, or are in general succeeded by
inflammation; so those from defect of motion either gradually subside, or
are in general succeeded by convulsion, or madness. These pains are easily
distinguishable from each other by this circumstance, that the former are
attended with heat of the pained part, or of the whole body; whereas the
latter exists without increase of heat in the pained part, and is generally
attended with coldness of the extremities of the body; which is the true
criterion of what have been called nervous pains.

Thus when any acrid material, as snuff or lime, falls into the eye, pain
and inflammation and heat are produced from the excess of stimulus; but
violent hunger, hemicrania, or the clavus hystericus, are attended with
coldness of the extremities, and defect of circulation. When we are exposed
to great cold, the pain we experience from the deficiency of heat is
attended with a quiescence of the motions of the vascular system; so that
no inflammation is produced, but a great desire of heat, and a tremulous
motion of the subcutaneous muscles, which is properly a convulsion in
consequence of this pain from defect of the stimulus of heat.

It was before mentioned, that as sensation consists in certain movements of
the sensorium, beginning at some of the extremities of it, and propagated
to the central parts of it; so volition consists of certain other movements
of the sensorium, commencing in the central parts of it, and propagated to
some of its extremities. This idea of these two great powers of motion in
the animal machine is confirmed from observing, that they never exist in a
great degree or universally at the same time; for while we strongly exert
our voluntary motions, we cease to feel the pains or uneasinesses, which
occasioned us to exert them.

Hence during the time of fighting with fists or swords no pain is felt by
the combatants, till they cease to exert themselves. Thus in the beginning
of ague-fits the painful sensation of cold is diminished, while the patient
exerts himself in the shivering and gnashing of his teeth. He then ceases
to exert himself, and the pain of cold returns; and he is thus perpetually
induced to reiterate these exertions, from which he experiences a temporary
relief. The same occurs in labour-pains, the exertion of the parturient
woman relieves the violence of the pains for a time, which recur again soon
after she has ceased to use those exertions. The same is true in many other
painful diseases, as in the strangury, tenesmus, and the efforts of
vomiting; all these disagreeable sensations are diminished or removed for a
time by the various exertions they occasion, and recur alternately with
those exertions.

The restlessness in some fevers is an almost perpetual exertion of this
kind, excited to relieve some disagreeable sensations; the reciprocal
opposite exertions of a wounded worm, the alternate emprosthotonos and
opisthotonos of some spasmodic diseases, and the intervals of all
convulsions, from whatever cause, seem to be owing to this circumstance of
the laws of animation; that great or universal exertion cannot exist at the
same time with great or universal sensation, though they can exist
reciprocally; which is probably resolvable into the more general law, that
the whole sensorial power being expended in one mode of exertion, there is
none to spare for any other. Whence syncope, or temporary apoplexy,
succeeds to epileptic convulsions.

3. Hence when any violent pain afflicts us, of which we can neither avoid
nor remove the cause, we soon learn to endeavour to alleviate it, by
exerting some violent voluntary effort, as mentioned above; and are
naturally induced to use those muscles for this purpose, which have been in
the early periods of our lives most frequently or most powerfully exerted.

Now the first muscles, which infants use most frequently, are those of
respiration; and on this account we gain a habit of holding our breath, at
the same time that we use great efforts to exclude it, for this purpose of
alleviating unavoidable pain; or we press out our breath through a small
aperture of the larynx, and scream violently, when the pain is greater than
is relievable by the former mode of exertion. Thus children scream to
relieve any pain either of body or mind, as from anger, or fear of being
beaten.

Hence it is curious to observe, that those animals, who have more
frequently exerted their muscles of respiration violently, as in talking,
barking, or grunting, as children, dogs, hogs, scream much more, when they
are in pain, than those other animals, who use little or no language in
their common modes of life; as horses, sheep, and cows.

The next most frequent or most powerful efforts, which infants are first
tempted to produce, are those with the muscles in biting hard substances;
indeed the exertion of these muscles is very powerful in common
mastication, as appears from the pain we receive, if a bit of bone is
unexpectedly found amongst our softer food; and further appears from their
acting to so great mechanical disadvantage, particularly when we bite with
the incisores, or canine teeth; which are first formed, and thence are
first used to violent exertion.

Hence when a person is in great pain, the cause of which he cannot remove,
he sets his teeth firmly together, or bites some substance between them
with great vehemence, as another mode of violent exertion to produce a
temporary relief. Thus we have a proverb where no help can be had in pain,
"to grin and abide;" and the tortures of hell are said to be attended with
"gnashing of teeth."

Hence in violent spasmodic pains I have seen people bite not only their
tongues, but their arms or fingers, or those of the attendants, or any
object which was near them; and also strike, pinch, or tear, others or
themselves, particularly the part of their own body, which is painful at
the time. Soldiers, who die of painful wounds in battle, are said in Homer
to bite the ground. Thus also in the bellon, or colica saturnina, the
patients are said to bite their own flesh, and dogs in this disease to bite
up the ground they lie upon. It is probable that the great endeavours to
bite in mad dogs, and the violence of other mad animals, is owing to the
same cause.

4. If the efforts of our voluntary motions are exerted with still greater
energy for the relief of some disagreeable sensation, convulsions are
produced; as the various kinds of epilepsy, and in some hysteric paroxysms.
In all these diseases a pain, or disagreeable sensation is produced,
frequently by worms, or acidity in the bowels, or by a diseased nerve in
the side, or head, or by the pain of a diseased liver.

In some constitutions a more intolerable degree of pain is produced in some
part at a distance from the cause by sensitive association, as before
explained; these pains in such constitutions arise to so great a degree,
that I verily believe no artificial tortures could equal some, which I have
witnessed; and am confident life would not have long been preserved, unless
they had been soon diminished or removed by the universal convulsion of the
voluntary motions, or by temporary madness.

In some of the unfortunate patients I have observed, the pain has risen to
an inexpressible degree, as above described, before the convulsions have
supervened; and which were preceded by screaming, and grinning; in others,
as in the common epilepsy, the convulsion has immediately succeeded the
commencement of the disagreeable sensations; and as a stupor frequently
succeeds the convulsions, they only seemed to remember that a pain at the
stomach preceded the fit, or some other uneasy feel; or more frequently
retained no memory at all of the immediate cause of the paroxysm. But even
in this kind of epilepsy, where the patient does not recollect any
preceding pain, the paroxysms generally are preceded by a quivering motion
of the under jaw, with a biting of the tongue; the teeth afterwards become
pressed together with vehemence, and the eyes are then convulsed, before
the commencement of the universal convulsion; which are all efforts to
relieve pain.

The reason why these convulsive motions are alternately exerted and
remitted was mentioned above, and in Sect. XII. 1. 3. when the exertions
are such as give a temporary relief to the pain, which excites them, they
cease for a time, till the pain is again perceived; and then new exertions
are produced for its relief. We see daily examples of this in the loud
reiterated laughter of some people; the pleasureable sensation, which
excites this laughter, arises for a time so high as to change its name and
become painful: the convulsive motions of the respiratory muscles relieve
the pain for a time; we are, however, unwilling to lose the pleasure, and
presently put a stop to this exertion, and immediately the pleasure recurs,
and again as instantly rises into pain. All of us have felt the pain of
immoderate laughter; children have been tickled into convulsions of the
whole body; and others have died in the act of laughing; probably from a
paralysis succeeding the long continued actions of the muscles of
respiration.

Hence we learn the reason, why children, who are so easily excited to laugh
by the tickling of other people's fingers, cannot tickle themselves into
laughter. The exertion of their hands in the endeavour to tickle themselves
prevents the necessity of any exertion of the respiratory muscles to
relieve the excess of pleasurable affection. See Sect. XVII. 3. 5.

Chrysippus is recorded to have died laughing, when an ass was invited to
sup with him. The same is related of one of the popes, who, when he was
ill, saw a tame monkey at his bedside put on the holy thiara. Hall. Phys.
T. III. p. 306.

There are instances of epilepsy being produced by laughing recorded by Van
Swieten, T. III. 402 and 308. And it is well known, that many people have
died instantaneously from the painful excess of joy, which probably might
have been prevented by the exertions of laughter.

Every combination of ideas, which we attend to, occasions pain or pleasure;
those which occasion pleasure, furnish either social or selfish pleasure,
either malicious or friendly, or lascivious, or sublime pleasure; that is,
they give us pleasure mixed with other emotions, or they give us unmixed
pleasure, without occasioning any other emotions or exertions at the same
time. This unmixed pleasure, if it be great, becomes painful, like all
other animal motions from stimuli of every kind; and if no other exertions
are occasioned at the same time, we use the exertion of laughter to relieve
this pain. Hence laughter is occasioned by such wit as excites simple
pleasure without any other emotion, such as pity, love, reverence. For
sublime ideas are mixed with admiration, beautiful ones with love, new ones
with surprise; and these exertions of our ideas prevent the action of
laughter from being necessary to relieve the painful pleasure above
described. Whence laughable wit consists of frivolous ideas, without
connections of any consequence, such as puns on words, or on phrases,
incongruous junctions of ideas; on which account laughter is so frequent in
children.

Unmixed pleasure less than that, which causes laughter, causes sleep, as in
singing children to sleep, or in slight intoxication from wine or food. See
Sect. XVIII. 12.

5. If the pains, or disagreeable sensations, above described do not obtain
a temporary relief from these convulsive exertions of the muscles, those
convulsive exertions continue without remission, and one kind of catalepsy
is produced. Thus when a nerve or tendon produces great pain by its being
inflamed or wounded, the patient sets his teeth firmly together, and grins
violently, to diminish the pain; and if the pain is not relieved by this
exertion, no relaxation of the maxillary muscles takes place, as in the
convulsions above described, but the jaws remain firmly fixed together.
This locked jaw is the most frequent instance of cataleptic spasm, because
we are more inclined to exert the muscles subservient to mastication from
their early obedience to violent efforts of volition.

But in the case related in Sect. XIX. on Reverie, the cataleptic lady had
pain in her upper teeth; and pressing one of her hands vehemently against
her cheek-bone to diminish this pain, it remained in that attitude for
about half an hour twice a day, till the painful paroxysm was over.

I have this very day seen a young lady in this disease, (with which she has
frequently been afflicted,) she began to-day with violent pain shooting
from one side of the forehead to the occiput, and after various struggles
lay on the bed with her fingers and wrists bent and stiff for about two
hours; in other respects she seemed in a syncope with a natural pulse. She
then had intervals of pain and of spasm, and took three grains of opium
every hour till she had taken nine grains, before the pains and spasm
ceased.

There is, however, another species of fixed spasm, which differs from the
former, as the pain exists in the contracted muscle, and would seem rather
to be the consequence than the cause of the contraction, as in the cramp in
the calf of the leg, and in many other parts of the body.

In these spasms it should seem, that the muscle itself is first thrown into
contraction by some disagreeable sensation, as of cold; and that then the
violent pain is produced by the great contraction of the muscular fibres
extending its own tendons, which are said to be sensible to extension only;
and is further explained in Sect. XVIII. 15.

6. Many instances have been given in this work, where after violent motions
excited by irritation, the organ has become quiescent to less, and even to
the great irritation, which induced it into violent motion; as after
looking long at the sun or any bright colour, they cease to be seen; and
after removing from bright day-light into a gloomy room, the eye cannot at
first perceive the objects, which stimulate it less. Similar to this is the
syncope, which succeeds after the violent exertions of our voluntary
motions, as after epileptic fits, for the power of volition acts in this
case as the stimulus in the other. This syncope is a temporary palsy, or
apoplexy, which ceases after a time, the muscles recovering their power of
being excited into action by the efforts of volition; as the eye in the
circumstance above mentioned recovers in a little time its power of seeing
objects in a gloomy room; which were invisible immediately after coming out
of a stronger light. This is owing to an accumulation of sensorial power
during the inaction of those fibres, which were before accustomed to
perpetual exertions, as explained in Sect. XII. 7. 1. A slighter degree of
this disease is experienced by every one after great fatigue, when the
muscles gain such inability to further action, that we are obliged to rest
them for a while, or to summon a greater power of volition to continue
their motions.

In all the syncopes, which I have seen induced after convulsive fits, the
pulse has continued natural, though the organs of sense, as well as the
locomotive muscles, have ceased to perform their functions; for it is
necessary for the perception of objects, that the external organs of sense
should be properly excited by the voluntary power, as the eye-lids must be
open, and perhaps the muscles of the eye put into action to distend, and
thence give greater pellucidity to the cornea, which in syncope, as in
death, appears flat and less transparent.

The tympanum of the ear also seems to require a voluntary exertion of its
muscles, to gain its due tension, and it is probable the other external
organs of sense require a similar voluntary exertion to adapt them to the
distinct perception of objects. Hence in syncope as in sleep, as the power
of volition is suspended, no external objects are perceived. See Sect.
XVIII. 5. During the time which the patient lies in a fainting fit, the
spirit of animation becomes accumulated; and hence the muscles in a while
become irritable by their usual stimulation, and the fainting fit ceases.
See Sect. XII. 7. 1.

7. If the exertion of the voluntary motions has been still more energetic,
the quiescence, which succeeds, is so complete, that they cannot again be
excited into action by the efforts of the will. In this manner the palsy,
and apoplexy (which is an universal palsy) are frequently produced after
convulsions, or other violent exertions; of this I shall add a few
instances.

Platernus mentions some, who have died apoplectic from violent exertions in
dancing; and Dr. Mead, in his Essay on Poisons, records a patient in the
hydrophobia, who at one effort broke the cords which bound him, and at the
same instant expired. And it is probable, that those, who have expired from
immoderate laughter, have died from this paralysis consequent to violent
exertion. Mrs. Scott of Stafford was walking in her garden in perfect
health with her neighbour Mrs. ----; the latter accidentally fell into a
muddy rivulet, and tried in vain to disengage herself by the assistance of
Mrs. Scott's hand. Mrs. Scott exerted her utmost power for many minutes,
first to assist her friend, and next to prevent herself from being pulled
into the morass, as her distressed companion would not disengage her hand.
After other assistance was procured by their united screams, Mrs. Scott
walked to a chair about twenty yards from the brook, and was seized with an
apoplectic stroke: which continued many days, and terminated in a total
loss of her right arm, and her speech; neither of which she ever after
perfectly recovered.

It is said, that many people in Holland have died after skating too long or
too violently on their frozen canals; it is probable the death of these,
and of others, who have died suddenly in swimming, has been owing to this
great quiescence or paralysis; which has succeeded very violent exertions,
added to the concomitant cold, which has had greater effect after the
sufferers had been heated and exhausted by previous exercise.

I remember a young man of the name of Nairne at Cambridge, who walking on
the edge of a barge fell into the river. His cousin and fellow-student of
the same name, knowing the other could not swim, plunged into the water
after him, caught him by his clothes, and approaching the bank by a
vehement exertion propelled him safe to the land, but that instant, seized,
as was supposed, by the cramp, or paralysis, sunk to rise no more. The
reason why the cramp of the muscles, which compose the calf of the leg, is
so liable to affect swimmers, is, because these muscles have very weak
antagonists, and are in walking generally elongated again after their
contraction by the weight of the body on the ball of the toe, which is very
much greater than the resistance of the water in swimming. See Section
XVIII. 15.

It does not follow that every apoplectic or paralytic attack is immediately
preceded by vehement exertion; the quiescence, which succeeds exertion, and
which is not so great as to be termed paralysis, frequently recurs
afterwards at certain periods; and by other causes of quiescence, occurring
with those periods, as was explained in treating of the paroxysms of
intermitting fevers; the quiescence at length, becomes so great as to be
incapable of again being removed by the efforts of volition, and complete
paralysis is formed. See Section XXXII. 3. 2.

Many of the paralytic patients, whom I have seen, have evidently had
diseased livers from the too frequent potation of spirituous liquors; some
of them have had the gutta rosea on their faces and breasts; which has in
some degree receded either spontaneously, or by the use of external
remedies, and the paralytic stroke has succeeded; and as in several
persons, who have drank much vinous spirits, I have observed epileptic fits
to commence at about forty or fifty years of age, without any hereditary
taint, from the stimulus, as I believed, of a diseased liver; I was induced
to ascribe many paralytic cases to the same source; which were not
evidently the effect of age, or of unacquired debility. And the account
given before of dropsies, which very frequently are owing to a paralysis of
the absorbent system, and are generally attendant on free drinkers of
spirituous liquors, confirmed me in this opinion.

The disagreeable irritation of a diseased liver produces exertions and
consequent quiescence; these by the accidental concurrence of other causes
of quiescence, as cold, solar or lunar periods, inanition, the want of
their usual portion of spirit of wine, at length produces paralysis.

This is further confirmed by observing, that the muscles, we most
frequently, or most powerfully exert, are most liable to palsy; as those of
the voice and of articulation, and of those paralytics which I have seen, a
much greater proportion have lost the use of their right arm; which is so
much more generally exerted than the left.

I cannot dismiss this subject without observing, that after a paralytic
stroke, if the vital powers are not much injured, that the patient has all
the movements of the affected limb to learn over again, just as in early
infancy; the limb is first moved by the irritation of its muscles, as in
stretching, (of which a case was related in Section VII. 1. 3.) or by the
electric concussion; afterwards it becomes obedient to sensation, as in
violent danger or fear; and lastly, the muscles become again associated
with volition, and gradually acquire their usual habits of acting together.

Another phænomenon in palsies is, that when the limbs of one side are
disabled, those of the other are in perpetual motion. This can only be
explained from conceiving that the power of motion, whatever it is, or
wherever it resides, and which is capable of being exhausted by fatigue,
and accumulated in rest, is now less expended, whilst one half of the body
is capable of receiving its usual proportion of it, and is hence derived
with greater ease or in greater abundance into the limbs, which remain
unaffected.

II. 1. The excess or defect of voluntary exertion produces similar effects
upon the sensual motions, or ideas of the mind, as those already mentioned
upon the muscular fibres. Thus when any violent pain, arising from the
defect of some peculiar stimulus, exists either in the muscular or sensual
systems of fibres, and which cannot be removed by acquiring the defective
stimulus; as in some constitutions convulsions of the muscles are produced
to procure a temporary relief, so in other constitutions vehement voluntary
exertions of the ideas of the mind are produced for the same purpose; for
during this exertion, like that of the muscles, the pain either vanishes or
is diminished: this violent exertion constitutes madness; and in many cases
I have seen the madness take place, and the convulsions cease, and
reciprocally the madness cease, and the convulsions supervene. See Section
III. 5. 8.

2. Madness is distinguishable from delirium, as in the latter the patient
knows not the place where he resides, nor the persons of his friends or
attendants, nor is conscious of any external objects, except when spoken to
with a louder voice, or stimulated with unusual force, and even then he
soon relapses into a state of inattention to every thing about him. Whilst
in the former he is perfectly sensible to every thing external, but has the
voluntary powers of his mind intensely exerted on some particular object of
his desire or aversion, he harbours in his thoughts a suspicion of all
mankind, lest they should counteract his designs; and while he keeps his
intentions, and the motives of his actions profoundly secret; he is
perpetually studying the means of acquiring the object of his wish, or of
preventing or revenging the injuries he suspects.

3. A late French philosopher, Mr. Helvetius, has deduced almost all our
actions from this principle of their relieving us from the ennui or tædium
vitæ; and true it is, that our desires or aversions are the motives of all
our voluntary actions; and human nature seems to excel other animals in the
more facil use of this voluntary power, and on that account is more liable
to insanity than other animals. But in mania this violent exertion of
volition is expended on mistaken objects, and would not be relieved, though
we were to gain or escape the objects, that excite it. Thus I have seen two
instances of madmen, who conceived that they had the itch, and several have
believed they had the venereal infection, without in reality having a
symptom of either of them. They have been perpetually thinking upon this
subject, and some of them were in vain salivated with design of convincing
them to the contrary.

4. In the minds of mad people those volitions alone exist, which are
unmixed with sensation; immoderate suspicion is generally the first
symptom, and want of shame, and want of delicacy about cleanliness.
Suspicion is a voluntary exertion of the mind arising from the pain of
fear, which it is exerted to relieve: shame is the name of a peculiar
disagreeable sensation, see Fable of the Bees, and delicacy about
cleanliness arises from another disagreeable sensation. And therefore are
not found in the minds of maniacs, which are employed solely in voluntary
exertions. Hence the most modest women in this disease walk naked amongst
men without any kind of concern, use obscene discourse, and have no
delicacy about their natural evacuations.

5. Nor are maniacal people more attentive to their natural appetites, or to
the irritations which surround them, except as far as may respect their
suspicions or designs; for the violent and perpetual exertions of their
voluntary powers of mind prevents their perception of almost every other
object, either of irritation or of sensation. Hence it is that they bear
cold, hunger, and fatigue, with much greater pertinacity than in their
sober hours, and are less injured by them in respect to their general
health. Thus it is asserted by historians, that Charles the Twelfth of
Sweden slept on the snow, wrapped only in his cloak, at the siege of
Frederickstad, and bore extremes of cold and hunger, and fatigue, under
which numbers of his soldiers perished; because the king was insane with
ambition, but the soldier had no such powerful stimulus to preserve his
system from debility and death.

6. Besides the insanities arising from exertions in consequence of pain,
there is also a pleasurable insanity, as well as a pleasurable delirium; as
the insanity of personal vanity, and that of religious fanaticism. When
agreeable ideas excite into motion the sensorial power of sensation, and
this again causes other trains of agreeable ideas, a constant stream of
pleasurable ideas succeeds, and produces pleasurable delirium. So when the
sensorial power of volition excites agreeable ideas, and the pleasure thus
produced excites more volition in its turn, a constant flow of agreeable
voluntary ideas succeeds; which when thus exerted in the extreme
constitutes insanity.

Thus when our muscular actions are excited by our sensations of pleasure,
it is termed play; when they are excited by our volition, it is termed
work; and the former of these is attended with less fatigue, because the
muscular actions in play produce in their turn more pleasurable sensation;
which again has the property of producing more muscular action. An
agreeable instance of this I saw this morning. A little boy, who was tired
with walking, begged of his papa to carry him. "Here," says the reverend
doctor, "ride upon my gold-headed cane;" and the pleased child, putting it
between his legs, gallopped away with delight, and complained no more of
his fatigue. Here the aid of another sensorial power, that of pleasurable
sensation, superadded vigour to the exertion of exhausted volition. Which
could otherwise only have been excited by additional pain, as by the lash
of slavery. On this account where the whole sensorial power has been
exerted on the contemplation of the promised joys of heaven, the saints of
all persecuted religions have borne the tortures of martyrdom with
otherwise unaccountable firmness.

7. There are some diseases, which obtain at least a temporary relief from
the exertions of insanity; many instances of dropsies being thus for a time
cured are recorded. An elderly woman labouring with ascites I twice saw
relieved for some weeks by insanity, the dropsy ceased for several weeks,
and recurred again alternating with the insanity. A man afflicted with
difficult respiration on lying down, with very irregular pulse, and
oedematous legs, whom I saw this day, has for above a week been much
relieved in respect to all those symptoms by the accession of insanity,
which is shewn by inordinate suspicion, and great anger.

In cases of common temporary anger the increased action of the arterial
system is seen by the red skin, and increased pulse, with the immediate
increase of muscular activity. A friend of mine, when he was painfully
fatigued by riding on horseback, was accustomed to call up ideas into his
mind, which used to excite his anger or indignation, and thus for a time at
least relieved the pain of fatigue. By this temporary insanity, the effect
of the voluntary power upon the whole of his system was increased; as in
the cases of dropsy above mentioned, it would appear, that the increased
action of the voluntary faculty of the sensorium affected the absorbent
system, as well as the secerning one.

8. In respect to relieving inflammatory pains, and removing fever, I have
seen many instances, as mentioned in Sect. XII. 2. 4. One lady, whom I
attended, had twice at some years interval a locked jaw, which relieved a
pain on her sternum with peripneumony. Two other ladies I saw, who towards
the end of violent peripneumony, in which they frequently lost blood, were
at length cured by insanity supervening. In the former the increased
voluntary exertion of the muscles of the jaw, in the latter that of the
organs of sense, removed the disease; that is, the disagreeable sensation,
which had produced the inflammation, now excited the voluntary power, and
these new voluntary exertions employed or expended the superabundant
sensorial power, which had previously been exerted on the arterial system,
and caused inflammation.

Another case, which I think worth relating, was of a young man about
twenty; he had laboured under an irritative fever with debility for three
or four weeks, with very quick and very feeble pulse, and other usual
symptoms of that species of typhus, but at this time complained much and
frequently of pain of his legs and feet. When those who attended him were
nearly in despair of his recovery, I observed with pleasure an insanity of
mind supervene: which was totally different from delirium, as he knew his
friends, calling them by their names, and the room in which he lay, but
became violently suspicious of his attendants, and calumniated with
vehement oaths his tender mother, who sat weeping by his bed. On this his
pulse became slower and firmer, but the quickness did not for some time
intirely cease, and he gradually recovered. In this case the introduction
of an increased quantity of the power of volition gave vigour to those
movements of the system, which are generally only actuated by the power of
irritation, and of association.

Another case I recollect of a young man, about twenty-five, who had the
scarlet-fever, with very quick pulse, and an universal eruption on his
skin, and was not without reason esteemed to be in great danger of his
life. After a few days an insanity supervened, which his friends mistook
for delirium, and he gradually recovered, and the cuticle peeled off. From
these and a few other cases I have always esteemed insanity to be a
favourable sign in fevers, and have cautiously distinguished it from
delirium.

III. Another mode of mental exertion to relieve pain, is by producing a
train of ideas not only by the efforts of volition, as in insanity; but by
those of sensation likewise, as in delirium and sleep. This mental effort
is termed reverie, or somnambulation, and is described more at large in
Sect. XIX. on that subject. But I shall here relate another case of that
wonderful disease, which fell yesterday under my eye, and to which I have
seen many analogous alienations of mind, though not exactly similar in all
circumstances. But as all of them either began or terminated with pain or
convulsion, there can be no doubt but that they are of epileptic origin,
and constitute another mode of mental exertion to relieve some painful
sensation.

1. Master A. about nine years old, had been seized at seven every morning
for ten days with uncommon fits, and had had slight returns in the
afternoon. They were supposed to originate from worms, and had been in vain
attempted to be removed by vermifuge purges. As his fit was expected at
seven yesterday morning, I saw him before that hour; he was asleep, seemed
free from pain, and his pulse natural. About seven he began to complain of
pain about his navel, or more to the left side, and in a few minutes had
exertions of his arms and legs like swimming. He then for half an hour
hunted a pack of hounds; as appeared by his hallooing, and calling the dogs
by their names, and discoursing with the attendants of the chase,
describing exactly a day of hunting, which (I was informed) he had
witnessed a year before, going through all the most minute circumstances of
it; calling to people, who were then present, and lamenting the absence of
others, who were then also absent. After this scene he imitated, as he lay
in bed, some of the plays of boys, as swimming and jumping. He then sung an
English and then an Italian song; part of which with his eyes open, and
part with them closed, but could not be awakened or excited by any
violence, which it was proper to use.

After about an hour he came suddenly to himself with apparent surprise, and
seemed quite ignorant of any part of what had passed, and after being
apparently well for half an hour, he suddenly fell into a great stupor,
with slower pulse than natural, and a slow moaning respiration, in which he
continued about another half hour, and then recovered.

The sequel of this disease was favourable; he was directed one grain of
opium at six every morning, and then to rise out of bed; at half past six
he was directed fifteen drops of laudanum in a glass of wine and water. The
first day the paroxysm became shorter, and less violent. The dose of opium
was increased to one-half more, and in three or four days the fits left
him. The bark and filings of iron were also exhibited twice a day; and I
believe the complaint returned no more.

2. In this paroxysm it must be observed, that he began with pain, and ended
with stupor, in both circumstances resembling a fit of epilepsy. And that
therefore the exertions both of mind and body, both the voluntary ones, and
those immediately excited by pleasurable sensation, were exertions to
relieve pain.

The hunting scene appeared to be rather an act of memory than of
imagination, and was therefore rather a voluntary exertion, though attended
with the pleasurable eagerness, which was the consequence of those ideas
recalled by recollection, and not the cause of them.

These ideas thus voluntarily recollected were succeeded by sensations of
pleasure, though his senses were unaffected by the stimuli of visible or
audible objects; or so weakly excited by them as not to produce sensation
or attention. And the pleasure thus excited by volition produced other
ideas and other motions in consequence of the sensorial power of sensation.
Whence the mixed catenations of voluntary and sensitive ideas and muscular
motions in reverie; which, like every other kind of vehement exertion,
contribute to relieve pain, by expending a large quantity of sensorial
power.

Those fits generally commence during sleep, from whence I suppose they have
been thought to have some connection with sleep, and have thence been
termed Somnambulism; but their commencement during sleep is owing to our
increased excitability by internal sensations at that time, as explained in
Sect. XVIII. 14. and 15., and not to any similitude between reverie and
sleep.

3. I was once concerned for a very elegant and ingenious young lady, who
had a reverie on alternate days, which continued nearly the whole day; and
as in her days of disease she took up the same kind of ideas, which she had
conversed about on the alternate day before, and could recollect nothing of
them on her well-day; she appeared to her friends to possess two minds.
This case also was of epileptic kind, and was cured, with some relapses, by
opium administered before the commencement of the paroxysm.

4. Whence it appears, that the methods of relieving inflammatory pains, is
by removing all stimulus, as by venesection, cool air, mucilaginous diet,
aqueous potation, silence, darkness.

The methods of relieving pains from defect of stimulus is by supplying the
peculiar stimulus required, as of food, or warmth.

And the general method of relieving pain is by exciting into action some
great part of the system for the purpose of expending a part of the
sensorial power. This is done either by exertion of the voluntary ideas and
muscles, as in insanity and convulsion; or by exerting both voluntary and
sensitive motions, as in reverie; or by exciting the irritative motions by
wine or opium internally, and by the warm bath or blisters externally; or
lastly, by exciting the sensitive ideas by good news, affecting stories, or
agreeable passions.

       *       *       *       *       *

SECT. XXXV.

DISEASES OF ASSOCIATION.

    I. 1. _Sympathy or consent of parts. Primary and secondary parts of an
    associated train of motions reciprocally affect each other. Parts of
    irritative trains of motion affect each other in four ways. Sympathies
    of the skin and stomach. Flushing of the face after a meal. Eruption of
    the small-pox on the face. Chilness after a meal._ 2. _Vertigo from
    intoxication._ 3. _Absorption from the lungs and pericardium by
    emetics. In vomiting the actions of the stomach are decreased, not
    increased. Digestion strengthened after an emetic. Vomiting from
    deficiency of sensorial power._ 4. _Dyspnoea from cold bathing. Slow
    pulse from digitalis. Death from gout in the stomach._ II. 1. _Primary
    and secondary parts of sensitive associations affect each other. Pain
    from gall-stone, from urinary stone, Hemicrania. Painful epilepsy._ 2.
    _Gout and red face from inflamed liver. Shingles from inflamed kidney._
    3. _Coryza from cold applied to the feet. Pleurisy. Hepatitis._ 4.
    _Pain of shoulders from inflamed liver._ III. _Diseases from the
    associations of ideas._

I. 1. Many synchronous and successive motions of our muscular fibres, and
of our organs of sense, or ideas, become associated so as to form
indissoluble tribes or trains of action, as shewn in Section X. on
Associate Motions. Some constitutions more easily establish these
associations, whether by voluntary, sensitive, or irritative repetitions,
and some more easily lose them again, as shewn in Section XXXI. on
Temperaments.

When the beginning of such a train of actions becomes by any means
disordered, the succeeding part is liable to become disturbed in
consequence, and this is commonly termed sympathy or consent of parts by
the writers of medicine. For the more clear understanding of these
sympathies we must consider a tribe or train of actions as divided into two
parts, and call one of them the primary or original motions, and the other
the secondary or sympathetic ones.

The primary and secondary parts of a train of irritative actions may
reciprocally affect each other in four different manners. 1. They may both
be exerted with greater energy than natural. 2. The former may act with
greater, and the latter with less energy. 3. The former may act with less,
and the latter with greater energy. 4. They may both act with less energy
than natural. I shall now give an example of each kind of these modes of
action, and endeavour to shew, that though the primary and secondary parts
of these trains or tribes of motion are connected by irritative
association, or their previous habits of acting together, as described in
Sect. XX. on Vertigo. Yet that their acting with similar or dissimilar
degrees of energy, depends on the greater or less quantity of sensorial
power, which the primary part of the train expends in its exertions.

The actions of the stomach constitute so important a part of the
associations of both irritative and sensitive motions, that it is said to
sympathize with almost every part of the body; the first example, which I
shall adduce to shew that both the primary and secondary parts of a train
of irritative associations of motion act with increased energy, is taken
from the consent of the skin with this organ. When the action of the fibres
of the stomach is increased, as by the stimulus of a full meal, the
exertions of the cutaneous arteries of the face become increased by their
irritative associations with those of the stomach, and a glow or flushing
of the face succeeds. For the small vessels of the skin of the face having
been more accustomed to the varieties of action, from their frequent
exposure to various degrees of cold and heat become more easily excited
into increased action, than those of the covered parts of our bodies, and
thus act with more energy from their irritative or sensitive associations
with the stomach. On this account in small-pox the eruption in consequence
of the previous affection of the stomach breaks out a day sooner on the
face than on the hands, and two days sooner than on the trunk, and recedes
in similar times after maturation.

But secondly, in weaker constitutions, that is, in those who possess less
sensorial power, so much of it is expended in the increased actions of the
fibres of the stomach excited by the stimulus of a meal, that a sense of
chilness succeeds instead of the universal glow above mentioned; and thus
the secondary part of the associated train of motions is diminished in
energy, in consequence of the increased activity of the primary part of it.

2. Another instance of a similar kind, where the secondary part of the
train acts with less energy in consequence of the greater exertions of the
primary part, is the vertigo attending intoxication; in this circumstance
so much sensorial power is expended on the stomach, and on its nearest or
more strongly associated motions, as those of the subcutaneous vessels, and
probably of the membranes of some internal viscera, that the irritative
motions of the retina become imperfectly exerted from deficiency of
sensorial power, as explained in Sect. XX. and XXI. 3. on Vertigo and on
Drunkenness, and hence the staggering inebriate cannot completely balance
himself by such indistinct vision.

3. An instance of the third circumstance, where the primary part of a train
of irritative motions acts with less, and the secondary part with greater
energy, may be observed by making the following experiment. If a person
lies with his arms and shoulders out of bed, till they become cold, a
temporary coryza or catarrh is produced; so that the passage of the
nostrils becomes totally obstructed; at least this happens to many people;
and then on covering the arms and shoulders, till they become warm, the
passage of the nostrils ceases again to be obstructed, and a quantity of
mucus is discharged from them. In this case the quiescence of the vessels
of the skin of the arms and shoulders, occasioned by exposure to cold air,
produces by irritative association an increased action of the vessels of
the membrane of the nostrils; and the accumulation of sensorial power
during the torpor of the arms and shoulders is thus expended in producing a
temporary coryza or catarrh.

Another instance may be adduced from the sympathy or consent of the motions
of the stomach with other more distant links of the very extensive tribes
or trains of irritative motions associated with them, described in Sect.
XX. on Vertigo. When the actions of the fibres of the stomach are
diminished or inverted, the actions of the absorbent vessels, which take up
the mucus from the lungs, pericardium, and other cells of the body, become
increased, and absorb the fluids accumulated in them with greater avidity,
as appears from the exhibition of foxglove, antimony, or other emetics in
cases of anasarca, attended with unequal pulse and difficult respiration.

That the act of nausea and vomiting is a decreased exertion of the fibres
of the stomach may be thus deduced; when an emetic medicine is
administered, it produces the pain of sickness, as a disagreeable taste in
the mouth produces the pain of nausea; these pains, like that of hunger, or
of cold, or like those, which are usually termed nervous, as the head-ach
or hemicrania, do not excite the organ into greater action; but in this
case I imagine the pains of sickness or of nausea counteract or destroy the
pleasurable sensation, which seems necessary to digestion, as shewn in
Sect. XXXIII. 1. 1. The peristaltic motions of the fibres of the stomach
become enfeebled by the want of this stimulus of pleasurable sensation, and
in consequence stop for a time, and then become inverted; for they cannot
become inverted without being previously stopped. Now that this inversion
of the trains of motion of the fibres of the stomach is owing to the
deficiency of pleasurable sensation is evinced from this circumstance, that
a nauseous idea excited by words will produce vomiting as effectually us a
nauseous drug.

Hence it appears, that the act of nausea or vomiting expends less sensorial
power than the usual peristaltic motions of the stomach in the digestion of
our aliment; and that hence there is a greater quantity of sensorial power
becomes accumulated in the fibres of the stomach, and more of it in
consequence to spare for the action of those parts of the system, which are
thus associated with the stomach, as of the whole absorbent series of
vessels, and which are at the same time excited by their usual stimuli.

From this we can understand, how after the operation of an emetic the
stomach becomes more irritable and sensible to the stimulus, and the
pleasure of food; since as the sensorial power becomes accumulated during
the nausea and vomiting, the digestive power is afterwards exerted more
forceably for a time. It should, however, be here remarked, that though
vomiting is in general produced by the defect of this stimulus of
pleasurable sensation, as when a nauseous drug is administered; yet in long
continued vomiting, as in sea-sickness, or from habitual dram-drinking, it
arises from deficiency of sensorial power, which in the former case is
exhausted by the increased exertion of the irritative ideas of vision, and
in the latter by the frequent application of an unnatural stimulus.

4. An example of the fourth circumstance above mentioned, where both the
primary and secondary parts of a train of motions proceed with energy less
than natural, may be observed in the dyspnoea, which occurs in going into a
very cold bath, and which has been described and explained in Sect. XXXII.
3. 2.

And by the increased debility of the pulsations of the heart and arteries
during the operation of an emetic. Secondly, from the slowness and
intermission of the pulsations of the heart from the incessant efforts to
vomit occasioned by an overdose of digitalis. And thirdly, from the total
stoppage of the motions of the heart, or death, in consequence of the
torpor of the stomach, when affected with the commencement or cold paroxysm
of the gout. See Sect. XXV. 17.

II. 1. The primary and secondary parts of the trains of sensitive
association reciprocally affect each other in different manners. 1. The
increased sensation of the primary part may cease, when that of the
secondary part commences. 2. The increased action of the primary part may
cease, when that of the secondary part commences. 3. The primary part may
have increased sensation, and the secondary part increased action. 4. The
primary part may have increased action, and the secondary part increased
sensation.

Examples of the first mode, where the increased sensation of the primary
part of a train of sensitive association ceases, when that of the secondary
part commences, are not unfrequent; as this is the general origin of those
pains, which continue some time without being attended with inflammation,
such as the pain at the pit of the stomach from a stone at the neck of the
gall-bladder, and the pain of strangury in the glans penis from a stone at
the neck of the urinary bladder. In both these cases the part, which is
affected secondarily, is believed to be much more sensible than the part
primarily affected, as described in the catalogue of diseases, Class II. 1.
1. 11. and IV. 2. 2. 2. and IV. 2. 2. 4.

The hemicrania, or nervous headach, as it is called, when it originates
from a decaying tooth, is another disease of this kind; as the pain of the
carious tooth always ceases, when the pain over one eye and temple
commences. And it is probable, that the violent pains, which induce
convulsions in painful epilepsies, are produced in the same manner, from a
more sensible part sympathizing with a diseased one of less sensibility.
See Catalogue of Diseases, Class IV. 2. 2. 8. and III. 1. 1. 6.

The last tooth, or dens sapientiæ, of the upper jaw most frequently decays
first, and is liable to produce pain over the eye and temple of that side.
The last tooth of the under-jaw is also liable to produce a similar
hemicrania, when it begins to decay. When a tooth in the upper-jaw is the
cause of the headach, a slighter pain is sometimes perceived on the
cheek-bone. And when a tooth in the lower-jaw is the cause of headach, a
pain sometimes affects the tendons of the muscles of the neck, which are
attached near the jaws. But the clavus hystericus, or pain about the middle
of the parietal bone on one side of the head, I have seen produced by the
second of the molares, or grinders, of the under-jaw; of which I shall
relate the following case. See Class IV. 2. 2. 8.

Mrs. ----, about 30 years of age, was seized with great pain about the
middle of the right parietal bone, which had continued a whole day before I
saw her, and was so violent as to threaten to occasion convulsions. Not
being able to detect a decaying tooth, or a tender one, by examination with
my eye, or by striking them with a tea-spoon, and fearing bad consequences
from her tendency to convulsion, I advised her to extract the last tooth of
the under-jaw on the affected side; which was done without any good effect.
She was then directed to lose blood, and to take a brisk cathartic; and
after that had operated, about 60 drops of laudanum were given her, with
large doses of bark; by which the pain was removed. In about a fortnight
she took a cathartic medicine by ill advice, and the pain returned with
greater violence in the same place; and, before I could arrive, as she
lived 30 miles from me, she suffered a paralytic stroke; which affected her
limbs and her face on one side, and relieved the pain of her head.

About a year afterwards I was again called to her on account of a pain as
violent as before exactly on the same part of the other parietal bone. On
examining her mouth I found the second molaris of the under-jaw on the side
before affected was now decayed, and concluded, that this tooth had
occasioned the stroke of the palsy by the pain and consequent exertion it
had caused. On this account I earnestly entreated her to allow the sound
molaris of the same jaw opposite to the decayed one to be extracted; which
was forthwith done, and the pain of her head immediately ceased, to the
astonishment of her attendants.

In the cases above related of the pain existing in a part distant from the
seat of the disease, the pain is owing to defect of the usual motions of
the painful part. This appears from the coldness, paleness, and emptiness
of the affected vessels, or of the extremities of the body in general, and
from there being no tendency to inflammation. The increased action of the
primary part of these associated motions, as of the hepatic termination of
the bile-duct; from the stimulus of a gall-stone, or of the interior
termination of the urethra from the stimulus of a stone in the bladder, or
lastly, of a decaying tooth in hemicrania, deprives the secondary part of
these associated motions, namely, the exterior terminations of the
bile-duct or urethra, or the pained membranes of the head in hemicrania, of
their natural share of sensorial power: and hence the secondary parts of
these sensitive trains of association become pained from the deficiency of
their usual motions, which is accompanied with deficiency of secretions and
of heat. See Sect. IV. 5. XII. 5. 3. XXXIV. 1.

Why does the pain of the primary part of the association cease, when that
of the secondary part commences? This is a question of intricacy, but
perhaps not inexplicable. The pain of the primary part of these associated
trains of motion was owing to too great stimulus, as of the stone at the
neck of the bladder, and was consequently caused by too great action of the
pained part. This greater action than natural of the primary part of these
associated motions, by employing or expending the sensorial power of
irritation belonging to the whole associated train of motions, occasioned
torpor, and consequent pain in the secondary part of the associated train;
which was possessed of greater sensibility than the primary part of it. Now
the great pain of the secondary part of the train, as soon as it commences,
employs or expends the sensorial power of sensation belonging to the whole
associated train of motions; and in consequence the motions of the primary
part, though increased by the stimulus of an extraneous body, cease to be
accompanied with pain or sensation.

If this mode of reasoning be just it explains a curious fact, why when two
parts of the body are strongly stimulated, the pain is felt only in one of
them, though it is possible by voluntary attention it may be alternately
perceived in them both. In the same manner, when two new ideas are
presented to us from the stimulus of external bodies, we attend to but one
of them at a time. In other words, when one set of fibres, whether of the
muscles or organs of sense, contract so strongly as to excite much
sensation; another set of fibres contracting more weakly do not excite
sensation at all, because the sensorial power of sensation is pre-occupied
by the first set of fibres. So we cannot will more than one effect at once,
though by associations previously formed we can move many fibres in
combination.

Thus in the instances above related, the termination of the bile duct in
the duodenum, and the exterior extremity of the urethra, are more sensible
than their other terminations. When these parts are deprived of their usual
motions by deficiency of sensorial power, as above explained, they become
painful according to law the fifth in Section IV. and the less pain
originally excited by the stimulus of concreted bile, or of a stone at
their other extremities ceases to be perceived. Afterwards, however, when
the concretions of bile, or the stone on the urinary bladder, become more
numerous or larger, the pain from their increased stimulus becomes greater
than the associated pain; and is then felt at the neck of the gall bladder
or urinary bladder; and the pain of the glans penis, or at the pit of the
stomach, ceases to be perceived.

2. Examples of the second mode, where the increased action of the primary
part of a train of sensitive association ceases, when that of the secondary
part commences, are also not unfrequent; as this is the usual manner of the
translation of inflammations from internal to external parts of the system,
such as when an inflammation of the liver or stomach is translated to the
membranes of the foot, and forms the gout; or to the skin of the face, and
forms the rosy drop; or when an inflammation of the membranes of the
kidneys is translated to the skin of the loins, and forms one kind of
herpes, called shingles; in these cases by whatever cause the original
inflammation may have been produced, as the secondary part of the train of
sensitive association is more sensible, it becomes exerted with greater
violence than the first part of it; and by both its increased pain, and the
increased motion of its fibres, so far diminishes or exhausts the sensorial
power of sensation; that the primary part of the train being less sensible
ceases both to feel pain, and to act with unnatural energy.

3. Examples of the third mode, where the primary part of a train of
sensitive association of motions may experience increased sensation, and
the secondary part increased action, are likewise not unfrequent; as it is
in this manner that most inflammations commence. Thus, after standing some
time in snow, the feet become affected with the pain of cold, and a common
coryza, or inflammation of the membrane of the nostrils, succeeds. It is
probable that the internal inflammations, as pleurisies, or hepatitis,
which are produced after the cold paroxysm of fever, originate in the same
manner from the sympathy of those parts with some others, which were
previously pained from quiescence; as happens to various parts of the
system during the cold fits of fevers. In these cases it would seem, that
the sensorial power of sensation becomes accumulated during the pain of
cold, as the torpor of the vessels occasioned by the defect of heat
contributes to the increase or accumulation of the sensorial power of
irritation, and that both these become exerted on some internal part, which
was not rendered torpid by the cold which affected the external parts, nor
by its association with them; or which sooner recovered its sensibility.
This requires further consideration.

4. An example of the fourth mode, or where the primary part of a sensitive
association of motions may have increased action, and the secondary part
increased sensation, may be taken from the pain of the shoulder, which
attends inflammation of the membranes of the liver, see Class IV. 2. 2. 9.;
in this circumstance so much sensorial power seems to be expended in the
violent actions and sensations of the inflamed membranes of the liver, that
the membranes associated with them become quiescent to their usual stimuli,
and painful in consequence.

There may be other modes in which the primary and secondary parts of the
trains of associated sensitive motions may reciprocally affect each other,
as may be seen by looking over Class IV. in the catalogue of diseases; all
which may probably be resolved into the plus and minus of sensorial power,
but we have not yet had sufficient observations made upon them with a view
to this doctrine.

III. The associated trains of our ideas may have sympathies, and their
primary and secondary parts affect each other in some manner similar to
those above described; and may thus occasion various curious phenomena not
yet adverted to, besides those explained in the Sections on Dreams,
Reveries, Vertigo, and Drunkenness; and may thus disturb the deductions of
our reasonings, as well as the streams of our imaginations; present us with
false degrees of fear, attach unfounded value to trivial circumstances;
give occasion to our early prejudices and antipathies; and thus embarrass
the happiness of our lives. A copious and curious harvest might be reaped
from this province of science, in which, however, I shall not at present
wield my sickle.

       *       *       *       *       *

SECT. XXXVI.

OF THE PERIODS OF DISEASES.

    I. _Muscles excited by volition soon cease to contract, or by
    sensation, or by irritation, owing to the exhaustion of sensorial
    power. Muscles subjected to less stimulus have their sensorial power
    accumulated. Hence the periods of some fevers. Want of irritability
    after intoxication._ II. 1. _Natural actions catenated with daily
    habits of life._ 2. _With solar periods. Periods of sleep. Of
    evacuating the bowels._ 3. _Natural actions catenated with lunar
    periods. Menstruation. Venereal orgasm of animals. Barrenness._ III.
    _Periods of diseased animal actions from stated returns of nocturnal
    cold, from solar and lunar influence. Periods of diurnal fever, hectic
    fever, quotidian, tertian, quartan fever. Periods of gout, pleurisy, of
    fevers with arterial debility, and with arterial strength, Periods of
    rhaphania, of nervous cough, hemicrania, arterial hæmorrhages,
    hæmorrhoids, hæmoptoe, epilepsy, palsy, apoplexy, madness._ IV.
    _Critical days depend on lunar periods. Lunar periods in the small
    pox._

I. If any of our muscles be made to contract violently by the power of
volition, as those of the fingers, when any one hangs by his hands on a
swing, fatigue soon ensues; and the muscles cease to act owing to the
temporary exhaustion of the spirit of animation; as soon as this is again
accumulated in the muscles, they are ready to contract again by the efforts
of volition.

Those violent muscular actions induced by pain become in the same manner
intermitted and recurrent; as in labour-pains, vomiting, tenesmus,
strangury; owing likewise to the temporary exhaustion of the spirit of
animation, as above mentioned.

When any stimulus continues long to act with unnatural violence, so as to
produce too energetic action of any of our moving organs, those motions
soon cease, though the stimulus continues to act; as in looking long on a
bright object, as on an inch-square of red silk laid on white paper in the
sunshine. See Plate I. in Sect. III. 1.

On the contrary, where less of the stimulus of volition, sensation, or
irritation, have been applied to a muscle than usual; there appears to be
an accumulation of the spirit of animation in the moving organ; by which it
is liable to act with greater energy from less quantity of stimulus, than
was previously necessary to excite it into so great action; as after having
been immersed in snow the cutaneous vessels of our hands are excited into
stronger action by the stimulus of a less degree of heat, than would
previously have produced that effect.

From hence the periods of some fever-fits may take their origin, either
simply, or by their accidental coincidence with lunar and solar periods, or
with the diurnal periods of heat and cold, to be treated of below; for
during the cold fit at the commencement of a fever, from whatever cause
that cold fit may have been induced, it follows, 1. That the spirit of
animation must become accumulated in the parts, which exert during this
cold fit less than their natural quantity of action. 2. If the cause
producing the cold fit does not increase, or becomes diminished; the parts
before benumbed or inactive become now excitable by smaller stimulus, and
are thence thrown into more violent action than is natural; that is a hot
fit succeeds the cold one. 3. By the energetic action of the system during
the hot fit, if it continues long, an exhaustion of the spirit of animation
takes place; and another cold fit is liable to succeed, from the moving
system not being excitable into action from its usual stimulus. This
inirritability of the system from a too great previous stimulus, and
consequent exhaustion of sensorial power, is the cause of the general
debility, and sickness, and head-ach, some hours after intoxication. And
hence we see one of the causes of the periods of fever-fits; which however
are frequently combined with the periods of our diurnal habits, or of heat
and cold, or of solar or lunar periods.

When besides the tendency to quiescence occasioned by the expenditure of
sensorial power during the hot fit of fever, some other cause of torpor, as
the solar or lunar periods, is necessary to the introduction of a second
cold fit; the fever becomes of the intermittent kind; that is, there is a
space of time intervenes between the end of the hot fit, and the
commencement of the next cold one. But where no exteriour cause is
necessary to the introduction of the second cold fit; no such interval of
health intervenes; but the second cold fit commences, as soon as the
sensorial power is sufficiently exhausted by the hot fit; and the fever
becomes continual.

II. 1. The following are natural animal actions, which are frequently
catenated with our daily habits of life, as well as excited by their
natural irritations. The periods of hunger and thirst become catenated with
certain portions of time, or degrees of exhaustion, or other diurnal habits
of life. And if the pain of hunger be not relieved by taking food at the
usual time, it is liable to cease till the next period of time or other
habits recur; this is not only true in respect to our general desire of
food, but the kinds of it also are governed by this periodical habit;
insomuch that beer taken to breakfast will disturb the digestion of those,
who have been accustomed to tea; and tea taken at dinner will disagree with
those, who have been accustomed to beer. Whence it happens, that those, who
have weak stomachs, will be able to digest more food, if they take their
meals at regular hours; because they have both the stimulus of the aliment
they take, and the periodical habit, to assist their digestion.

The periods of emptying the bladder are not only dependent on the acrimony
or distention of the water in it, but are frequently catenated with
external cold applied to the skin, as in cold bathing, or washing the
hands; or with other habits of life, as many are accustomed to empty the
bladder before going to bed, or into the house after a journey, and this
whether it be full or not.

Our times of respiration are not only governed by the stimulus of the blood
in the lungs, or our desire of fresh air, but also by our attention to the
hourly objects before us. Hence when a person is earnestly contemplating an
idea of grief, he forgets to breathe, till the sensation in his lungs
becomes very urgent; and then a sigh succeeds for the purpose of more
forceably pushing forwards the blood, which is accumulated in the lungs.

Our times of respiration are also frequently governed in part by our want
of a steady support for the actions of our arms, and hands, as in threading
a needle, or hewing wood, or in swimming; when we are intent upon these
objects, we breathe at the intervals of the exertion of the pectoral
muscles.

2. The following natural animal actions are influenced by solar periods.
The periods of sleep and of waking depend much on the solar period, for we
are inclined to sleep at a certain hour, and to awake at a certain hour,
whether we have had more or less fatigue during the day, if within certain
limits; and are liable to wake at a certain hour, whether we went to bed
earlier or later, within certain limits. Hence it appears, that those who
complain of want of sleep, will be liable to sleep better or longer, if
they accustom themselves to go to rest, and to rise, at certain hours.

The periods of evacuating the bowels are generally connected with some part
of the solar day, as well as with the acrimony or distention occasioned by
the feces. Hence one method of correcting costiveness is by endeavouring to
establish a habit of evacuation at a certain hour of the day, as
recommended by Mr. Locke, which may be accomplished by using daily
voluntary efforts at those times, joined with the usual stimulus of the
material to be evacuated.

3. The following natural animal actions are connected with lunar periods.
1. The periods of female menstruation are connected with lunar periods to
great exactness, in some instances even to a few hours. These do not
commence or terminate at the full or change, or at any other particular
part of the lunation, but after they have commenced at any part of it, they
continue to recur at that part with great regularity, unless disturbed by
some violent circumstance, as explained in Sect. XXXII. No. 6. their return
is immediately caused by deficient venous absorption, which is owing to the
want of the stimulus, designed by nature, of amatorial copulation, or of
the growing fetus. When the catamenia returns sooner than the period of
lunation, it shows a tendency of the constitution to inirritability; that
is to debility, or deficiency of sensorial power, and is to be relieved by
small doses of steel and opium.

The venereal orgasm of birds and quadrupeds seems to commence, or return
about the most powerful lunations at the vernal or autumnal equinoxes; but
if it be disappointed of its object, it is said to recur at monthly
periods; in this respect resembling the female catamenia. Whence it is
believed, that women are more liable to become pregnant at or about the
time of their catamenia, than at the intermediate times; and on this
account they are seldom much mistaken in their reckoning of nine lunar
periods from the last menstruation; the inattention to this may sometimes
have been the cause of supposed barrenness, and is therefore worth the
observation of those, who wish to have children.

III. We now come to the periods of diseased animal actions. The periods of
fever-fits, which depend on the stated returns of nocturnal cold, are
discussed in Sect. XXXII. 3. Those, which originate or recur at solar or
lunar periods, are also explained in Section XXXII. 6. These we shall here
enumerate; observing, however, that it is not more surprising, that the
influence of the varying attractions of the sun and moon, should raise the
ocean into mountains, than that it should affect the nice sensibilities of
animal bodies; though the manner of its operation on them is difficult to
be understood. It is probable however, that as this influence gradually
lessens during the course of the day, or of the lunation, or of the year,
some actions of our system become less and less; till at length a total
quiescence of some part is induced; which is the commencement of the
paroxysms of fever, of menstruation, of pain with decreased action of the
affected organ, and of consequent convulsion.

1. A diurnal fever in some weak people is distinctly observed to come on
towards evening, and to cease with a moist skin early in the morning,
obeying the solar periods. Persons of weak constitutions are liable to get
into better spirits at the access of the hot fit of this evening fever; and
are thence inclined to sit up late; which by further enfeebling them
increases the disease; whence they lose their strength and their colour.

2. The periods of hectic fever, supposed to arise from absorption of
matter, obeys the diurnal periods like the above, having the exacerbescence
towards evening, and its remission early in the morning, with sweats, or
diarrhoea, or urine with white sediment.

3. The periods of quotidian fever are either catenated with solar time, and
return at the intervals of twenty-four hours; or with lunar time, recurring
at the intervals of about twenty-five hours. There is great use in knowing
with what circumstances the periodical return or new morbid motions are
conjoined, as the most effectual times of exhibiting the proper medicines
are thus determined. So if the torpor, which ushers in an ague fit, is
catenated with the lunar day: it is known, when the bark or opium must be
given, so as to exert its principal effect about the time of the expected
return. Solid opium should be given about an hour before the expected cold
fit; liquid opium and wine about half an hour; the bark repeatedly for six
or eight hours previous to the expected return.

4. The periods of tertian fevers, reckoned from the commencement of one
cold fit to the commencement of the next cold fit, recur with solar
intervals of forty-eight hours, or with lunar ones of about fifty hours.
When these of recurrence begin one or two hours earlier than the solar
period, it shews, that the torpor or cold fit is produced by less external
influence; and therefore that it is more liable to degenerate into a fever
with only remissions; so when menstruation recurs sooner than the period of
lunation, it shews a tendency of the habit to torpor of inirritability.

5. The periods of quartan fevers return at solar intervals of seventy-two
hours, or at lunar ones of about seventy-four hours and an half. This kind
of ague appears most in moist cold autumns, and in cold countries replete
with marshes. It is attended with greater debility, and its cold access
more difficult to prevent. For where there is previously a deficiency of
sensorial power, the constitution is liable to run into greater torpor from
any further diminution of it; two ounces of bark and some steel should be
given on the day before the return of the cold paroxysm, and a pint of wine
by degrees a few hours before its return, and thirty drops of laudanum one
hour before the expected cold fit.

6. The periods of the gout generally commence about an hour before
sun-rise, which is usually the coldest part of the twenty-four hours. The
greater periods of the gout seem also to observe the solar influence,
returning about the same season of the year.

7. The periods of the pleurisy recur with exacerbation of the pain and
fever about sun-set, at which time venesection is of most service. The same
may be observed of the inflammatory rheumatism, and other fevers with
arterial strength, which seem to obey solar periods; and those with
debility seem to obey lunar ones.

8. The periods of fevers with arterial debility seem to obey the lunar day,
having their access daily nearly an hour later; and have sometimes two
accesses in a day, resembling the lunar effects upon the tides.

9. The periods of rhaphania, or convulsions of the limbs from rheumatic
pains, seem to be connected with solar influence, returning at nearly the
same hour for weeks together, unless disturbed by the exhibition of
powerful doses of opium.

So the periods of Tussis ferina, or violent cough with slow pulse, called
nervous cough, recurs by solar periods. Five grains of opium, given at the
time the cough commenced disturbed the period, from seven in the evening to
eleven, at which time it regularly returned for some days, during which
time the opium was gradually omitted. Then 120 drops of laudanum were given
an hour before the access of the cough, and it totally ceased. The laudanum
was continued a fortnight, and then gradually discontinued.

10. The periods of hemicrania, and of painful epilepsy, are liable to obey
lunar periods, both in their diurnal returns, and in their greater periods
of weeks, but are also induced by other exciting causes.

11. The periods of arterial hæmorrhages seem to return at solar periods
about the same hour of the evening or morning. Perhaps the venous
hæmorrhages obey the lunar periods, as the catamenia, and hæmorrhoids.

12. The periods of the hæmorrhoids, or piles, in some recur monthly, in
others only at the greater lunar influence about the equinoxes.

13. The periods of hæmoptoe sometimes obey solar influence, recurring early
in the morning for several days; and sometimes lunar periods, recurring
monthly; and sometimes depend on our hours of sleep. See Class I. 2. 1. 9.

14. Many of the first periods of epileptic fits obey the monthly lunation
with some degree of accuracy; others recur only at the most powerful
lunations before the vernal equinox, and after the autumnal one; but when
the constitution has gained a habit of relieving disagreeable sensations by
this kind of exertion, the fit recurs from any slight cause.

15. The attack of palsy and apoplexy are known to recur with great
frequency about the equinoxes.

16. There are numerous instances of the effect of the lunations upon the
periods of insanity, whence the name of lunatic has been given to those
afflicted with this disease.

IV. The critical days, in which fevers are supposed to terminate, have
employed the attention of medical philosophers from the days of Hippocrates
to the present time. In whatever part of a lunation a fever commences,
which owes either its whole cause to solar and lunar influence, or to this
in conjunction with other causes; it would seem, that the effect would be
the greatest at the full and new moon, as the tides rise highest at those
times, and would be the least at the quadratures; thus if a fever-fit
should commence at the new or full moon, occasioned by the solar and lunar
attraction diminishing some chemical affinity of the particles of blood,
and thence decreasing their stimulus on our sanguiferous system, as
mentioned in Sect. XXXII. 6. this effect will daily decrease for the first
seven days, and will then increase till about the fourteenth day, and will
again decrease till about the twenty-first day, and increase again till the
end of the lunation. If a fever-fit from the above cause should commence on
the seventh day after either lunation, the reverse of the above
circumstances would happen. Now it is probable, that those fevers, whose
crisis or terminations are influenced by lunations, may begin at one or
other of the above times, namely at the changes or quadratures; though
sufficient observations have not been made to ascertain this circumstance.
Hence I conclude, that the small-pox and measles have their critical days,
not governed by the times required for certain chemical changes in the
blood, which affect or alter the stimulus of the contagious matter, but
from the daily increasing or decreasing effect of this lunar link of
catenation, as explained in Section XVII. 3. 3. And as other fevers
terminate most frequently about the seventh, fourteenth, twenty-first, or
about the end of four weeks, when no medical assistance has disturbed their
periods, I conclude, that these crises, or terminations, are governed by
periods of the lunations; though we are still ignorant of their manner of
operation.

In the distinct small-pox the vestiges of lunation are very apparent, after
inoculation a quarter of a lunation precedes the commencement of the fever,
another quarter terminates with the complete eruption, another quarter with
the complete maturation, and another quarter terminates the complete
absorption of a material now rendered inoffensive to the constitution.

       *       *       *       *       *

SECT. XXXVII.

OF DIGESTION, SECRETION, NUTRITION.

    I. _Crystals increase by the greater attraction of their sides.
    Accretion by chemical precipitations, by welding, by pressure, by
    agglutination._ II. _Hunger, digestion, why it cannot be imitated out
    of the body. Lacteals absorb by animal selection or appetency._ III.
    _The glands and pores absorb nutritious particles by animal selection.
    Organic particles of Buffon. Nutrition applied at the time of
    elongation of fibres. Like inflammation._ IV. _It seems easier to have
    preserved animals than to reproduce them. Old age and death from
    inirritability. Three causes of this. Original fibres of the organs of
    sense and muscles unchanged._ V. _Art of producing long life._

I. The larger crystals of saline bodies may be conceived to arise from the
combination of smaller crystals of the same form, owing to the greater
attractions of their sides than of their angles. Thus if four cubes were
floating in a fluid, whose friction or resistance is nothing, it is certain
the sides of these cubes would attract each other stronger than their
angles; and hence that these four smaller cubes would so arrange themselves
as to produce one larger one.

There are other means of chemical accretion, such as the depositions of
dissolved calcareous or siliceous particles, as are seen in the formation
of the stalactites of limestone in Derbyshire, or of calcedone in Cornwall.
Other means of adhesion are produced by heat and pressure, as in the
welding of iron-bars; and other means by simple pressure, as in forcing two
pieces of caoutchou, or elastic gum, to adhere; and lastly, by the
agglutination of a third substance penetrating the pores of the other two,
as in the agglutination of wood by means of animal gluten. Though the
ultimate particles of animal bodies are held together during life, as well
as after death, by their specific attraction of cohesion, like all other
matter; yet it does not appear, that their original organization was
produced by chemical laws, and their production and increase must therefore
only be looked for from the laws of animation.

II. When the pain of hunger requires relief, certain parts of the material
world, which surround us, when applied to our palates, excite into action
the muscles of deglutition; and the material is swallowed into the stomach.
Here the new aliment becomes mixed with certain animal fluids, and
undergoes a chemical process, termed digestion; which however chemistry has
not yet learnt to imitate out of the bodies of living animals or
vegetables. This process seems very similar to the saccharine process in
the lobes of farinaceous seeds, as of barley, when it begins to germinate;
except that, along with the sugar, oil and mucilage are also produced;
which form the chyle of animals, which is very similar to their milk.

The reason, I imagine, why this chyle-making, or saccharine process, has
not yet been imitated by chemical operations, is owing to the materials
being in such a situation in respect to warmth, moisture, and motion; that
they will immediately change into the vinous or acetous fermentation;
except the new sugar be absorbed by the numerous lacteal or lymphatic
vessels, as soon as it is produced; which is not easy to imitate in the
laboratory.

These lacteal vessels have mouths, which are irritated into action by the
stimulus of the fluid, which surrounds them; and by animal selection, or
appetency, they absorb such part of the fluid as is agreeable to their
palate; those parts, for instance, which are already converted into chyle,
before they have time to undergo another change by a vinous or acetous
fermentation. This animal absorption of fluid is almost visible to the
naked eye in the action of the puncta lacrymalia; which imbibe the tears
from the eye, and discharge them again into the nostrils.

III. The arteries constitute another reservoir of a changeful fluid; from
which, after its recent oxygenation in the lungs, a further animal
selection of various fluids is absorbed by the numerous glands; these
select their respective fluids from the blood, which is perpetually
undergoing a chemical change; but the selection by these glands, like that
of the lacteals, which open their mouths into the digesting aliment in the
stomach, is from animal appetency, not from chemical affinity; secretion
cannot therefore be imitated in the laboratory, as it consists in a
selection of part of a fluid during the chemical change of that fluid.

The mouths of the lacteals, and lymphatics, and the ultimate terminations
of the glands, are finer than can easily be conceived; yet it is probable,
that the pores, or interstices of the parts, or coats, which constitute
these ultimate vessels, may still have greater tenuity; and that these
pores from the above analogy must posses a similar power of irritability,
and absorb by their living energy the particles of fluid adapted to their
purposes, whether to replace the parts abraded or dissolved, or to elongate
and enlarge themselves. Not only every kind of gland is thus endued with
its peculiar appetency, and selects the material agreeable to its taste
from the blood, but every individual pore acquires by animal selection the
material, which it wants; and thus nutrition seems to be performed in a
manner so similar to secretion; that they only differ in the one retaining,
and the other parting again with the particles, which they have selected
from the blood.

This way of accounting for nutrition from stimulus, and the consequent
animal selection of particles, is much more analogous to other phenomena of
the animal microcosm, than by having recourse to the microscopic
animalcula, or organic particles of Buffon, and Needham; which being
already compounded must themselves require nutritive particles to continue
their own existence. And must be liable to undergo a change by our
digestive or secretory organs; otherwise mankind would soon resemble by
their theory the animals, which they feed upon. He, who is nourished by
beef or venison, would in time become horned; and he, who feeds on pork or
bacon, would gain a nose proper for rooting into the earth, as well as for
the perception of odours.

The whole animal system may be considered as consisting of the extremities
of the nerves, or of having been produced from them; if we except perhaps
the medullary part of the brain residing in the head and spine, and in the
trunks of the nerves. These extremities of the nerves are either of those
of locomotion, which are termed muscular fibres; or of those of sensation,
which constitute the immediate organs of sense, and which have also their
peculiar motions. Now as the fibres, which constitute the bones and
membranes, possessed originally sensation and motion; and are liable again
to possess them, when they become inflamed; it follows, that those were,
when first formed, appendages to the nerves of sensation or locomotion, or
were formed from them. And that hence all these solid parts of the body, as
they have originally consisted of extremities of nerves, require an
apposition of nutritive particles of a similar kind, contrary to the
opinion of Buffon and Needham above recited.

Lastly, as all these filaments have possessed, or do possess, the power of
contraction, and of consequent inertion or elongation; it seems probable,
that the nutritive particles are applied during their times of elongation;
when their original constituent particles are removed to a greater distance
from each other. For each muscular or sensual fibre may be considered as a
row or string of beads; which approach, when in contraction, and recede
during its rest or elongation; and our daily experience shews us, that
great action emaciates the system, and that it is repaired during rest.

Something like this is seen out of the body; for if a hair, or a single
untwisted fibre of flax or silk, be soaked in water; it becomes longer and
thicker by the water, which is absorbed into its pores. Now if a hair could
be supposed to be thus immersed in a solution of particles similar to
those, which compose it; one may imagine, that it might be thus increased
in weight and magnitude; as the particles of oak-bark increase the
substance of the hides of beasts in the process of making leather. I
mention these not as philosophic analogies, but as similes to facilitate
our ideas, how an accretion of parts may be effected by animal appetences,
or selections, in a manner somewhat similar to mechanical or chemical
attractions.

If those new particles of matter, previously prepared by digestion and
sanguification, only supply the places of those, which have been abraded by
the actions of the system, it is properly termed nutrition. If they are
applied to the extremities of the nervous fibrils, or in such quantity as
to increase the length or crassitude of them, the body becomes at the same
time enlarged, and its growth is increased, as well as its deficiences
repaired.

In this last case something more than a simple apposition or selection of
particles seems to be necessary; as many parts of the system during its
growth are caused to recede from those, with which they were before in
contact; as the ends of the bones, or cartilages, recede from each other,
as their growth advances: this process resembles inflammation, as appears
in ophthalmy, or in the production of new flesh in ulcers, where old
vessels are enlarged, and new ones produced; and like that is attended with
sensation. In this situation the vessels become distended with blood, and
acquire greater sensibility, and may thus be compared to the erection of
the penis, or of the nipples of the breasts of women; while new particles
become added at the same time; as in the process of nutrition above
described.

When only the natural growth of the various parts of the body are produced,
a pleasurable sensation attends it, as in youth, and perhaps in those, who
are in the progress of becoming fat. When an unnatural growth is the
consequence, as in inflammatory diseases, a painful sensation attends the
enlargement of the system.

IV. This apposition of new parts, as the old ones disappear, selected from
the aliment we take, first enlarges and strengthens our bodies for twenty
years, for another twenty years it keeps us in health and vigour, and adds
strength and solidity to the system; and then gradually ceases to nourish
us properly, and for another twenty years we gradually sink into decay, and
finally cease to act, and to exist.

On considering this subject one should have imagined at first view, that it
might have been easier for nature to have supported her progeny for ever in
health and life, than to have perpetually reproduced them by the wonderful
and mysterious process of generation. But it seems our bodies by long habit
cease to obey the stimulus of the aliment, which should support us. After
we have acquired our height and solidity we make no more new parts, and the
system obeys the irritations, sensations, volitions; and associations,
with, less and less energy, till the whole sinks into inaction.

Three causes may conspire to render our nerves less excitable, which have
been already mentioned, 1. If a stimulus be greater than natural, it
produces too great an exertion of the stimulated organ, and in consequence
exhausts the spirit of animation; and the moving organ ceases to act, even
though the stimulus be continued. And though rest will recruit this
exhaustion, yet some degree of permanent injury remains, as is evident
after exposing the eyes long to too strong a light. 2. If excitations
weaker than natural be applied, so as not to excite the organ into action,
(as when small doses of aloe or rhubarb are exhibited,) they may be
gradually increased, without exciting the organ into action; which will
thus acquire a habit of disobedience to the stimulus; thus by increasing
the dose by degrees, great quantities of opium or wine may be taken without
intoxication. See Sect. XII. 3. 1.

3. Another mode, by which life is gradually undermined, is when irritative
motions continue to be produced in consequence of stimulus, but are not
succeeded by sensation; hence the stimulus of contagious matter is not
capable of producing fever a second time, because it is not succeeded by
sensation. See Sect. XII. 3. 6. And hence, owing to the want of the general
pleasurable sensation, which ought to attend digestion and glandular
secretion, an irksomeness of life ensues; and, where this is in greater
excess, the melancholy of old age occurs, with torpor or debility.

From hence I conclude, that it is probable that the fibrillæ, or moving
filaments at the extremities of the nerves of sense, and the fibres which
constitute the muscles (which are perhaps the only parts of the system that
are endued with contractile life) are not changed, as we advance in years,
like the other parts of the body; but only enlarged or elongated with our
growth; and in consequence they become less and less excitable into action.
Whence, instead of gradually changing the old animal, the generation of a
totally new one becomes necessary with undiminished excitability; which
many years will continue to acquire new parts, or new solidity, and then
losing its excitability in time, perish like its parent.

V. From this idea the art of preserving long health and life may be
deduced; which must consist in using no greater stimulus, whether of the
quantity or kind of our food and drink, or of external circumstances, such
as heat, and exercise, and wakefulness, than is sufficient to preserve us
in vigour; and gradually, as we grow old to increase the stimulus of our
aliment, as the irritability of our system increases.

The debilitating effects ascribed by the poet MARTIAL to the excessive use
of warm bathing in Italy, may with equal propriety be applied to the warm
rooms of England; which, with the general excessive stimulus of spirituous
or fermented liquors, and in some instances of immoderate venery,
contribute to shorten our lives.

  _Balnea, vina, venus, corrumpunt corpora nostra_,
  _At faciunt vitam balnea, vina, venus!_

  Wine, women, warmth, against our lives combine;
  But what is life without warmth, women, wine!

       *       *       *       *       *

SECT. XXXVIII.

OF THE OXYGENATION OF THE BLOOD IN THE LUNGS, AND IN THE PLACENTA.

    I. _Blood absorbs oxygene from the air, whence phosphoric acid changes
    its colour, gives out heat, and some phlogistic material, and acquires
    an ethereal spirit, which is dissipated in fibrous motion._ II. _The
    placenta is a pulmonary organ like the gills of fish. Oxygenation of
    the blood from air, from water, by lungs, by gills, by the placenta;
    necessity of this oxygenation to quadrupeds, to fish, to the foetus in
    utero. Placental vessels inserted into the arteries of the mother. Use
    of cotyledons in cows. Why quadrupeds have not sanguiferous lochia.
    Oxygenation of the chick in the egg, of feeds._ III. _The liquor amnii
    is not excrementitious. It is nutritious. It is found in the esophagus
    and stomach, and forms the meconium. Monstrous births without heads.
    Question of Dr. Harvey._

I. From the recent discoveries of many ingenious philosophers it appears,
that during respiration the blood imbibes the vital part of the air, called
oxygene, through the membranes of the lungs; and that hence respiration may
be aptly compared to a slow combustion. As in combustion the oxygene of the
atmosphere unites with some phlogistic or inflammable body, and forms an
acid (as in the production of vitriolic acid from sulphur, or carbonic acid
from charcoal,) giving out at the same time a quantity of the matter of
heat; so in respiration the oxygene of the air unites with the phlogistic
part of the blood, and probably produces phosphoric or animal acid,
changing the colour of the blood from a dark to a bright red; and probably
some of the matter of heat is at the same time given out according to the
theory of Dr. Crawford. But as the evolution of heat attends almost all
chemical combinations, it is probable, that it also attends the secretions
of the various fluids from the blood; and that the constant combinations or
productions of new fluids by means of the glands constitute the more
general source of animal heat; this seems evinced by the universal
evolution of the matter of heat in the blush of shame or of anger; in which
at the same time an increased secretion of the perspirable matter occurs;
and the partial evolution of it from topical inflammations, as in gout or
rheumatism, in which there is a secretion of new blood-vessels.

Some medical philosophers have ascribed the heat of animal bodies to the
friction of the particles of the blood against the sides of the vessels.
But no perceptible heat has ever been produced by the agitation of water,
or oil, or quicksilver, or other fluids; except those fluids have undergone
at the same time some chemical change, as in agitating milk or wine, till
they become sour.

Besides the supposed production of phosphoric acid, and change of colour of
the blood, and the production of carbonic acid, there would appear to be
something of a more subtile nature perpetually acquired from the
atmosphere; which is too fine to be long contained in animal vessels, and
therefore requires perpetual renovation; and without which life cannot
continue longer than a minute or two; this ethereal fluid is probably
secreted from the blood by the brain, and perpetually dissipated in the
actions of the muscles and organs of sense.

That the blood acquires something from the air, which is immediately
necessary to life, appears from an experiment of Dr. Hare (Philos.
Transact. abridged, Vol. III. p. 239.) who found, "that birds, mice, &c.
would live as long again in a vessel, where he had crowded in double the
quantity of air by a condensing engine, than they did when confined in air
of the common density." Whereas if some kind of deleterious vapour only was
exhaled from the blood in respiration; the air, when condensed into half
its compass, could not be supposed to receive so much of it.

II. Sir Edward Hulse, a physician of reputation at the beginning of the
present century, was of opinion, that the placenta was a respiratory organ,
like the gills of fish; and not an organ to supply nutriment to the foetus;
as mentioned in Derham's Physico-theology. Many other physicians seem to
have espoused the same opinion, as noticed by Haller. Elem. Physiologiæ, T.
1. Dr. Gipson published a defence of this theory in the Medical Essays of
Edinburgh, Vol. I. and II. which doctrine is there controverted at large by
the late Alexander Monro; and since that time the general opinion has been,
that the placenta is an organ of nutrition only, owing perhaps rather to
the authority of so great a name, than to the validity of the arguments
adduced in its support. The subject has lately been resumed by Dr. James
Jeffray, and by Dr. Forester French, in their inaugural dissertations at
Edinburgh and at Cambridge; who have defended the contrary opinion in an
able and ingenious manner; and from whose Theses I have extracted many of
the following remarks.

First, by the late discoveries of Dr. Priestley, M. Lavoisier, and other
philosophers, it appears, that the basis of atmospherical air, called
oxygene, is received by the blood through the membranes of the lungs; and
that by this addition the colour of the blood is changed from a dark to a
light red. Secondly, that water possesses oxygene also as a part of its
composition, and contains air likewise in its pores; whence the blood of
fish receives oxygene from the water, or from the air it contains, by means
of their gills, in the same manner as the blood is oxygenated in the lungs
of air-breathing animals; it changes its colour at the same time from a
dark to a light red in the vessels of their gills, which constitute a
pulmonary organ adapted to the medium in which they live. Thirdly, that the
placenta consists of arteries carrying the blood to its extremities, and a
vein bringing it back, resembling exactly in structure the lungs and gills
above mentioned; and that the blood changes its colour from a dark to a
light red in passing through these vessels.

This analogy between the lungs and gills of animals, and the placenta of
the fetus, extends through a great variety of other circumstances; thus
air-breathing creatures and fish can live but a few minutes without air or
water; or when they are confined in such air or water, as has been spoiled
by their own respiration; the same happens to the fetus, which, as soon as
the placenta is separated from the uterus, must either expand its lungs,
and receive air, or die. Hence from the structure, as well as the use of
the placenta, it appears to be a respiratory organ, like the gills of fish,
by which the blood in the fetus becomes oxygenated.

From the terminations of the placental vessels not being observed to bleed
after being torn from the uterus, while those of the uterus effuse a great
quantity of florid arterial blood, the terminations of the placental
vessels would seem to be inserted into the arterial ones of the mother; and
to receive oxygenation from the passing currents of her blood through their
coats or membranes; which oxygenation is proved by the change of the colour
of the blood from dark to light red in its passage from the placental
arteries to the placental vein.

The curious structure of the cavities or lacunæ of the placenta,
demonstrated by Mr. J. Hunter, explain this circumstance. That ingenious
philosopher has shewn, that there are numerous cavities of lacunæ formed on
that side of the placenta, which is in contact with the uterus; those
cavities or cells are filled with blood from the maternal arteries, which
open into them; which blood is again taken up by the maternal veins, and is
thus perpetually changed. While the terminations of the placental arteries
and veins are spread in fine reticulation on the sides of these cells. And
thus, as the growing fetus requires greater oxygenation, an apparatus is
produced resembling exactly the air-cells of the lungs.

In cows, and other ruminating animals, the internal surface of the uterus
is unequal like hollow cups, which have been called cotyledons; and into
these cavities the prominencies of the numerous placentas, with which the
fetus of those animals is furnished, are inserted, and strictly adhere;
though they may be extracted without effusion of blood. These inequalities
of the uterus, and the numerous placentas in consequence, seem to be
designed for the purpose of expanding a greater surface for the
terminations of the placental vessels for the purpose of receiving
oxygenation from the uterine ones; as the progeny of this class of animals
are more completely formed before their nativity, than that of the
carnivorous classes, and must thence in the latter weeks of pregnancy
require greater oxygenation. Thus calves and lambs can walk about in a few
minutes after their birth; while puppies and kittens remain many days
without opening their eyes. And though on the separation of the cotyledons
of ruminating animals no blood is effused, yet this is owing clearly to the
greater power of contraction of their uterine lacunæ or alveoli. See
Medical Essays, Vol. V. page 144. And from the same cause they are not
liable to a sanguiferous menstruation.

The necessity of the oxygenation of the blood in the fetus is farther
illustrated by the analogy of the chick in the egg; which appears to have
its blood oxygenated at the extremities of the vessels surrounding the
yolk; which are spread on the air-bag at the broad end of the egg, and may
absorb oxygene through that moist membrane from the air confined behind it;
and which is shewn by experiments in the exhausted receiver to be
changeable though the shell.

This analogy may even be extended to the growing seeds of vegetables; which
were shewn by Mr. Scheele to require a renovation of the air over the
water, in which they were confined. Many vegetable seeds are surrounded
with air in their pods or receptacles, as peas, the fruit of staphylea, and
lichnis vesicaria; but it is probable, that those seeds, after they are
shed, as well as the spawn of fish, by the situation of the former on or
near the moist and aerated surface of the earth, and of the latter in the
ever-changing and ventilated water, may not be in need of an apparatus for
the oxygenation of their first blood, before the leaves of one, and the
gills of the other, are produced for this purpose.

III. 1. There are many arguments, besides the strict analogy between the
liquor amnii and the albumen ovi, which shew the former to be a nutritive
fluid; and that the fetus in the latter months of pregnancy takes it into
its stomach; and that in consequence the placenta is produced for some
other important purpose.

First, that the liquor amnii is not an excrementitious fluid is evinced,
because it is found in greater quantity, when the fetus is young,
decreasing after a certain period till birth. Haller asserts, "that in some
animals but a small quantity of this fluid remains at the birth. In the
eggs of hens it is consumed on the eighteenth day, so that at the exclusion
of the chick scarcely any remains. In rabbits before birth there is none."
Elem. Physiol. Had this been an excrementitious fluid, the contrary would
probably have occurred. Secondly, the skin of the fetus is covered with a
whitish crust or pellicle, which would seem to preclude any idea of the
liquor amnii being produced by any exsudation of perspirable matter. And it
cannot consist of urine, because in brute animals the urachus passes from
the bladder to the alantois for the express purpose of carrying off that
fluid; which however in the human fetus seems to be retained in the
distended bladder, as the feces are accumulated in the bowels of all
animals.

2. The nutritious quality of the liquid, which surrounds the fetus, appears
from the following considerations. 1. It is coagulable by heat, by nitrous
acid, and by spirit of wine, like milk, serum of blood, and other fluids,
which daily experience evinces to be nutritious. 2. It has a saltish taste
according to the accurate Baron Haller, not unlike the whey of milk, which
it even resembles in smell. 3. The white of the egg which constitutes the
food of the chick, is shewn to be nutritious by our daily experience;
besides the experiment of its nutritious effects mentioned by Dr. Fordyce
in his late Treatise on Digestion, p. 178; who adds, that it much resembles
the essential parts of the serum of blood.

3. A fluid similar to the fluid, with which the fetus is surrounded, except
what little change may be produced by a beginning digestion, is found in
the stomach of the fetus; and the white of the egg is found, in the same
manner in the stomach of the chick.

Numerous hairs, similar to those of its skin, are perpetually found among
the contents of the stomach in new-born calves; which must therefore have
licked themselves before their nativity. Blasii Anatom. See Sect. XVI. 2.
on Instinct.

The chick in the egg is seen gently to move in its surrounding fluid, and
to open and shut its mouth alternately. The same has been observed in
puppies. Haller's El. Phys. I. 8. p. 201.

A column of ice has been seen to reach down the oesophagus from the mouth
to the stomach in a frozen fetus; and this ice was the liquor amnii frozen.

The meconium, or first fæces, in the bowels of new-born infants evince,
that something has been digested; and what could this be but the liquor
amnii together with the recrements of the gastric juice and gall, which
were necessary for its digestion?

There have been recorded some monstrous births of animals without heads,
and consequently without mouths, which seem to have been delivered on
doubtful authority, or from inaccurate observation. There are two of such
monstrous productions however better attested; one of a human fetus,
mentioned by Gipson in the Scots Medical Essays; which having the gula
impervious was furnished with an aperture into the wind-pipe, which
communicated below into the gullet; by means of which the liquor amnii
might be taken into the stomach before nativity without danger of
suffocation, while the fetus had no occasion to breathe. The other
monstrous fetus is described by Vander Wiel, who asserts, that he saw a
monstrous lamb, which had no mouth; but instead of it was furnished with an
opening in the lower part of the neck into the stomach. Both these
instances evidently favour the doctrine of the fetus being nourished by the
mouth; as otherwise there had been no necessity for new or unnatural
apertures into the stomach, when the natural ones were deficient?

From these facts and observations we may safely infer, that the fetus in
the womb is nourished by the fluid which surrounds it; which during the
first period of gestation is absorbed by the naked lacteals; and is
afterwards swallowed into the stomach and bowels, when these organs are
perfected; and lastly that the placenta is an organ for the purpose of
giving due oxygenation to the blood of the fetus; which is more necessary,
or at least more frequently necessary, than even the supply of food.

The question of the great Harvey becomes thus easily answered. "Why is not
the fetus in the womb suffocated for want of air, when it remains there
even to the tenth month without respiration: yet if it be born in the
seventh or eighth month, and has once respired, it becomes immediately
suffocated for want of air, if its respiration be obstructed?"

For further information on this subject, the reader is referred to the
Tentamen Medicum of Dr. Jeffray, printed at Edinburgh in 1786. And it is
hoped that Dr. French will some time give his theses on this subject to the
public.

       *       *       *       *       *

SECT. XXXIX.

OF GENERATION.

  Felix, qui causas altà caligine mersas
  Pandit, et evolvit tenuissima vincula rerum.

    I. _Habits of acting and feeling of individuals attend the soul into a
    future life, and attend the new embryon at the time of its production.
    The new speck of entity absorbs nutriment, and receives oxygene.
    Spreads the terminations of its vessels on cells, which communicate
    with the arteries of the uterus; sometimes with those of the
    peritoneum. Afterwards it swallows the liquor amnii, which it produces
    by its irritation from the uterus, or peritoneum. Like insects in the
    heads of calves and sheep. Why the white of egg is of two
    consistencies. Why nothing is found in quadrupeds similar to the yolk,
    nor in most vegetable seeds._ II. 1. _Eggs of frogs and fish
    impregnated out of their bodies. Eggs of fowls which are not
    fecundated, contain only the nutriment for the embryon. The embryon is
    produced by the male, and the nutriment by the female. Animalcula in
    semine. Profusion of nature's births._ 2. _Vegetables viviparous. Buds
    and bulbs have each a father but no mother. Vessels of the leaf and bud
    inosculate. The paternal offspring exactly resembles the parent._ 3.
    _Insects impregnated for six generations. Polypus branches like buds.
    Creeping roots. Viviparous flowers. Tænia, volvox. Eve from Adam's rib.
    Semen not a stimulus to the egg._ III. 1. _Embryons not originally
    created within other embryons. Organized matter is not so minute._ 2.
    _All the parts of the embryon are not formed in the male parent. Crabs
    produce their legs, worms produce their heads and tails. In wens,
    cancers, and inflammations, new vessels are formed. Mules partake of
    the forms of both parents. Hair and nails grow by elongation, not by
    distention._ 3. _Organic particles of Buffon._ IV. 1. _Rudiment of the
    embryon a simple living filament, becomes a living ring, and then a
    living tube._ 2. _It acquires irritabilities, and sensibilities with
    new organizations, as in wounded snails, polypi, moths, gnats,
    tadpoles. Hence new parts are acquired by addition not by distention._
    3. _All parts of the body grow if not confined._ 4. _Fetuses deficient
    at their extremities, or have a duplicature of parts. Monstrous births.
    Double parts of vegetables._ 5. _Mules cannot be formed by distention
    of the seminal ens._ 6. _Families of animals from a mixture of their
    orders. Mules imperfect._ 7. _Animal appetency like chemical affinity.
    Vis fabricatrix and medicatrix of nature._ 8. _The changes of animals
    before and after nativity. Similarity of their structure. Changes in
    them from lust, hunger, and danger. All warm-blooded animals derived
    from one living filament. Cold-blooded animals, insects, worms,
    vegetables, derived also from one living filament. Male animals have
    teats. Male pigeon gives milk. The world itself generated. The cause of
    causes. A state of probation and responsibility._ V. 1. _Efficient
    cause of the colours of birds eggs, and of hair and feathers, which
    become white in snowy countries. Imagination of the female colours the
    egg. Ideas or motions of the retina imitated by the extremities of the
    nerves of touch, or rete mucosum._ 2. _Nutriment supplied by the female
    of three kinds. Her imagination can only affect the first kind. Mules
    how produced, and mulattoes. Organs of reproduction why deficient in
    mules. Eggs with double yolks._ VI. 1. _Various secretions produced by
    the extremities of the vessels, as in the glands. Contagious matter.
    Many glands affected by pleasurable ideas, as those which secrete the
    semen._ 2. _Snails and worms are hermaphrodite, yet cannot impregnate
    themselves. Final cause of this._ 3. _The imagination of the male forms
    the sex. Ideas, or motions of the nerves of vision or of touch, are
    imitated by the ultimate extremities of the glands of the testes, which
    mark the sex. This effect of the imagination belongs only to the male.
    The sex of the embryon is not owing to accident._ 4. _Causes of the
    changes in animals from imagination as in monsters. From the male. From
    the female._ 5. _Miscarriages from fear._ 6. _Power of the imagination
    of the male over the colour, form, and sex of the progeny. An instance
    of._ 7. _Act of generation accompanied with ideas of the male or female
    form. Art of begetting beautiful children of either sex._ VII.
    _Recapitulation._ VIII. _Conclusion. Of cause and effect. The atomic
    philosophy leads to a first cause._

I. The ingenious Dr. Hartley in his work on man, and some other
philosophers, have been of opinion, that our immortal part acquires during
this life certain habits of action or of sentiment, which become for ever
indissoluble, continuing after death in a future state of existence; and
add, that if these habits are of the malevolent kind, they must render the
possessor miserable even in heaven. I would apply this ingenious idea to
the generation or production of the embryon, or new animal, which partakes
so much of the form and propensities of the parent.

Owing to the imperfection of language the offspring is termed a _new_
animal, but is in truth a branch or elongation of the parent; since a part
of the embryon-animal is, or was, a part of the parent; and therefore in
strict language it cannot be said to be entirely _new_ at the time of its
production; and therefore it may retain some of the habits of the
parent-system.

At the earliest period of its existence the embryon, as secreted from the
blood of the male, would seem to consist of a living filament with certain
capabilities of irritation, sensation, volition, and association; and also
with some acquired habits or propensities peculiar to the parent: the
former of these are in common with other animals; the latter seem to
distinguish or produce the kind of animal, whether man or quadruped, with
the similarity of feature or form to the parent. It is difficult to be
conceived, that a living entity can be separated or produced from the blood
by the action of a gland; and which shall afterwards become an animal
similar to that in whose vessels it is formed; even though we should
suppose with some modern theorists, that the blood is alive; yet every
other hypothesis concerning generation rests on principles still more
difficult to our comprehension.

At the time of procreation this speck of entity is received into an
appropriated nidus, in which it must acquire two circumstances necessary to
its life and growth; one of these is food or sustenance, which is to be
received by the absorbent mouths of its vessels; and the other is that part
of atmospherical air, or of water, which by the new chemistry is termed
oxygene, and which affects the blood by passing through the coats of the
vessels which contain it. The fluid surrounding the embryon in its new
habitation, which is called liquor amnii, supplies it with nourishment; and
as some air cannot but be introduced into the uterus along with a new
embryon, it would seem that this same fluid would for a short time, suppose
for a few hours, supply likewise a sufficient quantity of the oxygene for
its immediate existence.

On this account the vegetable impregnation of aquatic plants is performed
in the air; and it is probable that the honey-cup or nectary of vegetables
requires to be open to the air, that the anthers and stigmas of the flower
may have food of a more oxygenated kind than the common vegetable
sap-juice.

On the introduction of this primordium of entity into the uterus the
irritation of the liquor amnii, which surrounds it, excites the absorbent
mouths of the new vessels into action; they drink up a part of it, and a
pleasurable sensation accompanies this new action; at the same time the
chemical affinity of the oxygene acts through the vessels of the rubescent
blood; and a previous want, or disagreeable sensation, is relieved by this
process.

As the want of this oxygenation of the blood is perpetual, (as appears from
the incessant necessity of breathing by lungs or gills,) the vessels become
extended by the efforts of pain or desire to seek this necessary object of
oxygenation, and to remove the disagreeable sensation, which that want
occasions. At the same time new particles of matter are absorbed, or
applied to these extended vessels, and they become permanently elongated,
as the fluid in contact with them soon loses the oxygenous part, which it
at first possessed, which was owing to the introduction of air along with
the embryon. These new blood-vessels approach the sides of the uterus, and
penetrate with their fine terminations into the vessels of the mother; or
adhere to them, acquiring oxygene through their coats from the passing
currents of the arterial blood of the mother. See Sect. XXXVIII. 2.

This attachment of the placental vessels to the internal side of the uterus
by their own proper efforts appears further illustrated by the many
instances of extra-uterine fetuses, which have thus attached or inserted
their vessels into the peritoneum; or on the viscera, exactly in the same
manner as they naturally insert or attach them to the uterus.

The absorbent vessels of the embryon continue to drink up nourishment from
the fluid in which they swim, or liquor amnii; and which at first needs no
previous digestive preparation; but which, when the whole apparatus of
digestion becomes complete, is swallowed by the mouth into the stomach, and
being mixed with saliva, gastric juice, bile, pancreatic juice, and mucus
of the intestines, becomes digested, and leaves a recrement, which produces
the first feces of the infant, called meconium.

The liquor amnii is secreted into the uterus, as the fetus requires it, and
may probably be produced by the irritation of the fetus as an extraneous
body; since a similar fluid is acquired from the peritoneum in cases of
extra-uterine gestation. The young caterpillars of the gadfly placed in the
skins of cows, and the young of the ichneumon-fly placed in the backs of
the caterpillars on cabbages, seem to produce their nourishment by their
irritating the sides of their nidus. A vegetable secretion and concretion
is thus produced on oak-leaves by the gall-insect, and by the cynips in the
bedeguar of the rose; and by the young grasshopper on many plants, by which
the animal surrounds itself with froth. But in no circumstance is
extra-uterine gestation so exactly resembled as by the eggs of a fly, which
are deposited in the frontal sinus of sheep and calves. These eggs float in
some ounces of fluid collected in a thin pellicle or hydatide. This bag of
fluid compresses the optic nerve on one side, by which the vision being
less distinct in that eye, the animal turns in perpetual circles towards
the side affected, in order to get a more accurate view of objects; for the
same reason as in squinting the affected eye is turned away from the object
contemplated. Sheep in the warm months keep their noses close to the ground
to prevent this fly from so readily getting into their nostrils.

The liquor amnii is secreted into the womb as it is required, not only in
respect to quantity, but, as the digestive powers of the fetus become
formed, this fluid becomes of a different consistence and quality, till it
is exchanged for milk after nativity. Haller. Physiol. V. 1. In the egg the
white part, which is analogous to the liquor amnii of quadrupeds, consists
of two distinct parts; one of which is more viscid, and probably more
difficult of digestion, and more nutritive than the other; and this latter
is used in the last week of incubation. The yolk of the egg is a still
stronger or more nutritive fluid, which is drawn up into the bowels of the
chick just at its exclusion from the shell, and serves it for nourishment
for a day or two, till it is able to digest, and has learnt to choose the
harder seeds or grains, which are to afford it sustenance. Nothing
analogous to this yolk is found in the fetus of lactiferous animals, as the
milk is another nutritive fluid ready prepared for the young progeny.

The yolk therefore is not necessary to the spawn of fish, the eggs of
insects, or for the seeds of vegetables; as their embryons have probably
their food presented to them as soon as they are excluded from their
shells, or have extended their roots. Whence it happens that some insects
produce a living progeny in the spring and summer, and eggs in the autumn;
and some vegetables have living roots or buds produced in the place of
seeds, as the polygonum viviparum, and magical onions. See Botanic Garden,
p. 11. art. anthoxanthum.

There seems however to be a reservoir of nutriment prepared for some seeds
besides their cotyledons or seed-leaves, which may be supposed in some
measure analogous to the yolk of the egg. Such are the saccharine juices of
apples, grapes and other fruits, which supply nutrition to the seeds after
they fall on the ground. And such is the milky juice in the centre of the
cocoa-nut, and part of the kernel of it; the same I suppose of all other
monocotyledon seeds, as of the palms, grasses, and lilies.

II. 1. The process of generation is still involved in impenetrable
obscurity, conjectures may nevertheless be formed concerning some of its
circumstances. First, the eggs of fish and frogs are impregnated, after
they leave the body of the female; because they are deposited in a fluid,
and are not therefore covered with a hard shell. It is however remarkable,
that neither frogs nor fish will part with their spawn without the presence
of the male; on which account female carp and gold-fish in small ponds,
where there are no males, frequently die from the distention of their
growing spawn. 2. The eggs of fowls, which are laid without being
impregnated, are seen to contain only the yolk and white, which are
evidently the food or sustenance for the future chick. 3. As the
cicatricula of these eggs is given by the cock, and is evidently the
rudiment of the new animal; we may conclude, that the embryon is produced
by the male, and the proper food and nidus by the female. For if the female
be supposed to form an equal part of the embryon, why should she form the
whole of the apparatus for nutriment and for oxygenation? the male in many
animals is larger, stronger, and digests more food than the female, and
therefore should contribute as much or more towards the reproduction of the
species; but if he contributes only half the embryon and none of the
apparatus for sustenance and oxygenation, the division is unequal; the
strength of the male, and his consumption of food are too great for the
effect, compared with that of the female, which is contrary to the usual
course of nature.

In objection to this theory of generation it may be said, if the animalcula
in femine, as seen by the microscope, be all of them rudiments of
homunculi, when but one of them can find a nidus, what a waste nature has
made of her productions? I do not assert that these moving particles,
visible by the microscope, are homunciones; perhaps they may be the
creatures of stagnation or putridity, or perhaps no creatures at all; but
if they are supposed to be rudiments of homunculi, or embryons, such a
profusion of them corresponds with the general efforts of nature to provide
for the continuance of her species of animals. Every individual tree
produces innumerable seeds, and every individual fish innumerable spawn, in
such inconceivable abundance as would in a short space of time crowd the
earth and ocean with inhabitants; and these are much more perfect animals
than the animalcula in femine can be supposed to be, and perish in
uncounted millions. This argument only shews, that the productions of
nature are governed by general laws; and that by a wise superfluity of
provision she has ensured their continuance.

2. That the embryon is secreted or produced by the male, and not by the
conjunction of fluids from both male and female, appears from the analogy
of vegetable seeds. In the large flowers, as the tulip, there is no
similarity of apparatus between the anthers and the stigma: the seed is
produced according to the observations of Spallanzani long before the
flowers open, and in consequence long before it can be impregnated, like
the egg in the pullet. And after the prolific dust is shed on the stigma,
the seed becomes coagulated in one point first, like the cicatricula of the
impregnated egg. See Botanic Garden, Part I. additional note 38. Now in
these simple products of nature, if the female contributed to produce the
new embryon equally with the male, there would probably have been some
visible similarity of parts for this purpose, besides those necessary for
the nidus and sustenance of the new progeny. Besides in many flowers the
males are more numerous than the females, or than the separate uterine
cells in their germs, which would shew, that the office of the male was at
least as important as that of the female; whereas if the female, besides
producing the egg or seed, was to produce an equal part of the embryon, the
office of reproduction would be unequally divided between them.

Add to this, that in the most simple kind of vegetable reproduction, I mean
the buds of trees, which are their viviparous offspring, the leaf is
evidently the parent of the bud, which rises in its bosom, according to the
observation of Linnaeus. This leaf consists of absorbent vessels, and
pulmonary ones, to obtain its nutriment, and to impregnate it with oxygene.
This simple piece of living organization is also furnished with a power of
reproduction; and as the new offspring is thus supported adhering to its
father, it needs no mother to supply it with a nidus, and nutriment, and
oxygenation; and hence no female leaf has existence.

I conceive that the vessels between the bud and the leaf communicate or
inosculate; and that the bud is thus served with vegetable blood, that is,
with both nutriment and oxygenation, till the death of the parent-leaf in
autumn. And in this respect it differs from the fetus of viviparous
animals. Secondly, that then the bark-vessels belonging to the dead-leaf,
and in which I suppose a kind of manna to have been deposited, become now
the placental vessels, if they may be so called, of the new bud. From the
vernal sap thus produced of one sugar-maple-tree in New-York and in
Pennsylvania, five or six pounds of good sugar may be made annually without
destroying the tree. Account of maple-sugar by B. Rushes. London, Phillips.
(See Botanic Garden, Part I. additional note on vegetable placentation.)

These vessels, when the warmth of the vernal sun hatches the young bud,
serve it with a saccharine nutriment, till it acquires leaves of its own,
and shoots a new system of absorbents down the bark and root of the tree,
just as the farinaceous or oily matter in seeds, and the saccharine matter
in fruits, serve their embryons with nutriment, till they acquire leaves
and roots. This analogy is as forceable in so obscure a subject, as it is
curious, and may in large buds, as of the horse-chesnut, be almost seen by
the naked eye; if with a penknife the remaining rudiment of the last year's
leaf, and of the new bud in its bosom, be cut away slice by slice. The
seven ribs of the last year's leaf will be seen to have arisen from the
pith in seven distinct points making a curve; and the new bud to have been
produced in their centre, and to have pierced the alburnum and cortex, and
grown without the assistance of a mother. A similar process may be seen on
dissecting a tulip-root in winter; the leaves, which inclosed the last
year's flower-stalk, were not necessary for the flower; but each of these
was the father of a new bud, which may be now found at its base; and which,
as it adheres to the parent, required no mother.

This paternal offspring of vegetables, I mean their buds and bulbs, is
attended with a very curious circumstance; and that is, that they exactly
resemble their parents, as is observable in grafting fruit-trees, and in
propagating flower-roots; whereas the seminal offspring of plants, being
supplied with nutriment by the mother, is liable to perpetual variation.
Thus also in the vegetable class dioicia, where the male flowers are
produced on one tree, and the female ones on another; the buds of the male
trees uniformly produce either male flowers, or other buds similar to
themselves; and the buds of the female trees produce either female flowers,
or other buds similar to themselves; whereas the seeds of these trees
produce either male or female plants. From this analogy of the production
of vegetable buds without a mother, I contend that the mother does not
contribute to the formation of the living ens in animal generation, but is
necessary only for supplying its nutriment and oxygenation.

There is another vegetable fact published by M. Koelreuter, which he calls
"a complete metamorphosis of one natural species of plants into another,"
which shews, that in seeds as well as in buds, the embryon proceeds from
the male parent, though the form of the subsequent mature plant is in part
dependant on the female. M. Koelreuter impregnated a stigma of the
nicotiana rustica with the farina of the nicotiana paniculata, and obtained
prolific seeds from it. With the plants which sprung from these seeds, he
repeated the experiment, impregnating them with the farina of the nicotiana
paniculata. As the mule plants which he thus produced were prolific, he
continued to impregnate them for many generations with the farina of the
nicotiana paniculata, and they became more and more like the male parent,
till he at length obtained six plants in every respect perfectly similar to
the nicotiana paniculata; and in no respect resembling their female parent
the nicotiana rustica. _Blumenbach_ on Generation.

3. It is probable that the insects, which are said to require but one
impregnation for six generations, as the aphis (see Amenit. Academ.)
produce their progeny in the manner above described, that is, without a
mother, and not without a father; and thus experience a lucina sine
concubitu. Those who have attended to the habits of the polypus, which is
found in the stagnant water of our ditches in July, affirm, that the young
ones branch out from the side of the parent like the buds of trees, and
after a time separate themselves from them. This is so analogous to the
manner in which the buds of trees appear to be produced, that these polypi
may be considered as all male animals, producing embryons, which require no
mother to supply them with a nidus, or with nutriment, and oxygenation.

This lateral or lineal generation of plants, not only obtains in the buds
of trees, which continue to adhere to them, but is beautifully seen in the
wires of knot-grass, polygonum aviculare, and in those of strawberries,
fragaria vesca. In these an elongated creeping bud is protruded, and, where
it touches the ground, takes root, and produces a new plant derived from
its father, from which it acquires both nutriment and oxygenation; and in
consequence needs no maternal apparatus for these purposes. In viviparous
flowers, as those of allium magicum, and polygonum viviparum, the anthers
and the stigmas become effete and perish; and the lateral or paternal
offspring succeeds instead of seeds, which adhere till they are
sufficiently mature, and then fall upon the ground, and take root like
other bulbs.

The lateral production of plants by wires, while each new plant is thus
chained to its parent, and continues to put forth another and another, as
the wire creeps onward on the ground, is exactly resembled by the
tape-worm, or tænia, so often found in the bowels, stretching itself in a
chain quite from the stomach to the rectum. Linnæus asserts, "that it grows
old at one extremity, while it continues to generate young ones at the
other, proceeding ad infinitum, like a root of grass. The separate joints
are called gourd-worms, and propagate new joints like the parent without
end, each joint being furnished with its proper mouth, and organs of
digestion." Systema naturæ. Vermes tenia. In this animal there evidently
appears a power of reproduction without any maternal apparatus for the
purpose of supplying nutriment and oxygenation to the embryon, as it
remains attached to its father till its maturity. The volvox globator,
which is a transparent animal, is said by Linnæus to bear within it sons
and grand-sons to the fifth generation. These are probably living fetuses,
produced by the father, of different degrees of maturity, to be detruded at
different periods of time, like the unimpregnated eggs of various sizes,
which are found in poultry; and as they are produced without any known
copulation, contribute to evince, that the living embryon in other orders
of animals is formed by the male-parent, and not by the mother, as one
parent has the power to produce it.

This idea of the reproduction of animals from a single living filament of
their fathers, appears to have been shadowed or allegorized in the curious
account in sacred writ of the formation of Eve from a rib of Adam.

From all these analogies I conclude, that the embryon is produced solely by
the male, and that the female supplies it with a proper nidus, with
sustenance, and with oxygenation; and that the idea of the semen of the
male constituting only a stimulus to the egg of the female, exciting it
into life, (as held by some philosophers) has no support from experiment or
analogy.

III. 1. Many ingenious philosophers have found so great difficulty in
conceiving the manner of the reproduction of animals, that they have
supposed all the numerous progeny, to have existed in miniature in the
animal originally created; and that these infinitely minute forms are only
evolved or distended, as the embryon increases in the womb. This idea,
besides its being unsupported by any analogy we are acquainted with,
ascribes a greater tenuity to organized matter, than we can readily admit;
as these included embryons are supposed each of them to consist of the
various and complicate parts of animal bodies: they must possess a much
greater degree of minuteness, than that which was ascribed to the devils
that tempted St. Anthony; of whom 20,000 were said to have been able to
dance a saraband on the point of the finest needle without incommoding each
other.

2. Others have supposed, that all the parts of the embryon are formed in
the male, previous to its being deposited in the egg or uterus; and that it
is then only to have its parts evolved or distended as mentioned above; but
this is only to get rid of one difficulty by proposing another equally
incomprehensible: they found it difficult to conceive, how the embryon
could be formed in the uterus or egg, and therefore wished it to be formed
before it came thither. In answer to both these doctrines it may be
observed, 1st, that some animals, as the crab-fish, can reproduce a whole
limb, as a leg which has been broken off; others, as worms and snails, can
reproduce a head, or a tail, when either of them has been cut away; and
that hence in these animals at least a part can be formed anew, which
cannot be supposed to have existed previously in miniature.

Secondly, there are new parts or new vessels produced in many diseases, as
on the cornea of the eye in ophthalmy, in wens and cancers, which cannot be
supposed to have had a prototype or original miniature in the embryon.

Thirdly, how could mule-animals be produced, which partake of the forms of
both the parents, if the original embryon was a miniature existing in the
semen of the male parent? if an embryon of the male ass was only expanded,
no resemblance to the mare could exist in the mule.

This mistaken idea of the extension of parts seems to have had its rise
from the mature man resembling the general form of the fetus; and from
thence it was believed, that the parts of the fetus were distended into the
man; whereas they have increased 100 times in weight, as well as 100 times
in size; now no one will call the additional 99 parts a distention of the
original one part in respect to weight. Thus the uterus during pregnancy is
greatly enlarged in thickness and solidity as well as in capacity, and
hence must have acquired this additional size by accretion of new parts,
not by an extension of the old ones; the familiar act of blowing up the
bladder of an animal recently slaughtered has led our imaginations to apply
this idea of distention to the increase of size from natural growth; which
however must be owing to the apposition of new parts; as it is evinced from
the increase of weight along with the increase of dimension; and is even
visible to our eyes in the elongation of our hair from the colour of its
ends; or when it has been dyed on the head; and in the growth of our nails
from the specks sometimes observable on them; and in the increase of the
white crescent at their roots, and in the growth of new flesh in wounds,
which consists of new nerves as well as of new blood-vessels.

3. Lastly, Mr. Buffon has with great ingenuity imagined the existence of
certain organic particles, which are supposed to be partly alive, and
partly mechanic springs. The latter of these were discovered by Mr. Needham
in the milt or male organ of a species of cuttle fish, called calmar; the
former, or living animalcula, are found in both male and female secretions,
in the infusions of seeds, as of pepper, in the jelly of roasted veal, and
in all other animal and vegetable substances. These organic particles he
supposes to exist in the spermatic fluids of both sexes, and that they are
derived thither from every part of the body, and must therefore resemble,
as he supposes, the parts from whence they are derived. These organic
particles he believes to be in constant activity, till they become mixed in
the womb, and then they instantly join and produce an embryon or fetus
similar to the two parents.

Many objections might be adduced to this fanciful theory, I shall only
mention two. First, that it is analogous to no known animal laws. And
secondly, that as these fluids, replete with organic particles derived both
from the male and female organs, are supposed to be similar; there is no
reason why the mother should not produce a female embryon without the
assistance of the male, and realize the lucina sine concubitu.

IV. 1. I conceive the primordium, or rudiment of the embryon, as secreted
from the blood of the parent, to consist of a simple living filament as a
muscular fibre; which I suppose to be an extremity of a nerve of
loco-motion, as a fibre of the retina is an extremity of a nerve of
sensation; as for instance one of the fibrils, which compose the mouth of
an absorbent vessel; I suppose this living filament, of whatever form it
may be, whether sphere, cube, or cylinder, to be endued with the capability
of being excited into action by certain kinds of stimulus. By the stimulus
of the surrounding fluid, in which it is received from the male, it may
bend into a ring; and thus form the beginning of a tube. Such moving
filaments, and such rings, are described by those, who have attended to
microscopic animalcula. This living ring may now embrace or absorb a
nutritive particle of the fluid, in which it swims; and by drawing it into
its pores, or joining it by compression to its extremities, may increase
its own length or crassitude; and by degrees the living ring may become a
living tube.

2. With this new organization, or accretion of parts, new kinds of
irritability may commence; for so long as there was but one living organ,
it could only be supposed to possess irritability; since sensibility may be
conceived to be an extension of the effect of irritability over the rest of
the system. These new kinds of irritability and of sensibility in
consequence of new organization, appear from variety of facts in the more
mature animal; thus the formation of the testes, and consequent secretion
of the semen, occasion the passion of lust; the lungs must be previously
formed before their exertions to obtain fresh air can exist; the throat or
oesophagus must be formed previous to the sensation or appetites of hunger
and thirst; one of which seems to reside at the upper end, and the other at
the lower end of that canal.

Thus also the glans penis, when it is distended with blood, acquires a new
sensibility, and a new appetency. The same occurs to the nipples of the
breasts of female animals, when they are distended with blood, they acquire
the new appetency of giving milk. So inflamed tendons and membranes, and
even bones, acquire new sensations; and the parts of mutilated animals, as
of wounded snails, and polypi, and crabs, are reproduced; and at the same
time acquire sensations adapted to their situations. Thus when the head of
a snail is reproduced after decollation with a sharp rasor, those curious
telescopic eyes are also reproduced, and acquire their sensibility to
light, as well as their adapted muscles for retraction on the approach of
injury.

With every new change, therefore, of organic form, or addition of organic
parts, I suppose a new kind of irritability or of sensibility to be
produced; such varieties of irritability or of sensibility exist in our
adult state in the glands; every one of which is furnished with an
irritability, or a taste, or appetency, and a consequent mode of action
peculiar to itself.

In this manner I conceive the vessels of the jaws to produce those of the
teeth, those of the fingers to produce the nails, those of the skin to
produce the hair; in the same manner as afterwards about the age of puberty
the beard and other great changes in the form of the body, and disposition
of the mind, are produced in consequence of the new secretion of semen; for
if the animal is deprived of this secretion those changes do not take
place. These changes I conceive to be formed not by elongation or
distention of primeval stamina, but by apposition of parts; as the mature
crab-fish, when deprived of a limb, in a certain space of time has power to
regenerate it; and the tadpole puts forth its feet long after its exclusion
from the spawn; and the caterpillar in changing into a butterfly acquires a
new form, with new powers, new sensations, and new desires.

The natural history of butterflies, and moths, and beetles, and gnats, is
full of curiosity; some of them pass many months, and others even years, in
their caterpillar or grub state; they then rest many weeks without food,
suspended in the air, buried in the earth, or submersed in water; and
change themselves during this time into an animal apparently of a different
nature; the stomachs of some of them, which before digested vegetable
leaves or roots, now only digest honey; they have acquired wings for the
purpose of seeking this new food, and a long proboscis to collect it from
flowers, and I suppose a sense of smell to detect the secret places in
flowers, where it is formed. The moths, which fly by night, have a much
longer proboscis rolled up under their chins like a watch spring; which
they extend to collect the honey from flowers in their sleeping state; when
they are closed, and the nectaries in consequence more difficult to be
plundered. The beetle kind are furnished with an external covering of a
hard material to their wings, that they may occasionally again make holes
in the earth, in which they passed the former state of their existence.

But what most of all distinguishes these new animals is, that they are new
furnished with the powers of reproduction; and that they now differ from
each other in sex, which does not appear in their caterpillar or grub
state. In some of them the change from a caterpillar into a butterfly or
moth seems to be accomplished for the sole purpose of their propagation;
since they immediately die after this is finished, and take no food in the
interim, as the silk-worm in this climate; though it is possible, it might
take honey as food, if it was presented to it. For in general it would
seem, that food of a more stimulating kind, the honey of vegetables instead
of their leaves, was necessary for the purpose of the seminal reproduction
of these animals, exactly similar to what happens in vegetables; in these
the juices of the earth are sufficient for their purpose of reproduction by
buds or bulbs; in which the new plant seems to be formed by irritative
motions, like the growth of their other parts, as their leaves or roots;
but for the purpose of seminal or amatorial reproduction, where sensation
is required, a more stimulating food becomes necessary for the anther, and
stigma; and this food is honey; as explained in Sect. XIII. on Vegetable
Animation.

The gnat and the tadpole resemble each other in their change from natant
animals with gills into aerial animals with lungs; and in their change of
the element in which they live; and probably of the food, with which they
are supported; and lastly, with their acquiring in their new state the
difference of sex, and the organs of seminal or amatorial reproduction.
While the polypus, who is their companion in their former state of life,
not being allowed to change his form and element, can only propagate like
vegetable buds by the same kind of irritative motions, which produces the
growth of his own body, without the seminal or amatorial propagation, which
requires sensation; and which in gnats and tadpoles seems to require a
change both of food and of respiration.

From hence I conclude, that with the acquisition of new parts, new
sensations, and new desires, as well as new powers, are produced; and this
by accretion to the old ones, and not by distention of them. And finally,
that the most essential parts of the system, as the brain for the purpose
of distributing the power of life, and the placenta for the purpose of
oxygenating the blood, and the additional absorbent vessels for the purpose
of acquiring aliment, are first formed by the irritations above mentioned,
and by the pleasurable sensations attending those irritations, and by the
exertions in consequence of painful sensations, similar to those of hunger
and suffocation. After these an apparatus of limbs for future uses, or for
the purpose of moving the body in its present natant state, and of lungs
for future respiration, and of testes for future reproduction, are formed
by the irritations and sensations, and consequent exertions of the parts
previously existing, and to which the new parts are to be attached.

3. In confirmation of these ideas it may be observed, that all the parts of
the body endeavour to grow, or to make additional parts to themselves
throughout our lives; but are restrained by the parts immediately
containing them; thus, if the skin be taken away, the fleshy parts beneath
soon shoot out new granulations, called by the vulgar proud flesh. If the
periosteum be removed, a similar growth commences from the bone. Now in the
case of the imperfect embryon, the containing or confining parts are not
yet supposed to be formed, and hence there is nothing to restrain its
growth.

4. By the parts of the embryon being thus produced by new apportions, many
phenomena both of animal and vegetable productions receive an easier
explanation; such as that many fetuses are deficient at the extremities, as
in a finger or a toe, or in the end of the tongue, or in what is called a
hare-lip with deficiency of the palate. For if there should be a deficiency
in the quantity of the first nutritive particles laid up in the egg for the
reception of the first living filament, the extreme parts, as being last
formed, must shew this deficiency by their being imperfect.

This idea of the growth of the embryon accords also with the production of
some monstrous births, which consist of a duplicature of the limbs, as
chickens with four legs; which could not occur, if the fetus was formed by
the distention of an original stamen, or miniature. For if there should be
a superfluity of the first nutritive particles laid up in the egg for the
first living filament; it is easy to conceive, that a duplicature of some
parts may be formed. And that such superfluous nourishment sometimes
exists, is evinced by the double yolks in some eggs, which I suppose were
thus formed previous to their impregnation by the exuberant nutriment of
the hen.

This idea is confirmed by the analogy of the monsters in the vegetable
world also; in which a duplicate or triplicate production of various parts
of the flower is observable, as a triple nectary in some columbines, and a
triple petal in some primroses; and which are supposed to be produced by
abundant nourishment.

5. If the embryon be received into a fluid, whose stimulus is different in
some degree from the natural, as in the production of mule-animals, the new
irritabilities or sensibilities acquired by the increasing or growing
organized parts may differ, and thence produce parts not similar to the
father, but of a kind belonging in part to the mother; and thus, though the
original stamen or living ens was derived totally from the father, yet new
irritabilities or sensibilities being excited, a change of form
corresponding with them will be produced. Nor could the production of mules
exist, if the stamen or miniature of all the parts of the embryon is
previously formed in the male semen, and is only distended by nourishment
in the female uterus. Whereas this difficulty ceases, if the embryon be
supposed to consist of a living filament, which acquires or makes new parts
with new irritabilities, as it advances in its growth.

The form, solidity, and colour, of the particles of nutriment laid up for
the reception of the first living filament, as well as their peculiar kind
of stimulus, may contribute to produce a difference in the form, solidity,
and colour of the fetus, so as to resemble the mother, as it advances in
life. This also may especially happen during the first state of the
existence of the embryon, before it has acquired organs, which can change
these first nutritive particles, as explained in No. 5. 2. of this Section.
And as these nutritive particles are supposed to be similar to those, which
are formed for her own nutrition, it follows that the fetus should so far
resemble the mother.

This explains, why hereditary diseases may be derived either from the male
or female parent, as well as the peculiar form of either of their bodies.
Some of these hereditary diseases are simply owing to a deficient activity
of a part of the system, as of the absorbent vessels, which open into the
cells or cavities of the body, and thus occasion dropsies. Others are at
the same time owing to an increase of sensation, as in scrophula and
consumption; in these the obstruction of the fluids is first caused by the
inirritability of the vessels, and the inflammation and ulcers which
succeed, are caused by the consequent increase of sensation in the
obstructed part. Other hereditary diseases, as the epilepsy, and other
convulsions, consist in too great voluntary exertions in consequence of
disagreeable sensation in some particular diseased part. Now as the pains,
which occasion these convulsions, are owing to defect of the action of the
diseased part, as shewn in Sect. XXXIV. it is plain, that all these
hereditary diseases may have their origin either from defective
irritability derived from the father, or from deficiency of the stimulus of
the nutriment derived from the mother. In either case the effect would be
similar; as a scrophulous race is frequently produced among the poor from
the deficient stimulus of bad diet, or of hunger; and among the rich, by a
deficient irritability from their having been long accustomed to too great
stimulus, as of vinous spirit.

6. From this account of reproduction it appears, that all animals have a
similar origin, viz. from a single living filament; and that the difference
of their forms and qualities has arisen only from the different
irritabilities and sensibilities, or voluntarities, or associabilities, of
this original living filament; and perhaps in some degree from the
different forms of the particles of the fluids, by which it has been at
first stimulated into activity. And that from hence, as Linnæus has
conjectured in respect to the vegetable world, it is not impossible, but
the great variety of species of animals, which now tenant the earth, may
have had their origin from the mixture of a few natural orders. And that
those animal and vegetable mules, which could continue their species, have
done so, and constitute the numerous families of animals and vegetables
which now exist; and that those mules, which were produced with imperfect
organs of generation, perished without reproduction, according to the
observation of Aristotle; and are the animals, which we now call mules. See
Botanic Garden, Part II. Note on Dianthus.

Such a promiscuous intercourse of animals is said to exist at this day in
New South Wales by Captain Hunter. And that not only amongst the quadrupeds
and birds of different kinds, but even amongst the fish, and, as he
believes, amongst the vegetables. He speaks of an animal between the
opossum and the kangaroo, from the size of a sheep to that of a rat. Many
fish seemed to partake of the shark; some with a shark's head and
shoulders, and the hind part of a shark; others with a shark's head and the
body of a mullet; and some with a shark's head and the flat body of a
sting-ray. Many birds partake of the parrot; some have the head, neck, and
bill of a parrot, with long straight feet and legs; others with legs and
feet of a parrot, with head and neck of a sea gull. Voyage to South Wales
by Captain John Hunter, p. 68.

7. All animals therefore, I contend, have a similar cause of their
organization, originating from a single living filament, endued indeed with
different kinds of irritabilities and sensibilities, or of animal
appetencies; which exist in every gland, and in every moving organ of the
body, and are as essential to living organization as chemical affinities
are to certain combinations of inanimate matter.

If I might be indulged to make a simile in a philosophical work, I should
say, that the animal appetencies are not only perhaps less numerous
originally than the chemical affinities; but that like these latter, they
change with every new combination; thus vital air and azote, when combined,
produce nitrous acid; which now acquires the property of dissolving silver;
so with every new additional part to the embryon, as of the throat or
lungs, I suppose a new animal appetency to be produced.

In this early formation of the embryon from the irritabilities,
sensibilities, and associabilities, and consequent appetencies, the faculty
of volition can scarcely be supposed to have had its birth. For about what
can the fetus deliberate, when it has no choice of objects? But in the more
advanced state of the fetus, it evidently possesses volition; as it
frequently changes its attitude, though it seems to sleep the greatest part
of its time; and afterwards the power of volition contributes to change or
alter many parts of the body during its growth to manhood, by our early
modes of exertion in the various departments of life. All these faculties
then constitute the vis fabricatrix, and the vis conservatrix, as well as
the vis medicatrix of nature, so much spoken of, but so little understood
by philosophers.

8. When we revolve in our minds, first, the great changes, which we see
naturally produced in animals after their nativity, as in the production of
the butterfly with painted wings from the crawling caterpillar; or of the
respiring frog from the subnatant tadpole; from the feminine boy to the
bearded man, and from the infant girl to the lactescent woman; both which
changes may be prevented by certain mutilations of the glands necessary to
reproduction.

Secondly, when we think over the great changes introduced into various
animals by artificial or accidental cultivation, as in horses, which we
have exercised for the different purposes of strength or swiftness, in
carrying burthens or in running races; or in dogs, which have been
cultivated for strength and courage, as the bull-dog; or for acuteness of
his sense or smell, as the hound and spaniel; or for the swiftness of his
foot, as the greyhound; or for his swimming in the water, or for drawing
snow-sledges, as the rough-haired dogs of the north; or lastly, as a
play-dog for children, as the lap-dog; with the changes of the forms of the
cattle, which have been domesticated from the greatest antiquity, as
camels, and sheep; which have undergone so total a transformation, that we
are now ignorant from what species of wild animals they had their origin.
Add to these the great changes of shape and colour, which we daily see
produced in smaller animals from our domestication of them, as rabbits, or
pigeons; or from the difference of climates and even of seasons; thus the
sheep of warm climates are covered with hair instead of wool; and the hares
and partridges of the latitudes, which are long buried in snow, become
white during the winter months; add to these the various changes produced
in the forms of mankind, by their early modes of exertion; or by the
diseases occasioned by their habits of life; both of which became
hereditary, and that through many generations. Those who labour at the
anvil, the oar, or the loom, as well as those who carry sedan-chairs, or
who have been educated to dance upon the rope, are distinguishable by the
shape of their limbs; and the diseases occasioned by intoxication deform
the countenance with leprous eruptions, or the body with tumid viscera, or
the joints with knots and distortions.

Thirdly, when we enumerate the great changes produced in the species of
animals before their nativity; these are such as resemble the form or
colour of their parents, which have been altered by the cultivation or
accidents above related, and are thus continued to their posterity. Or they
are changes produced by the mixture of species as in mules; or changes
produced probably by the exuberance of nourishment supplied to the fetus,
as in monstrous births with additional limbs; many of these enormities of
shape are propagated, and continued as a variety at least, if not as a new
species of animal. I have seen a breed of cats with an additional claw on
every foot; of poultry also with an additional claw, and with wings to
their feet; and of others without rumps. Mr. Buffon mentions a breed of
dogs without tails, which are common at Rome and at Naples, which he
supposes to have been produced by a custom long established of cutting
their tails close off. There are many kinds of pigeons, admired for their
peculiarities, which are monsters thus produced and propagated. And to
these must be added, the changes produced by the imagination of the male
parent, as will be treated of more at large in No. VI. of this Section.

When we consider all these changes of animal form, and innumerable others,
which may be collected from the books of natural history; we cannot but be
convinced, that the fetus or embryon is formed by apposition of new parts,
and not by the distention of a primordial nest of germs, included one
within another, like the cups of a conjurer.

Fourthly, when we revolve in our minds the great similarity of structure,
which obtains in all the warm-blooded animals, as well quadrupeds, birds,
and amphibious animals, as in mankind; from the mouse and bat to the
elephant and whale; one is led to conclude, that they have alike been
produced from a similar living filament. In some this filament in its
advance to maturity has acquired hands and fingers, with a fine sense of
touch, as in mankind. In others it has acquired claws or talons, as in
tygers and eagles. In others, toes with an intervening web, or membrane, as
in seals and geese. In others it has acquired cloven hoofs, as in cows and
swine; and whole hoofs in others, as in the horse. While in the bird kind
this original living filament has put forth wings instead of arms or legs,
and feathers instead of hair. In some it has protruded horns on the
forehead instead of teeth in the fore part of the upper jaw; in others
tushes instead of horns; and in others beaks instead of either. And all
this exactly as is daily seen in the transmutations of the tadpole, which
acquires legs and lungs, when he wants them; and loses his tail, when it is
no longer of service to him.

Fifthly, from their first rudiment, or primordium, to the termination of
their lives, all animals undergo perpetual transformations; which are in
part produced by their own exertions in consequence of their desires and
aversions, of their pleasures and their pains, or of irritations, or of
associations; and many of these acquired forms or propensities are
transmitted to their posterity. See Sect. XXXI. 1.

As air and water are supplied to animals in sufficient profusion, the three
great objects of desire, which have changed the forms of many animals by
their exertions to gratify them, are those of lust, hunger, and security. A
great want of one part of the animal world has consisted in the desire of
the exclusive possession of the females; and these have acquired weapons to
combat each other for this purpose, as the very thick, shield-like, horny
skin on the shoulder of the boar is a defence only against animals of his
own species, who strike obliquely upwards, nor are his tushes for other
purposes, except to defend himself, as he is not naturally a carnivorous
animal. So the horns of the stag are sharp to offend his adversary, but are
branched for the purpose of parrying or receiving the thrusts of horns
similar to his own, and have therefore been formed for the purpose of
combating other stags for the exclusive possession of the females; who are
observed, like the ladies in the times of chivalry, to attend the car of
the victor.

The birds, which do not carry food to their young, and do not therefore
marry, are armed with spurs for the purpose of fighting for the exclusive
possession of the females, as cocks and quails. It is certain that these
weapons are not provided for their defence against other adversaries,
because the females of these species are without this armour. The final
cause of this contest amongst the males seems to be, that the strongest and
most active animal should propagate the species, which should thence become
improved.

Another great want consists in the means of procuring food, which has
diversified the forms of all species of animals. Thus the nose of the swine
has become hard for the purpose of turning up the soil in search of insects
and of roots. The trunk of the elephant is an elongation of the nose for
the purpose of pulling down the branches of trees for his food, and for
taking up water without bending his knees. Beasts of prey have acquired
strong jaws or talons. Cattle have acquired a rough tongue and a rough
palate to pull off the blades of grass, as cows and sheep. Some birds have
acquired harder beaks to crack nuts, as the parrot. Others have acquired
beaks adapted to break the harder seeds, as sparrows. Others for the softer
seeds of flowers, or the buds of trees, as the finches. Other birds have
acquired long beaks to penetrate the moister soils in search of insects or
roots, as woodcocks; and others broad ones to filtrate the water of lakes,
and to retain aquatic insects. All which seem to have been gradually
produced during many generations by the perpetual endeavour of the
creatures to supply the want of food, and to have been delivered to their
posterity with constant improvement of them for the purposes required.

The third great want amongst animals is that of security, which seems much
to have diversified the forms of their bodies and the colour of them; these
consist in the means of escaping other animals more powerful than
themselves. Hence some animals have acquired wings instead of legs, as the
smaller birds, for the purpose of escape. Others great length of fin, or of
membrane, as the flying fish, and the bat. Others great swiftness of foot,
as the hare. Others have acquired hard or armed shells, as the tortoise and
the echinus marinus.

Mr. Osbeck, a pupil of Linnæus, mentions the American frog fish, Lophius
Histrio, which inhabits the large floating islands of sea-weed about the
Cape of Good Hope, and has fulcra resembling leaves, that the fishes of
prey may mistake it for the sea-weed, which it inhabits. Voyage to China,
p. 113.

The contrivances for the purposes of security extend even to vegetables, as
is seen in the wonderful and various means of their concealing or defending
their honey from insects, and their seeds from birds. On the other hand
swiftness of wing has been acquired by hawks and swallows to pursue their
prey; and a proboscis of admirable structure has been acquired by the bee,
the moth, and the humming bird, for the purpose of plundering the nectaries
of flowers. All which seem to have been formed by the original living
filament, excited into action by the necessities of the creatures, which
possess them, and on which their existence depends.

From thus meditating on the great similarity of the structure of the
warm-blooded animals, and at the same time of the great changes they
undergo both before and after their nativity; and by considering in how
minute a portion of time many of the changes of animals above described
have been produced; would it be too bold to imagine, that in the great
length of time, since the earth began to exist, perhaps millions of ages
before the commencement of the history of mankind, would it be too bold to
imagine, that all warm-blooded animals have arisen from one living
filament, which THE GREAT FIRST CAUSE endued with animality, with the power
of acquiring new parts, attended with new propensities, directed by
irritations, sensations, volitions, and associations; and thus possessing
the faculty of continuing to improve by its own inherent activity, and of
delivering down those improvements by generation to its posterity, world
without end!

Sixthly, The cold-blooded animals, as the fish-tribes, which are furnished
with but one ventricle of the heart, and with gills instead of lungs, and
with fins instead of feet or wings, bear a great similarity to each other;
but they differ, nevertheless, so much in their general structure from the
warm-blooded animals, that it may not seem probable at first view, that the
same living filament could have given origin to this kingdom of animals, as
to the former. Yet are there some creatures, which unite or partake of both
these orders of animation, as the whales and seals; and more particularly
the frog, who changes from an aquatic animal furnished with gills to an
aerial one furnished with lungs.

The numerous tribes of insects without wings, from the spider to the
scorpion, from the flea to the lobster; or with wings, from the gnat and
the ant to the wasp and the dragon-fly, differ so totally from each other,
and from the red-blooded classes above described, both in the forms of
their bodies, and their modes of life; besides the organ of sense, which
they seem to possess in their antennæ or horns, to which it has been
thought by some naturalists, that other creatures have nothing similar;
that it can scarcely be supposed that this nation of animals could have
been produced by the same kind of living filament, as the red-blooded
classes above mentioned. And yet the changes which many of them undergo in
their early state to that of their maturity, are as different, as one
animal can be from another. As those of the gnat, which passes his early
state in water, and then stretching out his new wings, and expanding his
new lungs, rises in the air; as of the caterpillar, and bee-nymph, which
feed on vegetable leaves or farina, and at length bursting from their
self-formed graves, become beautiful winged inhabitants of the skies,
journeying from flower to flower, and nourished by the ambrosial food of
honey.

There is still another class of animals, which are termed vermes by
Linnæus, which are without feet, or brain, and are hermaphrodites, as
worms, leeches, snails, shell-fish, coralline insects, and sponges; which
possess the simplest structure of all animals, and appear totally different
from those already described. The simplicity of their structure, however,
can afford no argument against their having been produced from a living
filament as above contended.

Last of all the various tribes of vegetables are to be enumerated amongst
the inferior orders of animals. Of these the anthers and stigmas have
already been shewn to possess some organs of sense, to be nourished by
honey, and to have the power of generation like insects, and have thence
been announced amongst the animal kingdom in Sect. XIII. and to these must
be added the buds and bulbs which constitute the viviparous offspring of
vegetation. The former I suppose to be beholden to a single living filament
for their seminal or amatorial procreation; and the latter to the same
cause for their lateral or branching generation, which they possess in
common with the polypus, tænia, and volvox; and the simplicity of which is
an argument in favour of the similarity of its cause.

Linnæus supposes, in the Introduction to his Natural Orders, that very few
vegetables were at first created, and that their numbers were increased by
their intermarriages, and adds, suadent hæc Creatoris leges a simplicibus
ad composita. Many other changes seem to have arisen in them by their
perpetual contest for light and air above ground, and for food or moisture
beneath the soil. As noted in Botanic Garden, Part II. Note on Cuscuta.
Other changes of vegetables from climate, or other causes, are remarked in
the Note on Curcuma in the same work. From these one might be led to
imagine, that each plant at first consisted of a single bulb or flower to
each root, as the gentianella and daisy; and that in the contest for air
and light new buds grew on the old decaying flower stem, shooting down
their elongated roots to the ground, and that in process of ages tall trees
were thus formed, and an individual bulb became a swarm of vegetables.
Other plants, which in this contest for light and air were too slender to
rise by their own strength, learned by degrees to adhere to their
neighbours, either by putting forth roots like the ivy, or by tendrils like
the vine, or by spiral contortions like the honeysuckle; or by growing upon
them like the misleto, and taking nourishment from their barks; or by only
lodging or adhering on them, and deriving nourishment from the air, as
tillandsia.

Shall we then say that the vegetable living filament was originally
different from that of each tribe of animals above described? And that the
productive living filament of each of those tribes was different originally
from the other? Or, as the earth and ocean were probably peopled with
vegetable productions long before the existence of animals; and many
families of these animals long before other families of them, shall we
conjecture that one and the same kind of living filaments is and has been
the cause of all organic life?

This idea of the gradual formation and improvement of the animal world
accords with the observations of some modern philosophers, who have
supposed that the continent of America has been raised out of the ocean at
a later period of time than the other three quarters of the globe, which
they deduce from the greater comparative heights of its mountains, and the
consequent greater coldness of its respective climates, and from the less
size and strength of its animals, as the tygers and allegators compared
with those of Asia or Africa. And lastly, from the less progress in the
improvements of the mind of its inhabitants in respect to voluntary
exertions.

This idea of the gradual formation and improvement of the animal world
seems not to have been unknown to the ancient philosophers. Plato having
probably observed the reciprocal generation of inferior animals, as snails
and worms, was of opinion, that mankind with all other animals were
originally hermaphrodites during the infancy of the world, and were in
process of time separated into male and female. The breasts and teats of
all male quadrupeds, to which no use can be now assigned, adds perhaps some
shadow of probability to this opinion. Linnæus excepts the horse from the
male quadrupeds, who have teats; which might have shewn the earlier origin
of his exigence; but Mr. J. Hunter asserts, that he has discovered the
vestiges of them on his sheath, and has at the same time enriched natural
history with a very curious fact concerning the male pigeon; at the time of
hatching the eggs both the male and female pigeon undergo a great change in
their crops; which thicken and become corrugated, and secrete a kind of
milky fluid, which coagulates, and with which alone they for a few days
feed their young, and afterwards feed them with this coagulated fluid mixed
with other food. How this resembles the breasts of female quadrupeds after
the production of their young! and how extraordinary, that the male should
at this time give milk as well as the female! See Botanic Garden, Part II.
Note on Curcuma.

The late Mr. David Hume, in his posthumous works, places the powers of
generation much above those of our boasted reason; and adds, that reason
can only make a machine, as a clock or a ship, but the power of generation
makes the maker of the machine; and probably from having observed, that the
greatest part of the earth has been formed out of organic recrements; as
the immense beds of limestone, chalk, marble, from the shells of fish; and
the extensive provinces of clay, sandstone, ironstone, coals, from
decomposed vegetables; all which have been first produced by generation, or
by the secretions of organic life; he concludes that the world itself might
have been generated, rather than created; that is, it might have been
gradually produced from very small beginnings, increasing by the activity
of its inherent principles, rather than by a sudden evolution of the whole
by the Almighty fire.--What a magnificent idea of the infinite power of THE
GREAT ARCHITECT! THE CAUSE OF CAUSES! PARENT OF PARENTS! ENS ENTIUM!

For if we may compare infinities, it would seem to require a greater
infinity of power to cause the causes of effects, than to cause the effects
themselves. This idea is analogous to the improving excellence observable
in every part of the creation; such as in the progressive increase of the
solid or habitable parts of the earth from water; and in the progressive
increase of the wisdom and happiness of its inhabitants; and is consonant
to the idea of our present situation being a state of probation, which by
our exertions we may improve, and are consequently responsible for our
actions.

V. 1. The efficient cause of the various colours of the eggs of birds, and
of the air and feathers of animals, is a subject so curious, that I shall
beg to introduce it in this place. The colours of many animals seem adapted
to their purposes of concealing themselves either to avoid danger, or to
spring upon their prey. Thus the snake and wild cat, and leopard, are so
coloured as to resemble dark leaves and their lighter interstices; birds
resemble the colour of the brown ground, or the green hedges, which they
frequent; and moths and butterflies are coloured like the flowers which
they rob of their honey. Many instances are mentioned of this kind in
Botanic Garden, p. 2. Note on Rubia.

These colours have, however, in some instances another use, as the black
diverging area from the eyes of the swan; which, as his eyes are placed
less prominent than those of other birds, for the convenience of putting
down his head under water, prevents the rays of light from being reflected
into his eye, and thus dazzling his sight, both in air and beneath the
water; which must have happened, if that surface had been white like the
rest of his feathers.

There is a still more wonderful thing concerning these colours adapted to
the purpose of concealment; which is, that the eggs of birds are so
coloured as to resemble the colour of the adjacent objects and their
interfaces. The eggs of hedge-birds are greenish with dark spots; those of
crows and magpies, which are seen from beneath through wicker nests, are
white with dark spots; and those of larks and partridges are russet or
brown, like their nests or situations.

A thing still more astonishing is, that many animals in countries covered
with snow become white in winter, and are said to change their colour again
in the warmer months, as bears, hares, and partridges. Our domesticated
animals lose their natural colours, and break into great variety, as
horses, dogs, pigeons. The final cause of these colours is easily
understood, as they serve some purposes of the animal, but the efficient
cause would seem almost beyond conjecture.

First, the choroid coat of the eye, on which the semitransparent retina is
expanded, is of different colour in different animals; in those which feed
on grass it is green; from hence there would appear some connexion between
the colour of the choroid coat and of that constantly painted on the retina
by the green grass. Now, when the ground becomes covered with snow, it
would seem, that that action of the retina, which is called whiteness,
being constantly excited in the eye, may be gradually imitated by the
extremities of the nerves of touch, or rete mucosum of the skin. And if it
be supposed, that the action of the retina in producing the perception of
any colour consists in so disposing its own fibres or surface, as to
reflect those coloured rays only, and transmit the others like
soap-bubbles; then that part of the retina, which gives us the perception
of snow, must at that time be white; and that which gives us the perception
of grass, must be green.

Then if by the laws of imitation, as explained in Section XII. 3. 3. and
XXXIX. 6. the extremities of the nerves of touch in the rete mucosum be
induced into similar action, the skin or feathers, or hair, may in like
manner so dispose their extreme fibres, as to reflect white; for it is
evident, that all these parts were originally obedient to irritative
motions during their growth, and probably continue to be so; that those
irritative motions are not liable in a healthy state to be succeeded by
sensation; which however is no uncommon thing in their diseased state, or
in their infant state, as in plica polonica, and in very young
pen-feathers, which are still full of blood.

It was shewn in Section XV. on the Production of Ideas, that the moving
organ of sense in some circumstances resembled the object which produced
that motion. Hence it may be conceived, that the rete mucosum, which is the
extremity of the nerves of touch, may by imitating the motions of the
retina become coloured. And thus, like the fable of the camelion, all
animals may possess a tendency to be coloured somewhat like the colours
they most frequently inspect, and finally, that colours may be thus given
to the egg-shell by the imagination of the female parent; which shell is
previously a mucous membrane, indued with irritability, without which it
could not circulate its fluids, and increase in its bulk. Nor is this more
wonderful than that a single idea of imagination mould in an instant colour
the whole surface of the body of a bright scarlet, as in the blush of
shame, though by a very different process. In this intricate subject
nothing but loose analogical conjectures can be had, which may however lead
to future discoveries; but certain it is that both the change of the colour
of animals to white in the winters of snowy countries, and the spots on
birds eggs, must have some efficient cause; since the uniformity of their
production shews it cannot arise from a fortuitous concurrence of
circumstances; and how is this efficient cause to be detected, or
explained, but from its analogy to other animal facts?

2. The nutriment supplied by the female parent in viviparous animals to
their young progeny may be divided into three kinds, corresponding with the
age of the new creature. 1. The nutriment contained in the ovum as
previously prepared for the embryon in the ovary. 2. The liquor amnii
prepared for the fetus in the uterus, and in which it swims; and lastly,
the milk prepared in the pectoral glands for the new born-child. There is
reason to conclude that variety of changes may be produced in the new
animal from all these sources of nutriment, but particularly from the first
of them..

The organs of digestion and of sanguification in adults, and afterwards
those of secretion, prepare or separate the particles proper for
nourishment from other combinations of matter, or recombine them into new
kinds of matter, proper to excite into action the filaments, which absorb
or attract them by animal appetency. In this process we must attend not
only to the action of the living filament which receives a nutritive
particle to its bosom, but also to the kind of particle, in respect to
form, or size, or colour, or hardness, which is thus previously prepared
for it by digestion, sanguification, and secretion. Now as the first
filament of entity cannot be furnished with the preparative organs above
mentioned, the nutritive particles, which are at first to be received by
it, are prepared by the mother; and deposited in the ovum ready for its
reception. These nutritive particles must be supposed to differ in some
respects, when thus prepared by different animals. They may differ in size,
solidity, colour, and form; and yet may be sufficiently congenial to the
living filament, to which they are applied, as to excite its activity by
their stimulus, and its animal appetency to receive them, and to combine
them with itself into organization.

By this first nutriment thus prepared for the embryon is not meant the
liquor amnii, which is produced afterwards, nor the larger exterior parts
of the white of the egg; but the fluid prepared, I suppose, in the ovary of
viviparous animals, and that which immediately surrounds the cicatricula of
an impregnated egg, and is visible to the eye in a boiled one.

Now these ultimate particles of animal matter prepared by the glands of the
mother may be supposed to resemble the similar ultimate particles, which
were prepared for her own nourishment; that is, to the ultimate particles
of which her own organization consists. And that hence when these become
combined with a new embryon, which in its early state is not furnished with
stomach, or glands, to alter them; that new embryon will bear some
resemblance to the mother.

This seems to be the origin of the compound forms of mules, which evidently
partake of both parents, but principally of the male parent. In this
production of chimeras the antients seem to have indulged their fancies,
whence the sphinxes, griffins, dragons, centaurs, and minotaurs, which are
vanished from modern credulity.

It would seem, that in these unnatural conjunctions, when the nutriment
deposited by the female was so ill adapted to stimulate the living filament
derived from the male into action, and to be received; or embraced by it,
and combined with it into organization, as not to produce the organs
necessary to life, as the brain, or heart, or stomach, that no mule was
produced. Where all the parts necessary to life in these compound animals
were formed sufficiently perfect, except the parts of generation, those
animals were produced which are now called mules.

The formation of the organs of sexual generation, in contradistinction to
that by lateral buds, in vegetables, and in some animals, as the polypus,
the tænia, and the volvox, seems the chef d'oeuvre, the master-piece of
nature; as appears from many flying insects, as in moths and butterflies,
who seem to undergo a general change of their forms solely for the purpose
of sexual reproduction, and in all other animals this organ is not complete
till the maturity of the creature. Whence it happens that, in the
copulation of animals of different species, the parts necessary to life are
frequently completely formed; but those for the purpose of generation are
defective, as requiring a nicer organization; or more exact coincidence of
the particles of nutriment to the irritabilities or appetencies of the
original living filament. Whereas those mules, where all the parts could be
perfectly formed, may have been produced in early periods of time, and may
have added to the numbers of our various species of animals, as before
observed.

As this production of mules is a constant effect from the conjunction of
different species of animals, those between the horse and the female ass
always resembling the horse more than the ass; and those, on the contrary,
between the male ass and the mare, always resembling the ass more than the
mare; it cannot be ascribed to the imagination of the male animal which
cannot be supposed to operate so uniformly; but to the form of the first
nutritive particles, and to their peculiar stimulus exciting the living
filament to select and combine them with itself. There is a similar
uniformity of effect in respect to the colour of the progeny produced
between a white man, and a black woman, which, if I am well informed, is
always of the mulatto kind, or a mixture of the two; which may perhaps be
imputed to the peculiar form of the particles of nutriment supplied to the
embryon by the mother at the early period of its existence, and their
peculiar stimulus; as this effect, like that of the mule progeny above
treated of, is uniform and consistent, and cannot therefore be ascribed to
the imagination of either of the parents.

Dr. Thunberg observes, in his Journey to the Cape of Good Hope, that there
are some families, which have descended from blacks in the female line for
three generations. The first generation proceeding from an European, who
married a tawny slave, remains tawny, but approaches to a white complexion;
but the children of the third generation, mixed with Europeans, become
quite white, and are often remarkably beautiful. V. i. p. 112.

When the embryon has produced a placenta, and furnished itself with vessels
for selection of nutritious particles, and for oxygenation of them, no
great change in its form or colour is likely to be produced by the
particles of sustenance it now takes from the fluid, in which it is
immersed; because it has now acquired organs to alter or new combine them.
Hence it continues to grow, whether this fluid, in which it swims, be
formed by the uterus or by any other cavity of the body, as in
extra-uterine gestation; and which would seem to be produced by the
stimulus of the fetus on the sides of the cavity, where it is found, as
mentioned before. And thirdly, there is still less reason to expect any
unnatural change to happen to the child after its birth from the difference
of the milk it now takes; because it has acquired a stomach, and lungs, and
glands, of sufficient power to decompose and recombine the milk; and thus
to prepare from it the various kinds of nutritious particles, which the
appetencies of the various fibrils or nerves may require.

From all this reasoning I would conclude, that though the imagination of
the female may be supposed to affect the embryon by producing a difference
in its early nutriment; yet that no such power can affect it after it has
obtained a placenta, and other organs; which may select or change the food,
which is presented to it either in the liquor amnii, or in the milk. Now as
the eggs in pullets, like the seeds in vegetables, are produced gradually,
long before they are impregnated, it does not appear how any sudden effect
of imagination of the mother at the time of impregnation can produce any
considerable change in the nutriment already thus laid up for the expected
or desired embryon. And that hence any changes of the embryon, except those
uniform ones in the production of mules and mulattoes, more probably depend
on the imagination of the male parent. At the same time it seems manifest,
that those monstrous births, which consist in some deficiencies only, or
some redundancies of parts, originate from the deficiency or redundance of
the first nutriment prepared in the ovary, or in the part of the egg
immediately surrounding the cicatricula, as described above; and which
continues some time to excite the first living filament into action, after
the simple animal is completed; or ceases to excite it, before the complete
form is accomplished. The former of these circumstances is evinced by the
eggs with double yolks, which frequently happen to our domesticated
poultry, and which, I believe, are so formed before impregnation, but which
would be well worth attending to, both before and after impregnation; as it
is probable, something valuable on this subject might be learnt from them.
The latter circumstance, or that of deficiency of original nutriment, may
be deduced from reverse analogy.

There are, however, other kinds of monstrous births, which neither depend
on deficiency of parts, or supernumerary ones; nor are owing to the
conjunction of animals of different species; but which appear to be new
conformations, or new dispositions of parts in respect to each other, and
which, like the variation of colours and forms of our domesticated animals,
and probably the sexual parts of all animals, may depend on the imagination
of the male parent, which we now come to consider.

VI. 1. The nice actions of the extremities of our various glands are
exhibited in their various productions, which are believed to be made by
the gland, and not previously to exist as such in the blood.

Thus the glands, which constitute the liver, make bile; those of the
stomach make gastric acid; those beneath the jaw, saliva; those of the
ears, ear-wax; and the like. Every kind of gland must possess a peculiar
irritability, and probably a sensibility, at the early state of its
existence; and must be furnished with a nerve of sense, or of motion, to
perceive, and to select, and to combine the particles, which compose the
fluid it secretes. And this nerve of sense which perceives the different
articles which compose the blood, must at least be conceived to be as fine
and subtile an organ, as the optic or auditory nerve, which perceive light
or sound. See Sect. XIV. 9.

But in nothing is this nice action of the extremities of the blood-vessels
so wonderful, as in the production of contagious matter. A small drop of
variolous contagion diffused in the blood, or perhaps only by being
inserted beneath the cuticle, after a time, (as about a quarter of a
lunation,) excites the extreme vessels of the skin into certain motions,
which produce a similar contagious material, filling with it a thousand
pustules. So that by irritation, or by sensation in consequence of
irritation, or by association of motions, a material is formed by the
extremities of certain cutaneous vessels, exactly similar to the
stimulating material, which caused the irritation, or consequent sensation,
or association.

Many glands of the body have their motions, and in consequence their
secreted fluids, affected by pleasurable or painful ideas, since they are
in many instances influenced by sensitive associations, as well as by the
irritations of the particles of the passing blood. Thus the idea of meat,
excited in the minds of hungry dogs, by their sense of vision, or of smell,
increases the discharge of saliva, both in quantity and viscidity; as is
seen in its hanging down in threads from their mouths, as they stand round
a dinner-table. The sensations of pleasure, or of pain, of peculiar kinds,
excite in the same manner a great discharge of tears; which appear also to
be more saline at the time of their secretion, from their inflaming the
eyes and eye-lids. The paleness from fear, and the blush of shame, and of
joy, are other instances of the effects of painful, or pleasurable
sensations, on the extremities of the arterial system.

It is probable, that the pleasurable sensation excited in the stomach by
food, as well as its irritation, contributes to excite into action the
gastric glands, and to produce a greater secretion of their fluids. The
same probably occurs in the secretion of bile; that is, that the
pleasurable sensation excited in the stomach, affects this secretion by
sensitive association, as well as by irritative association.

And lastly it would seem, that all the glands in the body have their
secreted fluids affected, in quantity and quality, by the pleasurable or
painful sensations, which produce or accompany those secretions. And that
the pleasurable sensations arising from these secretions may constitute the
unnamed pleasure of exigence, which is contrary to what is meant by tedium
vitæ, or ennui; and by which we sometimes feel ourselves happy, without
being able to ascribe it to any mental cause, as after an agreeable meal,
or in the beginning of intoxication.

Now it would appear, that no secretion or excretion of fluid is attended
with so much agreeable sensation, as that of the semen; and it would thence
follow, that the glands, which perform this secretion, are more likely to
be much affected by their catenations with pleasurable sensations. This
circumstance is certain, that much more of this fluid is produced in a
given time, when the object of its exclusion is agreeable to the mind.

2. A forceable argument, which shews the necessity of pleasurable sensation
to copulation, is, that the act cannot be performed without it; it is
easily interrupted by the pain of fear or bashfulness; and no efforts of
volition or of irritation can effect this process, except such as induce
pleasurable ideas or sensations. See Sect. XXXIII. 1. 1.

A curious analogical circumstance attending hermaphrodite insects, as
snails and worms, still further illustrates this theory; if the snail or
worm could have impregnated itself, there might have been a saving of a
large male apparatus; but as this is not so ordered by nature, but each
snail and worm reciprocally receives and gives impregnation, it appears,
that a pleasurable excitation seems also to have been required.

This wonderful circumstance of many insects being hermaphrodites, and at
the same time not having power to impregnate themselves, is attended to by
Dr. Lister, in his Exercitationes Anatom. de Limacibus, p. 145; who,
amongst many other final causes, which he adduces to account for it, adds,
ut tam tristibus et frigidis animalibus majori cum voluptate perficiatur
venus.

There is, however, another final cause, to which this circumstance may be
imputed: it was observed above, that vegetable buds and bulbs, which are
produced without a mother, are always exact resemblances of their parent;
as appears in grafting fruit-trees, and in the flower-buds of the dioiceous
plants, which are always of the same sex on the same tree; hence those
hermaphrodite insects, if they could have produced young without a mother,
would not have been, capable of that change or improvement, which is seen
in all other animals, and in those vegetables, which are procreated by the
male embryon received and nourished by the female. And it is hence
probable, that if vegetables could only have been produced by buds and
bulbs, and not by sexual generation, that there would not at this time have
existed one thousandth part of their present number of species; which have
probably been originally mule-productions; nor could any kind of
improvement or change have happened to them, except by the difference of
soil or climate.

3. I conclude, that the imagination of the male at the time of copulation,
or at the time of the secretion of the semen, may so affect this secretion
by irritative or sensitive association, as described in No. 5. 1. of this
section, as to cause the production of similarity of form and of features,
with the distinction of sex; as the motions of the chissel of the turner
imitate or correspond with those of the ideas of the artist. It is not here
to be understood, that the first living fibre, which is to form an animal,
is produced with any similarity of form to the future animal; but with
propensities, or appetences, which shall produce by accretion of parts the
similarity of form, feature, or sex, corresponding to the imagination of
the father.

Our ideas are movements of the nerves of sense, as of the optic nerve in
recollecting visible ideas, suppose of a triangular piece of ivory. The
fine moving fibres of the retina act in a manner to which I give the name
of white; and this action is confined to a defined part of it; to which
figure I give the name of triangle. And it is a preceding pleasurable
sensation existing in my mind, which occasions me to produce this
particular motion of the retina, when no triangle is present. Now it is
probable, that the acting fibres of the ultimate terminations of the
secreting apertures of the vessels of the testes, are as fine as those of
the retina; and that they are liable to be thrown into that peculiar
action, which marks the sex of the secreted embryon, by sympathy with the
pleasurable motions of the nerves of vision or of touch; that is, with
certain ideas of imagination. From hence it would appear, that the world
has long been mistaken in ascribing great power to the imagination of the
female, whereas from this account of it, the real power of imagination, in
the act of generation, belongs solely to the male. See Sect. XII. 3. 3.

It may be objected to this theory, that a man may be supposed to have in
his mind, the idea of the form and features of the female, rather than his
own, and therefore there should be a greater number of female births. On
the contrary, the general idea of our own form occurs to every one almost
perpetually, and is termed consciousness of our existence, and thus may
effect, that the number of males surpasses that of females. See Sect. XV.
3. 4. and XVIII. 13. And what further confirms this idea is, that the male
children most frequently resemble the father in form, or feature, as well
as in sex; and the female most frequently resemble the mother, in feature,
and form, as well as in sex.

It may again be objected, if a female child sometimes resembles the father,
and a male child the mother, the ideas of the father, at the time of
procreation, must suddenly change from himself to the mother, at the very
instant, when the embryon is secreted or formed. This difficulty ceases
when we consider, that it is as easy to form an idea of feminine features
with male organs of reproduction, or of male features with female ones, as
the contrary; as we conceive the idea of a sphinx or mermaid as easily and
as distinctly as of a woman. Add to this, that at the time of procreation
the idea of the male organs, and of the female features, are often both
excited at the same time, by contact, or by vision.

I ask, in my turn, is the sex of the embryon produced by accident?
Certainly whatever is produced has a cause; but when this cause is too
minute for our comprehension, the effect is said in common language to
happen by chance, as in throwing a certain number on dice. Now what cause
can occasionally produce the male or female character of the embryon, but
the peculiar actions of those glands, which form the embryon? And what can
influence or govern these actions of the gland, but its associations or
catenations with other sensitive motions? Nor is this more extraordinary,
than that the catenations of irritative motions with the apparent
vibrations of objects at sea should produce sickness of the stomach; or
that a nauseous story should occasion vomiting.

4. An argument, which evinces the effect of imagination on the first
rudiment of the embryon, may be deduced from the production of some
peculiar monsters. Such, for instance, as those which have two heads joined
to one body, and those which have two bodies joined to one head; of which
frequent examples occur amongst our domesticated quadrupeds, and poultry.
It is absurd to suppose, that such forms could exist in primordial germs,
as explained in No. IV. 4. of this section. Nor is it possible, that such
deformities could be produced by the growth of two embryons, or living
filaments; which should afterwards adhere together; as the head and tail
part of different polypi are said to do (Blumenbach on Generation, Cadel,
London); since in that case one embryon, or living filament, must have
begun to form one part first, and the other another part first. But such
monstrous conformations become less difficult to comprehend, when they are
considered as an effect of the imagination, as before explained, on the
living filament at the time of its secretion; and that such duplicature of
limbs were produced by accretion of new parts, in consequence of
propensities, or animal appetencies thus acquired from the male parent.

For instance, I can conceive, if a turkey-cock should behold a rabbit, or a
frog, at the time of procreation, that it might happen, that a forcible or
even a pleasurable idea of the form of a quadruped might so occupy his
imagination, as to cause a tendency in the nascent filament to resemble
such a form, by the apposition of a duplicature of limbs. Experiments on
the production of mules and monsters would be worthy the attention of a
Spallanzani, and might throw much light upon this subject, which at present
must be explained by conjectural analogies.

The wonderful effect of imagination, both in the male and female parent, is
shewn in the production of a kind of milk in the crops both of the male and
female pigeons after the birth of their young, as observed by Mr. Hunter,
and mentioned before. To this should be added, that there are some
instances of men having had milk secreted in their breasts, and who have
given suck to children, as recorded by Mr. Buffon. This effect of
imagination, of both the male and female parent, seems to have been
attended to in very early times; Jacob is said not only to have placed rods
of trees, in part stripped of their bark, so as to appear spotted, but also
to have placed spotted lambs before the flocks, at the time of their
copulation. Genesis, chap. xxx. verse 40.

5. In respect to the imagination of the mother, it is difficult to
comprehend, how this can produce any alteration in the fetus, except by
affecting the nutriment laid up for its first reception, as described in
No. V. 2. of this section, or by affecting the nourishment or oxygenation
with which she supplies it afterwards. Perpetual anxiety may probably
affect the secretion of the liquor amnii into the uterus, as it enfeebles
the whole system; and sudden fear is a frequent cause of miscarriage; for
fear, contrary to joy, decreases for a time the action of the extremities
of the arterial system; hence sudden paleness succeeds, and a shrinking or
contraction of the vessels of the skin, and other membranes. By this
circumstance, I imagine, the terminations of the placental vessels are
detached from their adhesions, or insertions, into the membrane of the
uterus; and the death of the child succeeds, and consequent miscarriage.

Of this I recollect a remarkable instance, which could be ascribed to no
other cause, and which I shall therefore relate in few words. A healthy
young woman, about twenty years of age, had been about five months
pregnant, and going down into her cellar to draw some beer, was frighted by
a servant boy starting up from behind the barrel, where he had concealed
himself with design to alarm the maid-servant, for whom he mistook his
mistress. She came with difficulty up stairs, began to flood immediately,
and miscarried in a few hours. She has since borne several children, nor
ever had any tendency to miscarry of any of them.

6. In respect to the power of the imagination of the male over the form,
colour, and sex of the progeny, the following instances have fallen under
my observation, and may perhaps be found not very unfrequent, if they were
more attended to. I am acquainted with a gentleman, who has one child with
dark hair and eyes, though his lady and himself have light hair and eyes;
and their other four children are like their parents. On observing this
dissimilarity of one child to the others he assured me, that he believed it
was his own imagination, that produced the difference; and related to me
the following story. He said, that when his lady lay in of her third child,
he became attached to a daughter of one of his inferior tenants, and
offered her a bribe for her favours in vain; and afterwards a greater
bribe, and was equally unsuccessful; that the form of this girl dwelt much
in his mind for some weeks, and that the next child, which was the
dark-ey'd young lady above mentioned, was exceedingly like, in both
features and colour, to the young woman who refused his addresses.

To this instance I must add, that I have known two families, in which, on
account of an intailed estate in expectation, a male heir was most eagerly
desired by the father; and on the contrary, girls were produced to the
seventh in one, and to the ninth in another; and then they had each of them
a son. I conclude, that the great desire of a male heir by the father
produced rather a disagreeable than an agreeable sensation; and that his
ideas dwelt more on the fear of generating a female, than on the
pleasurable sensations or ideas of his own male form or organs at the time
of copulation, or of the secretion of the semen; and that hence the idea of
the female character was more present to his mind than that of the male
one; till at length in despair of generating a male these ideas ceased, and
those of the male character presided at the genial hour.

7. Hence I conclude, that the act of generation cannot exist without being
accompanied with ideas, and that a man must have at that time either a
general idea of his own male form, or of the form of his male organs; or an
idea of the female form, or of her organs; and that this marks the sex, and
the peculiar resemblances of the child to either parent. From whence it
would appear, that the phalli, which were hung round the necks of the Roman
ladies, or worn in their hair, might have effect in producing a greater
proportion of male children; and that the calipædia, or art of begetting
beautiful children, and of procreating either males or females, may be
taught by affecting the imagination of the male-parent; that is, by the
fine extremities of the seminal glands, imitating the actions of the organs
of sense either of sight or touch. But the manner of accomplishing this
cannot be unfolded with sufficient delicacy for the public eye; but may be
worth the attention of those, who are seriously interested in the
procreation of a male or female child.

_Recapitulation._

VII. 1. A certain quantity of nutritive particles are produced by the
female parent before impregnation, which require no further digestion,
secretion, or oxygenation. Such are seen in the unimpregnated eggs of
birds, and in the unimpregnated seed-vessels of vegetables.

2. A living filament is produced by the male, which being inserted amidst
these first nutritive particles, is stimulated into action by them; and in
consequence of this action, some of the nutritive particles are embraced,
and added to the original living filament; in the same manner as common
nutrition is performed in the adult animal.

3. Then this new organization, or additional part, becomes stimulated by
the nutritive particles in its vicinity, and sensation is now superadded to
irritation; and other particles are in consequence embraced, and added to
the living filament; as is seen in the new granulations of flesh in ulcers.

By the power of association, or by irritation, the parts already produced
continue their motions, and new ones are added by sensation, as above
mentioned; and lastly by volition, which last sensorial power is proved to
exist in the fetus in its maturer age, because it has evidently periods of
activity and of sleeping; which last is another word for a temporary
suspension of volition.

The original living filament may be conceived to possess a power of
repulsing the particles applied to certain parts of it, as well as of
embracing others, which stimulate other parts of it; as these powers exist
in different parts of the mature animal; thus the mouth of every gland
embraces the particles or fluid, which suits its appetency; and its
excretory duct repulses those particles, which are disagreeable to it.

4. Thus the outline or miniature of the new animal is produced gradually,
but in no great length of time; because the original nutritive particles
require no previous preparation by digestion, secretion, and oxygenation:
but require simply the selection and apposition, which is performed by the
living filament. Mr. Blumenbach says, that he possesses a human fetus of
only five weeks old, which is the size of a common bee, and has all the
features of the face, every finger, and every toe, complete; and in which
the organs of generation are distinctly seen. P. 76. In another fetus,
whose head was not larger than a pea, the whole of the basis of the skull
with all its depressions, apertures, and processes, were marked in the most
sharp and distinct manner, though without any ossification. Ib.

5. In some cases by the nutriment originally deposited by the mother the
filament acquires parts not exactly similar to those of the father, as in
the production of mules and mulattoes. In other cases, the deficiency of
this original nutriment causes deficiencies of the extreme parts of the
fetus, which are last formed, as the fingers, toes, lips. In other cases, a
duplicature of limbs are caused by the superabundance of this original
nutritive fluid, as in the double yolks of eggs, and the chickens from them
with four legs and four wings. But the production of other monsters, as
those with two heads, or with parts placed in wrong situations, seems to
arise from the imagination of the father being in some manner imitated by
the extreme vessels of the seminal glands; as the colours of the spots on
eggs, and the change of the colour of the hair and feathers of animals by
domestication, may be caused in the same manner by the imagination of the
mother.

6. The living filament is a part of the father, and has therefore certain
propensities, or appetencies, which belong to him; which may have been
gradually acquired during a million of generations, even from the infancy
of the habitable earth; and which now possesses such properties, as would
render, by the apposition of nutritious particles, the new fetus exactly
similar to the father; as occurs in the buds and bulbs of vegetables, and
in the polypus, and tænia or tape-worm. But as the first nutriment is
supplied by the mother, and therefore resembles such nutritive particles,
as have been used for her own nutriment or growth, the progeny takes in
part of the likeness of the mother.

Other similarity of the excitability, or of the form of the male parent,
such as the broad or narrow shoulders, or such as constitute certain
hereditary diseases, as scrophula, epilepsy, insanity, have their origin
produced in one or perhaps two generations; as in the progeny of those who
drink much vinous spirits; and those hereditary propensities cease again,
as I have observed, if one or two sober generations succeed; otherwise the
family becomes extinct.

This living filament from the father is also liable to have its
propensities, or appetencies, altered at the time of its production by the
imagination of the male parent; the extremities of the seminal glands
imitating the motions of the organs of sense; and thus the sex of the
embryon is produced; which may be thus made a male or a female by affecting
the imagination of the father at the time of impregnation. See Sect. XXXIX.
6. 3. and 7.

7. After the fetus is thus completely formed together with its umbilical
vessels and placenta, it is now supplied with a different kind of food, as
appears by the difference of consistency of the different parts of the
white of the egg, and of the liquor amnii, for it has now acquired organs
for digestion or secretion, and for oxygenation, though they are as yet
feeble; which can in some degree change, as well as select, the nutritive
particles, which are now presented to it. But may yet be affected by the
deficiency of the quantity of nutrition supplied by the mother, or by the
degree of oxygenation supplied to its placenta by the maternal blood.

The augmentation of the complete fetus by additional particles of nutriment
is not accomplished by distention only, but by apposition to every part
both external and internal; each of which acquires by animal appetencies
the new addition of the particles which it wants. And hence the enlarged
parts are kept similar to their prototypes, and may be said to be extended;
but their extension must be conceived only as a necessary consequence of
the enlargement of all their parts by apposition of new particles.

Hence the new apposition of parts is not produced by capillary attraction,
because the whole is extended; whereas capillary attraction would rather
tend to bring the sides of flexible tubes together, and not to distend
them. Nor is it produced by chemical affinities, for then a solution of
continuity would succeed, as when sugar is dissolved in water; but it is
produced by an animal process, which is the consequence of irritation, or
sensation; and which may be termed animal appetency.

This is further evinced from experiments, which have been instituted to
shew, that a living muscle of an animal body requires greater force to
break it, than a similar muscle of a dead body. Which evinces, that besides
the attraction of cohesion, which all matter possesses, and besides the
chemical attractions of affinities, which hold many bodies together, there
is an animal adhesion, which adds vigour to these common laws of the
inanimate world.

8. At the nativity of the child it deposits the placenta or gills, and by
expanding its lungs acquires more plentiful oxygenation from the currents
of air, which it must now continue perpetually to respire to the end of its
life; as it now quits the liquid element, in which it was produced, and
like the tadpole, when it changes into a frog, becomes an aerial animal.

9. As the habitable parts of the earth have been, and continue to be,
perpetually increasing by the production of sea-shells and corallines, and
by the recrements of other animals, and vegetables; so from the beginning
of the existence of this terraqueous globe, the animals, which inhabit it,
have constantly improved, and are still in a state of progressive
improvement.

This idea of the gradual generation of all things seems to have been as
familiar to the ancient philosophers as to the modern ones; and to have
given rise to the beautiful hieroglyphic figure of the [Greek: proton ôon],
or first great egg, produced by NIGHT, that is, whose origin is involved in
obscurity, and animated by [Greek: eros], that is, by DIVINE LOVE; from
whence proceeded all things which exist.

_Conclusion._

VIII. 1. Cause and effect may be considered as the progression, or
successive motions, of the parts of the great system of Nature. The state
of things at this moment is the effect of the state of things, which
existed in the preceding moment; and the cause of the state of things,
which shall exist in the next moment.

These causes and effects may be more easily comprehended, if motion be
considered as a change of the figure of a group of bodies, as proposed in
Sect. XIV. 2. 2. inasmuch as our ideas of visible or tangible objects are
more distinct, than our abstracted ideas of their motions. Now the change
of the configuration of the system of nature at this moment must be an
effect of the preceding configuration, for a change of configuration cannot
exist without a previous configuration; and the proximate cause of every
effect must immediately precede that effect. For example, a moving ivory
ball could not proceed onwards, unless it had previously began to proceed;
or unless an impulse had been previously given it; which previous motion or
impulse constitutes a part of the last situation of things.

As the effects produced in this moment of time become causes in the next,
we may consider the progressive motions of objects as a chain of causes
only; whose first link proceeded from the great Creator, and which have
existed from the beginning of the created universe, and are perpetually
proceeding.

2. These causes may be conveniently divided into two kinds, efficient and
inert causes, according with the two kinds of entity supposed to exist in
the natural world, which may be termed matter and spirit, as proposed in
Sect. I. and further treated of in Sect. XIV. The efficient causes of
motion, or new configuration, consist either of the principle of general
gravitation, which actuates the sun and planets; or of the principle of
particular gravitation, as in electricity, magnetism, heat; or of the
principle of chemical affinity, as in combustion, fermentation,
combination; or of the principle of organic life, as in the contraction of
vegetable and animal fibres. The inert causes of motion, or new
configuration, consist of the parts of matter, which are introduced within
the spheres of activity of the principles above described. Thus, when an
apple falls on the ground, the principle of gravitation is the efficient
cause, and the matter of the apple the inert cause. If a bar of iron be
approximated to a magnet, it may be termed the inert cause of the motion,
which brings these two bodies into contact; while the magnetic principle
may be termed the efficient cause. In the same manner the fibres, which
constitute the retina, may be called the inert cause of the motions of that
organ in vision, while the sensorial power may be termed the efficient
cause.

3. Another more common distribution of the perpetual chain of causes and
effects, which constitute the motions, or changing configurations, of the
natural world, is into active and passive. Thus, if a ball in motion
impinges against another ball at rest, and communicates its motion to it,
the former ball is said to act, and the latter to be acted upon. In this
sense of the words a magnet is said to attract iron; and the prick of a
spur to stimulate a horse into exertion; so that in this view of the works
of nature all things may be said either simply to exist, or to exist as
causes, or to exist as effects; that is, to exist either in an active or
passive state.

This distribution of objects, and their motions, or changes of position,
has been found so convenient for the purposes of common life, that on this
foundation rests the whole construction or theory of language. The names of
the things themselves are termed by grammarians Nouns, and their modes of
existence are termed Verbs. The nouns are divided into substantives, which
denote the principal things spoken of; and into adjectives, which denote
some circumstances, or less kinds of things, belonging to the former. The
verbs are divided into three kinds, such as denote the existence of things
simply, as, to be; or their existence in an active state, as, to eat; or
their existence in a passive state, as, to be eaten. Whence it appears,
that all languages consist only of nouns and verbs, with their
abbreviations for the greater expedition of communicating our thoughts; as
explained in the ingenious work of Mr. Horne Tooke, who has unfolded by a
single flash of light the whole theory of language, which had so long lain
buried beneath the learned lumber of the schools. Diversions of Purley.
Johnson. London.

4. A third division of causes has been into proximate and remote; these
have been much spoken of by the writers on medical subjects, but without
sufficient precision. If to proximate and remote causes we add proximate
and remote effects, we shall include four links of the perpetual chain of
causation; which will be more convenient for the discussion of many
philosophical subjects.

Thus if a particle of chyle be applied to the mouth of a lacteal vessel, it
may be termed the remote cause of the motions of the fibres, which compose
the mouth of that lacteal vessel; the sensorial power is the proximate
cause; the contraction of the fibres of the mouth of the vessel is the
proximate effect; and their embracing the particle of chyle is the remote
effect; and these four links of causation constitute absorption.

Thus when we attend to the rising sun, first the yellow rays of light
stimulate the sensorial power residing in the extremities of the optic
nerve, this is the remote cause. 2. The sensorial power is excited into a
state of activity, this is the proximate cause. 3. The fibrous extremities
of the optic nerve are contracted, this is the proximate effect. 4. A
pleasurable or painful sensation is produced in consequence of the
contraction of these fibres of the optic nerve, this is the remote effect;
and these four links of the chain of causation constitute the sensitive
idea, or what is commonly termed the sensation of the rising sun.

5. Other causes have been announced by medical writers under the names of
causa procatarctica, and causa proegumina, and causa sine quâ non. All
which are links more or less distant of the chain of remote causes.

To these must be added the final cause, so called by many authors, which
means the motive, for the accomplishment of which the preceding chain of
causes was put into action. The idea of a final cause, therefore, includes
that of a rational mind, which employs means to effect its purposes; thus
the desire of preserving himself from the pain of cold, which he has
frequently experienced, induces the savage to construct his hut; the fixing
stakes into the ground for walls, branches of trees for rafters, and turf
for a cover, are a series of successive voluntary exertions; which are so
many means to produce a certain effect. This effect of preserving himself
from cold, is termed the final cause; the construction of the hut is the
remote effect; the action of the muscular fibres of the man, is the
proximate effect; the volition, or activity of desire to preserve himself
from cold, is the proximate cause; and the pain of cold, which excited that
desire, is the remote cause.

6. This perpetual chain of causes and effects, whose first link is rivetted
to the throne of GOD, divides itself into innumerable diverging branches,
which, like the nerves arising from the brain, permeate the most minute and
most remote extremities of the system, diffusing motion and sensation to
the whole. As every cause is superior in power to the effect, which it has
produced, so our idea of the power of the Almighty Creator becomes more
elevated and sublime, as we trace the operations of nature from cause to
cause, climbing up the links of these chains of being, till we ascend to
the Great Source of all things.

Hence the modern discoveries in chemistry and in geology, by having traced
the causes of the combinations of bodies to remoter origins, as well as
those in astronomy, which dignify the present age, contribute to enlarge
and amplify our ideas of the power of the Great First Cause. And had those
ancient philosophers, who contended that the world was formed from atoms,
ascribed their combinations to certain immutable properties received from
the hand of the Creator, such as general gravitation, chemical affinity, or
animal appetency, instead of ascribing them to a blind chance; the doctrine
of atoms, as constituting or composing the material world by the variety of
their combinations, so far from leading the mind to atheism, would
strengthen the demonstration of the existence of a Deity, as the first
cause of all things; because the analogy resulting from our perpetual
experience of cause and effect would have thus been exemplified through
universal nature.

_The heavens declare the glory of _GOD_, and the firmament sheweth his
handywork! One day telleth another, and one night certifieth another; they
have neither speech nor language, yet their voice is gone forth into all
lands, and their words into the ends of the world. Manifold are thy works,
_O LORD!_ in wisdom hast thou made them all._ Psal. xix. civ.

       *       *       *       *       *

SECT. XL.

    On the OCULAR SPECTRA of Light and Colours, by Dr. R. W. Darwin, of
    Shrewsbury. Reprinted, by Permission, from the Philosophical
    Transactions, Vol. LXXVI. p. 313.

    _Spectra of four kinds._ 1. _Activity of the retina in vision._ 2.
    _Spectra from defect of sensibility._ 3. _Spectra from excess of
    sensibility_. 4. _Of direct ocular spectra._ 5. _Greater stimulus
    excites the retina into spasmodic action._ 6. _Of reverse ocular
    spectra._ 7. _Greater stimulus excites the retina into various
    successive spasmodic actions._ 8. _Into fixed spasmodic action._ 9.
    _Into temporary paralysis._ 10. _Miscellaneous remarks;_ 1. _Direct and
    reverse spectra at the same time. A spectral halo. Rule to predetermine
    the colours of spectra._ 2. _Variation of spectra from extraneous
    light._ 3. _Variation of spectra in number, figure, and remission._ 4.
    _Circulation of the blood in the eye is visible._ 5. _A new way of
    magnifying objects. Conclusion._

When any one has long and attentively looked at a bright object, as at the
setting sun, on closing his eyes, or removing them, an image, which
resembles in form the object he was attending to, continues some time to be
visible; this appearance in the eye we shall call the ocular spectrum of
that object.

These ocular spectra are of four kinds: 1st, Such as are owing to a less
sensibility of a defined part of the retina; or _spectra from defect of
sensibility._ 2d, Such as are owing to a greater sensibility of a defined
part of the retina; or _spectra from excess of sensibility_. 3d, Such as
resemble their object in its colour as well as form; which may be termed
_direct ocular spectra_. 4th, Such as are of a colour contrary to that of
their object; which may be termed _reverse ocular spectra_.

The laws of light have been most successfully explained by the great
Newton, and the perception of visible objects has been ably investigated by
the ingenious Dr. Berkeley and M. Malebranche; but these minute phenomena
of vision have yet been thought reducible to no theory, though many
philosophers have employed a considerable degree of attention upon them:
among these are Dr. Jurin, at the end of Dr. Smith's Optics; M. Æpinus, in
the Nov. Com. Petropol. V. 10.; M. Beguelin, in the Berlin Memoires, V. II.
1771; M. d'Arcy, in the Histoire de l'Acad. des Scienc. 1765; M. de la
Hire; and, lastly, the celebrated M. de Buffon, in the Memoires de l'Acad.
des Scien. who has termed them accidental colours, as if subjected to no
established laws, Ac. Par. 1743. M. p. 215.

I must here apprize the reader, that it is very difficult for different
people to give the same names to various shades of colours; whence, in the
following pages, something must be allowed, if on repeating the experiments
the colours here mentioned should not accurately correspond with his own
names of them.

I. _Activity of the Retina in Vision._

From the subsequent experiments it appears, that the retina is in an active
not in a passive state during the existence of these ocular spectra; and it
is thence to be concluded, that all vision is owing to the activity of this
organ.

1. Place a piece of red silk, about an inch in diameter, as in plate 1, at
Sect. III. 1., on a sheet of white paper, in a strong light; look steadily
upon it from about the distance of half a yard for a minute; then closing
your eyelids cover them with your hands, and a green spectrum will be seen
in your eyes, resembling in form the piece of red silk: after some time,
this spectrum will disappear and shortly reappear; and this alternately
three or four times, if the experiment is well made, till at length it
vanishes entirely.

2. Place on a sheet of white paper a circular piece of blue silk, about
four inches in diameter, in the sunshine; cover the center of this with a
circular piece of yellow silk, about three inches in diameter; and the
center of the yellow silk with a circle of pink silk, about two inches in
diameter; and the center of the pink silk with a circle of green silk,
about one inch in diameter; and the centre of this with a circle of indigo,
about half an inch in diameter; make a small speck with ink in the very
center of the whole, as in plate 3, at Sect. III. 3. 6.; look steadily for
a minute on this central spot, and then closing your eyes, and applying
your hand at about an inch distance before them, so as to prevent too much
or too little light from passing through the eyelids, you will see the most
beautiful circles of colours that imagination can conceive, which are most
resembled by the colours occasioned by pouring a drop or two of oil on a
still lake in a bright day; but these circular irises of colours are not
only different from the colours of the silks above mentioned, but are at
the same time perpetually changing as long as they exist.

3. When any one in the dark presses either corner of his eye with his
finger, and turns his eye away from his finger, he will see a circle of
colours like those in a peacock's tail: and a sudden flash of light is
excited in the eye by a stroke on it. (Newton's Opt. Q. 16.)

4. When any one turns round rapidly on one foot, till he becomes dizzy, and
falls upon the ground, the spectra of the ambient objects continue to
present themselves in rotation, or appear to librate, and he seems to
behold them for some time still in motion.

From all these experiments it appears, that the spectra in the eye are not
owing to the mechanical impulse of light impressed on the retina, nor to
its chemical combination with that organ, nor to the absorption and
emission of light, as is observed in many bodies; for in all these cases
the spectra must either remain uniformly, or gradually diminish; and
neither their alternate pretence and evanescence as in the first
experiment, nor the perpetual changes of their colours as in the second,
nor the flash of light or colours in the pressed eye as in the third, nor
the rotation or libration of the spectra as in the fourth, could exist.

It is not absurd to conceive, that the retina may be stimulated into
motion, as well as the red and white muscles which form our limbs and
vessels; since it consists of fibres, like those, intermixed with its
medullary substance. To evince this structure, the retina of an ox's eye
was suspended in a glass of warm water, and forcibly torn in a few places;
the edges of these parts appeared jagged and hairy, and did not contract,
and become smooth like simple mucus, when it is distended till it breaks;
which shews that it consists of fibres; and that its fibrous construction
became still more distinct to the sight, by adding some caustic alkali to
the water, as the adhering mucus was first eroded, and the hair-like fibres
remained floating in the vessel. Nor does the degree of transparency of the
retina invalidate the evidence of its fibrous structure, since Leeuwenhoek
has shewn that the crystalline humour itself consists of fibres. (Arcana
Naturæ, V. 1. p. 70.)

Hence it appears, that as the muscles have larger fibres intermixed with a
smaller quantity of nervous medulla, the organ of vision has a greater
quantity of nervous medulla intermixed with smaller fibres; and it is
probable that the locomotive muscles, as well as the vascular ones, of
microscopic animals have much greater tenuity than these of the retina.

And besides the similar laws, which will be shewn in this paper to govern
alike the actions of the retina and of the muscles, there are many other
analogies which exist between them. They are both originally excited into
action by irritations, both are nearly in the same quantity of time, are
alike strengthened or fatigued by exertion, are alike painful if excited
into action when they are in an inflamed state, are alike liable to
paralysis, and to the torpor of old age.

II. OF SPECTRA FROM DEFECT OF SENSIBILITY.

    _The retina is not so easily excited into action by less irritation
    after having been lately subjected to greater._

1. When any one passes from the bright daylight into a darkened room, the
irises of his eyes expand themselves to their utmost extent in a few
seconds of time; but it is very long before the optic nerve, after having
been stimulated by the greater light of the day, becomes sensible of the
less degree of it in the room; and, if the room is not too obscure, the
irises will again contract themselves in some degree, as the sensibility of
the retina returns.

2. Place about half an inch square of white paper on a black hat, and
looking steadily on the center of it for a minute, remove your eyes to a
sheet of white paper; and after a second or two a dark square will be seen
on the white paper, which will continue some time. A similar dark square
will be seen in the closed eye, if light be admitted through the eyelids.

So after looking at any luminous object of a small size, as at the sun, for
a short time, so as not much to fatigue the eyes, this part of the retina
becomes less sensible to smaller quantities of light; hence, when the eyes
are turned on other less luminous parts of the sky, a dark spot is seen
resembling the shape of the sun, or other luminous object which we last
beheld. This is the source of one kind of the dark-coloured _muscæ
volitantes_. If this dark spot lies above the center of the eye, we turn
our eyes that way, expecting to bring it into the center of the eye, that
we may view it more distinctly; and in this case the dark spectrum seems to
move upwards. If the dark spectrum is found beneath the centre of the eye,
we pursue it from the same motive, and it seems to move downwards. This has
given rise to various conjectures of something floating in the aqueous
humours of the eyes; but whoever, in attending to these spots, keeps his
eyes unmoved by looking steadily at the corner of a cloud, at the same time
that he observes the dark spectra, will be thoroughly convinced, that they
have no motion but what is given to them by the movement of our eyes in
pursuit of them. Sometimes the form of the spectrum, when it has been
received from a circular luminous body, will become oblong; and sometimes
it will be divided into two circular spectra, which is not owing to our
changing the angle made by the two optic axises, according to the distance
of the clouds or other bodies to which the spectrum is supposed to be
contiguous, but to other causes mentioned in No. X. 3. of this section. The
apparent size of it will also be variable according to its supposed
distance.

As these spectra are more easily observable when our eyes are a little
weakened by fatigue, it has frequently happened, that people of delicate
constitutions have been much alarmed at them, fearing a beginning decay of
their sight, and have thence fallen into the hands of ignorant oculists;
but I believe they never are a prelude to any other disease of the eye, and
that it is from habit alone, and our want of attention to them, that we do
not see them on all objects every hour of our lives. But as the nerves of
very weak people lose their sensibility, in the same manner as their
muscles lose their activity, by a small time of exertion, it frequently
happens, that sick people in the extreme debility of fevers are perpetually
employed in picking something from the bed-clothes, occasioned by their
mistaking the appearance of these _muscæ volitantes_ in their eyes.
Benvenuto Celini, an Italian artist, a man of strong abilities, relates,
that having passed the whole night on a distant mountain with some
companions and a conjurer, and performed many ceremonies to raise the
devil, on their return in the morning to Rome, and looking up when the sun
began to rise, they saw numerous devils run on the tops of the houses, as
they passed along; so much were the spectra of their weakened eyes
magnified by fear, and made subservient to the purposes of fraud or
superstition. (Life of Ben. Celini.)

3. Place a square inch of white paper on a large piece of straw-coloured
silk; look steadily some time on the white paper, and then move the centre
of your eyes on the silk, and a spectrum of the form of the paper will
appear on the silk, of a deeper yellow than the other part of it: for the
central part of the retina, having been some time exposed to the stimulus
of a greater quantity of white light, is become less sensible to a smaller
quantity of it, and therefore sees only the yellow rays in that part of the
straw-coloured silk.

Facts similar to these are observable in other parts of our system: thus,
if one hand be made warm, and the other exposed to the cold, and then both
of them immersed in subtepid water, the water is perceived warm to one
hand, and cold to the other; and we are not able to hear weak sounds for
some time after we have been exposed to loud ones; and we feel a chilliness
on coming into an atmosphere of temperate warmth, after having been some
time confined in a very warm room: and hence the stomach, and other organs
of digestion, of those who have been habituated to the greater stimulus of
spirituous liquor, are not excited into their due action by the less
stimulus of common food alone; of which the immediate consequence is
indigestion and hypochondriacism.

III. OF SPECTRA FROM EXCESS OF SENSIBILITY.

    _The retina is more easily excited into action by greater irritation
    after having been lately subjected to less._

1. If the eyes are closed, and covered perfectly with a hat, for a minute
or two, in a bright day; on removing the hat a red or crimson light is seen
through the eyelids. In this experiment the retina, after being some time
kept in the dark, becomes so sensible to a small quantity of light, as to
perceive distinctly the greater quantity of red rays than of others which
pass through the eyelids. A similar coloured light is seen to pass through
the edges of the fingers, when the open hand is opposed to the flame of a
candle.

2. If you look for some minutes steadily on a window in the beginning of
the evening twilight, or in a dark day, and then move your eyes a little,
so that those parts of the retina, on which the dark frame-work of the
window was delineated, may now fall on the glass part of it, many luminous
lines, representing the frame-work, will appear to lie across the glass
panes: for those parts of the retina, which were before least stimulated by
the dark frame-work, are now more sensible to light than the other parts of
the retina which were exposed to the more luminous parts of the window,

3. Make with ink on white paper a very black spot, about half an inch in
diameter, with a tail about an inch in length, so as to represent a
tadpole, as in plate 2, at Sect. III. 3. 3.; look steadily for a minute on
this spot, and, on moving the eye a little, the figure of the tadpole will
be seen on the white part of the paper, which figure of the tadpole will
appear whiter or more luminous than the other parts of the white paper; for
the part of the retina on which the tadpole was delineated, is now more
sensible to light, than the other parts of it, which were exposed to the
white paper. This experiment is mentioned by Dr. Irwin, but is not by him
ascribed to the true cause, namely, the greater sensibility of that part of
the retina which has been exposed to the black spot, than of the other
parts which had received the white field of paper, which is put beyond a
doubt by the next experiment.

4. On closing the eyes after viewing the black spot on the white paper, as
in the foregoing experiment, a red spot is seen of the form of the black
spot: for that part of the retina, on which the black spot was delineated,
being now more sensible to light than the other parts of it, which were
exposed to the white paper, is capable of perceiving the red rays which
penetrate the eyelids. If this experiment be made by the light of a tallow
candle, the spot will be yellow instead of red; for tallow candles abound
much with yellow light, which passes in greater quantity and force through
the eyelids than blue tight; hence the difficulty of distinguishing blue
and green by this kind of candle light. The colour of the spectrum may
possibly vary in the daylight, according to the different colour of the
meridian or the morning or evening light.

M. Beguelin, in the Berlin Memoires, V. II. 1771, observes, that, when he
held a book so that the sun shone upon his half-closed eyelids, the black
letters, which he had long inspected, became red, which must have been thus
occasioned. Those parts of the retina which had received for some time the
black letters, were so much more sensible than those parts which had been
opposed to the white paper, that to the former the red light, which passed
through the eyelids, was perceptible. There is a similar story told, I
think, in de Voltaire's Historical Works, of a Duke of Tuscany, who was
playing at dice with the general of a foreign army, and, believing he saw
bloody spots upon the dice, portended dreadful events, and retired in
confusion. The observer, after looking for a minute on the black spots of a
die, and carelessly closing his eyes, on a bright day; would see the image
of a die with red spots upon it, as above explained.

5. On emerging from a dark cavern, where we have long continued, the light
of a bright day becomes intolerable to the eye for a considerable time,
owing to the excess of sensibility existing in the eye, after having been
long exposed to little or no stimulus. This occasions us immediately to
contract the iris to its smallest aperture, which becomes again gradually
dilated, as the retina becomes accustomed to the greater stimulus of the
daylight.

The twinkling of a bright star, or of a distant candle in the night, is
perhaps owing to the same cause. While we continue to look upon these
luminous objects, their central parts gradually appear paler, owing to the
decreasing sensibility of the part of the retina exposed to their light;
whilst, at the same time, by the unsteadiness of the eye, the edges of them
are perpetually falling on parts of the retina that were just before
exposed to the darkness of the night, and therefore tenfold more sensible
to light than the part on which the star or candle had been for some time
delineated. This pains the eye in a similar manner as when we come suddenly
from a dark room into bright daylight, and gives the appearance of bright
scintillations. Hence the stars twinkle most when the night is darkest, and
do not twinkle through telescopes, as observed by Musschenbroeck; and it
will afterwards be seen why this twinkling is sometimes of different
colours when the object is very bright, as Mr. Melvill observed in looking
at Sirius. For the opinions of others on this subject, see Dr. Priestley's
valuable History of Light and Colours, p. 494.

Many facts observable in the animal system are similar to these; as the hot
glow occasioned by the usual warmth of the air, or our clothes, on coming
out of a cold bath; the pain of the fingers on approaching the fire after
having handled snow; and the inflamed heels from walking in snow. Hence
those who have been exposed to much cold have died on being brought to a
fire, or their limbs have become so much inflamed as to mortify. Hence much
food or wine given suddenly to those who have almost perished by hunger has
destroyed them; for all the organs of the famished body are now become so
much more irritable to the stimulus of food and wine, which they have long
been deprived of, that inflammation is excited, which terminates in
gangrene or fever.

IV. OF DIRECT OCULAR SPECTRA.

    _A quantity of stimulus somewhat greater than natural excites the
    retina into spasmodic action, which ceases in a few seconds._

A certain duration and energy of the stimulus of light and colours excites
the perfect action of the retina in vision; for very quick motions are
imperceptible to us, as well as very slow ones, as the whirling of a top,
or the shadow on a sun-dial. So perfect darkness does not affect the eye at
all; and excess of light produces pain, not vision.

1. When a fire-coal is whirled round in the dark, a lucid circle remains a
considerable time in the eye; and that with so much vivacity of light, that
it is mistaken for a continuance of the irritation of the object. In the
same manner, when a fiery meteor shoots across the night, it appears to
leave a long lucid train behind it, part of which, and perhaps sometimes
the whole, is owing to the continuance of the action of the retina after
having been thus vividly excited. This is beautifully illustrated by the
following experiment: fix a paper sail, three or four inches in diameter,
and made like that of a smoke jack, on a tube of pasteboard; on looking
through the tube at a distant prospect, some disjointed parts of it will be
seen through the narrow intervals between the sails; but as the fly begins
to revolve, these intervals appear larger; and when it revolves quicker,
the whole prospect is seen quite as distinct as if nothing intervened,
though less luminous.

[Illustration: Fig. 3.]

2. Look through a dark tube, about half a yard long, at the area of a
yellow circle of half an inch diameter, lying upon a blue area of double
that diameter, for half a minute; and on closing your eyes the colours of
the spectrum will appear similar to the two areas, as in fig. 3.; but if
the eye is kept too long upon them, the colours of the spectrum will be the
reverse of those upon the paper, that is, the internal circle will become
blue, and the external area yellow; hence some attention is required in
making this experiment.

3. Place the bright flame of a spermaceti candle before a black object in
the night; look steadily at it for a short time, till it is observed to
become somewhat paler; and on closing the eyes, and covering them
carefully, but not so as to compress them, the image of the blazing candle
will continue distinctly to be visible.

4. Look steadily, for a short time, at a window in a dark day, as in Exp.
2. Sect. III. and then closing your eyes, and covering them with your
hands, an exact delineation of the window remains for some time visible in
the eye. This experiment requires a little practice to make it succeed
well; since, if the eyes are fatigued by looking too long on the window, or
the day be too bright, the luminous parts of the window will appear dark in
the spectrum, and the dark parts of the frame-work will appear luminous, as
in Exp. 2. Sect. III. And it is even difficult for many, who first try this
experiment, to perceive the spectrum at all; for any hurry of mind, or even
too great attention to the spectrum itself, will disappoint them, till they
have had a little experience in attending to such small sensations.

The spectra described in this section, termed direct ocular spectra, are
produced without much fatigue of the eye; the irritation of the luminous
object being soon withdrawn, or its quantity of light being not so great as
to produce any degree of uneasiness in the organ of vision; which
distinguishes them from the next class of ocular spectra, which are the
consequence of fatigue. These direct spectra are best observed in such
circumstances that no light, but what comes from the object, can fall upon
the eye; as in looking through a tube, of half a yard long, and an inch
wide, at a yellow paper on the side of a room, the direct spectrum was
easily produced on closing the eye without taking it from the tube; but if
the lateral light is admitted through the eyelids, or by throwing the
spectrum on white paper, it becomes a reverse spectrum, as will be
explained below.

The other senses also retain for a time the impressions that have been made
upon them, or the actions they have been excited into. So if a hard body is
pressed upon the palm of the hand, as is practised in tricks of
legerdemain, it is not easy to distinguish for a few seconds whether it
remains or is removed; and tastes continue long to exist vividly in the
mouth, as the smoke of tobacco, or the taste of gentian, after the sapid
material is withdrawn.

    V. _A quantity of stimulus somewhat greater than the last mentioned
    excites the retina into spasmodic action, which ceases and recurs
    alternately._

1. On looking for a time on the setting sun, so as not greatly to fatigue
the sight, a yellow spectrum is seen when the eyes are closed and covered,
which continues for a time, and then disappears and recurs repeatedly
before it entirely vanishes. This yellow spectrum of the sun when the
eyelids are opened becomes blue; and if it is made to fall on the green
grass, or on other coloured objects, it varies its own colour by an
intermixture of theirs, as will be explained in another place.

2. Place a lighted spermaceti candle in the night about one foot from your
eye, and look steadily on the centre of the flame, till your eye becomes
much more fatigued than in Sect. IV. Exp. 3.; and on closing your eyes a
reddish spectrum will be perceived, which will cease and return
alternately.

The action of vomiting in like manner ceases, and is renewed by intervals,
although the emetic drug is thrown up with the first effort: so after-pains
continue some time after parturition; and the alternate pulsations of the
heart of a viper are renewed for some time after it is cleared from its
blood.

VI. OF REVERSE OCULAR SPECTRA.

    _The retina, after having been excited into action by a stimulus
    somewhat greater them the last mentioned falls into opposite spasmodic
    action._

The actions of every part of animal bodies may be advantageously compared
with each other. This strict analogy contributes much to the investigation
of truth; while those looser analogies, which compare the phenomena of
animal life with those of chemistry or mechanics, only serve to mislead our
inquiries.

When any of our larger muscles have been in long or in violent action, and
their antagonists have been at the same time extended, as soon as the
action of the former ceases, the limb is stretched the contrary way for our
ease, and a pandiculation or yawning takes place.

By the following observations it appears, that a similar circumstance
obtains in the organ of vision; after it has been fatigued by one kind of
action, it spontaneously falls into the opposite kind.

1. Place a piece of coloured silk, about an inch in diameter, on a sheet of
white paper, about half a yard from your eyes; look steadily upon it for a
minute; then remove your eyes upon another part of the white paper, and a
spectrum will be seen of the form of the silk thus inspected, but of a
colour opposite to it. A spectrum nearly similar will appear if the eyes
are closed, and the eyelids shaded by approaching the hand near them, so as
to permit some, but to prevent too much light falling on them.

  Red silk produced a green spectrum.
  Green produced a red one.
  Orange produced blue.
  Blue produced orange.
  Yellow produced violet.
  Violet produced yellow.

That in these experiments the colours of the spectra are the reverse of the
colours which occasioned them, may be seen by examining the third figure in
Sir Isaac Newton's Optics, L. II. p. 1, where those thin laminæ of air,
which reflected yellow, transmitted violet; those which reflected red,
transmitted a blue green; and so of the rest, agreeing with the experiments
above related.

2. These reverse spectra are similar to a colour, formed by a combination
of all the primary colours except that with which the eye has been fatigued
in making the experiment: thus the reverse spectrum of red must be such a
green as would be produced by a combination of all the other prismatic
colours. To evince this fact the following satisfactory experiment was
made. The prismatic colours were laid on a circular pasteboard wheel, about
four inches in diameter, in the proportions described in Dr. Priestley's
History of Light and Colours, pl. 12. fig. 83. except that the red
compartment was entirely left out, and the others proportionably extended
so as to complete the circle. Then, as the orange is a mixture of red and
yellow, and as the violet is a mixture of red and indigo, it became
necessary to put yellow on the wheel instead of orange, and indigo instead
of violet, that the experiment might more exactly quadrate with the theory
it was designed to establish or confute; because in gaining a green
spectrum from a red object, the eye is supposed to have become insensible
to red light. This wheel, by means of an axis, was made to whirl like a
top; and on its being put in motion, a green colour was produced,
corresponding with great exactness to the reverse spectrum of red.

3. In contemplating any one or these reverse spectra in the closed and
covered eye, it disappears and re-appears several times successively, till
at length it entirely vanishes, like the direct spectra in Sect. V.; but
with this additional circumstance, that when the spectrum becomes faint or
evanescent, it is instantly revived by removing the hand from before the
eyelids, so as to admit more light: because then not only the fatigued part
of the retina is inclined spontaneously to fall into motions of a contrary
direction, but being still sensible to all other rays of light, except that
with which it was lately fatigued, is by these rays at the same time
stimulated into those motions which form the reverse spectrum.

From these experiments there is reason to conclude, that the fatigued part
of the retina throws itself into a contrary mode of action, like oscitation
or pandiculation, as soon as the stimulus which has fatigued it is
withdrawn; and that it still remains sensible, that is, liable to be
excited into action by any other colours at the same time, except the
colour with which it has been fatigued.

    VII. _The retina after having been excited into action by a stimulus
    somewhat greater than the last mentioned falls into various successive
    spasmodic actions._

1. On looking at the meridian sun as long as the eyes can well bear its
brightness, the disk first becomes pale, with a luminous crescent, which
seems to librate from one edge of it to the other, owing to the
unsteadiness of the eye; then the whole phasis of the sun becomes blue,
surrounded with a white halo; and on closing the eyes, and covering them
with the hands, a yellow spectrum is seen, which in a little time changes
into a blue one.

M. de la Hire observed, after looking at the bright sun, that the
impression in his eye first assumed a yellow appearance, and then green,
and then blue; and wishes to ascribe these appearances to some affection of
the nerves. (Porterfield on the Eye, Vol. I. p. 313.)

2. After looking steadily on about an inch square of pink silk, placed on
white paper, in a bright sunshine, at the distance of a foot from my eyes,
and closing and covering my eyelids, the spectrum of the silk was at first
a dark green, and the spectrum of the white paper became of a pink. The
spectra then both disappeared; and then the internal spectrum was blue; and
then, after a second disappearance, became yellow, and lastly pink, whilst
the spectrum of the field varied into red and green.

These successions of different coloured spectra were not exactly the same
in the different experiments, though observed, as near as could be, with
the same quantity of light, and other similar circumstances; owing, I
suppose, to trying too many experiments at a time; so that the eye was not
quite free from the spectra of the colours which were previously attended
to.

The alternate exertions of the retina in the preceding section resembled
the oscitation or pandiculation of the muscles, as they were performed in
directions contrary to each other, and were the consequence of fatigue
rather than of pain. And in this they differ from the successive dissimilar
exertions of the retina, mentioned in this section, which resemble in
miniature the more violent agitations of the limbs in convulsive diseases,
as epilepsy, chorea S. Viti, and opisthotonos; all which diseases are
perhaps, at first, the consequence of pain, and have their periods
afterwards established by habit.

    VIII. _The retina, after having been excited into action by a stimulus
    somewhat greater than the last mentioned falls into a fixed spasmodic
    action, which continues for some days._

1. After having looked long at the meridian sun, in making some of the
preceding experiments, till the disks faded into a pale blue, I frequently
observed a bright blue spectrum of the sun on other objects all the next
and the succeeding day, which constantly occurred when I attended to it,
and frequently when I did not previously attend to it. When I closed and
covered my eyes, this appeared of a dull yellow; and at other times mixed
with the colours of other objects on which it was thrown. It may be
imagined, that this part of the retina was become insensible to white
light, and thence a bluish spectrum became visible on all luminous objects;
but as a yellowish spectrum was also seen in the closed and covered eye,
there can remain no doubt of this being the spectrum of the sun. A similar
appearance was observed by M. Æpinus, which he acknowledges he could give
no account of. (Nov. Com. Petrop. V. 10. p. 2. and 6.)

The locked jaw, and some cataleptic spasms, are resembled by this
phenomenon; and from hence we may learn the danger to the eye by inspecting
very luminous objects too long a time.

IX. _A quantity of stimulus greater than the preceding induces a temporary
paralysis of the organ of vision._

1. Place a circular piece of bright red silk, about half an inch in
diameter, on the middle of a sheet of white paper; lay them on the floor in
a bright sunshine, and fixing your eyes steadily on the center of the red
circle, for three or four minutes, at the distance of four or six feet from
the object, the red silk will gradually become paler, and finally cease to
appear red at all.

2. Similar to these are many other animal facts; as purges, opiates, and
even poisons, and contagious matter, cease to stimulate our system, after
we have been habituated to their use. So some people sleep undisturbed by a
clock, or even by a forge hammer in their neighbourhood: and not only
continued irritations, but violent exertions of any kind, are succeeded by
temporary paralysis. The arm drops down after violent action, and continues
for a time useless; and it is probable, that those who have perished
suddenly in swimming, or in scating on the ice, have owed their deaths to
the paralysis, or extreme fatigue, which succeeds every violent and
continued exertion.

X. MISCELLANEOUS REMARKS.

There were some circumstances occurred in making these experiments, which
were liable to alter the results of them, and which I shall here mention
for the assistance of others, who may wish to repeat them.

1. _Of direct and inverse spectra existing at the same time_; _of
reciprocal direct spectra_; _of a combination of direct and inverse
spectra_; _of a spectral halo_; _rules to pre-determine the colours of
spectra_.

a. When an area, about six inches square, of bright pink Indian paper, had
been viewed on an area, about a foot square, of white writing paper, the
internal spectrum in the closed eye was green, being the reverse spectrum
of the pink paper; and the external spectrum was pink, being the direct
spectrum of the pink paper. The same circumstance happened when the
internal area was white, and external one pink; that is, the internal
spectrum was pink, and the external one green. All the same appearances
occurred when the pink paper was laid on a black hat.

b. When six inches square of deep violet polished paper was viewed on a
foot square of white writing paper, the internal spectrum was yellow, being
the reverse spectrum of the violet paper, and the external one was violet,
being the direct spectrum of the violet paper.

c. When six inches square of pink paper was viewed on a foot square of blue
paper, the internal spectrum was blue, and the external spectrum was pink;
that is, the internal one was the direct spectrum of the external object,
and the external one was the direct spectrum of the internal object,
instead of their being each the reverse spectrum of the objects they
belonged to.

d. When six inches square of blue paper were viewed on a foot square of
yellow paper, the interior spectrum became a brilliant yellow, and the
exterior one a brilliant blue. The vivacity of the spectra was owing to
their being excited both by the stimulus of the interior and exterior
objects; so that the interior yellow spectrum was both the reverse spectrum
of the blue paper, and the direct one of the yellow paper; and the exterior
blue spectrum was both the reverse spectrum of the yellow paper, and the
direct one of the blue paper.

e. When the internal area was only a square half-inch of red paper, laid on
a square foot of dark violet paper, the internal spectrum was green, with a
reddish-blue halo. When the red internal paper was two inches square, the
internal spectrum was a deeper green, and the external one redder. When the
internal paper was six inches square, the spectrum of it became blue, and
the spectrum of the external paper was red.

f. When a square half-inch of blue paper was laid on a six-inch square of
yellow paper, the spectrum of the central paper in the closed eye was
yellow, incircled with a blue halo. On looking long on the meridian sun,
the disk fades into a pale blue surrounded with a whitish halo.

These circumstances, though they very much perplexed the experiments till
they were investigated, admit of a satisfactory explanation; for while the
rays from the bright internal object in exp. a. fall with their full force
on the center of the retina, and, by fatiguing that part of it, induce the
reverse spectrum, many scattered rays, from the same internal pink paper,
fall on the more external parts of the retina, but not in such quantity as
to occasion much fatigue, and hence induce the direct spectrum of the pink
colour in those parts of the eye. The same reverse and direct spectra occur
from the violet paper in exp. b.: and in exp. c. the scattered rays from
the central pink paper produce a direct spectrum of this colour on the
external parts of the eye, while the scattered rays from the external blue
paper produce a direct spectrum of that colour on the central part of the
eye, instead of these parts of the retina falling reciprocally into their
reverse spectra. In exp. d. the colours being the reverse of each other,
the scattered rays from the exterior object falling on the central parts of
the eye, and there exciting their direct spectrum, at the same time that
the retina was excited into a reverse spectrum by the central object, and
this direct and reverse spectrum being of similar colour, the superior
brilliancy of this spectrum was produced. In exp. e. the effect of various
quantities of stimulus on the retina, from the different respective sizes
of the internal and external areas, induced a spectrum of the internal area
in the center of the eye, combined of the reverse spectrum of that internal
area and the direct one of the external area, in various shades of colour,
from a pale green to a deep blue, with similar changes in the spectrum of
the external area. For the same reasons, when an internal bright object was
small, as in exp. f. instead of the whole of the spectrum of the external
object being reverse to the colour of the internal object, only a kind of
halo, or radiation of colour, similar to that of the internal object, was
spread a little way on the external spectrum. For this internal blue area
being so small, the scattered rays from it extended but a little way on the
image of the external area of yellow paper, and could therefore produce
only a blue halo round the yellow spectrum in the center.

If any one should suspect that the scattered rays from the exterior
coloured object do not intermix with the rays from the interior coloured
object, and thus affect the central part of the eye, let him look through
an opake tube, about two feet in length, and an inch in diameter, at a
coloured wall of a room with one eye, and with the other eye naked; and he
will find, that by shutting out the lateral light, the area of the wall
seen through a tube appears as if illuminated by the sunshine, compared
with the other parts of it; from whence arises the advantage of looking
through a dark tube at distant paintings.

Hence we may safely deduce the following rules to determine before-hand the
colours of all spectra. 1. The direct spectrum without any lateral light is
an evanescent representation of its object in the unfatigued eye. 2. With
some lateral light it becomes of a colour combined of the direct spectrum
of the central object, and of the circumjacent objects, in proportion to
their respective quantity and brilliancy. 3. The reverse spectrum without
lateral light is a representation in the fatigued eye of the form of its
objects, with such a colour as would be produced by all the primary
colours, except that of the object. 4. With lateral light the colour is
compounded of the reverse spectrum of the central object, and the direct
spectrum of the circumjacent objects, in proportion to their respective
quantity and brilliancy.

2. _Variation and vivacity of the spectra occasioned by extraneous light._

The reverse spectrum, as has been before explained, is similar to a colour,
formed by a combination of all the primary colours, except that with which
the eye has been fatigued in making the experiment: so the reverse spectrum
of red is such a green as would be produced by a combination of all the
other prismatic colours. Now it must be observed, that this reverse
spectrum of red is therefore the direct spectrum of a combination of all
the other prismatic colours, except the red; whence, on removing the eye
from a piece of red silk to a sheet of white paper, the green spectrum,
which is perceived, may either be called the reverse spectrum of the red
silk, or the direct spectrum of all the rays from the white paper, except
the red; for in truth it is both. Hence we see the reason why it is not
easy to gain a direct spectrum of any coloured object in the day-time,
where there is much lateral light, except of very bright objects, as of the
setting sun, or by looking through an opake tube; because the lateral
external light falling also on the central part of the retina, contributes
to induce the reverse spectrum, which is at the same time the direct
spectrum of that lateral light, deducting only the colour of the central
object which we have been viewing. And for the same reason, it is difficult
to gain the reverse spectrum, where there is no lateral light to contribute
to its formation. Thus, in looking through an opake tube on a yellow wall,
and closing my eye, without admitting any lateral light, the spectra were
all at first yellow; but at length changed into blue. And on looking in the
same manner on red paper, I did at length get a green spectrum; but they
were all at first red ones: and the same after looking at a candle in the
night.

The reverse spectrum was formed with greater facility when the eye was
thrown from the object on a sheet of white paper, or when light was
admitted through the closed eyelids; because not only the fatigued part of
the retina was inclined spontaneously to fall into motions of a contrary
direction; but being still sensible to all other rays of light except that
with which it was lately fatigued, was by these rays stimulated at the same
time into those motions which form the reverse spectrum. Hence, when, the
reverse spectrum of any colour became faint, it was wonderfully revived by
admitting more light through the eyelids, by removing the hand from before
them: and hence, on covering the closed eyelids, the spectrum would often
cease for a time, till the retina became sensible to the stimulus of the
smaller quantity of light, and then it recurred. Nor was the spectrum only
changed in vivacity, or in degree, by this admission of light through the
eyelids; but it frequently happened, after having viewed bright objects,
that the spectrum in the closed and covered eye was changed into a third
spectrum, when light was admitted through the eyelids: which third spectrum
was composed of such colours as could pass through the eyelids, except
those of the object. Thus, when an area of half an inch diameter of pink
paper was viewed on a sheet of white paper in the sunshine, the spectrum
with closed and covered eyes was green; but on removing the hands from
before the closed eyelids, the spectrum became yellow, and returned
instantly again to green, as often as the hands were applied to cover the
eyelids, or removed from them: for the retina being now insensible to red
light, the yellow rays passing through the eyelids in greater quantity than
the other colours, induced a yellow spectrum; whereas if the spectrum was
thrown on white paper, with the eyes open, it became only a lighter green.

Though a certain quantity of light facilitates the formation of the reverse
spectrum, a greater quantity prevents its formation, as the more powerful
stimulus excites even the fatigued parts of the eye into action; otherwise
we should see the spectrum of the last viewed object as often as we turn
our eyes. Hence the reverse spectra are best seen by gradually approaching
the hand near the closed eyelids to a certain distance only, which must be
varied with the brightness of the day, or the energy of the spectrum. Add
to this, that all dark spectra, as black, blue, or green, if light be
admitted through the eyelids, after they have been some time covered, give
reddish spectra, for the reasons given in Sect. III. Exp. 1.

From these circumstances of the extraneous light coinciding with the
spontaneous efforts of the fatigued retina to produce a reverse spectrum,
as was observed before, it is not easy to gain a direct spectrum, except of
objects brighter than the ambient light; such as a candle in the night, the
setting sun, or viewing a bright object through an opake tube; and then the
reverse spectrum is instantaneously produced by the admission of some
external light; and is as instantly converted again to the direct spectrum
by the exclusion of it. Thus, on looking at the setting sun, on closing the
eyes, and covering them, a yellow spectrum is seen, which is the direct
spectrum of the setting sun; but on opening the eyes on the sky, the yellow
spectrum is immediately changed into a blue one, which is the reverse
spectrum of the yellow sun, or the direct spectrum of the blue sky, or a
combination of both. And this is again transformed into a yellow one on
closing the eyes, and so reciprocally, as quick as the motions of the
opening and closing eyelids. Hence, when Mr. Melvill observed the
scintillations of the star Sirius to be sometimes coloured, these were
probably the direct spectrum of the blue sky on the parts of the retina
fatigued by the white light of the star. (Essays Physical and Literary, p.
81. V. 2.)

When a direct spectrum is thrown on colours darker than itself, it mixes
with them; as the yellow spectrum of the setting sun, thrown on the green
grass, becomes a greener yellow. But when a direct spectrum is thrown on
colours brighter than itself, it becomes instantly changed into the reverse
spectrum, which mixes with those brighter colours. So the yellow spectrum
of the setting sun thrown on the luminous sky becomes blue, and changes
with the colour or brightness of the clouds on which it appears. But the
reverse spectrum mixes with every kind of colour on which it is thrown,
whether brighter than itself or not; thus the reverse spectrum, obtained by
viewing a piece of yellow silk, when thrown on white paper, was a lucid
blue green; when thrown on black Turkey leather, becomes a deep violet. And
the spectrum of blue silk, thrown on white paper, was a light yellow; on
black silk was an obscure orange; and, the blue spectrum, obtained from
orange-coloured silk, thrown on yellow, became a green.

In these cases the retina is thrown into activity or sensation by the
stimulus of external colours, at the same time that it continues the
activity or sensation which forms the spectra; in the same manner as the
prismatic colours, painted on a whirling top, are seen to mix together.
When these colours of external objects are brighter than the direct
spectrum which is thrown upon them, they change it into the reverse
spectrum, like the admission of external light on a direct spectrum, as
explained above. When they are darker than the direct spectrum, they mix
with it, their weaker stimulus being inefficient to induce the reverse
spectrum.

3. _Variation of spectra in respect to number, and figure, and remission._

[Illustration: Fig. 4.]

When we look long and attentively at any object, the eye cannot always be
kept entirely motionless; hence, on inspecting a circular area of red silk
placed on white paper, a lucid crescent or edge is seen to librate on one
side or other of the red circle: for the exterior parts of the retina
sometimes falling on the edge of the central silk, and sometimes on the
white paper, are less fatigued with red light than the central part of the
retina, which is constantly, exposed to it; and therefore, when they fall
on the edge of the red silk, they perceive it more vividly. Afterwards,
when the eye becomes fatigued, a green spectrum in the form of a crescent
is seen to librate on one side or other of the central circle, as by the
unsteadiness of the eye a part of the fatigued retina falls on the white
paper; and as by the increasing fatigue of the eye the central part of the
silk appears paler, the edge on which the unfatigued part of the retina
occasionally falls will appear of a deeper red than the original silk,
because it is compared with the pale internal part of it. M. de Buffon in
making this experiment observed, that the red edge of the silk was not only
deeper coloured than the original silk; but, on his retreating a little
from it, it became oblong, and at length divided into two, which must have
been owing to his observing it either before or behind the point of
intersection of the two optic axises. Thus, if a pen is held up before a
distant candle, when we look intensely at the pen two candles are seen
behind it; when we look intensely at the candle two pens are seen. If the
sight be unsteady at the time of beholding the sun, even though one eye
only be used, many images of the sun will appear, or luminous lines, when
the eye is closed. And as some parts of these will be more vivid than
others, and some parts of them will be produced nearer the center of the
eye than others, these will disappear sooner than the others; and hence the
number and shape of these spectra of the sun will continually vary, as long
as they exist. The cause of some being more vivid than others, is the
unsteadiness of the eye of the beholder, so that some parts of the retina
have been longer exposed to the sunbeams. That some parts of a complicated
spectrum fade and return before other parts of it, the following experiment
evinces. Draw three concentric circles; the external one an inch and a half
in diameter, the middle one an inch, and the internal one half an inch;
colour the external and internal areas blue, and the remaining one yellow,
as in Fig. 4.; after having looked about a minute on the center of these
circles, in a bright light, the spectrum of the external area appears first
in the closed eye, then the middle area, and lastly the central one; and
then the central one disappears, and the others in inverted order. If
concentric circles of more colours are added, it produces the beautiful
ever changing spectrum in Sect. I. Exp. 2.

From hence it would seem, that the center of the eye produces quicker
remissions of spectra, owing perhaps to its greater sensibility; that is,
to its more energetic exertions. These remissions of spectra bear some
analogy to the tremors of the hands, and palpitations of the heart, of weak
people: and perhaps a criterion of the strength of any muscle or nerve may
be taken from the time it can be continued in exertion.

4. _Variation of spectra in respect to brilliancy; the visibility of the
circulation of the blood in the eye._

1. The meridian or evening light makes a difference in the colours of some
spectra; for as the sun descends, the red rays, which are less refrangible
by the convex atmosphere, abound in great quantity. Whence the spectrum of
the light parts of a window at this time, or early in the morning, is red;
and becomes blue either a little later or earlier; and white in the
meridian day; and is also variable from the colour of the clouds or sky
which are opposed to the window.

2. All these experiments are liable to be confounded, if they are made too
soon after each other, as the remaining spectrum will mix with the new
ones. This is a very troublesome circumstance to painters, who are obliged
to look long upon the same colour; and in particular to those whose eyes,
from natural debility, cannot long, continue the same kind of exertion. For
the same reason, in making these experiments, the result becomes much
varied if the eyes, after viewing any object, are removed on other objects
for but an instant of time, before we close them to view the spectrum; for
the light from the object, of which we had only a transient view, in the
very time of closing our eyes acts as a stimulus on the fatigued retina;
and for a time prevents the defined spectrum from appearing, or mixes its
own spectrum with it. Whence, after the eyelids are closed, either a dark
field, or some unexpected colours, are beheld for a few seconds, before the
desired spectrum becomes distinctly visible.

3. The length of time taken up in viewing an object, of which we are to
observe the spectrum, makes a great difference in the appearance of the
spectrum, not only in its vivacity, but in its colour; as the direct
spectrum of the central object, or of the circumjacent ones, and also the
reverse spectra of both, with their various combinations, as well as the
time of their duration in the eye, and of their remissions or alternations,
depend upon the degree of fatigue the retina is subjected to. The Chevalier
d'Arcy constructed a machine by which a coal of fire was whirled round in
the dark, and found, that when a luminous body made a revolution in eight
thirds of time, it presented to the eye a complete circle of fire; from
whence he concludes, that the impression continues on the organ about the
seventh part of a second. (Mem. de l'Acad. des Sc. 1765.) This, however, is
only to be considered as the shortest time of the duration of these direct
spectra; since in the fatigued eye both the direct and reverse spectra,
with their intermissions, appear to take up many seconds of time, and seem
very variable in proportion to the circumstances of fatigue or energy.

4. It sometimes happens, if the eyeballs have been rubbed hard with the
fingers, that lucid sparks are seen in quick motion amidst the spectrum we
are attending to. This is similar to the flashes of fire from a stroke on
the eye in fighting, and is resembled by the warmth and glow, which appears
upon the skin after friction, and is probably owing to an acceleration of
the arterial blood into the vessels emptied by the previous pressure. By
being accustomed to observe such small sensations in the eye, it is easy to
see the circulation of the blood in this organ. I have attended to this
frequently, when I have observed my eyes more than commonly sensible to
other spectra. The circulation may be seen either in both eyes at a time,
or only in one of them; for as a certain quantity of light is necessary to
produce this curious phenomenon, if one hand be brought nearer the closed
eyelids than the other, the circulation in that eye will for a time
disappear. For the easier viewing the circulation, it is sometimes
necessary to rub the eyes with a certain degree of force after they are
closed, and to hold the breath rather longer than is agreeable, which, by
accumulating more blood in the eye, facilitates the experiment; but in
general it may be seen distinctly after having examined other spectra with
your back to the light, till the eyes become weary; then having covered
your closed eyelids for half a minute, till the spectrum is faded away
which you were examining, turn your face to the light, and removing your
hands from the eyelids, by and by again shade them a little, and the
circulation becomes curiously distinct. The streams of blood are however
generally seen to unite, which shews it to be the venous circulation,
owing, I suppose, to the greater opacity of the colour of the blood in
these vessels; for this venous circulation is also much more easily seen by
the microscope in the tail of a tadpole.

5. _Variation of spectra in respect to distinctness and size; with a new
way of magnifying objects._

1. It was before observed, that when the two colours viewed together were
opposite to each other, as yellow and blue, red and green, &c. according to
the table of reflections and transmissions of light in Sir Isaac Newton's
Optics, B. II. Fig. 3. the spectra of those colours were of all others the
most brilliant, and best defined; because they were combined of the reverse
spectrum of one colour, and of the direct spectrum of the other. Hence, in
books printed with small types, or in the minute graduation of
thermometers, or of clock-faces, which are to be seen at a distance, if the
letters or figures are coloured with orange, and the ground with indigo; or
the letters with red, and the ground with green; or any other lucid colour
is used for the letters, the spectrum of which is similar to the colour of
the ground; such letters will be seen much more distinctly, and with less
confusion, than in black or white: for as the spectrum of the letter is the
same colour with the ground on which they are seen, the unsteadiness of the
eye in long attending to them will not produce coloured lines by the edges
of the letters, which is the principal cause of their confusion. The beauty
of colours lying in vicinity to each other, whose spectra are thus
reciprocally similar to each colour, is owing to this greater ease that the
eye experiences in beholding them distinctly; and it is probable, in the
organ of hearing, a similar circumstance may constitute the pleasure of
melody. Sir Isaac Newton observes, that gold and indigo were agreeable when
viewed together; and thinks there may be some analogy between the
sensations of light and sound. (Optics, Qu. 14.)

In viewing the spectra of bright objects, as of an area of red silk of half
an inch diameter on white paper, it is easy to magnify it to tenfold its
size: for if, when the spectrum is formed, you still keep your eye fixed on
the silk area, and remove it a few inches further from you, a green circle
is seen round the red silk: for the angle now subtended by the silk is less
than it was when the spectrum was formed, but that of the spectrum
continues the same, and our imagination places them at the same distance.
Thus when you view a spectrum on a sheet of white paper, if you approach
the paper to the eye, you may diminish it to a point; and if the paper is
made to recede from the eye, the spectrum will appear magnified in
proportion to the distance.

[Illustration: Fig. 5.]

I was surprised, and agreeably amused, with the following experiment. I
covered a paper about four inches square with yellow, and with a pen filled
with a blue colour wrote upon the middle of it the word BANKS in capitals,
as in Fig. 5, and sitting with my back to the sun, fixed my eyes for a
minute exactly on the center of the letter N in the middle of the word;
after closing my eyes, and shading them somewhat with my hand, the word was
distinctly seen in the spectrum in yellow letters on a blue field; and
then, on opening my eyes on a yellowish wall at twenty feet distance, the
magnified name of BANKS appeared written on the wall in golden characters.

_Conclusion._

It was observed by the learned M. Sauvage (Nosol. Method. Cl. VIII. Ord.
i.) that the pulsations of the optic artery might be perceived by looking
attentively on a white wall well illuminated. A kind of net-work, darker
than the other parts of the wall, appears and vanishes alternately with
every pulsation. This change of the colour of the wall he well ascribes to
the compression of the retina by the diastole of the artery. The various
colours produced in the eye by the pressure of the finger, or by a stroke
on it, as mentioned by Sir Isaac Newton, seem likewise to originate from
the unequal pressure on various parts of the retina. Now as Sir Isaac
Newton has shewn, that all the different colours are reflected or
transmitted by the laminæ of soap bubbles, or of air, according to their
different thickness or thinness, is it not probable, that the effect of the
activity of the retina may be to alter its thickness or thinness, so as
better to adapt it to reflect or transmit the colours which stimulate it
into action? May not muscular fibres exist in the retina for this purpose,
which may be less minute than the locomotive muscles of microscopic
animals? May not these muscular actions of the retina constitute the
sensation of light and colours; and the voluntary repetitions of them, when
the object is withdrawn, constitute our memory of them? And lastly, may not
the laws of the sensations of light, here investigated, be applicable to
all our other senses, and much contribute to elucidate many phenomena of
animal bodies both in their healthy and diseased state; and thus render
this investigation well worthy the attention of the physician, the
metaphysician, and the natural philosopher?

November 1, 1785.

       *       *       *       *       *

  Dum, Liber! astra petis volitans trepidantibus alis,
    Irruis immemori, parvula gutta, mari.
  Me quoque, me currente rotâ revolubilis ætas
    Volverit in tenebras,--i, Liber, ipse sequor.

       *       *       *       *       *

INDEX TO THE SECTIONS OF PART FIRST.


                  A.

  Abortion from fear, xxxix. 6. 5.
  Absorbent vessels, xxiii. 3. xxix. 1.
  ---- regurgitate their fluids, xxix. 2.
  ---- their valves, xxix. 2.
  ---- communicate with vena portarum, xxvii. 2.
  Absorption of solids, xxxiii. 3. 1. xxxvii.
  ---- of fluids in anasarca, xxxv. 1. 3.
  Accumulation of sensorial power, iv. 2. xii. 5. 2.
  Activity of system too great, cure of, xii. 6.
  ---- too small, cure of, xii. 7.
  Age, old, xii. 3. 1. xxxvii. 4.
  Ague-fit, xii. 7. 1. xxxii. 3. 4. xxxii. 9.
  ---- how cured by bark, xii. 3. 4.
  ---- periods, how occasioned, xii. 2. 3. xxxii. 3. 4.
  Ague cakes, xxxii. 7. xxxii. 9.
  Air, sense of fresh, xiv. 8.
  ---- injures ulcers, xxviii. 2.
  ---- injected into veins, xxxii. 5.
  Alcohol deleterious, xxx. 3.
  Alliterations, why agreeable, xxii. 2.
  Aloes in lessened doses, xii. 3. 1.
  American natives indolent, xxxi. 2.
  ---- narrow shouldered, xxxi. 1.
  Analogy intuitive, xvii. 3. 7.
  Animals less liable to madness, xxxiii. 1.
  ---- less liable to contagion, xxxiii. 1.
  ---- how to teach, xxii. 3. 2.
  ---- their similarity to each other, xxxix. 4. 8.
  ---- their changes after nativity, xxxix. 4. 8.
  ---- their changes before nativity, xxxix. 4. 8.
  ---- less liable to contagious diseases, why, xxxiii. 1. 5.
  ---- less liable to delirium and insanity, why, xxxiii. 1. 5.
  ---- easier to preserve than to reproduce, xxxvii.
  ---- food, distaste of, xxviii. 1.
  ---- appetency, xxxix. 4. 7.
  Antipathy, x. 2. 2.
  Aphthæ, xxviii.
  Apoplexy, xxxiv. 1. 7.
  ---- not from deficient irritation, xxxii. 2. 1.
  Appetites, xi. 2. 2. xiv. 8.
  Architecture, xxii. 2. xvi. 10.
  Arts, fine, xxii. 2.
  Asparagus, its smell in urine, xxix.
  Association defined, ii. 2. 11. iv. 7. v. 2.
  ---- associate motions, x.
  ---- stronger than irritative ones, xxiv. 2. 8.
  ---- formed before nativity, xi. 3.
  ---- with irritative ones, xxiv. 2. 8.
  ---- with retrograde ones, xxv. 7. xxv. 10. xxv. 15.
  ---- diseases from, xxxv.
  Asthma, xviii. 15.
  Attention, language of, xvi. 8. 6.
  Atrophy, xxviii.
  Aversion, origin of, xi. 2. 3.

                  B.

  Balance ourselves by vision, xx. 1.
  Bandage increases absorption, xxxiii. 3. 2.
  Barrenness, xxxvi. 2. 3.
  Battement of sounds, xx. 7.
  Bath, cold.  See Cold Bath.
  Beauty, sense of, xvi. 6. xxii. 2.
  Bile-ducts, xxx.
  ---- stones, xxx. 1. 3.
  ---- regurgitates into the blood, xxiv. 2. 7.
  ---- vomiting of, xxx. 1. 3.
  Birds of passage, xvi. 12.
  ---- nests of, xvi. 13.
  ---- colour of their eggs, xxxix. 5.
  Biting in pain, xxxiv. 1. 3.
  ---- of mad animals, xxxiv. 1. 3.
  Black spots on dice appear red, xl. 3.
  Bladder, communication of with the intestines, xxix. 3.
  ---- of fish, xxiv. 1. 4.
  Blood, transfusion of in nervous fevers, xxxii. 4.
  ---- deficiency of, xxxii. 2. and 4.
  ---- from the vena portarum into the intestines, xxvii. 2.
  ---- its momentum, xxxii. 5. 2.
  ---- momentum increased by venesection, xxxii. 5. 4.
  ---- drawn in nervous pains, xxxii. 5. 4.
  ---- its oxygenation, xxxviii.
  Breasts of men, xiv. 8.
  Breathing, how learnt, xvi. 4.
  Brutes differ from men, xi. 2. 3. xvi. 17.
  Brutes. See Animals.
  Buxton bath, why it feels warm, xii. 2. 1. xxxii. 3. 3.

                  C.

  Capillary vessels are glands, xxvi. 1.
  Catalepsy, xxxiv. 1. 5.
  Catarrh from cold skin, xxxv. 1. 3. xxxv. 2. 3.
  ---- from thin caps in sleep, xviii. 15.
  Catenation of motions defined, ii. 2. 11. iv. 7.
  ---- cause of them, xvii. 1. 3.
  ---- described, xvii.
  ---- continue some time after their production, xvii. 1. 3.
  ---- voluntary ones dissevered in sleep, xvii. 1. 12. xvii. 3. 7.
  Cathartics, external, their operation, xxix. 7. 6.
  Causation, animal, defined, ii. 2. 11. iv. 7.
  Cause of causes, xxxix. 4. 8.
  Causes inert and efficient, xxxix. 8. 2.
  ---- active and passive, xxxix. 8. 3.
  ---- proximate and remote, xxxix. 8. 4.
  Chick in the egg, oxygenation of, xxxviii. 2.
  Child riding on a stick, xxxiv. 2. 6.
  Chilness after meals, xxi. 3. xxxv. 1. 1.
  Cholera, case of, xxv. 13.
  Circulation in the eye visible, xl. 10. 4.
  Cold in the head, xii. 6. 5.
  ---- perceived by the teeth, xxxii. 3. 1. xiv. 6.
  ---- air, uses of in fevers, xxxii. 3. 3.
  ---- feet, produces coryza, xxxv. 2. 3. xxxv. 1. 3.
  ---- bath, why it strengthens, xxxii. 3. 2.
  ---- short and cold breathing in it, xxxii. 3. 2.
  ---- produces a fever-fit, xxxii. 3. 2.
  ---- fit of fever the consequence of hot fit, xxxii. 9. 3.
  ---- bathing in pulmonary hæmorrhage, xxvii. 1.
  ---- fits of fever, xxxii. 4. xxxii. 9. xvii. 3. 3.
  Colours of animals, efficient cause of, xxxix. 5. 1.
  ---- of eggs from female imagination, xxxix. 5. 1.
  ---- of the choroid coat of the eye, xxxix. 5. 1.
  ---- of birds nests, xvi. 13.
  Comparing ideas, xv. 3.
  Consciousness, xv. 3. 4.
  ---- in dreams, xviii. 13.
  Consent of parts. See Sympathy.
  Consumption, its temperament, xxxi. 1. and 2.
  ---- of dark-eyed patients, xxvii. 2.
  ---- of light-eyed patients, xxviii. 2.
  ---- is contagious, xxxiii. 2. 7.
  Contagion, xii. 3. 6. xix. 9. xxxiii. 2. 6. and 8. xxii. 3. 3.
  ---- does not enter the blood, xxxiii. 2. 10. xxii. 3. 3.
  Contraction and attraction, iv. 1.
  ---- of fibres produces sensation, iv. 5. xii. 1. 6.
  ---- continues some time, xii. 1. 5.
  ---- alternates with relaxation, xii. 1. 3.
  Convulsion, xvii. 1. 8. xxxiv. 1. 1. and 4. iii. 5. 8.
  ---- of particular muscles, xvii. 1. 8.
  ---- periods of, xxxvi. 3. 9.
  Coryza. See Catarrh.
  Cough, nervous, periods of, xxxvi. 3. 9.
  Cramp, xviii. 15. xxxiv. 1. 7.
  Critical days from lunations, xxxvi. 4.

                  D.

  Darkish room, why we see well in it, xii. 2. 1.
  Debility sensorial and stimulatory, xii. 2. 1.
  ---- direct and indirect of Dr. Brown, xii. 2. 1. xxxii. 3. 2.
  ---- See Weakness.
  ---- from drinking spirits, cure of, xii. 7. 8.
  ---- in fevers, cure of, xii. 7. 8.
  Deliberation, what, xxxiv. 1.
  Delirium, two kinds of, xxxiii. 1. 4. xxxiv. 2. 2.
  ---- cases of, iii. 5. 8.
  ---- prevented by dreams, xviii. 2.
  Desire, origin of, xi. 2. 3.
  Diabetes explained, xxix. 4.
  ---- with bloody urine, xxvii. 2.
  ---- in the night, xviii. 15.
  Diarrhoea, xxix. 4.
  Digestion, xxxiii. 1. xxxvii.
  ---- strengthened by emetics, xxxv. 1. 3.
  ---- strengthened by regular hours, why, xxxvi. 2. 1.
  Digitalis, use of in dropsy, xxix. 5. 2.
  Distention acts as a stimulus, xxxii. 4.
  ---- See Extension.
  Distinguishing, xv. 3.
  Diurnal circle of actions, xxv. 4.
  Doubting, xv. 3.
  Dreams, viii. 1. 2. xiv. 2. 5.
  ---- their inconsistency, xviii. 17.
  ---- no surprise in them, xviii. 17.
  ---- much novelty of combination, xviii. 9.
  Dropsies explained, xxix. 5. 1.
  Dropsy cured by insanity, xxxiv. 2. 7.
  ---- cure of, xxix. 5. 2.
  Drunkards weak till next day, xvii. 1. 7.
  ---- stammer, and stagger, and weep, xii. 4. 1. xxi. 4.
  ---- see objects double, why, xxi. 7.
  ---- become delirious, sleepy, stupid, xxi. 5.
  Drunkenness. See Intoxication, xxi.
  ---- diminished by attention, xxi. 8.
  Dyspnoea in cold bath, xxxii. 3. 2.

                  E.

  Ear, a good one, xvi. 10.
  ---- noise in, xx. 7.
  Eggs of frogs, fish, fowl, xxxix. 2.
  ---- of birds, why spotted, xxxix. 5.
  ---- with double yolk, xxxix. 4. 4.
  Electricity, xii. 1. xiv. 9.
  ---- jaundice cured by it, xxx. 1. 2.
  Embryon produced by the male, xxxix. 2.
  ---- consists of a living fibre, xxxix. 4.
  ---- absorbs nutriment, receives oxygen, xxxix. 1.
  ---- its actions and sensations, xvi. 2.
  Emetic. See Vomiting.
  Emotions, xi. 2. 2.
  Ennui, or tædium vitæ, xxxiv. 2. 3. xxxiii. 1. 1. xxxix. 6.
  Epileptic fits explained, xxxiv. 1. 4. xxvii. 2.
  ---- in sleep, why, xviii. 14. & 15.
  Equinoxial lunations, xxxii. 6.
  Excitability perpetually varies, xii. 1. 7.
  ---- synonymous to quantity of sensorial power, xii. 1. 7.
  Exercise, its use, xxxii. 5. 3.
  Exertion of sensorial power defined, xii. 2. 1.
  Existence in space, xiv. 2. 5.
  Extension, sense of, xiv. 7.
  Eyes become black in some epilepsies, xxvii. 2.

                  F.

  Face, flushing of after dinner, xxxv. 1. 1.
  ---- why first affected in small-pox, xxxv. 1. 1.
  ---- red from inflamed liver, xxxv. 2. 2.
  Fainting fits, xii. 7. 1. xiv. 7.
  Fear, language of, xvi. 8. 1.
  ---- a cause of fever, xxxii. 8.
  ---- cause of, xvii. 3. 7.
  Fetus.  See Embryon, xvi. 2. xxxix. 1.
  Fevers, irritative, xxxii. 1.
  ---- intermittent, xxxii. 1. xxxii. 3.
  ---- sensitive, xxxiii. 1.
  ---- not an effort of nature for relief, xxxii. 10.
  ---- paroxysms of, xii. 7. 1. xii. 2. 3. xii. 3. 5.
  ---- why some intermit and not others, xxxvi. 1.
  ---- cold fits of, xxxii. 4. xxxii. 9. xvii. 3. 3.
  ---- periods of, xxxvi. 3.
  ---- have solar or lunar periods, xxxii. 6.
  ---- source of the symptoms of, xxxii. 1.
  ---- prostration of strength in, xii. 4. 1. xxxii. 3. 2.
  ---- cure of, xii. 6. 1.
  ---- how cured by the bark, xii. 3. 4.
  ---- cured by increased volition, xii. 2. 4. xxxiv. 2. 8.
  ---- best quantity of stimulus in, xii. 7. 8.
  Fibres. See Muscles.
  Fibres, their mobility, xii. 1. 7. xii. 1. 1.
  ---- contractions of, vi. xii. 1. 1.
  ---- four classes of their motions, vi.
  ---- their motions distinguished from sensorial ones, v. 3.
  Figure, xiv. 2. 2. iii. 1.
  Fish, their knowledge, xvi. 14.
  Foxglove, its use in dropsies, xxix. 5. 2.
  ---- overdose of, xxv. 17.
  Free-will, xv. 3. 7.

                  G.

  Gall-stone, xxv. 17.
  ---- See Bile-stones.
  Generation, xxxiii. 1. xxxix.
  Gills of fish, xxxviii. 2.
  Glands, xxiii. 2.
  ---- conglobate glands, xxiii. 3.
  ---- have their peculiar stimulus, xi. 1.
  ---- their senses, xiv. 9. xxxix. 6.
  ---- invert their motions, xxv. 7.
  ---- increase their motions, xxv. 7.
  Golden rule for exhibiting wine, xii. 7. 8.
  ---- for leaving off wine, xii. 7. 8.
  Gout from inflamed liver, xxxv. 2. 2. xviii. 16. xxiv. 2. 8.
  ---- in the stomach, xxiv. 2. 8. xxv. 17.
  ---- why it returns after evacuations, xxxii. 4.
  ---- owing to vinous spirit only, xxi. 10.
  ---- periods of, xxxvi. 3. 6.
  Grinning in pain, xxxiv. 1. 3.
  Gyration on one foot, xx. 5. and 6.

                  H.

  Habit defined, ii. 2. 11. iv. 7.
  Hæmorrhages, periods of, xxxvi. 3. 11.
  ---- from paralysis of veins, xxvii. 1. and 2.
  Hair and nails, xxxix. 3. 2.
  ---- colour of, xxxix. 5. 1.
  Harmony, xxii. 2.
  Head-achs, xxxv. 2. 1.
  Hearing, xiv. 4.
  Heat, sense of, xiv. 6. xxxii. 3. 1.
  ---- produced by the glands, xxxii. 3.
  ---- external and internal, xxxii. 3. 1.
  ---- atmosphere of heat, xxxii. 3. 1.
  ---- increases during sleep, xviii. 15.
  Hemicrania, xxxv. 2. 1.
  ---- from decaying teeth, xxxv. 2. 1.
  Hepatitis, cause of, xxxv. 2. 3.
  Hereditary diseases, xxxix. 7. 6.
  Hermaphrodite insects, xxxix. 5.
  Herpes, xxviii. 2.
  ---- from inflamed kidney, xxxv. 2. 2.
  Hilarity from diurnal fever, xxxvi. 3. 1.
  Hunger, sense of, xiv. 8.
  Hydrophobia, xxii. 3. 3.
  Hypochondriacism, xxxiii. 1. 1. xxxiv. 2. 3.

                  I.

  Ideas defined, ii. 2. 7.
  ---- are motions of the organs of sense, iii. 4. xviii. 5. xviii. 10.
      xviii. 6.
  ---- analogous to muscular motions, iii. 5.
  ---- continue some time, xx. 6.
  ---- new ones cannot be invented, iii. 6. 1.
  ---- abstracted ones, iii. 6. 4.
  ---- inconsistent trains of, xviii. 17.
  ---- perish with the organ of sense, iii. 4. 4.
  ---- painful from inflammation of the organ, iii. 5. 5.
  ---- irritative ones, vii. 1. 4. vii. 3. 2. xv. 2. xx. 7.
  ---- of resemblance, contiguity, causation, viii. 3. 2. x. 3. 3.
  ---- resemble the figure and other properties of bodies, xiv. 2. 2.
  ---- received in tribes, xv. 1.
  ---- of the same sense easier combined, xv. 1. 1.
  ---- of reflection, xv. 1. 6. ii. 2. 12.
  Ideal presence, xv. 1. 7.
  Identity, xv. 3. 5. xviii. 13.
  Iliac passion, xxv. 15.
  Imagination, viii. 1. 2. xv. 1. 7. xv. 2. 2.
  ---- of the male forms the sex, xxxix. 6.
  Imitation, origin of, xii. 3. 3. xxxix. 5. xxii. 3. xvi. 7.
  Immaterial beings, xiv. 1. xiv. 2. 4.
  Impediment of speech, xvii. 1. 10. xvii. 2. 10.
  Infection. See Contagion.
  Inflammation, xii. 2. 3. xxxiii. 2. 2.
  ---- great vascular exertion in, xii. 2. 1.
  ---- not from pains from defect of stimulus, xxxiii. 2. 3.
  ---- of parts previously insensible, xii. 3. 7.
  ---- often distant from its cause, xxiv. 2. 8.
  ---- observes solar days, xxxii. 6.
  ---- of the eye, xxxiii. 3. 1.
  ---- of the bowels prevented by their continued action in sleep, xviii.
      2.
  Inoculation with blood, xxxiii. 2. 10.
  Insane people, their great strength, xii. 2. 1.
  Insanity (see Madness) pleasurable one, xxxiv. 2. 6.
  Insects, their knowledge, xvi. 15. and 16.
  ---- in the heads of calves, xxxix. 1.
  ---- class of, xxxix. 4. 8.
  Instinctive actions defined, xvi. 1.
  Intestines, xxv. 3.
  Intoxication relieves pain, why, xxi. 3.
  ---- from food after fatigue, xxi. 2.
  ---- diseases from it, xxi. 10.
  ---- See Drunkenness.
  Intuitive analogy, xvii. 3. 7.
  Invention, xv. 3. 3.
  Irritability increases during sleep, xviii. 15.
  Itching, xiv. 9.

                  J.

  Jaundice from paralysis of the liver, xxx. 1. 2.
  ---- cured by electricity, xxx. 1. 2.
  Jaw-locked, xxxiv. 1. 5.
  Judgment, xv. 3.

                  K.

  Knowledge of various animals, xvi. 11.

                  L.

  Lachrymal sack, xvi. 8. xxiv. 2. 2. and 7.
  Lacteals, paralysis of, xxviii.
  ---- See Absorbents.
  Lady playing on the harpsichord, xvii. 2.
  ---- distressed for her dying bird, xvii. 2. 10.
  Language, natural, its origin, xvi. 7. & 8.
  ---- of various passions described, xvi. 8.
  ---- artificial, of various animals, xvi. 9.
  ---- theory of, xxxix. 8. 3.
  Lapping of puppies, xvi. 4.
  Laughter explained, xxxiv. 1. 4.
  ---- from tickling, xvii. 3. 5. xxxiv. 1. 4.
  ---- from frivolous ideas, xxxiv. 1. 4. xviii. 12.
  Life, long, art of producing, xxxvii.
  Light has no momentum, iii. 3. 1.
  Liquor amnii, xvi. 2. xxxviii. 2.
  ---- is nutritious, xxxviii. 3.
  ---- frozen, xxxviii. 3.
  Liver, paralysis of, xxx. 1. 4.
  ---- large of geese, xxx. 1. 6.
  Love, sentimental, its origin, xvi. 6.
  ---- animal, xiv. 8. xvi. 5.
  Lunar periods affect diseases, xxxii. 6.
  Lust, xiv. 8. xvi. 5.
  Lymphatics, paralysis of, xxviii.
  ---- See Absorbents.

                  M.

  Mad-dog, bite of, xxii. 3. 3.
  Madness, xxxiv. 2. 1. xii. 2. 1.
  Magnetism, xii. 1. 1.
  Magnifying objects, new way of, xl. 10. 5.
  Male animals have teats, xxxix. 4. 8.
  ---- pigeons give milk, xxxix. 4. 8.
  Man distinguished from brutes, xi. 2. 3. xvi. 17.
  Material world, xiv. 1. xiv. 2. 5. xviii. 7.
  Matter, penetrability of, xiv. 2. 3.
  ---- purulent, xxxiii. 2. 4.
  Measles, xxxiii. 2. 9.
  Membranes, xxvi. 2.
  Memory defined, ii. 2. 10. xv. 1. 7. xv. 3.
  Menstruation by lunar periods, xxxii. 6.
  Miscarriage from fear, xxxix. 6. 5.
  Mobility of fibres, xii. 1. 7.
  Momentum of the blood, xxxii. 5. 2.
  ---- sometimes increased by venesection, xxxii. 5. 4.
  Monsters, xxxix. 4. 4. and 5. 2.
  ---- without heads, xxxviii. 3.
  Moon and sun, their influence, xxxii. 6.
  Mortification, xxxiii. 3. 3.
  Motion is either cause or effect, i. xiv. 2. 2.
  ---- primary and secondary, i.
  ---- animal, i. iii. 1.
  ---- propensity to, xxii. 1.
  ---- animal, continue some time after their production, xvii. 1. 3.
  ---- defined, a variation of figure, iii. 1. xiv. 2. 2. xxxix. 8.
  Mucus, experiments on, xxvi. 1.
  ---- secretion of, xxvi. 2.
  Mules, xxxix. 4. 5. and 6. xxxix. 5. 2.
  Mule plants, xxxix. 2.
  Muscæ volitantes, xl. 2.
  Muscles constitute an organ of sense, xiv. 7. ii. 2. 4.
  ---- stimulated by extension, xi. 1. xiv. 7.
  ---- contract by spirit of animation, xii. 1. 1. and 3.
  Music, xvi. 10. xxii. 2.
  Musical time, why agreeable, xii. 3. 3.

                  N.

  Nausea, xxv. 6.
  Nerves and brain, ii. 2. 3.
  ---- extremities of form the whole system, xxxvii. 3.
  ---- are not changed with age, xxxvii. 4.
  Nervous pains defined, xxxiv. 1. 1.
  Number defined, xiv. 2. 2.
  Nutriment for the embryon, xxxix. 5. 2.
  Nutrition owing to stimulus, xxxvii. 3.
  ---- by animal selection, xxxvii. 3.
  ---- when the fibres are elongated, xxxvii. 3.
  ---- like inflammation, xxxvii. 3.

                  O.

  Objects long viewed become faint, iii. 3. 2.
  Ocular spectra, xl.
  Oil externally in diabætes, xxix. 4.
  Old age from inirritability, xxxvii.
  Opium is stimulant, xxxii. 2. 2.
  ---- promotes absorption after evacuation, xxxiii. 3. 1.
  ---- in increasing doses, xii. 3. 1.
  Organs of sense, ii. 2. 5. and 6.
  Organs when destroyed cease to produce ideas, iii. 4. 4.
  Organic particles of Buffon, xxxvii. 3. xxxix. 3. 3.
  Organ-pipes, xx. 7.
  Oxygenation of the blood, xxxviii.

                  P.

  Pain from excess and defect of motion, iv. 5. xii. 5. 3. xxxiv. 1. xxxv.
      2. 1.
  ---- not felt during exertion, xxxiv. 1. 2.
  ---- from greater contraction of fibres, xii. 1. 6.
  ---- from accumulation of sensorial power, xii. 5. 3.
  ---- from light, pressure, heat, caustics, xiv. 9.
  ---- in epilepsy, xxxv. 2. 1.
  ---- distant from its cause, xxiv. 2. 8.
  ---- from stone in the bladder, xxxv. 2. 1.
  ---- of head and back from defect, xxxii. 3.
  ---- from a gall-stone, xxxv. 2. 1. xxv. 17.
  ---- of the stomach in gout, xxv. 17.
  ---- of shoulder in hepatitis, xxxv. 2. 4.
  ---- produces volition, iv. 6.
  Paleness in cold fit, xxxii. 3. 2.
  Palsies explained, xxxiv. 1. 7.
  Paralytic limbs stretch from irritation, vii. 1. 3.
  ---- patients move their sound limb much, xii. 5. 1.
  Paralysis from great exertion, xii. 4. 6.
  ---- from less exertion, xii. 5. 6.
  ---- of the lacteals, xxviii.
  ---- of the liver, xxx. 1. 4.
  ---- of the right arm, why, xxxiv. 1. 7.
  ---- of the veins, xxvii. 2.
  Particles of matter will not approach, xii. 1. 1.
  Passions, xi. 2. 2.
  ---- connate, xvi. 1.
  Pecking of chickens, xvi. 4.
  Perception defined, ii. 2. 8. xv. 3. 1.
  Periods of agues, how formed, xxxii. 3. 4.
  ---- of diseases, xxxvi.
  ---- of natural actions and of diseased actions, xxxvi.
  Perspiration in fever-fits, xxxii. 9. See Sweat.
  Petechiæ, xxvii. 2.
  Pigeons secrete milk in their stomachs, xxxix. 4. 8.
  Piles, xxvii. 2.
  Placenta a pulmonary organ, xxxviii. 2.
  Pleasure of life, xxxiii. 1. xxxix. 5.
  ---- from greater fibrous contractions, xii. 1. 6.
  ---- what kind causes laughter, xxxiv. 1. 4.
  ---- what kind causes sleep, xxxiv. 1. 4.
  Pleurisy, periods of, xxxvi. 3. 7.
  ---- cause of, xxxv. 2. 3.
  Prometheus, story of, xxx. 3.
  Prostration of strength in fevers, xii. 4. 1.
  Pupils of the eyes large, xxxi. 1.
  Pulse quick in fevers with debility, xii. 1. 4. xii. 5. 4. xxxii. 2. 1.
  ---- in fevers with strength, xxxii. 2.
  ---- from defect of blood, xxxii. 2. 3. xii. 1. 4.
  ---- weak from emetics, xxv. 17.

                  Q.

  Quack advertisements injurious. Preface.
  Quadrupeds have no sanguiferous lochia, xxxviii. 2.
  ---- have nothing similar to the yolk of egg, xxxix. 1.

                  R.

  Rhaphania, periods of, xxxvi. 3. 9.
  Reason, ix. 1. 2. xv. 3.
  Reasoning, xv. 3.
  Recollection, ii. 2. 10. ix. 1. 2. xv. 2. 3.
  Relaxation and bracing, xxxii. 3. 2.
  Repetition, why agreeable, xii. 3. 3. xxii. 2.
  Respiration affected by attention, xxxvi. 2. 1.
  Restlessness in fevers, xxxiv. 1. 2.
  Retrograde motions, xii. 5. 5. xxv. 6. xxix. 11.
  ---- of the stomach, xxv. 6.
  ---- of the skin, xxv. 9.
  ---- of fluids, how distinguished, xxix. 8.
  ---- how caused, xxix. 11. 5.
  ---- vegetable motions, xxix. 9.
  Retina is fibrous, iii. 2. xl. 1.
  ---- is active in vision, iii. 3. xl. 1.
  ---- excited into spasmodic motions, xl. 7.
  ---- is sensible during sleep, xviii. 5. xix. 8.
  Reverie, xix. 1. xxxiv. 3.
  ---- case of a sleep-walker, xix. 2.
  ---- is an epileptic disease, xix. 9.
  Rhymes in poetry, why agreeable, xxii. 2.
  Rheumatism, three kinds of, xxvi. 3.
  Rocking young children, xxi. 3.
  Ruminating animals, xxv. 1.

                  S.

  Saliva produced by mercury, xxiv. 1.
  ---- by food, xxiv. 1. 1.
  ---- by ideas, xxiv. 1. 2. and 5.
  ---- by disordered volition, xxiv. 1. 7.
  Schirrous tumours revive, xii. 2. 2.
  Screaming in pain, xxxiv. 1. 3.
  Scrophula, its temperament, xxxi. 1.
  ---- xxviii. 2. xxxix. 4. 5.
  Scurvy of the lungs, xxvii. 2.
  Sea-sickness, xx. 4.
  ---- stopped by attention, xx. 5.
  Secretion, xxxiii. 1. xxxvii.
  ---- increased during sleep, xviii. 16.
  Seeds require oxygenation, xxxviii. 2.
  Sensation defined, ii. 2. 9. v. 2. xxxix. 8. 4.
  ---- diseases of, xxxiii.
  ---- from fibrous contractions, iv. 5. xii. 1. 6.
  ---- in an amputated limb, iii. 6. 3.
  ---- affects the whole sensorium, xi. 2.
  ---- produces volition, iv. 6.
  Sensibility increases during sleep, xviii. 15.
  Sensitive motions, viii. xxxiii. 2. xxxiv. 1.
  ---- fevers of two kinds, xxxiii. 1. 2.
  ---- ideas, xv. 2. 2.
  Sensorium defined, ii. 2. 1.
  Senses correct one another, xviii. 7.
  ---- distinguished from appetites, xxxiv. 1. 1.
  Sensorial power. See Spirit of Animation.
  ---- great expence of in the vital motions, xxxii. 3. 2.
  ---- two kinds of excited in sensitive fevers, xxxiii. 1. 3.
  ---- powers defined, v. 1.
  ---- motions distinguished from fibrous motions, v. 3.
  ---- not much, accumulated in sleep, xviii. 2.
  ---- powers, accumulation of, xii. 5. 1.
  ---- exhaustion of, xii. 4. 1.
  ---- wasted below natural in hot fits, xxxii. 9. 3.
  ---- less exertion of produces pain, xii. 5. 3.
  ---- less quantity of it, xii. 5. 4.
  Sensual motions distinguished from muscular, ii. 2. 7.
  Sex owing to the imagination of the father, xxxix. 7. 6. xxxix. 6. 3.
      xxxix. 6. 7. xxxix. 5.
  Shingles from inflamed kidney, xxxv. 2. 2.
  Shoulders broad, xxxi. 1. xxxix. 7. 6.
  Shuddering from cold, xxxiv. 1. 1. and 2.
  Sight, its accuracy in men, xvi. 6.
  Skin, skurf on it, xxvi. 1.
  Sleep suspends volition, xviii. 1.
  ---- defined, xviii. 21.
  ---- remote causes, xviii. 20.
  ---- sensation continues in it, xviii. 2.
  ---- from food, xxi. 1.
  ---- from rocking, uniform sounds, xxi. 1.
  ---- from wine and opium, xxi. 3.
  ---- why it invigorates, xii. 5. 1.
  ---- pulse slower and fuller, xxxii. 2. 2.
  ---- interrupted, xxvii. 2.
  ---- from breathing less oxygene, xviii. 20.
  ---- from being whirled on a millstone, xviii. 20.
  ---- from application of cold, xviii. 20.
  ---- induced by regular hours, xxxvi. 2. 2.
  Sleeping animals, xii. 2. 2.
  Sleep-walkers. See Reverie, xix. 1.
  Small-pox, xxxiii. 2. 6. xxxix. 6. 1.
  ---- eruption first on the face, why, xxxv. 1. 1. xxxiii. 2. 10.
  ---- the blood will not infect, xxxiii. 2. 10.
  ---- obeys lunations, xxxvi. 4.
  Smell, xiv. 5. xvi. 5.
  Smiling, origin of, xvi. 8. 4.
  Solidity, xiv. 2. 1.
  Somnambulation. See Reverie, xix. 1.
  Space, xiv. 2. 2.
  Spasm, doctrine of, xxxii. 10.
  Spectra, ocular, xl.
  ---- mistaken for spectres, xl. 2.
  ---- vary from long inspection, iii. 3. 5.
  Spirit of animation. See Sensorial Power.
  ---- of animation causes fibrous contraction, iv. 2. ii. 2. 1. xiv. 2. 4.
  ---- possesses solidity, figure, and other properties of matter, xiv. 2.
      4.
  Spirits and angels, xiv. 2. 4.
  Stammering explained, xvii. 1. 10. xvii. 2. 10.
  Stimulus defined, ii. 2. 13. iv. 4. xii. 2. 1.
  ---- of various kinds, xi. 1.
  ---- with lessened effect, xii. 3. 1.
  ---- with greater effect, xii. 3. 3.
  ---- ceases to produce sensation, xii. 3. 6.
  Stomach and intestines, xxv.
  ---- inverted by great stimulus, xxv. 6.
  ---- its actions decreased in vomiting, xxxv. 1. 3.
  ---- a blow on it occasions death, xxv. 17.
  Stools black, xxvii. 2.
  Strangury, xxxv. 2. 1.
  Sucking before nativity, xvi. 4.
  Suckling children, sense of, xiv. 8.
  Suggestion defined, ii. 2. 10. xv. 2. 4.
  Sun and moon, their influence, xxxii. 6.
  Surprise, xvii. 3. 7. xviii. 17.
  Suspicion attends madness, xxxiv. 2. 4.
  Swallowing, act of, xxv. 1. xvi. 4.
  Sweat, cold, xxv. 9. xxix. 6.
  ---- in hot fit of fever, xxxii. 9.
  ---- in a morning, why, xviii. 15.
  Sweaty hands cured by lime, xxix. 4. 9.
  Swinging and rocking, why agreeable, xxi. 3.
  Sympathy, xxxv. 1.
  Syncope, xii. 7. 1. xxxiv. 1. 6.

                  T.

  Tædium vitæ. See Ennui.
  Tape-worm, xxxix. 2. 3.
  Taste, sense of, xiv. 5.
  Tears, secretion of, xxiv.
  ---- from grief, xvi. 8. 2.
  ---- from tender pleasure, xvi. 8. 3.
  ---- from stimulus of nasal duct, xvi. 8. xxiv. 2. 4.
  ---- by volition, xxiv. 2. 6.
  Teeth decaying cause headachs, xxxv. 2. 1.
  Temperaments, xxxi.
  Theory of medicine, wanted. Preface.
  Thirst, sense of, xiv. 8.
  ---- why in dropsies, xxix. 5.
  Tickle themselves, children cannot, xvii. 3. 5.
  Tickling, xiv. 9.
  Time, xiv. 2. 2. xviii. 12.
  ---- lapse of, xv. 3. 6.
  ---- poetic and musical, why agreeable, xxii. 2.
  ---- dramatic, xviii. 12.
  Tooth-edge, xvi. 10. iii. 4. 3. xxii. 3. 3.
  Touch, sense of, xiv. 2. 1.
  ---- liable to vertigo, xxi. 9.
  ---- of various animals, xvi. 6.
  Trains of motions inverted, xii. 5. 5.
  Transfusion of blood in nervous fever, xxxii. 4.
  Translations of matter, xxix. 7.
  Typhus, best quantity of stimulus in, xii. 7. 8.
  ---- periods of observe lunar days, xxxii. 6.

                  U.

  Ulcers, art of healing, xxxiii. 3. 2.
  ---- of the lungs, why difficult to heal, xxviii. 2.
  Uniformity in the fine arts, why agreeable, xxii. 2.
  Urine pale in intoxication, xxi. 6.
  ---- paucity of in anasarca, why, xxix. 5.
  ---- its passage from intestines to bladder, xxix. 3.
  ---- copious during sleep, xviii. 15.

                  V.

  Variation, perpetual, of irritability, xii. 2. 1.
  Vegetable buds are inferior animals, xiii. 1.
  ---- exactly resemble their parents, xxxix.
  ---- possess sensation and volition, xiii. 2.
  ---- have associate and retrograde motions, xiii. 4. xxix. 9.
  ---- their anthers and stigmas are alive, xiii. 5.
  ---- have organs of sense and ideas, xiii. 5.
  ---- contend for light and air, xxxix. 4. 8.
  ---- duplicature of their flowers, xxxix. 4. 4.
  Veins are absorbents, xxvii. 1.
  ---- paralysis of, xxvii. 1.
  Venereal orgasm of brutes, xxxii. 6.
  Venesection in nervous pains, xxxii. 5. 4.
  Verbs of three kinds, xv. 3. 4.
  Verses, their measure, xxii. 2.
  Vertigo, xx.
  ---- defined, xx. 11.
  ---- in looking from a tower, xx. 1.
  ---- in a ship at sea, xx. 4.
  ---- of all the senses, xxi. 9.
  ---- by intoxication, xxxv. 1. 2.
  Vibratory motions perceived after sailing, xx. 5. xx. 10.
  Vinegar makes the lips pale, xxvii. 1.
  Vis medicatrix of nature, xxxix. 4. 7.
  Vision, sense of, xiv. 3.
  Volition defined, v. 2. xxxiv. 1.
  ---- affects the whole sensorium, xi. 2.
  ---- diseases of, xxxiv.
  Voluntarity, xi. 2. 4.
  Voluntary motions, ix. xxxiv. 1.
  Voluntary ideas, xv. 2. 3.
  ---- criterion of, xi. 2. 3. xxxiv. 1.
  Vomiting from vertigo, xx. 8.
  ---- from drunkenness, xx. 8. xxi. 6.
  ---- by intervals, xxv. 8.
  ---- by voluntary efforts, xxv. 6.
  ---- of two kinds, xxxv. 1. 3.
  ---- in cold fit of fever, xxxii. 9. 1.
  ---- stopped by quicksilver, xxv. 16.
  ---- weakens the pulse, xxv. 17.

                  W.

  Waking, how, xviii. 14.
  Walking, how learnt, xvi. 3.
  Warmth in sleep, why, xviii. 15.
  Weakness defined, xii. 1. 3. xii. 2. 1. xxxii. 3. 2.
  ---- cure of, xii. 7. 8.
  ---- See Debility.
  Wit producing laughter, xxxiv. 1. 4.
  World generated, xxxix. 4. 8.

       *       *       *       *       *

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