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SYDENHAM SOCIETY

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MDCCCXLIII

LONDON

THE

PRINCIPLES OF PHYSIOLOGY,

BY

JOHN AUGUSTUS UNZER;

A DISSERTATION

FUNCTIONS OF THE NERVOUS SYSTEM,

BY

GEORGE PROCHASKA.

TRANSLATED AND EDITED BY

THOMAS LAYCOCK, M.D. (Gottingen),

LICENTIATE OF THE KOYAL COLLEGE OF PHYSICIANS, LONDON ;

PHYSICIAN TO THE YOKK DISPENSARY ; AND

LECTUEEB ON THE THEOKY AND PEACTICE OF MEDICINE AT THE YOBK MEDICAL SCHOOL.

LONDON

PRINTED FOR THE SYDENHAM SOCIETY

MDCCCLI.

1^

/^ 0

rrf^i

q«

C. AND J. ADLARD, PRINTERS,

BAUTHOi-OMKW CIOSK.

CONTENTS.

PAGE

Preface ....... xi

Introduction. By the Editor . . . . i

Notice of the Life and Writings of Unzer . . . i-viii

Notice of the Life and Writings of Prochaska . . ix-xiv
List of Words and Phrases used by Unzer, and their English

Synonymes . . . . . . xv

PRINCIPLES OF A PHYSIOLOGY OF THE PROPER
ANIMAL NATURE OF ANIMAL ORGANISMS.

Preface . . . . . . .3

Introduction . . . . . .13

PART I.

ANIMAL NATURE IN ITS CONNECTION WITH THE SENTIENT
FACULTY OF THE SOUL OF THE ANIMAL.

CHAPTER L
The Animal Machines in general, and especially as they are

adapted to the Animal-Sentient Forces . . .17

CHAPTER II.
The Animal Forces considered abstractedly, and particularly as

Animal-Sentient Forces . . . . .21

Sect. I. — The Functions of the Vital Spirits .... ib.
II. — The Animal Forces of the Brain considered abstractedly as Animal-

Sentient Forces . . . . .23

\I

CONTENTS.

III. — The Animal Forces of the Nerves considered solely in their relation
with the Animal-Sentient Forces of the Brain
Of the External Impressions
On External Sensations .
The External Senses
The Sensational Conceptions
Imaginations .
Expectations .
The Understanding
Sensational Pleasure and Suffering
Desires and Aversions
Instincts, — Passions
The Free- Will .

Actions excited by the Mind, or Sentient Actions
Actions of Material Ideas in the Nervous System
Actions of Material Ideas in the Brain
Actions of Material Ideas through the Nerves generally
Actions of the Material Ideas in the Nerves exclusively

CHAPTER III.
On the Influence of the Animal-Sentient Forces in the Mechanism

OF Animal Organisms
Actions of Material Ideas in the Mechanical Machines of the Brain
Actions of Material Ideas in the Mechanical Machines through the Nerves 85
Actions of External Sensations in the Mechanical Machines
Actions of Imaginations in the Mechanical Machines
Actions of the Sensational Foreseeings in the Mechanical Machines
Actions of Sensational Pleasure and Pain in the Mechanical Machines
Actions of the Sensational Desires and Aversions in the Mechanical

Machines .....

Actions of the Sensational Instincts in the Mechanical Machines
Self-Love .....

Instinct foi? Food .....
Instinct to perform Sensational-voluntary Movements

CONTENTS.

VIl

Instinct for Repose and Exhilaration

Instinct of Self-Defence

Instinct for the Propagation of the Species

Instinct to give Suck

The Instinctive Passions

Actions of the Passions in the Mechanical Machines

Actions of the Understanding in the Mechanical Machines

Actions of Intellectual Pleasure and Pain in the Mechanical Machines

Actions of the Will in the Mechanical Machines

FAOB
153

155
157
158
161
166
176
178
179

CHAPTER IV.
The Reciprocal Connection of the Body with the Soul

. 184

PART 11.

ANIMAL NATURE IN RELATION TO ITS PURELY ANIMAL

FORCES, OR VIS NERVOSA.
Introduction . . . . . .188

CHAPTER I.
On the Vis Nervosa, and on Nerve-Actions in general

189

CHAPTER II.

On the Vis Nervosa of External Impressions . . . 222

Sect. I. — On the Vis Nervosa of External Impressions in general . . ib.

II. — On the Vis Nervosa of External Impressions in Special Relation to

direct Nerve-Actions .... . 238

CHAPTER III.
On the Vis Nervosa of Internal Impressions (without conceptions).

Sect. I. — . . . . . .

II. — On the Vis Nervosa of Internal Impressions in particular

"TnfCT
. 262

VIII CONTENTS.

CHAPTER IV.

PAGE

Relations of the Animal-Sentient (Cerebral) Forces and of the

Vis Nervosa to each other ..... 275

Sect. 1. — On the Substitution of Nerve-Actions for Sentient Actions . 275

II. — On the Substitution of Sentient Actions for Nerve-Actions . 299

III. — The Reciprocal Connection of the Animal-Sentient (Cerebral) Forces,

with the Vis Nervosa in the Natural State . . . 302

PART III.
ANIMAL NATURE CONSIDERED AS A WHOLE.

Introduction . . . . . . . 308

CHAPTER I.
On Animal Nature in General .... 309

CHAPTER II.
The principal Genera of Existing Animals . . .317

CHAPTER III.
On the Origin of Animal Nature .... 327

CHAPTER IV.
On Animal Life ...... 330

CHAPTER V.
The System of the Forces of Animal Life . . . 337

CHAPTER VI.
On Old Age and Death ..... 354

e:nd or contents to vkzku's 'I'mncirLiis oi' physiology.'

CONTENTS. IX

A DISSERTATION ON THE FUNCTIONS OF THE
NERVOUS SYSTEM.

PAGE

Introduction ..... . 363

CHAPTER I.
The Principal Opinions of Authors, regarding the Uses and

Functions of the Nervous System, concisely stated.

Sect. I. — The Opinions of Aristotle . . . . 365

II.— The Opinions of Galen . . . . .366

III.— The Followers of Galen . . . . .369

IV. — The Animal Spirits are dislodged from the Ventricles . . 370

V. — Another office attributed to the Ventricles of the Brain, by Galen, is

also shown to be erroneous . . . .372

VI. — It is proposed, with other special Functions of the Nervous System,
that the Cortical Portion of the Brain be substituted for the
Ventricles, as the part where the Animal Spirits are secreted, and
that the Medullary Matter has the Function of collecting and
distributing them to the Nerves .... 374
VII. — Those who have denied the existence of Animal Spirits . . 378

VIII. — The Functions of the Nwvous System are explained by the Vis

Nervosa . . . . . .380

CHAPTER II.
The Nervous System in general.
I.— What Parts it includes . . . . .381

II. — How the Nervous System is constituted in other Animals, and how

far it extends through the whole Animal Kingdom . . 384

III. — What is understood by the Vis Nervosa, and what are its general

Properties ...... 389

CHAPTER III.
The Functions of the Nerves.
Sect. I. — On the Action of the Nerves in producing Sensation and Motion . 406
II. — The Action of the Nerves on the Vessels and Fluids . . 408

X CONTENTS.

PAGE

III. — By this Derivation of the Fluids to the stimulated part, the
Muscles are made to contract, and many other phenomena pro-
produced . . . . . .413

IV. — Does an opposite Property exist in the Nerves, so that they can repel

the Blood from the Vessels under their Influence into other parts? 417
V. — Have the Nerves any Influence on Secretion ' . .418

VI. — Do the Nerves exert any Influence in the Production of Animal

Heat? . . . . . .421

VII. — Are the Nerves necessary to Nutrition ? . . . 423

CHAPTER IV.
The Functions of the SensoriuiiI Commune.
Sect. I. — What is the Sensorium Commune ; what its Functions, and what its

Seat? . . . . . .429

II. — Does every Consensus of the Nerves take place through the Sen-
sorium Commune only ? . . . . 433

III. — Does Consensus of the Nerves also take place in the Ganglia ? . 435

CHAPTER V.
The Animal Functions.
Sect. I. — A short Enumeration of them .... 439

II. — Is the faculty of Thought the special property of the Mind, or is it
necessary to Thought that the Mind use the hrain as an
Instrument? ..... 442

III. — Do each of the Divisions of the Intellect occupy a separate portion

of the Brain ..... 446

IV. — "WTiat movements are properly termed Animal ? . .447

Index to Unzer's First Principles . . . . .451

Index to Prochaska's Dissertation .... 460

PREFACE.

The Introduction which 1 have written, at the request
of the Council of the Sydenham Society, might suffice for a
Preface also, if it were not that there are one or two matters
to be mentioned which a Preface only can include.

In the first place, I earnestly request the reader's close at-
tention to the works contained in this Volume ; partly, for my
own sake, that I may not lose the sweetest reward of literary
labour ; but principally for his and for the interests of medical
science and art. They belong to a field of research not yet
fully entered upon by the medical profession. Emigrants from
its ranks have been the " Pilgrim Fathers" of many, if not
most, of the natural history sciences ; but there is one that
has yet to be perfected by its labours — the science of mind.

The study of Life and Organisation is confessedly essential
to the progress of medical science and art ; and it appears to
me, that that true intellectual system of the universe, which
will and must comprehend, in orderly arrangement, all the phe-
nomena of Life and Mind, ought, therefore, to emanate from
the medical profession. If so glorious a result of philosophical
inquiry be within its scope and aim, then are the works con-
tained in this Volume of double value and interest to it, since
they not only powerfully elucidate the Physiology and Patho-
logy of the Nervous System, but constitute an important con-
tribution to Mental Philosophy.

Having said so much for the works entrusted to my care, I
must now say something, by way of thanks, to those who have

XII PREFACE.

assisted me in bringing them out. My kind friend, Professor
Marx of Gottingen, has not only readily afforded me his
advice as to the translation of Unzer's work, but has also con-
tributed much valuable and interesting information respecting
the life and writings of his countrymen, which I have embodied
in the Introduction. I have also to acknowledge my obliga-
tions to Professor Sharpey, and Dr. Adams of Banchory, (so
well known to the Sydenham Society for his translations of
Hippocrates and Paulus ^ gin eta,) for the valuable criticisms
with which they favoured me when the ' Dissertation on the
Nervous System^ was going through the press. To these
three gentlemen both reader and translator owe their thanks.

But there is one other valued name I cannot omit here without
injustice. To Dr. Forbes we owe the first substantial intro-
duction of Unzer^s work to the English reader ; to him, there-
fore, our thanks are also due; — and not for this service only,
but for many others rendered to the medical profession and to
medical science and literature, the value of which have yet to
be acknowledged.

Of my own share in this work I have only to say, that I
feel I had an important trust committed to me, and laboured
accordingly; — laboured, it is true, with the usual drawbacks
of an active professional life; — and if this be admitted by the
critic as an excuse for errors and failures, I shall be grateful
to him.

T. L.

York; February 1851.

INTEODUCTION

BY THE TRANSLA.TOR.

It having been thought expedient to facilitate the com-
prehension of the Physiological Systems laid down in this
volume, by a short notice of the labours and literary course of
the writers, I subjoin the following remarks.

John Augustus Unzer (or Untzer) was born at Halle,
April 29, 1727, and commenced the study of medicine at the
university of his native town, when only 12 years old. He
showed an early inclination to neuiJo-metaphysical studies, for, at
the age of 18 (while yet a student), he attempted to elucidate
mental philosophy by the physiology of the nervous system, in an
essay, published anonymously, entitled ' New Views regarding
the Emotions,' i in which he attributed the emotions to varying
tension of the nerves; in the same year (1746,) he wrote a
defence of the doctrines of Stahl, entitled ' Thoughts on the
Influence of the Soul on its Body/^ also ' Thoughts on Sleep
and Dreams, together with a Letter showing that there may
be Sensation without the Head,' under the somewhat curious
signature of ' S. C. I. S/^ From this date to the year 1771,
when the work now translated was published, a quarter of
a century elapsed, during the whole of which period his at-
tention was continuously directed to his favorite subject,
as is shown by the essays and treatises he gave to the world
during that period. In 1747 he published a ' Treatise on
Sighing.' * On taking his Doctor's degree, in the following
year, he defended -his dissertation ' De Sternutatione ;' and,

' Neue Lehre von den Gemiiths Bewegungen. — Halle, 1746.
' Gedancken vom Einflusse der Seele in ihren Kbrper. — 1746.
^ Gedancken vom Schlafe und den Traiimen nebst einera Send-schreiben dass man
ohne Kopf empfinden konne. Halle, 1746.
* Abhandlung vom Seufzen. Halle, 1747.

b

ii TRANSLATOR'S INTRODUCTION.

in 1749, his dissertation ' De Nexu Metaphysices cum Medi-
cina generatim/ In 1750 he published a ' Philosophical View
of the Human Body generally/ ^ in which the germ of his
future views may be distinctly traced. Towards the close of
this year he left Halle to reside at Hamburgh,^ where he im-
mediately became connected with the * Hamburgh Magazine'
(vide vol. vi), and communicated to it various essays of a
neuro-metaphysical character : amongst them was one, entitled
'Reflections on the fundamental Principle of StahVs Theory.'^
In 1759 he established a weekly medical journal, ' The
Physician,'* on the model of Addison's ' Spectator,' with the
view of securing a proper estimate of physicians and of the
art of healing, and of extending sound medical knowledge, re-
moving prejudices, and checking the misdoings of ignorant
practitioners ; it is an amusing medley. The first part contains
his portrait by Tischbein. This journal was translated
into Danish, Swedish, and Dutch, and was published during
the years 1759-64; the neuro-psychological essays he inserted
in it are frequently referred to in the present work. From
1766 to 1769 he published ' Collections of Minor Physical
Essays :'^ and in the latter year, a new edition of ' Der Arzt,'
in six volumes. His portrait, taken in the 42d year of his
age, painted and engraved by H. G. Fritzsch, fronts the title-
page of the first volume. In 1768 he made an attempt at a
better and more systematic arrangement of his views, in a work
entitled ' Outlines of a System treating of the Sentiency of
Animal Organisms;'^ and, finally, three years after, he pub-
lished the work now translated, which he dedicated to his brother.
Dr. J. C. Unzer, and which may be looked upon as a new
and much improved edition of the last-mentioned publication.
Thus his 'Principles of a Physiology of the Animal Nature pro-
per to Animal Organisms,' was given to the world at the mature
age of 44, after it had been virtually a quarter of a century

* Philosophische Betrachtung des Menschlichen Korpers uberhaupt. 1750.

^ Haller makes a statement in his ' Bibliotheca Anatom.,' (vol. 2, p. 400), which,
on careful inquiry, I find to be erroneous, namely, that Unzer was Professor of
Medicine at the University of Rinteln.

3 Betrachtungen iiber Stahl's theoretischen Grundsatz. — Hamburg. Magaz. Bd. 10.

* Der Arzt ; — eine Medicinische Wochenschrift.

* Saramlung Kleiner physicalischer Schriften; — the third in 1769.

^ Grundriss eines Lehrgebaudes von der Sinnlichkeit der thierischen Korper.

TRANSLATOR'S INTRODUCTION. iii

in preparation, and may therefore be considered as the work of
a powerful metaphysical intellect, in the prime of its strength,
and thoroughly informed on the subject to which it had been
so long, so perseveringly, and so assiduously directed. With
the exception of a reply to various reviews of the work,^ Unzer
wrote no more on his favorite subject, but turned his atten-
tion to the pathology of contagion, and contagious diseases,
which he elucidated with his usual acuteness. He died, rich,
April 22, 1799, being a week less than 72 years old.

Having thus given a brief sketch of Unzer's literary career,
I will notice, as shortly as possible, the origin and progress of
his peculiar views, as finally perfected in this, his greatest work.
Although he must have been eminently qualified by natural
endowments, and by a natural bias to metaphysical research
for grappling successfully with the profound and very difficult
questions of physiological metaphysics, it is probable, that to his
early associations at the University of Halle we owe the special
direction of his mind to the subject. Both Hoffmann and Stahl
were professors at Halle for a lengthened period; but when
Unzer commenced his medical studies, the former was still
professor, at the venerable age of 79, and died at Halle, in
his 83d year, so that Unzer must have known him personally.
It was, however, as the pupil of Juncker, an avowed Stahlian,
that he specially directed his attention to the metaphysics of
vital actions, and to him Unzer dedicated his defence of the
doctrines of Stahl, in a long and highly complimentary
dedication. At this time physiology, and especially the phy-
siology of the nervous system, was fast losing its purely
hypothetical character, and assuming the rank of a science.
Mental philosophy had long taken cognisance of the different
kinds of motion in animals of which every man is led to dis-
criminate at least three : — namely ; 1st, those dependent solely
on the will ; 2d, those of which he is conscious, but which are
independent of the will as the exciting cause; 3d, those of
which he is wholly unconscious, and which can neither be excited
nor restrained by volition. The first class of actions could be
readily ascribed to the soul ; but the second and third classes,

' Physiologische Untersuchungen auf Veranlassung der Gottingisclien, Frank-
furter, &c. Recensionen seiner Physiologic der thierischen Natur. — Leipzig, 1773.

iv TRANSLATOR'S INTRODUCTION.

although independent of reason, volition, and even consciousness,
were equally characterised by their intelligent and exact adap-
tation to the wants of the animal. To explain the origin of
these adapted acts, and to determine their relations to those
of the reason and will, was a problem which had occupied and
baffled the greatest intellects, from Plato downwards, and a
satisfactory solution had never been given to the world. In
the theory of Aristotle, these various actions were considered
to result from the operation of a sentient, or intelligent
principle, endowed with certain faculties or powers. All the
faculties that, according to this theory, can exist in a living
creature, are five: — namely; 1, the faculty of receiving nu-
triment ; 2, of sensation ; 3, of motion in place ; 4, of impulse
or desire ; 5, of intelligence : so that soul, considered as
endowed with only the nutritive faculty (which is present in
all beings), may be attributed to vegetables. The soul of man
differs from the soul of lower beings, in being endowed with the
faculty of intelligence, in addition to all the others ; consequently
it may be considered as containing three portions, — logically,
not materially, separated, — one, absolutely without reason ;
a second, rational ; a third, participant of reason.

The Aristotelian philosophy was long exclusively current in
the universities and schools ; but, with the revival of anatomy
and physiology, the outlines of various systems oi physiological
metaphysics appeared, and anatomy, physiology, and natural
philosophy, were brought into direct relation with psychology.
Our own Willis took the lead in this new department of medical
science. He illustrated the human and comparative anatomy
of the brain and nervous systems, by drawings and copper-
plates ; he distinguished two kinds of souls, namely, the corporeal
or sensitive (the anima — the soul of brutes), and the rational
or intellectual (the animus) : and he assigned the cerebrum
to the latter, and the cerebellum to the former, the diseases,
faculties, and operations of which he treated of specially in his
two discourses, ' De Anima Brutorum.'^ The first discourse is
physiological, and, in many respects, is the analogue and
prototype of Unzer's work ; the second is pathological, and

* De Anima Brutorum quee Hominis vitalis ac sensitiva est, Exercitationes
nvM quarum prior Physiologic a ejus naturam Partes, Potentias, et Affectiones
tradit ; altera Pathologica, &c.

TRANSLATOR'S INTRODUCTION. v

treats of the diseases of the brain and nervous system. In
these, as well as in his other neurological works, Willis follows
the line of research which his peculiar position, as Sidley
Professor of Natural Philosophy at Oxford, would almost
necessarily incline him to take. According to Willis, the vital,
sensitive, or corporeal soul, performs two principal offices;
namely, first, to form the body of the animal and its organs,
and then to render it and them apt and fit for all the purposes
of the life of the individual. The better to illustrate his views,
he devotes a chapter to a description of the various kinds of
lower animals, including therein zoology, and comparative
anatomy and physiology. To this corporeal soul he ascribes
all the emotional, instinctive, and involuntary acts. Touching
this class of movements, he observes, (I quote the quaint,
vigorous language of Pordage's translation,) — " First, as to
what regards natural Instincts, it is a great and most ancient
Notion, That there is, in all Living Creatures, an innate Conser-
vation of themselves; to wit, that every Individual might
preserve itself as long as it can. This is a Law of Divine
Providence, inbred in all creatures, which gathers together the
Principles of Life like a Bond, otherways apt to be dissipated
and to depart one from another, and on which, as the Basis,
the Duration or Continuance of the whole World stands.^'
" This being supposed, it necessarily follows, that all Animals
ordained for this end, are furnished also with certain fit means
for following the same, wherefore they ought to know, by
Natural Instinct, whatsoever things are Congruous and benign,
and what are incongruous or hurtful to them ; and that they
should follow these with hatred and aversion, and those vdth
Love and delight. Hence it is, that every one of them are able
to choose Food proper for themselves, and to seek it, being
absent, and remote from their eyes ; And, from an implanted
disposition of their Nature, are skilful to know and oppose
Enemies, to love their Friends, to get a female fit for themselves,
and to make ready whatever may conduce to the Procreating
and Cherishing their young; besides many other Kinds of
powers and habits, granted to us not without Learning and
Study, are originally fixed on the prcecordia of the Beast.'' ^

' *' Quod autern spectat ad imtinctus naturales, antiquissima, et maxime generalis
notio, cunctis animalibus innata est sui ipsius conservatio, nempe ut unumquodque

vi TRANSLATOR'S INTRODUCTION.

Willis was not_, however, solitary in his doctrine as to the
existence of two souls in man ;^ Gassendus, and Dr. Hammond,
a learned English divine (both his contemporaries), are specially-
quoted by him ; nor was he alone in his direct application of
natural science to mental philosophy, for Sylvius was diligently
pursuing at Leyden the same course of research which he was
following at Oxford. Sylvius, however, followed Descartes,
while Willis was influenced in the formation of his theories by
the doctrines of Paracelsus. There was, however, yet another
neuro-psychologist, whose name is less known in England, but
who was the contemporary of Sylvius and WilUs, and taught
identical or analogous doctrines, with brilliant success, at Jena,
— this was G. W. Wedel, the teacher of Hoffmann and Stahl,
— and it is through him that we have to trace the views of
Unzer in a direct line from Willis.

Hoffmann and Stahl ran a singularly parallel course through
life. They were born in the same year (1660), and studied at
the same time and place, under Wedel, at Jena, then the
most renowned university in Germany. They were appointed
professors of medicine at Halle, in the same year (1694), and
at the same age ; and both became physicians to the king of
Prussia ; Hoffmann was the first to leave HaUe, and fill that
office, but, in three years, he abandoned court, and resumed
his professor's chair, where he died, in the 83d year of his
age. Stahl died at Berlin, the physician to royalty; but,
previously to his removal from Halle, he was a professor
for twenty -two years. In the neuro-metaphysical doctrines
of both these great men, the influence of WiUis's views may
be traced, but the purely metaphysical bias of StahFs mind
soon showed itself; for he repudiated all histological, ana-
tomical, and bio-chemical researches, as worse than useless
in medicine. The foundation of his theory was wholly meta-
physical; the organism, considered as matter, had no power
to originate movement ; it could only be put into motion by
an immaterial principle, — the soul; and the laws of action

individuum, quamdiu possit, sese tueatur: hsec divinae providentise lex est, creaturis
omnibus indita, quae vinculi instar vitae priiicipia alioqui dissipari, et ab invicem
discedere apta, una coUigat, et cui tanquam basi totius mundi duratio innititur," &c.
De Anima. Brutorum, Pars Physiolog. cap. vi.

' Prochaska gives an account of Willis's views on this and other points, in his
* Dissertation on the Functions of the Nervous System,' chap, i, § vi.

(

TRANSLATOR'S INTRODUCTION. vii

of that principle were alone to be investigated. According to
his viewSj the involuntary, instinctive, and habitual acts of the
organism, are produced unconsciously by the soul ; being
adapted, they result ratione, or Xoyw, but not ratiocinioy or
Xoyiafxw. Hoffmann, on the contrary, seems to have been
eclectic, and to have constructed his system by modifying
those of Sylvius, Willis, Wedel, and Stahl. He recognises a
sensational soul, or anima sensitivay as distinct from the rational
soul ; and an etherial fluid, diffused throughout nature, is the
means by which this soul acts on the body. The blood receives
this ether from the atmosphere ; it is secreted from the blood
by the brain ; and, being transmitted thence along the nerves,
the anima sensitiva is enabled thereby to produce all the in-
stinctive and involuntary acts displayed by animal organisms.
The conservative and remedial powers manifested by the latter,
which Stahl attributed to the soul, Hoffmann considered to be
a law of life, seated in the general organisation, as Willis did
before him. He distinguished the nervous tissue from the
mus(5ular, and attributed the motive power of the former to a
vis nerve a, of the latter to a vis insita.

Professor Juncker, the disciple and successor, at Halle, of
Stahl, and to whom Unzer attached himself, was the contem-
porary of Hoffmann, and therefore, in some respects, the
antagonist. Unzer seems to have attached himself to his
master with youthful enthusiasm, and to have defended the
Stahlian doctrines, at the outset of his literary career, rather
from feeling than conviction. Perhaps he was influenced by
the doctrines of Hoffmann unconsciously to himself; — it is
certain that, imbued with the same spirit of eclecticism, he
quickly abandoned the Stahlian system and method of phi-
losophising, to investigate the phenomena of life and mind by
anatomical and physiological researches. During the time that
he was a student, and subsequently, general and histological
anatomy and experimental physiology were assiduously culti-
vated, and every year some interesting experiment or discovery
was made. It was then, or a few years previously, that
Lancisi, Valsalva, Pacchioni, Baglivi, Santorini, Morgagni,
and Spallanzani flourished in Italy, — Winslow and Vicq d'Azyr
in France, — Albinus in Holland, — and Lieberkiihn, Haller,
(his distinguished pupils,) and Sommerring in Germany ; while

viii TRANSLATOR'S INTRODUCTION.

Cowper, Cheselden, and the Monros, laboured in Great Britain.
There were others, who made the structure and functions of
the nervous system their special study, — as Kriiger, Wrisberg,
Meckel, Lobstein, Walther, de Asche, &c. ; and thus, every
year, new facts and opinions were brought before the eclectic
intellect of Unzer, and, every year, he extended and perfected
his views. John Gottlieb Kriiger was a popular professor at
Halle, the native place and alma mater of Unzer, and he,
Haller, and Alexander Monro, appear to have had the greatest
influence on his mind; — Kriiger, by his doctrines as to the
involuntary nature of purely sensational movements ; HaUer,
by his inquiries into the nature of muscular action ; and
Monro, by his researches into the anatomy and physiology of
the nervous system. The doctrines of Haller as to the powers
and properties of the vis insita, he extended to the whole class
of purely automatic movements excited by mere impressions on
the nerves or nervous centres; the doctrines of Kriiger he
adapted to the preceding, and to that great class of excited
movements accompanied by, but not necessarily dependent on,
sensation : the ordinary metaphysical doctrines of the day, as
propounded by Baumgarten,^ were adapted to the current
physiology of the cerebrum ; and, finally, with all were incorpo-
rated the doctrine of Willis and Hoffmann, as to the nature and
seat of the conservative and curative powers of the organism.

Thus, after twenty-five years had been devoted to his subject,
Unzer gave to the world his system of physiological meta-
physics. He lived and wrote far in anticipation of his age and
his contemporaries. That which he established hypothetically,
but logically, has since been demonstrated by dissection and
experiment; what he thought to be only perceptible to the
eye of reason, has been revealed to the eye of the histologist ;
what he discovered, intuitively but speculatively, has been duly
enrolled on the records of science as a proved thing. Yet,
after the lapse of eighty years, much that he advanced remains
to be duly appreciated; and the present age has still to
acknowledge, that his work is a model of psychological inquiry,
and a mine of suggestive ideas.

» The translation from the Latin into German by Professor Meier, of Halle (1766),
is the edition of Baumgarten's * Metaphysics, to which Unzer refers in his work.

TRANSLATOR'S INTRODUCTION. ix

George Prochaska was bom at Lospitz, in Moravia,
April 10, 1749. In 1776 he graduated at Vienna; in 1778
he became Professor of Anatomy and Diseases of the Eye, at
Prague; and, in 1791, Professor of Anatomy, Physiology, and
Diseases of the Eye, at Vienna. In 1805 he was appointed a
Regierungsrath, and died on July 17, 1820, of hydrothorax
and pulmonary disease, aged 71. His portrait was published,
in 1812, with his ^Disquisitio Anatomico-physiologica Organismi
Corporis humani.'

At the commencement of his career, Prochaska specially
investigated the anatomy and physiology of the muscular and
nervous systems ; and, throughout his whole life, endeavoured
to elucidate the vital processes. His first essay was published
at Vienna, in 1778, and entitled, ' Qusestiones Physiologicse de
Viribus Cordis,^ and was followed, in the same year, by ^ De
came musculari; Tractatus Anatomico-physiologicus.' In 1779
he published a histological essay, entitled ' De Structura
Nervorum ; Tractatus Anatomicus :' and this was followed by
his 'Adnotationes Academicse.^ The first fasciculus, published
in 1780, contained anatomical observations (with plates) on
the wear of the teeth, and an elucidation of the causes of the
second dentition ; together with a description, dissection, and
plates, of a human bicephalous monster ; the second, published
in 1781, contained various contributions to pathological ana-
tomy, a description of four monsters, and a commentary on
their mode of generation ; the third, published in 1784, con-
tained contributions to pathology and pathological anatomy,
together with a dissertation, ' De Functionibus Systematis
Nervosi,* the translation of which has been intrusted to me
by the Sydenham Society.^ In 1797, he repeated the views ad-
vanced in this essay, with certain modifications, in a class-book he
published, for the use of his pupils, at Vienna.^ The text of
the essay sufficiently shows, that the works of Unzer were well
known to him, for not only is direct reference made to the
* Erste Griinde,' but the doctrines as to the functions of the

• This was republished, with few alterations, amongst the ' Opera Minora*
(Vienna, 1800,) of the author ; but the translation is from the first edition.

' Lehrsatze aus der Physiologic des Menschen, 2 vols. 1797. A second edition
appeared in 1802, and a third in 1810. This work was also published in Latin, in
two volumes, under the title of * Institutiones Physiologiae Humanae,' 1805.

X TRANSLATOR'S INTRODUCTION.

sensorium commune contained therein are but a synopsis of
the views in Unzer's great work. He obviously was also
familiar with the views of Willis, of which he gives a synopsis.
In his ' Lehrsatze/ (first edition,) Prochaska adopts the prin-
ciple of a general sensorium commune, but subdivides it so as
to correspond with the views of Willis as to the existence of a
rational and a corporeal soul in man ; he therefore constitutes
it of two separate elements, namely, the sensorium commune
of the soul, which is seated in the brain only, and reflects
those impressions of which we are conscious; and the sensorium
commune of the body, which is seated in the brain, spinal cord,
and ganglia and plexuses of the sympathetic system. A
literal translation of one or two paragraphs from this work
will more distinctly show his relations to Willis and Unzer.

'^ XXXV. The relations of the vis nervosa to stimuli.

" § 1 78. The operation of the nervous system and of its vis is specially
related in this respect, — that it feels external impressions by means of
the brain, and thereupon causes adapted movements by means of the
muscles. The transition of sensation into motion takes place according
to the law of self-conservation, written, as it were, on the organisation
of the nervous system;^ for sensations that are agreeable, and con-
ducive to our preservation, cause such movements as are adapted to
retain the impression ; while movements result from unpleasant im-
pressions, such, that by them the disagreeable impression must be
averted from us.

"§ 179. This transition of sensation into adapted movements,
occurs partly with the consciousness of the soul, whereby it is taken,
as it were, into counsel, and its will obeyed ; now these are termed the
sentient operations. In other instances, sensations pass into adapted
movements without the consciousness of the soul, and often in oppo-
sition to its will; and this transition is termed simply the nerve -
operations. Following out this fact, Unzer has divided sensation into
soul-sensation, or sensation with consciousness ; and corporeal feeling,
or sensation without consciousness.^ By this, and the preceding pro-
position, the relations of the vis nervosa to stimuli can be easily
determined." ^

1 On the Functions of the Nervous System, chap, iv, § i, in Adnotat. academ.
Fasc. iii, p. 117.

2 Grundriss eines Lehrgebaudes von der Sinnlichkeit der thierischen Korper. — 1 768.

3 Op. cit. p. 113.

translator's introduction. xi

" xxxvii. Function of the common Sensorium.

"§ 215. That point of the nervous system is termed the common
sensorium (Sensorium commune), in which external impressions meet,
and from which internal impressions are diffused to all parts of our
body ; in which, consequently, the consensus of the nerves takes place
that is necessary to Life, and in which external impressions are reflected
into internal impressions, according to the law of self-conservation
(178), with, or without, consciousness.

"§ 216. That sensorium in which impressions are reflected with
the consciousness of the soul, may be termed the soul-sensorium ; and
the other, the corporeal sensorium ; just as Willis has already divided
it, into the rational and the corporeal soul.

"§ 217. The brain, only, is the seat of the soul-sensorium; the
seat of the body-sensorium is the brain, spinal cord, and (as all obser-
vation shows) the ganglia and plexuses of the nerves. That external
impressions can also be reflected in the brain, without conscious-
ness, is shown by the involuntary convulsions of voluntary muscles.
Monsters, born without brain and spinal cord, and which live up to
the moment of birth, show that the consensus of the nerves necessary
to this form of life, imperfect though it be, may take place, and that
there may be a corporeal sensorium independently of the brain and
spinal cord, and which, consequently, must be constituted by the
plexuses and ganglia of the nerves. The movements observed to take
place on irritating the nerves of a headless frog, and seen also in
decapitated men, prove the same thing. The sympathetic nerve ap-
pears likewise to reflect its impressions in its ganglia and plexuses,
without the consciousness of the soul.

" § 218. In accordance with this consensus of the nerves, as well
in the brain as in the spinal cord, ganglia, and plexuses, the operation
of a stimulus is not limited to the nerves immediately irritated, but is
extended to distant nerves, in known or unknown connection with the
irritated nerves ; and this is demonstrated by innumerable examples of
consensus of nerves [consensus nervorum], as, for instance, the irri-
tation in the pregnant uterus often causes nausea, vomiting, headache,
toothache, &c.

" § 219. Both the soul-sensorium and body-sensorium operate ac-
cording to the law of self-conservation (178), a truth which may be
illustrated by numerous examples. For instance, the irritation or
impression of too strong a light goes to the optic nerve, from whence
it can only get at the ciliary nerves through the brain, and induce

xii TRANSLATOR'S INTRODUCTION.

contraction of the pupil, so as to exclude the too vivid light from the
eye, and obviate its unpleasant impression."

Prochaska then adds other illustrations, which he explains
in a similar manner; namely, the closure of the eyelids when
a finger is brought near to the eye ; the act of sneezing, from
irritation of the nostrils ; of coughing, from irritation of the
bronchi; the increased action of the heart and arteries, from
the presence of a poison or other irritating materies in the
blood, " whereby the blood is circulated more rapidly, and all
the powers of those structures are called forth, as it were, to
diminish the irritation, to render it harmless, or to expel it
from the organism.^^ He then proceeds :

" § 220. These adduced examples sufficiently show that the sen-
sorium commune acts, in all its operations, strictly according to the
law of self-conservation, and that it is ever studious to do the best for
our preservation, so long as it is not prevented by disease, or the
cessation of vital action ; in which cases it is seen that it is thrown
into confusion, and no longer always takes the best steps for the cure
of disease ; often, indeed, proving itself altogether incompetent thereto ;
just as a delirious or idiotic person, from the disordered state of his
soul-sensorium, neither knows what is necessary to his preservation,
nor does it." ^

In his details, we find Prochaska repeating several of the
views of Unzer, although they are mixed up with opinions
derived from the writings of others, or his own researches.
He thus notices an important distinction between the two
great classes of involuntary and voluntary acts :

** § 175. Nevertheless, this need for rest seems only to be a charac-
teristic of the nerves which are subordinate to the will, and not to the
involuntary, which have to provide for the motion of the heart, respi-
ration, and digestion ; and whose vis nervosa is active, without inter-
mission, during the whole of life, although it may be weaker or
stronger. Though it cannot be doubted that both kinds of vis have a
similar origin (§§ 171, 173), and are of the same nature, still obser-
vation shows, that the one belongs to the will, the other is involuntary ;
that the former is exhausted by sensation and motion, and requires
rest and repose ; with the latter, the contrary takes place ; and, finally,
that the two kinds of vis are independent of each other. This dis-

' Op. cit.

TRANSLATOR'S INTRODUCTION. xii

tinctoess and independence of the voluntary and involuntary vis nervosa
is shown, not only in sleep, but also in apoplexy, when the voluntary
vis nervosa is quite arrested, but the involuntary performs its duty.
So, also, in cases of fever, the voluntary vis nervosa is quite weakened,
but the involuntary so much the more active." '

Subsequently to the publication of this work, Prochaska,
being attracted by the singularity and novelty of the results of
the experiments of Galvani and others, laboured diligently to
elucidate the nature of the vital processes by electro-galvanic
theories ; he also published numerous works, essays, and
observations, on physiology, pathology, pathological anatomy,
diseases of the eye, &c. A list is before me, supplied to
me by my friend Professor Marx, of Gottingen, containing the
titles of twenty-seven works, or papers.

A few explanatory sentences are necessary, with regard to
the translations. The Council of the Society having required
that the two works should be comprised in one volume, a
question arose as to the mode in which this condition should
be accomplished. It was obvious that one of the two must be
abridged ; and the work of Unzer being an octavo of 800 pages,
while the tract of Prochaska is very short, it was equally
obvious that the condition could only be fulfilled by abridging
the larger. But an abridgment implies a free translation, and
a free translation great responsibility on the part of the
translator. This feeling of responsibility was not diminished,
when, on consultation with Professor Marx, that accomplished
scholar, while recommending a free translation, stated that the
antiquated style, and singular phrases of the work, rendered it
somewhat difficult for even the modern German physician to
comprehend.

The plan I finally resolved upon was this : — To give a full
and literal translation of the ^ Dissertation^ of Prochaska ;
omitting only the Appendix, which, being on a controversial
topic, (that the brain and nerves are made up of globules,) and

• Op. cit. p. 110.

xiv TRANSLATOR'S INTRODUCTION.

having reference to another work published by him, ' De
Structura Nervorum/ had no immediate connection with the
dissertation to which it is appended. To give as condensed an
abridgment of Unzer's work as was consistent with a due regard
to a full and complete exposition of the writer's views, on the
following principles : — 1. To omit all quotations from Haller
and others, except such as were absolutely necessary to under-
stand the text. 2. To omit all controversial matter, on points
of secondary importance. 3. To leave out all anatomical and
physiological descriptions and disquisitions, not of an original
character, and to be found in the standard works of the day.
4. To condense, wherever that could be done without injury
to the meaning of the author, and to avoid numerous repe-
titions, which he thought to be necessary to the perfect com-
prehension of his views. 5. Where the sense was doubtful,
to give a literal translation. 6. To remodel and freely trans-
late various words and phrases used by the author in a special
sense. That the critical reader may be in a position, however,
to judge for himself on this point, I have subjoined a glossary
of these words and phrases, and a reference to the paragraphs,
to which I have appended my reasons for the adoption of the
English terms. These have only been decided upon after the
most mature deliberation, and with careful reference to other
writings of Unzer ; I therefore venture to express a hope, that
the reader will not criticise hastily, nor without a reference
to the entire scope and intent of the work.

T. L.

i

XV

List of German words and phrases used by Unzee, and their English
synonymes. {The figures refer to paragraphs, to which explana-
tory notes are added by the Translator.)

Paragraph

6. Ein Thierischer K'drper — an animal organism, or, organism,
simply.

6, 10. Vorstellungskrafty and Vorstellungskraft der Seele — the
conceptive force ; the sentient force ; mind.

6,25. Vorstellung — act of mind ; conception.
6, 25. Thierische Seelenkrafte—diXi\v[\?i\. sentient forces; cerebral
forces.

6, 31. Thierische JTra/ife— animal forces ; vis nervosa.
6. Seelenwirkungen — (actiones aniince) mental, sentient, or sen-
sational actions ; actions, simply.

9. Thierischen Maschinen — the nervous system.
27. Naturlich — Physical, corporeal, organic, natural.
27. Eigenm'dchtig, Selbstth'dtig — arbitrary, spontaneous.
3 1 . Thierische Kr'dfte der Nerven, Nervenkrdfte — vis nervosa.
31. Sinnlicher Eindruck — sensational or sense-like impression;
impression, simply.

31, 66, 262, 403. Sinnlich — sensational, sense-like, impressional.

32. Sinnlichkeit — property of respondence to impressions ; sense-
likeness ; impressibility.

88. Triebfedern des Gemiiths — excitants of the feelings.

121. Inner e sinnliche Eindriicke — internal impressions, cerebral
impressions.

122, 359. Inner e sinnliche. Eindriicke der Vorstellungen — concep-
tional impressions.

191. Der naturlichen Verrichtung gem'dss — connatural.

191. Der naturlichen Verrichtung nicht gem'dss — contranatural.

283. Willkiihrlich — volitional, sensational-voluntary, voluntary.

335. Freiwillig — free-will (adjectively).

6, 349. Beseelte, and Unbeseelte — sentient, insentient.

PRINCIPLES OF A PHYSIOLOGY

OF THE PROPER

ANIMAL NATURE OF ANIMAL ORGANISMS.

BY

JOHN AUGUSTUS UNZER.

PRINCIPLES OF PHYSIOLOGY.

PREFACE.

We observe, that in a corpse, purely physical and mechanical
forces imitate the processes of our bodies, and can originate
that motion in its machines, of which in virtue of their structure
and composition they are capable. The fluid portions are com-
bined and separated according to the laws of gravity, of the
power of attraction and repulsion, and remain in equilibrium
according to the laws of hydrostatics. When an anatomist
injects the vascular system, it is made, by merely mechanical
forces, to repeat in some degree its former natural function,
according to the laws of hydraulics. The muscle, the fibres
which are contracted by cold, keeps the limb in the same posi-
tion in which it had placed it, and, by a mere mechanical action,
the arteries of a corpse contract and compress the finger when
pushed into them, &c.

These purely physical and mechanical forces are not the pecu-
liar forces which usually move the living animal organism in its
natural condition, but there are other forces operating in it, ac-
cording to a fixed arrangement, and according to laws altogether
different from the physical and mechanical laws already known;
and it is through these, that the organism performs those
natural processes which its structure renders it capable of.
That stimulus, which excites no movement in the lifeless heart,
or in the perfectly dead muscle, or in the arteries of a corpse,
in the natural or living condition keeps up the circulation,
changes the pulse in the arteries, and moves the muscles and
limbs. Those peculiar motive powers, which give the living
organism the advantage over the corpse, although they may
co-operate with the purely physical and mechanical forces com-
mon to both, T term the proper animal forces, and they
communicate to the living animal that nature which I call the

PROPER ANIMAL NATURE OF ANIMAL ORGANISMS.

4 PRINCIPLES OF PHYSIOLOGY.

The ordinary science of physiology considers the forces of
animal organisms in their natural condition, and as they act
together in connection with each other, but without distin-
guishing the simply physical and mechanical from the proper
animal forces. This presupposes that we know the laws accord-
ing to which each of these peculiar forces acts separately ; and,
indeed, as to the physical and mechanical, whose laws are known,
there is in general no difficulty. The physiological w^orks of
Haller teach us, in a manner almost impossible to be surpassed,
the mechanism of all parts of the animal body, of which the
structure developes the functions according to the laws of me-
chanics, hydrostatics, hydraulics, optics, acoustics, &c. But do
we know those laws by which the proper animal forces govern
the body when acting separately from the physical and me-
chanical, and independently of them ? Truly, no ! or at least
very imperfectly. The thoughts and desires are animal moving
forces of the animal organism. But do we at this moment
know anything of the laws by which these forces regulate their
appropriate organs? or have we hitherto troubled ourselves to
observe the operation of these laws in each particular class of
ideas and desires ? We have disputed stoutly enough, whether
the soul be matter or brain; whether thought be an electric fire
or a movement of the vital spirits ; whether souls and bodies
exercise a real or an ideal influence on each other ; whether souls
form their bodies, or whether they are diffused through them,
or dwell only in the head ; whether an instinctive impulse or
a passion belongs to the body or the soul ; or whether the vital
spirits be elastic or inflexible, electrical or ethereal, &c. All these
inquiries will remain for ever inscrutable mysteries, and do not
belong to our subject; they can remain altogether uninvestigated
without any disadvantage to the real usefulness of theoretical
medicine, but we have pursued them with profitless diligence,
and have done our best to confuse them more and more. How
much have we effected in resolving questions useful to our art,
as, for example, in determining by what laws the mind moves the
machinery of the animal organism? Under what circumstances
the nerves excite sensation ? Under what the sensation becomes
an animal moving force, so as to move this or that limb, in such
a manner and not otherwise? After what laws the imaginations,
the conceptions of the understanding, pleasure, pain, the in-

PREFACE. 5

stincts, the passions, and the will, impel various portions of the
animal to perform the actions intended by the Creator in uniting
the machines with a thinking force ? If the doctrines of the first
part of this work (which are, however, an imperfect sketch of
the elements of the science of the laws which regulate the in-
fluence of the mind on the body) be compared with what our
physiologists have hitherto produced, it will be seen that^ as yet,
this whole science has been in some degree a waste field.

As regards the other animal motive forces, with the exception
of the conceptions, there scarcely was a notion until the time
of Haller, who at least pointed out their existence ; and yet the
doctrine of irritability, which that great man has taught, com-
prises only a portion of those animal motive forces which are
independent of the mind, as the whole of the Second Part of
this work will sufficiently prove. The laws of action of these
forces have not as yet been illustrated by any one, and the first
elements thereof which this Second Part contains, exhibit to us
a large and fertile branch of science with which medical art can
and must ultimately be enriched, if Physiology — that science
which has to elucidate the mechanism of animal bodies com-
pounded of such multifarious motive forces — is ever to be freed
from at least existing defects. It was always premature to
attempt to explain the natural actions of the animal body
(which are brought about by the common operation of physical,
mechanical, and animal forces), by the laws of physics and

I machines, so long as there were no principles by which to
judge of the co-operation of the proper animal forces; but
especially premature to attempt their elucidation by the aid of
untenable, imperfect opinions, and inadmissible suppositions,
when the principles of physics and mechanics were found to be
insufficient. Thus Stahl erred, who knew well the necessity
there was for the co-operation of the animal forces with the
mechanism of the animal body, because it did not occur to him,
that it possessed other animal motive forces besides the influ-
ence of the mind on the body. So also the mechanical phy-
sicians erred, who would deduce all natural phenomena from
the physical and mechanical forces of the elements of the animal
organism, and absolutely deny the manifest influence of the
mind and of the other purely animal forces on animal acts.
So at this moment physiologists err, when they exclude the

6 PRINCIPLES OF PHYSIOLOGY.

co-operation of the auimal forces, in actions wliich they attempt
to explain mechanically; or, when they think that that which
cannot be explained mechanically, must necessarily be attributed
to mind; or when they would elucidate the animal motive
forces by the laws of natural philosophy and mechanics, and
never know how to determine the forces, laws, and connection,
by and through which the moving springs of animal life, so
totally different, regulate the wonderful machines of the living
organism.

This defect in Physiology becomes continually the more ap-
parent, now that inquiry has commenced into the diseases
of the proper animal forces and their cure ; and the present
appears to be the proper time to supply it by carefully con-
sidering proper animal nature in its uncomplicated state, and
distinctly deducing the laws by which the animal forces, as
such, act in animal organisms. The pathology of the mind,
or of the nervous system, and of other diseases of the animal
forces, ought to demonstrate to us the deviations of the animal
forces from their proper laws ; but what can be really expected
from pathology so long as we have no distinct idea of those
laws, and are even ignorant of the animal forces themselves ?
This knowledge will never be rendered in any degree perfect,
if the operations of the proper animal forces are not considered
quite separately and by themselves, and the laws studied by
which they ensue in animal organisms independently of the
physical and mechanical forces in operation at the same time.

From these considerations originated my idea of a physiology
of the proper animal nature of animal organisms, of which the
present work supplies the first principles, and by which the phy-
siology of the whole animal economy, which hitherto has been
extremely deficient in these principles, may for the future be
corrected, completed, and extended. Although I do not overlook
the imperfection of my own plan, and have never considered it
to be so well carried out, as to be satisfied with my performance,
still I thought it deserved to be made public even in its imper-
fect state ; since it would, for the first time, make known the
utility and necessity of separating the proper animal physiology
from the general physiology of the entire animal economy ; of
which hitherto no one seems to have ever thought. If I am
not deceived in my expectations, some better student of animal

PREFACE. 7

nature (and there are at present many with whom I am not
to be placed in comparison), being stimulated by this first essay,
will project and carry out a much more perfect system ; to me
it will be a matter of satisfaction that I had the honour of
affording the first ideas ; and if I might flatter myself that such
an one would also publish a special pathology of the proper
animal nature, according to these principles of a special phy-
siology, I should certainly think myself fortunate in having laid
the foundation for so great an improvement of our art. Any
one who is acquainted with the present condition of medical
science, and has at all attempted to remedy the striking defects
in the theory of proper animal nature, must be aware it was
necessary to any degree of progress that these first steps should
be taken.

I will now briefly describe the plan of my work.
The primary seat of the animal forces is in the so-called
proper animal machines, namely, the brain with its animal spirits,
together with the nerves, through which the latter are com-
municated to the mechanical machines. I originally intended
to have given a general division, containing a general account
of the animal machines, and their structure and moving forces,
in which I should have included an anatomical description of
the brain and nerves ; but I determined to omit this part, so
as not with useless prolixity to extend a simple sketch, inas-
much as this description of the animal machines is already to
be found as complete as possible in the fourth volume of
Haller's larger work on Physiology, .and 1 have nothing to add
to it. I have, however, made extracts from, and given reference
to, the most indisputable statements with reference to the
animal machines and properties (most of which will be noticed
in the following pages), and thus originated the following plan
of a physiology of the proper animal nature of animal bodies.

Animal nature is the aggregate of the proper animal forces,
and the science of these, uncomplicated, is the physiology of
animal nature. All animal forces act, when untrammelled, either
necessarily in connection with the mind of the animal, or not ;
and thus the science is divided into two great divisions. The
first treats of the animal nature in its connection with mind,
that is, in other words, with reference to the animal-sentient

8 PRINCIPLES OF PHYSIOLOGY.

forces ; but the second^ in reference to the nerve-forces^ inde-
pendently of the mind; out of these a third division arises,
which describes the animal nature as an independent whole,
compounded of these two animal forces.

The First Part is devoted exclusively to the animal-sentient
forces of the animal machines above-mentioned ; and an epitome
of the general doctrines applicable to the brain and nerves,
and to the animal spirits and their general properties, is
concisely given in the First Chapter and the beginning of
the Second. The animal- sentient forces are considered with
reference to their action, in two ways ; namely, partly per se,
as they themselves act in the animal machines, — the brain
and nerves, — and partly in reference to their influence on the
mechanical machines, with which the nerves are incorporated.
These constitute the contents of the Second and Third Chapters ;
to these may be added the Fourth, in which the connection of
the conceptive force and the animal moving forces, or in other
words, of mind and body, is generally set forth.

The whole philosophy of the reciprocal influence of body
and mind, as laid down in our works on Physiology, is as yet
imperfect, being without true principles, and partly confusedly,
partly erroneously, propounded. Probably this has arisen from
the little acquaintance of physicians with theoretical philosophy
except physics, and still less with psychology; as if mental
philosophy were not necessary to the science of the nature of
man^s organism. Nevertheless, our physiologists have only
worked at the useless subtilties mentioned before, and the
only useful knowledge which they teach as to the union of
body and soul, refers to the external sensations, and also to
the imaginations and passions. There are others who aspire,
with Bonnet, rather to analyse the different mental faculties
by means of movements in the brain, of which we are totally
ignorant, than to study what is peculiarly within the sphere of
the physician, and investigate the laws according to which the
faculties act in the body; which, nevertheless, can be easily
learnt by observation, if people would only cease from the
attempt to deduce them from inscrutable principles.

These doctrines present a somewhat different appearance in
the present work. I have endeavoured to define the laws by
which the various faculties of the mind operate either through

PREFACE. 9

the animal motive forces, or by and through themselves in the
entire mechanism of the body. This is peculiarly important
with reference to the sensations, and the instincts and passions,
and of consequence in every department of medical science.

In the Second Part, the nerve-forces are treated of so far
as they act independently of the mind. It is shown that,
besides the animal-sentient forces of the brain, there are only
two kinds of forces of the nerves which act in the body as
animal- motive forces, namely, the sense-like [sinnlich] im-
pressions, which are divided into internal and external (Part II,
Chap. I). These two kinds of impressions are considered in
the Second and Third Chapters respectively; and in the Fourth,
their relations to the mental forces are elucidated. Modern
physiologists, whose names Europe knows and honours, — Haller,
Zimmermann, Whytt, and Oeder, — have rendered much ser-
vice to this department of physiology by contributing materials
thereto. Haller has, indeed, begun to trace out the plan of
this new department, which certainly did not exist before him ;
but there he has stopped. I have ventured to extend this
outline, with the hope of inducing able men to complete it.
The most important progress that has been accomplished in
this matter, consists in the following : I have defined the two
kinds of impressions, and the entirely diff'erent laws by which
they move the body, without having recourse to the hypothesis
of vital spirits as a motive power; for these sense-like [sinnlich]
impressions can be considered simply as phenomena, and their
laws of action discovered without a knowledge of their nature.
I have derived primarily from the nerves, that motive force of
the external impression, which Haller assigned to the muscular
fibres under the designation of irritability, but denied it to be
a property of the nerves ; I have demonstrated the deflection
[declination] and reflection of the impressions in the nerves,
whereby many phenomena of the animal economy, hitherto
inexplicable, can be understood; and I have shown how the
vis nervosa is sufficient of itself to develope those movements
in bodies, which were formerly attributed to the influence of
the mind or soul, and vice versa.

I have added the Third Part to describe the economy of the
animal forces in general, and trace, as it were, the course of
life in animal nature. The First Chapter contains a sketch

10 PRINCIPLES OF PHYSIOLOGY.

of animal nature ; but since every animal is not provided with
those animal forces, which the most perfect possess, in the
Second Chapter the different genera of animals are classified
from the irrational to the rational. I have taken this oppor-
tunity to state reasons for the possibility and existence of
animals without souls. The other Chapter of this Part treats
of the origin, life, maturity, decline, and death of animal nature.
Hitherto we have only had scattered notices of these various
matters in our physiological works, or, at most, of the peculiar
mechanism of generation ; and the growth, decline, and death
of animal organisms have only been considered, without sepa-
rating that which has reference to the proper animal nature
from the other portions of the subject. In this Part, the most
interesting chapters are the last three on the periods of animal
life, the system of animal forces, and on animal death; these
have a wide and useful application to the pathology of proper
animal nature. I have adopted a short, simple, dry, and me-
thodical plan of writing, that the reader may continually be
enabled to examine and thoroughly understand the truth of
the views and principles, both in the abstract and in their
application, — the connection and consequences of the doctrines,
— and the whole system of animal physiology. I have avoided,
as much as possible, all medical researches of a confusing, imper-
fect, or merely subtle character, and all hypotheses ; or, at least,
have made no use of the latter in establishing my own prin-
ciples ; for a system of presupposed ideas, which in a short
time must itself be set aside, would not be well received as a
commencement in this new division of medical science, instead
of true natural laws, the result of accurate observations.

As to the doctrines themselves, and the various controversies
that have already arisen concerning them, I can only most
sincerely beg the reader to examine them with the greatest
rigour; and if the author of a work so extensive, and attempted
for the first time from the present point of view, have described
anything untruly, indistinctly, or incorrectly, or have omitted
anything, not to blame him too harshly. The justice of such
an exculpation can only be understood by those who have
undertaken to write on such a subject, and experienced the
difficulty of avoiding errors and omissions. I desire no in-
dulgence for the doctrines themselves. Truth has been sought.

PREFACE. 11

and Avhere I have not found it, I will endeavour to find it.
Consequently, I can only ask a mature consideration for those
passages of my principles which are open to controversy, or
suspected of error. I am confident that there are many errors,
and still more defects, in this work ; but I have thought much
and written little, and I can therefore ask that the critics shall
think before they controvert. If any one would reply to any
of the doctrines, whether for the purpose of proving them, or
limiting them, or correcting misunderstandings, or refuting an
error, I will absolutely act only as the interests of truth re-
quire, and as an indifi'erent reader, who has no feeling for
personalities, whether they be civilities or insults, and to
whom no objecter exists, but only an objection. It is my
general rule to answer no attack on my writings, still less on
my character and conduct; and I willingly permit many a one
to use this advantage, who may think me a very troublesome
person to attack, and who I would not for the world should
know what I thought on the matter. Why should not every
one be at liberty to criticise another as much as he likes, if he
thinks him of sufficient importance ? And why should the
other be bound to answer him, if he do not think it of suffi-
cient importance to entertain the public with his justification ?
It is seldom that controversial writings are of any great service
to science ; but it is difficult to avoid explanations with a newly-
invented science, only a sketch of the first principles of which
I has appeared, not supplied with ample illustrations, without
any of the advantages of an introductory discourse, and with
the disadvantages of unusual terms and expressions, which at
first always excite subordinate ideas that lead the reader away
from the meaning of the author : thus explanations may not
only be required, but cannot be withheld without disadvantage
to the reception of the science itself.
I must especially ask the reader^ s forgiveness with regard to
these unusual terms and phrases. It will be seen that they
were indispensable to an accurate exposition of the ideas^
without which it would be altogether impossible to give the
physiology of animal nature that first degree of completeness
which it now possesses. At one time I was not inclined to
seek unusual phrases; but when, two years since, I used the
word "feehng"' [Gefiihl] with an unusual meaning, from a

12 PRINCIPLES OF PHYSIOLOGY.

similar necessity^ in a little work I published on ' The Sense-
likeness [Sinnlichkeit] of Animal Bodies/ I found that this
use of the word with a new meaning was of little advantage,
because the majority of the critics dwelt too much on the ex-
pression itself, and hardly noticed the weightier matters to
which it owed its origin. In the present work I have avoided
this objectionable word, and in its stead selected the expression
" eocternal and internal sense -like [sinnlich] infipressions,'' al-
though I have shown in § 402, &c., the usefulness and propriety
of the former. At any rate, the reader must get accustomed
to the use of one of the two expressions.

The reader will be reminded in many places that I have not
considered any of my principles practically, nor shown their
application to the practice of medicine, although I well knew
that this step would not only have been useful generally, but
would have also disposed many to grant me their approval.
But my principal object was to show convincingly, that the
physiology of the proper animal nature is a branch of science
altogether distinct from the physiology of the entire mechanism
of the body ; and to determine satisfactorily the boundaries of
the two, which, indeed, are generally laid down in this work.
A mere sketch would have been sufficient for this purpose, and
it would have been much shorter if it had not contained so
many new views, which it was necessary to treat somewhat in
full, to render them intelligible ; nevertheless I have quoted
briefly only all those doctrines belonging to peculiar Animal
Physiology, which are contained in the physiology of the whole
mechanism of animals, so as to indicate their places in the
present work. Now that the principles of a proper animal
physiology can be surveyed connectedly, it will be found much
easier to separate what is defective, obscure, confused, un-
intelligible, and false, from what is really useful, and to bring
the whole system to perfection. For this reason I earnestly
wish that this sketch may not be read and judged of super-
ficially and unconnectedly ; but that the reader will endeavour
to follow me in the chain of ideas from the beginning throughout
the work.

INTRODUCTION.

1. The nature of a body is the aggregate of its peculiar
powers, capabilities, and forces. These depend upon the con-
dition of its parts and the manner of their connection.

2. The aggregate of the forces of a purely physical body is
termed its physical nature.

3. The general forces of physical bodies belong to the animal
and the human organism, so far as it is considered in its con-
stituent parts, and the union of these as a physical body only,
and not as a machine ; and to that extent we can philosophically
apply the general laws of natural philosophy to the fluids and
the matter of the solids. To these general forces particularly
belong general and specific gravity, the force of attraction,
which, in the matter composing the solids of animals, is the
so-called contractility [Reiz], or the dead force of Haller,
and which is simply the effect of cohesion; — also heat, elec-
tricity, &c.

4. The aggregate of the forces which a physical body pos-
sesses, in so far as it is a machine, is termed its mechanical
nature, and depends upon the physical nature and the kind
of union of its parts, whereby it becomes a machine. [Its
structure.)

5. In addition to its mechanical nature, the animal or
human organism (so far as it is not a living body, but only a
mechanical machine), is endowed with the mechanical forces of
the machines, and to that extent we can philosophically apply
the laws of mechanics to the machines of such a body. The
forces of the lever, of hydraulic machines, of the force-pump,
&c., belong to this class of mechanical forces.

Mechanical machines may be divided into the artistic and
natural {organic). The latter diff'er principally from the
former in having a highly compound structure, so that the
wdiole machine, even to its minutest details, is composed of

14 PRINCIPLES OF PHYSIOLOGY.

other machines, which by their union communicate equally
compound forces to the general machine. On the other hand, in
the artistic machines, the coarser elements are either not me-
chanical machines at all, but only mere physical bodies, or else
impart to the whole machinery no other mechanical forces than
those which they would still have, if their constituent elements
were not machines. The nature of the organic machines, con-
sidered as such only, is termed their organic nature, and the
continuance of organic nature is organic life, which is common
to anim^als and vegetables.

6. Organic (or natural) machines are termed animal ma-
chines when, in addition to their physical composition, organical
structure, and the general forces of physical and mechanical
bodies, they are endowed with other forces, which do not regu-
late such bodies and machines, according to the general laws of
motion, but are only adapted to them by means of an arrange-
ment, the nature of which is unknown. These forces are termed
(primary) animal forces ; and the movements directly produced
by them are (primary) animal movements. When animal ma-
chines are combined with those that are purely mechanical, and
the latter are moved by the animal forces of the former, they
possess communicated animal forces, and by means of these the}^
also perform animal movements. The aggregate of the animal
forces in the body of an animal is termed its animal nature.
The animal nature of a body depends on the peculiar condition
of the materials of which the animal machines, as such, consist ;
on the structure of the animal machines ; on the animal forces
themselves; and on the connection of the animal with the other
organic machines of the organism, whereby the forces and
movements of the latter are stamped with the animal character.
The continuance of animal nature is animal life, and its termi-
nation animal death. In all living animals the animal forces
act either in perfect accord with the sentient force of the mind,
or not : if the former, then a distinct class of animal movements
in the body is connected with each class of ideas, and conse-
quently both reciprocally contain the basis of their twofold ex-
istence. These united animal and sentient forces are termed
animal-sentient forces; and the movements they produce are
sentient actions (actiones animse). When the animal forces act
independently of the sentient force, they are termed pure animal

INTRODUCTION. 15

forces or nerve forces [vis nervosa], and their movements are
purely animal or nerve-actions}

Note. — It is absolutely necessary, that these various animal
forces and their modes of action should each have their distin-
guishing designations, and I have not been able to invent more
convenient terms than the preceding. They might have been
termed simply mental forces and nerve forces ; but since the
former term is already applied to designate the powers of the
mind, the affix animal must be used to distinguish the mental
forces of the sentient animal body.

7. By virtue of their animal nature, the bodies of animals
acquire forces, which cannot be explained by the physical and
mechanical laws applicable to the motion of other bodies and
machines, and which can act only through the proper animal
machines. Their workings are manifested partly in the latter,
partly in the other machines of the bodies, upon the forces and
movements of which they stamp the animal characteristics.
With these (primary) animal forces the influence of the soul
on the body, and also the moving forces peculiar to the animal
machines, are to be classed.

' The term Thierischer kbrper, as used by Unzer, exactly corresponds to the
modern phrase, animal organism. The word kr'dfte might he rendered forces,
powers, properties, faculties, or vis. In (3), kraft is applied to express the force of
attraction and repulsion ; and I have, therefore, used that word as its synonym,
although it is evident that Unzer uses the word rather indefinitely ; and the
Thierische krdfte, mentioned in the text, might more fitly be designated powers or
properties than forces. The true synonym is vis nervosa (639). Thierische-seelen-
krafte is a compound word, for which it is impossible to find an English synonym ;
it is used to signify the properties or functions of the brain, so far as that organ is
the seat of consciousness, or, more abstractedly, the combination in action of the
purely animal force {vis nervosa) with the mental. In either case the term implies
the action of mind and the existence of consciousness or will. When used in the
former sense, I have rendered the phrase by cerebral forces ; when in the latter, by
animal- sentient forces. Whenever the word seele is used in the original, either
adjectively or in compound words, to express circumstances dependent on the exist-
ence of soul or mind, as in beseelte, &c. (349, 603), I have rendered it by sentient.
Vorstellung is used indefinitely in the sense of sensation, perception, conception,
thought, or of an act of mind generally (vide 25, 34-36) ; and Vorstellungskraft to
signify the power or force by which we feel, perceive, think, or will. I have trans-
lated Vorstellung generally by the term conception, and consequently use the word
conceptive force as the best rendering of Vorstellungskraft ; but where the context
required or allowed, I have also rendered it by sentient force, or, more simply, by
mmrf.— Vide note to $ 25.— Ed.

16 PRINCIPLES OF PHYSIOLOGY.

8. The doctrines of animal nature presuppose the doctrine
of physical and organic nature (3, 5, 6), and must contan :

i. A description of the animal machines in the bodies of
animals, comprising the composition and structure of their
parts, and of their system of relation to each other.

ii. The determination of the animal forces proper to them
alone, and without reference to their influence on the other
parts and functions of the organism.

iii. The determination of their influence on these other
organs and functions.

All primary animal forces are either animal-sentient forces,
or nerve-forces (purely animal) (6) ; and hence arises the great
divisions of the entire philosophy of animal nature.

The First Part considers animal nature in its connection with
the thinking power of the soul of the animal, and includes :

i. The animal machines in general, in so far as they are
capable of the action of the animal-sentient forces (6). —
Part I, Chap. I.

ii. The animal forces, per se, without reference to their
influence on the rest of the mechanism, and considered specially
as animal sentient forces (6, 7). — Part I, Chap. II.

iii. The influence of the animal- sentient forces on the rest of
the mechanism of the animal body (6, 7). — Part I, Chap. III.

iv. The connection of the body and soul generally. — Part I,
Chap. IV.

The Second Part treats of animal nature with reference to its
simply animal forces, according to which the animal machines
do not act in connection with the sentient faculty of the animal
(355).

Lastly, in the Third Part, animal nature is treated of as a
whole (599) : in this Part we consider its essential characte-
ristics in the difl'erent kinds of animals, its origin, continuance,
and state of perfection ; its entire system of animal forces, its
decline, and finally its cessation.

Man is by no means the only object of this work, although,
as the most perfect of animals, he is its principal object ; it
contains rather the principles of a Zoology, or natural history
of every species of animal, but only according to their peculiar
animal forces; and as to these, only in outline (15).

PAET I.

ANIMAL NATURE IN ITS CONNECTION WITH

THE SENTIENT FACULTY OF THE

SOUL OF AN ANIMAL.

CHAPTER I.

I

THE ANIMAL MACHINES IN GENERAL, AND ESPECIALLY AS THEY
ARE ADAPTED TO THE ANIMAL-SENTIENT FORCES.

9. The proper animal macliines in animal organisms are the
brain and nerves/ in which the vital spirits (the nervous fluid)
are produced and distributed, with the object of constituting
the medium of the functions of these organs.

10. The brain is the seat of the soul. We feel that we think
in the head ; nowhere else are we conscious of our existence ;
in no other organ is there a thought^ or an idea, or consci-
ousness. Now, since the sentient faculty [Vorstellungskraft^]
of animals is their soul, the soul can have its seat nowhere else
than in the brain, and it would be absurd to maintain that it
is diffused throughout the body (597). It is sufficient to a
physician to know, that the thinking faculty can have no other
seat than the medullary matter of the brain.

11. The brain is the laboratory of the vital spirits (15, i).
" It appears certain that there is such a fluid essence secreted

' As the phrase thierischen maschinen is used for the most part by Unzer to
indicate the nervous system, it is so translated throughout the work wherever the
context permits. — Ed.

'•' The term VorstellungsJcraft is of very frequent occurrence, and has been trans-
lated by the terms sentient faculty or force, conceptive faculty or force, and simply
mind. — See note to $ 6, 25. — Ed.

2

18 THE BRAIN AND NERVES AS [i.

from the vessels of the gray matter of the brain into the hollow
tubes of the medullary matter, which is carried in the tubes
of the nerves to their termination, and supplies the principle
whereby the nerves are rendered capable of being the organs of
the senses and of movements/^ (Haller's ^Physiology/ sect. 383.)
As the gray or cortical substance of the brain is the secreting
organ of the vital spirits, the medullary substance must be the
seat of the animal-sentient forces. The secretion and action
of the vital spirits will be considered afterwards (374).

12. The brain also gives origin to all the nerves, which are
continuations of the cortical substance, given off partly from
it directly in small bundles, termed the cranial nerves, and
partly from a thick cord of it, termed the spinal marrow, which
passes downwards through the spine, whence the nerves are
distributed to all parts of the body.

13. The nerves generally are enclosed in an investing mem-
brane, and, like the blood-vessels, divide and subdivide in the
greater part of the body, which they either penetrate or form
loops in ; or, having lost their investing membrane, are so incor-
porated with the soft parts, that they can be no longer traced.
Their essential element is the medullary matter of the brain,
or the soft substance enclosed within the cortical substance;
whereas their investing membrane seems to have no share in
the proper animal functions allotted to them. Every nerve is
a bundle of much smaller fibrils, each of which rims an inde-
pendent course to and from the brain. Every nerve has its
special point of origin in the brain, and every fibril must have
its special origin from that point, from whence it takes an
entirely independent and separate course through the medulla
oblongata and the spinal cord, to its minutest termination.
According to all probability, the fibrils of the nerves are hollow
canals.

Since these propositions are of very great importance in
the present work, and much will be deduced from them, it isj
proper to state that they are taken from the Physiology of j
Haller, the greatest anatomist and physiologist of the day.

14. The nerves so terminate externally, that either they are)
incorporated with other machines of the organism appropriated;
to certain movements; or they are distributed over the skin or ■
other parts of the body, as the eyes, ears, &c., without exciting

CH. I.] ANIMAL MACHINES. 19

such machines to motion, if they be appropriated to certain
movements, or at least without co-operating therein. The
first are termed, in relation to their function, motor nerves;
the other are sensitive nerves. They are, however, identical
in structure, and only differ in this local relation. Each nerve
may be either the one or the other, according to its distribu-
tion ; and each motor nerve is at the same time endowed with
the properties of the sensitive. The motor nerves have ganglia,
composed partly of their own fibres, and partly of other nervous
twigs and nerves which accompany them, whereby the direct
course of the fibrils and nerves is interrupted. The nerves of
the senses, which have no motive influence on the mechanical
machines of the organism, have no ganglia.

15. i. All the phenomena of motion and sensation mani-
fested through the nerves, render probable the existence of a
remarkably subtle fluid essence, which is present invisibly in
the medulla of the brain and nerves, and is the means whereby
all the functions of both are performed. It is termed the
vital spirits or nervous fluid, but it is not known how and
when it contributes to the animal actions. It is not that fluid
matter which is seen in the medulla of the brain and nerves,
but a much more subtle spirit, imperceptible to the senses.
It is inferred from the phenomena which betray its existence,
that this nervous fluid is a remarkably mobile fluid, a spirituous
vapour, which can be neither aqueous, nor glutinous, nor
elastic, nor etherial, nor electrical.

ii. Although animal machines are indeed proper to all
animals (6), still every species does not possess those which
have been just described, but only the most perfect, namely,
man and the animals immediately below him. But since our
object is not to lay down the principles of a physiology of the
proper animal nature of man only, but rather of animals in
general, these principles will be found applicable to an expla-
nation of the functions of animal machines in the various
classes of animals, a detailed description of which may be
found in Haller^s greater Physiology, and in his ^ Opera
Minora.^ ^

From these statements we may draw the conclusion, with

* The author here gives a sketch of the comparative anatomy of the nervous
system, as known in his day ; this has been omitted for the sake of brevity. — Ed.

20 THE ANIMAL MACHINES. [i.

reference to the wliole animal kingdom, that the general animal
machines in which no species (so far as is known) is defective,
and which, consequently, are the most essential elements of
animal life, are the nerves, the ganglia, and the spinal cord,
with their (probably) accompanying cortical substance — or the
analogues of those structures — in which the vital spirits reside
and circulate ; and in which, in those cases, there is no cere-
bral cortical matter, the latter must be secreted directly from
the blood (11); and that the cerebrum and cerebellum, to-
gether with their cortical substance and the nerves of the
external senses, are not so general, and only essentially neces-
sary to certain species of animals, especially those endowed
with mind. Those only of the cerebrate animals, however,
which, without question, think and desire, are supplied with
a large and considerable brain; whilst those which manifest
ambiguous traces of ideas have a small, simple, and irregular
brain, differing little from the spinal cord, to which it appears
to be an appendage ; and, consequently, has probably only the
same functions.

In this, the First Part of the Physiology, we investigate the
animal nature of the most perfect animals, in which all these
animal machines, or, at least, the most important, are com-
bined ; and which render them capable of acting in connection
with the thinking force. All other animals only differ, in
descending the scale, in a continually increasing defect in
the animal organs and forces ; and there are some whose whole
life is so simple and mechanical, that they scarcely manifest
any traces of the animal forces. In the Second Part of this
Physiology it will be shown how animal life can equally sub-
sist in these with only the most general and most essential
animal machines, and without the co-operation of those pecu-
liar to more perfect animals ; and it will be shown, also, how
far they are similar or inferior to the latter. Finally, the
Third Part will exhibit a general view of animal nature, and
will explain how the forces in each species of animal connect
the machines together, and complete animal life in each (8).

CHAPTER II.

THE ANIMAL FORCES CONSIDERED ABSTRACTEDLY, AND
PARTICULARLY AS ANIMAL-SENTIENT FORCES.

16. To what end are the animal forces peculiar to the
animal machines only, without reference to their influence on
the other portions of the organism, so that the latter would
still possess them, even if not united with the mechanical
machines which move the body? The answer to this question
is the object of the present chapter.

SECTTON I.— THE FUNCTIONS OF THE VITAL SPIRITS.

17. The vital spirits originate in the brain (11). If, con-
sequently, they contribute, in some degree, to the functions of
the nerves, and are present in them, or carry the impressions
made on the brain from time to time along the trunks, twigs,
and terminating fibrils of the nerves, they must flow from the
brain to the most remote termination of the nerves, or, at
least, propagate the impression on the brain in this direction,
namely, downwards to the termination of the nerves; and have
also a natural motion from the brain downwards along the
trunks, branches, and terminating fibrils of tl^e nerves, whereby
they become the medium of the direct action of the brain on
the nerves (122).

18. If the vital spirits already secreted in the nerves con-
tribute somewhat to the functions of the brain, and carry to
it the impressions received from time to time by the termi-
nations of the nerves (11), they must also flow from the latter
to the former, or at least propagate the external impression
in that direction upwards to the brain, and possess a natural
motion from the terminating fibrils of the nerves upwards to
the brain, whereby they become the medium of the direct action
of the nerves in the brain (36 — Haller).

19. This interposition of the nervous fluid between the re-

23 FUNCTIONS OF THE VITAL SPIRITS. [i.

ciprocal actions of the brain and nerves on each other, derives
great probability from all observation of the operations of the
animal forces, and takes place so quickly and immediately,
that the fluid acts with inconceivable rapidity, either as to its
own movements, or in propagating impressions (Haller, § 381),

20. It is a natural inference, and one established by facts,
that the vital spirits are diminished, or rendered unfit for their
functions, by frequent or prolonged use; and, consequently,
the animal forces, of which they are the medium, become
weakened or disappear (17, 18), or increase, when they are sup-
plied to the brain and nerves.

21. If the vital spirits are duly secreted from the blood in
the brain, and their influence goes uninterruptedly thence to
the nerves, or vice versa, the functions of the sentient forces or
the nerve-forces, of which they are the medium, are performed
naturally; and, consequently, those forces can act freely, so
far as they are influenced by the vital spirits.

22. The free action of the animal-sentient or nerve-forces,
in so far as it is dependent on the vital spirits, is prevented
by whatever prevents the production of the vital spirits in the
brain ; by whatever destroys their normal, but to us unknown,
condition ; by whatever interrupts their influence directed from
the brain to the nerves, or vice versa ; or, finally, by whatever
destroys them or wears them out. Obstruction of the cerebral
circulation, the compression or destruction of the brain, or its
entire removal from the body, prevent the production of vital
spirits. A general corruption of the fluids must also neces-
sarily destroy their natural condition; ligature, or compression,
or section of the spinal cord, prevents their influence being
communicated from the brain to the nerves, or from the nerves
to the brain ; and an undue straining of the powers of body
and mind consumes the vital spirits (20).

23. Experience teaches us, that sleep, wine and other spiri-
tuous drinks, light nourishing food, the odour of spirituous
vapours, ablution of the limbs with spirituous fluids, friction,
gentle bodily exercise, mental enjoyment, cheerful society,
moderate and agreeable use of the senses, all strengthen and
enliven the sentient and nerve-forces ; and it is probable that
this occurs either from an increased secretion, or a renewed
natui'al good state of the nervous fluid, or from a greater

CH. II.] CEREBRAL FORCES. 28

facility of flux and reflux which it acquires. In like manner it is
probable that prolonged watching, starvation, debilitating food
and drugs, the emotions, and the active elements of certain
matters which, from their destructive qualities, are injurious to
the nervous fluid, as opium, for example; also cold, indolence,
want of exercise, fatigue, vexation, intense application of the
mind or of the senses, all interrupt or diminish the animal
forces, because they either diminish the vital spirits, or impede
their secretion, or render them morbid, or hinder their flux and
reflux.

Note. — Although little is known of the nature and proper-
ties of the forces of the vital spirits, the physician can content
himself therewith, even although the little that we think we
know is doubtful, and at the best only probable : for they may
remain undetermined for ever without any loss to science, be-
cause we are under no necessity to show the origin and nature
of the animal forces, inasmuch as we learn their true actions
and laws from observation only.

SECTION II. THE FORCES OF THE BRAIN CONSIDERED

ABSTRACTEDLY AS ANIMAL-SENTIENT FORCES.

24. The brain has a regular double movement, which is
mechanical only, and not peculiar to its animal nature. One
movement is simply the motion communicated to it by the
arteries; the other consists in an alternate eff'ort to expand
and contract, which Haller attributes to the connection between
the respiration and the cerebral veins, so that the latter, like
the brain itself, become turgid at each expiration, and flaccid
at every inspiration (Haller's ^ Physiology^). Although this me-
chanical motor power of the brain, as well as the consequent
secretions, together with the cerebral circulation and its purely
physical forces, do not properly come under our notice here,
but belong to the physiology of the mechanical nature of animal
organisms, still it is necessary to remember them in an inquiry
into its animal forces, so far as the existence of the latter pre-
supposes their existence. Since respiration is the cause of the
continual movements of the brain just mentioned, and without
it, indeed, the animal-sentient forces cannot act, because their
action presupposes the existence of the mechanical forces (6),

24 CEREBRAL FORCES. [i.

its absence appears to be the reason why the embryos of animals
endowed with a sentient brain, display no trace of those animal
functions for which the animal-sentient forces of the brain are
absolutely requisite.

25. The seat of the soul is the brain (10). Whenever the
brain is destroyed, or its natural functions interrupted, the sen-
tient force ceases to act. So soon as it is restored to its natural
functions, conceptions return. The whole brain is not imme-
diately necessary to thought, since large portions of it may be
lost or be defective, or be compressed, or ossified, or its functions
otherwise interrupted, without any perceptible influence on the
mental powers, which, as to the cortical substance at least, is not
remarkable, because it is not the seat of mind (11) ; but it can-
not be deduced from any observation whatever, that the whole
brain may be wanting (as, for example, when the head is re-
moved, or the brain entirely destroyed, or the functions of all
its parts generally interrupted), and the slightest trace of mental
operations ever be perceived. Further, when a thought arises
in the mind, a change must necessarily occur concurrently
therewith in the brain, and particularly in the medullary sub-
stance, without which the sentient force cannot act ; and when
this change occurs in the brain, the sentient force is necessarily
excited into action. Whatever may be reasoned on the matter,
a change in the brain must consist in a movement, and the
medullary matter must also be endowed with a motive force,
which acts in harmony with the sentient force. So that each
distinct class of perceptions is always connected with certain
animal movements (6), and with these movements a certain
class of perceptions ; for it is ascertained from numerous ob-
servations, that after certain injuries of the medullary portion
of the brain, especially of that part from which nerves of sensa-
tion arise (14), certain kinds of perceptions [Vorstellung] , as
for example, certain sensations, are prevented or disappear, and
together with them all the ideas, desires, and instincts, dependent
thereon, as well as other faculties of the mind. (Haller.) This
motive power of the brain, which is connected with the sentient
force [mind], is an animal-sentient force, and hence arises
the fundamental general principle in the doctrines of the con-
nection between body and mind, that the medullary matter of
the brain possesses an animal- sentient force, by means of which.

CH. II.] MATERIAL IDEAS. 25

at every act of mind,^ whether it be a sensation, imagination,
desire, reflection, or conclusion, there is produced in it a cer-
tain animal movement, necessary thereto, without which the
act of thought [Vorstellung] can neither arise nor continue,
and with which it infallibly arises and continues. This animal-
sentient force is peculiar to the brain, and is the property of
no other portion of the nervous system^ because in none other
except in the brain does an animal movement develope per-
ceptions (10). The medullary matter of the brain can also, with
propriety, be designated as the only instrument of the sentient
force, for it is through its animal movements that the mind
puts its force into action, and maintains it, and without which,
it would absolutely remain inactive. Philosophers have already
introduced the phrase, material ideas, to express those move-
ments in the brain that are necessarily connected with each
act of thought. (Baumgarten's Metaphysics, § 416.) A psy-
chological materialist considers these material ideas as the ideas
of the mind itself. But since it must be firmly maintained,
that the thinking faculty is an immaterial substance [Substanz),
it cannot certainly be granted that these material changes in
the brain are really the ideas themselves ; but since the two
are inseparately connected with each other, and the mind never
acts, nor can act, in animals, without these movements, it is
fully established that every act of thought presupposes and
causes a movement in the brain (material idea), and every such
movement in the brain presupposes and causes a conception in
the mind ; that the same or a similar conception excites the
same or a similar material idea, and that the same or a similar
material idea excites the same or a similar conception in the
mind ; that when there are no conceptions excited in the mind,
there are no material ideas, although probably similar movements
may take place in the brain; that when no material ideas take
place in the brain, no conceptions come into real existence in the
mind (112) ; and that the perfection or imperfection of the mental

' The phrase Vorstellung der Seele is here translated act of mind. Vorstellung is
of very frequent occurrence throughout the work, and is ordinarily translated con-
ception. The reader must, however, bear in mind, that the term " conception " does
not so exactly express the author's meaning as " act of mind," inasmuch as Vorstel-
lung is applied to signify sensation, perception, and thought generally, — in short,
evert/ mental operation ; whereas conception has a more limited application. No other
word could be found, however, more nearly expressing the author's meaning. — Ed.

26 CEREBRAL FORCES. [i.

powers depends very mucli on the natural perfection or imper-
fection of the brain, or on the full or faulty development of the
brain at birth, or during growth, &c., of which we have illus-
trations in the deformed and compressed heads of many stupid
races.

Note. — The reader must not object to the expression
" material idea,^^ because it has been very variously misapplied.
By it we understand no hieroglyphical figures of the objects of
the conceptions, no impressions stamped on the medullary
substance of which one has no conception, and which can only
be considered as the fancies of too contemplative philosophers.
It is least in our intention, with Bonnet, to analyse the faculties
of the soul by means of their altogether unknown qualities.
It need only be granted, that the change which takes place
in the medullary substance at each conception, is a movement
which, since it is unknown, every one may conceive for himself
as he pleases; and that we term these movements material ideas ,
so as to have a short phrase alreadj^ used by writers, instead of a
long circumlocution. It will be seen, that throughout the work,
we use this expression in no other than this general signification.
26. Since every continuous conception in the mind is to be
considered at each moment as a prolonged action of the sentient
force, and no act of the latter takes place without material ideas
in the brain (25), it follows that each continuous conception
excites continuous movements in the brain which are usually
considered under the term impressions, or representations of the
conceptions. The more a conception is developed, or, in other
words, the clearer it becomes (Baumgarten^s 'Metaphysics,'
§ 415), by so much the more fully must the material idea be
developed ; if, on the other hand, the conceptions be obscure,
there are only imperfect and undeveloped movements in the
brain. A more forcible conception requires more vigorous
movements (material ideas) in the brain, and more vigorous
material ideas develope more forcible conceptions. Since every
conception is the origin of a material idea in the brain, and
vice versa (25), the more vigorous conceptions are larger con-
ceptions so far as they are the origins of material ideas.
(Baumgarten's 'Metaphysics' § 379). A large conception
contains small conceptions as its constituent parts, and con-
sequently it is made up of several, each of which causes a

CH. II.] MATERIAL IDEAS. 27

material idea in the brain (25). Consequently, the material
ideas of more vigorous conceptions are more compound and more
vigorous movements than those of the weaker ; and for similar
reasons, the conceptions of more vigorous material ideas are more
compound and larger conceptions than those of the weaker.

27. All conceptions are operations of the sentient force, and
consequently acts of the soul. All material ideas are operations
of the animal-sentient force of the brain (25, 26), consequently
they are operations of the animal motor forces of an animal
machine. But since neither can exist without the other, the
conceptions, as well as the material ideas in general, are effected
by means of the two co-operating forces of the soul and brain.
When the animal machines produce material ideas in virtue
of antecedent impressions derived from without, and thus induce
the co-operation of the conceptive force, — such as takes place,
for example, in external sensations, — conceptions thus origi-
nated are termed purely natural)- (impressional) conceptions^
which arise in the mind, necessarily and physically (Baum-
garten^s ^Metaphysics,' § 522), and succeed each other according
to the laws of external impressions, so far as they put the
animal- sentient force of the brain into activity. When, on
the other hand, conceptions, and their material ideas, are de-
veloped by the sentient force, independently of any previous
external impressions in the animal machines, and thus induce
the co-operation of the animal-sentient force of the brain, as,
for example, in volitional acts, — these conceptions are termed
arhitrary , spontaneous, physiologically free^ (Baumgartner, §520 ;
Hallers's 'Physiology,' § 570); and they succeed each other ac-
cording to the laws of the sentient force. Neither the purely
impressional, nor the spontaneous conceptions, can have a real
existence, independently of material ideas (25), and when they
continue, must embody their impressions in the brain (26). But

* The term naturlich, here translated natural, has a pecuUar meaning, being used
generally in the sense of organic, somatic, or corporeal, or to express something antago-
nistic to spiritual. I have ordinarily translated it by natural, organic, or physical.

* The reader is particularly requested to observe, that the words " arbitrary" and
'* spontaneous" are used here and elsewhere throughout the work in their strict
etymological and metaphysical sense, and indicate conceptions or actions caused or
excited by the will, as a faculty of mind. This remark is necessary, because, popu-
larly, the word " arbitrary," indicates acts that are despotic, absolute, or capricious ;
while " spontaneous" is applied to acts done without compulsion. The words in
the original are eigenmdchtig and selhstthdtig. — Ed.

28 CEREBRAL FORCES. [i.

as to the former, the mind cannot, by its own power alone,
produce the material ideas in the brain, but must wait for
the external impressions which form them in the brain ; while, on
the other hand, no immediately antecedent impression on the
nervous system is necessary to the latter — the ideas of the
intellect — but the soul forms them by its own proper power,
and lets them follow each other according to their natural
psychological laws, free from the restraint of external impressions.
Note. — It is necessary to comprehend clearly this difference
between the conceptions, otherwise nothing can be accurately
distinguished and taught in the physiology of the connection
between body and soul ; for this reason, the new expressions
must be excused, and their subjoined definitions closely adhered
to in the subsequent portions of the work; and there is nothing
in them which does not fully harmonise with established psy-
chological ideas.

28. Probably these material ideas and representations of the
conceptions in the brain, consist simply in a play of the vital
spirits in it ; for when the brain of an animal is examined, there
IS nothing visible, of all the animal movements, or at all events
of the material ideas ; and its purely mechanical movements in
no wise harmonise with the conceptions, but are much more
simple, and are in accordance with the mechanism of the cir-
culation and respiration.

29. This fundamental principle of the animal nature of all
sentient animals, namely, that every operation of the soul
originates, continues, ceases, is defective, and increases or
diminishes, in connection with an operation of the animal-sentient
force of the brain (25, 26), — connects the souls of animals most
intimately with their bodies, and the conceptions with the move-
ments, and lays the basis for the whole doctrines of the animal
nature of the sentient forces, or in other words, of the union
of soul and body, (compare 345). This union is known to,
and conceded by, philosophers and physicians, although they
explain it in totally different ways ; which explanations, how-
ever, are unnecessary and foreign to medical art, because it
is of no real importance whether the union be explained
'^ materially,'^ ^*^ harmonically," '^influxionistically,'' or ^^occa-
sionalistically.'^ And although the peculiar relations of the
movements in the brain (its material ideas), which accompany
the conceptions be unknown (28), nevertheless their existence

CH. II.] EXTERNAL IMPRESSIONS. 29

is rendered evident from the continual operations of each concep-
tion on the body, and which must necessarily have their origin
in the brain, where the mind has its seat, and is in intimate
relation with the nervous system.

30. The doctrines of the animal-sentient forces which follow
from these principles, divide naturally into two principal divi-
sions; namely: 1st. How are the material ideas produced in the
brain? (31-112.) 2d. What functions do they perform in the
animal economy? (113-344.) These two take place mainly
through the connection of the brain with the nerves, whereby
the animal forces of the nerves keep up a physical relation with
the animal-sentient forces of the brain.

SECTION III. THE ANIMAL FORCES OF THE NERVES, CONSIDERED

SOLELY IN THEIR RELATION WITH THE ANIMAL-SENTIENT
FORCES OF THE BRAIN.^

Of the External Impressions [Aussern sinnlichen Eindriicke] —
[Nerve feelings) .

31. Every nerve has its beginning or origin in the brain (12) ;
and if an impression be made there, and propagated along the
nerve, it must necessarily take a direction from the brain outwards
towards the branches and their terminations, as the vital spirits
would also propagate it (17). If, on the contrary, a similar im-
pression be made on the terminations and propagated along the
trunk of the nerve, its direction must be toward the brain in the
same course as the vital spirits (18). If a nerve be divided, an im-
pression made on that point separated from the terminating fibrils,
but still in connection with the brain, takes the same direction if
it be propagated, just as if it had been made on the terminating
fibrils themselves, namely, upwards to the brain. On the con-
trary, if an impression be made on that end of the cut nerve which
is separated from its connection with the brain, but in connection
with the terminating fibrils, if propagated, it will go towards the
terminating fibrils. If an impression be made on the cerebral
origin, or on the terminating fibrils of the nerve, and it is
propagated, it will in both cases traverse the nerve only as far
as the point of section ; consequently, when an impression takes

' The thierische kr'dfte of the nerves, here translated animal forces of the nerves,
are termed elsewhere nervenkrdfte, or nerve-forces ; both phrases are used in exactly
the same sense as the Latin term vis nervosa^ which has therefore been preferred,
wherever possible, to the literal rendering. — Vide note to § 353.

30 CEREBRAL FORCES. [i.

place sideways on an undivided nerve, that is to say, neither at
its origin nor termination, but on the trunk between these two
points, if it be propagated, it can pass onwards from the point
of impression (not from its termination !) upwards to the brain,
and in like manner from the same point, (and not from the
cerebral origin of the nerve !) downwards to the terminating
fibrils. When by a touch or some movement communicated to
it, or by any other agency whatever, an animal machine (and
consequently a nerve) is so changed that it produces actions,
which cannot be satisfactorily explained by the physical and
mechanical laws of motion, or in other words, so that it mani-
fests animal actions (6) ; the change thus excited in it is termed
a sense-like [sinnlich] impression {nerve-feeling). A sense-like
impression made on the cerebral origin of a nerve in a direction
downwards, or on its trunk, if propagated, passes outwards to-
wards the terminating fibrils of the nerve ; on the contrary, a
sense-like impression made on the terminating fibrils of a nerve,
or on its trunk, in a direction upwards from the termination to
the brain, if propagated, is transmitted in that direction.^

» The indefinite use of the words " sinnlich," " sensible" " sentient," and " sensa-
tional," by German, French, and English writers, on the physiology of the nervous
system, has led to innumerable misconceptions by both authors and readers. Agents
frequently change the condition of the nervous system, and excite it to action with-
out being felt : that is to say, without exciting pleasure or pain, or the feeling of
self-consciousness, or any perception whatever of the agent or agents, or of the re-
sults of their action ; yet movements result therefrom as much adapted to attain a
definite and designed end, as if the agents were felt, and the mind itself acted. In
the text, Unzer analyses these phenomena, and terms the change which takes place
in a nerve, when agents so act upon it, a sinnlich impression or Nervengefuhl —
nerve-feeling. It is obvious from the context, that to render sinnlich by sensational
or sentient would give an erroneous idea of the author's meaning, if by those words
we mean " of or belonging to sensation or perception ;" for he emphatically dis-
criminates, in a subsequent paragraph (34), and elsewhere, between the property of
mere respondence to impressions seated in the nerves (** nerve-feeling"), and the
property of sensation or perception requiring a special organ, — a cerebrum.

There is no English word which corresponds to sinnlich as thus used by Unzer,
which I have hitherto rendered by sense-like. The term sinnlicher Eindruck may
be very correctly rendered, however, by the word '* impression," as used by modern
neurologists ; for when we say that light makes no impression on the nerves of the
skin, we mean to say that it excites no change in their medulla, so that appropriate
vital movements shall follow. I therefore propose to use the word "impression"
simply, as conveying the meaning of sinnlicher EindrucA, deducing therefrom the
adjective impressional.

It is to be observed, however, that sinnlich is used by Unzer in other senses,
when it may be rendered by sentient or sensational. When sinnlich impressions

CH. ii.J EXTERNAL IMPRESSIONS. 31

32. When an impression is received on the terminating fibrils
or branches of a nerve, it is termed an external impression (a
nerve-feeling from without inwards) (31,403), to distinguish it
from an impression passing from within outwards (31, 121),
and which must not be confounded with the sense of touch.
Whether the impression be made on nerves distributed in the
interior of the body or on the exterior, it is the same, provided
that when it is propagated, it passes upwards to the brain (31).
As to this external impression, experience teaches us, that it is
developed in living animals by every touch of the nerve, or by
some communicated movement, provided it excites a certain
definite, although unknown, change in the medulla of the nerve,
and is transmitted upwards to the brain. Every impression on
the terminating fibres of a nerve is not an external impression,
nor causes one, but only those which so act on the medulla of
the nerve, that animal actions directly result (31). For example,
light excites no external impression on the most exposed and
most delicate nerves of the skin, &c. The most undoubted
observations teach us, that animal actions are excited by the
agency of contact or movement, not in the investing mem-
brane, but in and through the medullary matter of the nerve.
(Haller's 'Physiology,' §§365,372,373.) The mode in which
the medulla is acted upon by a touch, or any other agent, is
purely animal, and difi'ers altogether from the physical and
mechanical laws of communicated motion. In every case where
a touch of the medulla excites most vivid animal actions, whether
they be acts of mind, or motions caused by the animal- sentient
forces, or simply by the animal forces (6), there is no perceptible
movement in the medulla, nor any change visible therein. Nor
are the animal actions resulting from such a touch in proportion
to its nature and strength, as when bodies act physically on each
other by a blow, pressure, &c.; but often the slightest influences
will, in the same nerve, excite the most energetic actions, and
a more forcible agent the weakest. Certain agencies cannot

reach the hrain and are felt, they excite an act of mind, or a Vorstellung, as sensa-
tion, perception, desire, &c. All acts of mind necessarily and directly dependent
upon such impressions are termed by him sinnlich ; and in this case the word may
be rendered by sensational. It must be remembered, however, that the word so
used implies causation as well as condition, — vide § 66, and would, I think, be as
correctly rendered impressional as sensational.

32 CEREBRAL FORCES. [i.

stimulate a nerve to the performance of its function, although
in reality they, act strongly physically ; as, for example, a sound
which shakes every bone in the head, excites no animal actions
in the optic nerves. There is also the mode in which a nerve
receives an external impression j for the working of an animal
force in the medulla of the nerve is one thing, the propagation
to the brain of the impression received by the nerve, another.
Then there is nothing in the medulla whereby this transmission
can be explained according to mechanical or physical laws. The
medulla is neither hard nor elastic, but a soft body, which
according to the laws of physics must prevent or arrest the
communication of motion. Besides, this transmission takes
place so rapidly, and so soon after the external impression is
received, that the mind can perceive no space of time to occur
between the stimulation of the nerve, and the animal action
excited in a part of the body far distant from the point where
the impression was made. Nor can this transmission be effected
like a motion in fluids, for the medulla is not fluid matter, nor
so filled with fluid as to have the mobility of fluids, but is a soft
material which retards motion. Lastly, the properties of ethereal
fluids are not observable in the medulla, nor even in the vital
spirits, as, for example, such as ether, the electric fluid, &c.,
which transmit motion in an unknown physical way. (Haller^s
' Physiology,' § 379.) Since both the external impression and
its transmission along the nerves are operations of the vis nervosa
(6), and the aggregate of the animal forces in animal bodies is
termed their Senselikeness \_Sinnlichkeit] , it follows that the
mode in which the medulla of the nerve receives impressions
generally, and external impressions particularly (31), as well as
the mode in which it transmits them, together indeed with the
impression itself, (it being an animal force,) belong to the Sense-
likeness [Sinnlichkeit] of animal bodies, and cannot be deduced
from or explained by the mechanical and physical laws of motion.
33. There is no difference between the nerves of motion
and sensation in respect to the method of receiving and trans-
mitting external impressions (14, 31). — See Haller's 'Physiol./
§ 384. But as in the present section we have to consider the
animal forces abstractedly, and without reference to their motive
force on the mechanical machines (16), that which has been
stated must be understood to apply to the motor nerves only,

CH. II.] EXTERNAL SENSATIONS. 33

in so far as they are at the same time sensitive nerves. In the
Third Chapter we shall state how far the animal forces of both
kinds of impressions on the nerves act on the mechanical
machines appropriated to the motion of animal bodies^ and in
particular how far they regulate these, as animal-sentient forces
of the nerves (8). But how do the impressions, per se, act on
the nervous system ? And what animal forces, and especially
what animal-sentient forces, become thereby participants in that
action ?

On External Sensations.

34. When a nerve of a sentient animal receives an external
impression, it is transmitted along it, and unanimous observa-
tions show, that at each impression, certain animal actions
result therefrom, either in the brain, from which the nerve
arises (12), or in those parts of the body with which it is in
connection ; but these actions no longer result, even when the
external impression is made, if its transmission to the structure
in which they previously took place be prevented by section
or ligature of the nerve (43). This transmission takes place
from the point of impression upwards (31, 32), and either
arrives at the brain or not. Both cases occur in nature (see
illustrations of the latter in 47-51). In* the former case, the
external impression entering the brain, instantaneously develops
that material idea in it which is required for the development
of the conception it originates. Since the conceptions [Vorstel-
lungen] thus excited in the mind by external impressions are
termed ea^ternal sensations, this animal force of the nerves,
in virtue of which they excite sensations by means of external
impressions, is termed their sensational force, or sensibility
[Empfindlichkeit], — (see § 62).

Note. — The word sensation [Empfindung] is commonly used
in a threefold sense. 1. As in the preceding sentence, where
it expresses the involuntary sensations [Vorstellungen], which
we obtain through the nerves of the external senses. 2. When
it expresses the inner feeling of the soul, — its consciousness
of itself (80). 3. When it denotes generally the perception
[Vorstellung] of the existing condition indefinitely, or equally,
whether this perception be excited by an external impression or
not. It is of the highest importance, that these three meanings

3

34 CEREBRAL FORCES. [i.

be distinguished^ for otherwise the doctrines as to the recriprocal
influence of body and soul can only be indistinctly and inde-
finitely comprehended. We have, therefore, for want of more
elegant expressions, determined to designate sensations of the first
c\a,ssea^ternalj and of the second internal, and never to vary from
these terms, except when we use the verb to feel, in the third,
general, or indefinite meaning, when it is not necessary to say
whether external or internal sensations are meant. The reader
will sometimes find it necessary in the sequel, to remember these
remarks.

35. A true external sensation is never excited without there
being an external impression on the nerves, and consequently
the latter is rightly considered the only primary animal force (6),
whereby the soul feels. But since external sensations are con-
ceptions which cannot possibly arise without material ideas in
the brain (25), it follows that in each case an external impres-
sion must excite a material external sensation in the brain, and
itself develop true external sensations, independently of the
co-operation of the conceptive force.^

» The Gottingen reviewer of Unzer's work, referring to this doctrine as to the
development of external impressions into material ideas (the "species" of Haller),
objects "that nerves pass from and to the spinal cord and enter it, and, conse-
quently, that the external impressions made on them ought to be developed therein
into material ideas ; yet it is certain that the soul neither feels nor has its seat in
the spine." This and other objections raised against Unzer's views in this review
are the more interesting, because it seems probable that Haller was the writer, and
because it gives Unzer an opportunity of explaining some points more fully. He
then replies to the objection : — " Although this is hardly advanced as an objection,
and although I have not only not neglected to notice the matter referred to, but
have entered into details in illustration ; still it is sufficiently important to merit
further consideration. It is not merely a change caused at the origin of a nerve by
impressions, that induces sensation and thought, but it is always necessary thereto,
that there be a cerebral tissue into which the nerve must penetrate. Since new
fibrils frequently pass out from the ganglia, it might be inferred that all might feel ;
but as there is that peculiar structure wanting in them, which is present in the brain,
and is subservient to the formation of material ideas, the change which the nerves
undergo in the ganglia from external influences, is only a motor force — a reflexion
of the impression upon other nerve-fibrils, — and which has been fully explained
already in my work (399, 421). It is the same with the nerves which arise from
the spinal cord, and which probably have the twofold function of transmitting to the
spinal cord the impressions they receive, that they may be sent directly forwards to
the brain and subserve to sensation ; or that they may be reflected in the spinal
cord on other nerves, and thus induce certain movements which otherwise would
not have resulted from these impressions." — Physiologische Untersuchungen, p. 24.
Compare also § 624.— Ed.

CH. II.] EXTERNAL SENSATIONS. 35

36. True external sensations are conceptions excited by
external impressions on the nerves. Thereby the mind dis-
tinguishes at each act of attention the point where the external
impression takes place. Consequently, the sphere of action of
the external impression, which causes the external sensation, is
only between the point of impression and the material external
sensation in the brain; and since there is first the external
impression, and then its transmission, the vital changes which
cause the external sensations must be propagated from the
point of impression upwards to the brain, and not downwards,
from the brain, in so far as they are felt (31). If, consequently,
a branch of a nerve is irritated at a point nearest to the
brain, the external impression which ascends thence to excite
a material external sensation, can excite it in the most distant
branches, and by their means develope impossible animal actions.
And if these actions should arise in the distant branches, or
through them, they are the actions resulting from an impression
occurring contiguous to the brain which is sent downwards,
and contributes nothing to sensation. The probable motion of
the vital spirits accords with this view.

37. It may, however, be quite possible, with regard to many
external impressions, that the impression on the nerve may so
take place, that it concusses it, or its lower or more distant
branches, only mechanically. The impressions excited by this
mechanical concussion of the nerves are sometimes duly received,
and, like other external impressions, propagated to the brain,
and there produce external sensations. Thus, an external
impression may appear to be transmitted downwards without
that being actually the case. An example of this kind is
afforded by the tingling which a blow of the elbow causes to
be felt as far as the tips of the fingers, the nerve being
mechanically concussed ; it cannot be said that the external
impression felt at the elbow had been propagated backwards,
and felt through the fingers.

38. The mind determines the point of external impression
in external sensations by an act of the judgment. At first
it learns to distinguish the point of contact by a due observa-
tion of its external sensations, and a comparison of them with
the place where the external impression takes place ; but after
frequent repetition it determines it in a shorter way, by analogy.

36 CEREBRAL FORCES. [i.

It is accustomed, for example, to decide as to the external
sensations which it feels through the terminating nerve-fibrils
of the left hand, which transmit the impressions they receive
to the brain, along the trunk of the nerve, that they take place
in virtue of external impression on the left hand. But if this
hand be amputated, and these terminating fibrils be altogether
removed, still every external impression made on the cut end
of the trunk of the nerve of the left arm, being likewise trans-
mitted to the brain, seems to come from the left hand, when,
from a want of attention, the accustomed method of estimating
the point of contact is adopted ; and the mind is only aware
from due observation, that its estimate is erroneous. This
case (in which there is no true external sensation from the left
hand) cannot prove that a true external sensation of an external
impression can reach the mind from a more distant spot than
the true point of impression of the nerve ; but simply that the
judgment may sometimes err respecting the external sensations,
which error is a defect of the judgment, and not of sensation.
In this way a thousand phenomena must be estimated, as when
a person thinks he has sensations in a lost limb, or when he
seeks the point of sensation in a broken limb, in a natural
direct line, and finds it in quite another place.

39. External impressions may be made on many nerves at
the same time, and the mind can distinguish all and each of
the external sensations thence arising, although the impressions
come from the most distinct nerves into a common trunk (as
for example, the spinal cord), before they reach the brain, and
there form the material ideas of an external sensation. In
the same nerve, and, at the same time, different impressions
may be made, yet the mind accurately distinguishes them ; so
that every external impression on each point of a nerve takes
also an uninterrupted course to the brain, and can there form
the material sensation peculiar to itself, and distinct from all
others, without being confounded or mingled, either on its way
with other impressions ascending at the same time, along the
nerve, or with the material sensations which arise at the same
time in the brain. The reason of this is, that the terminating
fibrils ^hich receive the impressions run a distinct course to their
origin, and remain quite separate, however they may be united
with other fibrils to form an entire nerve, or, however the

I

CH. II.] EXTERNAL SENSATIONS. 37

latter may be united to form larger trunks, as the spinal cord.^
Further, at the place of origin of the nerve in the brain, there
is a distinct point where the material ideas must be developed
from the external impressions which it brings to the brain.

40. It is useless to attempt an arrangement of the various
kinds of external impressions according to the variation in their
external sensations. Everything is ordered according to laws
altogether unknown, and which we can never fathom. Pain,
for example, is a sensation which usually arises from very
vehement external impressions on the nerves; nevertheless,
the most violent disturbance of a nerve is not always the most
painful. A corrosive fluid can excite a far more intolerable
pain in a nerve, than a blow which shatters the bone of the
limb. Neither is it the separation of the components of a
nerve by the corrosion, which causes the pain to be so acute,
for a sharp knife divides it without any remarkable pain. It

' This important doctrine of the distinct course of each nerve-fibril was taught
at Leyden during the first half of the last century. The following quotation will
interest the reader : — '< The doctrine of Albinus, — indeed, of the whole school of
Boerhaave, — in regard to the nervous system, and, in particular, touching the dis-
tinction and the isolation of the ultimate nervous filaments, seems, during a century
of interval, not only to have been neglected, but absolutely forgotten ; and a counter-
opinion of the most erroneous character, with here and there a feeble echo of the
true, to have become generally prevalent in its stead. For, strange to say, this very
doctrine is that recently promulgated as the last consummation of nervous physiology
by the most illustrious physiologist in Europe. ' That the primitive fibres of all
the cerebro-spinal nerves are to be regarded as isolated and distinct from their
origin to their termination, and as radii issuing from the axis of the nervous
system,' is the grand result, as stated by himself, of the elaborate researches of
Johann Mueller; and to the earliest discovery of this general fact he carefully
vindicates his right against other contemporary observers, by stating that it had
been privately communicated by him to Van der Kolk, of Utrecht, so long ago as
the year 1830." (Phys., pp. 596-603 ; Supplementary Dissertations to Reid's Works,
by Sir W. Hamilton, Bart., &c., note D ; ' On the Distinction of the Primary and Se-
condary Qualities of Body,' p. 874.)

This whole essay is a mine of suggestive thought to the neurologist, but is specially
interesting from containing a general abstract of the doctrines taught by the younger
Albinus, in his lectures delivered at Leyden, and which Sir W. Hamilton has obtained
from a manuscript copy in his Ubrary of the ' Dictata,' of Albinus, taken very fully
after the middle of the last century by Dr. William Grant, and collated with another
copy by an anonymous hand of 1741. Having, by the kindness of Sir William
Hamilton, had an opportunity of perusing a portion of these ' Dictata,' I cannot but
concur with that profound metaphysician in au expression of regret that they have
never been printed. — Ed.

38 CEREBRAL FORCES. [i.

is the same with the tickling which a fine feather, or particle
of dust, can excite, for it is a state of the nerve allied to that
of pain, and sensations much pleasanter than it require much
stronger external impressions. Indeed, the more indifferent
external sensations of heat and cold, hardness and softness,
moist and dry, of light, of dissolved salts, &c., are so totally-
different in the mind, that it is certain the external impressions
on the nerves must be different also ; but we know of nothing
generally, as to this difference, which may serve as a general rule.
41, 42. It is equally impossible to compare the material ideas
with the external impressions, or both these with the external
sensations {vide Haller^s ' Phys.,' § 556). Every external im-
pression does not necessarily excite external sensations (34),
although external sensations are the only conceptions it can
excite (35). Since an external impression differs from every
other in this, that it excites animal operations, and these can
be either in the mind as external sensations, or only in the
body, and consist simply in animal movements (7) j and since
we have only to consider here the operations on the mind of
an external impression (33), we must inquire under what con-
ditions an external impression develops external sensations, and
under what conditions it does not.

43. If a nerve of special sense be compressed or divided, the
sense is lost. If the brain be compressed, sensation ceases in
the whole body ; and when the spinal cord is compressed, sen-
sation ceases in the part below the point compressed. The
reason in all these cases is, that either external impressions are
not transmitted to the brain, or, if transmitted, do not excite
in it the material ideas requisite to sensation.

44. That a part be sensitive, it is requisite that it be endowed
with nerves capable of receiving those external impressions,
which can be transmitted uninterruptedly to the brain, and
there excite the material idea of a conception. The more a
part is endowed with such nerves, the more readily it receives
an external impression ; and the more uninterruptedly it can be
transmitted to their origin in the brain (43), the more sensitive
it is. The less a part is supplied with such nerves, although
it may have many others of a different kind, and the more diffi-
cult it is to convey external impressions to them, that is to say,
the more they are covered and protected from contact, and the

CH. II.] EXTERNAL SENSATIONS. 89

more hindrances there are to an uninterrupted transmission to
the brain, of an external impression, in the same proportion
the part is insensible (34).

45. We are now able to say what is requisite to the develop-
ment of an external sensation.

i. A nerve must be so acted on, that its medulla thereby
receives an external impression (31, 32).

ii. This impression must be propagated into the brain, so
far as the origin of the nerve (43, 44) .

iii. It must there excite the animal movement (a material
idea), which naturally arises from this external impression ; and
so soon as this takes place, the conceptive force of the soul
develops the external sensation (34, 25).

46. An external sensation derived from a given nerve may
be interrupted, or cannot arise.

i. When the nerve is not acted on, or not sufficiently so,
that its medulla receives an external impression (45, i) . All con-
ceptions, consequently, which are considered to be such external
sensations, but which arise only from the conceptive force with-
out an external impression, are not true external sensations :
of this kind are imaginations, recollections, anticipations, &c.

ii. When the external impression does not reach the brain at
all, but particularly that point where the material sensation is to
be developed. It does not follow because a nerve has been acted
on, and an external impression excited, that the latter must
necessarily be felt (42), for to this end the impression must
find its way uninterruptedly to the brain (45, ii).

iii. When the material idea, which ought naturally to result
from the external impression, cannot arise in the brain (45, iii).
The brain may be defective at those points whence the nerve
arises, and thus the limb, to which the nerve is distributed, may
be rendered insensible to all external impressions, although their
existence along their whole course to the brain, be rendered
manifest by other animal movements.

47. Since, in the normal condition of animal organisms, all
external impressions do not excite material external sensations,
so also there are portions amply supplied with nerves which
have little sensation ; so that the amount of sensibility of a part
cannot be deduced, from the number of nerves without certain
limitations. Nevertheless, these numerous nerves may be of great

40 CEREBRAL FORCES. [i.

use in the animal economy, by means of other animal opera-
tions (42) ; and as, in fact, experience teaches us, that many parts
well supplied with nerves have little sensation, feeling but rarely,
and only a few external impressions, and those of a special kind,
as the heart, stomach, &c., it is very probable, that in animals
in a state of health many external sensations are prevented by
similar natural obstacles, and that this is no abnormal condition
of many nerves. That this important matter may be placed
in its proper light, we will endeavour in every possible way to
demonstrate from observations, how external sensations are
prevented naturally.

i. Nature protects many nerves from contact by coverings,
by envelopes of cutis, or mucus, or so distributes them, that they
are only exposed to slight or gentle contact, or to certain im-
pressions expressly adapted to them, and little, if at all, to any
other. By this means, also, external sensations are so moderated
as not to be painful (46, i) .

ii. There are many nerves, so situated and distributed, that
they are only exposed to certain agencies, the optic for example ;
which, in general, are only susceptible of external impressions
from the rays of light ; while the nerves of the skin receive no
impressions from the rays of light (40). In the same way, the
undulations of the atmosphere, which duly act as impressions on
the auditory nerves, cause no external impression on the delicate
and sensitive nerves of vision. The odorous particles which are
so perceptible by the olfactory nerves, have no effect on the
tactile, gustatory, auditory, or visual nerves. Sometimes certain
nerves are endowed for a period only, with the capability of
receiving external impressions from certain irritations and
influences, which they afterwards lose, as, for example, in the
sensational instincts (265).

iii. Further, certain external impressions act so feebly on
nerves otherwise sensitive, that they do not go onwards to the
brain, but are weakened or lost in their course thereto. That
this feeble influence on the nerve has certainly excited an
external impression, is made clear by other animal actions, as,
for example, by certain animal movements which the impression
excites ; and the cause of its not being felt must be in its not
having reached the brain. Flatus in the stomach often excites
a tension of the nerves, which is so feeble, that we do not feel

CH. II.] EXTERNAL SENSATIONS. 41

it ; although the external impression that takes place at the same
time, betrays itself by animal actions, namely, contraction of
the stomach, as is proved by the rumbling of the flatus. But
the transmission of the external impression to the brain is
prevented in the natural state, or state of health, in a way which
requires a copious elucidation.

48. iv. It is incontrovertible, that many nerves, although
sensitive, are mainly appropriated to certain special movements ;
and that the external impressions necessary thereto, are seldom
or never transmitted to the brain, or only those of a certain
kind ; but that, for the most part, it is their normal condition
to remain in the nerve. The nerves of the stomach, intestines,
and heart, illustrate this point. Food which gives rise to a
strong sensation in the mouth, causes no sensation whatever
when passed into the stomach. Whether it be bitter, sweet,
or salt, it is the same in the stomach. Yet the stomach is
more amply supplied with nerves than most other viscera, and
these are highly sensitive to other impressions, as those of acrid
poisons, for example, and consequently quite susceptible of ex-
ternal impressions. As food comes into contact with them as
certainly as poisons, and excites an external impression, which
undeniably develops the animal movements of digestion that
result from the contact, it necessarily follows, that the external
impressions on these nerves are not generally transmitted to
the brain, but are lost in the mechanical machines, to the
movement of which they are specially appropriate. An
acridity in the stomach will be felt little, if at all ; but if it be
in the mouth, it almost suffocates us, and bites the tongue ; on
the other hand, it will excite a gastric spasm in the gastric nerves
by its external impression. The heart is abundantly supplied
with nerves, and remarkably sensitive. The impression of the
blood flowing through it excites its movement, which, even
when it has ceased, can be renewed by the injection of warm
fluids, and yet the mind feels nothing of this external impression.
The special destiny of these nerves is to excite the motion of
the heart, which, according to the views of all physicians, is
vital and not mechanical in its nature. It is so little necessary
that the external impression made on the nerves which move it
be felt, that motion can be re-excited in a heart detached from
the body by an external impression on the terminating fibrils

42 CEREBRAL FORCES. [i.

of the nerves, as when salt is sprinkled on them ; and by this
experiment all probability of a mere mechanical excitement by
the impression, (as in filling the heart with warm fluids, or with
air,) is taken away. Since, also, external sensation is not neces-
sary to the ordinary motion of the heart, there must be natural
hindrances to transmission, in virtue of which certain external
impressions are retained in these and analogous nerves, so that
they cannot pass upwards to the brain (see § 55 — 61). It is diffi-
cult to say, in what these hindrances consist. The external im-
pression on the heart is really there, since every motion of the
heart is excited by it. It is also in the stomach after taking food,
since the peristaltic motion of the latter is renewed by it. What
prevents the propagation of all these impressions to the brain ?
There is nothing to be found in the nerves adapted to this end,
except certain formations found scattered on the motor nerves,
termed ganglia (14), and the point of insertion of the smaller
fibrils in the larger trunks, where also a sort of ganglion is
formed. At these points, the direct course of the fibrils is
interrupted, and here the external impression traversing them
can be deflected from its course, and its transmission to the brain
prevented (13, 14); the more especially, as the outer thick coat
of the ganglion acts in some degree as a muscle, and, by a slight
compression, can hinder the transmission (Monro) . But is it not
probable, that an external impression on motor nerves of this
kind, is expressly intended, when it reaches the ganglia, to be
deflected to the trunk or branch of another nerve, or to another
fibril of the same nerve interwoven in the ganglion ? For thereby
it would cause a reflected or retrogressive action in the fibril,
as if an impression were excited in it, and sent from above
downwards, or, as if sent from the brain ; when thus deflected,
it puts certain parts into movement, just as an impression really
transmitted along the nerves from above downwards, and so
imitates the latter by this reflected course (31, 121, 122, 137).
If, however, this conjecture be groundless, still the fact remains,
that external impressions on certain nerves, not received directly,
excite movements without reaching the brain, and without being
felt.

49. V. Amongst the natural impediments to external sensa-
tions, those also may be classed (according to 46, iii) which
prevent the external impression from developing in its proper

CH. II.] EXTERNAL SENSATIONS. 48

place the material idea belonging to it, although it has arrived
at the brain ; that there are such impediments is certain, and
sleep is an example. This is a periodic state of insensibility
natural to all animals endowed with sensation, and enables them
to collect new strength after the weariness resulting from ac-
tivity, and which arises, as some think, from the want or
weakness of the vital spirits ; light may shine into the eyes,
sound fall on the ears, and the nerves may be stimulated in a
thousand waj^s, and yet no external sensation be excited.
Consequently, either the external impression never reaches
the brain (and for this conclusion, there is not the slightest
foundation), or else no material ideas are formed therein,
or at least only imperfectly ; and this is probably the true
doctrine, since a compression of the brain, either by haemor-
rhage, or effusion, or depression of a portion of the cranium,
or even excessive distension of the blood-vessels, develops the
same insensible state, and induces true sleep. It appears as if
the brain were in a state of torpor in profound sleep, so that
the material ideas are prevented being developed by the external
impression on the nerves ; whilst the purely animal movements
excited by the impression on the latter only appear to ex-
perience no change, — (see § 182, 183.)

50. vi. There is still another special cause which prevents
external sensations arising in the mind, in one or other of the
five methods described (47-49) ; and this is the frequent repetition
of an external sensation. By this, as observation teaches,
many external sensations become gradually weaker and weaker,
and at last cease altogether, although the impression on the
nerve still takes place. This diminution and destruction of
external sensations by frequent repetition, is termed the habit
of external sensations, and since it cannot be explained on
mechanical principles, it must be classed with the properties
peculiar to animal bodies (6).

51. Habit weakens or destroys external sensations in the
five following ways :

i. By their frequent repetition the susceptibility of the
nerve may be weakened or prevented (47, i). For example, a
thick cuticle is developed, and protects the terminating fibrils,
in consequence of certain oft-repeated impressions on the organs
of touch.

44 CEREBRAL FORCES. [i.

ii. An impression^ often repeated on a nerve, may render
it unfit to receive that particular impression, although it may
receive every other; as when one who, accustomed to cold,
neither feels the cold, nor has goose-skin produced, and yet
would feel a tickling from the slightest touch of a feather.

iii. The frequent repetition of the same external sensation
may render a nerve insensible (47, iii.)

iv. When the frequent repetition of the same external im-
pression (48), renders the nerve so insensible, that thereby
the ganglia and points of anastomosis are so changed that
they retain an impression which they previously allowed to
pass. This may only be observed in the cases in which an
external impression, in an unweakened nerve, excites both
sensation and movements at the same moment ; but in the ab-
normal condition excites the latter only. In such a case the
occurrence of the animal movement (a proof wanting in other
instances), shows that the external impression is really received
by the nerve and transmitted to the point, where, on its way
to the brain, it is reflected and sent downwards along the
trunk of the nerve, being the direction taken by an impression
transmitted from the brain itself (31, 122). This is the only
explanation admissible, since as the nerve is not enfeebled, the
principle just laid down (iii) cannot apply. Instances will be
remembered of persons who experienced spasms in their limbs
from various external impressions made on nerves in a distant
part, and in whom the same spasms continue to occur,
although the mind has become at last habituated to the pain,
and it is no longer felt. So, also, many epileptic and gouty
patients — the paroxysms they suffer being excited by worms or
gouty humors, causing external impressions on the nerves of
the stomach — can foretell an attack from the sensations thus
excited. After a time, however, when the disease is rendered
chronic, these sensations are no longer felt, and the paroxysms
come on quite unexpectedly.

V. Lastly, the frequent repetition of the same external im-
pression can weaken or destroy the external sensations. The
point in the brain, where the impression ought to excite the
material' external sensation, undergoes such a change, that the
development of the material idea is prevented (49). This is
the case when a miller becomes so accustomed to the noise

CH. II.] EXTERNAL SENSATIONS. 45

of his mill, that he does not hear it at all, or only with an in-
distinct consciousness. Again, we know that when the mind
is abstracted from other conceptions, and devotes itself to one
only (an act termed attention) ^ it can only do this by a cessa-
tion of the movements in the brain; or, in other words, of
the material ideas of the conceptions from which it is ab-
stracted (21). Such a repose of the brain probably takes
place in cases of the kind under consideration.

52. When the nerves of an organism receive external im-
pressions with greater comparative facility, and when the latter
meet with fewer or less important natural obstructions to their
transmission to the brain, and to the formation of material
external sensations therein (47, 51), the organism is termed
sensitive, in a special sense [excitablej susceptible) ; or, if the con*
trary, insensible (harsh, unfeeling); and the qualities themselves
are termed individual sensibility (94), individual insensibility.
The property of animal nature, in relation to sensibility and
insensibility, is the temperament of an animal body : the bodily
constitution, — the nature. By habit, sensitive organisms become
insensible ; consequently the temperament is changed, and this
may take place in all the modes indicated (51). An individual
sensibility towards certain external impressions, not shown by
the majority of persons of a similar temperament, is termed

53. Mental philosophers maintain, that external sensations
have greater strength than other conceptions, because they
consist of a greater number of elements [merkmalen],
(Baumgarten's ' Metaphysics,' § 402). Now, since each element
of a conception is also a conception itself, and every conception
requires a material idea in the brain (25), it follows, that the
material ideas of external sensations are compounded of more
movements in the brain, than the material ideas of all other
conceptions. Consequently, they exceed the latter in intensity,
that is to say, the movements in the brain which external
sensations produce, are greater, and consequently have greater
results, than those which accompany other conceptions.

54. Every thing that enfeebles external sensations, diminishes
also the force of their material ideas in the brain, and of their
action in the organism ; and this diminution of force can take
place by the same means, that enfeeble the external sensations

46 CEREBRAL FORCES. [i.

themselves (46, 50). The material ideas of external sen-
sations, and their operation on the body, are the strongest
when they are recent and not habitual, provided other circum-
stances are the same.

The External Senses.

55. The nerves are the organs of external sensations, but
only by means of the brain (43). Those parts of organisms
wherein the nerves are distributed that are susceptible only of
special external impressions, and consequently only of special
external sensations, are termed organs of the {external) senses.
In man, these are five; other animals have fewer, a few have
probably more.

56 — 64. The senses are — 1st, touch ; which has its seat in the
tips of the fingers, but it is mixed up with general sensation ;
2d, taste, subservient to nutrition ; 3d, smell, in many animals
much more acute than in man ; 4th, hearing ; 5th, sight. The
anatomical relations are to be found in works of anatomy ; the
metaphysical questions, as for example, why we do not hear
two tones, or see two images, or perceive the rays of light and
the undulations of the air, or feel the forms of salts, are dis-
cussed at length in works of metaphysics, and therefore need
not detain us.

The Sensational Conceptions.

It has so far been shown how material ideas are produced
in the brain by means of external impressions. In this way the
mind receives conceptions corporeally, necessarily, and involun-
tarily (27), in consequence of the animal force of the nerves
developing external sensations. But the mind can also produce
voluntarily, in itself, many kinds of conceptions, and through
these, material ideas are formed in the brain, as an effect of the
conceptive force, and by conceptions only, without the inter-
vention of any external impressions (27). This other kind of
material ideas so produced must be defined, before their in-
fluence on the animal economy can be explained. Since,
however, some of these voluntary conceptions induce only
material ideas of a kind that do not manifest externally to
the brain any perceptible efiects in the animal economy, and

CH. II.] SENSATIONAL CONCEPTIONS. 47

nothing therefore can be stated scientifically regarding them,
we will only consider those, of whose effects we know something.

65. No animal thinks without feeling. Those which have
the smallest external senses, manifest the feeblest mental
power. Sensations precede all their other conceptions. How-
ever possible it may appear, that animals which have felt for a
time, can still continue to think after all sensation is lost, there
is no well-established example of this ; much less of an animal
possessing conceptions which it has never felt. Thus sensi-
bility [Empfindlichkeit] is the first stimulus of the conceptive
force in animals, and to this extent all their other conceptions
originate in their external sensations. Now, since external sen-
sations presuppose material ideas, produced by external im-
pressions on the nerves (34), it follows that the latter must
regulate all the mental phenomena, either directly through
external sensations, or indirectly. But since all conceptions
are connected with material ideas in the brain, the material
ideas of all conceptions must depend either directly or in-
directly, on external sensations in the brain, and on the external
impressions on the nerves.

66. When, therefore, the matter is very closely considered,
we find that even the most spontaneous conceptions are oc-
casioned by external impressions on the nerves ; but this causa-
tion occurs in many so very indirectly, that the connection
becomes imperceptible ; in others, on the contrary, it is more
direct, often immediate, and this constitutes an important dis-
tinction in that class of conceptions which, in our arrangement
of external sensations, we have termed spontaneous (27) . It is
necessary, therefore, to bear this difference well in mind, and
not to adhere too closely, in a physiological inquiry, to the
ordinary psychological division of the conceptions and desires,
into the obscure, the indefinite, and the definite; a division
neither precise in itself, nor tending to the advancement of
physiology. When the mind is compelled to set in operation
and exercise its conceptive force by various external sensations,
each of which presents to it many sub-impressions of a single
object (53), it soon acquires a facility of conceiving some of these
sub-impressions spontaneously, although it can never attain to
the power to renew completely an external sensation, without the
aid of an external impression (35). Or this may be presented

48 CEREBRAL FORCES. [i.

in another aspect, as follows : when the animal- sentient force
of the brain is frequently excited into action by various material
external sensations derived from external impressions (which must
be very compound movements in the brain, since they consist
of so many sub-impressions), it partly renews these material
external sensations by means of the inner animal mechanism
of the cerebral medulla, in conjunction with the free-will opera-
tion of its own conceptive force, although it cannot develope
them fully without the aid of the external impressions. These
spontaneous conceptions, which are nothing more than incom-
plete external sensations, are imaginations ^ so far as they
appertain to antecedent external sensations^ and anticipations,
so far as they may belong to future external sensations. Con-
sequently, so soon as the conceptive force has attained to that
degree of perfection by means of external sensations, that it
can of itself form imaginations and anticipations, it is led to
re-perceive an antecedent external sensation by every new ex-
ternal sensation that has something in common with the latter;
the material ideas of the antecedent sensation being again, in
some degree, excited into activity. It can, however, conceive
the antecedent sensation again only so far as is possible with-
out the aid of the antecedent external impression; and the
animal-sentient force of the brain also co-operates therewith in
renewing each material external sensation, but only so far as
is possible without the entire antecedent external impression ;
there being only some of its sub-impressions in the existing
similar impression. Now the spontaneous conceptions which
are developed by external sensations in the way just described,
whether directly or secondarily, are termed sensational concep-
tions in the true sense of the word (32) [sinnliche im eigentlichen
Verstande].^ There are also sensational imaginations ^ndi fore-
seeing s. When sensational conceptions, acting in the same way
as external sensations, excite other spontaneous conceptions,
the conceptions thus produced are termed less sensational,

' The word sinnlich may clearly be used here in the sense of semational, — see
ante § 31 note, and § 34 ; but it strictly implies that the class of conceptions or act
of thought referred to are sinnlich, because necessarily dependent upon a sinnlich
impression. Hence the term " sensational," as used in this work, must be considered
to have a double meaning, expressive both of the origin of certain acts of mind (or
conceptions), and of their nature.

CH. II.] IMAGINATIONS. 49

physiologically more free (27) ; these, again^ may induce other
conceptions, still more free ; and when at length conceptions
arise, so far removed from sensations induced hy external
impressions, that the connection between them is no longer
traceable, and containing only few elements in common with
all the sensational conceptions which have induced them, they
are termed conceptions of the understanding or reason ; higher,
abstract, general ideas. In proportion as a conception is less
sensational, it is the less to be deduced from, and explained by
the sensations induced by external impressions; and the less it
is under their control, the more it is to be referred to psycho-
logical principles (27). On the other hand, when the mind
collects and combines from external sensations, associated sub-
impressions, which it perceives, sua sponte, without the assist-
ance of their external impressions, and only by the inducement
of similar external impressions, it causes material ideas in the
brain, such that they have something in common with the
material ideas of the external sensations from which they are
compounded or drawn. They imitate imperfectly those move-
ments in the brain, which can only be fully developed by the
co-operation of the external impressions of those external sen-
sations from which the sensational conception is compounded;
and when sensational conceptions of this kind excite any actions
in the animal economy, the actions must in part correspond
with those that result from the external sensations themselves.

Imaginations [Einbildungen] .

67. Sensational imaginations are conceptions of past external
sensations (66), — (Baumgarten^s ^ Metaphysics,^ § 414), which
the mind renews spontaneously, so far as it is able, without the
assistance of external impressions (Baumgarten, § 415). Con-
sequently, they are wholly sensational conceptions. The ma-
terial ideas of imaginations are also those of past external
sensations, but in that imperfect condition, which necessarily
results from the want of an external impression (35, 53); iu
other words, when the mind excites spontaneous imaginations,
movements are also excited in the brain, which are partly the
material ideas of former external sensations [QQ). Generally con-
sidered, the material ideas of imaginations are feebler than those

4

50 CEREBRAL FORCES. [i.

of external sensations. Some may, however, surpass the latter, if
compounded of many external sensations (53). The stronger the
imaginations, the more effective are their material ideas (26).

68. That which is wanting in the material ideas of the
imaginations, so that they do not form the perfect material
ideas of external sensations, is, the external impression trans-
mitted along the nerves to the brain ; which also renders the
material ideas more perfect, and consequently, the conceptions
richer in sub-impressions [merkmale] than those which the
mind can produce without it (53).

69. If material ideas act as animal-sentient forces of the
brain (6) in the animal economy, and excite animal actions, the
actions excited by material ideas of imaginations must partly
accord with those of antecedent external sensations {67, 66).

70. Since dreams are often imaginations of the sleeping
state (sensational conceptions), which in somnambulism, and
during the waking state in insanity, become so distinct that
they cannot be distinguished from external sensations, the
rules stated previously (67 — 69), with reference to imaginations,
are applicable to all these. When the mind spontaneously
combines many imaginations, it invents poetically [dichtet sie] .
(Baumgarten's ^ Metaphysics,^ § 438.) All that has been
stated as to imaginations and their material ideas, is applicable
also to fictions (Erdichtungen).

71. All conceptions are connected with their proper material
ideas (25). But for the mind to know regarding the same
conception returning at different times, that the last is the
same as the first, a renewed conception is requisite, and it
remembers, or an act of memory takes place; but it is not
necessary to this end, that the first should be continuous with
the last. So little, indeed, is this continuity necessary, that
a long period may elapse before the renewal, without there
being a trace of the conception in the mind, and still when re-
developed, the mind knows that it is the same as the previously
existing conception. It is equally unnecessary for the material
idea of a conception thus remembered to have a continuous
impression on the brain, or to leave traces behind it, of which
the mind makes use, so as to recognise the renewed conception
as having previously been present to it. Each recognition of
a conception is much rather an operation of the mind [con-

CH. II.] FORESEEINGS— EXPECTATIONS. 61

ceptive force], and is accompanied by its own proper material
ideas, of which we know nothing, and of which we can trace no
action in the rest of the economy. Granted, however, that a
certain continuance of the conceptions is necessary to the
recollections of the memory, it follows that the material ideas
of these continuous conceptions must continue also in the
brain (26), and this is the view usually taken of the conceptions
of the memory. But a conception may continue in the mind
for a century, and be never remembered, until a new con-
ception is formed to the effect that it is the same as that
which formerly existed.

72. Sensational memory induces by its recollections those
material ideas in the brain, which have something in common
with the antecedent material sensations (71, 66), and, in so far
as they can excite animal actions, their actions will accord
in some degree with those of the antecedent sensations or
imaginations.

Foreseeings. — Expectations.

73. The sensational foreseeings and expectations arise from
true present external sensations and the renewal of former sen-
sations {Imaginations, 67), which have an element in common
with each other; if the mind considers that, wherein they
differ as something to come, it foresees; or the same as that
which is actually coming, it expects. (Baumgarten, §§ 444, 454.)
They are more remotely dependent on external sensations than
are imaginations, because they depend on the latter, which them-
selves are directly derived from external sensations (66) . Purely
sensational expectations are termed forebodings [Ahndungen]
(Baumgarten, § 454). Foreseeings, expectations, and fore-
bodings are consequently conceptions of future external sensa-
tions, which have also their proper sub-impressions [merkmale]
on the brain. Consequently the material ideas, also of all
these foreseeings, must be those of future external sensations,
but still very imperfect ones, since the mind can develope them
spontaneously, only so far as is possible, without the direct aid
of external impressions on the nerves (35, 36) ; that is to say,
when the mind developes foreseeings, movements arise in the
brain, which are the imperfect material ideas of future external
sensations. Since foreseeings are weaker than external sensa-

52 CEREBRAL FORCES. [i.

tions, or the imaginations themselves (Baiimgarten, §§ 445, 446),
their material ideas are less energetic than those of either (53).
Still, the stronger the foreseeings are, the greater the strength
of their material ideas (26).

74. When the material ideas of sensational foreseeings and
forebodings excite animal actions, the actions must in part
accord with those of the future external sensations, and be
regulated according to the strength of the ideas.

75. Sensational foreseeings and forebodings are often pro-
duced in dreaming and in insanity (Baumgarten, § 458). What
has been already stated generally with reference to sensational
foreseeings (73, 74) is equally applicable to this class, and
especially to those of soothsayers, — persons who have skill in
foreseeing the future (Baumgarten, § 456).

Understanding,

76. The aggregate of the sensational powers of the mind {^Q)
is termed the sensational perceptive power ; and the true ex-
ternal sensations, as well as the other sensational conceptions,
are sensational perceptions [Erkenntnisse] . All conceptions
which are only remotely determined by external sensations
(65, 66), are termed conceptions of the understanding [the
higher perceptive faculty); the faculty of judgment, of intel-
lectual memory, of prevision, &c., belong to this class. The
material ideas of all these conceptions are not developed directly,
either by external impressions, or by the material ideas which
they produce; but are impressed on the brain by the most
spontaneous action of the mind, and are developed by the very
obscure mechanism of the animal-sentient forces (6, 27).

77. Attention (the directing of the mind to anything) is
such an application of the mind, that it retains a certain con-
ception, while it neglects the rest. During attention, the
material ideas of a certain conception are retained when those
of the other conceptions become w^eak, or disappear ; and the
greater the attention, the more vigorous are the material ideas
and their operations. This turning of the conceptive force from
other inferior conceptions, in behalf of that to which the mind
attends, is termed abstraction, and a continuous act of attention
to the components of an entire conception or perception, is

CH. II.] PLEASURE AND SUFFERING. 53

meditation, reflection. In abstraction, many material ideas cease
in the brain, or become weaker; the weaker, indeed, in proportion
as the abstraction is deep. In reflection, they follow each
other continuously, and each is immediately determined by its
predecessor.

78, 79. Since material ideas of the understanding develope
actions in the organism, it follows that the acts of meditation,
abstraction, and attention, by causing those material ideas to
cease, will diminish, or abrogate those actions {77).

Sensational Pleasure and Suffering.

80. The mind has its own feeling of its present condition,
or a feeling of its own conceptions, which has been termed the
inner sense (" consciousness,^' " inner feeling,'' '' conscience,"
"self-feeling," Baumgarten, § 396). Under circumstances
which metaphysical writers explain (ibid., § 478), many a con-
ception is agreeable or disagreeable, or in other words, pleases,
satisfies, gives pleasure or displeasure, dissatisfies, excites un-
easiness. This feeling is a property of the conceptions, and
may belong to all. Conceptions either please or displease ; that
which makes them agreeable or disagreeable is a sub-impression
in them [merkmal] , which the mind perceives at the same time.
But since no conception is at once both pleasing and dis-
pleasing, except when considered from another point of view,
or in other words, when it becomes a new conception, an
agreeable conception differs in its nature from a disagreeable
conception ; and each consequently makes its characteristic
impression at the point in the brain where the material ideas
of the conception are (25), and which can have also its peculiar
and distinct action in the animal economy (26). This is
termed the impression of pleasure (lust), or suffering (unlust).

This difference in the impressions on the origin of the
nerves made by an agreeable or unpleasant conception, implies
that there is also a distinct external impression, when pleasure
or suffering accompanies external sensations, which it forms
in the brain as its material idea. A very strong pleasure of
the external senses is termed sensual gratification, or titilla-
tion [Kitzel], a very strong disagreeable impression is pain
[Schmertz]. Both are, therefore, external sensations, differing

54 CEREBRAL FORCES. [i.

in their nature, and exciting different material sensations at
the origin of the nerve which feels. The pleasure or suf-
fering which the proper sensational conceptions (66) excite,
is termed sensational pleasure, or sensational suffering; and
under this term pleasure or pain of the senses is often in-
cluded. The more sensational the spontaneous conceptions
are in their character, the more their agreeableness or disagree-
ableness is in accordance with the sensual pleasure or pain of
the external sensations from which they are derived, or to which
they are related ; and when they excite actions in the economy,
the latter are similar to those of the external sensations. We
can know and understand from the external impressions of
the sensations, which either directly or proximately excite these
sensational conceptions, why the conceptions ensue ; they ensue,
also, according to the same laws (66). On the contrary, pleasure
or suffering of the intellectual conceptions is developed accord-
ing to purely psychological laws, and has no manifest relation
to the external impressions of external sensations, which excite
them quite remotely. From an unpardonable confusion of
ideas, even modern physicians have taught, that the sensational
kinds of pleasure and pain have their seat in the body, those of
the intellect in the mind. They have also fallen into the same
error as to the passions, of which more afterwards (579, iii).

Desires, Aversions.

81. When the mind foresees anything pleasing to it, or
(what amounts to the same thing) the conception of anything
pleasing, it exerts its conceptive force, it endeavours to bring
this foreseen agreeable conception forward, to make it pre-
sent, or to accomplish its fulfilment, that is to say, to feel it
(in the third sense of the word, § 34, note) ; and to develope
the contrary conception to a foreseen unpleasant conception
(to feel it, to accomplish its fulfilment), in so far as in either case
it expects to be able to effect these objects by the exertion of
its forces. This effort, this straining of its conceptive force,
which it makes with the intention of realizing a foreseen
external or internal sensation (34, 80), is termed, in the first
case, desire, in the second, aversion. When the foreseen
agreeable conception (or thing), or the opposite to a disagree-

CH. II.] DESIRES, AVERSIONS. 55

able conception, becomes present (is felt), the effort terminates;
that is to say, the desires and aversions are satisfied or con-
tented, or the foreseeings are fulfilled (Baumgarten, § 450).
When the objects of these are true external sensations, the
mind cannot produce them independently of the proper ante-
cedent external impression (34, 27) ; consequently, desires and
aversions of this kind cannot be fulfilled or satisfied without
the external impression itself.

Note. — It will be necessary to bear in mind the definitions
of the word feeling, as given in the Note to § 34.

82. The efforts of the conceptive force are special applications
of its power with the object of producing a certain special con-
ception (81); and they manifest their actions on the brain
through similar efforts of the cerebral forces^ to develope a
certain material idea suitable to the conception (26). It is,
consequently, the same also in the desires and aversions (81).

83. Since pleasure and pain are the motives of the efforts,
and consequently the bases of the desires and aversions (80, 81),
in which relation they are incitements of the feelings, it follows
that the impressions of pleasure or pain of a foreseen conception
excite to that extent an effort of the cerebral forces to produce
the material idea of this future conception (81, 82), and this
is the material expression of the desire or aversion in the brain.

84. 85, 86, 87. In every desire and aversion, consequently,
we must distinguish :

i. The foreseeing and expectation of a future sensation, or
of one the opposite to it, which therefore consists of the sub-
impressions of the future sensation [merkmale], and excites
material ideas in the brain, that are partly the material ideas
of the coming sensation or its opposite, and consequently con-
stitute an imperfect material sensation.

ii. The incitements of the feelings — pleasure or pain — which
communicate the impression of pleasure or pain to the imperfect
material sensation in the brain (80).

iii. The spontaneous effort of the mind to develope the
entire foreseen conception, or its opposite, which is connected

' As the animal-sentient forces [Thierische seelenkrafte] are peculiar to the brain,
the term " cerebral force," here used by Unzer himself in that sense, will be used to
designate them whenever it maybe most in accordance with previous definitions, 25.
—Ed.

56 CEREBRAL FORCES. [i.

with the effort of the cerebral forces to complete the imperfect
material sensation which the soul foresees, or in other words to
render it perfect, and realize the anticipation (83, 83).

If, consequently, a desire or aversion, by its influence on the
brain, manifests actions in the economy, they are compounded :
1. Of the actions excited by the material ideas of a foreseeing
and expectation. 3. Of the actions excited by the impression of
pleasure or pain in the brain. 3. Of the actions resulting from
the eflbrt of the cerebral forces of the brain, to produce the
entire material sensation, which is anticipated, or the contrary
to it (84) j and the stronger all these are, the more energetic
the actions of the desire or aversion (26).

88. The conceptions which are necessary to the excitement
of desires and aversions, namely, the incitements of the feelings
[Triebfedern des Gemiiths] (83), pleasure and pain, are in so
far as they excite the effort of the conceptive force, either sen-
sational (66) or intellectual {76, 80). When they are sensa-
tional, that is to say, when they are true external sensations,
or other sensational conceptions (67), or foreseeings (73), they
are termed sensational stimuli {sensual stimuli, incitements of
the flesh) ; if, on the contrary, they belong to the understand-
ing, they are motives, reasons. Sensual gratification or titilla-
tion [Kitzel], and smarting are, consequently, sensational sti-
muli (80).

89. The sensational stimuli (which must by no means be con-
founded with mere impressions or nerve-feelings) (31, 32, 121),
excite desires and aversions, which are termed sensational (88);
on the contrary, motives are termed intellectual {desires or
aversions of the will). The development of a sensational desire
or aversion from sensational stimuli may be considered in
various ways. Various kinds of conceptions, anticipations, ex-
pectations, and efforts of the conceptive force (84, 86), are
requisite, all which impress their material ideas and impres-
sions in the brain (25). On one hand, the sensational desires
and conceptions may result from sensational stimuli, organically
and necessarily (as external sensations result from their external
impressions), according to the laws of action of external impres-
sions, and be equally sensational. Or the sensational desires
and aversions do not result from these stimuli organically and
necessarily; and we can only explain their excitation by at the

CH. II.] INSTINCTS, PASSIONS. 57

same time taking into consideration the intervention of the
spontaneous conceptions which they produce in the mind, and
which commingle with the former, according to their laws.
Now, when the sensational desires and aversions manifest their
workings in the economy as in the former case, they can be
explained and deduced by the laws of action of the external
impressions of the sensational stimuli on the cerebral forces;
but in the latter case, we must bear in mind the concurrence
of the spontaneous intervention of the conceptive force. The
first class, therefore, being almost as fully developed as external
sensations, may be termed wholly sensational^ but the latter
being more like conceptions of the understanding in their
origin, are more spontaneous or more physiologically free (27).
In the latter, the mind is necessarily conscious of the inter-
vening conceptions ; in the former, it need not be conscious
of either the conception or of the external impressions of the

;nsational stimuli, out of which the conceptions are formed.
Note. — It is not possible, in this stage of the work, to render
this matter clearer ; subsequently (564, 579) it will be made

lore intelligible.

Instincts, Passions.

90. A strong and wholly sensational desire, which arises from
[obscure sensational stimuli, and the material ideas of which are

jonsequently little- developed in the brain (26), is termed a
Hind impulse {instinct, sympathy, sensual propensity, sensual
\inclination, natural instinct generally), (295) ; an analogous
aversion is a blind abhorrence {antipathy, sensual dislike, enmity);
I both are sensational instincts (''the flesh'^). They are divided
into the instincts of self-preservation, self -maintenance, the pro-
pagation of the species, and love of offspring.

91. Strong desires and aversions arising from confused sen-
sational stimuli, of which there is a consciousness, although
it is indefinite, and the material ideas of which are more de-
veloped in the brain than those of the sensational instincts (26),
are termed passions, emotions, affections. Those arising from
the sensational stimuli of pleasure are termed pleasing ; those
from the sensational stimuli of pain, painful.

92. In every sensational instinct, and in each passion, we
must distinguish :

58 CEREBRAL FORCES. [i.

i. An obscure or confused anticipation or expectation of an
internal or external future sensation, produced by a nearly direct
external sensation (34, 80), which anticipation or expectation
consequently contains sub-impressions of the future sensation
within itself (73), and developes similar material ideas in the
brain, consisting of the constituents of the material ideas of
the future sensation, that is to say, they are imperfect future
material sensations (84, 66).

ii. The sensational stimuli (84 — 88), pleasure or pain, which
communicate to the imperfect material sensation in the brain,
the impression of pleasure or pain.

iii. The spontaneous strong effort of the mind to develope
the entire foreseen sensation (81), which is connected with a
strong endeavour of the cerebral forces to complete the im-
perfect material sensation that the mind foresees : or, in other
words, to develope the foreseeing of the instinct or passion
(82, 90, 91).

93. When a sensational instinct or a passion excites actions
in the economy, in virtue of its influence on the brain, they
will be compounded : 1. Of those arising from the material
ideas of a sensational foreseeing or anticipation. 2. From
those of the stronger sensational stimuli in the brain. 3. From
those of the more active endeavour of the cerebral forces to
develope the entire material sensation which is foreseen (92).
The stronger each of these are, the more vigorous its actions
in the economy (85, 87, 90, 91).

94. The proper development or excitement of a sensational
instinct or of a passion is as follows : Firstly, there is an
external sensation or other sensational conception in the mind.
This causes the obscure and confused anticipation and expecta-
tion of a complete future sensation, that is highly pleasing or
annoying, which indeed is no other than a portion, — a collec-
tion of many sub-impressions (merkmale) of the future sen-
sation, or, in other words, an imperfect sensation with its
sensational stimuli. Hereby the mind is moved to apply its
spontaneous conceptive force with stronger energy to produce
this foreseen sensation (whether it be the opposite of another
or not), — that is, to produce all the sub-impressions wanting
to complete the true sensation, and thereby to satisfy the
instinct or passion (to fulfil its anticipation) (81) ; this cannot

CH. II.] INSTINCTS, PASSIONS. 59

be accomplished, however, when it refers to true external sen-
sations, unless the appropriate external impression be attained.
When we apply this doctrine to animal functions in accordance
with the principles laid down in § 25, we find that the material
element of a sensational instinct or passion is thus developed :
Firstly, there are material external sensations, imaginations, or
other sensational conceptions in the brain. Through their
action arise in the brain the material ideas of the anticipation
or expectation of a future sensation, which contains within
itself the impressions of pleasure or suffering. With this is
a new impulse of the cerebral forces now associated, to render
this incomplete material sensation perfect, either because it
results from the impression organically and necessarily, or
because the mind has previously spontaneously resolved to com-
plete its foreseen incomplete sensation, and direct its efforts to
this end (89). Next, through this effort of the animal-sen-
tient force of the brain, an endeavour is made for the develop-
ment of the whole material sensation, a portion of which is
actually there, — partly to produce more of its elements, to which
the mind can add spontaneously the sub-impressions of the
anticipations, — partly to impress the elements of the material
sensations already present more forcibly, and render them
more active, until the remaining elements wanting to complete
the entire material sensation, are actually produced through
this effort of the cerebral forces. The effort then ceases, the
instinct or passion being satisfied; or the effort ceases from
enfeebling of the instinct or passion, without the completion
being achieved. The satisfaction cannot, however, take place,
if to perfect the incomplete sensation it must become a true
external sensation, unless an external impression be also added
(35). All actions, consequently, which the instincts and pas-
sions excite directly in the brain, are material ideas of an
anticipation or expectation, which constitute portions of the
perfect material idea of the future sensation, together with the
strong sensational impressions of pleasure or suffering which
belong to this material anticipation ; and when these material
ideas produce actions in the economy, they are no other than
those of the imperfect material sensation combined with the
actions of the superadded impressions of pleasure or pain ex-
pressed with unusual force (93).

60 CEREBRAL FORCES. [i.

95. A sensational instinct and a passion cease, or are pre-
vented being satisfied, either by tlie enfeebling of the sensational
stimuli which incite the mind to the strong effort, and this may-
occur partly psychologically, partly physiologically, or — by the
contentment of the anticipation, or by the prevention of the
requisites thereto (81, 94).

The Free Will.

96. The motives [Bewegungsgriinde] add the impression of
pleasure or suffering to the material ideas of every conception
not in equilibrio or passive, and consequently to those of a
similar future sensation, which must be stronger in proportion
as the feeling of pleasure or suffering is greater, and, according
to these views, be able to exercise a corresponding influence in
the animal economy (80, 88). But as incitements of the
mind, they also excite desires and aversions (83), which are
termed intellectual (to will, and not to will, intentions of the
will) free conclusions (89), and which arise from an anticipation
and expectation of the understanding, and the motives it con-
tains (84, 86, 88). The laws of action in this case are the
same as laid down in § 94 ; the effort of the cerebral forces is
strong in proportion with the strength of the will.

The Actions excited by the Mind, or Sentient Actions.
[Seelenwirkungen] .

97 — 110. All material ideas (25, 26) with their impressions
of pleasure and pain (80) and all efforts of the cerebral forces,
so far as they are based on the conceptive force (27), together
with all real animal actions in the body dependent thereon
(Baumgarten, § 224), are termed actions of the animal-sentient
forces, operationes animce, sentient actions. Sentient actions
in the body may be divided into two classes : 1 . Those of the
perceptive faculty, or, in other words, those of the external sen-
sations, of sensational imaginations, forcseeings, and of the
understanding [017, 73, 70). 2. Those of the incitements of
the feelings (80, 83), including sensational stimuli and motives
(88), the desires and aversions (81), the instincts and passions
(90, 91), and the will (96). The sentient actions which are
excited by an entire conception (" tot ale," Baumgarten, § 378),

CH. 11.] SENTIENT ACTIONS. 61

without the intervention of another, are termed direct sentient
actions ; all others are indirect (incidental) actions of this entire
conception. The nature and origin of these various sentient
actions may be learnt from the paragraphs to which reference
is made.

111. Although the sentient actions of the various conceptions
are developed, and follow each other, partly according to the
laws of action of external impressions on the cerebral forces,
partly according to psychological laws, still the conceptive force
co-operates in each as well as the cerebral forces (25); and con-
sequently each may be developed, facilitated, hindered, and
interrupted in two different ways ; namely, physiologically,
because the actions of the animal machines requisite to each
are partly so developed, facilitated, hindered, or interrupted;
and psychologically, because the mind has a similar influence
on those actions. It has already been shown (45, 46), how the
sentient actions of the external sensations, and consequently
through these, those of the sensational conceptions, desires,
aversions, instincts, and highly sensational passions are physio-
logically developed and prevented, in so far as the external
sensations themselves are physiologically developed or pre-
vented. But it has not been possible hitherto to explain how
the sentient actions of the conceptions, desires, &c., are physio-
logically developed in the brain out of each other as material
ideas, and transmitted to the nerves, for we know nothing of
the nature of the cerebral forces, or of the mode in which the
conceptions excite the cerebral functions. Nevertheless, we
know generally under what conditions these sentient actions
are physiologically developed or prevented in the animal ma-
chines external to the brain, as we shall subsequently show,
(121, &c.) But how all this happens psychologically, is taught
by metaphysics ; and therefore in both ways, and on principles
entirely dissimilar, sentient actions may be produced, facilitated,
and increased ; and, on the contrary, in both ways, and on
principles as widely different, they may be prevented, weakened,
and destroyed. This is the ground of difference in the nature
of diseases of the cerebral forces and sentient actions, which
arise both from corporeal and mental causes; and in their
therapeutical and psychological treatment.

112. The varying degree of senselikeness [Sinnlichkeit] in the

62 CEREBRAL FORCES. [i.

conceptions raises the questions^ whether the external sensations
and their sentient actions depend solely on the body ; whether
the sensational perceptions, stimuli, desires, aversions, instincts,
and passions, with their sentient actions, depend partly on the
body, and partly on the mind; and whether the intellectual
conceptions, motives, the will, and the unwill, together with
their actions, depend solely on the mind. Indeed, properly,
all sentient actions are produced by the cerebral forces excited
into action by the conceptions, but while the mind produces
all its conceptions in virtue of its conceptive force, they again
are dependent on the material ideas in the brain (25), and
consequently on sentient actions (97), as is fully shown in
metaphysics. (Vide § 119, and Baumgarten^s 'Metaphysics,^
§§ 563, 567.)

Action of the Material Ideas in the Nervous System.

113. We have hitherto followed the arrangement laid down
in § 30, and shown how material ideas are produced in the brain,
namely, partly by external impressions on the nerves (through
external sensations), which are propagated to the brain (31 — 64)
partly by the influence of the conceptions which the mind,
by its own power, produces in the brain (65 — 112). There is
now another question to answer, namely, what functions do
the material ideas perform in the economy? In this chapter,
according to § 16, we can only consider them in their relations
to the animal machines — the brain and nerves — leaving out
any reference to the mechanical machines.

114. The material ideas are animal forces, in so far as they
manifest their operations in the economy. Now since they
act in accord with the mind (97), they are also animal-sentient
forces (6).

115. All material ideas are solely and exclusively in the
brain (25). Consequently, they produce their eff*ects either
directly through the brain, or indirectly through the nerves, by
means of which the brain is extended through the entire
animal body (12, 13) ; because the nerves are the only animal
machines in those animals which possess true conceptions (9);
but the vital spirits are only the means by which they perform
their functions (17, 18).

CH. II.] MATERIAL IDEAS. 63

116. All actions of the material ideas, whether arising directly
through the brain, or indirectly through the nerves (115), are
extended solely into the sensitive or animal machines (34, 14),
which are the brain and nerves only, or they at the same time
put mechanical machines into motion.

117. All actions of the material ideas are therefore : — 1,
directly cerebral, and not extended either to the mechanical
machines or to the nerves; 2, directly cerebral, but extended
to the mechanical machines without the intervention of the
nerves ; or 3, cerebral indirectly through the nerves, and in this
case, either remain simply in the nerves, so far, at least, as not
to affect mechanical machines, or are in fact, extended to the
latter at the same time, and move them (115, 116). Now
since we have only to consider the actions of the material ideas
restricted to the nervous system exclusively (113), they may be
arranged under two heads :

i. The direct cerebral actions of material ideas not extended
either to the nerves or to the mechanical machines ; and —

ii. The indirect cerebral actions of material ideas excited
through the nerves, so far as they do not put mechanical ma-
chines into motion.

Actions of Material Ideas in the Brain.

118. All material ideas are movements in the brain (25);
consequently, their actions in animal bodies can be none other
than movements; but animal (114) and sentient actions (97),
which, when they are not extended beyond the brain, are
actions of its own animal- sentient force (114). Now, the latter
is no other than the power to produce the material ideas of the
conceptions (25, 26) . Further, the direct actions of the material
ideas which remain in the brain, and are not extended either
to the nerves or to the mechanical machines, are simply other
material ideas, which produce other conceptions, and, con-
sequently, can be developed in other points of the brain
than the first, as is certainly the case with various external
sensations (43).

119. The primary material ideas in the brain, which are pro-
duced by either external impressions (31, 32), or by spontaneous
conceptions of the mind (27, 114), excite, consequently, of them-
selves material ideas of a second kind which are necessary to

64 CEREBRAL FORCES. [i.

those conceptions which arise directly either from external sen-
sations, or from primary spontaneous conceptions (118). Or,
in other words, as the conceptions arise from and follow the
primary material ideas ; so, also, all the material ideas belong-
ing to the secondary conceptions arise from and succeed each
other in virtue of the cerebral force put into action by the
primary material ideas (112). We are ignorant, however, of
these processes.

120. So soon, however, as the actions of the material ideas
are extended beyond the brain to the nerves, whether tliey put
mechanical machines into motion at the same time or not, many
traces of them can be discovered, and it is these which we have
now to consider (117, ii). We will first, however, notice the
actions of material ideas through the nerves generally; or, in
other words, of the proper cerebral force (121 — 111), and
afterwards their actions as manifested solely in the nerves, and
not in mechanical machines. — (Vide §§ 142 — 152.)

Actions of Material Ideas through the Nerves generally : the
Internal Lnpression in the Brain.

121. Material ideas are to be considered as impressions made
by conceptions (acts of mind) on the brain, for even those pro-
duced by external impressions only arise when the latter excite
external sensations ; and we can discover no other source for
those which accompany the intellectual conceptions, than the
conceptions themselves (25, 112). To distinguish these im-
pressions from external impressions, we will term them, for want
of a better phrase, internal senselike impressions, senselike impres-
sions on the brain — internal nerve-feeling ; and include, under
these terms, all impressions made on the cerebral origin of a
nerve, or on its trunk, and transmitted downwards from the
brain, in a direction contrary to that taken by the external im-
pi'ession (31, 32, 406).^ Although a nerve may receive an
internal impression which is not derived from the brain, just
as it may receive an external impression which does not reach
the brain (47, 199), still internal impressions on the nerves,

> The reader is particularly requested to refer to § 31, and the foot-note appended
thereto, for an explanation of the word sinnlich, here translated senselike. In accord-
ance with the views there stated, the word sinnliche Eindriick, here used, will be
translated simply impression.

CH. II.] CEREBRAL IMPRESSIONS. 65

caused by animal-sentient forces, — material ideas (114), — take
place solely through the brain, and may very properly be termed
cerebral impressions (sinnliclie Eindriicke durchs Gehirn).^

122. The actions of material ideas in the nerves are there-
fore impressions of conceptions propagated along the nerves
from the brain downwards to the terminating fibrils (31, 121);
and since, in this respect, the material ideas act as animal-
sentient forces (114), their actions in the nerves are true
sentient actions (97), which probably are extended through the
system of nerves by means of the vital spirits. (See § 17
and § 28 ; also Haller's ' Physiology,' § 377.)

123. Since no other animal movements in animal organisms
are sentient actions except material ideas and the actions
actually resulting from them (97) ; it follows that, to every
true sentient action, a conceptional impression is necessary,
which is either confined to the brain, or propagated downwards
along the nerves (122).

124. Since there is a particular point in the brain from
which each nerve arises (13), and at which alone the material
ideas of its external sensations are developed, — no other por-
tion of the brain having a part therein — (43) ; it follows, that
the impressions of the conceptions act upon the origin of a
nerve when they excite sentient actions in it (31, 118). Con-
sequently, the whole brain will not be put into action by each
conception, but only a certain locality, or that point in which the
material ideas are formed ; and this action is directly propagated
only along the nerve and its branches to the terminating fibrils
arising from this point of the brain, although it m|iy also be
communicated indirectly to other nerves when in connection
with the former in ganglia, and when, in both cases, there is
no hinderance to this transmission. The impressions of pleasure
and pain are only difi'erent conditions of the material ideas of
the conceptions which please or displease (80). They con-
sequently take place at the same point as the material ideas of
the conceptions themselves, and are only impressions of a
difi'erent kind at the same origins of nerves.

125. Just as an external impression, — whether made on
trunks of nerves, in which many fibrils are collected, or on the

' These impressions, caused by, or accompanying, acts of thought or feeling, are
also termed conceptional impressions. (Vide § 359.) — Ed.

5

66 CEREBRAL FORCES. [i.

common trunk of nerves altogether different, or even in the
spinal cord itself, which is the general stem of a great number
of nerves — equally reaches the brain at the point of origin of
the nerve which receives it, unmingled with any of the other
external impressions taking place at the same time, and in the
same direction, and there forms its own proper material ideas ;
so, also, the conceptional internal impressions travel from the
points in the brain in which they take place, along the nerves
arising from those points, and are propagated downwards through
the branches and terminating fibrils without being commingled
with other conceptional impressions taking place in the brain at
the same time, although they all pass together along one and the
same trunk, or rather first along the spinal cord to the larger
branches, and thence to the smaller branches and fibrils (124).
The cause of the two phenomena is identical (39) . The fibrils
of a nerve are already separated at its origin, and run each a
separate course as portions of the same larger nerve to their
allotted termination in the body (13). Each complete nerve
has, again, its special point of origin in the brain, and although
it passes downwards combined with many others into a large
trunk, such as, for example, the spinal cord, it is afterwards
given off again and remains distinct, and continues its own
special course to its final termination at the allotted spot.
Thus, consequently, an impression in the brain, made on the
origin of a nerve, or on one of its fibrils, takes its course along
the fibril, although ten other impressions may have been made in
the same nerve, or on other fibrils of the same nerve, and pro-
duces its results without being intermingled with the others.

126. Although at the same time that conceptional im-
pressions are transmitted along a certain nerve-fibril, and by its
means perform their sentient actions, an external impression is
made on the same fibril, and takes its course upwards to the
brain along the same track, as far as the origin of the nerve
from whence the internal impression had set forth, still these
two impressions are in no wise interrupted in their course to
and from the brain, although opposed to each other, but each are
followed by their proper actions, as if the contrar}^ impression
had never been received (§§ 17, 18, Haller's ^Physiology,' § 377).
Is it not highly probable from this statement of facts, that some
of the numerous fibrils of which each nerve consists (17), are

CH. II.] CEREBRAL IMPRESSIONS. 67

destined solely to the transmission upwards of external im-
pressions made on the terminating fibrils (perhaps the vital
spirits being present in them), while on the other hand, other
fibrils are destined solely to the transmission downwards to the
terminating fibrils of internal impressions on the brain (perhaps
the vital spirits being present at the cerebral origin), just as
there are two classes of blood-vessels having similarly opposed
functions ? According to this analogy (which comes nearest to
the idea of Borellus (^De Motu Anim.,^ § 159, and which
A. Monro does not entirely disprove), the brain that produces
the vital spirits sends them downwards through certain fibrilli
in a nerve to the terminal points (the sensitive papillae), where
they are received by the terminating points of other nerves, and
transmitted back to the brain, as if to a heart. Although
this theory cannot be fully demonstrated, it has a great degree
of probability, since by it we can comprehend many phenomena
which otherwise would remain incomprehensible. It will be
worth while to render this matter more explicit.

127. When an external expression has been made on a
nerve on the surface of the body, it passes upwards if there be
no impediment (13), and reaches the brain at the point of origin
of the nerve. The other nerve-fibrils, which cannot transmit
the impression upwards, are not affected by the influence from
without. At the point of origin of the nerve in the brain,
the transmitted external impression produces a material idea
which excites an external sensation. By this material idea (a
movement) at the origin of the nerve, those fibrils are impressed
that propagate the internal impression downwards; whilst on
the other hand, those fibrils that transmitted the external im-
pression to the brain, receive no impression from the external
sensation. The former, however, propagate the conceptional
impression to those structures, in which the sentient actions of
the external sensation can arise, and these result accordingly.
It is now more intelligible, how these opposite movements,
arising from opposite impressions in the same nerve, are not
impeded by each other, and why the same nerve can, at the
same time that it transmits an external impression to the
brain, produce a sentient action in some organ of the body, as
for example, a voluntary movement. Since a nerve in its
course from the brain is divided into many branches, which

68 CEREBRAL FORCES. [i.

are distributed to various organs of the body, it follows that
some of its fibrils that transmit the impression from the brain
downwards may go to one tissue, and some of those which
transmit the external impression upwards again into other
tissues widely distant, and thus a sensation in a limb trans-
mitted along the same principal nerve, may, by means of the
cerebral impression, develope a sentient action (movement) in
limbs far distant from the point of irritation. This connection
between the sentient actions of various parts is termed the
sympathy of sentient actions. When the fibrilli of a nerve
which transmits external impressions to the brain, to pro-
duce corresponding material ideas at the point of its origin
in the brain, have experienced some injury at its origin, being
compressed or stretched, for example, in such a way, that those
fibrilli only have their function interrupted which transmit the
cerebral impression downwards, — the consequence is, that the
sentient action (as, for example, a voluntary motion), which
formerly resulted from this external sensation (excited by the
material idea in the brain), ceases to be excited, until the
impediment is removed. Thus, it is intelligible, how a nerve
may retain its sensibility and yet have lost its motor power ;
being sensitive and yet paralysed, as is often observed. If, on
the other hand, the obstruction involves those fibrils only at
the cerebral origin of the nerve which transmit the external
impression to the brain, the latter will develope no material
idea in the brain and no sensation in the mind ; but a sponta-
neous conception can excite a material idea (an internal im
pression) at the origin of the nerve, and this may be transmitted
along the fibrils, and produce actions in the body, such as a
voluntary movement, for example. In other words, the same
nerve may be insensible, and still the channel of the will.
How could it be possible to explain these two classes of phe-
nomena, if the existence of this diff*erence in the fibrils of the
same nerve be not admitted ? It is manifest to every one, that
the nervous fibrils are distinct and separated from each other
at their origin. From these and other considerations, which
will be stated subsequently, this doctrine of two distinct classes
of nerve-fibrils existing in the same nerve, and which are appro-
priated to the two kinds of internal and external impressions
respectively, acquires an air of truthfulness which renders it

CH. II.] CEREBRAL IMPRESSIONS. 69

worthy of acceptance ; still, in the course of this work, I shall
only consider it as a mere opinion, so that what is true, and
what is only probable, may be kept perfectly distinct.

Note. — Haller seems to object to this doctrine, but his
objections appear to be of little importance. He observes, for
example, that tubuli of two kinds in the same nerve are not
to be distinguished by our senses, and all ganglia seem to be
identical with each other. But on similar grounds we may
deny the existence of the vital spirits themselves, as they also
are invisible. Other arguments of no greater validity are also
brought forward as well by Haller as by Monro.^

128. When a nerve is compressed by a ligature, or divided,
sentient actions are no longer produced by internal impressions
in the parts separated from the brain, but are observed only in
those still in connection with the brain (31) ; but if the ligature
be removed from the nerve, they are again manifested as before,
provided the ligature have not destroyed the structure of the
nerve. (Haller's ^ Physiology,^ § 367.) But if the nerve be
injured by the ligature, its sensibility is destroyed (43) ; hence
neither class of impressions can be propagated along either
kind of fibril, their progress being impeded by the divided or
ligatured portion of the nerve (126, 127). If the brain itself
be compressed, as it often is, that portion of the body supplied
with nerves from the compressed part of the brain, becomes
incapable of sentient actions. The capability returns, however,
so soon as the compression of the brain is taken off. When
the whole brain is compressed, all animal operations caused by
impressions acting on the brain, cease throughout the whole

' In this paragraph and elsewhere ($§ 487, 488), Unzer advances the hypothesis, as
he terms it, of afferent (aufleitenden) and efferent (ableitenden), fibrils in the same
nerve. His Gottingen reviewer (probably Haller) thus objects to it : " Herr Unzer
considers that it is probable there are afferent and efferent nerves going to and re-
turning from the brain ; and that the objections raised against the doctrine are not
of much weight. He forgets that the proof rests with himself, for neither experi-
mental nor anatomical researches support his conjecture." Unzer replies : " Neither
anatomy nor experiment can determine the question; for it is so microscopically
minute, as to escape the cognisance of our senses. It was no part of my plan to
prove the existence of the two kinds of fibrils. I meditated on certain phenomena,
and found that it was absolutely impossible to explain them, except by assuming
that afferent and efferent fibrils do exist. The doctrine cannot be absolutely
demonstrated; it is but a hypothesis, and I treated it as such." (Physiologische
Uutersuchungen, p. 26.) — Ed.

70 CEREBRAL FORCES. [i.

body. (Haller's ' Physiology/ § 368.) The cause of this may
be^ that either no impression can be made in the brain, on
account of the compression, consequently no conceptions can
arise in the mind (121, 25) because the pressure entirely destroys
the animal force and consequently the sentient force of the brain
(6), and then no operations can take place in the body ; or, it may
be, that by pressure on individual portions of the brain, as when
blood or water overflows it, or projecting points of the cranium
are forced into it, only those fibrils at the origin of certain
nerves, which formerly developed sentient actions in the body,
have their functions arrested, so that internal impressions
cannot be transmitted; in this case, the external sensations
and spontaneous conceptions are unaffected, but the sentient
actions resulting from them can no longer be produced. This
opinion is based on the doctrines laid down in §§ 126, 127, and
without this it is impossible to explain those cases in which
certain limbs are paralysed by a pressure on the brain, and yet
external sensations and spontaneous conceptions continue. It is
impossible that this can depend upon the want of material ideas
of the external sensations and other conceptions, for without
these the sensations and conceptions could not exist at all (25).

129. When sentient actions are produced directly through
the nerves by external sensations, it is necesssiry thereto :

i. That there be all that is requisite for the production of
external sensations (45).

ii. That the external material sensation duly impress the
origin of that individual nerve which has to propagate the im-
pression outwards from the brain (122, 124, 126, 127).

iii. That this cerebral impression be actually transmitted
along the nerve to the point where the sentient actions are to
be developed (128).

iv. In those instances in which the sentient action consists
in a movement of a mechanical machine to which the nerves
are distributed, it is also requisite, that the mechanical machines
themselves be in a condition to perform the movements which
constitute the sentient action.

130. When sentient actions are produced through the nerves
by conceptions of the mind, it is necessary thereto :

i. That the material idea of the conception make such an
impression on the origin of the nerve, and on those fibrilli which

CH. II.] CEREBRAL IMPRESSIONS. 71

are appropriate to the sentient action, as to be transmitted (121);
in this case, the impression must be made on those fibrilli of the
nerve which propagate it from the brain outwards (126, 127).
ii. That the further transmission take place, as stated in iii
and iv of last paragraph.

131. When the material idea of an external sensation makes
an impression on the origin of another nerve than its own, it
becomes the material idea (121) of another (118), and indeed
of a sensational conception ; or of instincts and passions by
means of the sensational stimuli of thie conception (88, 90, 91) ;
and, consequently, of analogous purer conceptions, which
although induced by means of external sensations, are also
spontaneously (27) developed, as stated in § 130.

132. The medulla of the nerves is naturally adapted to the
external impressions of the external sensations (31) ; but since
it is no other than cerebral medulla, the latter is also naturally
adapted to external impressions. When, consequently, certain
fibrilli of the cerebral medulla are touched or stimulated, they
receive an external impression (just as the terminating fibrilli
of the nerves), which is propagated along the fibrilli to their
cerebral origin (45, ii), and there excites a material external
sensation. This latter causes an impression on the brain,
which either produces sentient actions directly by means of a
nerve at that point, or in the way stated in last paragraph.
Consequently when the cerebral medulla of living animals en-
dowed with conceptions is irritated, an external material sen-
sation is produced (as for example that belonging to pain),
which produces sentient actions through the nerves (e. g.,
convulsive movements from pain), in the same way as other
external sensations (129, 130, ' Haller's Physiol.' §368).

133. In proportion as the cerebral impressions, and the forces

I which excite them, namely, the external sensations (129), and
the spontaneous mental conceptions (130) are powerful, in the
same proportion the sentient actions which they excite through
the nerves are vigorous (121, 26).
134. A sentient action produced directly through the nerves
by an external sensation may be prevented :
i. By everything which prevents the external sensation
(46, 129, i.)
ii. By this, that the material external sensation in the
I

73 CEREBRAL FORCES. [i.

braiu cannot so duly stimulate the origin of the sensitive nerve as
to induce the propagation outwards of the impression (129, ii.).
Supposing that the material external sensation makes its ap-
propriate impression in the brain at the point of origin of
another nerve^ and not of that which brought it to the braiu;
this would be the material idea of another conception of the
mind, and the sentient action which it excites through
the nerve would not be similar to those produced directly by
the external sensation (131). Again, supposing the external
sensation only makes such an impression on the origin of the
nerve, that it cannot be propagated downwards from the brain
along the same nerve, no corresponding direct sentient action
can be produced thereby (129, ii, iii). Further, — since ex-
ternal impressions do really occur which develope an external
sensation in the mind (a material external sensation in the
brain), and yet do not thereby excite the ordinary direct sen-
tient actions (Haller^s ' Physiology,^ ^ 384), although the
origin of the nerve actually possesses the material external sen-
sation, which is proper to it, and which constitutes the internal
impression on the origin of the nerve (121), — we could not
explain why the direct sentient action of the external sensation
does not take place through the same nerve, unless we assume
that there are two classes of fibrils in the nerve, according to
the doctrines previously stated (126, 127). The case is explained
by assuming that the fibrils of the nerve which receive the
cerebral impression, and transmit it downwards, are rendered
incapable, in consequence of there being some of the impedi-
ments to the reception of the impression described above
(127, 128). (As when a limb, for example, which the mind
governs through the nerve that receives the impression, remains
motionless and paralysed in spite of its external sensations,
although the same sensation can excite other sentient actions
in other portions of the body, e. g., certain voluntary move-
ments by means of other spontaneous conceptions, and the
material ideas produced by them at the origins of other
nerves — § 128).

iii. The direct sentient action of an external sensation
caused through the nerves is also prevented, when the appro-
priate impression received at the cerebral origin of the sensitive
nerve cannot be transmitted to the point where the sentient

CH. II.] CEREBRAL IMPRESSIONS. 73

action ought to be developed ; as, for example, when the spinal
cord, or the trunk or branch of a nerve, is tied, compressed, or
divided below the point, or mechanical machine, to which the
sensation ought to be transmitted (128, 129, iii).

iv. When the sentient action produced by a nerve consists
in a movement of a mechanical machine, to which the nerve is
distributed, its production is prevented when the machine is
not in a condition to effect the movement organically ap-
propriate to it (129, iv).

135. When sentient actions produced by means of the nerves,
are caused by spontaneous conceptions, they may be prevented
as follows : —

i. When the material idea of the conception at the origin of
the nerve appropriate to the sentient action cannot so make
its impression, that it may be transmitted (130, i).

ii. When the further transmission cannot take place (134,
iii, iv).

136. There are various kinds of conceptions which do not
usually develope sentient actions in the body through the nerves,
as inferences, witty thoughts, &c. — (vide 238, 249, 330); nay,
many external sensations and other conceptions which ordinarily
develope sentient actions through the nerves do not do it,
although the animal is in its natural condition. Consequently,
just as there are material hinderances which prevent the
continuous transmission of many external impressions to the
brain (47 — 51), so similar hinderances may prevent the sentient
actions of conceptions, and it is a matter of importance to
know every possible hinderance of this kind.

i. Nature has so distributed the origins of the nerves in the
brain, that every material idea of a conception has not neces-
sarily relations with any of them, or if it excite one origin, it
does not necessarily excite all the others at the same time,
or even any one origin. Consequently, when material ideas
are formed at points of the brain from whence no nerves arise,
they excite no sentient action through the nerves (124). Nay,
when the material ideas of external sensations, or other concep-
tions duly (sinnlich) impress the origin of a nerve, and excite
sentient actions through it, all other origins of nerves may
remain unaffected thereby, and no sentient actions result,
unless under special circumstances (124).

74 CEREBRAL FORCES. [i.

ii. It may be, also, that many nerves are not adapted natu-
rally, or become unadapted to the internal impressions of many
conceptions (material ideas), although the change caused by
the material ideas really involves their origin ; and that only
certain kinds of conceptions (material ideas) can affect them,
just as certain external impressions only are received by the
nerves (47, ii). An agreeable taste, for example, or the imagi-
nation or anticipation of it, cannot excite the sentient actions
of vomiting, while an unpleasant taste, or the imagination or
anticipation of it, produces that effect. Although both sensations
pass along the same nerve to the same origin in the brain, and
there excite a material idea, and both ideas or anticipations
must develope their material ideas or impressions at the same
point in the brain (124), yet, from the one kind the sentient
action of vomiting results, but nothing from the other.

iii. Internal sensations and other conceptions may some-
times be so feeble, that they do not make so powerful an im-
pression in the brain as is necessary to the production of a
sentient action ; and this is also the case with sensations from
without (47, iii). A slight irritation of the nose, for example,
by snuff, does not produce, as a stronger would, the sentient
action of sneezing (80); thus it is, that the phantasies being
weak in dreams, we omit many voluntary movements which we
should otherwise perform, if the latter were as strong as in the
waking state, or as in somnambulism. In these cases there
is doubtless an impression in the brain from very feeble con-
ceptions (25, 121), only it is not propagated along the nerves
to its destined point, but is lost, as it would appear, in the way.

137. iv. The bifurcations and the ganglia of the nerves may
act as impediments to the transmission of internal impressions
and to the consequent production of sentient actions, just as
they prevent the transmission of external impressions, and the
consequent production of material external sensations (48).
That this must be the case, is demonstrable from numerous
facts. The acquisition of skill in the manual arts depends on
a removal of these impediments. It is falsely termed habit,
but it is really eocpertness. The frequent repetition of the same
impression in the brain, acts each time on the natural hinderance
at the divisions of the nerves, just as occurs in the action of
two opposing forces, when that which continually repeats its

CH. II.] CEREBRAL IMPRESSIONS. 75

shocks must overcome the other which is totally unsupported ;
in like manner, the natural hinderance is destroyed, and the
impression takes its uninterrupted course to the production of
its sentient action.

138. V. Lastly, mechanical machines may act as impediments
to the production of sentient actions, when a change in them is
necessary before the impression in the brain can produce its
sentient action. This is the case with the mountebank, whose
gestures and postures cannot be imitated by another until his
joints are stretched, his muscles practised, and even his viscera
partly displaced, so that the machines can instantaneously
follow the act of willing.

139. The sentient actions which are produced directly by
external sensations, can also be partly enfeebled, partly pre-
vented, in various ways, by the habit of reception of sensations
(50, 51, 134, i, 54); and since the actions of sensational con-
ceptions depend proximately upon external sensations (66), the
habitual reception of external sensations may have a consider-
able influence on their development. But it is unnecessary to
quote instances of this kind, as they are of daily occurrence.

140. The sentient actions which ideas excite through the
nerves in dreaming and in insanity, partly accord with those
of former external sensations (69) ; so also those of sensa-
tional memory (72). Those of the sensational foreseeings,
expectations, and forebodings, as well as those of dreams and
of mania (75) partly produce the actions of coming future
external sensations (74). These actions are forcible in pro-
portion to the strength of the conceptions exciting them
(69, 74) ; abstraction of the mind can cause many actions of
the understanding to cease ; attention on the other hand can
excite and maintain many. The sentient actions of pleasure
or suffering are powerful in proportion to the strength of these
internal sensations (80, 96). The sentient actions of a desire
or aversion are composed of those of a foreseeing, of an
expectation, of a pleasure or pain, and of an effort of the
conceptive force ; and are powerful in proportion as these are
vigorous (85,87). So, also,, those of the sensational instincts
and emotions (93), and of willing and not willing (96), all
these sentient actions result according to general laws, partly
physiological, partly psychological (111).

76 CEREBRAL FORCES. [i.

141. Although all operations through the nerves of impres-
sions in the brain are movements (122)^ it is not a necessary
consequence, that these movements arise in proper mechanical
machines, as muscles, glands, viscera, &c., for they may occur in
nerves of sensation which are not distributed to these machines
(14) ; or may, even in motor nerves, be only movements of the
vital spirits, which are not manifested by visible movements;
yet they are as certainly operations of the cerebral impression
acting through the nerves (sentient actions, § 123), and as
certainly cause important phenomena in the animal economy
(as we shall shortly see), as those which are manifested by
visible movements in the animal machines. (This shows inci-
dentally the correctness of the division, § 117).

Actions of the Material Ideas in the Nerves exclusively , and
when not extended to Mechanical Machines.

142. After the general consideration of the actions of the
material ideas on the nerves, we have now to investigate their
special action in the nerves exclusively, without reference to
their extension to the mechanical machines. Indeed all kinds
of nerves are subject to this influence of the material ideas in
the same way. But while internal impressions are distinctly
manifested by the movements of mechanical machines, there
are only shght traces of movements in the brain, in the nerves
themselves, (no action in a mechanical machine following,) or
in purely sensitive nerves, with which no mechanical machines
are connected. They are best observed in the nerves of the
external senses which simply feel.

143. Every nerve in animals endowed with sensation receives
external impressions, some of which at least are transmitted
onwards to the brain, where they produce, at the origin of the
nerve in the brain, a material external sensation (45, 124) ; or,
in other words, an internal or cerebral impression, which must
directly excite sentient actions in the nerve itself, even if it only
feels, provided it be a nerve capable of so receiving an internal
impression ; and it must be so capable, if the impression is to
be propagated outwards from the brain (129, ii, iii.) That every
nerve, whether purely sensitive, or both sensitive and motor,
must possess this capability, although it may not be able to

CH. II.] SENSITIVE NERVES. 77

receive and transmit both kinds of impressions (136, ii), is as
certain as that the vital spirits of the external impressions pass
on to the brain (18, 36), and that their laboratory is in the
latter (11). Since there must be an opening at the point of
origin of the nerve in the brain, at which the vital spirits must
enter to pass along the sensitive nerves to their terminating
fibrils, for the purpose of receiving external impressions, we
conclude that this is the course which the internal or cerebral
impression takes. In other words, the sensitive nerves have
fibrils like the motor nerves, which transmit internal impres-
sions from the brain to their terminating fibrils (126, 127).

144. The external sensations develope their direct actions in
the sensitive nerves themselves (129, ii, 143) . But all sensational
perceptions (76) with their sensational stimuli (88), all sensational
instincts (90), and all the passions (91), efi'ect their sentient
actions through those nerves by which external sensation is
received. Now, since all these require such material ideas or
impressions in the brain, as the material external sensations
partly develope, and by which they are proximately determined
{66, 88) ; it follows, that their material ideas must excite at the
same time a corresponding impression at the origin of the
nerve, which is propagated downwards along the nerve, and
developes actions in it (123). On the other hand, the intel-
lectual conceptions, motives, volition, and involition (which
only depend remotely upon external sensations), have less
influence on the sensitive than on the motor nerves.

145. By what means can the sentient actions, produced in
the nerves by the cerebral impressions of all these sensational
conceptions be ascertained, when their influence on the me-
chanical machines cannot be observed ? The nerves have in
themselves no visible movements ; yet the impressions of the
sensational conceptions can only act upon them as movements.
But these escape observation quite as much as those of external
impressions (31). They are probably only movements of the
vital spirits in the hollow fibrilli of the nerves (13). How can
the existence of these hidden movements be demonstrated?
VV^e infer their existence in the external impressions from their
action on the brain, inasmuch as they produce external sensa-
tions, and because compression of the nerve, in its course to the
brain, arrests or interrupts the propagation upwards of the im-

78 CEREBRAL FORCES. [i.

pression. We infer it to be in the motor nerves from the
actions which the cerebral impressions of conceptions produce
in those structures to which these nerves are distributed, and
because compression of the nerve prevents the transmission of
internal impressions to the mechanical machines. As to the
sensitive nerves which simply feel, and manifest no visible
movements from either kind of impression, we know that the
cerebral impression is in them by its operations, which, although
certainly taking place, are not visible.

146. The cerebral conceptional impression causes, at the
origin of each nerve on which it duly acts, a movement (of the
vital spirits) from above downwards towards the terminating
fibrils which feel (122). It is at this, the extremest point of the
nerves, that this movement is either wholly reflected, or ceases
(126); for from that point the external impression causes an
opposite movement towards the brain. Further observation
may enable us to determine something as to this change, as for
example, when a strong sensational conception acts on the
nerve with unusual vigour.

147. When the terminations of the nerves are carefully
observed in powerful sensational foreseeings, particularly in the
instincts or passions, it is obvious that they are erected, and
become more prominent. Thus the papillae of the tongue, in
which the gustatory nerves terminate, are visibly elevated when
the expectation or desire to taste a piece of sugar or salt is
excited by bringing it near to the tongue. So also the nerve-
points in the fingers are evidently elevated, when one attempts
to feel something more distinctly, which is the foreseeing in a
desire. " The sensitive points of the fingers,^^ Haller remarks,
'^ are slightly elevated during an act of attention (an expecta-
tion), just as we see in rigors, in the nipple of the mamma, and
in a portion of bowel hanging out of the abdomen.^^ {' Phys.,^
§431.) Probably shivering ought to be classed with the sen-
tient actions produced through the nerves in the mechanical
machines. That the sensitive points in the nipple are elevated
by the expectation of an act of suckling, or simply by titillation,
is quite certain. With regard to the senses of feeling and taste
many similar observations have been made, but not with regard
to the other senses. This erection of the nerve-points is there-
fore a true sentient action.

CH. II.] IMPERFECT EXTERNAL SENSATIONS. 79

148. Erection of the nerve-points is a movement, or change,
which, when strong enough, may become an external impres-
sion (31), and on arriving at the brain, may excite a concep-
tion similar to external sensations ; but having no true material
impression as its basis, has consequently no real external cir-
cumstance. In this way, remarkably powerful impressions in
the brain (from very vigorous conceptions) may produce an
external impression on the nerves to which they have reference,
as if it came from a real thing without ; this reaching the brain
will excite the analogue to a real external sensation, and some-
times contains so much of the real, that the mind can only dis-
tinguish, by great attention, this class of sensations and their con-
comitant conceptions, from those which have a true external
origin. To distinguish these sensations from the latter class,
we shall term them imperfect external sensations. Hitherto
they have been confounded with very vivid imaginations ; but
their extraordinary distinctness shows that they differ from
these, inasmuch as often they are in no respect dissimilar from
true external sensations. They are necessarily, however, the
results only of very powerful impressions in the brain of other
conceptions, as shown above ; consequently, they can be the
actions of a too-active imaginative faculty, and may, there-
fore, accompany insanity, drunkenness, impressive dreams,
strong forebodings, and very strong and violent passions.
These imperfect external sensations are known as appearances^
apparitions, delusions, spectres, ghosts, &c., and it is of not
less importance to pathology and practical medicine than to
the present subject, that these be traced to their origin, and
distinguished from the feeble images of imaginations and
foreseeings. If a vigorous effort be made to see with the eye-
lids closed, a red colour is seen : if the fear of a sudden fall
from a height excites the nerves of vision to give a false im-
pression of surrounding objects, they seem to move, or vertigo
occurs : a loud stunning noise is heard long after it has ceased,
but with decreasing indistinctness : if food be desired with
great longing, its taste is perceived beforehand : if a delightful
sensation be anticipated earnestly, the nerves become so sen-
sitive, that every slight impression causes it, although previously
they would have had no effect. All these are instances of
imperfect sensations of this kind, which happen to the most

80 CEREBRAL FORCES. [r.

healthy persons. Consequently, they are not peculiar to an
unnatural condition of animal bodies, but occur in the natural.
149. It will be worth the while to consider more closely the
origin of imperfect external sensations. A strongly sensational
conception makes a forcible impression in the brain, at the point
of origin of a certain nerve (144, 26). This is propagated
along the nerve to its terminating fibrils, which are thereby
stimulated and erected (147). This action imparts an external
impression to the fibrils, just as if they had been acted upon
from without, which is returned to the brain, and becomes an
imperfect external sensation (148). But inasmuch as the real
external circumstance is wanting, the question arises, what is
really felt imperfectly ? The answer is as follows : The sen-
sational conception from which the whole delusion arises, pos-
sesses the sub-impressions (merkmale) of a past or future ex-
ternal sensation (66), and their material ideas also partly excite,
at the origin of the nerve which they impress, the corresponding
material external sensation. This, which is a movement at the
cerebral origin of the nerve (43), and is now, in fact, its impres-
sion (121), is transmitted downwards to the terminal fibrils, and
there makes the baseless external impression, which is returned
to the brain, to the same point of the nerve whence it came.
The imperfect material external sensation thus excited is a
movement at the origin of the nerve, which is partly the same
as would have originated if the actual external thing, of which
the sensational conception contains sub-impressions, had made
an external impression on the terminal fibrils, and which is
only defective in that which the external impression alone can
supply, to render it a true external sensation. Now, since a
true external impression takes place, although without the
impression of a real external object, the imperfect external
sensation is thereby rendered more similar and equal to a true
external sensation, than it previously was by the sensational
conception alone. Further, the apparent object of the imperfect-
external sensation is always the object of that external past or
future sensation, which was already the basis of the con-
ception that constitutes the first element of the delusion.
Consequently, the maniac, the drunkard, the dreamer, the
soothsayer, the enamoured, the scorner, &c., each according
to their delusion, feel what their imaginations, foreseeings,

CH. II.] MATERIAL IDEAS. 81

expectations, forebodings, instincts, and emotions bring into
the mind.

150. When the nerves which feel these imperfect sensations
are distributed to mechanical machines, they excite the same
movements, as if the sensation had been real. But these im-
perfect sensations must not be confounded with others aiising
from circumstances external to the nerves, although not external
to the organs of the senses ; as for example, when sparks are
seen in inflammation of the eye, or singing and humming in
inflammation or diseases of the cavity of the ear. These are
true external sensations, connected with an erroneous judgment.
The nerves of the eye and ear are really impressed by some-
thing external to them, but it is within the organ of hearing
or of vision itself, and the mind judges falsely, that the sen-
sations arise from objects which have customarily excited them ;
as, for example, that sparks of fire are seen, that bells are
heard ringing, water rushing, &c. [Vide § 378.)

151. Since cerebral impressions excite movements at the
terminations of the nerves, where their course is obstructed
or reflected (147), it is highly probable, that very vivid sensa-
tional impressions are also deflected in their course from the
brain downwards to the periphery, either at the bifurcations of
the nerves, or in the ganglia, especially whei*e nerves are given
ofi* to other parts, or to surround the arteries, and excite such
gentle movements, as may have an influence on the contiguous
mechanical machines.

CHAPTER III.

ON THE INFLUENCE OF THE ANIMAL-SENTIENT FORCES IN THE
MECHANISM OF ANIMAL ORGANISMS.

153. In the foregoing chapter, we have treated of the animal-
sentient forces abstractedly, without reference to their influence
in the mechanical machines of the body. We must now bring
this influence under notice (8), as being the second class of
actions, which the material ideas excite in the animal eco-
nomy (16, 113). According to § 117, we have to inquire into :

i. The direct actions of the material ideas, which they alone
perform in the mechanical machines of the brain, without the
aid of the nerves (153 — 159).

ii. The indirect actions of the material ideas through the
nerves in the mechanical machines generally (344), and spe-
cially the material ideas of all the various kinds of conceptions.

Actions of Material Ideas in the Mechanical Machines
of the Brain.

153. The mechanical machines of animal organisms are
capable of many kinds of movement, in virtue of their struc-
ture ; but they are put in motion much more by animal than
physical and mechanical forces. Since the animal forces are
not regulated in their operation according to physical or me-
chanical laws (7), we cannot bring them into the same category ;
and as their laws are unknown, we can only infer their actions
in the animal machines from observation.

154. The influence of the soul on the body is exercised
by means of the material ideas, or the impressions of their
conceptions in the brain (25, 121), and all the movements
of mechanical machines which are actually efi*ected through
these, are sentient actions (97). All sentient actions in the
mechanical machines are excited either directly, by the material
ideas developed in the brain itself, or indirectly, by means of

CH. III.] THE BRAIN. 83

the nerves along which conceptional or internal impressions are
transmitted from the brain.

155. To understand this matter rightly^ the meaning of the
term mechanical machines used in this whole treatise, must
be properly comprehended ; it must be understood to include
all the organs of the body, except the brain and nerves, which
are proper animal machines. Consequently muscles, tendons,
membranes, vessels, glands, bones, cartilages, viscera, &c., are all
mechanical machines. Although many of these are endowed
with animal moving forces, they are so endowed, only through,
and in virtue of, the nerves with which they are supplied. So
also the organs of the external senses, although endowed with
sensitive nerves, are only mechanical machines, and even the
brain and nerves contain the latter.

156. There are no other mechanical machines in direct con-
nection with the brain, than certain glands, the meninges, and
the circulating and lymphatic vessels. Consequently, these are
the only machines, in which material ideas can develope sentient
actions directly in the brain itself, without the aid of the nerves.

157. The uses of the glands situate on the membranes of the
brain, and in close proximity to it, are altogether unknown ; but
they probably constitute a part of its mechanical structure.

158. The membranes enclosing the brain, and partly the
nerves, belong to the same class (the mechanical) as tendons,
ligaments, &c. They are not only insensible, but the brain
itself seems to have no influence on them, except in commu-
nicating the mechanical movement (24) which it possesses itself.

159. The tubes, and especially the vascular system, remain
only to be noticed among the mechanical machines which are
in connection with the brain, and in these, material ideas can
develope true sentient actions. The cortical substance is almost
wholly a tissue of tubes ; it is not the organ of the conceptive
faculty, nor the seat of the animal-sentient forces, but the
organ for secreting the vital spirits, which it supplies to the
medulla of the brain, and thence to the entire system of animal
machines (the nervous system) (11) ; in this respect it can be
considered as a viscus of the head, whose proper function is the
secretion of certain fluids from the blood; which fluids con-
stitute, however, an essential part of the animal machines (9) ;
it is, therefore, really a mechanical machine (155), but in virtue

84 ANIMAL-SENTIENT FORCES. [i.

of its function to give existence to the animal forces, it differs as
little from the proper animal machines, and as necessarily be-
longs to them, as the roots of a tree to the tree itself (9, 11).
This mechanical machine is unique, for while it belongs to the
animal machines, it secretes the vital spirits from the blood
in its infinitely numerous minute canals, just as other secreting
organs secrete other fluids in their minute tubuli. Secretion
generally, as physiology teaches us, takes place according to
physical laws, rather than animal. But, nevertheless, since
the fluids entering the tubuli act as stimuli, and excite them to
the performance of their natural functions, as will be shown
subsequently (168, 172, 460), the natural function of the cortical
substance of the brain must be considered as animal ; only its
functions do not belong to the proper sentient actions, however
necessary and indispensable to them ; for, although requisite to
the production of material ideas in the cerebral medulla, it is
not a direct result of these, nor is it in itself a material idea,
since the secretion of the vital spirits is not directly caused
by conceptions (25, 97). Nevertheless, the cortical substance
can be influenced indirectly by sentient actions, as when con-
ceptions, desires, &c., influence the heart and the circulation ;
and thus, either by increasing or diminishing the amount of
blood sent to the brain, increases or diminishes the secretion of
vital spirits ; which phenomena are rather the results, however,
of sentient actions, than sentient actions themselves. It is
probable, although not established, that the material ideas in
the medullary substance exercise, as sentient actions, a direct
influence on the vessels of the brain. The brain receives at each
stroke of the left ventricle at least a sixth part of the whole
mass of blood, and this is distributed through every part of
• the brain, by means of the almost infinitely numerous capillaries
which enter into its substance (Haller), so that the smallest move-
ment in the brain would act almost necessarily on these minute
vessels. The vessels w^hich return the blood to the heart, the
source of vital movements (Lebensbewegungen), are equally
numerous. It is, therefore, probable, that the material ideas
in the brain, however hidden they may be from observation (28),
have some influence on the vital movements, independently of
the nerves, and that this may be one of the causes, why so
many conceptions, but especially painful sensations in the

CH. III.] NERVES OF BLOOD-VESSELS. 85

brain (headache), change the circulation of the blood, and some-
times distend, sometimes empty, the vessels of the head, and
render the colour of the face so variable. All this it is
true is conjecture, but it is probable; we cannot decide the
question, for proper observations as to the mode are impossible.
We see, indeed, that some species of conceptions regularly
and powerfully modify the vital movements, and especially the
circulation within the head ; but still since this may probably
take place through the nerves distributed to the heart (for the
impressions of such conceptions influence its movements by
means of its nerves), it remains undetermined whether the
direct action on the cerebral capillaries of the cerebral im-
pression has a share in these sentient actions, and to what extent.

Actions of the Material Ideas in the Mechanical Machines
through the Nerves.

160. The most common and most general mode of connec-
tion between the nerves and mechanical machines is the rami-
fication and subdivision of the former in the latter, until they
become imperceptible (13). Another is, however, possible : the
nerves come in their course into contact with various me-
chanical machines, without being specially distributed to or
lost in them. As the cerebral impression on the nerve pro-
duces no visible or observable movement at the point of im-
pression, so neither in traversing the nerve does it excite any
action in the parts with which in its direct course it comes into
contact. But as it is probable, that its deflection at the
points where it is turned from its direct course, is caused
y a vivid cerebral impression (151) ; it is probable, also, in
ch a case it may communicate some movement to the me-
chanical machines it comes into contact with at such points,
and this may be termed a sentient action (97). This conjecture
is very probable as to the loops of nerves, which wind round
numerous blood-vessels, and enclose them, certainly not without
an object. Probably, many vivid cerebral impressions slightly
compress the vessels by this means, and so retard the circulation,
as Haller has supposed, who by this hypothesis has explained the
redness of the face in blushing. {' Opera Minora,' tom. i, p. 513.)
Subsequently, however, this distinguished man discarded the

m

86 ANIMAL-SENTIENT FORCES. [i.

hypothesis, and other learned persons have rejected it entirely,
on the ground that although impressions, whether external or
internal, may excite convulsions in muscles, they excite no
perceptible movement in the nerves. Nevertheless, as the
cerebral impression undoubtedly excites movement in the ter-
minal points of the nerves (147), this may be possible and pro-
bable, wherever else it is deflected from its direct course (151).
Further proofs on this point will be given subsequently (178).

161. Amongst the mechanical machines, in which the
nerves are so distributed as to be completely incorporated with
them, the muscles hold the first place. Nerves penetrate all
muscles, being distributed together with the blood-vessels through
the cellular tissue, losing, however, their firm coat, and be-
coming soft, before they become so minute as to be no longer
traceable (^ Haller^s Physiol.,^ § 398). It maybe also asserted,
that the soft medulla of the nerve is lost in the muscular fibrils,
and incorporated with their substance (^ Monro de Nervis,^ § 22).
When a muscle is thrown into contraction by an impulse sent
along the nerve, its fibrils are contracted, and the two ends are
drawn together, so that the whole muscle is shortened; con-
sequently, it also draws the parts together to which, by means
of its tendons, it is attached. The latter are passive, and are
neither contractile, nor capable of receiving an impression. The
muscle may be moved either wholly or partly. The arteries
which are distributed to muscles are necessary to their com-
pleteness, so that without them they soon become unfit for
their functions, or diseased (129, iv) ; but the animal actions
themselves do not immediately cease when the influence of the
blood ceases {' Monro de Nervis,^ § 44), and are in no wise pro-
duced by it (Haller's 'Physiol.,' § 406).

162. This action of the nerves on the muscles cannot be
explained by any of the laws of mechanical motion (Haller's
' Physiol.,' § § 394, 412.) It is also manifest from all phenomena,
that the vibrations transmitted along the nerves, and com-
municated to the muscles, do not produce the movements of the
latter in any mechanical way (Ibid., §§ 376, 377); and as all
other methods of explaining mechanically these movements are
insufficient, we must turn to other moving forces. The move-
ment in the muscle which it receives from the nerves, only
takes place after an impression made on the nerve, — it may be

CH. III.] THE NERVES OF MUSCLES. 87

an external impression transmitted to the brain, or one which
does not reach the brain (3i, 47), or a cerebral impression from
conceptions, or not, or an internal impression in the medulla of
the nerve itself in its course (121). An irritation of the nerve
of a muscle (an external impression) produces movement in the
muscle it supplies ; it does this also when the animal is de-
capitated, or with its nerves tied and rendered insensible, nay,
even in the separated muscle itself (Haller's ' Physiol.,' § § 404,
409, 575.) If the medulla of a nerve be irritated, the muscle
or muscles to which it is distributed, are convulsively con-
tracted; and this so long as the animal lives, or even after
death, so long as it is moist. It is not at all necessary that
the nerve be entire, since if it be divided and then irritated,
contractions are equally excited. If a nerve be compressed, or
tied, the muscles to which it is distributed are paralysed, and
although the will endeavours to act on them, they remain
motionless. But if the ligature, or compression, be relaxed,
the muscles regain the power of movement, provided the
nerve be uninjured. If the crura cerebri be irritated deeply
in their substance, the most violent convulsive movements are
excited in the whole body; the same occurs when the spinal
cord is irritated. If the brain be compressed, that portion
of the body is deprived of motion, the nerves of which arise
from the compressed portion : in injuries of the spinal cord
it is more distinctly manifest, that convulsions or paralyses are
induced in that part of the body supplied with nerves from
the injured portion. When the spinal cord is injured in the
neck, death follows immediately, because the nerves of the
heart arise from this portion (Haller's ^ Physiol.,^ §§ 367, 368).
An impression on a motor nerve, of whatever kind it may be,
developes the movements proper to the muscle with which it is
incorporated in a way quite incomprehensible. It is a movement
caused by an animal force (7), and in so far as it is produced
by the impressions of conceptions in the brain, it is a sentient
action (97) . No other movement of a muscle is such, whether
it be from mechanical or physical forces, or even from im-
pressions (except those of conceptions), although in the latter
case they are animal (6, 7) . On the other hand, the volitional
movements must not be considered as the only sentient actions,
— as is carelessly taught in many elementary treatises, causing

88 ANIMAL-SENTIENT FORCES. [i.

numerous errors, — since there are also those which arise
from spontaneous conceptions and from external sensations
(97, 98, 351). It is, consequently, equally incorrect to say, that
the functions of certain muscles, as the heart, intestinal canal,
&c., do not depend on the mind, because the mind has no
control over them, for the external sensations, imaginations,
instincts, and passions equally change, increase, or diminish
them, although the mind exercises at the same time no vo-
litional influence.

Note. — Haller seems to be of the opinion, that no movements
except the voluntary are produced by the soul, " ^Eterna lege
separatur voluntatis imperium ab irritabiiitatis provincia'^
('Elem. Phys.,^ torn, iv, p. 528). He recognises, nevertheless,
the action of the imaginations, sensations, instincts, and emo-
tions, and proves somewhat unnecessarily that they are not
volitional movements (ibid., p. 525). It necessarily follows
that the sensational conceptions, desires, instincts, &c., are not
mental, but corporeal, as Haller, in his *^ Physiology,' § 564,
and other places in his writings, seems to maintain. But no
sound metaphysician can grant such a confusion of ideas, as we
shall subsequently show it to be (579, iii).

163. All muscular actions are animal actions, in so far as
they are excited by the nerves; they are only sentient when
excited by conceptional impressions in the brain. We may
enumerate walking, standing, sitting, flexion and extension
of the limbs, respiration and its modifications, as speaking,
laughing, singing, wailing, sighing, coughing, sneezing, de-
glutition, digestion in the stomach and intestines, the action
of the heart, and the circulation in connection with cardiac
action, as animal functions, which may be sentient (167). On
the other hand every action of a muscle, which takes place in
virtue of its physical contraction, or of physical or mechanical
moving forces, or by the influence of the vessels, or through
its membranes or tendons, or other impressions than the ap-
propriate ones, is neither animal nor sentient (162).

164, i. When a muscular movement, or an action resulting
therefrom, is a sentient action, a special impression on the
cerebral origin of the nerve that controls the muscle is neces-
sary thereto (123, 124), and which is propagated downwards
through special fibrils of the nerve to the muscle into \vhich it

CH. III.] THE NERVES OF MUSCLES. 89

arrives, together with the nerve, and excites it to that action, of
which, in virtue of its structure, it is capable.

ii. The same nerve, can at the same time in which it excites
the muscle into action, receive an external impression, and
transmit it to the brain, there to excite external sensations,
without the two impressions as they pass in opposite directions,
interrupting each other in their course (126).

iii. When a nerve is compressed, or divided, in its course
between the brain and the muscle to which it is distributed,
the latter cannot be excited into action by cerebral impressions
until the compression is taken off (128. Haller's ' Physiology,^
§§ 403, 367).

iv. If the brain be compressed, all sentient actions in the
muscles cease, and all actions dependent on them (128). If
only a portion of the brain be compressed, then the actions
cease in those muscles which receive their nerves from the
compressed portion, inasmuch as they can no longer receive
conceptional impressions.

V. A general irritation of the brain, or such an irritation
that the origin of all the motor nerves is implicated, must
excite disorder of the whole, or of the greater part of the
muscular system (128. Mailer's ' Physiology,' §§ 367-8, 568).
165, i. If a muscle be directly excited into action by external
sensations, the nerve which perceived the latter must move it
(129, 131), although the movement may take place through
other and far distant branches (127). This is the sympathy
of sentient actions in the muscles. Direct sentient actions of
this kind frequently take place, as for example, if by a powerful
injury the muscles are excited to spasmodic action, or cramps,
other sympathising muscles are frequently excited into similar
movements.

ii. When the medulla of the brain is irritated, violent

lovements may be excited in the muscles by the pain (132,

Laller's ' Physiology,' § 308), which are sentient actions^ and

•e produced in the same way as those resulting from external

jnsations (132).
iii. When the mind, by means of spontaneous conceptions,

lOves the muscles and other parts through them, the con-
jeptions must act on the cerebral origin of the nerves which

jgulate the muscles (130). All kinds of imaginations and

90 ANIMAL-SENTIENT FORCES. [i.

foreseeings, also imperfect external sensations (148), internal
sensations^ pleasure or pain, desires, aversions, instincts, emo-
tions, and ideas of the understanding, in so far as they are
mixed up with sensational conceptions, or are pleasing or
painful (330, &c.), and the desires and aversions of the will,
have a manifold influence on some muscles, as experience
teaches, and the domain of the animal- sentient forces is con-
sequently very general in the muscular system.

iv. The more energetic the impressions of all these concep-
tions are, the more energetic are the movements which they
can produce in the muscles (133).

V. When these movements are caused by conceptions wholly
spontaneous, as for example, by volitions, the principle of their
sequence must be sought for in the laws of the conceptive
faculty (110). On the other hand, the muscular actions pro-
duced by sensational conceptions are known to us, partly
through the sequence of external sensations and their external
impressions.

VI. The sentient actions of the muscular system may be
prevented in the same modes as all other sentient actions ex-
cited through the nerves (136 — 139).

166. The muscular action excited by animal-sentient forces,
represents the thoughts as it were by external delineations,
especially in the face, by which their existence may be dis-
covered ; and by a frequent repetition of these movements, in
consequence of vivid and oft-repeated conceptions, certain
marks are necessarily traced in the skin covering and surround-
ing the muscles. Hence arises the art of discovering the modes
of thought, and the predominant mental characteristics of men,
from the lineaments of the face, termed Physiognomy.

167. The nerves may have an influence on the blood-vessels,
on the secretions, and on the whole circulation, in various
ways. In the first place, through the heart, a compound hollow
muscle, throughout which nerves from various sources are dis-
tributed as in other muscles (161). These nerves, like all others,
can receive external impressions, since an animal feels when the
heart is pricked or irritated (32). They consequently transmit
external impressions in Such cases to the brain, and produce
therein at their origin external sensations (34, 25), or cerebral
impressions (129). When there is no impediment, these

CH. III.] THE CARDIAC NERVES. 91

are propagated downwards along the same nerve (129, 131),
and, consequently, may not only have an influence on the
movements of the heart (7), but may excite sentient actions (97).
In the same way, the sensational conceptions, desires, and
aversions, sometimes excite cardiac movements, which are
sentient actions produced through the nerves by various
material external sensations (66, 93) : examples of this kind
are numerous, as when ideas, foreseeings, and emotions change
the movements. It is acknowledged by the most eminent
physiologists, that the action of the heart generally is not
mechanical, but animal; yet that it is absolutely a sentient
action is undoubtedly erroneous, since it will continue and
be re-excited even after the heart has been removed from
the body (164, iii). Neither is it any proof thereof, that an
external impression on the terminal fibrils renews the move-
ments of the heart, since the action of that impression be-
comes sentient only after reaching the brain, and not before
(98, 1 62) . If it be asked, whether the motion of the heart is
not sometimes changed by numerous impressions made on the
origin of its nerves in the brain, and consequently that many a
change in its motion maybe a sentient action (97)? — I answer,
— this by no means proves the contrary, for no change in the
heart's movement is subject to the will (162, 163). It is much
more indisputable, that such a change is a sentient action, when
an external sensation or another spontaneous conception excites
the change. Now the mind actually feels many external im-
pressions on the nerves of the heart. It feels its palpitation,
or wounds and other irritants ; and violent actions result from
these, which are necessarily direct sentient actions of its ex-
ternal sensations (129). That its nerves do not respond to all
stimuli, is a peculiarity they have in common with all other
nerves. Further, it is indisputable, that although the will has
no power over the heart, still many sensational conceptions have,
and particularly the instincts and emotions; and it is clear
from this, that many changes in the heart's action are true
sentient actions, in so far as they are produced by conceptions
by means of their cerebral impressions (97, 163). Lastly,
although the movement of the heart is neither weakened nor
ceases, when the brain is compressed, or the nerves tied,
nothing more can be inferred therefrom, than that the entire

92 ANIMAL-SENTIENT FORCES. [i.

movement is not generally a sentient action, which is indeed
the fact ; but rather that the undoubted animal force, which con-
tinually produces it, is not derived from the brain, and has its
seat in other animal machines (the nerves) and forces (the purely
animal, ^7), which will be treated of subsequently in the Second
Part (448, 514). But in so far as the heart is capable of certain
sentient actions excited through the brain, no one would deny
that they must cease, when the brain, or the origins of the
nerves, are compressed, or the nerves tied, or divided in some
part of their course. In such a case, the external sensation
from the strongest irritant applied to the heart, or any emotion,
would fail to excite its action (164, i, iii, iv).

168. The nerves have another influence; namely, on the
vascular system generally, since they are incorporated with the
coats of the arteries, and thereby probably supply animal force
to the muscular fibres which they surround. This influence
of the nerves on the blood-vessels is very obscure, and they
scarcely appear to efi*ect a sentient action, for, in the experi-
ments which have been instituted, the arteries have never once
shown any sensibility (Haller's 'Physiology,^ § 32). Neverthe-
less, Haller asks whether it is not probable, that the arteries
derive from these nerves the powder of contracting ? — Compare
what has been already stated (160) and subsequent statements
(178.)

1 69. A third kind of influence possessed by the nerves, is on
the vessels distributed to the muscles. It almost necessarily
follows, that the numerous blood-vessels distributed in them
are aff'ected by the contractions excited by the nerves. Con-
sequently, the latter indirectly favour the circulation of the
blood in the veins, and agitate and mix that in the arteries,
thereby favouring its course towards the lungs. They regulate
the secretions of the liver, mesentery, &c., and diminish or
retard them; they urge on the blood, and the large muscles
of the abdomen impel the blood contained in that cavity towards
the heart (Haller^s 'Physiology,^ § 416). Many of these acts
are sentient, nay, are even volitional (165) ; and if to aU these
actions of the nerves on the blood-vessels and the circulation,
the direct action of the brain on its multitudinous capillaries
be added (159), it is clear that this apparently simple me-
chanical motion of the heart is much under the important

CH. III.] THE NERVES OF MUSCULAR TUBES. 93

influence of the mind, and the still more important influence
of the nerves. — (Compare § 207.)

170. The nerves act principally in the other canals which
have a muscular structure, and numerous nerves, as the
oesophagus, intestinal canal, &c., by the stimulus of muscular
motion, so that these tubes are put in motion by the nerves for
the performance of those acts, of which their structure renders
them capable. When no natural obstacle is present in the
perves (47, &c.) to prevent the transit of the external impres-
Isions to the brain, and they are really sensitive (34), they may
be stimulated to action by the cerebral impression of external
sensations, and then the action is sentient (97, 129, 131),
although their actions are not usually sentient, but nervine
(162, 163). The oesophagus and intestines are often really sen-
sitive, and are then affected with spasms, as is proved by colic,
which has its seat in the intestines. Now, since in these cases,
the spasms are true sentient actions from external sensations
(from pain), these tubes do actually manifest some sentient
actions; although, in other cases, they are excited wholly by
other animal forces, and, although the will has no power over
them (162, 163). Nay, since the other sensational conceptions,
imaginations, foreseeings, &c., and the sensational desires and
aversions, can partly re-excite the material external sensations,
of which the sensitive nerves are susceptible at their origin
(66, &c., 93), so in like manner, they can excite movements in
these muscular tubes which are sentient actions ; as, for example,
when retching is excited by the anticipation of a nauseous taste,
and when the bowels are acted on by the imagination of a
purgative being taken.

171. The membranes of the human body differ very much in
structure, — glandular, cellular, vascular, &c. ; the latter will be
treated of subsequently (208). The muscular membranes, as
the diaphragm and others which enclose different parts of the
body, particularly certain glands, are also sensitive, as we learn
from observation ; the diaphragm, in particular, has large nerves
which influence its movements by means of external im-
pressions, and the ligature of which causes the movements to
cease (Haller's ^ Physiology,^ § 403). Further, the motion of
the diaphragm is subject to the will, inasmuch as we can
change the respiration at pleasure. The remarks previously

94 ANIMAL-SENTIENT FORCES. [i.

made (161 — 168) as to the action of the nerves on the muscles
and blood-vessels, are equally applicable to these flat muscles
and muscular membranes.

172. The glands are a tissue of vessels and nerves, and their
function is to separate the secretions from the blood. The
nerves exercise the same influence on these as on other vessels,
and, consequently, secretion, which ordinarily appears to be
simply physical, is not only animal, but is also sometimes a
sentient action. The nerves have the most manifest influence
on those glands which are surrounded by muscular tissue, or so
placed between muscles that the latter, by their action, express
the fluid from the glands when secreted ; so that it is poured
out. Examples of this kind are the penis [Geilen],the urinary
bladder, the bowels, the stomach; also the parotid glands,
which are emptied by the actiou of the muscles of mastication
(Haller^s ' Physiology,^ § 233.) Many glands pour out their
secretions from external sensations (titillation — pain, 80) ; many
from imaginations, sensational anticipations, desires, &c., as, for
example, the salivary glands from the recollection or expectation
of an agreeable taste, or in hunger ; many from passions, as the
lachrymal and sexual glands; many even from acts of will, as
when the saliva is stimulated to flow by voluntary mastication,
or weeping is feigned.

173. The action of the nerves in the viscera is yerj complex,
varying with the number of the nerves distributed, or with the
various impressions of which the latter are susceptible (34, 47,
121); or, as they are influenced by the muscles, muscular tissues,
glands, &c., which surround, or are in relation to them ; or, as
the nerves act directly or by sympathy (127, 165). We can
only notice some of the most important.

174. The stomach has many and considerable nerves, and
remarkable sensibility. When the trunk of these nerves (the
eighth pair) is tied, the powers of digestion fail. Its nerves
are susceptible of special external impressions, so that acrid
substances which are not distinguishable by the tongue excite
the stomach. On the contrary, other things which the tongue
perceives most sensibly, cause not only no distinct sensation,
but no sensation at all, although it is manifest from the move-
ments which they sometimes excite, that they must cause
another external impression, which is not felt, because, probably.

t H. III.] THE VISCERAL NERVES. 95

there are natural obstacles that prevent the transmission of the
impression to the brain (47); of these we shall treat in the
second part (428, 429) . In virtue of its sensibility, the stomach
is susceptible of impressions from conceptions in the brain (98),
which are sentient actions, as, for example, a violent pain causes
spasms of the stomach. The observations made with reference
to the action of the sensational conceptions and desires on the
oesophagus and intestinal canal, are equally applicable to the
stomach (170); they induce sentient actions, as, for example, when
by an imagination or anticipation of a loathing, its action is in-
verted, and vomiting is excited; or, when it is excited to motion by
hunger ; or is thrown into spasmodic action by violent emotions.
The will has little influence over it ; but the connection between
disorders of the mind and the nervous system, and disorder of
the digestive powers of the stomach and bowels, is well known.

175. Although the sensibility of the liver is not great, and,
consequently, only few external impressions made on its nerves
reach the brain, still it is capable of sentient actions. They
are observable only in the most vivid external sensations and
sensational conceptions, as, for example, in the pain of inflam-
mation, or in rage, fury, &c., inasmuch as it can be inferred from
the bilious disorders which follow, as icterus, &c., that the
secretion of bile must be prevented or increased. The nerves
can also exercise an indirect influence on the liver through the
diaphragm, and the abdominal muscles, and the other organs
in relation with it, and the results are also sentient actions.

176. The kidneys have but few nerves, and are only afi'ected
by powerful external impressions and sensations, as when there
is a stone or inflammation present ; in which cases only, certain
sentient actions occur, as spasms. The external impressions
made by the urine, and which excite vivid external sensations
in the nerves of the tongue, the nose, and even the skin itself,
are either not made at all on the renal nerves, or a natural
obstacle (47, &c.) prevents their transmission to the brain.
The urinary bladder, on the other hand, is much more sensitive.
Vivid external sensations (pain) cause spasms and spasmodic
discharge of urine, which are sentient actions. The sensational
conceptions and foreseeings act upon it, whence persons are
often induced to pass urine in dreams. The will has also some
influence upon it through the sphincters.

96 ANIMAL-SENTIENT FORCES. [r.

177. The organs of the external senses, considered as me-
chanical machines only (155) are subject to the same laws as
others. Through external sensations, sensational conceptions,
instincts, emotions, and even through the will, the nerves cause
movement in the tongue, the nose, the ears, the eyes — even the
skin in which are placed the nerves of touch, is contracted by
many external sensations (as cold); all which movements are
true sentient actions.

178. The sexual organs of man, and especially the testes and
penis, are supplied with numerous and large nerves, which are
extremely sensitive. The sensibility of the testes is so great,
that syncope and convulsions are induced by injuries to them,
and locked jaw, in particular, from the sympathy of their
sentient actions. The sensitive nerves of the penis, which every
impression excites, afford a remarkable example of the action
of conceptional impressions on the vessels through the nervous
loops around them, and independently of muscular action, of
which mention has been already made (160), for the tume-
faction of the corpora spongiosa must be caused by a reten-
tion of the blood in the vessels ; which can only be explained
by the theory that the nerves induce the vessels to contract,
in fact, this tumefaction is excited by every kind of external
impression on these nerves, especially by external sensations, as
when urine irritates the bladder; semen the seminal ducts;
the venereal poison, and Spanish flies the urethra, — which is
very sensitive; and other causes, as flogging, and friction of
the glans penis. In like manner, it is caused by imaginations,
foreseeings, sensational desires, instincts, and emotions, as is
well known, and altogether independently of the will. Haller
maintains the doctrine, that this swelling takes place without
the assistance of the muscles, and solely by the blood-vessels,
finding analogous instances in the erection of the nipples in
sucking, the distension of the wattle of the turkey, and of the
organs of generation in lower animals ('Physiology,' § 840),
all which are sentient actions. (Compare § 274.)

179. The numerous nerves distributed to the female organs
of generation, render them extremely sensitive, and the re-
marks in the preceding section are equally applicable to
them (274).

180. It is the most important mechanical machines of animal

CH. III.] EXTERNAL SENSATIONAL ACTIONS. 97

bodies, that are susceptible of the sentient actions just described,
in virtue of their nerves. We will now consider, in what me-
chanical machines, and by what laws, the different conceptive
forces of the soul manifest their actions externally to the brain,
in animal bodies, and in what these consist. We will begin
with the sensational perception and desires {76, 89), and
afterwards consider those of the intellect.

The Actions of External Sensations through the Nerves in the
Mechanical Machines.

181. It is not so easy a task as it appears, to discover the
direct sentient actions of external sensations in the mechanical
machines. All those produced by an irritation of a nerve,
or by the external impression transmitted along the nerve, or
even by its propagation to the brain, or deflection thence, are
its animal actions ; but none is a sentient action of an external
sensation (98), unless it belong to the class caused in the me-
chanical machines by an external sensation, or by the material
cerebral sensation acting as an impression in the brain (121, 97).
All movements, consequently, in the mechanical machines,
which the external impression excites by its own proper animal
forces, before it has formed external sensations in the brain,
and all that it produces in other nerves and mechanical ma-
chines in its course to the brain, in virtue of the motive force
peculiar to itself, cannot be considered as the sentient actions
of external sensations, even although they be also developed
by the external sensations of the external impressions. All
the sentient actions produced in the mechanical machines
through the nerves only, of imaginations, foreseeings, sensa-
tional instincts, emotions, intellectual conceptions, or desires and
aversions of the will, excited in the mind by external sensations,
are not true direct sentient actions of the external sensations,
although all the material ideas of the conceptions produced
by the latter are their indirect sentient actions (97, 98).

182. Hitherto, these actions (altogether distinct) have been
indiscriminately considered as direct sentient actions of external
sensations, and so the physiological doctrines of external sen-
sations have been sadly confused. It is, consequently, of im-

7

98 ANIMAL-SENTIENT FORCES. [i.

portance, that we make this distinction as clear as possible ;
and to this end, we must assume^ — what will be demonstrated
in another part of this book for the first time, namely, —
that the external impressions on the nerves (nerve-feeling, § 32),
becomes itself an animal motive force, before it reaches the brain,
and develops external sensations therein. The most certain
answer to the question, whether a movement, excited in a me-
chanical machine by the external irritation of a nerve, be simply
an action of the external impression (feeling), or whether it
result from an external sensation, is found in the experiment
of repeating the irritation, of which the movement is the result,
after the nerve is cut off from connection with the brain ; or, for
greater security against sympathetic action, after the head of
the animal has been separated entirely from the body. So
long as traces of animal life remain after this separation, the
same movement results from irritation of the nerve, although
the external impression is no longer propagated to the brain,
and no longer able to excite a material sensation therein ; con-
sequently, the movement cannot be a sentient action caused
by the external sensation, but is an animal action produced by
the motive force peculiar to the external impression. When
after this demonstration, the apparently sentient actions of
external sensations in the animal machines are investigated,
it is found, that the animal motive force of unfelt external
impressions can produce, although somewhat less perfectly, the
greater number of these movements, which we consider as
being solely sentient actions resulting from external sensations,
and which are in fact sentient actions also, as will be shown in
the second division of the work.

183. The movements developed in organisms by the pe-
culiar animal moving force of the nervous system, not being
at the same time an animal-sentient force (6), are termed
nerve-actions i to distinguish them from sentient actions; con-
sequently, the movements excited in organisms by the motive
force of an unfelt external impression, are nerve-actions. The
majority of the sentient actions in mechanical machines of
external sensations are, therefore, at the same time, nerve-
actions (182); and the following propositions must be rejected
as erroneous. 1, That an animal movement in the mechanical
machines, which is a sentient action of external sensations, is

CH. III.] EXTERNAL SENSATIONAL ACTIONS. 99

never a nerve-action ; 2, that the movement, which is a nerve-
action, is never a sentient action of external sensations; for
there is nothing more certain than that a sentient action result-
ing from external sensations may be at the same time a nerve-
action, and vice versa. On the other hand, there may be
nerve-actions in the mechanical machines, which are not, at the
same time sentient actions, nor resulting from external sensa-
tions, because the external impression is prevented developing
a material sensation by a natural or other obstacle (47, 48, 199).
Thus, the movement of the heart is usually a nerve-action only,
and seldom a sentient action (167), for we but rarely feel the
external impression which excites the movement, although we
often feel the stroke itself, which is the nerve-action. — (Com-
pare §225.) It is not necessary to inquire here, whether there
be sentient actions in the mechanical machines from external
.sensations which are not also nerve-actions.

184, i. When an external impression on the nerves is not
^felt, then the movement which it causes in the machines is
^not a sentient action from an external sensation. If, however,
the movement itself be felt, and this acts as an external sen-
sation in exciting new movements, the latter are sentient
^actions from the external sensation produced by a nerve-
faction (183, 443).

ii. It is not manifest what influence is exercised by feeling,

|iOr the consciousness of an impression in the production of

Jsentient actions which can also be simply nerve-actions, more

.than by the external impression itself; unless it be that the

■actions are rendered more complete and regular when the two

:CO-operate. Generally, however, the feeling or consciousness

;of the external impression seems to have no other object than

to excite other conceptions in the mind, and other sentient

factions, so that its operation is extended evidently through the

organism generally, and becomes of compound utility. For

example, if the movement of the stomach when empty from

fasting, remain such as it really is, — a nerve-action, — and be

f.not a sentient action at the same time, the desire cannot be

j^excited which we term hunger, and the organism is neglected.

(If a violent spasm of a muscle were a nerve-action only, and

fnot also a sentient action from pain, the functions of the muscle

.might be destroyed without our taking any steps to prevent it.

100 ANIMAL-SENTIENT FORCES. [i.

According to this view^ external sensations must be considered
as watching over our preservation.

185. Again, we often confound the sentient actions in the
mechanical machines, resulting from other conceptions, with
those resulting directly from external sensations. When we
smell or see some nauseous article of food, which, on some
previous occasion has made us vomit, the external sensation
excites in us the imagination of the previous vomiting, and it
again comes on, because this imagination conjoins with it in
its action the partially re-excited external sensation {67). In
this case, vomiting is not the immediate result of the smell, or
perception (the external sensation) of the article of food, but
of the imagination thereby excited. When we see a stone
coming upon us and try to avoid it, the movement is not a
direct sentient action excited by the seeing the stone (the ex-
ternal sensation), but is the result of the abhorrence of the
impending danger, which the sight of the stone occasions.
Such examples are infinitely numerous, and if we compare
them with those mentioned in ^ 182, it is found that we have
mistaken the greater number for the movements connected
directly with external sensations, these being either nerve-
actions also, or purely nerve-actions (182, 183), or sentient
actions of other mental forces which are excited to action solely
by external sensations (219, 199).

186. It is to be understood, however, that those inner sen-
sations of the soul of pleasure and suffering excited by external
sensations (80) must, on no account, be classed with the con-
ceptions produced by external sensations, the sentient actions of
which are so often confounded with those belonging to external
sensations ; for pleasure and suffering are only qualities in the
external sensations of the soul, and not other conceptions excited
by them ; their sentient actions are consequently to be classed
with those arising directly from external sensations, and they
extend their influence to no other nerves than those which feel
the agreeable or disagreeable (124). But since the two distinct
conditions of agreeable and disagreeable external sensations con-
stitute external sensations for two distinct kinds of conceptions,
and these presuppose distinct material sensations in the brain
(80), and, consequently, distinct external impressions in the
nerves (35), they certainly constitute two perfectly distinct

CH. III.] EXTERNAL SENSATIONAL ACTIONS. 101

kinds of external sensations which develope totally distinct
sentient actions in the body.

187. All external sensations are either agreeable or dis-
agreeable; and if they be intense, the one is gratification
[Kitzel], the other suffering [Schmerz] (80). There is no ex-
ternal sensation without these qualities of pleasure or suflfering.
(See Baumgarten's 'Metaphysics/ § 481, 405.) Consequently
all direct actions of external sensations comprise at the same
time those of pleasure and pain, and cannot be separated from
them, because one or other is present on every external sen-
sation.

188. All direct sentient actions in the mechanical machines,
are efi'ected through the same nerve which produces the ex-
ternal material sensation in the brain (129, 131), whether it
be the same fibril which received the external impression, or
another, in virtue of the sympathy of sentient actions (165, i),
or from reflexion (48, iv). But, should the action of an ex-
ternal sensation occur in the same machine that received the
external impression, the material sensation must necessarily
excite in the brain the efferent fibrils of the same nerve which
is distributed to the affected mechanical machines as their
motor nerve (129, iii).

189. The difference in the nature of the external impressions
on the terminating fibrils of the same nerve, causes the dif-
ference between agreeable or disagreeable external sensations.
Now, since the external impression is itself an animal moving
force of the mechanical machines (182), it follows, that the
impression exciting agreeable external sensations, and the
impression exciting disagreeable external sensations, can each
develope appropriate movements in the mechanical machines.

190. Since we know nothing of the peculiar nature of an ex-
ternal impression, we cannot say wherein it differs when, through
the same nerve, it excites in the mind at one time an agreeable,
at another a disagreeable external sensation, or when it excites
gratification or suffering (40). But since we are no better ac-
quainted with the nature of material external sensations in the
brain, the only sources of actions in the mechanical machines,
dependent on external sensations (55, 129), the resulting move-
ments can only be known by observation ; but by this, we are
able sufficiently to discriminate between nerve- actions merely

102 ANIMAL-SENTIENT FORCES. [i.

(183), and sentient actions of conceptions dependent on external
sensations (181, 185).

191. It appears that the external impression for agreeable,
or for neutral external sensations, if such there be, is con-
formable to the natural function (destination) of the nerves,
or connatural ; on the other hand, that of disagreeable external
sensations is not conformable to the animal structure and pro-
perties of the nerve, but does them violence in some degree,
or is contra-natural} This difference arises probably, because
it is in the nature of the soul to be adjusted, as it were, to
all which relates to the preservation of the body, and finds
nothing to be agreeable which is injurious to the latter (196).

192. So far as is known, all the nerves of sentient animals
are sensitive to at least some external impressions. Con-
sequently, all have the power to receive at least some of these
sensationally, and transmit them to the brain, where they are
changed into material external sensations (34). Material ex-
ternal sensations are animal-sentient forces (114), that cause
an internal impression on the nerve that has felt the external
influence (121), which internal impression is propagated down-
wards from the brain along the nerve (143), and if the latter
be incorporated with any mechanical machines, may excite
actions which are direct sentient actions of external sensations
(160). In this way, all those mechanical machines of sentient
animals which are supplied with nerves, are in fact capable of
at least some direct sentient actions of external sensations,
although they may be incapable of a greater number from

1 Der naturlichen Verrichtung gem'dss and nicht gem'dss are terms used here in
the same sense as natiirlich and widernaturlich used elsewhere. The terms natural
and unnatural would not, however, exactly express the author's meaning. The
doctrine laid down in the text is as profound and truthful as any of the remarkable
views advanced by him ; the terms referred to imply, that there are agents to which
the animal organism is expressly and beneficially adapted, and the impressions of
which excite its mechanism beneficially, in accordance with that scheme of adaptation;
while other agents act upon it in a contrary sense, and impair or derange the normal
and beneficial working of the organism. In the former case the term connatural best
expresses the character of the agents ; in the latter, the term contra-natural. In
the Second and Third Parts of the work, these doctrines have an important appli-
cation in explaining the conservative and other actions resulting from the operation
of the vis nervosa, when excited into action by impressions, where the same words are
used with the same meaning. (Vide § 546, et alia.)

CH. III.] EXTERNAL SENSATIONAL ACTIONS. 103

natural or other hinderances (47) . Now, since it is not observed
of other conceptions, and of the desires and aversions (which
^come next to external sensations, §§ 68, 89), that they can extend
bheir influence to all the mechanical machines supplied with
lervesj nay, that the greater number seem to act only in
jome, and, indeed, many to act on none (79), it results, that the
sphere of the sentient actions from external sensations is the
lost extensive of all, and that those mechanical machines supplied
dth nerves, which are excited at all by animal- sentient forces,
ire capable of certain sentient actions from external sensations.
193. The circumstance which is common to all move-
Lcnts of mechanical machines, whether they be nerve-actions
>nly, or excited by cerebral impressions, or sentient actions
[resulting from external sensations, or from other conceptions,
jand in which they differ from simply mechanical movements,
iis this, — that the stimulus to those movements to which the
jmechanical machines in virtue of their structure are adapted,
is received through the nerves as an internal or external im-
^pression (31). The movements themselves, would, conse-
quently, be the same as those produced by simply mechanical
forces, since all movements excited in a machine by whatever
force, must necessarily be such as are in accordance with its
structure. It follows, therefore, that the circumstance which
renders the movement of a mechanical machine in organisms
simply animal is, — that it proceeds solely from an unfelt im-
pression on the nerve, and not from cerebral impressions caused
by conceptions ; that the circumstance which renders the move-
ment a sentient action is,— that it is excited by an internal
impression arising from conceptions (154); and lastly, that that
which constitutes it a sentient action of external sensations
is, — that it originates from the internal impression in the
brain of external sensations (34, 121).

194. The more vivid the external sensations are, the more
energetic is their action on the mechanical machines, and,
therefore, the actions they excite in the latter are vigorous in
the same proportion (133).

195. All movements, of which a mechanical machine is
capable in virtue of its structure, are either normal, or in ac-
cordance with its natural structure in a state of health, or are
abnormal, and opposed to that natural function. Consequently,

104 ANIMAL-SENTIENT FORCES. [i.

all sentient actions of external sensations stimulate the me-
chanical machines to which they are extended, either to those
movements that are their natural function^ in which case they
are sentient actions of agreeable, or at least of neutral sen-
sationSj or to those which deviate from their natural function,
and these are sentient actions of disagreeable external sensations
(191). This applies also to the sentient actions of titillation
[Kitzel] and pain [Schmerz], which only differ in degree
from the preceding (80).

196. To understand these views properly, it must be remem-
bered, that every pain and every unpleasant external sensation
is of itself something contra-natural, and is considered as
disease (191), whereas the healthy, that is, the natural condition,
is maintained so long as either pleasant or no unpleasant sen-
sations are felt. But since effects are as their causes, it follows,
that the actions of unpleasant external sensations are contra-
natural, while those of pleasant sensations are connatural. All
experience supports this view, and since suffering is to be con-
sidered as the sentinel of our preservation (184), so also its
actions are to be considered as a natural medicine which
develops contra-natural changes for the purpose of thereby
expelling contra-natural disorders of the organism.

197. Titillation [Kitzel] is a vivid agreeable external sen-
sation (80) ; consequently, its sentient actions render the natural
functions of the mechanical machines violent and exaggerated
(195, 193).

198. Pain is a vivid disagreeable external sensation (80);
consequently, the mechanical machines are excited by its sentient
actions to very violent contra-natural movements (195).

199. Since a violent and exaggerated natural function of a
mechanical machine borders on the contra-natural, the actions
from very vivid titillations are nearly allied to pain (197, 198).
Consequently, a violent titillation, like pain, often produces
convulsive movements.

200. The mechanical machines to which the nerve that has
felt, is distributed, are excited to those movements of which
they are capable, in virtue of their structure (193). If the
external sensations be agreeable, the movements excited are
conformable to the functions of the mechanical machine; if
disagreeable, are not conformable (195).

CH. III.] EXTERNAL SENSATIONAL ACTIONS. 105

201. If external sensations develope actions directly in me-
chanical machines, they re-act by means of their material ideas
along the same nerve that received the impression (188).
Hence it would follow (contrary to observation), that all me-
chanical machines, in which a branch of the same nerve is dis-
tributed, must be all put into action at once by every external
sensation of the nerve, unless it be granted, either that the
impression which excites an external sensation in the brain
at the point of origin of the nerve, can only act upon certain
fibrils of the brain in connection with one or a few branches
going to certain mechanical machines, which fibrils do not
accompany other twigs of the same nerve (188); or, that (136
et seq.) there are certain natural hinderances to the transmis-
sion of the cerebral impressions (136, iii), or, that it is turned
aside, or conducted away, in its course along the nerve from
various mechanical machines, and permitted to reach only those
appropriate to it, as is detailed ante (136 — 139, also 165, vi).

What influence sleep (49, 136, iii), and habit (51, 139), and
the ganglia (48, 137), may exercise in this respect, ought also
to be considered. It is probable, that all these hinderances
actually occur in nature.

202. The mechanical machines can develope nerve-actions
(183), but no sentient actions, if the brain, or the cerebral
origin of its nerves, or of those special fibres of the nerve
which receives and transmits the external impression appropriate
to the sensation (126), be compressed, or their function des-
troyed ; or if the course of the nerve or of the fibrils be inter-
rupted between the brain and their terminating fibrils (128,
164, iii, iv): also when the function of the mechanical machines
themselves are interrupted (129, iv).

208. The direct sentient actions developed in the various
mechanical machines by external sensations, are as varied as
the adaptations of the machines themselves to impressions (193).
We will consider their functions more in detail with reference
to this point.

204. The sentient actions of external sensations excite con-
tractions in muscular tissue which, when violent, are termed
spasms. Spasms, frequently repeated, are . convulsions ; if con-
tinuous, they are tetanic [Erstarrungen] . The limbs moved
by the muscles thus aff'ected, and the other functions which the

106 ANIMAL-SENTIENT FORCES. [i.

muscles perform, participate naturally in all these movements,
partly from sympathy, partly in consequence of a mechanical con-
nection (165, i, 161, 169, 179). Hence, the sensibility of muscles
is a very general principle in animal mechanism, since all these
movements are developed at each external impression and also
when it is felt, and the more vividly it is felt, the stronger the
movements (194, 165, iv); consequently, they must all be con-
sidered to be direct sentient actions of external sensations (163,
98), although they may be at the same time nerve-actions (183,
162). The muscles are excited to action by various external
impressions, as, for example, the urinary bladder by the injection
of water, the heart from the entrance of the blood, the bowels
by inflation with air, &c. The agreeable, or connatural external
sensations, maintain, sc^ far as they act on muscles, the order
and degree of movements and functions appointed by nature
to the muscles, and to the parts of the animal body regulated
in their function by them (195, 196). On the other hand, the
disagreeable excite contra-natural movements of the kind
mentioned. Tickling [Kitzel] excites vivid contractions; pain
excites sometimes violent cramps of a spasmodic character,
sometimes tetanic convulsions [Erstarrungen], which are also
occasionally caused by tickling. How direct sentient actions
from external sensations are induced in the muscular system
and in other parts of the body, and how they may be prevented,
has been already shown (129, 13 i, 136) ; and the doctrines have
an extensive application to pathology and therapeutics.

205. The sentient actions which external sensations excite
in the other mechanical machines, may be deduced for the^
most part from the preceding. External sensations act upoi
the blood-vessels, either through the heart, which is a muscle]
(167), or through their muscular fibres (168), or directly]
through the muscles which contain blood-vessels (169). lv\
this respect, therefore, they can change the circulation. The
action on the blood-vessels, through their muscular fibres and
muscles, consists in a contraction of the blood-vessels (204),
(as is manifest in spasmodic attacks, which sometimes excite
congestion, sometimes accumulation of blood in parts not
implicated in the spasms). Probably, the nerves themselves
have the power of directly causing contraction of the vessels,
especially at their capillary terminations, as has been already

CH. III.] EXTERNAL SENSATIONAL ACTIONS. 107

observed (160). Although the distinguished Haller wishes to
withdraw this proposition once stated by him, he cannot with-
stand the force of facts, and observes : '^ Aliquid autem in
luinimis vasis esse, quod laqueorum nerveorum similitudiuem
certe in effectu habeat, adparet ex suppress© sanguinis venosi
motu in pene, analogo effectui vinculorum, et ex tuberculis
cutaneis, quse perinde a terrore ut ex frigore nascuntur.'^
(Element. Physiol.,, torn, v, p. 590.)

206. External sensations also cause contraction of the mus-
cular tubes, as the oesophagus and intestines, whereby their
natural function — the transmission of the food (170) — is fur-
thered. Pain causes a spasm in these organs which hinders
their natural functions (204).

207. All observation shows, that every external impression
at the mouths of the capillary vessels, whether they contain
blood or other fluids, which is felt (and also an impression
which is not felt, as will be proved in the Second Part),
attracts their fluid contents to their mouths, where the fluid
either accumulates, or is effused. " Dolori multa fere cum
voluptate communia sunt ; fortior nempe sensus, fortior etiam
sanguinis confluxus ad eam partem, quse vel voluptate emovetur
vel dolore; exempla sunt in venereis organis, in ipsis oculis
acrius tuentibus, in fricta cute.^^ (Haller, ' Elem. Physiol.,'
tom. V, p. 597.) This action is animal, for it is not a property
of other mechanical machines, although they also possess similar
canals ; nor is it observed in dead animals ; and, consequently,
does not result from mere mechanism (7) ; and so far as it usually
follows in the same parts on external sensation, it is a direct sen-
tient action from external sensation (98, 186). The direct action
of external sensations on the blood-vessels, is a contraction (205).
When the terminations of the arterial capillaries, which are either
continuous with the venous radicles, or open into cavities, become
contracted, the continually flowing stream accumulates in them,
and they are stretched and dilated, and thus, according to the
mechanical principles of pathology, congestion, swelling, and in-
flammation arise. It is in this way that those arteries are ex-
cited to pulsation by the pain of inflammation, in which it usually
does not occur. (Haller^s ' Physiology,' § 33.) If the capillaries
open into shut sacs, the great distension of their mouths dilates
the opening, and then copious effusion of the congested fluids

108 ANIMAL-SENTIENT FORCES. [i.

takes place into the cavities. This action is the greater in pro-
portion as the sensation is more vivid. Hence contra-natural
inflammations and swellings in the muscles and other me-
chanical machines arise from painful external sensations. From
pleasant sensations, as warmth, friction, itching, titillation, arise
a gentle glow and excitement ; and in cavities, such as the nares,
or intestines, in which the capillaries can pour out their con-
tents, an accumulation of fluid, as, for example, a discharge from
tickling of the nose (199), a purging from colicky pain, purgatives,
poison, &c. (198.) This afflux of fluids to the mouths of these
capillary vessels, when an external sensation stimulates their
own nerves, or by sympathy, those adjoining (165), constitutes
the basis of many important phenomena in the animal economy,
and has the most important bearing on the instincts, emotions,
and diseases of animal organisms, (Haller's ' Physiol.,' § 561.)
The greater number of mechanical machines of the body are
as thoroughly interpenetrated by capillary vessels as by nerves ;
it follows, therefore, that this particular action of external sen-
sations is observed to be almost always coincident with all
external impressions which are felt ; and thus it is a general
physiological law, that concurrently with each external sensation
there is an afflux of fluid to the point where the external im-
pression is made. This is not, however, the sole law, nor is it
quite general, since this afflux cannot take place as a consequence
of external sensation ia those parts not supplied with capillaries
and tubuli ; nor does it even take place in other parts, if the
external sensation be not of a certain degree of intensity or
strength.

208. External sensations excite direct sentient actions in the
flat muscles, particularly the diaphragm (171), which consist of
such contractions, or other movements, as they are capable of,
in virtue of their structure (193). Thus a painful sensation
from inflammation of the diaphragm, causes unnatural respira-
tion, in consequence of the convulsive movement excited in it.
Those membranes of the organism, which do not consist of a
true muscular tissue, but rather of minute glands, papillae, cel-
lular tissue, and capillaries and tubuli, must be considered quite
difi'erently with reference to their sensibility, and the sentient
actions resulting therefrom. Some of these membranes have
numerous nerves, and are very sensitive, as the skin, and the

CH. III.] EXTERNAL SENSATIONAL ACTIONS. 109

mucous membrane of the nostrils, throat, and other parts.
It appears also, that nerves are intimately incorporated with
these tissues (160), for every portion of the surface which
the point of a needle touches, is sensitive, and the final
distribution of the nerves in them cannot be traced. But
since their structure differs from that of the muscles, we cannot
expect them to manifest similar sentient actions. Never-
theless external impressions on their nerves can proceed to
the brain without exciting a visible movement in the point
touched, — can be felt, — and can be reflected by means of
the internal impressions of the sensation along the principal
nerve and its branches, and if there be no hinderances, can
excite movements in the mechanical machines to which the
nerves are distributed, and, consequently, develope sentient
actions in other parts by means of the external sensation thus
excited on such surface (129). Thus, titillation of the mucous
membrane of the nostrils excites sneezing, and a convulsive
movement of the diaphragm and respiratory muscles, the nerves
of which are in natural connection with those of the nasal mucous
membrane : thus also many an external sensation of the cu-
taneous surface excites, by means of the nerves, a tremor of the
muscles in relation to it, which is termed a shudder. Thus also
a titillation of the nasal mucous membrane excites eff'usion of
mucus, which is a sentient action of titillation in the capillaries
or terminating tubuli of the minute glands (207, 172) : thus
also the cutaneous surface becomes inflamed, and swells from
the stimulus of an acrid irritant : thus also cold contracts
the respiratory pores by a sentient action on the minute
terminations of the arteries, and interrupts perspiration (168).
Other non-muscular tissues have either no nerves at all, or
very few distributed here and there in their structure. Hence
their sensibility is doubtful. Of this kind, according to Haller's
researches, are the serous membranes covering the thorax and
diaphragm, the pericardium, peritoneum, &c. Nevertheless,
experience proves that they are susceptible of certain actions of
external sensations; and that actions may also be excited in
other parts by sensations originating in their nerves. Thus
it is seen, that if a nerve be injured or divided which traverses
a tendon, or the periosteum, paralysis or convulsive movement
is induced in the adjoining limbs, or in those in relation with

110 ANIMAL-SENTIENT FORCES. [i.

the injured nerve, which may be considered as the sentient action
of pain in those tissues, although their proper substance be
insensible. Besides, in such tissues, an injured blood-vessel or
gland, or other structure supplied with nerves, or with muscular
fibrils, may excite a painful inflammation, and therewith the
appropriate sentient actions, as an afflux or effusion of fluids,
congestions, inflammations, &c. (168, 172), from which as ex-
perience teaches, neither the pleura nor peritoneum, nor other in-
sensible tissues, are exempt (Vide §§460 — 465, 470, 522 — 530.)

209. External sensations excite the functions of the glands;
namely, the excretion of fluids; and when they are enclosed in
muscular tissues, the evacuation takes place according to their
mode of action on muscular tissues (172) ; but when there is no
muscular tissue, they excite an afflux of fluid, in virtue of their
action on the terminating mouths of the tubuli (207). Thus,
a strong flavour excites the secretion and discharge of the
saliva ; irritation, or pain in the eye, excites a flow of tears ; thus,
also, titillation causes parts to be lubricated, by irritating the
nerves of the glands, and favouring a secretion and discharge
of their fluids ; thus also irritation and pain of the bronchi
cause a mucous discharge from the irritated glands, — all
being manifestly sentient actions in the glands from external
sensations.

210. The direct sentient actions, from external sensations
in the viscera, properly so called, are very complicated and
varied, inasmuch as these machines are compounded of many
others in which external sensations act very variously. We
can only mention some of the more important in this sketch,
referring the reader to § § 204 — 209 for general principles.

211. The heart, as a compound hollow muscle, is stimulated
by external sensations (167) to the performance of its func-
tion, namely contraction, whereby the circulation of the blood
through the body is kept up. Consequently a painful sensation
in the heart causes a convulsive contraction and an accelerated
circulation.

212. The external sensations which are excited in and
about the stomach, stimulate it and the intestines to gentle
writhings, whereby digestion and the transmission of the food
onwards is attained. There is a movement excited in the
stomach when an external impression is made on it, but this

CH. III.] EXTERNAL SENSATIONAL ACTIONS. Ill

takes place, for the most part, through nerve- actions (183), for
the external sensation of each impression is seldom perceived,
only the vivid external impressions being felt, when the
painful actions of external sensations caused in it are contra-
natural. Thus arises the violent peristaltic action of the
stomach and bowels from griping purgatives, poisons, inflamma-
tions; hence also the spasm of the stomach from similar causes,
or from flatulency, or indigestible food painfully pressing the
stomach. The muscles of the limbs participate largely in such
contra-natural movements of the stomach and bowels, as is
shown by the paralysis which supervenes on violent colic.
This takes place in virtue of the sympathy between the sentient
actions of muscles, but the question belongs properly to the
pathology of organisms.

213. The liver and gall-bladder are little susceptible of ex-
ternal sensations : an external impression is only perceived when
it is remarkably vivid, and also contra-natural, or painful (198).
Violent pain in the region of the liver exercises an injurious
influence on the secretion and excretion of bile (175). Other
conceptions, like external sensations, have a manifest influence
on most of the proper viscera of the body by sentient actions
on their nerves.

214. Ordinary external impressions on the lungs are rarely
felt; when, however, they experience tickling or pain, the
respiration is partly accelerated, partly rendered contra-natural
and spasmodic, as in cough ; in cases of this kind the sentient
actions are from sympathy (98, 165). Respiration is not excited
solely by irritation of the nerves of the lungs, but also by
irritation of the diaphragm, and of the respiratory muscles
of the thorax.

215. The kidneys also are susceptible only of extraordinary
and unnatural external impressions ; spasm is almost the only
example of sentient action from external sensations that can be
deduced. It is otherwise with the bladder.

216. The organs of the senses, considered as mechanical
machines, are moved by external sensations in various ways,
having reference to their particular functions. When a sound
enters the ear, and is heard, the muscles which stretch the
tympanum are so put into action, as to render the latter tense
in accordance with the tone : so when light enters the eye, and

112 ANIMALSENTIENT FORCES. [i.

is perceived, the muscular pupil of the eye undergoes a change.
The light has no more such effect upon the pupil of the
blind than in a corpse, consequently it is a true direct sentient
action from an external sensation. When a savoury drop
or two is tasted posteriorly, by means of the tongue, the
throat is stimulated to the act of swallowing ; and when the
skin is affected by an acute external sensation, as from cold or
itching, it is contracted, and its exhalation altered (177).
These are obviously sentient actions in the organs of the senses
from external sensations, rendering them more fit for their
functions, and testifying to a fore-seeing wisdom.

217. All that need be said as to the direct sentient actions
of external sensations in the sexual organs has been already
stated ; it is their great characteristic that they render the
organs fit for the function of reproduction.

218. We may now estimate from previous considerations
(204 — 207) the law laid down by Kriiger, in his ' Physiology,'
that every external sensation is followed by a movement in the
body proportionate to the sensation. In the ordinary state of
the body, whenever an external sensation is excited in the mind
through a nerve which is distributed to mechanical machines,
such movements are developed in the machines by means of the
nerve, its branches and fibrils, provided there are no natural
hinderances there (136, 199), as in virtue of their structure they
are capable of, and the movements are the stronger in propor-
tion as the external sensation is more vivid (194). But it may so
occur (as will be demonstrated in another part of this work,)
that the same movements may result from an external im-
pression which is not felt, and thus be nerve-actions (83, 462).
This law is, however, not to be understood, to the effect that
the movements will be stronger in proportion as the external
contact on the nerve is stronger, or according to the measure
of physical forces, but the stronger the external impression is,
which may sometimes be very strong from a slight contact, and
vice versa (40).

219. Besides the direct sentient actions of external sensations
that we have hitherto considered (204 — 218), we have also to
consider the incidental^ [zufallig] which are so often confounded
with the former. It may be stated generally, that the sentient
actions of both kinds, and all the mental forces possessed

CH. III.] INCIDENTAL SENTIENT ACTIONS. 113

by animals in addition to the sensational force, are indirect
sentient actions of external sensations, although in very different
degrees of connection (65). We will glance at the most
prominent of the series.

We connect with our external sensations the conception of
another like to it, which we have had before, and thus a direct
imagination is attached to our external sensation (67), that com-
mingles its action in the mechanical machines with those of the
external sensation. In this way we sigh at the sight of a
person who is like another, with respect to whom we have had
sorrowful sensations. This sighing is the sentient action of
the imagination, and only indirectly of the external sensation
(97, 99).

220. We often connect with our external sensations the
expectations of others formerly connected with them, and thus
a foreseeing (73) accompanies our external sensation, which
mingles its actions in the mechanical machines with those
arising from the external sensation. A certain person always
faints during the operation of venesection ; some time after-
wards he meets the surgeon in the street, and becomes faint :
this faintness was the sentient action of a foreseeing of the blood-
letting, and only incidental to the external sensation (97, 99).

221. Since all our external sensations are made vivid by
pleasure or suffering (187), and accompanied by imaginations
and expectations (219, 220), so they are also associated with
desires and aversions, which unite their actions in the mechanical
machines with those arising directly from external sensations,
and are most manifest in the instincts and passions (93). Thus,
an agreeable or odious countenance instantaneously renders a
man enamoured or angry ; in animals, an odour, or a sound,
excites the sexual instinct ; or, in one who has fasted, the sight
of food excites hunger. Here the whole process of the instincts
and passions is set forth, and it is by no mean^ the external
sensations that directly excite their sentient actions. The last
will serve as an illustration : a man with an empty stomach
sees bread, and he recollects that under similar circumstances
he has been relieved by the eating of bread. From this
external sensation and imagination, there arises the expectation
that the same result would follow again if he ate bread, and now
there arises the seeking to eat, whereby the mouth fills with

8

114 ANIMAL-SENTIENT FORCES. [i.

water, — a sentient action of the desire (of the instinct) inci-
dentally produced by the external sensation (97, 103).

222. The strongest sensational conceptions and desires most
readily excite imperfect external sensations (148). Now since
true external sensations excite all conceptions, and consequently
the strongest conceptions and desires (219-221), they can inci-
dentally give rise to the sentient actions of phantoms, visions,
ghosts, and illusions (148). We seek with the greatest anxiety
to lay hold of the object which threatens us with imminent
danger, and this vivid conception works so intensely, and as an
aversion so contra-naturally (195), in our muscles, that the
arm remains stiff, swells, and inflames. This is not an unusual
circumstance where real objects are concerned. When we see
a form in the dark, which we take for a ghost, and the im-
perfect external sensation excites the instinct of terror, and we
reach towards it, the above-mentioned condition may occur to
the arm, not directly through the real external sensation, as,
for example, the sight of a shadow, but incidentally, inasmuch
as the latter excited the imperfect external sensation which
produced the phenomenon of the ghost.

223. We often connect thoughts of the understanding with our
external sensations, when we reflect upon objects that appear to
the senses, and thus a reflection {^"7^ accompanies our external
sensation, which combines the action it probably may develope
in the mechanical machines (330) with those resulting directly
from external sensations (100). Thus a glance may quickly
cause deep thoughts in us, together with vertigo, the vertigo
being the sentient action of deep thought, and only incidentally
that of the external sensation (97, 100; see also 331).

224. We connect desires and aversions of the will with oui'
external sensations, and so the actions of the latter accompany
those of the former (96). Thus, at the sight of a ravening
beast, we exert our muscles, and flee. This flight is the sentient
action of the conclusion of our will, and only incidentally that
of the external sensation (97, 104).

225. All sentient actions of external sensations consist of
movements, in which all those structures must take part that
are incorporated with the substance of the organ of movement,
and, consequently, the nerves (160). When these nerves receive
an external impression through their ultimate ramifications in

CH. III.] SUBORDINATE SENTIENT ACTIONS. 115

the mechanical machines, from a movement produced in the
latter, by means of material external sensation sent from the
brain, they can thereby excite new external sensations (31),
and these can develope sentient actions, either in the same
mechanical machines by means of the same nerves, or their
branches ; or in other machines to which they are distributed,
or to which their cerebral impression is transmitted (188).
Sentient actions from external sensations of this second class
are subordinate, or secondary, as to their origin, and if we
would avoid many errors in explaining the phenomena of the
animal economy, they must be carefully distinguished from
those which arise directly from external sensations. Pain in
a muscle excites cramp of the muscle, its direct sentient action.
But this cramp causes also a violent pain, from which con-
vulsions result, involving many other muscles. These con-
vulsions are subordinate sentient actions of the primary pain.
A poison excites a burning sensation in the stomach and bowels,
in consequence of which they writhe, and are spasmodically
contracted. These are the primary sentient actions of the ex-
ternal sensations of burning from the poison. But the writhing
and spasmodic contraction cause new pain (colic, spasms of the
stomach), whereby the circulation of the blood in the abdomen,
and the digestion and transmission forwards of the food, are
hindered, the bowels constipated, dysuria induced, and the legs
paralysed (212). These are the subordinate or secondary actions
of the sensation of burning excited by the poison, and the
direct sentient actions of the gastric spasm or colic. It is
obvious, that when these subordinate actions excite new sen-
sations, new sentient actions may result which are again sub-
ordinate. Thus, therefore, a single external sensation can, by
means of its subordinate and continuous direct sentient actions
excite most, if not all, the mechanical machines of the body to
movement; spasmodic diseases, from titillation, &c., present
the most frequent examples of this kind. It must therefore
be remembered, (and it will be subsequently advanced in treating
of the actions arising from other sentient forces,) that the
subordinate external sensations of the mind constitute, when
combined with the primary, a compound external sensa-
tion (an entire or complete [conception] external sensation,
— Baumgarten^s ' Metaphysics,' § 378), which consists of the

116 ANIMAL-SENTIENT FORCES. [i.

primary and all its subordinate sensations; and that the pri-
mary and subordinate, separately considered, are the elements
of an entire external sensation. The same principles apply to
the actions of compound conceptions.

226. Just as the subordinate sensations are developed at the
same time as the entire external sensations, so also their sentient
actions are produced in the machines in which they act (225).
But since the subordinate, like all other external sensations,
do not necessarily set the mechanical machines into movement,
to which the nerve is distributed that has received their cerebral
impression, on account of natural hinderances (201), it follows,
that the sentient actions of a complex external sensation may
occupy sometimes a greater, sometimes a less, sphere of action,
according to the variety in the impressions in the brain, which
make up the constituents of the total external sensation, and
according to the nature of those normal hinderances, which im-
pede or divert the course of the impressions from the brain to
the machines (165, vi). The stronger, however, the subordinate
external sensations, the stronger are the actions which they
actually excite (218, 225).

227. All external sensations arc entire conceptions, consist-
ing of many elements. (Baumgarten's 'Metaph.,' §§ 378, 405.)
It follows, therefore, that all their direct actions may consist
of many elements, and this may occiu" when no natural hin-
derances exist to the transmission of their cerebral impres-
sion (116) . But all their actions do not depend upon subordinate
sensations, since at the same moment distinct primary external
sensations may be in the mind, which manifest, at the same
time, their proper sentient actions, according to the laws of
primary external sensations ; these may be termed co-ordinate
external sensations, and sentient actions.

Actions of Imaginations on the Mechanical Machines through
the Nerves.

228. The sensational conceptions are external sensations,
spontaneously imitated or repeated by the soul, the external
impression which can give them the reality of external sensa-
tions not being present {Q7) ; that is to say, in each imagination
many sub-impressions [Merkmale] of the external sensation

CH. III.] ACTIONS OF IMAGINATIONS. 117

are wanting, tlie conception of which is necessarily induced by
the external impression, and which are not perceived therefore
by the soul (68). The material idea, which the external im-
pression develops in the brain, consists of more numerous
sub-impressions, and is much more perfect, than that which
the mind when it repeats it can develope without its assistance.
Further, as the imaginations are only imperfect external sen-
sations, the material ideas of the imaginative force are only
constituents of the material external sensations, which the
external impression, by reaching the brain, can alone render
perfect and complete. Both are conceptions and material ideas
of one and the same kind, but the imaginations are weaker
and more imperfect (68).

229. It may be readily inferred from these views, that the
sentient actions of imaginations in the mechanical machines,
correspond generally with those of external sensations; that their
range of influence is equally extensive ; that they excite similar
kinds of movements in the various machines ; and that they
are only diff'erent in being somewhat less complete. Experience
teaches us the same thing. An imagination excites in the
same mechanical machines, the same movements that the
previous external sensation developed. An object which causes
us to shudder, produces a similar eff'ect when we recall it to
recollection; the remembrance of some food that has caused
us to vomit, excites vomiting again ; and the recollection of a
gratification excites the same conditions of the organs as that
in which it was enjoyed. The diff'erence is, that the actions of
imaginations are weaker, simpler, and more imperfect than those
of external sensations (69). And all this could not be other-
wise, since the imaginations produce their material ideas at the
cerebral origins of those nerves afifected by those of external
sensations (124,67); consequently, the same machines must be
put into movement (129, 130), for the same kind of cerebral
impression, but more feebly, is made at the origin of the nerves,
as by external sensations (67, 228) ; and the resulting movements
are similar, but feebler (133).

230. An entire imagination consists only of some of the
elements of a previous external sensation, and, consequently,
of only some of their material ideas or impressions on the
origins of the nerves. The law, then, of the sentient actions

118 ANIMAL-SENTIENT FORCES. [i.

of imaginations in the mechanical machines, is this: — whatever
portions of the elements of a preceding entire (225) external
sensation are contained in an imagination, the sentient actions
of those elements are repeated, although feebly, in the same
mechanical machines (229, 106.)

231. Since many elements of an entire external sensation
may consist of subordinate external sensations, and an imagination
therefrom be made up principally or wholly of the latter (228,
225), it follows, that an imagination may produce few or none
of the sentient actions of the original sensation, but principally
or solely those of the subordinate (230). Certain food formerly
taken excited spasm of the stomach ; this cramp caused a new
pain, — a subordinate external sensation (225), from which
general convulsions arose, or subordinate sentient actions.
Now when this food is brought to the recollection, convulsions
are immediately excited, but without the gastric spasm being
excited also. In this case the imagination excites only the
subordinate sentient actions of the antecedent primary external
sensation, passing over the primary sentient actions.

232. Although the absence of the external impression is the
cause why the sentient actions of imaginations are less perfect
and more feeble than those of external sensations, yet strong
imaginations can cause imperfect external sensations which
imitate the action of external impressions on the nerves (148);
and so imaginations, accompanied by imperfect external sensa-
tions, may develope such perfect and vigorous sentient actions,
that they can hardly be distinguished from those of real external
sensations (229, 150). Thus, an insane person, or one that
dreams, or any individual with a vivid imagination, imagines he
has swallowed an active purgative, and is purged in consequence;
or vomits from dreaming of taking nauseous food, &c.

233. i. A mere external impression can excite no imagination
if it be not felt ; consequently its nerve-action, as such, is never
at any time a sentient action of an imagination, if it be not the
sentient action of its sensation (228, 184, i). But such a nerve-
action may be felt and therefore imagined, and this imagination
can have sentient actions in the mechanical machines.

ii. The external impressions often excite by its own vis
nervosa (7) those movements which are sentient actions of the
external sensation, in which case they are nerve actions (183).

CH. III.] ACTIONS OF IMAGINATIONS. 119

Now, as the external impression is wanting in the sentient
actions of imaginations (228, 229), the co-operation of its vis
^^ervosa is wanting, and, consequently, the movements dependent
^ftpon it do not enter into the sentient actions of imaginations,
^Br, at least, are not excited by it, but occur only incidentally.
^Bf, therefore, an imagination repeats the sub-impressions a, h, c,
^Hf a preceding external sensation, with which certain movements
in the mechanical machines are connected, but which are not
sentient actions of the external sensations «, h, c, but simply
nerve-actions of the co-operating external impression, — these
actions do not occur, if the impression itself be not made.
Thus, an external impression of food, although not felt, will
excite a movement in the bowels as a nerve-action (183), but
the imagination of food not actually eaten cannot possibly excite
the movement, nor can a mere imagination excite any subor-
dinate action resulting as a nerve action from the impression, as,
for example, the micturition which follows the taking of food.

234, i. The sentient actions of imaginations, like those of
external sensations, extend to all the mechanical machines
which can be moved by external sensations (192, 229), and
stimulate them to the same movements, although more feebly
and imperfectly ; nay, those connected with imperfect external
sensations excite the machines to these movements, with a
force almost equal to that of external sensations (232, 229).

ii. The imaginations of agreeable external sensations (186,
228) develope connatural actions (195); those of unpleasant
external sensations, contra-natural actions ; those of titillation
and pain excite more violent movements (197, 198).

iii. Just as external sensations do not actually put in motion
all the mechanical machines which have nerves to move them
(201), so also it is with imaginations (228).

iv. Just as external sensations, in developing sentient actions,
act on the mechanical machines according to the capabilities
of each, so is it also with imaginations, and all that has been
stated with reference to the former (204-217), applies equally
to the latter.

235. The direct sentient actions of imaginations (hitherto
considered exclusively) are often accompanied, in addition to
those of true external sensations, and of other imaginations not
belonging to them, by incidental actions (219), as those of fore-

120 ANIMAL-SENTIENT FORCES. [i.

seeings (73), desires, aversions, passions nay, more remotely, by
those of ideas of the understanding, and of intellectual desires
and aversions of the will. All these actions, which are either
only coincident with those of imaginations, or are only incidently
connected with them, must be carefully distinguished from
those proceeding directly from imaginations. Yesterday a
person ran ; at night he dreams that he is running, and begins
to breathe quickly. This is the sentient action of his imagi-
nation. Then he thinks he is falling and calls out; this is
the sentient action of his foreseeing. He seeks to place him-
self upright, and strains his muscles to that end ; this is the
sentient action of a desire (223, 224) .

236. As sometimes in dreaming, and especially in somnam-
bulism and insanity, the imaginations are so vivid, that they
equal true external sensations, so also, in such cases, they de-
velope the same sentient actions in the mechanical machines,
as if they really proceeded from the latter (70, 69) .

237. When the mind is in reverie [dichtet], it combines the
constituents of various imaginations with each other, and then
each develops its actions in the mechanical machines, according
to the laws of imaginations. In a prolonged reverie [dichten],
which consists of the most vivid imaginations and imperfect
external sensations, as, for example, in somnambulism, insanity,
or delirium, the sentient actions are as distinct as if they resulted
from real external sensations (236), only they are not so per-
fect, complete, and regular, and are not so accordant with the
natural functions of the body (184), so that there arises danger
to its health and conservation. The principles laid down as to
imaginations (231 — 236) are also applicable to reveries of the
imagination [Erdictungen] .

238. The remembrance of a conception (71) does not appear
to be a species of conception, which develops actions externally
to the brain, except so far as the conception which is remem-
bered is an external sensation or imagination that so acts. A
person sees a visionary figure, and becomes pale with fear. It
is the resemblance of an individual who long ago caused him
bitter vexation. The pallor comes on before it is remembered
whom the figure resembles, and simply from the repeated ex-
ternal sensation, without the recognition. How often in such
cases we hear persons say : " this appearance terrifies, affects.

CH. III.] ACTIONS OF FORESEEINGS. 121

aud calms me, without my knowing why, some subordinate
ideas, which I cannot remember, must be the cause." When
the person whose figure we have seen, actually appears also, no
other action results than as stated above; we become pale as
before, but now we know why. Hence it appears, that the
memory itself [das eigentliche Erinnern] belongs to that class
of conceptions, the sentient actions of which are limited to the
brain, and excite only material ideas of another kind ; whereas
the conceptions which are remembered develope their usual
actions externally to the brain in the mechanical machines.

Actions of the Sensational Foreseeings on the Mechanical
Machines through the Nerves.

239. The sensational foreseeings are future external sensa-
tions, to which the external impression must supply what con-
stitutes the element of external sensations (73). In other
words, a number of sub-impressions of the external sensation
are wanting in every sensational foreseeing, the conception of
which must be induced by the external impression, and without
which the mind does not conceive them. The material idea
excited in the brain by the external impression contains many
more sub-impressions, and is far more complete than that which
the mind can impress spontaneously on the brain, without the
aid of the external impression (53, 73) ; and as foreseeings are
only imperfect external sensations, more imperfect, indeed,
than imaginations (73), the material ideas of the foreseeing force
are only portions of the material external sensations, which the
accession of the external impression alone can render complete
and perfect. Both are conceptions and material ideas of the
same kind, but the foreseeings are much more feeble and im-
perfect (73).

240, i. The material ideas of foreseeings arise at the origins
of the same nerves, as those of the foreseen sensations them-
selves (73, 124) : consequently, their sentient actions, external
to the brain, must be similar (129, 130.)

ii. Foreseeings cause the same kind of impressions (73, 121)
in these cerebral origins of the nerves as the foreseen sen-
sations, consequently their sentient actions in the mechanical
machines must be similar to those of the future sensations.

122 ANIMAL-SENTIENT FORCES. [i.

iii. As these impressions are more feeble than those of sen-
sations^ and even of imaginations, so also must be the resulting
actions. And this is confirmed by observation. When, for
example, a person sees another eat, and himself thinks of
eating, this foreseeing, in conjunction with the accompanying
desire, stimulates the salivary glands as food itself would have i
done. The foreseeing of a fall from a height excites us to
hold fast, even against our will and purpose, as we should do,
if the fall actually took place. When a person dreams that
he will empty the urinary bladder, the act often takes place.
The expectation of the action of a remedy often causes us to
experience its operation beforehand. Yawning, from imitation,
belongs to this class of phenomena.

241. The entirety of a foreseeing is compounded only of
certain of the constituents of a future external sensation;
consequently, its material ideas, or impressions on the cerebral
origin of the nerves, are a portion of those of the future
sensation, and therefore its sentient actions are expressed in
the same mechanical machines, but more feebly (240, 106).

242. Since many of the elements of a complete external
sensation may be subordinate external sensations, and a fore-
seeing arising from it may consist wholly or principally of these
(239, 225); it follows that a foreseeing may develope few or
none of the primary actions, but principally or wholly those of
the subordinate sensations (241). A cold air coming in contact
with the cutaneous nerves, when we are warm, contracts the
pores, and drives the perspiration inwards. This is the sentient
action of the primary external sensation of cold. The re-
pressed acrid perspiration irritates the nerves of the muscles,
and our limbs tremble, and our teeth chatter, and this is the
sentient action of the subordinate sensation in the muscles
which move the limbs and the lower jaw (225). A person in
a warm bed dreams, or vividly foresees, that he falls into a
river full of floating ice, and he forthwith shivers : a case of
this kind really occurred, and may be found in the ' Diction-
naire Encyclop.,^ article " Somnambule.^' A somnambulist
once fancied in winter, that as he was walking by the side
of a river, he saw a child fall in and drown. The bitter cold
did not restrain him from saving it. He threw himself out
of bed in the posture, and with the movements of a person

CH. III.] ACTIONS OF FORESEEINGS. 123

swimming, and when he had laboured diligently, he seized
the bed-clothes with one hand, thinking it was the child, while
with the other he attempted to swim to the imaginary shore.
Then he laid his burden down, shivered with cold, his teeth
chattering, as if he had come out of an ice-cold river. He
said that he was stiff with cold, and asked for a glass of
brandy. The dreamer had not really felt the ice-cold river,
nor had repressed perspiration irritated the nerves of the
muscles. The whole mental action of his foreseeing of both,
manifested itself only by shivering and chattering of the teeth.
In this case, the foreseeing develops the subordinate sentient
action of the future external sensation only, omitting the
primary, because the mind thought principally, in its foreseeing,
of the subordinate external sensation, — the irritation of the
muscles, — and did not combine with it the foreseeing the
antecedent primary sensation in the cutaneous nerves (241).

243, The cause why the sentient actions of foreseeings are
more imperfect and more feeble than those of external sen-
sations, is the want of the external impression (239, 240).
Still, very strong sensational foreseeings may cause imperfect
external sensations, which resemble the external impression
(74, 148) ; and foreseeings, accompanied by their imperfect
external sensations, may develope such perfect sentient actions
in the mechanical machines, that they are generally similar to
the sentient actions of true external sensations (150, 240).
Thus, a person who dreams vividly that he hears it thundering,
may start so violently in the bed as to shake it. Thus, also,
an infant in the cradle sucks the air with all its might, from
the foreseeing that it is sucking the breast.

244, i. An impression can excite no foreseeing if not felt,
for it is, of course, not imagined (233, i) ; consequently its
nerve-action, purely as such, is never at the same time the
sentient action of a foreseeing, until it is the sentient action
of its sensation (239, 184, i.) On the other hand, the mind
can feel and imagine (223), and, consequently, foresee such a
nerve-action (73), and these foreseeings can excite sentient
actions in the mechanical machines.

ii. The external impressions often excite by its own vis
nervosa (7) those movements which are sentient actions of the
external sensation, in which case they are nerve actions (183).

124 ANIMAL-SENTIENT FORCES. [i.

Now, as the external impression is wanting in the sentient
actions of foreseeings (228, 229), the co-operation of its vis
nervosa is wanting, and, consequently, the movements dependent
upon it do not enter into the sentient actions of foreseeings,
or, at least, are not excited by it, but occur only incidentally.
If, therefore, a foreseeing repeats the sub-impressions «, b, c,
of a preceding external sensation, with which certain movements
in the mechanical machines are connected, but which are not
sentient actions of the external sensations a, h, c, but simply
nerve-actions of the co-operating external impression, — these
actions do not occur, if the impression itself be not made.

245, i. The sentient actions of foreseeings, as well as those
of external sensations (192) and imaginations (234, i), take
place in all those mechanical machines which can be moved by
external sensations and imaginations, and excite the same move-
ments as the latter, but more feebly and imperfectly (193).
Nay, even the foreseeings connected with imperfect external
sensations, excite the mechanical machines to the same move-
ments as are excited by true external sensations (240, 243).

ii. The foreseeings of agreeable or disagreeable sensations
contain, in some degree, the impressions of pleasure or pain
(186), and develope such actions as are in accordance with, or
opposed to, their normal function (195, 197, 198).

iii. As external sensations do not excite to movement all
those mechanical machines which the nerves can move (201,
239), so is it also with regard to foreseeings.

iv. As external sensations, when they produce actions in
the mechanical machines, act upon them according to their
respective capabilities, so is it also with regard to foreseeings,
so that the principles laid down previously under this head
(204 — 217) are also applicable to the latter.

246. There are often connected with the sentient actions of
foreseeings certain others of an incidental kind, as, for instance,
those of desires, aversions, and even more remotely, those of
understanding and efforts of the will (65), and in addition
to the sentient actions of co-existing true external sensations,
imaginations, and other foreseeings. All these actions, whether
co-existent, or incidentally connected with those of foreseeings,
must be distinguished from the latter. The foreseeing of a
lascivious action acts directly on the organs which have to per-

CH. III.] ACTIONS OF PLEASURE AND PAIN. 125

form it. Therewith is combined the emotion of shame, and
the face reddens. This reddening is incidental. A philosopher
studies from a foreseeing of fame, until he is hypochondriacal
and loses his digestive powers. This action of deep thought
(vide § 332) is only incidental to the anticipation of fame, &c.

247. Since sensational foreseeings and prophetic visions are
occasionally so vivid in dreams, and especially in somnambulism,
as well as in insanity and prophetic ecstasy, that they equal true
sensations, particularly as they become usually in such persons
imperfect external sensations, and constitute the greater number
of apparitions, spectres, &c. (148, 243), — they develope the same
actions as are produced by true external sensations.

248. The poetic faculty [Dichtungskraft] is occupied with
foreseeings as well as imaginations, and according to the same
laws. Hence it is that somnambulists, visionaries, lunatics,
inspired persons, soothsayers, &c., are as much deluded by the
foreseeings of their bodings and expectations as by their ima-
ginations, taking both for true sensations, while their sentient
actions are equally erroneous (237).

249. The true expectations differ from the foreseeings in
this, that their sentient actions are confined to the brain, and
do not extend to the mechanical machines.

Actions of Sensational Pleasure and Pain through the Nerves
on the Mechanical Machines.

250. So soon as a sensation, or other conception of the mind,
pleases or displeases, or contains the excitants of the feelings
(88), it is said that they touch the heart, that the heart sympa-
thizes, &c. This mode of expression has its rise in the universal
experience, that the movements of the heart, and especially
those actions termed vital by physiologists, are manifestly
affected by all conceptions which please or displease. It is
said of the pleasant external sensation excited by food, drink,
or medicine, that it goes to the heart, enlivens, strengthens the
heart. A beautiful sight, or music, soothes the soul and
exhilarates the heart. Tickling excites convulsive respiration
and laughter, and accelerates the whole circulation. Pain
causes fever, and sighing, groaning, and weeping. Pleasant
condolence, or a kind visit, refreshes the heart ; a reproof that

126 ANIMAL.SENTIENT FORCES. [i.

we feel to be merited, goes to the heart ; the recollection of a
cruel action shocks the heart ; the anticipation of a joyous
thing causes it to beat more freely and easily. And in short,
every sensational and intellectual conception which awakens
happiness or misery in the mind, causes changes in the pulse
and in the action of the heart, in which the respiration also
participates, and thereby exercises an important influence on
the whole economy, which a mere perception or a neutral ex-
ternal sensation, imagination, or foreseeing entirely wants. It
is consequently a general law of animal nature, that all excitants
of the feelings add a special sentient action to the other sentient
actions of the conceptions, so that they modify the functions of
the mechanical machines subservient to vital movements. But
since the sensational stimuli, or in other words, the pleasure or
pain of the external senses (80), and of the sensational con-
ceptions, imaginations, foreseeings (88), are, from their nature,
stronger stimuli than mere motives [Bewegungsgrunde] (53,88),
it follows, that their action on the vital movements is more
obvious and powerful.

251. The direct sentient actions of the excitants of the
feelings generally, and considered per se, are consequently the
impressions in the brain of pleasure and pain, in so far as
being special conditions of the material ideas of each neutral
sensational conception, they excite the origin of those nerves in
the brain by which the vital movements are regulated; and this
applies, in particular, to the sentient actions of the pleasure or
pain of the senses (80), and to all other sensational stimuli, and
to motives [Bewegungsgrunde] (88, 250). In addition, there-
fore, to the direct sentient actions hitherto described, as resulting
from external sensations, imaginations, and foreseeings, the latter
excite other direct and special actions in virtue of these excitants
of the feelings, whenever they become agreeable or painful, so
that they modify the vital movements, and in consequence of
the physical, mechanical, and vital inter-connection of the latter,
powerfully influence the whole animal economy, and this pro-
portionately to the degree of excitation. This doctrine applies
also to the motives of the intellect. As to the cause of this
action of the sensational stimuli on the vital movements, we
can only say, that these inner sensations of the soul must make
an impression peculiar to themselves on the cerebral origin of

)

Lii. III.] ACTIONS OF PLEASURE AND PAIN. 127

le nerves distributed to the vital organs (124), and it is pro-
bable that by exciting the mind into action (81), the numerous
capillaries of the brain are stimulated, and thus by a change in
so large a portion of the mass of the blood, a change is pro-
duced in the action of the heart, in the respiration, and in all
the vital movements (159).

252. The sentient actions of the pleasure of the senses are
movements in accordance with the natural functions of the
mechanical machines; those of annoyance of the senses are
contrary to the natural functions (80). The same apphes to
the sentient actions resulting from pleasing or displeasing
sensational conceptions, imaginations, and foreseeings (234, ii;
245, ii). But since a very active and inordinate discharge of a
function borders on the contra-natural, the sentient actions of
very vivid pleasurable stimuli are in some degree contra-
natural (199). Consequently, a state of gentle calm pleasure is
more favorable to the maintenance of life and to health, than
excess in pleasurable sensations, or than distressing painful
sensations.

253. All experience establishes this doctrine. A person
describes a condition of health, by saying that he is well ; — of
sickness, by the expression he is ill. This being well and ill,
are sensations of what is pleasant and unpleasant (80). One
perfectly in health says, that not a finger aches, one out of
health, that nothing goes right with him ; obviously expressions
of what is pleasant and unpleasant, whereby we designate a
natural or contra -natural condition of the body. In particular,
it is also observed, that the change in the vital movements ex-
cited by moderate pleasures, are favorable to the organism, —
the immoderate on the painful are unfavorable. Moderate
laughter is beneficial, immoderate is hurtful. Agreeable exer-
cise of the understanding is favorable to health; and it was
for this reason that the ancient philosophers maintained, that
the study of nature favoured the attainment of old age;
while, on the contrary, excessive study and tiresome subtle
meditations led to premature decrepitude, and caused nervous
diseases.

254. The general law, whereby the direct sentient actions of
the excitants of all the feelings are regulated, is this : — ^just as
a sensational or intellectual conception pleases or displeases, so

128 ANIMAL-SENTIENT FORCES. [i.

are the nerves acted on in the brain, and corresponding vital
movements excited thereby in the vital organs ; in the former
case in accordance with their natural functions ; in the latter,
in opposition thereto (252), but always in another way than
when the conception is neutral.

Actions of the Sensational Desires and Aversions in the
Mechanical Machines through the Nerves.

255. The direct sentient actions of the sensational desires
and aversions, are produced according to the laws already laid
down (80 — 88). They are made up by the sentient actions:
— 1, of the sensational foreseeings of a coming sensation, or
its opposite, expected by the mind (239 — 247); 2, by those of
this expectation (249); 3, by those of the impressions of sen-
sational pleasure and pain (84 — 87, 250).

256. The same doctrines apply equally to the sensational
instincts and passions, since these are only desires and aversions
of a greater intensity, arising out of obscure or simple sensa-
tional stimuli (90, 91).

257. In each sensational instinct and emotion, there is a
sensational foreseeing of coming sensations, the sentient actions
of which are none other than those of the imperfect material
sensation which is foreseen ; when it is external, the actions are
developed in those mechanical machines external to the brain,
which the foreseen external sensation sets in motion, &c.
(240, i, ii.)

258. There are strong sensational stimuli conjoined in every
sensational instinct and emotion, the actions of which are the
same as those arising from the impressions of sensational
pleasure or pain, which impressions depend on the foreseen
material sensation. These stimuli change the vital actions in
a remarkable manner, and excite the animal-sentient force of
the brain to render perfect the imperfect actions of the coming
sensation. In all these cases, if the objects of the instinct or
emotion be true external sensations, the efforts of the soul
cannot attain them, and consequently the instincts or emotion
cannot be satisfied without the appropriate external impressions
(81,256); and in the sensational instincts and emotions, there-
fore, only those sentient actions of the future sensation can be

CH. iii.J ACTIONS OF DESIRES OR AVERSIONS. 129

excited, which are not dependent on the external impression
(81, 94).

259. The effects of the pleasing or distressing instincts and
emotions on the organism, are regulated by the same laws as
those of simple pleasure or pain (191 — 199), or of the agree-
able or distressing foreseeings, (245, ii, 252, &c.) Consequently,
every kind of joy is beneficial to health, all sorrow injurious ;
but the former may be injurious too, if excessive (252).

260. The direct sentient actions of the sensational pro-
pensities and emotions, are produced according to the same laws
as those of sensational pleasure and pain. (Compare 254, 199.)

261. It may be useful to illustrate these views by special
facts.

i. Observations prove, that in the propensities and emotions,
the actions of the coming foreseen external sensation therein
imperfectly expressed, are produced (257). In the appetite for
food, the gratification of which is the taking of nutriment, saliva
is poured out into the mouth, as if nutriment were taken ; in
the sexual appetite, the gratification of which is copulation, the
organs of generation are put into a condition suitable to its
gratification ; in the desire to give suck, the satisfaction for which
is the discharge of milk from the nipples during suckling, the
nipples become erect, and there is a flow of milk towards them.
In the desire of children to suck, the lips are placed in a pro-
per position, and the child sucks the air. In the desire for
revenge, the satisfaction of which is an injury to the individual
who has offended, the natural weapons partly manifest the
functions whereby they inflict injury ; animals put their stings
or claws into action ; they eject or pour forth their poison ;
they endeavour to bite, to strike, to tear ; man doubles his fist,
stamps, and gnashes, as he would do if actually taking revenge.
In terror, the satisfaction of which is the averting of a great
impending danger, the struggles for preservation are seen in
starting back, stooping, leaping, standing still, &c. In shame,
the satisfaction of which emotion is the avoidance of the glance
of the person whose contempt we fear to perceive, we drop the
eyelids, and endeavour to withdraw ourselves as much as possible
from that glance, &c.

ii. That the propensities and emotions connected with im-
perfect external sensations, excite the mechanical machines

9

130 ANIMAL-SENTIENT FORCES. [i.

appropriate to them to almost as perfect functions as when
they act normally (257), is manifest from various facts. In
lascivious feelings, an emission not unfrequently takes place;
when we lament for a deceased friend, he so often appears
before our eyes, that we believe we see him, speak with him,
embrace him ; when afraid of ghosts, an individual is often in
the same condition as if a ghost had actually appeared, &c.

iii. It is equally a general and undoubted observation, that
in all the instincts and emotions, as well as in all the desires and
aversions, the vital movements of the organism (the respiratory
and cardiac movements) are modified. And this change is the
greater, the more powerfully the instincts and emotions operate.

iv. That this change in the agreeable instincts and emotions,
is in accordance with nature and with healthy action, or con-
natural, and in the disagreeable is opposed thereto, or contra-
natural is established by universal experience (Haller^s ' Phy-
siology,^ § 565).

V. Lastly, that those sensational instincts and emotions,
whose objects are true external sensations (258), cannot be
satisfied without the adjunct of the external impression, is
proved by all the pleasures of the senses. The satisfaction
of the instincts and emotions must not, however, be con-
founded with their enfeebling. {Vide § 95.)

Actions of the Sensational Instincts in the Mechanical Machines
through the Nerves.

262. The sensational^ instincts in particular may be arranged
under four heads :

i. Strong desires which arise from obscure sensational stimuli,
and whose object is our preservation and well-being. This is
the instinct of self-preservation.

ii. Powerful aversions, which arise from obscure sensational

1 The word sinnlich is here translated sensational, for want of a better term ; but
the reader will please to remember the special meaning attached to the word {vide
notes, §§ 31, 66). It is obvious from the context (§§ 263 — 269) that these instincts
are not sensational, because sensation is the cause oiihe instinctive acts, but because
sensation accompanies the cause, namely, the external senselike impressions. With
this understanding, that the word sensational does not indicate the cause of the
instincts, but simply a certain condition of the cause, — it may be properly used
here. — Ed.

CH. III.] ACTIONS OF INSTINCTS. 131

stimuli, and whose object is to prevent our destruction or ill-
being. The instinct of self-defence,

iii. Strong desires, which arise out of obscure sensational
stimuli, and whose object is the propagation of the species by-
means of copulation. The instinct of propagation.

iv. Strong desires and aversions, which arise from obscure
sensational stimuli, and whose object is the preservation and
well-being of the offspring, and the prevention of its destruction,
or its ill-being. The instinct for offspring.

263. Since the natural instincts of self-preservation, of well-
being, and of propagation, are specially implanted in animals
by nature, that these objects may be attained certainly and
infallibly, they are distinguished from all other desires, aversions,
and passions, firstly, because nature has so placed them under
the control of external impressions, and so arranged the natural
functions of organs, that animals cannot prevent their mani-
festation; while, on the contrary, the others are more left to
the proper power of the animal to develop, or suppress, increase
or diminish, or even to prevent altogether (89, 90). Secondly,
the animals themselves, and tte whole of nature around them,
are so reciprocally adapted, that these instincts never become
inactive until their object, or, in other words, the satisfaction
of the instinct is fully attained, which is also the object
and will of the Creator (95). Consequently, there is in the
instincts of animals a something that points to the attainment
of a great object of the Creator, a sufiicient origin of which
is not to be found in the conceptive force alone, but in certain
predetermined adaptations external to animals, whereby they
are necessitated to follow their instincts according to their
organism : this is termed the wonderful, the magical [Be-
zauberung], the divine in instincts. Consequently, to this ex-
tent the blind instincts bear the same relation to other desires
and aversions, as external sensations bear to spontaneous con-
ceptions (27, 89). Both are excited conceptions, which cannot
arise nor be satisfied, independently of an external impression on
the nerves, and which nature has preordained, especially for the
former. This, however, requires a more minute investigation.

264. In animals which think, or in all animals, if it be
maintained that all have conceptions, the acts to which they
are excited by their natural instinct, or in other words, the

132 ANIMAL-SENTIENT FORCES. [i.

movements of the mechanical machines_, are sentient actions of
certain pleasing or unpleasing sensational conceptions (262,
81). NoWj since the natural instincts have for their objects,
the preservation and well-being of animals, and of their offspring,
but the means to these ends are not taught to animals, nor
even to man himself by experience, it follows that the concep-
tions are imparted to them without their knowledge and choice,
nay, even against their inclination, by means of previously
arranged inducements (external impressions on the nerves),
dispersed throughout nature by the Creator, wherein the
sensational stimuli lie concealed, which by means of their im-
pression on the brain develop those sentient actions in the
mechanical machines according to the laws of the actions of
desires and aversions, that have as their object, and in accord-
ance with the views of the Creator, the preservation and well-
being of animals or their offspring. Why the Creator has not
so restricted the mental faculty, that it could only develop
those conceptions which are in accordance with these objects,
and none other, is hidden from our knowledge. It is enough
that it is not so in nature ; but it has been determined so to
use the obscurest sensational faculty [Sinnlichkeit] of animals,
as to force upon them, as it were, as often and when it appears
necessary, such conceptions as must develop in them instinctive
actions in accordance with the objects of the Creator ; for the
obscure sensational conceptions, and especially external sensa-
tions, which are the principal means used by nature to this end,
are the only conceptions that the mind cannot develop inde-
pendently and at pleasure, but must receive from the external im-
pression on the nerves, which nature transmits to them (35, 66).
265. The double object of nature, namely, the excitement
and the satisfaction of the instincts, is attained thereby ; for the
obscure feelings which excite them and the external circum-
stances which satisfy them by means of their external impres-
sion, are so numerous at the fixed times and for the appointed
objects of each instinct, and the natural hindrances whereby
desires and aversions are weakened and do not attain to satis-
faction, so few, that the great object of nature in general is
always fully attained. Experience proves this irrefragably.
At the moment, when, according to the order of nature, an
instinct should be put into action, the nerves are certain to

CH. in.] ACTIONS OF INSTINCTS. 133

receive the external impressions necessary thereto, and which
are appointed, as it were, to this end. For example, when
nutriment is necessary to the body, the fluids collected in the
empty stomach must impress on it an external impression,
which excites the sensational instinct of hunger ; when animals
ought to propagate their kind, the male inhales from the female
during heat an odour which causes the instinct of copulation to
be active. On such occasions, even certain external sensations
become sensational stimuli to the animal that formerly were
not so, or had even a contrary effect, as, for example, the sight
or smell of the sexual organs, previously unnoticed or even
disagreeable and disgusting, become the sensational stimuli
of the strongest sensual pleasure. At the same time, when the
instincts are regularly excited into activity in accordance with
the object of nature, the circumstances whereby they can be
satisfied are so carefully provided for previously, that the satis-
faction of the instincts can hardly fail. Thus, hunger is rarely
excited in animals that lie dormant through the winter, until
they can find food in the fields. So also the instinct of self-
preservation operates, when they fatten themselves towards
winter, or return into a warmer climate, or creep into a retreat
from the cold, no sooner than they have occasion. Lastly,
when once the natural instincts are excited, it is difficult to
cause them to cease, by means of psychological or physiological
hindrances, before they are satisfied, which may, however, be
done as to desires, aversions, and even emotions. A hungry,
or vindictive, or enamoured person is not easily appeased by
artful management, but the satisfaction of the instinct must
be effected, that is to say, repletion of the stomach, or accom-
plishment of copulation, or wreaking of vengeance. Nature,
indeed, seems to have actually weakened or diminished those
hindrances which on previous occasions moderated or prevented
sensational stimuli (47), so that the instincts might break forth
without restraint and overcome all obstacles, and continue their
appointed time until their satisfaction has been sufficiently re-
peated. In other desires and even in emotions, the animal with-
draws the sensational stimulus voluntarily, being conscious of it,
and its effects ; but in the instinct it is not conscious of the
stimulus as it is only obscurely perceived (262) ; consequently, its
effects are unknown, and the animal is carried blindly on by

134 ANIMAL-SENTIENT FORCES. [i.

the instinct. In cases of this kind, the nerves themselves
appear to change their nature and to favour the instinct, since
they receive new impressions and stimuli, from which they
were previously secured ; and, lastly, experience also sufficiently
shows to us, how little all psychological means avail in weak-
ening the desires and aversions, when moralists apply them to
human nature, with the object of preventing the outbreak or satis-
faction of its feelings, or restraining them within certain limits.
266. The sensational instincts act in the mechanical machines
in accordance with this preordained arrangement, established
by the wisdom of the Creator in the whole creation, as well as
in the animal kingdom, for their development and for the
attainment of their main objects. They are in no way dependent
upon an innate wisdom present in the mind of the animal, by
which it spontaneously and voluntarily excites these instincts,
and their operations in the body (89, 90). And indeed, those
actions which in true sensational animals are sentient actions of
the sensational instincts, are excited in other animals, or in the
former under circumstances in which they can no longer be sen-
tient actions, by precisely the same external impressions (183) :
as, for example, when a decapitated animal being brought to
another, copulates and lays eggs ; when a decapitated frog with-
draws its leg on its foot being pinched, and leaps away, in
accordance with the instinct of self-preservation, &c., of which
more in the Second Part of the work. It is manifest, also, that
although these animals, in which the instinctive actions are sen-
tient actions, feel the sensational stimuli so strongly, although
obscurely, as to long for their gratification, they have not the
least knowledge of the objects of the instincts, or why these
movements are produced; but, on the contrary, their other
actions are not in harmony with those objects, and this is the
reason why so much surprise is felt at the stupidity of animals,
which otherwise display so much apparent sagacity in the actions
appropriate to their natural instincts ; as, for example, when a
hen, which has trod upon her chicken, hearing its cry, calls it
to some food, without at the same time lifting its foot ; or when
a lobster having one of its legs fixed in and pinched by one of
its claws, excited by the pain, violently tears away the limb,
instead of opening its claw ; or, when a lark, while over the sea,
blindly following its instinct to ascend into the air, and to fall

i

CH. III.] ACTIONS OF INSTINCTS. 135

again, descends to the sea, and is drowned. Lastly, experience
teaches us, that when men attempt to develop the instincts in
themselves or other animals voluntarily, or to regulate, limit,
or extend them, they usually fail, and miss the object of nature,
which would more rarely happen, if the instincts were blindly
allowed to act, without the interference of their own notions.

267. Nevertheless, it is also certain, that the operations of
the blind instincts do not appear to harmonise in all cases with
the objects of nature : this may arise possibly from the fact, that
we do not sufficiently comprehend those objects ; or else that the
instincts are rendered incapable of their attainment, where their
actions are influenced volitionally by the intermingling of the
actions of other sentient forces. It is observed, for example,
that many animals are not sufficiently taught by their instinct,
not to eat or do certain things which are injurious to them.
Some eat poisonous herbs without suspicion, and are poisoned.
Many exceed their strength so much in the accomplishment of
their instincts, that they become quite enfeebled and die. In
cases of this kind we are ignorant what are the designs of nature
in the implantation of instincts, or what is the object in limiting
the sphere of their utility to the personal weal of the animal,
and not extending it to all possible cases. To what extent we
ourselves hinder the designs of nature in the instincts, and limit
their operations by the interference of our will, is shown by
their great uncertainty in mankind, and their much greater cer-
tainty in those animals which follow them blindly ; but especially
is it shown in disease, when we attribute that to an instinct of
nature, which is only the consequence of intellectual desires.

268. It is requisite to the attainment of the objects of the
instincts, that the inducements previously appointed by nature,
shall excite the pleasure or suffering, which will develop a cer-
tain foreseen future agreeable or unpleasant sensation (94, 262).
These sensational stimuli excite that effort which is the instinct
itself (80,83), and the satisfaction of which nature afterwards pro-
vides by means prepared beforehand (262) . In this development,
the natural inducements of the instinct are to be most carefully
distinguished from its sensational stimuli, — the latter from the
instinct itself, — and the instinct from its contentment or satis-
faction. It is thus that we find the whole order of the pheno-
mena of instinct to occur in nature. With the object of causing

136 ANIMAL-SENTIENT FORCES. [i.

an animal to think of supplying itself with food, at certain fixed
periods the stomach is emptied of all the food taken into it, and
from this emptiness an unpleasant external sensation arises,
termed hungriness. This is the sensational stimulusofthe instinct
of hunger, which is communicated to the mind by means of the
emptiness of the stomach naturally and necessarily ; nay, even
contrarily to the wish of the animal (27). This unpleasant
external sensation reminds it of the contrary pleasant sensation
experienced when the stomach was full. From this com-
bination arises the foreseeing and expectation (73) of the agree-
able sensation of a fall stomach, and the effort of the mind to
develop it (81), which is the instinct of hunger, and the con-
tentment of which by eating to satiety, is the object nature had in
view in exciting the instinct, so as to provide for the nutrition
of the animal (262). When an animal has remained motionless
for a length of time, the body becomes sickly, because the
functions of all organs go on imperfectly. This is the pre-
ordained cause of the instinct of muscular activity, because the
sickliness excites unpleasant external sensations, which the
animal cannot avoid, and which are the sensational stimuh of
the instinct. Out of this unpleasant external sensation of the
animal, and the recollection of the well-being experienced when
the limbs were moved, arise the foreseeing and expectation of
the opposite pleasant sensation of a future movement, and thus
results an effort — the instinct of movement — the satisfaction of
which by bodily exercise is the design of nature, so as to pro-
vide for the well-being of the animal. The same mechanism
and series of phenomena may be readily traced in the develop-
ment of other natural instincts.

269. In thinking animals, all the sentient instincts, together
with the sentient actions that accompany them, are thus
developed, although obscurely enough, from the natural in-
ducements pre-ordained by the Creator, according to the laws
of the conceptive force and of the animal sentient forces; but
only on the condition that the animals have lived so long, and
felt, thought, and compared so much as to be able to associate
imaginations with the sensations induced, and which must de-
velop the foreseeing into instinct (66, 89) . But it is impossible
to suppose that this takes place with newly born animals, that
have scarcely begun to feel, and seem to have no other concep-

(II. III.] ACTIONS OF INSTINCTS. 137

tionSj yet perform with remarkable readiness and completeness,
all the movements, that, as sentient actions, are appropriate to
the development and satisfaction of the instincts. No one
will be persuaded that the mind of an animal which has never
eaten, is led by the sensation of an empty stomach to the idea
of agreeable repletion, and that from this is formed the desire
to eat; that the mind of an animal which moves voluntarily
for the first time, is led by the unpleasant sensation of repose,
to the idea that movement has removed this sensation, and out
of this is formed the desire to move its limbs; or that the
mind of an animal which as yet knows nothing of an enemy,
of violence, or of danger, is reminded of the use of its natural
weapons (not yet in fact grown), by the sight of an enemy,
and that out of this is formed the desire to defend itself. But
since at the same time, an instinct cannot be developed natu-
rally in the mind, in any other mode than that just described
(268), according to premises already advanced (94), it follows
that in the inexperienced animals, and in all not endued with
mind, no instincts are developed ; but that those movements,
which by the analogy of our own nature we conclude to be
sentient actions, and which in many thinking animals really are
such, may continually be at least true nerve-actions excited by
external impressions (183, 89), and that the sensation itself of
the external impressions contributes nothing essential towards
the production of these movements. It is undoubted, that the
regular and adapted development of conceptions and of the entire
instinct, accompanies in thinking animals these nerve-actions,
which are also developed regularly and adaptively, in accordance
with the designs of nature (268), and this with special designs
which have been already noticed (184, ii). In this way these
nerve-actions are to be considered as sentient actions ; as nerve-
actions solely, they will be again treated of (439, 454, 551, &c.)
270. The stimuli of the instincts are obscure sensational fore-
seeings (262), either pleasing or unpleasing, being the imperfect
elements of a coming agreeable sensation, or of the opposite to
a disagreeable sensation, which becomes perfect, when the
instinct is fulfilled, or satisfied (94). Foreseeings of this kind
are highly sensational conceptions, almost as involuntary and
as necessarily produced as external sensations themselves, of
which, as obscure conceptions, the mind is never conscious;

138 ANIMAL-SENTIENT FORCES. [i.

which are scarcely regularly developed in the depths of the mind,
to the special astonishment of the animal when conscious of
their operations; and which consequently give rise to the magical
(bezauberung) in instincts (263). Consequently, just as they
differ from the corporeal inducements of the instincts (264), so
they must be distinguished from the instinct itself, which is
the effort of the conceptive force excited by them, to develop
the foreseen agreeable sensation, or the contrary to the dis-
agreeable sensation, although they act in and with it at the
same time (80). Thus satiety is the agreeable foreseen sen-
sation in hunger ; in the instinct of self-defence, the foreseen sen-
sation is the contrary to the sensation of danger ; in the instinct
of propagation of the species, that of copulation ; and in the
instinct to give suck, that of emptying of the mammae (94, 268).

271. The sentient actions of the stimuli of the instincts, as
such, are those of sensational pleasure and pain (88), and con-
sidered alone, change consequently the respiratory and cardiac
movements (250), but as foreseeings, they express imperfectly
the sentient action of the coming sensation (241). Conse-
quently, the vital movements are very strikingly altered in each
instinct (262, 258), and movements are partly excited in the
mechanical machines, similar to those which are fully developed
when the instinct is satisfied (257).

272. The instinct itself, (which is only the effort of the
conceptive force to develop the foreseen sensation,) manifests
its influence in the mechanical machines, so as to develop the
sentient actions of the coming sensation as powerfully as it
possibly can, short of the actual contentment of the instinct,
or without the intervention of the true sensation therein fore-
seen. Their nature, laws, and characteristics, may be learnt
from previous statements. (Compare 257 — 261 ; also 274.)

273. To each kind of sensational conceptions are usually
superadded others, which the mind connects therewith spon-
taneously, and at pleasure, and which develop their sentient ac-
tions at the same time, and incidentally to the preceding (219
— 224, 235, 246), nay, the direct sentient actions of the external
sensations, which play so important a part in the instincts, are
often felt, and induce subordinate sentient actions of sensations
(225, 226), and subordinate instincts which are often conjoined
with other instincts, as, for example, the instincts of jealousy.

CH. III.] ACTIONS OF INSTINCTS. 139

or of solitude, accompany the instinct of .love, whilst in man,
the understanding and will often co-operate with the instincts.
It follows from hence that many movements occur conjointly
with the actions of the instincts, particularly in those animals,
which are capable of conceptions only remotely connected with
external sensations (27) ; and thus a highly compound and
complicated condition of the mind and the body may arise,
which can never be explained by the nature of the instincts, as
has been often uselessly attempted, so long as the subordinate
conceptions, together with their accompanying actions, are not
carefully distinguished from the instinct itself and its acts. If
the acts, for example, resulting from the satisfaction of the
instinct, be confounded with those of the instinct itself, the
greatest mistake is made. And one great reason why the
nature and operations of the instincts and passions have been
hitherto so imperfectly elucidated is, that they have been cha-
racterised confusedly. It will, therefore, be worth while to
take an instinct as an example for analysis ; and for this pur-
pose I select the instinct of propagation, as the most important
and the most complicated.

274. In this instinct, nature in the first instance impart
certain inducements to the animal, — external impressions
which surprise it (in Staunen setzen), and by means of a pe-
culiar action in the sexual organs, prepare the latter for the
sensational stimulus of the instinct, so that their nerves become
more sensitive to touch, so as to receive the gentle titillation
which constitutes the incitement of the instinct. This peculiar
impression causes in the minds of animals during heat only,
and at no other time, certain external sensations, and other sen-
sational conceptions, in accordance with the prearrangement of
nature (265). For example, the odour of an animal of the oppo-
site sex, a sound, a song, a whining, a chirp, a look, or a sensa-
tional conception, imagination, or foreseeing of them by an animal
in a state of heat, &c., develops the sentient actions in the me-
chanical machines (sexual organs) assigned to them by nature ;
for example, an increased flow of fluids to those organs, and
the increased secretion of the seminal fluid, and its accumula-
tion in the vesciculse seminales, in consequence of which they
become gently distended and excited ; and thus the agreeable
external sensation in the sexual organs (the gentle titillation).

3arts^>^jv

140 ANIMAL-SENTIENT FORCES. [i.

is produced, that constitutes the sensational stimulus of the
instinct of propagation, and excites it in the mode described
above (268), together with all its sentient actions. — ( Vide
Haller^s 'Physiology,^ § 870). It is manifested by the strong
effort of the conceptive force to attain the complete development
of the highly pleasurable, obscure, foreseen sensation of copula-
tion (94), and by the sentient actions which accompany this effort
(255). The vital movements, consequently, are powerfully in-
fluenced by the instinct itself (251, 258). The heart beats with
greater force, the heated blood circulates violently, the respiration
becomes a sighing, or a corporeally-produced languishing and
moaning, as occur from any other similar heated state of the
blood : at the same time, the actions of the future sensation,
in the satisfaction of the instinct (in this case copulation), become
vividly, although incompletely manifested (257), so that the
sexual organs are in the same condition as in copulation, and
only the external impression is wanting to the satisfaction of
the instinct, which the animal often procures incidentally,
often experiences normally in copulation. These only are the
true, direct, sentient actions of the instinct. It hardly, how-
ever, excites these only in the mind; for other conceptions
are conjoined therewith, as subordinate sensations (225), and
in particular, spontaneous conceptions, imaginations, foreseeings,
imperfect sensations (148), other instincts and emotions, and
in men even reflections, and desires, and aversions of the
intellect, of which the object that gives pleasure is the exciting
cause. For example, similar circumstances are remembered
in the instinct with their subordinate impressions, scenes from
favorite romances are recollected, new images for the fore-
seeing faculty are produced, and pleasurable anticipations ex-
cited, which often grow into imperfect external sensations, so
that the individual l^ias the beloved object before his eyes, and
thinks that he converses with it (148). All movements of the
animal in accordance with these conceptions, and even all
influences which these conceptions exercise according to their
nature, on the mechanical machines of the body, — as singing,
chirping, crowing, whining, and all spontaneous enticements to
copulation, are not direct actions of the instinct (103), but inci-
dental sentient actions, contingent on secondary sensations, or
on ideas excited spontaneously, or on secondary conceptions.

CH. III.] ACTIONS OF INSTINCTS. 141

and sensational or intellectual desires and aversions, and their
satisfaction, which have nothing further in common with the
instinct than that they are usually connected with and accom-
pany it. The spontaneous and voluntary song of birds, the
chirping of insects, the whine of dogs, &c., whereby they allure
to sexual congress, may be no more considered as direct sen-
tient actions of their instinct, than the suicide of a lover ; for
all these are sentient actions of voluntary resolves, induced
and occasioned in the mind by the instinct, but which may
certainly take place without it, although not usually. Gratifica-
tion of the instinct ends it (95). The intense longing then
ceases, the vital movements become quiescent, the sexual
organs return to their former condition, and they lose their
excitability, for the parts formerly distended and irritated have
become empty. But so long as the period of heat continues,
the natural inducements and the secondary conceptions accom-
panying them and the instinct, exercise a continually-renewed
influence on the mind and body of the animal, and often re-
excite the instinct, until at last, either from its repeated gra-
tification, or its enfeeblement (95), it is no longer re-excited,
and its natural inducements in accordance with the designs of
nature, lose their magical influence (263). Hence animals
allure to sexual congress during the whole period of heat, be-
cause their minds are continually occupied with secondary
conceptions and instincts, having reference to the predominant
instinct, derived from the natural inducements continually
acting, and from the sensational stimuli and instincts repeatedly
renewed. Hence also man even often desires amorously the
satisfaction of the instinct, and is inclined to solitude and
jealousy, so long as he is held in enchantment by the object of
his passion ; all which were impossible, if these conceptions,
with their actions, belonged to the gratification of the instinct,
and were its direct actions (94, 95).

275. The gratification of the instinct is the actual de-
velopment of the foreseen sensation, and to attain which end
the conceptive force and the animal- sentient forces of the
instinct are excited (81, 90). The mental eifort consequently
ceases, and the sensational stimuli (pleasure or pain) are weakened
so soon as satisfaction is attained (83). Consequently, also,
the sentient actions cease, the vital movements return to

142 ANIMAL-SENTIENT FORCES. [i.

their usual order, and the imperfect expressions of move-
ments, which, during the gratification of the instinct, become
perfect, are abolished. But inasmuch as the gratification of
the instinct is itself a sensation, it also, like a true sensation,
develops special sentient actions in the mechanical machines,
and these do not belong to the instinct. To this class belong
the convulsions that occur during the satisfaction of the instinct
of sexual congress, being excited by the excessive titillation.
When, as in this case, and in all the true blind instincts, the
satisfying sensation is an external sensation, the external
impression can excite special nerve-actions in the mechanical
machines (183), which are altogether foreign to the instinct,
and never belong, as such, to its gratification (184, i).

276, i. Although strong sensational desires and aversions,
may and do frequently occur, which are not induced or satisfied
by external sensations, nor require to those ends an external
impression, but which are based on imaginations, fictions,
visions, appearances, forebodings, &c., and are satisfied by them,
yet still they all arise from sensational stimuli, and are indirectly
determined, both as to their excitation and satisfaction, by ex-
ternal impressions (66). But as regards the regular and truly
natural instincts, imparted by the Creator to animals for the
conservation of their existence and well-being (262), all, so far as
we observe them, are excited and satisfied by external sensations,
which require true external impressions (258); these are provided
before-hand by nature, and so brought into connection with the
whole phenomena of life, that they must aff'ect the animal at
the right time and place, at such a period, with such intensity,
and in such a way, too, that the instinct is duly excited, and at
last satisfied in the way already illustrated (265 — 268).

ii. Since pleasurable and painful feelings derived from ex-
ternal impressions constitute the stronger sensational stimuli
(80, 88), such constitute also the most suitable stimuli of the
peculiarly natural instincts of animals (262, 90), and nature has,
therefore, specially made use of them for the development of
the absolutely necessary instincts, so that the latter may be
kept in action in animals in the most eff'ectual manner.

iii. No disagreeable external sensation, and therefore no
pain, is ever an object of satisfaction to an instinct, but only
the agreeable sensation that is the contrary thereof (262, 80, 81).

CH. III.] ACTIONS OF INSTINCTS. 143

tf°

Even excessively pleasurable feelings, which border upon the
contra-natural (199), cease to be an object of gratification,
d are abhorred (191, 80, 81).

iv. The sentient actions of the agreeable sensational instincts
all agree in this, that if not excessive_, they are conformable
with the welfare of the body, but if excessive, they are like
the sentient actions of the unpleasant instincts, and are opposed
to it (259). But inasmuch as all have the best interests of the
animal in view (263), the latter are only serviceable so far as they
act like medicine, and compel the animal by abnormal actions to
pass from a condition injurious to it, and therefore opposed to
their object (as, for example, a state of indifference, of pleasure, or
of misery), into the opposite and more salutary condition (196).

V. The sensational stimuli, whether pleasurable or painful,
which have to excite the curative instincts of the animal
(270, 271), operate sometimes in this way, by maintaining the
health of the animal, of sometimes contrarily thereto, according
as they are either pleasurable or painful (252). Thus fasting,
which is the sensational stimulus of hunger, makes us ill, and
compels us to think of feeding ourselves.

vi. Since the gratification of all instincts is an agreeable ex-
ternal sensation (276, iii), their sentient actions in the body are
generally in accordance with its nature and welfare (196), pro-
vided they are not excessive (199). Thus the gratification of the
appetite for food, for sexual congress, &c., conduces to health, pro-
vided the appetites are not excessive ; in the latter case, however,
they cease to be agreeable, and are abhorred (excite disgust).

277. The combination of so many corporeal influences in
each instinct (which act partly from without through the
nerves, and are partly sentient actions of various kinds), renders
the explanation of the resulting corporeal phenomena pecu-
liarly difficult ; a knowledge of the peculiar sources of each of
these influences is, however, of considerable assistance. These
influences are :

i. The actions of the natural inducements of the instinct.
These inducements are external impressions on the nerves,
which they prepare before-hand, in a peculiar way, to receive the
sensational stimuli proper to the instinct (264).

ii. The sentient actions of the sensational stimuli on the
vital movements (271).

144 ANIMAL.SENTIENT FORCES. [i.

iii. The effort of the animal-sentient forces to develop the
complete sensation wherein the sensational stimulus is (272).

iv. The sentient actions of all subordinate conceptions (273,
274).

V. The development of the complete sensation, or the
satisfaction of the instinct, when it is fulfilled, for which, in
the true instincts, an external impression is requisite, and
which impressions themselves excite actions (275).

Since the mind cannot voluntarily satisfy the greater number
of the instincts, but must await to this end an external im-
pression, which cannot possibly occur immediately (276, i), we
can understand the reason, why the instincts and all other
sensational desires and aversions in general, to which an ex-
ternal impression is necessary for their satisfaction, often require
so long and fruitless an effort of the mind, and such a com-
bined effort of the animal sentient forces ; while others, as the
instinct to voluntary movement (283), and the desires and
aversions of the will, are much calmer, and are satisfied,
apparently, with much less effort of the mind and motor forces;
for a limb may be moved, as soon as the motion is willed.
In the latter class, the satisfying sensation is not an external
sensation, but a spontaneous conception of the mind, to the
perfect development of which no external impression on the
nerves need be awaited. {Vide 336).

278. We have now to consider the instincts in detail, in
accordance with this general view: with the object of inquiring
in what mechanical machines each kind manifests sentient
actions ; to what end these are manifested ; according to what
laws; and what is the great result they have in the animal
economy by means of the connection between the physical,
mechanical, and animal forces of the part in which they act.
But since each sensational instinct may be numerously sub-
divided, we will take only the chiefest into consideration, so as to
give the elementary principles of a more detailed doctrine
respecting the actions of the instincts.

279. The sensational instincts of self-preservation and self-
defence, may be classed together in reference to their objects
and natural intent, namely, the preservation and well-being
of the animal, and the modes in which those objects are
attained (262) . In this class, indeed, we place the instincts of

CH. III.] SELF-LOVE. 145

animals to seek dwellings, to keep themselves warm, to escape
the dangers of winter, to avoid or avert oppressive sensations,
&c., just as properly as the instincts for food, for movement,
for rest, &c., although, at the same time, they are defen-
sive instincts. But since certain natural organs have been
given to each animal, as >veapons for its defence against inju-
rious attacks, and inasmuch as for the proper use of these
weapons, it possesses special instincts, which, although defen-
sive, are different from those of self-preservation, we will at
least class the war-instinct (Wehrtrieb) with the defensive
instincts, but consider all others, which have the maintenance
and well-being of the animal as their object, amongst the
instincts of self-preservation, although their object be at the
same time the averting of dangers, and attained by means of
aversions.

Self-love [Selbstliebe] .

280. All the changes in an animal organism, which tend to
its preservation and well-being, must ensue in accordance with
its natural functions, or, at least, terminate in their full
attainment (263). Corporeal changes which thus ensue and
terminate are agreeable, if felt or perceived, or else soon
terminate in agreeable conceptions or sensations (276, iv, 252).
On the same grounds all contra-natural changes tend to the
ill-being and destruction of the body (263), and if felt, are
painful. Consequently, all instincts for the preservation and
well-being of the animal, are efforts of the conceptive force to
attain to agreeable sensations, and to avoid the painful (262, 257).
This general effort in the instincts is termed the instinct for
enjoyment (80); and since its objects cannot be attained without
the continuance of the forces, or, in other words, independently
of the existence of the animal, it follows that the instinct termed
love of life is the fundamental instinct in all animals; so
that the instinct for life and for enjoyment, that is to say,
sensational self-love (selfishness [Eignliebe] ), instigates all the
others.

10

146 ANIMAL-SENTIENT FORCES. [i.

Instinct for Food.

281. By the pre-arrangement of nature (263), whenever food
is wanting, there arises in the stomach of the animal an uneasy
sensation termed hungriness [Nuchternheit], and one which
ever}' animal dislikes (280). This is the sensational stimulus of
the instinct for food (Hunger), which consists in a strong effort
to excite the sensations in the stomach antagonistic to this
unpleasant external sensation, or, in other words, to feel the
stomach filled with food ; this being the design of the Creator
in the instinct and its object in the animal, although the latter
knows nothing whatever of that object (266). Everything
that excites an unpleasant external sensation in the stomach
develops the sensational stimulus of the instinct, as long fast-
ing, a too quick digestion, acrid fluids in the stomach, sto-
machic remedies, &c. The sensational stimulus manifests its
sentient actions in the vital movements, which it influences the .
more powerfully in proportion as it is excessive (271), as is
shown by faintness, in which the movements of the heart, of
the blood, and of respiration are manifestly changed, and these
actions are contra-natural (276, iv). In so far as the sensa-
tional stimulus is a foreseeing of a future repletion of the
stomach, it manifests its sentient actions therein, so that it
produces imperfectly in the stomach, and in the mechanism
of the instinct, the same movements which actual repletion
or the satisfaction of the instinct excites (271-72). Hunger,
therefore, acts on the mechanical machines appointed to re-
ceive food, and to co- operate in nutrition, as the stomach,
bowels, throat, salivary glands, &c. ; for it stimulates them to
discharge their natural functions (170 — 174), and which reple-
tion of the stomach in particular develops in them. Hence,
in hunger, the stomach and intestines are more vividly moved,
and rumble (212), the salivary glands pour out fluid, so that
the mouth waters, and the other digestive fluids, including the
bile, are discharged, &c. We purposely avoid noticing in this,
as well as all other special instincts, the sentient actions of all
the associated secondary conceptions, so as to avoid confusion
in stating the sentient actions proper to the instinct itself.
We pass over, also, the processes of digestion, although partly
belonging to the subject, inasmuch as it is already discussed
in physiological works. ( Vide Haller's ' Physiology.^)

II. III.] INSTINCT FOR FOOD. 147

282. By the pre-ordination of nature (263), animals that
drink, feel a painful external sensation (280) in the gullet,
throat, and mouth, whenever their bodies require more fluids.
This is the sensational stimulus of thirsty which consists in an
eff'ort to produce the sensation antagonistic to this painful
sensation; or, in other words, to feel moisture of the parts,
which is the intent of nature in the instinct, and its object in
animals, although it is concealed from them, and they are
quite ignorant why the parts should be moistened (266).
Everything which induces this unpleasant sensation, as heat,
dust, want of fluids and of saliva, salts, wine, spices, &c., in a
word, everything which dries and heats, excites the sensational
stimulus and the instinct to drink. The sensational stimulus
manifests its sentient actions more strongly and contra-naturally
(271, 276, iv) in proportion as it is excessive, as is shown by
the oppressive thirst of fevers, &c. Inasmuch as the sensational
stimulus is a foreseeing of a moistening of the mouth and throat,
it manifests its sentient actions in the parts by a frequent swal-
lowing of the saliva, for the purpose of moistening the mouth and
throat, and thereby attaining the object which results from the
real act of drinking, or the satisfying of the instinct : the efi'ort
of the animal- sentient forces to excite these movements is the
sentient action of thirst, or the instinct for drink itself. Thirst
acts consequently on the organs predetermined to be moistened,
— the tongue, the muscles of deglutition, the throat, &c., — so that
it develops certain movements necessary to the act of drinking,
according to the laws of the sentient actions of the sensational
instincts (277), which movements become perfect during the
resulting quenching of the thirst (257); and in such cases
have, as a consequence, beneficial actions in the animal economy,
in accordance with the connection of the physical, mechanical,
and animal forces of the body, constituting the design of nature
in the drinking of animals, and which are specially described in
works on the physiology of the peculiar mechanism of animal
bodies. {Vide Haller's 'Physiology,' § 639.)

Loathing is just the opposite to the instinct for food. The
unpleasant external sensation, or idea, of an overloaded or cor-
rupted stomach, excites the mind to develop the antagonistic
sensation, the emptying of the stomach, which is accomplished
by abstaining from food, and by the act of vomiting, &c.

148 ANIMAL-SENTIENT FORCES. [i.

The Instinct to perform Sensational Voluntary Movements
[Zur willkuhrlichen Bewegung].^

283. Nature has ordained bodily exercise to be a means of
the preservation and well-being of animals, and thereby they
are kept in the best health. When therefore to its injury,
exercisfe of the body is too long neglected, a number of unpleasant
sensations are excited, termed indisposition or sickliness, and
which all animals abhor (280). These constitute the sensational
stimulus of the instinct for bodily exercise, in which the vital
movements are more or less morbid, according to the strength
of the stimulus, the pulse becoming feverish, and the respiration
impeded. By this unpleasant sensational stimulus (induced by
long repose, too much sleep, too great corpulency, and many other
causes), the animal is induced to make an effort for the opposite
agreeable sensations, which it foresees will be obtained by the
movement of its muscles and limbs, and this is the intent of
nature and the object of the instinct, although the animal does not
know for what ulterior purpose it makes the movements (266).
The sentient actions of this sensational stimulus, in so far as they
are a foreseeing of corporeal exercise are, consequently, developed
in the muscles of voluntary motion, that is to say, in those
which conceptional impressions can excite to movement inde-
pendently of any other impression, so that it stimulates those
muscles to the same movements that are fully performed during
bodily exercise (271). In the effort of the animal-sentient forces
to perform these movements imperfectly consists the sentient
actions of the instinct to bodily exercise itself (272). This
instinct acts, therefore, in the mechanical machines which
formerly exercised the body, namely, the muscles of voluntary
motion, for it excites them to the performance of their natural
functions (161 — 166), and which especially the gratification of

* In a note to § 335, Unzer distinguishes two classes of voluntary movements,
namely, the willkiihrlich, or sensational, which accompany the sensations and all
sensational conceptions ; and the freiwillig, or intellectual, which are excited by the
will of the understanding. Wille and Willkiihr are also sometimes used to dis-
tinguish these two kinds of will, but more frequently Willkuhr is used to express
both, as in the note referred to, where Unzer distinguishes between the sensational
and intellectual Willkuhr. I know of no English word which corresponds to
Willkuhrlich ; I have, therefore, termed the actions of voluntary muscles to which
Unzer uses it in the stricter sense, sensational voluntary movements; but where
it is used indefinitely, I have translated it by voluntary simply, or volitional. — Ed,

CH. III.] SENSATIONAL MOVEMENTS. 149

the instinct, or bodily exercise, will develop fully (204). Con-
sequently, in this instinct the muscles contract, the limbs are
moved irregularly, and the animal often attempts to hop, leap,
soar, sit upright, &c., just as actually occurs during the grati-
fication of the instinct for corporeal -exercise ; and if there be
no extraneous impediment, it usually takes place instantaneously,
because a conception only, is enough to excite movement in the
voluntary muscles. In such cases, there results, in virtue of
the connection between the physical, mechanical, and vital
forces of the muscles appropriated to voluntary motion, the
further operations in the animal economy, such as a modification
of the fluids, promotion of secretion and excretion, increase
of muscular strength, and of the animal force itself (204), as is
the design of nature in the instinct. For details on the subject,
works on physiology may be consulted. {Vide Haller^s ^Phy-
siology,' § 11.)

281. The instincts of animals for particular kinds of sensa-
tional voluntary movements, are easily understood from the
principles laid down in the previous paragraph. The instinct
for song of birds, which is usually a secondary instinct of the
instinct for propagation, arises from the sensational stimulus
of an unpleasant sensation in the chest, produced by changes
in the respiration and circulation resulting from the primary
instinct, as is also the case in man and other animals in
the acts of sighing, sobbing, weeping, moaning, talking, &c.
Every inducement of such external sensations, excites the
instinct of similar movements. Warmth, which accelerates
the movements and impedes respiration, stimulates birds to
sing even in winter, in heated rooms, and compels other
animals to sigh and pant [lechzen]. Wine, not less an ex-
citant of the vital movements, causes talkativeness ; a too crass
state of the blood causes melancholy, and weeping, sighing,
sobbing, &c. All these movements constitute generally the
satisfaction of the instinct itself, the proper sentient actions
of which are only previous imperfect manifestations of them,
as, for example, instead of singing, a frequent chirping; instead
of sighing, sobbing, or weeping, a deep inspiration ; instead of
speech, a mere sound, &c. To this class belongs also the
instinct of laughter in man, which is often secondary to other
agreeable instincts and sensations, and is also an accom-

i

150 ANIMAL-SENTIENT FORCES. [i.

paniment of various pleasures of the senses (250). Its sen-
sational stimulus is an agreeable external sensation, resembling
titillation, about the diaphragm, which originates from the
vital movements being altered by a vivid feeling of pleasure,
particularly of the senses (titillation, § 80). Sensational stimuli
to laughter result from everything which excites this sensation
at the diaphragm, even by flatulency of the stomach. The
instinct is manifested by the well-known contractions of the
diaphragm and thoracic and facial muscles, and its gratification
is actual laughter. Further, to this class belong other move-
ments, as the migration and hybernation of animals, the acts of
cleaning, bathing, swimming, pluming, revolving; the seeking
the sun^s rays and a warmer climate, the manufacture of clothing
which many animals undertake (as in forming cocoons), the
preparation of habitations, the establishment of republics
amongst beavers, bees, and ants, if we presuppose that these
animals all think. All these follow the laws of the primary
instinct for bodily movement, and have all as a basis, certain
obscure pleasant or unpleasant sensations, whereby the animal
is induced to attempt certain movements without knowing the
ulterior object to be gained, but which, according to the plans of
nature, are actually accomplished with the co-operation of
external impressions, for the purpose of securing the pre-
servation and well-being of the animal.

285. It has not been to this day decided, whether the respi-
ratory movements are mechanical or volitional. Generally,
they are neither the one nor the other (Haller^s ^ Physiology,'
§ 274), but manifestly the sentient actions of an instinct. So
soon as they are suspended, a distressing external sensation
arises in the chest, which is abhorred (280). This is the sen-
sational stimulus of the instinct of respiration, namely, the
strong desire to produce the opposite to this anxious state,
which we remember to be attained by respiring. The desire to
breathe consequently arises, the performance of which function is
the design of nature and the object of the animal in the instinct,
although of its further ends the animal is quite ignorant (266).
The sensational stimulus, namely, the unpleasant external sen-
sation, manifests its action on the vital movements (which are
the more widely influenced in proportion as it is excessive, § 271)
by a contra-natural and powerful beating of the heart (276, iv.

CH. III.] RESPIRATORY MOVEMENTS. 151

252), and in as far as it is a foreseeing of a future agreeable
sensation of respiration, causes the necessary respiratory movC'
ments imperfectly (271). The instinct itself brings forth the
^effort of the animal- sentient forces to produce these same
imperfect respiratory movements (272), and acts consequently
m the parts subservient to respiration, the diaphragm, the
luscles, &c., since it stimulates these to their natural fiinc-
ions, and which the satisfaction of the instinct, namely,
ispiration produces perfectly (208, 214). The result is, that
this instinct the mouth is opened, the muscles exert them-
jlves to raise the ribs, and the diaphragm is forced downwards,
)eing evidently the movements necessary to respiration, which
jontinue, according to the laws of the actions of sensational
instincts, until respiration is actually restored (257); then
there results, according to the connection of the physical,
lechanical, and animal forces of the parts subservient to re-
spiration, further actions in the animal economy, namely, the
expansion and contraction of the lungs, the determination of
the circulation of the blood, the cooling of the blood, perhaps
the transformation of the chyle into blood, and many other
uses, in accordance with the design of nature, which may
be learnt in detail in works on physiology. {Vide Haller, § 8.)
Since in the natural condition, animals are able to satisfy this
instinct volitionally almost instantaneously after birth, it does
not continue so long a mere instinct as others, and probably
this is the sole reason why respiration has not been hitherto
recognised as the sentient action of an instinct. Haller has
fully shown, that it is a sentient action, {vide §§ 268, 273, of
that great man^s ^ Physiology,' for a lucid explanation of the
question;) and it is surprising, that his doctrine has not only
been opposed, but he has even been blamed for advancing it.

Other questions arising out of this subject will be referred
to again (526), or may be solved by the principles already
stated. Of this kind are the questions, whether respiration be
not at first and in the newly-born a nerve-action, or whether
it be not rather a nerve action in them (269) continued
afterwards by the co-operation of a sentient instinct (183),
resulting from the habit of sensation in the machines (51); or
whether it is not so little mechanical, that at each retardation
of the respiration the instinct scarcely induces its recom-

152 ANIMAL-SENTIENT FORCES. [i.

mencement^ but it is regulated by sensational and intellectual
volitions, according to the requirements of other instincts,
emotions, intellectual desires, &c., into laughing, or weeping,
or sighing, speaking, &c. It is incontrovertible, that these,
together with groaning, sobbing, cooing, moaning, screaming,
coughing, whistling, sneezing, and all other changes of the
respiratory movements which are caused by external sensations
or obscure complex conceptions, are in so far true sentient
actions of satisfied instincts, since the respiratory actions gene-
rally belong to this class.

286. It is manifest from the considerations already advanced,
that there are two classes of instincts ; the one comprising
those in which the acts are under the control of the animal,
so that they can be induced or intermitted at will (283^ — 285) ;
the other, comprising those in which the acts are the purely
corporeal functions of the mechanical machines, as in hunger
and thirst (281, 282). There are some instincts of both classes,
however, which gradually change into one or the other class.
Thus, at first, in children and animals the unpleasant external
sensations resulting from accumulation in the bladder and
rectum, and which bring the appropriate instinct into opera-
tion, are relieved in a natural and necessary manner, because
the sphincter muscles are compelled by mere physical pressure
to permit the exit of accumulated excretions ; afterwards, how-
ever, this takes place when the unpleasant external sensation
is again felt, by a voluntary relaxation of the sphincters. In
the same way, the first respiratory movement in a newly-born
animal is probably the natural and necessary result of a very
obscure external sensation ; but, afterwards, it takes place by
a voluntary movement of the thorax on the recurrence of the
unpleasant sensation (285). And, on the contrary, we seek
at first to avoid many pains and other unpleasant external sensa-
tions by voluntary movements, which afterwards become purely
automatic, as, for example, shouting, writhing, and retracting
when in pain; the quickened walk and the drawing up of the legs
to the body in severe cold ; the contraction of the eyelids in a
strong light; and a thousand other movements, the objects of
instincts, formerly volitional, but become mechanical from
frequent repetition. Neither can we infer that the sentient
actions of an instinct which, in us or in another animal, are

CH. III.] REPOSE AND EXHILARATION. 153

volitional movements, must have been such formerly, or will
be for the future, or are such in any other creature.

The Instinct for Repose and Exhilaration,

287, i. The animal-sentient forces are exhausted by long
activity, and the destruction of the animal would result there-
from if nature had not previously provided against this cause of
exhaustion. When the animal-sentient forces (that is to say,
the forces of the material ideas, as they may be now considered,
in so far as they cause conceptions or sentient actions,) have
been uninterruptedly used by the animal for so long a time
that any further effort would be injurious, it feels during
thought or during the performance of the sentient actions in
the body an unpleasant difficulty, which has been termed lassi-
tude, weariness, ov fatigue (280). This unpleasant sensation is
the natural stimulus of the instinct for repose or sleep, which
instinct consists in an effort to develop the contrary to this
unpleasant sensation, that is, the withdrawal of the mind from
the wearying thoughts, and letting the animal-sentient forces
be inactive, so as to experience the sweetness of repose, and
thereby collect new forces, as is the design of the Creator in
the instinct and its object with the animal, although the latter
knows nothing of the actual intent, namely, the renewal of the
strength (266) . Everything which causes the unpleasant sensation
of lassitude develops the sensational stimulus for repose, and the
instinct itself, the longing for repose. Causes of this kind are
hardships, every long-continued movement, meditation, and all
long-continued thought, attention, reflection, and abstraction {77) ;
also articles of food, or medicines, which interrupt the animal-sen-
tient forces, as wine, opium, heavy meals, pressure in or upon the
brain, the plethoric state, various poisons, and numerous others.
The sensational stimulus, namely, the disagreeable external
sensation of weariness, manifests its sentient action in the car-
diac and respiratory movements (271), which are at first languid
almost to faintness ; but in a higher degree the stimulus becomes
feverish, and these actions become contra-natural (276, iv. See
also Haller ^ Physiology,^ § 580). In so far as the sensational
stimulus is a foreseeing of the future sweet repose (the contrary
to the disagreeable feeling of lassitude), it manifests its sentient

154 ANIMAL-SENTIENT FORCES. [i.

actions in the parts appropriated to the animal-sentient forces,
so that it develops imperfectly the future state of repose (271);
and in fact, in the straining of the animal-sentient forces and
the effort of the mind to withdraw as much as possible from
all external sensations, and spontaneous conceptions, and thereby
to interrupt all their sentient actions in the body, consists the
sentient actions of the instinct to repose itself (272), so that
the organs which co-operate in the act of thinking, and which
produce sentient actions, are compelled involuntarily, by the
soul and by a purely corporeal process, to cease their functions
(270, 49, 51). Consequently, during the instinct to repose and
sleep, the external sensations derived from external impressions,
and from the spontaneous conceptions are gradually lost, in
consequence of the enfeebling of their material ideas in the
brain; the muscles, in so far as they perform sentient actions,
move heavily, and let the limbs sink ; the eyelids shut, and the
whole body totters. In short, the instinct induces imperfectly
that condition which comes on when the instinct is satisfied by
rest or sleep, and there results from the connection between
the physical, mechanical, and animal forces, the repose and
renewal of the forces appropriate to sentient actions, in accord-
ance with the object of nature in establishing the instinct {vide
Haller's 'Physiology,' §§ 578—590).

ii. Yawning and stretching are rather sentient actions of the
instinct for exhilaration, than for rest. For when we feel the
unpleasant condition of languor and weariness, we can attain
its opposite by new efforts of the animal-sentient forces, as well
as by their periodical relaxation during sleep. If, therefore, the
obscure stimulus leads us to the former, we then express the
anticipated condition of renewed activity of the animal-sentient
forces, by imperfect efforts, to which the agreeable obscure
foreseeing of the condition of activity excites us. Consequently,
although these movements are doubtless signs of weariness, and
of the need for sleep, yet they are not sentient actions of the
instinct for sleep, but of the instinct for activity, or the waking
state. All circumstances that excite the obscure foreseeing of
pleasing exhilaration, and, consequently, the above-mentioned
causes of weariness render the instinct active, if we desire
the antagonistic condition, namely exhilarated activity. Now,
as the sight of another person who yawns or stretches him-

CH. III.] SELF-DEFENCE. 155

self, reminds us of this condition antagonistic to disagreeable
weariness, it leads us to the instinct for exhilaration, and we
stretch and yawn with the person.

iii. It still remains to state specially, with reference to the
instinct for repose, that the physical and mechanical forces of
the machines of animal bodies, as also the vis nervosa on which
nerve- actions are dependent, in so far as they are not also
at the same time sentient actions, are not subject to this law
of nature, namely, that their uninterrupted activity shall cause
unpleasant external sensations, and, consequently, induce the
stimuli of the instinct for repose and sleep. The formation of
the blood, and its continuous internal movement, together with
its circulation ; the working of the elasticity and other purely
physical and mechanical forces of the machines ; nay, all those
processes of the mechanical machines which during the waking
state are sentient actions, but at the same time may be and
commonly are, even during the waking state, purely nerve-
actions (183), as, for example, the movements of the heart, sto-
mach, intestines, and various muscles, particularly the muscles
of respiration (285), all these, as such, are never accompanied
by a sensation of fatigue, never excite the instinct for repose,
never stand in need of repose, are never changed by this
instinct, nor directly by its satisfaction during the deepest
sleep, but go on continuously, and take no further part in it
unless they are at the same time sentient actions, or indirectly
influenced through the general connection of all the forces of
the animal (Haller's '^ Physiology,' § 579). On these principles,
all the phenomena of the animal economy, which depend upon
the sensational stimulus to sleep, on the instinct itself, and on
the satisfaction of the instinct, or the act of sleeping, may be
very readily explained.

The Instinct of Self-Defence.

288. Just as nature has supplied every animal with me-
chanical machines (organs), which serve as the instruments of
the instincts for self-preservation, for they receive both the
external sensational stimuli that excite these instincts and the
external sensations that satisfy them (281 — 285) ; nay, just as
every creature is taught and enjoined by other instincts to

156 ANIMAL-SENTIENT FORCES. [i.

furnish themselves with such instruments for self-preservation
as spiders, for example, which weave nets to take their food
more readily, or caterpillars, which spin a net around themselves
for the purpose of undergoing their transformations undisturbed,
&c., so also she has fitted out every animal with special instru-
ments (mechanical machines) for the other instincts of self-
defence and propagation of the species, which are partly
adapted to receive the sensational stimuli that excite these
instincts and partly subservient to the gratification of the
instincts, without the animal knowing their objects, or tlie
causes of the movements (266). The instruments appropriated
to the instinct of self-defence (262) are termed the natural
weapons of the animal, and each is provided with particular
kinds of weapons, adapted to avert its greatest and most pro-
bable dangers, and appropriate to the objects of nature in the
satisfying the instinct of self-defence. Thus, the soft animals,
which are easily crushed, are surrounded with hard shells ;
those which are appointed to be pursued and eaten by other
animals possess instruments whereby they can inflict as
much injury on their pursuers, as may be necessary to
check the pursuit ; teeth for biting, poisons, stings, talons for
wounding, hoofs for striking, claws for lacerating, &c. The
animals themselves are ignorant that they possess these weapons,
or, at least, of the object of nature in furnishing them (266).
They do not make use of them with a deliberate design, but
are impelled by their instinct to undertake blindly the other-
wise voluntary movements of the organs which are furnished
with weapons, whereby these become subservient to self defence
without the knowledge of the animal. Consequently, many
animals, when they find themselves in danger, make such
defensive movements, although their limbs are not yet supplied
with the weapons, or have lost them, and although the weapons
are useless against such dangers; they bite at a stone, they
sting at the air, they spurt out their poison without knowing
where, they strike at a thorn-bush or a wall, they even scratch
or bite themselves, &c. Now, since the instincts of self-defence
are really none other than instincts to voluntary movements
manifested in armed organs, they are subject to the same laws
as that class. {Vide §§ 283, 284.)

CH. III.] PROPAGATION OF THE SPECIES. 157

The Instinct for the Propagation of the Species.

289. By the pre-ordination of nature (263), with a view to
the continuation of the species, there arises in animals an
agreeable external sensation, the sensational stimulus of the
instinct for propagation, the sentient actions of which are
manifested by remarkably active vital movements (253, —
Haller's * Physiology,^ § 870), and this arises at a time when
the organism is in the most suitable state, at a certain age,
during a fixed period of existence, for the most part periodically,
in the sexual organs given by nature for this express object, by
means of natural inducements prepared beforehand, and already
described (268, 874); these depend on a plethoric state, nutri-
tious food, or food stimulating the nerves of the sexual organs,
wine, condiments, much rest, idleness, good living, freedom from
care, and various external sensations and other conceptions. In
man, who, as regards his instincts, is subject to the same laws
as brutes, this sensational stimulus is induced by a glance, an
imagination, a foreseeing, which surprises him without his
desire or even against it ; and he terms this operation which
amazes him, this wonderful change (263), the enchantment of
love. He is so little informed as to the design of nature in
this wondrous emotion, that at first he considers it to be the
feeling of friendship or of great esteem, in short, to be a noble
instinct, not arising from sensual stimuli, until at last he learns,
from its influence on the sexual organs, that it tends to an
object not observed by him, the excitement of the flesh (88),
and that it is the instinct for sexual congress, to which all the
stimuli converge. In both sexes, the instinct consists in the
desire to enjoy this sensual pleasure in the greatest degree which
takes place in coitu. Consequently, just as sexual congress is
the design of nature in this instinct (265), so is it also its object
in animals, which know nothing more of the ulterior object,
namely, the propagation of the species (266). The sentient
actions of the obscure foreseeing of an agreeable external sen-
sation, are manifested imperfectly as they actually occur (271),
and in the eff'ort of the animal-sentient forces to attain to these
imperfect movements consist the sentient actions of the instinct
itself. The instinct acts, consequently, in the mechanical

158 ANIMAL-SENTIENT FORCES. [i.

machines which have to accomplish sexual congress, namely,
the organs of generation, since it stimulates them to their ap-
propriate functions (178-179), and in particular is developed
fully the satisfaction of the instinct, namely, sexual congress.
Hence we understand why in this instinct the organs of gene-
ration fall into the same state as in coitus (217), that state
being induced according to the laws of the sentient actions of
sensational instincts. These incomplete movements becoming
complete in the satisfaction of this instinct, in accordance with
the designs of nature, other phenomena having reference to the
propagation of the species, result, as impregnation, conception,
the formation and nutrition of the embryo, and, lastly, its birth,
an account of which may be found in works on the Physiology
of the Special Mechanism of Animal Bodies. (Haller's ' Physio-
logy,' 28th Division.)

The Instinct to give Suck,

290. The instinct to suckle is one of the most remarkable
of the instincts of parent animals for their offspring. It arises
by the prevision of nature in the maternal animal, which gives
suck even at the period when a young creature is about to be
born, and in consequence of an unpleasant external sensation
from the distension of the mammse with milk, which is the
sensational stimulus of the instinct. Everything that induces
this sensation in the mammae, excites the instinct to give suck ;
so that bitches, whose mammse swell about the time when they
ought to whelp, have the instinct fully developed, although not
in pup at the time, and willingly allow a strange dog to suckle
them. The instinct itself is a strong desire to attain to the
sensation contrary to that of painful distension, or in other
words, a desire to empty the mammse, which is the design of
nature, as well as the object of the animal, although it is other-
wise ignorant to what end the suckiug of its mammae subserves.
The painful sensational stimulus changes the vital movements
contra-naturally (271, 276, iv), as is proved by the great un-
easiness, and by the milk fever ; and, as a foreseeing of a future
agreeable sensation of suckling, manifests its sentient actions
in such a way, that it stimulates the mammae to similar func-
tions, and partly develops them according to the laws of the

CH. III.] SUCKLING. 159

actions of sensational instincts (271-72, 277), as sentient
actions actually requisite to suckling, and resulting from the
completion of the instinct ; so that, for example, the milk fever,
whereby the milk is produced, supervenes, and the nipples are
erected (105, 247). The sentient actions of the instinct itself
consist in the effort of the animal-sentient forces to attain
these same imperfect movements (272), and through these, by
means of the connection of the physical, mechanical, and animal
forces of the organs adapted for suckling, the further operations
in the animal economy are attained, as the emptying of the
mammae, a more free circulation in them, the further quiet
secretion of good milk from the glands, and the prevention of
induration and impaction, all in accordance with the design of
nature in the instinct. {Vide Haller's 'Physiology,^ § 133.)
It is obvious from common experience, how this instinct is
adapted to another in the offspring, namely, the instinct to
suck; but inasmuch as this is only a particular form of the
instinct for food already treated of at length (281-82) it is
unnecessary to enter here into detail.

291. It would be equally unnecessary (and perhaps wearying)
to go through the other instincts in detail, inasmuch as the
preceding explanations and principles are applicable to all.
We need only here state the general laws by which the
phenomena must be explained, which the sensational instincts
develop in the animal economy. Whether all these pheno-
mena be always true sentient actions from sentient instincts,
or always such in all animals, or whether they are in some
degree, or altogether, nerve-actions (183), as has been often
mentioned (266, 269, 285), all these questions must be left
undetermined, until we come to the Second Part of the work.
It is sufficient to state at present, that the phenomena of the
instincts, in so far as they are true sentient actions, can be ex-
plained on no other principles than those hitherto laid down.
Nevertheless, it will not be useless to prepare the reader for the
doctrines of the Second Part by a few general statements and
deductions.

292. It is indubitably clear, from the nature of the instincts,
that the true sensational instincts, together with their sentient
actions, result naturally and necessarily from external im-
pressions, much in the same way as external sensations and

160 ANIMAL-SENTIENT FORCES. [i.

their sentient actions arise from external impressions, trans-
mitted to the brain (266, 269; 281 — 290). Although they
appear to be actions meditated on, and willed for a special
object, they occur without any other aim than those that relate
to the external sensation of satisfaction of the instinct, there
being no knowledge of the inducements or incitants, — of the
ulterior objects of the instinct, — or of the intention of nature.
It would be most erroneous to infer, that the skilfully adapted
actions of animal instincts are the operations of a sensational
uaderstanding or wisdom, and the result of thought. The
animal is not only ignorant of the inducements of its instincts,
but they act in spite of it. The obscure sensational stimuli
of the instinct spring from these inducements, also without the
knowledge or preference of the animal, and without its being
able to reason regarding them (264, 270). From these stimuli
the instinct results, according to the eternal laws of the con-
ceptive force (81, 94), naturally and necessarily, since no
animal can prevent itself desiring or avoiding sensationally
that which has once become unavoidably pleasant or unpleasant
(80, 81). This effort of the mind is forcibly directed to
the attainment of the satisfaction of the instinct without a
knowledge of the means, or, at least, of their use (266) ; nature
provides them for the animal, and brings them so near to it,
that it cannot avoid them; consequently it cannot suppress
the instinct, or avoid its gratification, by means of the reason
or the will, as man, in many instances, is able to do. Lastly,
the animal enjoys the pleasing external sensation accompanying
the gratification of the instinct blindly and quietly, without a
knowledge of its ulterior objects, and without troubling itself
in the least about them (266). Now, since all this applies to
the sensational instincts, it is equally applicable to their
voluntary movements (283, 284), and consequently it is also a
mistake to consider these as the result of reason and reflection.
293. But this is not all; for it can be proved, that these
various instinctive actions are, under varying circumstances,
only nerve-actions (183, 269), and can take place without any
external sensations or conceptions whatever, as will be demon-
strated in the Second Part of this work (see § 561), and that
it is consequently an error to conclude, that the apparent
care of animals for themselves and their young, the wise

i

CH. III.] INSTINCTIVE PASSIONS. 161

use of means to these ends, &c., prove the existence of a soul in
them.

294. The instincts of self-preservation and of the propaga-
tion of the species are common to all animals, and there are
therefore general instincts, as the love of life, of pleasure, —
the instinct for food, for sexual congress, &c. There are also
special instincts, which, are peculiar to certain animals, as
the instinct to breathe, to incubate, to take care of offspring,
&c. ; these are regulated in their development by the special
wants of the animal, and hence a manifestation in instinct of
the Godlike, the adapting. An animal, for example, which has
not to seek its food in water, has no instinct and no adaptation
for swimming : the animal, whose eggs are hatched by the sun,
has no instinct for incubation : the animal, which has not to
seek its food underground, has neither the instinct to dig, nor
the claws to dig with, &c.

295. Every instinct excites the development of a special class
of conceptions, which constitute the object and satisfaction of the
instinct, and are, at the same time, either in accordance with
the desires of nature or not (263). If they be the former,
they are natural instincts ; if the latter, unnatural (90) ; as the
instinct for self-torture, for suicide, sodomy, &c. The latter
never occur in animals left solely to nature, and only in those
which have the power to combine them with volitional
conceptions. The instinct of an animal for that class of con-
ceptions which are most common to it, because it finds the
greatest pleasure in them, and whereby its volitional actions
are determined, is termed its leading instinct ; and this gives
rise to the peculiar characteristics of the animal, or its animal
or sensational character [Character seiner sinnlichkeit] .
According as the instincts are vigorous or weak, the animal is
said to be active, vigorous, &c., or dull, lazy, inactive.

The Instinctive Passions [Affectentriebe] .

296. The primary passions are not excited, nor their satis-
faction designedly attained, by inducements prepared before-
hand by nature, as is the case with the true instincts (263).
We are affected by passions for the most part incidentally,
certainly not periodically, nor by a corporeal compulsory cause

11

162 ANIMAL-SENTIENT FORCES. [i.

unknown to us^ but volitionally^ and with the consciousness of
the sensational impulses. We can often avoid or weaken the
sensational stimuli at will^ so as to prevent the passion ; or, on
the contrary, seek and strengthen them so as to excite it.
During the access of the passions, we have often more power
than in the instincts to increase or diminish them at will, and
more means of weakening them without satisfying them,
because we know their objects. An angry man can more
readily mitigate his passion without avenging himself, than a
hungry man can quiet his instinct without taking food. A
man can often avoid at will every inducement to anger, but
hunger arises naturally and necessarily, without our know-
ledge, as soon as its cause is induced in the stomach. And
here it must be observed, that the passions are often not pri-
mary, but are excited in us by sensational instincts, and as
these are in close relation with the instincts, they may be
termed instinctive passions (affectentriebe) .

297. The main difference between the passions and instincts
consists in this, that in the former we are conscious of the
sensational excitants, in the latter we are unconscious (90,91).
The secondary conceptions in the former may be weakened by
abstraction, or antagonised, or rendered more vivid at will;
whereas in the instincts; their object cannot be brought
voluntarily into relation with the secondary conceptions, since
the object is unknown (273, 304).

298. When in the course of an instinct in an animal capable
of pure conceptions, the obscure sensational stimulus is com-
prehended, although it is still sensational and confused, a
passion is excited in and by the instinct, or an instinctive
passion (90, 91). The instinctive passions are at first instincts,
which become passions during their continuance. Conse-
quently they arise from the natural excitants of the instinct,
and manifest like them the Wonderful (263) ; but with this
difference, that during their continuance the sensational volition
of the animal is combined with the natural impulse to obtain
the satisfaction of the instinct : thus a voluntary power over it
is attained. We will consider briefly the more prominent
instinctive passions from this point of view.

299. Animals are impelled by nature to a love of life,
without knowing why; they are blindly led to abhor the

CH. III.] INSTINCTIVE PASSIONS. 163

danger of destruction. Nature^ without their aid, has prepared
beforehand for them the means of defending their life without
any knowledge of the object to be attained (285, 266, 280).
But when they become conscious of the object of their aver-
sion, namely, the danger of death, the designs of nature
hitherto blindly followed become their own, and nature and
the sensational volition of the animal co-operate to attain the
same object, so that the sentient actions now result as well
from the sensational inclination of the animal, as naturally and
necessarily from the instinct. Yet, although the animal still
follows the impulse of nature, it follows it willingly, since
from a consciousness of the abject of the blind instinct of life,
the latter is changed into an instinctive emotion, the fear of
\death. It is led by this knowledge to a sensational volition,
whereby it brings other conceptions, desires, instincts, and
emotions, which arise from it, according to the laws of the
conceptive force (273), to bear on the object now known, so
as to obtain the fulfilment of the instinct. It is thus we
understand the differences between passions and instincts. In
the primary passions, the natural impulse which characterises
the instinct is not present (263) : in pure instincts, the voli-
tional element is wanting : in the instinctive passions (or
emotional instincts), both are united.

300. In the instincts of hunger and thirst, animals eat and
drink before they can know that food and drink induce that
pleasant external sensation, which constitutes the satisfaction
of the instinct. But if the animal become conscious of the
object of the instinct, the volitional element is added, and the
blind impulse of nature co-operates with the inclination of the
animal to attain it. The blind instinct is become the volitional
instinct for food, the appetite, gluttony, longing for drinks.
The perception of the object leads to a sensational volition,
and thus other conceptions, desires, instincts, and passions are
brought to bear on its attainment, and the volitional actions of
voracity and rapacity are manifested.

301 . The war-instinct, a form of the instinct of self-defence,
stimulates animals to the blind use of the natural weapons
which nature has supplied, together with skill to use them.
They know nothing of the object (the injury of another) to
be gained by their use, so that they perform the requisite

164 ANIMAL-SENTIENT FORCES. [i.

movements before they actually possess the weapons (288,
266, 269). But if a knowledge of the object of the in-
stinct be added, namely, an infliction of an injury upon
another, the volitional element is added, so that the will and
the impulse of nature co-operate for the attainment of the
same object, and the blind instinct becomes the instinctive
passion of self-defence. A sensational volition follows this
perception of the object of the instinct, and other conceptions,
desires and passions are brought to bear on its attainment,
whereby the volitional actions of the desire of revenge are mani-
fested in the skilful and revengeful use of the natural weapons,
as, for example, in selecting the most dangerous point to
inflict injury, in the most crafty and violent infliction of it, &c.,
and in discriminating the objects which should be feared and
avoided, or pursued and seized.

Anger [Zorn] is always a passion, and never an emotional
instinct, because it consists in an abhorrence of a known
injury, of which consequently we are conscious. Animals
that possess no pure conceptions, and are incapable of primary
passions, never experience it ; nor is it even an emotional
instinct in them, as the desire of revenge is [Rachgier], but a
passion subordinate to the latter, developed by the instinct of
self-defence. Anger can excite the desire of revenge as a
subordinate passion, and then the latter is not an emotional
instinct, but a passion combined with another passion, namely,
anger. The special sentient action of anger on the liver, &c.,
will be considered subsequently (see § 325).

302. In the sexual instinct, as in the preceding, nature
impels animals to the blind use of the organs with which she
has supplied them, as well as with the knowledge how to use
them ; without their being aware that they will thereby pro-
pagate the species. It would appear, indeed, that no animal,
except man, is aware of this object. But even the immediate
object of nature in the instinct, namely, pleasure, is unknown
to many animals, so that they are stimulated solely by the
blind instinct to the use of the organs of generation (269).
But when an animal is conscious of this immediate object of
the instinct, namely, pleasure in sexual congress, the blind
instinct is combined in its action with the sensational will of
the animal, and becomes the instinctive passion of physical

CH. III.] INSTINCTIVE PASSIONS. 165

love (not the passion of love, § 308). Other conceptions,
desiresj instincts, and passions, are brought to bear upon the
object by the sensational volition of the animal, so that the
fulfilment of the instinct may be attained. Thus the volitional
actions of lasciviousness, jealousy, amorous enticements, as well
as the discrimination of the beloved object and its sensational
selection from all others, are to be explained. As a pure
instinct, there is no knowledge of its object and intent; so
that, even man, so long as it does not attain to be an in-
stinctive passion, does not know how to investigate the origin of
his enchantment and mental disorder (263). He never imagines,
that the final object of the strange disquiet which thrills
through his whole frame is sexual congress; and amidst the
effort, he literally does not know what he wishes, until the
blind instinct becomes an emotional instinct, and opens his
eyes (289). If amorousness were a primary passion, it would
not be accompanied by the natural impulse; it would be a
sensational desire for sexual congress more gentle and more
volitional, never found in animals, although sometimes in man.

303. The maternal instinct is usually excited blindly and
naturally. The parent animal knows neither why she broods,
nor what she hatches or gives birth to. She tends, allures,
covers, nourishes, and protects her young, blindly : nay, will
perform these offices for young animals she has never known
before, and which require attentions entirely different from
those she affords, consequently, without any knowledge of the
objects or aims of the instinct. When, however, an animal
becomes conscious of these, the volition co-operates with the
impulse of the instinct, and we have the emotional instinct of
love of offspring. This consciousness induces acts of sen-
sational volition, whereby other conceptions, desires, instincts,
and passions are directed towards the attainment of the objects
of the instinct, and thus the various actions connected with the
care of the young are developed.

304. But although in the instinctive passions or emotional
instincts, animals readily perform, by acts of sensational will,
that which nature works in them, naturally and necessarily,
by means of the instinct, and whether they will co-operate or
not ; still, as is to be shown subsequently (348), the mind has
not only no command over the conceptions and desires which it

166 ANIMAL^SENTIENT FORCES. [i.

directs by sensational volitions towards the objects of the
instinct, but it is prevented applying them in any other way
than in advancing the sensational pleasure, and in attaining
the object of the instinct, by the general instinct for enjoyment
(280), by the power of the spell of the instinct (263), and by
the close dependence of all complex sensational desires and
aversions, particularly of the emotional instincts (298), upon
the sensational faculty (Sinnlichkeit) (89). By these views we
can explain, why all animals, endowed though they be with
sensational volition and with free-will, when in circumstances to
encourage, excite, increase, or ennoble certain morally good
emotional instincts, or to avoid, repress, diminish, or counteract
the morally evil, have a natural infirmity to lean to the side of
instinct, and not to deduce from its morality any motives for
their voluntary conduct.

Actions of the Passions through the Nerves in the
Mechanical Machines.

305. The primary passions arise from pure but still con-
fused sensational stimuli, of which we are conscious, and not
from instincts (91). They are free from the powerful impulse
of the latter, or, at least, more free than the emotional instincts ;
and constitute, therefore, an entirely different class of desires,
more volitional, and less under the control of the sensational
faculty, although always sensational, and only half spontaneous
conceptions (27, 66, 89). The direct sentient actions of these
desires, and their general laws, have been already laid down
(255, 261). The incidental are in all respects analogous to
the incidental conceptions in the instincts, and subject to
the same laws (273). The desires and subordinate conceptions,
which are spontaneous, volitional, and incidental, influence the
passions more, either in strengthening or restraining them,
according to the pleasure of the animal, although they seldom
act in any other way than that most favorable to the instinct
of self-love (304). It is, therefore, only necessary here, to
distinguish the sentient actions peculiar to each passion ; and
we will limit our inquiry to the principal of them.

306. Every agreeable passion {joy^ § 259), is a strong desire
arising from confused sensational incitements (91, 94), developed

€

H. III.] ACTIONS OF THE JOYOUS PASSIONS. 167

cording to the general laws of the passions. It must be
distinguished from the instinct for enjoyment (380), in which
the object of the pleasure is neither known nor distin-
guished (262), while in every kind of joy the animal is con-
scious of the object, although imperfectly. In joyousness,
there is a future agreeable thing anticipated from the pre-
sent, in contentment^ from the past, in hope, from the future,
(Baumgarten's 'Metaphysics,' § 505 :) and since, consequently,
the various species of joy do not arise out of instincts (262),
they are never instinctive passions. Their sentient actions are
compounded of those of a sensational pleasure and a confused
sensational foreseeing (257, 258). Joy for honour is termed
ambition ; for the perfections of another, love (the passion) ;
in the various relations of the beloved to the loved, grati-
tude, compassion, kindness, benevolence, &c. (Baumgarten's
* Metaphysics/ § 506.)

307. In as far as every kind of joyous passion is pleasure,
their sentient actions act upon the vital movements beneficially
for the health (259). They excite the circulation, and further
all the natural functions and secretions, especially that of
insensible transpiration, and give a sensation of lightness of the
body : the last is more particularly felt in joy, contentment,
and hope. If violent, however, they act contra-naturally (259),
so that great and sudden joy renders the transpiration ex-
cessive, or the heart acts too violently, and so brings on an
apopletic fit, or causes paralysis of the heart by excessive
distension, and sudden death is induced. The gentle calm
feelings of satisfaction and contentment, maintained continu-
ously and equally, and the practice of the gentler virtues,
conduce, consequently, to health and long life, more than vio-
lent emotions of joy and happiness (252). Nevertheless, various
diseases of the body, dependent upon contra-natural changes, or
upon enfeebled vital movements, maybe cured by joyous emotion.

The sentient actions of joyous emotions, which result from the
foreseeing of their object, imperfectly express the condition of
their satisfaction (257), and are for the most part volitional
movements, such as dancing, leaping, laughing, singing, speak-
ing, and similar actions which accompany the actual enjoyment
of a vivid sensational pleasure, and the secondary conceptions
and desires thereby excited. These volitional movements are

168 ANIMAL-SENTIENT FORCES. [i.

excited in the emotions and instincts in a similar manner
{vide § 283 — 5). Everythiug that excites a vivid sensational
pleasure can induce the joyous emotions, as wine, music,
society, jests, the gratification of other desires, stimulating
sensations, imaginations, foreseeings, &c.

308. Every form of the emotion of love, as kindness, friend-
ship, gratitude, pity, and the benevolent virtues, are a species
of gentle joy for the perfection of another (306), and manifest
the sentient actions of the joyous emotions in a moderate
degree. Inasmuch as these are very favorable to health and
long life (307), it is a truth established by experience, that a
misanthropic or malicious person is his own enemy, and that
goodness is its own reward. These nobler passions must not be
confounded, however, with the instincts or the instinctive
emotions of love, for they arise primarily from pure perceptions
(91), and have sensational stimuli and objects of satisfaction,
altogether difi*erent from those of the latter. Every kind of
perfection which we observe in another can excite in us the
passion of love, while there is only one sensational stimulus of
the instinctive passion of love,

309. Every painful emotion {distress, § 259), is a strong
abhorrence excited by confused sensational impulses (91),
developed according to the general laws of the passions (94),
and consequently belonging neither to the class of instincts or
of instinctive emotions. Their mental actions are made up of
those of a sensational annoyance and a sensational confused
foreseeing (257-— 8). Distress for the past, in reference to
future consequences, is regret ; for the present in reference to
the future, is grief; and for the future itself, is anxiety,
care, dread, despair. To this class belong also the passion
excited by the delay of what is longed for, longing ; or by the
imperfection of another, sympathy; or by contempt inflicted
or anticipated, shame ; or by the perfection of another, hatred ;
or by a coveted perfection, envy ; or by an offence, anger ;

i or by the desire to retaliate on the off'ender, revenge; or,
I lastly, by a sudden, unexpected, and great evil, terror
\ (Baumgarten's 'Metaphysics,' §§ 507, 508). Each of these

passions have their peculiar sentient actions in the animal

economy.

310. The sentient actions of the distressing passions in

CH. III.] ACTIONS OF THE PAINFUL PASSIONS. 169

general, and of sorrow in particular, are vital movements
antagonistic to the natural movements, in so far as they depend
upon a sensational annoyance (259). The blood is retained
and accumulates in the lungs, as is shown by sighing, prse-
cordial anxiety, pallor of the face, small pulse, and coldness of
the extremities. Does this congestion take place in consequence
of feebleness of the heart ? or is it over dilated at each stroke,
and contracts again too feebly? or does it beat irregularly, not
expelHng a mass of blood equal to that which it receives ? The
latter is the more probable state, since in no true passion are
those movements which constitute its direct sentient actions,
weaker than in health, but stronger (94), although in the
distressing class they are tumultuous and contra-natural (209).
This is the more manifest, when the passion of sorrow is
distinguished from that condition of the mind, in which there
are unpleasant conceptions without a full development of the
instincts or emotions, — and termed a sorrowful, low-spirited,
melancholic state of mind, for in this, the continued annoyance
can debilitate the vital movements (254, 261, iii). To this class
belongs a continued state of secret anxiety, sorrow, carking
care, jealousy, hatred, envy, &c., which consists in a continued
state of suffering, seldom or never attaining the force of an
instinct or passion, and in which the vital movements are
obviously rendered weaker. But in a true passion of the
distressing class, the movements do not indicate debility ; but,
on the contrary, the restlessness, the loud cries, the wringing
of the hands, the tearing of the hair, &c., indicate increased
activity.

311. The disturbance of the hearths action, in sorrow and
in all the painful passions, leads to disturbance of all the
functions of the body, and, as experience teaches, to disease
and death. If these emotions or passions remove or alleviate
many diseases, it is only by their direct sentient actions, or by
those of the secondary conceptions (259).

312. Those sentient actions of regret, that depend upon the
foreseeing of its object, and which imperfectly express its fulfil-
ment (257), are closely accompanied by those of an imagination,
since the emotion is felt for some thing passed (309, 67), and
this imagination is often so vivid, that it becomes an imperfect
sensation (148). Thus it is that the form of a beloved indi-

170 ANIMAL-SENTIENT FORCES. [i.

vidual deceased still hovers around the mourner, and seems
to accompany him everywhere, while the latter acts accordingly,
addressing and embracing the shadowy form. As foreseeings
do not readily become so vivid, this circumstance takes place
more frequently in passions having reference to the past rather
than to the future. But still it may be observed in the latter
class, by a careful analysis. When, for example, we are in
sorrow, from the expectation of bad news respecting a dear
friend separated from us, and the sentient actions of sorrow
are excited, those of an expectation (foreseeing) of dreadful
news respecting him are distinctly connected with the sentient
actions of a recollection of the affectionate parting from him,
and of his last proceedings, so that we remember his farewell,
his tears, his gestures, while, at the same time, the expectation
of evil tidings causes us to feel all the workings of a dismaying
fear.

313. Grief, care, fear, anxiety, despair, are distressing pas-
sions, of whose causes we are conscious (309), whereby they
are distinguished as well from instincts, as from the instinctive
emotions (263 — 5, 296 — 8). They follow the laws of other
passions in every respect, and, for the most part, differ from
each other in degree only.

314. These emotions of grief, and every kind of fear, cer-
tainly exhibit the sentient actions of a sensational suffering in
common with every kind of afflictive emotion (309, 313), but
the close observer will mark differences in each (254). The
pulse is altered, is less full than usual, tremulous, and varying
in frequency and force; there is a feeling of constriction of
the chest from congestion, paleness of the face, cold extremi-
ties, corrugated skin, and the sense of constriction of the chest
often ends in syncope, and even death, as historical details
show. All these are the sentient actions of the vital move-
ments contra-naturally altered by the sensational suffering
(259), because, probably, an irregular influence of the vital
spirits on the nerves of the heart renders its movements at
one time, excessive, at another enfeebles them even to syncope,
whence various secondary phenomena result [vide §§310, 311).
It is in consequence of these results, and especially the repres-
sion of an injurious humour, in consequence of the suppression
of the cutaneous functions, that fear, grief, and all the depressing

ill. III.] ACTIONS OF THE DISTRESSING PASSIONS. 171

passions are so dangerous, when the plague and contagious
diseases are prevalent.

315. The sentient actions which accompany a foreseeing
in these passions, and whereby they are the most distinctly
distinguished from all other kind of distress, exhibit imperfectly
that state of the body which would arise during the fulfilment
of the foreseeing (257). A timid person abhors most strongly
that condition which he foresees ; hence a secondary instinct
is usually conjoined with the passion, namely, that of self-
preservation (288), the sentient actions of which are combined
with those of the foreseeing (241, 273). These subordinate
instincts of self-preservation or defence, accompany all kinds
of fear, and excite the corresponding volitional actions, ac-
cording to the laws of instinct, as running, shouting, seizing,
&c., only they are specially directed to an object by the fore-
seeing itself. Thus, when a person fears he will perish by the
fall of a house, he runs away in virtue of the instinct of self-
preservation, but with his head bent down, or his hands lifted
over it, induced to act thus by the foreseeing of the evil, exactly
as he would do if the house were falling upon him. In the
same way he would cover the heart if he feared being run
through with a sword.

316. Certain phenomena result from all the sentient actions
of these passions combined, which specially characterise them,
although only effected by the connection of all other forces of
the body with the animal sentient forces, and are to be con-
sidered, not as direct actions of the passions, but as purely
physical, mechanical, or animal movements caused thereby.
Thus all kinds of fear have this peculiarity, that they cause
the bowels to be moved ; that they contract the skin, causing
the phenomenon of shuddering ; and that they induce a peculiar
contortion (ausschlag) of the mouth ; fear, like grief, will also
soon turn the hair gray. Alexander Drummond attributes the
change of colour in the chameleon to its remarkable timidity.

317. Everything that can excite a strong sensational un-
pleasant feeling respecting present or future circumstances,
favours grief and all kinds of fear. The mind can be thus
injured by education, particularly by ghost-stories, which terrify
children. All causes of low spirits render the mind disposed
to grief or fear. The sensations, and other conceptions.

172 ANIMAL-SENTIENT FORCES, [i.

instincts, and passions, which excite this kind of unpleasant
feeling, naturally induce a disposition to sorrow, grief, and fear,
while the contrary prevent them. Similar results follow from
habits of life, diseases, and other circumstances that injure the
health, and cause the same sensations as the depressing
emotions.

318. Terror is a violent emotion analogous to fear, but
much more intense and sudden. For this reason, it is one of
the most dangerous to life (359). The action of the heart is
so rapidly and contra-naturally affected, that diseases of the vital
forces are thereby instantaneously produced, which not unfre-
quently induce immediate death. The pulse is not continu-
ously full, but remarkably quick, consequently the hearths action
is very irregular, and sometimes the contractions become so
convulsive and violent, that the arteries burst ; there is great
dyspnoea ; the complexion is deathly ; the extremities cold ;
and there are often dangerous fain tings, and even instant
death. The other phenomena are analogous to those produced
by fear (314).

319. The actions arising from a foreseeing in terror, are
similar to those of fear, and are developed in the same way
(compare § 315).

320. The special actions produced in the animal economy
by the direct actions of terror, are in some respects similar to
those of fear (316), although with many there is an opposite
condition, namely, spasmodic closure of the sphincters of the
rectum, bladder, &c., arising probably from the peculiar in-
fluence of terror on the muscular system, its effect being to
excite spasms and convulsions (Haller^s 'Physiology,^ § 565).
On the other hand, terror does not turn the hair gray, like
grief and fear.

321 . Whatever excites fear, predisposes to terror : whatever
prevents the one, prevents the other (309, 317). The habitua-
tion of youth to endure adversity ; that habitual lightness of
spirit, which meets great evils courageously ; the steady fortitude
which anticipates the distressing strokes of fortune ; and the
happy deception whereby an impending danger is made to
appear yet distant ; — these are the true means, by which many
may be preserved from terror, or at least from a timid temper.
Instead of terrific stories, the history of heroic deeds should

CH. III.] ACTIONS OF THE DISTRESSING PASSIONS. 173

occupy tlie memory ; cheerful society, travelling, excitement,
wine, &c., are all beneficial.

322. Anger and revenge, are depressing passions, we being
undoubtedly conscious of their stimuli ; they are therefore to
be distinguished from the general instinct of self-defence, and
from the war-instinct in particular (309, 301). They are
developed according to the general laws previously stated
(94), and their sentient actions are composed of those of a
sensational unpleasant feeling, and of a sensational confused
foreseeing (257, 258).

323. The actions of suffering [Unlust] in these, as in
all the depressing passions, are contra-natural and violent
(259) ; but they differ generally in this, that they attain a
greater degree of intensity, while the action of the heart
differs from that of anxiety and terror, in being characterised
by a continuous frequency and violence of movement. In
anger and revenge, the blood is impelled into the smallest
capillaries, so that those which seldom carry red blood are
injected, and hence redness of the face, increased temperature
of the whole body, haemorrhages, a full pulse, rapid and violent
breathing and panting, livid lips, and analogous phenomena.
Both passions are highly injurious to health, and sometimes
fatal, as experience shows. In virtue of the general connection
of the physical, mechanical, and animal forces of the body, there
arise also from this great disturbance of the vital movements, a
profuse perspiration, an immoderate agitation of the blood,
suffocative catarrh, inflammations of the viscera and of the
skin (roseola), apoplectic seizures from rupture of the cerebral
vessels, delirium from inflammation, particularly of the brain,
violent fevers, &c. On the other hand, diseases, particularly
those of the chronic land, and visceral obstructions have been
cured by these emotions (259).

324. The sentient actions of the foreseeings in these pas-
sions, and their subordinate conceptions, instincts, and emo-
tions, may have an equally injurious or beneficial influence on
health and life, since the greater proportion are of equal inten-
sity (259). In general, revenge is combined with anger as a
secondary passion, yet as it is usually an instinctive emotion
conjoined with the instinct of self-defence (301), and inasmuch
as in this case it is a violent desire excited by anger, to inflict

174 ANIMAL-SENTIENT FORCES. [i.

injury on the offending person (309), and, consequently, to
make use of the means most suitable to this end, it follows
that these efforts commingle with those of the foreseeing in
anger, and the actions of the two commingle with each other,
independently of those of many other subordinate conceptions.
The angry individual acts, therefore, as he would if inflicting
revenge : he strains all the organs subservient to self-defence
and combat, particularly the hands, arms, tongue, voice, often
as if really in conflict with his enemy; so that convulsions,
tetanus, and paralysis, or even epileptic paroxysms, may result.
As the foreseeings differ in character, so also do the various
motions excited thereby, and offensive words, grimaces, gnash-
ing of the teeth, blows, &c., are excited.

325. The special changes (316) produced in the animal
economy, by the sentient actions of anger and revenge, are an
increased secretion of bile, often hepatic inflammation, or such a
morbid state of the bile, that it sometimes inflames the stomach,
induces sometimes a malignant bilious fever; a peculiar poison-
ous state of the saliva is also induced, so that it is not only in-
jurious to the angry person who swallows it, but if mixed with
the blood, or applied to the nerves of another, poisons him,
exciting madness, or deranging the whole nervous system.
This peculiar and inexplicable influence of anger on the liver
and gall-bladder, the bile and the saliva, is observed also in the
war-instinct and revenge of many animals ; and when biting is
the means used for the satisfaction of the instinct, they have
either a special poisonous fluid, which is inserted into the
wound made by the bite, or their saliva is poisoned at each
outbreak of the instinct, as stated above. Hence arise the
horrible consequences caused by the bite of enraged animals or
men ; for hydrophobia is nothing else than a disease, in which
the animal is excited to anger by very slight causes, and its
body is permanently in such a condition, that it may be excited
to the highest degree of rage and revenge. All kinds of anger,
— as vexation, hatred, envy, &c., — have a marked influence on
the liver and its secretion, whence jaundice, congestion of the
liver, bilious vomitings, and diarrhoea, &c., result. In many
animals and in men, the hair, and in birds the feathers, are
erected and bristle up in the instincts of war and anger.

326. Since man himself has the war-instinct, exciting in

CH. III.] ACTIONS OF THE DISTRESSING PASSIONS. 175

him the instinctive emotion of revenge (301), and as instincts
and instinctive emotions are little under control, we possess
few means of guarding against their influence, although the
passion of anger is more under control. The excitement of
antagonistic ideas, instincts, and emotions, dissipation of the
mind, and abstraction of the thoughts, are the best psychological
means. Amongst the physiological, are those which prevent
the too great secretion and heating of the bile, since it is
actually the case, that those animals are least prone to anger,
and to quarrelling, which have the least bile.

327. Longiiig is a gentle passion, generally considered as
painful ; its sentient actions are, therefore, injurious to health,
and consist in palpitation, thoracic congestion, sighing, weep-
ing, &c. Its foreseeing manifests imperfectly the fulfilment of
the emotion (257), so that he who longs to embrace, often ex-
tends his arms as if about to embrace the object of his longing;
if he longs for a conversation, he talks loudly to himself, &c.
Its special action (316) in the animal economy is the absorption
of the fat ; hence probably the sunken appearance of the eyes,
and their slower movements, termed a languishing expression.

328. Shame is the slightest of the painful passions. It
nevertheless causes palpitation of the heart. The foreseeing
excites a casting-down of the eyes, and an averting of the face;
a further result of its operations is a redness of the face, as if
the vessels below were tied.

329. Just as every thinking animal has its predominant
instinct and peculiar sensational character (295), so also each
possesses a predominant passion, which in so far as it deter-
mines principally its volitional actions, co-operates to form its
sensational character (295), whereby the latter is made more
volitional, and more in the power of the animal, and thus
receives a moral relation (296, 297) . And since the passions, as
well as the instincts, but especially the latter, are dependent
proximately on the sensibility of the nerves (90, 91, 66), both
the predominant instincts and emotions presuppose a definite
sensibility of the nerves of an animal towards sensational
stimuli, and thus temperament mainly determines the sen-
sational faculty [Sinnlichkeit] of an animal, and its principal
inclinations, emotions, and sensational character, and may
modify them by habit in various ways (51, 52).

176 ANIMAL-SENTIENT FORCES. [i.

Actions of the Understanding in the Mechanical Machines.

330. The sentient actions of the intellectual concep-
tions {7Q>, 89, 180) when acting alone, and uncombined
with sensational conceptions, nor being at the same time
sensational stimuli of pleasure or pain [Triebfedern des
Gemuths], are not extended beyond the brain, neither
into the nerves, nor through them into the mechanical
machines (115, 116) ; at least we have no traces of such
actions. Being excited in the hidden mechanism of the brain
by the mind, according to psychological laws (111), and without
the co-operation of an external impression, they have no direct
action on the origin of the nerves in the brain (124), but their
impressions are made on the brain itself, so as to develop
material ideas of another kind there, which, according to the
laws of cerebral sentient actions, must accompany the chain
of intellectual conceptions excited by the mind (119). That
this is correct, is proved by the fact, that during the deepest
thought, or the most complete abstraction, no action in the
nerves is observed similar to a direct action of intellectual
conceptions, or like those of sensational conceptions, provided
there be nothing sensational commingled therewith, or no
sensational incitements of pleasure or pain [Triebfedern des
Gemuths], So little is this the result, that if the deepest
meditation be free from what is sensational, the natural move-
ments go on as in deep sleep, while the volitional movements
are forgotten, and the body is motionless as a statue.

331. It does not follow, because certain conceptions do not
excite direct actions externally to the brain, that they have
no influence on the body, since, in the first place, the de-
velopment of material ideas in the brain is an operation of its
animal forces, which, from their connection with all other forces,
must have its results. Secondly, although the material ideas
do not act upon the cerebral origin of any nerves, they act
upon other portions of the brain (124), and also on the me-
chanical machines (159) which enclose it, and through these
may exercise an important influence on the animal economy.
Thirdly, material ideas may readily develop unknown actions
in the nerves, which have their results in the animal economy.

(II. III.] ACTIONS OF THE UNDERSTANDING. 177

although we do not see their connection,, nor recognise them as
the results of sentient actions (141). Fourthly, since the vital
spirits are necessary for all animal functions, and consequently
to the production of the material ideas of intellectual concep-
tions (15), and since long and deep thought may waste or
destroy them (20), and thus the free action of the other animal
forces be restricted (22), it follows that in this way the con-
ceptions of the understanding may act powerfully in the animal
economy. Lastly, since they certainly develop some actions
in the body through the nerves, partly, as internal sensations,
(or as sensational incitements,) in so far as they are pleasing
or unpleasing (80), partly, because they are commingled each
time with sensational elements, it cannot be matter for sur-
prise, that many and important changes are produced in the
body by the exercise of the intellect, although the intellectual
conceptions, purely as such, do not act directly on the nerves.
(Compare §§136—141.)

332. The corporeal phenomena which are manifestly the
results of the effort of the intellect must be investigated on
these principles. By deep and intense thought, the body
wastes, the muscles become weaker, the blood is determined
to the head, the extremities become cold; the blood is
changed in composition, the sensational property of the nerves
is altered, and they become too sensitive, and excite irregular
sentient actions, which derange the sentient action of the
other sensational conceptive forces: the functions of the viscera
are irregularly performed, and in particular the digestion is
much impaired. Hence it follows, that deep studies and scien-
tific pursuits are not the natural objects of man, but opposed
to his health and well-being. Thus it is, that those learned
men who cultivate the abstract sciences are generally feeble,
meagre, sensitive, splenetic, hypochondriacal, and fanciful, and
have impaired digestion. On the contrary, the strongest and
healthiest men, with good digestion, are little given to study
the abstract sciences, and little capable of comprehending them.
These principles have an important bearing on pathology.

12

178 ANIMAL-SENTIENT FORCES. [i.

Actions of Intellectual Pleasure and Pain through the Nerves
on the Mechanical Machines.

333. The pleasure and pain which are connected with the
intellectual conceptions^ and render them motives to action, act
in virtue of their impressions in the brain (121, 80) on the
the vital movements, which are changed in proportion to the
strength of the impressions (250, 251). It is a well-known
and undoubted fact, that deep thought on abstract subjects
causes a manifest change in the circulation of the blood ; the
extremities become cold, while contrarily the vessels of the
head are filled, so that they beat more powerfully, and cause
redness and heat of the face, swelling of the head, headache,
perspiration on the forehead. Of the changes mentioned, those
which are most contra-natural are observed principally when
the thoughts are unpleasing, but even the pleasing may excite
such, if they be excessive. If a pleasing meditation be not
too deep, it excites only a vivid colour in the cheeks, and
favours the transpiration from the head ; a deep meditation on
painful subjects, on the contrary, causes vertigo, strong pulsa-
tion of the vessels, and a profuse perspiration, so that it is said
the head smokes. But since sensational stimuli accompany all
motives, and therefore all intellectual pleasure and pain (251),
it is not easy to determine, whether this operation of the
motives depends specially on intellectual pleasure and pain, or
on the accompanying sensational stimuli (252). Still the dif-
ference between the changed vital movements of deep thought
and those of sensational stimuli is so great, as to induce us to
doubt, whether they both spring from the same source. The
determination of the blood to the head, in operations of the
understanding, is not like that resulting from sensational stimuli,
for the blush of shame, and the violent derivation of the blood
to the head in anger, and in other instincts and passions, are
changes in the circulation of quite a different kind. Besides
these operations of the motives are weaker than those of the
sensational stimuli (250), and have this peculiarity, that they are
not excited either directly or proximately by external sensational
out according to the laws of the intellect (110). The intel-
lectual conceptions please or displease, according as they are
considered to be good or bad; the sensational conceptions

CH. III.] ACTIONS OF THE WILL. 179

please or displease, according as the external impressions from
which they directly or indirectly arise, are in accordance with,
or contrary to, the natural function of the nerves.

334. From an error of the understanding, the mind may
esteem something to be good or to be evil, which is the contrary.
But since in either case, nevertheless, the pleasure or pain there-
from is felt, it follows, according to the laws of the sentient
actions of both (254), that the agreeable motives will originate
changes favorable to health, while the disagreeable originate
unfavorable changes. Hence error and truth may alike some-
times advance, sometimes detract from, the well-being of an
animal ; so that in this respect, as is the case generally, it is not
every truth that is propitious, nor every error that is unpropitious.

Actions of the Will through the Nerves in the Mechanical
Machines,

335. When the mind wills in reference to the pleasure or pain
in a distinct foreseeing of the understanding, it exercises its
conceptive force to produce the foreseeing or its opposite (81) ;
and thus it wills, or not wills, from motives (88, 96). The
eflPorts of the cerebral forces connected with this act of willing
or not willing, partly express the perfect material idea of the
foreseen sensation (96) . If the circumstance in the intellectual
desire or aversion be only another spontaneous conception,
which has no direct influence on the mechanical machines,
as, for example, a general proposition (330), then the efforts
are limited to the development of the corresponding material
ideas, and the desires and aversions of the will have no
perceptible sentient actions, at least, on the mechanical
machines (332). But if the object of the act of willing, or
not willing, be a conception, that should act on the mechanical
machines, fitting material ideas are developed (96), and thus
the desires and aversions of the will have some sentient actions
in the mechanical machines (104, 110). For example, the
desire to comprehend a truth is manifested by no actions
exterior to the brain, but the desire to perform a certain act,
as, for instance, to rise and take hold of anything, is followed
by the proper movements. The sentient actions, which intel-
lectual desires and aversions develop directly through the

180 ANIMAL-SENTIENT FORCES. [i.

nerves, are termed free-will movements [freywillige Bewe-
gungen].

Note. — The free will [freywillige] movements are almost
always confounded with the sensational voluntary movements
[willkiihrlichen] . Volition [Willkiihr] may be either sensa-
tional or intellectual. Free-will movements are sentient actions
of the intellectual, and not of the sensational will [Willkiihr] .
Consequently, there is an infinite number of volitional [will-
kiirliche] movements (the sensational), which are not free-will
movements.^

336. In the sensational desires and aversions, especially in
the instincts, neither their sensational stimuli, nor their grati-
fication, is within the powers of the mind (292). It is
otherwise with the intellectual desires and aversions. As the
mind can choose for itself the favorable side of a thing, or
decide in what way it shall consider it, it can cause it either
to be pleasing, and therefore desires it; or, contrarily, dis-
pleasing, and therefore abhors it. And since the mind chooses
such conceptions for the objects of desire and aversion as it
has the full power to develop, as, for example, the direction
of the muscles to voluntary movements (283), it satisfies its
desires as soon as they are excited ; and if these conceptions
produce sentient actions (free-will movements), the latter
result the moment they are desired. This is the reason why
the free-will movements, as well as all volitional movements
generally (283), follow so implicitly the thoughts, so that the
simple pleasure of the mind is sufficient for their production.
A comparison of this power of volition (Willkiihrlichkeit) of
the will with the natural impulse of the sensational desires,
instincts, and passions, explains why the former, taken alone,
has entirely moral relations : the latter, either no moral rela-
tions whatever, or only in a subordinate degree (297) .

337. When sensational stimuli cause intellectual motives,
and both refer to one and the same object, or vice versa,
and with both it is either agreeable or unpleasant, the will

1 In an early work on Human Physiology, and which contains the germ of many
ideas more fully developed in this, Unzer distinguishes (as in this place) between
sensational and intellectual will, and characterises the movements resulting there-
from respectively as willkuhrlich and freiwilUg. (Philosoph. Betrachtung des
Menschlichen Korpers iiberhaupt. Halle, 1750.) See also note to § 283. — Ed.

III. III.]

ACTIONS OF THE WILL.

181

unbines with the seusational faculty, and free-will movements

[■are conjoined with the sentient actions of the sensational desires

|for the attainment of the object. In this way, the will urges

[a lover to go to his beloved, since, at the same time, the instinct

rorks for its satisfaction, and develops the sentient actions

lecessary thereto (289) . If, on the contrary, in a case of this

dnd, the object is desired on the one hand and avoided on the

)ther, there arises a conflict between the sensational faculty

[[Sinnlichkeit] and the will (the flesh, § 88, warring against

the spirit) ; in this, the victory is usually on the side of the

msational faculty, because its incitements are the stronger

(251). Thus the instinct of love will be victorious, in the case

where our intellectual motives are in conflict therewith, and

teach us to avoid the beloved object. Video meliora prohoque,

deteriora sequor.

338. When the conception of the object of the mil is either
sensational, or of that character that it cannot be produced

[solely by the conceptive force, the satisfaction of the will does
not take place as in the above cases (336) ; nor can the will

^perfectly perform the free-will movements desired (335). Thus
the most imperious will completes nothing to which external
sensation is necessary, so long as no external impression takes
place ; nor can the mind force itself into the belief of an
absurdity, nor can any effort of the muscles fulfil the desires of
the will, when we would leap over a tower, because such

^.fulfilment is an impossibility.

339. All our intellectual motives are intimately associated
I with sensational stimuli, and all the intellectual desires and

aversions are also sensational (65, Baumgarten^s ' Metaphysics,'
§ 512). Consequently, our will is not so free, that it does not
either combine its efforts with the sensational, or antagonise
them (337) ; and must, therefore, in some degree receive its
contentment from them. We therefore do nothing by a pure
will; the flesh has always a part in our efforts, conclusions,
and virtues, because it always makes them either more agreeable
or more difficult.

340. The muscles are the mechanical machines which are
under the influence of the will, and the origins of their nerves
must be stimulated by the efforts of the cerebral forces, excited
by the intellectual desires and aversions (164, i).

182 ANIMAL-SENTIENT FORCES. [i.

341. The reason why the free-will movements take place in
a given series^ and in no other_, can only be sought in the
arbitary and spontaneous production by the mind of the intel-
lectual desires and aversions, and no external inducements are
necessary thereto_, as in the sentient actions of the sensational
desires and aversions, except in so far as the will depends on
the sensational faculty (109, 339).

342. The free-will movements are produced by a special
impression of an intellectual desire or aversion in the brain,
which acts on the origin of the nerves distributed to the
muscles, and is propagated outwards from the brain (164, i).
Everything hinders the free-will movement, in spite of the
will, which prevents this impression being made or transmitted,
or which diverts it from its course to the muscles (164, iii, iv),
or renders the muscle unfit to perform its proper function
(165, vi). On the other hand, an impression may be made on
the origin or trunk of a motor nerve independently of the
will, and if it be propagated to the muscle, and the latter be in
a fit state to perform its functions, may excite movements,
usually voluntary, in spite of the will (162). It is, therefore,
erroneous to say, that a movement of the extremities, usually
voluntary, must always depend on the will, or that all free-will
movements must always take place whenever the mind wills.
Daily experience contradicts both propositions, for a natural
and incidental hindrance in the body, may prevent a movement
that we will, from taking place (see § 165, vi) ; and further,
movements that are usually voluntary, may be produced by
external sensations, or as nerve actions (183), not only without
an act of the will, but in spite of it (162).

343. The free-will movements have a very important and
general influence in the whole animal economy, through the
mutual connection of all the forces. Works on physiology
may be consulted as to the details {vide Haller^s ' Physiology,^
§ 416).

344. Just as every animal has its predominent instinct and
passion (295, 329), so those that possess an understanding and
will have their pj'edominant inclination, or, in other words,
intellectual desires for that class of conceptions which are most
usual with them, because the mind finds the most pleasure
therein ; and according to which its voluntary actions are for

CH. Til.]

ACTIONS OF THE WILL.

183

the most part determioed, or its mental character constituted.
Since all intellectual desires are the most voluntary and free,
as compared with the sensational^ although always closely
connected with the latter (295, 329, 339), they are the most
closely related to morals, and the mental character is termed
the moral character. In reference to their moral relations, the
)redominant inclinations are termed cardinal virtues or great

ices, both which, however, are connected closely with the sensa-
tional faculty (Sinnlichkeit), as is shown by their names, which

:e derived from leading instincts and passions, as avarice, or

lordinate desire for gold ; ambition, or inordinate desire for
lonour, sensuality, selfishness, self-love, &c. Like the instincts
md passions, therefore, they may be greatly but psychologi-

lUy changed by exercise and habit (329, iii, 111). As most of

le conceptions, and all the desires and aversions, are charac-
terised by special movements in the mechanical machines (as

las been shown throughout this entire chapter), we may by
^hem and by physiognomy know the mental capacities, the

;ading instincts and passions, the principal virtues and vices,
md the sensational and moral character, on which that physio-

)gical science which investigates the human mind is based.

CHAPTER IV.

THE RECIPROCAL CONNECTION \_GEMEimCHAFT] OF THE BODY
WITH THE SOUL.

345. When by the action of one thing, a change can be
perceived extending into another, the former is said to exercise
an influence on the latter (Baui/igarten's ' Metaphysics/ § 140,
141), and the connection in which they stand to each other, by
their reciprocal influence, is their reciprocal connection (ibid.,
§ 328).

346. It is sufficiently obvious, why, from an external
impression on the nerves, which produces material external
sensations in the brain, and consequently from the motive
force of the animal organism, an external sensation arises in
the mind (35) ; the animal organism, therefore, acts upon its
soul, and has an influence upon it (345) by its sensibility (34).
(Baumgarten's 'Metaphysics,' § 540).

347. All conceptions, without exception, have their foundation
in their external sensations (65), and are, therefore, partly sen-
sational. Now, since this sensational element of every conception
is produced by the influence of the body on the soul (346, 66),
it follows that the body, by means of its sensibility [Empfind-
lichkeit], exercises an influence on the mind in all its concep-
tions, without exception : and in virtue of the animal- sentient
force of sensibility (or the sensational force), the animal or-
ganism is constituted a co-operating force of all conceptions of the
mind. Consequently, the following depend more immediately
on the influence of the body on the mind, namely, the sensa-
tional conceptions, imaginations, and foreseeings; sensational
memory ; the sensational expectations and forebodings ;
dreams; poetic inventions [Erdictungen], and imperfect ex-
ternal sensations ; also pleasure and pain of the senses, and all
other sensational stimuli, the sensational desires and aversions,
the instincts, the instinctive emotions, and the passions. On
the other hand, conceptions of the understanding and of the
reason, intellectual motives, and the intellectual desires and

CH. IV.] CONNECTION OF BODY AND SOUL. 185

aversions, depend only remotely on the influence of the body
on the mind.

348. When sentient actions are excited in an animal organism,
it is sufficient to know that they proceed from the conceptive
force (97). Since all conceptions are connected with certain
actions (25, 97), the mind acts on the body and exercises an
influence on it, which extends to all those of its movements with-
out exception that have an origin in conceptions. The free-will
movements depend, however, more immediately on free-will (336) .
This dependence of the movements of the body on the will is
termed the dominion of the soul over the body, (Baumgarten^s
* Metaphysics,' § 538), but the actions of the sensational per-
ceptions, pleasure and pain, desires and aversions, are not directly
or immediately under the power of the soul, although they are
altogether produced by its influence.

349. The animal organism and the soul have a reciprocal
connection with each other (345), and since the influence of the
body is extended to all the conceptions by means of external
impressions on the nerves transmitted to the brain (347, 113),
and since also the influence of the soul is extended to all the
sentient actions of the body, by means of the impression of the
conceptions on the brain (113, 121), it follows, that this reci-
procal connection is more intimate and complete than that of
another animal with the soul, or of another soul with the
animal body. In virtue of this reciprocal connection, the body
is also most closely united to its soul in the brain, and this
united whole is a sentient [beseeltes] animal {vide §§ 6, 7),^
the idea of which consists in the closest reciprocal connection
of a body and a soul.

350. Those therefore are in error, who, with Stahl, wholly
deny the influence of the animal body on its soul ; as also are
those who limit that influence to the sensational perceptions,
and the feelings of pleasure and pain, and to the desires,
aversions, instincts, and passions ; inasmuch as the conceptions

' The exact meaning of the terras leseelte and unbeseelte is given in the text
(§ 605, et seq.), and the two kinds of sentient or beseelte animals defined. A literal
translation of the words might have been made in strict accordance with the idiom
of the English language ; but the term sentient seems to me to express as fully the
author's meaning as besouled would. — Ed.

180 CONNECTION OF BODY AND SOUL. [i.

of the understanding, the motives, and the desires and aversions
of the will, share in the influence of the body.

351. Those also are in error, who wholly deny the influence
of the soul over its body, as some mechanical physicians ; nor
are those less in error, who limit, the power of the soul to the
free-will movements, and deny that the involuntary movements
are under its influence, for the action of the heart, arteries,
stomach, and bowels, are manifestly influenced by it.

352. Lastly, those are also in error, who would explain
sentient actions by the physical and mechanical laws of motion
(7, 97), as well as those who would explain them by the laws
of other animal forces than the conceptive force, although
connected with conceptions. Nevertheless, movements identi-
cally the same, may take place without being accompanied by
conceptions, and since in this case, they are not sentient actions,
but take place independently of the influence of the soul, they
can be explained on other principles, yet not by the mechanical
and physical laws of motion, but rather by the laws of motion
of the animal forces (7).

PART II.

ANIMAL NATURE IN RELATION TO ITS PURELY

ANIMAL FORCES, OR VIS NERVOSA

[NERVENKRAFTE].

INTRODUCTION.

353. Animal forces acting without the co-operation of the
conceptive force, are termed nerve-forces (vis nervosa), or
purely animal forces (183, 186), and their actions are nerve-
actions [Nervenwirkungen], ov purely animal movements.

354. In virtue of the vis nervosa^ the animal body becomes
capable of functions, which cannot be explained either by the
mechanical and physical laws of motion, or by the laws of the
animal-sentient forces, but which are performed by the animal
machines, supplied according to special laws with vital spirits
(6,183). To these belong the purely animal movements caused 1
by an external impression on the nerves before it excites a
material external sensation in the brain (98, i), with which the
muscular irritability [Muskelreiz] of Haller must be classed
[vide § 388), as well as those excited by internal impressions
on the medulla of the nervous system and which excite no con-
ceptions ; or by other stimuli than conceptions, including many i
actions attributed to nervous irritability [Nervenreiz] by Haller.
(See § 386.)

The following is the plan of this, the Second Part :
In Chapter I, the vis nervosa and the nerve-actions are
considered generally. In Chapter II, the vis nervosa of the
external impression ; and in Chapter III, the vis nervosa of the
internal impression in the medulla of the brain and nerves, are
considered ; and lastly, in Chapter IV, the relations of the vis
nervosa and of the cerebral forces are reviewed.

CHAPTER I.

ON THE VIS NERVOSA AND ON NERVE-ACTIONS IN GENERAL.

^H 356. Only two primary animal forces of the animal machines
^^[the brain and nerves) are known; namely, the two kinds of
impressions on the nerves (33, 121). These animal machines
being incorporated with the mechanical machines (155), render
them capable of animal operations; and it is from the action
of the animal forces on the former, and through them on the
latter, that all the phenomena of animal organisms are produced.
These animal forces constitute the animal- sentient forces when
acting in and through the brain of an animal endowed with
mind, and are the means whereby the reciprocal connection of
the body and mind is effected. It is the external impression
which supplies the mind with all its external sensations, but on
the condition that it reaches the brain, and produces there
material external sensations (46) ; while the internal impression
excites all the sentient actions of the body, with the condition,
however, that it be caused by conceptions (123). But if these
conditions fail, that is to say, if the external impression be not
transmitted to the brain, or at least do not excite materi^ ex-
ternal sensations therein; or if an internal impression at the
cerebral origin, or on the medulla of the nervous trunks, is not
caused by conceptions, but by other irritants, the two kinds of
impressions still excite actions in the organism, and these are
the nerve-actions of the vis nervosa (353) . Every animal move-
ment is, in reference to the animal force that develops it,
either a sentient action or a nerve action; and if it be pro-
duced at the same time by both the cerebral forces and the vis
nervosa, it belongs to both classes of actions (193). Under such
circumstances, it would be erroneous to consider the one class
as distinct from the other, since they are identical in both cases,
just as a musical clock is the same, whether put in motion by
a performer or by machinery. "A muscle, when its nerve is
irritated, contracts and performs a movement the same as that

190 ANIMAL FORCES. [ii.

which nature has appointed^ and bends or extends the limb, &c/^
(Haller.) It now remains to prove, that the animal movements
which the cerebral forces excite by means of the impressions
caused by conceptions (as has been demonstrated in the First
Part) can be excited by impressions not produced by concep
tions. In the first place, we will prove by facts that this
actually occurs, and we will then investigate the nature and
properties and the conditions and laws of these peculiar animal
forces, and how they act in co-operation with the cerebral
forces.

357. If a nerve, which certain external impressions, when
felt, usually stimulate to produce certain movements in the
organism, be cut off from its connection with the seat of the
conceptive force, namely, the brain, or in other words, if it
be cut or tied, or the head of the animal be entirely separated
from the body, undoubted observations prove, that the same
external impression from the point of impression to the point
of division acts as a stimulus to the same movements so long
as any traces of life remain in the body, although the ex-
ternal impression never arrive at the brain, but only as far as
the point of division (31), and, consequently, is neither felt nor
excites material external sensations in the brain (46, ii). This
is the first fundamental principle, on which the doctrines to be
taught in this Second Part of the Physiology of Animal
Nature, are based. The experiment is successful in numerous
inst£g:ices with the most varied external impressions on the most
dissimilar nerves; and it would be successful still more frequently,
if the decapitation or destruction of the brain were not so rapidly
fatal, for it is to be remembered, that the structure of the nerves
experimented on must be unaltered, they must also still con-
tain vital spirits, they must be able to transmit the impression,]
and the parts must also retain some of their natural warmth o:
moisture, &c. (Haller's ^Physiology,' §§ 367, 960.) The large
mammalia bleed so profusely when experimented on, that th
circulation soon ceases, and the natural warmth and moistun
of the parts disappear; but so long as these conditions con
tinue, the experiment is successful with them, but still mo
so with smaller animals, as birds, worms, and insects* In th
Second Section of the next Chapter, it will be shown, that th
vis nervosa of the external impression regulates the animal ma-j

{

cu. 1.] NERVE ACTIONS IN GENERAL. 191

liines ; in the meanwhile it will be sufficient to prove its exist-
ce and reality by detailing a few of the most instructive and
most obvious facts. Thus, an external impression made on the
nerves of a portion of a muscle, or of the heart, or of the in-
testines separated from the body (as when, for example, the
outer or inner surface is burnt with acid, or pricked, or other-
wise irritated), excites the movements proper to the part, or
renews them for a time if they have already ceased, just as
when, in the natural condition of the animal, it was felt (167,
170). Thus, also, if immediately after decapitation, the body
be struck forcibly, the part struck becomes suffused with blood,
precisely as it would have been in the natural condition from
the external sensation of a blow (207). Thus, also, the glands
in an excised portion of intestine secrete on an external stimulus
being applied ; thus also the external impression of the gastric
juice, which in the natural condition excited the instinct of
hunger, stimulates the decapitated animal to rise up and seek
food, an act which is properly a sentient action of the instinct ;
thus, also decapitated insects allure with chirping wings to
sexual congress from the external irritations of the nerves of
their sexual organs ; thus, also, in decapitated butterflies, move-
ments necessary to copulation are excited, and the act itself
completed by the external stimuli proper to the instinct, while
decapitated female butterflies, flies, &c., are in the same way
excited to deposit their ova ; and thus, also the pinching of the
toe of a decapitated frog causes the same muscular contractions
and the same movements of the instinct of self-preservation, as
pain ordinarily excites in the natural condition. (Compare
Haller's ' Physiology,' § 402.)

Note. — These facts (of which a great number may be found
scattered through the writings of observers) are stated here
without reference to authorities, being generally known and
undoubted. If further proofs be required by the reader,
especially as to the irritability of muscles, he is referred to the
works of Haller, Zimmerman, and Oeder, for it will be shown
subsequently, that the experiments which demonstrate the
irritability of a muscle, establish also that the animal motive
force of an external impression acts independently of the
cerebral forces (338). (Compare Haller's 'Opera Minora,^
torn, i, pp. 368, seq.)

192 ANIMAL FORCES. [ii.

358. The external impression on the nerves can produce the
same movements in the body as if it were felt, although it is not
feltj nor transmitted to the brain. — These movements are
animal, inasmuch as they do not result from physical and
mechanical forces only (32, 42), (as Haller has shown, particu-
larly with reference to muscular movevent (162), (' Physiology,^
§ 412). They do not necessarily occur in accordance with
conceptions, because the impression is not felt, and, therefore,
there are no sentient actions excited by it, that is to say, no
actions from external sensations (98, 46); although in the
natural condition the two kinds of actions may occur together,
and often do (183). Consequently, there are nerve-actions
excited by the vis nervosa of the external impression (353),
and whether the external sensation of the mind co-operates
with it, or not.

359. If a nerve, ordinarily stimulated to excite certain
movements, by conceptional impressions^ acting on its
origin in the brain, be stimulated at its origin by other
internal impressions which are not material ideas (121) ; or if
its medulla be irritated by some other internal impression, at
any point of its course downwards, after its connection with its
cerebral origin, or with the brain generally, has been severed,
either by ligature or division of the nerve, or by the separation
of the head from the body, — in either case the same move-
ments are excited (provided animal life continues, and with the
other conditions previously stated, § 357), by the internal im-
pression simply, as are usually excited by internal impressions
caused by conceptions. This is also an irrefragable principle,
and is of tbe greatest importance in understanding the doc-
trines to be taught in this second part. In the Second Section
of the Third Chapter, abundant examples will be given of the
action of the vis nervosa of the internal impression : we can
here give only some of the most prominent. If the nerve
of a limb be irritated with a needle, movements take place

• By the term internal impressions of conceptions, Unzer means to express the
material ideas or changes which take place at each act of mind in the hrain, and
which are referred to in the First Part (§ 121, foot-note, et alia). For brevity's
sake, I have termed these impressions conci^ ^iowa/, becanse I have already translated
Vorstellung by conception ; but it is of importance to remember the wide and in-
definite meaning attached to the term. {Vide § 25.) — Ei'

CH. I.] NERVE-ACTIONS IN GENERAL.

exactly similar to those produced in the natural condition by
the volitional conceptions : thus, the diaphragm renews its
motions as in respiration, if the trunk of its nerve be irritated :
thus, the body of a dog, or of an ox, (nay, even of a man, as
is seen in executions by decapitation,) will be thrown into the
most violent volitional movements, when the spinal cord is cut
through : if in such an one the cord be irritated inferiorly,
the movements involve the feet only; if superiorly, panting
respiration, palpitation, deglutition, and vomiting result. When
an irritation of the spinal cord produces spasmodic convulsions
of the whole body, but a particular nerve has been previously
divided, the limb to which that nerve is distributed is
unaffected by spasmodic action, because the irritation cannot
be transmitted to it : thus also, a decapitated frog rises up and
springs forward, and if thrown into water begins to swim, so
soon as its spinal cord is irritated by a needle in the cer-
vical region, just as if it knew what it had to do. Bilguer
relates a somewhat similar case, in which if a certain part of
the neck where suppuration had taken place, was irritated,
the patient was obliged to stand upright in spite of himself, &c.
A great variety of well-authenticated facts of this kind may
be found in Haller^s * Physiology.'

360. An internal impression on the nerves can produce ike
same animal movements in the body, as the co7iceptions produce
by means of material ideas, although not caused by conceptions,
nor even taking place in the brain. — These movements are
animal, for they do not result from physical and mechanical
forces only (§ 121. Haller's 'Physiology,' § 412). They do
not necessarily occur in connection with conceptions, be-
cause the internal impression which excites them need not
be a material idea, and it is in no degree necessary that
conceptions cause it. These are not, therefore, sentient
actions (123), although the two kinds of actions may occur
at the same time, and often do (183). Consequently, there
are nerve actions which the vis nervosa of the internal im-
pressions produces (353), whether a conception co-operates with
it or not.

361. The following irrefragable truth follows from these
two leading principles : while the animal machines are endowed
by nature with the property of conducting external impressions

13

194 ANIMAL FORCES. [n.

to the brain, so that they may there excite material ideas,
giving rise to sensations, and of receiving internal impressions
caused by conceptions, they also possess another and entirely
different property, and are intended by nature to effect by means
of the external impressions they receive, whether the latter reach
the brain and are felt or not, the same movements which are
effected when they do reach the brain and are felt ; and to effect
by means of an internal impression, which they receive from a
touch or irritant caused by no conception whatever, the same
movements as are effected by means of the cerebral forces, when
the same internal imp^^ession is produced by a conception. The
animal machines are mysteriously and inscrutably endowed by
the Creator with these two distinct motor forces derived from
impressions, in addition to the equally-inscrutable animal force
originating also from them, partly that they may put the
animal-sentient forces into action, and partly that through
these they may move the organism animally ; and the greater
proportion of animal movements are so closely dependent upon
them, even when these are at the same time sentient actions,
that they must be considered as the most fundamental and most
general principium of the whole animal mechanism. But it is
also obvious, that these two kinds of vis nervosa have an essen-
tially distinct nature : that they produce their nerve actions in
some degree in an antagonistic manner; that the external
impression, considered also as simply a vis nervosa, is neverthe-
less a force as entirely different from that of the internal im-
pression as it is from the cerebral forces (32, 121) : that the
two kinds of vis nervosa are excited into action in opposite
ways : that they are regulated by different laws in their opera-
tions : and that all nerve actions of one and the same kind
cannot be all explained by one kind only of the vis nervosa,
nor that the existence of the one kind implies or excludes the
existence of the other. Hitherto, both have been generally
confounded too much with each other. Nevertheless, both
kinds oivis nervosa have certain properties in common, which
are now to be considered : those which are peculiar to each,
will be investigated in a subsequent chapter.

362. No vis nervosa requires necessarily the co-operation of
the cerebral forces (358, 360). Further, all nerve-actions may
take place in the animal machines [the brain and nerves], and

CH. I.] NERVE-ACTIONS IN GENERAL. 195

by their means in the mechanical without the co-operation of
the cerebral force, and in fact may take place without any
brain whatever. Consequently, we cannot infer,

i. That those actions cannot originate from a sentient brain
which are not animal actions or nerve-actions ; or if the sen-
tient brain be separated from the body, that no animal actions
or nerve-actions can take place in the latter.

ii. That those impressions which are not felt, and do not
reach the brain^ cannot develop animal or nerve-actions.

iii. That those impressions which are not produced by con-
ceptions, and do not depend upon material ideas, cannot cause
animal actions, or nerve- actions.

There is an important distinction to be noted in all. Nerve-
actions require the presence and free action of the vital spirits
in the animal machines (357, 359). The cortical substance
of the brain secretes the vital spirits from the blood, and dis-
tributes them to the nervous system. To this extent, the vital
spirits and the brain can be considered as being necessary to
the two kinds of vis nervosa. But again, the brain is not the
secreting organ of the vital spirits in all animals, since there
are some, in the first place, that have no brain or head distinct
from the trunk, yet are nevertheless endowed with vis nervosa,
and in which in all probability the vital spirits are secreted in
every part of the system, — in every nerve, and probably in
every ganglion — for their limbs often retain animal life, and
have an independent existence, when separated from the body.
Secondly, in those that have a distinct brain secreting nervous
fluid, it is not the medullary substance, the seat of the cerebral
forces (11) that is necessary to the vis nervosa, but the con-
nected cortical substance. Lastly, even in these the cortical
substance is only necessary, because it prepares and supplies
for the vis nervosa its animal nourishment, namely, the vital
spirits, and is, consequently, unnecessary so long as the nerves
retain a sufficient supply of the latter (1 59) ; just as animals

I will live for some time without food, or plants survive after being
separated from the stem. The reader will better understand
what follows by keeping this view in mind.
363. Although the two kinds of vis nervosa be thus inde-
pendent of the brain and of the cerebral forces, they can

196 ANIMAL FORCES. [ii.

action^ through the same nerves. External impressions can pro-
duce nerve-actions in their way upwards, before they reach the
brain (98, i), and at the same time reach the brain and be felt,
although their nerve-actions are independent of the brain and
of conceptions (362). The movements which a conceptional
internal impression excites as sentient actions, may be equally
produced by other internal impressions. Movements may, there-
fore, have a twofold origin, for an external impression may be
felt and excite sentient actions, which are also excited by it as
nerve-actions. In the same way an internal impression may, as
the result of conceptions, excite sentient actions, and as the re-
sult of an irritant applied to the cerebral origin of the same
nerve, or in any part of its course, excite the same movements as
nerve-actions. When a nerve going to the trunk of a decapitated
animal is irritated, movements like those arising volitionally are
excited by the irritation (359). It would be, therefore, erroneous
to conclude that movements might not be at the same time both
sentient actions and nerve- actions, or that actions exactly similar
to sentient actions in every respect may not be exclusively nerve-
actions, and vice versa.

364. The possibility that nerve-actions may be at the same
time sentient actions, is manifest from a simple consideration
of circumstances.

i. All animal movements in the mechanical machines (7),
consequently all sentient actions and nerve- actions, are produced
through the nerves. The impressions of the material ideas also
act as stimuli to the nerves (130), and produce the appropriate
movements (193) : but any other stimulus acting on the same
nerves, either at their cerebral origin or on any part of their
course dow nwards, must necessarily have a similar effect (359) ;
the two kinds of stimuli may occur therefore simultaneously,
and co-operate in exciting the same movements.

ii. If an external impression produces a sentient action, it
must act by producing a material external sensation in the
brain, the latter exciting the movement by its internal im-
pression on the cerebral origin of the nerves. But if this
external impression on its way to the brain be reflected in
the ganglia, or at the points where branches are given off,
on the same fibrils, as it would have acted on if it had
actually reached the brain (48, 151), movements must result

CH. I.] NERVEACTIONS IN GENERAL. 197

exactly resembling the sentient actions produced by the ex-
ternal impression.

iii. Hence follows the general principle (361), that those
movements in bodies which are most usually nerve-actions,
may at another time, or in another animal, be sentient actions,
or vice versa; or they may be at the same time both sentient
and nerve actions ; in every case being the same movements,
but only excited by different stimuli.

365, i. If a sentient action cannot be also at the same time
a nerve-action, no unfelt or non-conceptional impression can
cause it as a nerve-action.

ii. If a nerve- action cannot be also a sentient action, no im-
pression, either felt or produced by conceptions, can excite it (362).

iii. If a sentient action can be also a nerve-action, the im-
pression exciting it can act in both ways (364, i, ii).

366. Since sentient actions and nerve-actions are analogous
animal movements from impressions on the nerves, and differ
only in this, that in the former the impressions are felt or
originate from conceptions, but in the latter not, (193, 364,
iii,) it follows that all those movements which in one animal
are sentient actions only, or both sentient actions and nerve-
actions, may be nerve-actions only in another, excited by im-
pressions; so that the external impressions are never felt, and
the internal never produced by conceptions, but by other sti-
muli ; in this way an animal may not require for all its animal
actions, either material ideas, or a sentient brain, or conceptions,
or mind. This appears to be the case with those creatures
which have no brain, but only nerve-like fibrils, as polypes, in
which there is no brain, but the nerves are interwoven in
ganglia only. In animals with a sentient brain, every external
impression which is felt passes directly to it, and excites therein
a material idea, and in the mind a conception (35). Having
reached the brain, it is turned iDack or reflected, as it were, and
goes back as an internal impression of a conception, into those
nerve-fibrils that move the limb, which the external impression
is enabled to control by means of a sentient action of its sen-
sation (129) .j At the moment of this reflection, when the ex-
ternal impression is changed into the internal, thought takes
place in the mind, and thereby the movement which the ex-
ternal impression excites becomes a sentient action (97)1 When

198 ANIMAL FORCES. [ii.

a polype receives external impressions, they pass onwards (31)
to the nearest ganglion, whence they are reflected as if from a
brain, either entirely, or in such a way, that they only partly
reach other ganglia, and thus they can be reflected many times.
(Compare § 48.) It is sufficient that at these points the external
impressions are transformed into internal, and pass again from
the ganglia along the nerves to the mechanical machines, which
they put in motion, no act of thought taking place during the
transformation, because there is no brain (for in that only is
the seat of the conceptive force), nor are the internal impres-
sions adapted to excite a sentient action (97). In this way,
poises may be enabled to perform all their animal movements,
solely by means of external impressions on their nerves, without
having feeling, or thought, and without either brain or soul.
But inasmuch as all this is accomplished by means of animal
forces (32, 121), these animals do not act as mere machines, as
Descartes supposed, but according to purely animal laws, which
cannot be deduced from either mechanical or physical principles,
or explained by them. As Haller observes on the last page
of his introduction to the translation of Biiflijn^s^^ History
of Nature,' they are animals whose life consists simply in
irritability.

367. Other conclusions follow from the preceding propositions.
i. If the agency of material ideas on the cerebral origin of
the nerves, whereby they develop sentient actions in the me-
chanical machines, be sufficiently ascertained — that is to say, if
it be known on what nerve-fibrils, with what kind of stimulus
or movement, and in what direction and force, each received
material idea operates to produce certain sentient actions on
the muscles — another stimulus may be applied to the cerebral
origin of the nerves, or deeply in their trunks, instead of that
of conceptions, and thereby all the movements which the animal
performs as sentient acts, may be artificially produced without
brain, or mind, or conceptions, just as nature produces them in
anencephalous animals, by the transformation of the external
impression into the internal without any conceptions being
experienced. Thus, if the spinal cord or foot of a decapitated
frog be irritated, it moves from one place to another as if
acting volitionally, although deprived of both consciousness
and will (357, 359).

I

CH. I.] NERVE-ACTIONS IN GENERAL. 199

ii. It is possible, that in animals with a sentient brain,
movements are transformed from sentient actions into nerve-
actions, as is probably the case with the respiratory and other
movements (285-86); and vice versa from nerve-actions into
sentient actions, as in the sentient actions of the instincts of
newly-born animals (269); or become both when previously
they were only one or the other, or vice versa, become only
one or the other, when previously they were both. To establish
the possibility of these changes, each example must be specially
considered.

368, i. A sentient action may be changed into a nerve-
action, when the transmission of the external impression to
the brain is prevented, which may take place from natural or
contra-natural hindrances. (Compare § 51, iii, iv, v.)

ii. A sentient action from a conceptional impression may be
changed into a nerve-action when the conception ceases (136 —
139) and other stimuli, having a similar mode of action, are
applied to the conducting nerves (123, 360). Thus, the mere
physical irritation of an acrid humour acting upon the motor
nerves at their origin in the brain or along their course, will
excite contractions of the muscles which ordinarily are volitional.
The same may take place automatically, as when an external
impression which does not reach the brain, stimulates the nerves
in the same way as a volitional conception, in consequence of
being reflected downwards in the ganglia, or at the points of
division of the fibrils, thus producing movements as nerve-
actions, which are exactly identical with those excited by voli-
tion (48, 151). The closure of the sphincter of the bladder,
whereby the urine is retained, is usually a voluntary act ; but
when the volition ceases, and even when the contrary state is
willed, an irritation in the bladder, which is not felt, causes it
to be spasmodically closed, even until death ; in this case, the
former volitional action is changed by the vis nervosa of an
external impression into a nerve-action.

iii. A nerve-action may be transformed into a sentient
action, if it results from an external impression, when the
natural obstacle to the transmission of the latter to the brain
is removed (45); if, for example, a limb (as the leg), being
deprived of sensation by an injury to the nerve, and being
scourged, becomes inflamed, as a nerve-action (207, 357), and

200 ANIMAL FORCES. [ii.

then the power of sensation being restored, is inflamed in
consequence of the pain excited by the scourging, the inflam-
mation is a sentient action from an external sensation (207).

iv. A nerve-action proceeding from an internal non-concep-
tional impression may be changed into a sentient action by
the addition of conceptional impressions, which act upon the
fibrils of the motor nerves conducting the impression itself
(130, 360). Thus, in convulsions proceeding from mechanical
irritants applied to the motor fibrils at their origin, or in their
course, or from worms in the stomach, the external impression
is not perceived, and the convulsions are simply nerve-actions
(162, 360); but if a fright, or pain, or other powerful external
sensation, be superadded, which also excites convulsions, but as
sentient actions by means of conceptional impressions, then
the convulsive paroxysm is re-excited by the latter as a sen-
tient action. In this way epileptic paroxysms, originally purely
nerve- actions, may be reproduced as sentient actions, by fear,
or pain, or other violent conceptions capable in themselves of
exciting convulsive attacks.

V. An action may be both a nerve-action and sentient action
at the same time, if the causes of a change into one or the
other are superadded, as in the instances above mentioned,
yet neither ceasing to be what it was. If, after both
are excited, the causes of the one kind only cease, then the
other class remains (364).

369. There naturally arises a question out of the preceding
considerations (362 — 368), as to the advantages which animals
endowed with mind and brain derive from their movements
being often at the same time both nerve-actions and sentient
actions, and produced by a twofold cause ; since in fact, mere
impressions without the co-operation of the brain or mind may
be sufficient to produce the animal functions, as in anencephalous
animals. Although this question has been noticed already
(184, ii), it requires further consideration here.

370. To the end that an impression be felt, it is changed in
the brain into an internal impression (121, 129). But this
change of an external into an internal impression may take
place also by means of ganglia, or in some other way usual or
possible with animals ; only in such cases, the external impres-
sion will have no other reflex action in the animal machines

CH. I.] NERVE-ACTIONS IN GENERAL. 201

than that of which it is capable in virtue of its purely animal
force, which it reflects upon the motor nerves (364, ii); and
the whole of tliis action is purely corporeal and automatic, and
cannot be changed, or induced, or extended, or limited, or
directed volitionally. If, on the other hand, the external im-
^pression be also felt, then the mind, according to its psycho-
logical laws, connects volitionally with it many other conceptions
(2 1 9 — 224) , the internal impression s of which can produce through
the motor nerves such sentient actions as the unfelt external
impression could not have developed at all, or, at least, not in
(combination with the will of the animal. It is for this reason,
!that we find animals without brain and without any traces of
Imind, to be capable of very few kinds of animal movements ;
that those of which they are capable are excited by the external
'impressions automatically and necessarily ; and that they are so
.far from being under the control of the animal, as to be excited
ind continue just the same whether they be injurious or bene-
icial. In animals endowed with mind, on the contrary, every
external sensation develops by means of the series of secondary
conceptions caused by it, yet spontaneously or volitionally, a
number of new movements, which would not have resulted from
the unfelt external impression in this connection, and perhaps
not at all. Now, if nature has compensated brainless animals
for the want of spontaneous and volitional conceptions adapted
[to their preservation and well-being, by the automatic and
necessary results of mere impressions, as is particularly the
case in the instincts (266) ; it is obvious, that it is with the
same object in view that nature has endowed other animals
capable of so much more varied animal motor forces, with the
faculty of both feeling the external impressions and acting in
accordance with the resulting sensations. (Compare § 184, ii.)
371. The same relations exist with regard to internal im-
pressions. When they are not produced by conceptions, they
originate automatically and corporeally from mere animal stimuli
of the nerve- medulla, either at the cerebral origin, or in the
trunk of the nerves ; and nerve- actions in the machines result
just as automatically and corporeally ; either because a purely
physical influence suitably irritates the nerves from above
downward, or else, because unfelt external impressions reflected
in their course to the brain act in the same way. If, however.

202 ANIMAL FORCES. [ii.

tlie animal itself produces internal impressions^ and arranges
them by means of spontaneous or volitional or even free-will
conceptions^ the sentient actions result according to laws entirely
different from those of the automatic necessity just described
(119, 121), and are subject to the will and reason of the animal.
When a lobster gets one of its legs accidentally fixed in one of
its claws, and the claw is then made to contract by a mere
stimulus solely, the leg is crushed, and the animal is excited to
tear away the leg by the external impression of the forcible crush-
ing, and is thereby mutilated for a long time without suffering.
But if the closure of the claws and the insertion of the leg
between them were sentient actions from conceptions, its mind
would readily have deduced a third conception, namely, to open
the claws, and withdraw the leg. But as this does not occur,
the purely automatic actions are excited, and the animal loses
a limb in virtue of the working of a piece of mere animal
machinery, which it need not have lost, if the movements re-
sulting from its external impressions had been at the same
time sentient actions from its conceptive force. In such
cases, in sentient animals, the conceptive force regulates the
movements by means of internal impressions, although im-
pressions from mere animal stimuli may have the same effect
automatically.

372. Having considered the relation of the vis nervosa to
the animal-sentient forces, it becomes necessary to show the
special seat of the former. The animal- sentient forces, whose
seat is the sentient brain, extend their operations as well into
the animal machines, as (through these) into the mechanical
(117). The proper seat of the vis nervosa is the nerves, for all
primary animal forces have their seat in animal machines only
(6), although they are transmitted through the animal machines
into the mechanical, and excite animal actions therein (7). The
proper animal machines are the brain and nerves, in which the
vital spirits are contained (9) . But the operations of the brain as
a sentient animal machine, are for the most part only sentient
actions (25). Consequently, its peculiar animal forces are animal-
sentient forces (6). Now, the two kinds of vis nervosa are not
animal-sentient forces (356), consequently, are not peculiar to
the brain ; and since the nerves supplied with vital spirits are
the only true animal machines, except the sentient brain and

CH. I.] NERVE-ACTIONS IN GENERAL. 203

the cortical substance which surrounds it (159), it follows, that
the principal seat of the primary vis nervosa must be specially
in the nerves.

373. Nevertheless, it cannot be denied, that the medullary
substance of the brain itself has some share in the vis nervosa.
We cannot, however, determine by experiment, whether an ex-
ternal impression which reaches the brain but is not felt, does
not develop some animal action through the medullary matter
of the brain, although it causes no material external sensation
(46, iii). For, although it excites the most energetic movements
through the nerves, yet the same phenomena occur when the
head is wholly severed from the body (357), consequently the
external impression is changed into an internal lower down,
probably in the ganglia (48), to produce the nerve-actions, for
it would appear as if the condition absolutely requisite to the
change of the external impression into an internal in the brain
and its reflection is, that it develops therein a material external
sensation (25). Nevertheless, there are cases in which it must
remain doubtful whether an external impression does not produce
purely nerve-actions through the medullary substance of the
brain, for when the latter is injured in an animal, the body is
convulsively agitated (Haller^s ^ Physiology,^ § 368). It has
been already shown (132), that this may constitute sentient
actions of an external sensation of pain, because the medullary
substance also transmits external impressions to the origins of
the fibrils of the irritated nerve, or of the fibrils of the cerebral
medulla, and can excite therein material external sensations
which may act reflexly by means of their internal impression
on the brain, and through it on the nerves in the mechanical
machines. But if a similar external impression on the medul-
lary substance should not be felt, and yet excite movements
(convulsions), would not these be no other than mere nerve-
actions of an external impression on the brain, and must not
the brain, consequently, possess a vis nervosa of external impres-
sions in addition to its animal-sentient forces ? It is difficult to
determine, whether external impressions be felt or not, and in
the latter case, whether they produce the same movements as
in the former. Although indeed many injuries of the brain
are not at all painful or manifest, and foreign bodies may lodge
therein for a lengthened period without the knowledge of the

204 ANIMAL FORCES. [ii.

patient, still it is probable that sometimes external impressions
on the brain itself excite nerve-actions, and it may really be
capable in some degree of the vis nervosa of external impres-
sions. Many facts appear to corroborate this. ^'^A certain
person had a piece of bone driven into his brain. For a long
time no results followed, but at last spasms and death took
place from a large ulcer of the brain.'^ (Haller.) Still nothing
certain can be stated on this point (624, iv). It is more
probable, however, that an internal impression on the brain,
not proceeding from conceptions, excites, as nerve-actions, the
same movements that it would have excited if it had proceeded
from a conception, since this continually takes place in the
spinal cord, which is analogous to the brain (12^). Indeed, in
the case just mentioned, when an external impression, though
not felt, excites animal movements in the body, they must have
been caused by the external impression reflected independently
of the animal-sentient force, and without the intervention of a
conception, and acting as a mere internal impression. But
without laying much stress on this doubtful case, there are
many other reasons for recognising the existence of a vis
nervosa in impressions on the brain not caused by conceptions.
When in a plethoric person the brain becomes congested, as in
stooping, and the small arteries in the optic nerves are dis-
tended, and stimulate the origin or trunk of the nerves, this
internal impression in the brain is transmitted downwards to
the termination of the nerve in the eye, and there causes
an external impression which is transmitted upwards (31), and
excites in the mind an imperfect external sensation (148). This
imperfect external sensation of various false appearances before
the eyes, is a manifest proof, that internal impressions which do
not depend on conceptions, are transmitted through the brain,
and have the same actions as those which proceed from con-
ceptions ; for just as v&ry vivid imaginations, or passions, cause
(as sentient actions) imperfect external sensations of various
appearances before the eyes (148), so in this case, the pressure
of blood in the optic nerves at their cerebral origin acts as a
nerve-action, and sparks and motions are seen before the eyes
as vividly as if they were real. Now since the optic nerve is

• Fide foot-note to § 34.— Ed.

CH. 1.1 NERVE-ACTIONS IN GENERAL. 205

I!
in the brain, constitutes a portion of it, and is close to it in its

course, this fact can be received as a proof, that there is a vis '

nervosa seated in the brain itself, which develops the same

jinovements as if a conception irritated in a similar manner the

ime spot in the brain, and, consequently, as if the action were

jffected by the animal-sentient force of the brain.

374. The medullary matter of the brain having some share
Jn the vis nervosa, it is certain that the cortical substance also

endowed with it, since its peculiar function is to secrete the
ital spirits from the blood, and supply them to the other
dmal machines (11). Like all secretions, this process is at
jast partly animal, and not a sentient action (159); it is there-
fore a nerve-action of the vis nervosa of the cortical substance
(353), and subject to the same laws as other secretions, which,
is we shall subsequently show, are effected simply by means of
ihevis nervosa. (Vide §§ 471, 530.) As the secretion and dis-
dbution of the vital spirits is a process of the highest import-
ice to animal life, this vis nervosa of the brain demands great
jonsideration in animal physiology.

375. The nerves, however, must be considered as the prin-
sipal seat of the vis nervosa, and rightly give it its peculiar
lesignation. But the question arises, whether the nerves are
mdowed with their vis nervosa universally and without limita-
tion, or whether only in virtue of their relations to the me-
jhanical machines with which they are incorporated. As,
lowever, the sensory nerves possess a vis nervosa as well as the
lotor, it must be a general property of the nerves, or in

>ther words, the two kinds of vis nervosa are primary animal
Forces proper to the nerves.

376. An external impression on a sensory nerve passes directly
[upwards to the brain (31), and is not readily reflected on its

>urse, or changes into a non-conception al internal impression,

)ecause this class of nerves has no ganglia, in which the course

>f the impression could be changed and reflected (14, 48). The

|pnly way in which this occurs is the reflection in the brain,

diere the external impression, when the mind feels it, is trans-

[formed into a material idea for the internal impression of a

Iconception (121, 129, ii). But in this way, it produces sentient

actions only (97). It is not yet determined whether there be /'

hases in which an impression, when transmitted along sensory ^

206 ANIMAL FORCES. [ii.

nerves, excites visible animal actions in the brain, without
producing a material external sensation at the origin of its
nerves. At least such actions are not observed in syncope, or
profound sleep (49), when light streams into the open eye, or
a loud noise strikes on the ear without being felt. Yet in these
cases some animal actions in the nerve must result, because
the external impression made on it goes to the brain, which is
of itself an animal movement (32), and because the sensational
force of the nerves may be impaired at their cerebral origin, when
in cases of this kind, the external impressions are too violent,
although they are not felt. Thus, for example, deafness
gradually comes on in persons who sleep in a mill, and blindness
from the gleaming of the moon's rays into the eyes during
sleep, &c. Only, these are not perceptible nerve- actions, but
are probably only irregularities of the vital spirits, or imper-
ceptible changes in the medulla of the nerves, and consequently
no definite conclusion can be drawn as to the vis nervosa of
external impressions situate in the sensory nerves.

377. A non-conceptional internal impression on purely sensory
nerves, displays the traces of its actions distinctly enough, as
in the case of the nerves of vision previously mentioned (373).
All the visual and auditory phenomena so often noticed on
stooping, or whirling round too rapidly, or binding the neck
too tightly, are, in fact none other than animal actions (namely,
imperfect external sensations) in purely sensory nerves, excited
by non-conceptional impressions, which are usually produced by
conceptions, and exciting similar actions (148). Analogous
phenomena are manifested in the nerves of taste, and smell,
and touch, so that persons of great sensibility, and especially in
certain morbid states, think they perceive tastes or odours which
are not present, and are not caused by any conception.

378. It was previously observed (150), that true external
sensations may be regarded as being imperfect, when an ex-
ternal impression is really made on the sensory nerves, but by
something within the organ of sense; as, for example, when
in inflammation of the eyes, or in retention of air in the ears,
phenomena are seen or heard which are not in fact so real as
it is thought. These may be termed generally imperfect ex-
ternal sensations from an erroneous judgment ; those mentioned
in the preceding section may be termed imperfect external

CH. 1.] NERVE-ACTIONS IN GENERAL. 207

sensations from non-conceptional internal impressions, and those
in § 148 imperfect external sensations from conceptional internal
impressions. It is manifested^ that the first of these may be
easily but erroneously confounded with the second.

Note. — It may be permitted just to state here, a bearing
which these views have on pathology. Since the phenomena
mentioned, as arising from the causes aforesaid, may be excited
the more readily in proportion as the nerves are more sensitive,
and the conceptions vivid (148), it is obvious, why persons of
irritable temperaments and nerves, and patients in whom the
nerves are unusually susceptible of all kinds of impressions,
have those phenomena so frequently, and how erroneously they
are attributed to a too-vivid power of the imagination. *

379. Now since, therefore, both the brain and sensory
nerves are endowed with vis nervosa, it must be understood,
that its actions are developed independently of the brain
(375, 358, 360), although they can be rarely rendered visible,
as they can scarcely communicate any visible movement (151)
to a mechanical machine. But it is quite otherwise with
[motor nerves ; and as almost all movements of animal machines
are either muscular movements, or effected by means of
muscles, or at least by muscular fibrils, the vis nervosa would
appear, although erroneously (375, 377), to be peculiar to
muscles and muscular fibrils only. This has probably given
rise to the new doctrine in physiology propounded by the
otherwise correct observer, Haller, who has laid down the
principle, that the muscular fibre possesses in itself a primary
animal motor force, which he has termed vis insita, muscular
irritability [die angeborne kraft], {Vide Haller's ^Physiology,'
§ 400, 402.) It is, therefore, of importance to investigate the
subject, and see whether this opinion be well founded or not.

380. To prove that the muscular fibre possesses an animal
motor force peculiar to itself, it must be shown to put itself in
action without the co-operation or assistance of other animal
machines or forces. A probable way of doing this, would be
to separate a muscle from all other animal machines, and then
demonstrate the existence of an animal motor force. But since

j every muscle has its nerves (161), and is therefore connected
with animal machines, which enter -into its substance, and are
so intimately incorporated therewith and so constituting a

208 ANIMAL FORCES. [ii.

whole, that no one has been able hitherto to trace them to
their terminations, it follows that it is impossible to separate
the muscular fibrils from the nerve-fibrils, and so afford the
proof required; so that when it is affirmed, that a muscle
retains its animal force after being separated from its nerves,
it is first of all necessary to show how this separation has been
eff'ected.

381 . The trunks of the nerves distributed to a muscle have
been divided, and the latter have nevertheless been excited to
movement by an external irritant. Is this the required proof?
Certainly not. The division of the trunks does not destroy
the infinitely numerous twigs distributed to the muscle, and so
long as it retains these, the vis nervosa is incorporated with
it. Further :

i. Nerves retain their purely animal motor force derived
from external impressions from the point of impression to
the point of bisection (357, 358). So long, therefore, that it
cannot be shown, that the irritant which moves a muscle after
its nerves have been divided, cannot act impressionally on the
nerve-twigs in the muscle, and that the animal movement in
the latter is not excited thereby, the peculiar animal force of
the muscular fibre is not demonstrated by the experiment.
Consequenth^, although the movement of a heart separated
from the body be renewed and increased by puncture with a
needle, by acrid irritants, by injections of water, &c., still this
does not prove that the irritation induced this activity through
the muscular fibrils only, without the co-operation of the
nerves, for it is incontrovertible that it can produce them in
virtue of the impression on the nerves of the heart, because
every point of a muscle, and consequently of the heart, both
its inner and outer surface, which the needless point touches,
can, in the healthy state, so receive the irritation, that it is
felt, which is only possible by means of nerves ; while further,
the same increased activity of the heart results as an animal
action excited by the external impression which this irritation
causes, whether it goes to the brain or not (357, 358).

ii. The nerves retain also their vis nervosa, excited by non-
conceptional internal impressions from the point of impression
(whether it be at the origin of the nerves, or on their trunks),
to the terminating fibrils (359, 360). When, consequently, the

I

. I.] NERVE-ACTIONS IN GENERAL. 209

a separated muscle is irritated by a physical irritant applied to
the medulla of the trunk, or when an external impression is
reflected in the muscle itself and becomes an internal im-
pression, ia either case movement of the muscle may result,
without it necessarily following that the motor force is situate
in the muscular fibres, independently of the nerves. Unless
it can be proved that the irritant which moves a muscle, whose
nerves are divided, cannot have excited a non-conceptional im-
pression in the medulla of the nerve, whether by causing a
mere physical irritation of the latter, constituting an internal
impression, or by the reflexion of an external impression in
the muscle itself, and that the movement of the muscle is not
produced by such impression, it cannot be allowed that the
peculiar animal force of the muscular fibre is demonstrated by
the experiment (380).

382. But perhaps, it may be urged, a muscle may be so
irritated, as to be excited to movement without the irritant
causing at the same time an impression on its nerves, for it
is not every excitant which causes an impression (32) ; and
possibly the muscular fibres are excited to movement by
irritants which do not animally affect the nerves.

This proposition would be of importance, if it had been pre-
viously shown that muscular fibres are capable of movement,
independently of their nerves ; but this condition is wanting.
Besides, facts prove that the impressions which move muscles
affect also the nerves, because they can be felt. We will, how-
ever, notice the leading points which Haller advances in
defence of his doctrine.

383. Haller observes that muscle is excited to movement
when touched, but nerve is not. Consequently, this irritability,
or the property to be moved animally, from a certain contact,
is proper to muscular fibres rather than to nerves. May not,
however, they possess this property simply through their nerves ?
If the muscular fibres constitute a mechanical machine, excited
to movement by suitable impressions on its nerves, it is the
machine that possesses this capability of movement rather
than the nerves themselves, for an impression never visibly
excites movement in the nerves, but in the mechanical machines
with which they are incorporated (153). The same applies to
all movements of muscle excited by conceptions, or by the will.

14

210 ANIMAL FORCES. [ii.

The spring of a watch produces, by an invisible movement,
the visible movements of the wheels. But should the primary
force which sets them in motion be therefore attributed to
them?

384. Haller observes, that it cannot be proved that from so
few nerves as are distributed in a muscle, so many fibrils can
arise as there are muscular fibrils; consequently the latter
cannot be considered as prolongations of the former. But this
is not necessary ; it is enough that every part of a muscle is
supplied with nerves, and that every muscular fibril, where-
soever irritated by the point of a needle, is sensitive. And
if, as Haller thinks, the nervous fluid communicates this irri-
tability, the fluid is derived through the nerves.

385. Haller advances (§§ 402, 407), that animals without
brain, spinal cord, or nerves, such as polypes, are equally ex-
cited to motion by an irritant, and thus show that the structure
of the muscle alone is sufficient for animal movement. The
vital movements of plants lead to the same conclusion.

The movements of plants, even those of the sensitive plant,
are regulated according to the mechanical laws of movement of
organised bodies. The fibrils in insects, which a touch excites
to animal movements, are not such nerves or muscles as ours,
but still animal machines (6), which are capable of receiving
external impressions (31, 32), whereby they stimulate the
mechanical machines of insects to animal movements (7, 162),
and, consequently, a species of motor nerves (14), and thus
aff'ord no proof of the existence of the primary motor force of
muscular fibre.

386. The heart (it is advanced by Haller) and the intes-
tinal canal are regulated by the vis insita, or muscular force,
and by stimuli, for their movements are independent of the
mind, whilst the movements of the muscles actually dependent
upon the nerves are under the control of the will.

The error here is very manifest : the great man has not
properly distinguished between sentient actions and nerve-
actions. If, 'according to Haller, when movements are excited
in muscles through their nerves, they must be excited in con-
nection with the brain, or the mind, or the will, then it follows
that animal movements excited after division or ligature of
the nerve going to the muscle, are not produced through

I

ti. I.] NERVE-ACTIONS IN GENERAL. 211

the nerves. (Compare 362, iv, and 367, ii, for a further cor-
rection.)

387. The movements dependent on nerves (Haller states)
cease with life, those on the vis insita continue after death;
destruction of the brain, or ligature of the nerves, prevents the
former, the latter continue without brain. Parts that have no
sensation are moved, others that have are not moved; the
will excites or arrests the nerve-motions, it has no power over
the actions of the vis insita.

All this only demonstrates the difference between the cere-
bral [animal -sentient] forces and the nerve -forces, between
sentient actions and nerve-actions. It does not prove, how-
ever, that the nerve-actions are not produced through the
nerves, but that they are not produced through the brain or
the mind.

388. It does not appear then, that this doctrine of Haller
can be supported by valid arguments. There are other ob-
jections to it. No irritant applied to parts un supplied with
nerves, can excite movements. Then irritability is peculiar
to muscular fibre, but all muscular movements are motions of
mechanical machines intimately connected with the nerves, and
the latter cannot be entirely separated from them without at
the same time destroying their structure. Every impression
which excites the muscle irritates also the nerves. An internal
impression on the medulla of the nerves, excites the same move-
ments as when the muscular fibres are irritated. Opium,
which if applied to a nerve deprives it at the point where ap-
plied of its vis nervosa J also suddenly renders a muscle unirri-
table at the point of application (Whytt's Works). Every nerve
retains the animal motor force, even if cut, or tied, or otherwise
so treated that an external impression on it can no longer be
felt (381, i); and, in fact, the same muscular action is excited
by an irritant, whether it be felt or not (204, 357). Now since,
therefore, all muscular movements which are attributed without
adequate grounds to the irritability of muscles can also take
place in virtue of impressions on their nerves, and in undoubted
instances actually do so take place, and as there is no reason
why they should not occur in every case, so soon as the muscular
fibre is irritated, it is probable that no truth in all physiology
is so physically certain as this ; that all animal movements of

212 ANIMAL FORCES. [ii.

muscles are primarily effected through the nerves only, whether
in, or without connection with, the brain and the mind.

389. The two kinds oivis nervosa then, like the cerebral forces,
are primary properties of the true animal machines, and especially
of the nerves (372 — 388), and cause the same workings in the
mechanical machines, whether they be caused at the same time
by cerebral forces or not (362 — 371). That which renders a
mechanical machine external to the brain capable of sentient
actions, namely, the nerve incorporated with it, also renders it
capable of nerve-actions, and there is not a single animal motor
force, independently of it, nor even in muscular fibre.

390. The mechanical machines that are not endowed with
nerves, as tendons and tendinous tissues, bone and cartilage,
&c., are not adapted to the vis nervosa, and primarily their
movements are neither sentient actions nor nerve-actions,
although from their mechanical relations they are either or
both. All such parts of the body without exception have
neither irritability nor sensibility, being deficient in nerves.

391. On the other hand, those mechanical machines that are
supplied with nerves become thereby not only capable of sen-
sation and sentient actions (162 — 179), but also of nerve-actions,
as will be shown subsequently.

392. It has been already shown, that the muscles are moved
by the vis nervosa as well as by cerebral forces (162, 204);
the experiments already detailed prove this amply (357, 359).
The action of the heart (as proved also by experiment — § 357),
is usually a nerve-action, although it is likewise changed by
sentient actions (161, 211). The action of the blood-vessels can
be renewed and continued in decapitated animals that do not
bleed to death too quickly, by purely animal irritants. The
phenomena previously detailed (168, 207) may all take place
as nerve-actions.

393. The natural functions of the oesophagus, stomach, in-
testines, and other muscular canals, are ordinarily (as has been
already stated) rather nerve-actions than sentient actions (170,
174, 212), and experiments on portions separated from the
body confirm the statement. These remarks apply to the
diaphragm, and similar muscular structures (171, 359).

394. The glandular and other secreting tissues belong to the
same class as the preceding ; their functions going on without

IH. I.] ACTION OF THE VIS NERVOSA. 213

msation and after decapitation. {Vide §§ 172 — 176 and 209 —
115.) The cortical substance of the brain is to be classed with
le secreting organs.

395. The functions of the sexual organs both in the male
id female are carried on not solely by means of the cerebral

"forces^ but often through the vis nervosa only, as experiments
on decapitated animals demonstrate (357).

396. The movements of the limbs display the influence of
the vis nervosa strikingly, because its action is greatest on the
muscular portion of the organism. These, as a thousand ex-
periments prove, may arise as nerve-actions, although they
usually occur as sentient actions from external sensations and
sensational conceptions, instincts, and passions, as well as
volitionally. Thus, a decapitated animal will stand, move for-
wards, raise itself up, leap, fly, or flutter its wings, seek food,
clean, defend or conceal itself, copulate, &c. A decapitated
man immediately after decapitation struggles to free his hands,
attempts to stand upright, and to stamp with his feet ; if the
head of a pigeon be cut ofi* whilst it is running, it continues
to run on for some distance, until it knocks against something ;
a frog leaps forward without its head, so also a headless fly flies,
a snake, a fish, a worm, writhes and twists about, if touched,
although wholly deprived of sensation ; a fly makes the move-
ment of brushing its eyes by a natural instinct, although its
head be cut off^; a headless snail seeks its food by its usual
plan of feeling about; a decapitated tortoise does the same
thing, and will live for half a year after decapitation, and raise
itself up, or endeavour to do so if placed on its back ; an ear-
wig nips with the nippers of its abdomen at its own separated
head, when the head bites the abdomen; the abdomen of a
wasp will sting; animals that fight with their hind feet use
them vigorously when decapitated, at every irritation applied to
the nerves; butterflies, caterpillars, and silk-worms copulate
after decapitation, and they and flies deposit their ova; in
short, all the instinctive actions of animals are sometimes seen
to occur as nerve-actions; and it naturally follows that they
occur at first in newly-born animals as such, and that it is only
after the perception of external sensations that they become
sentient actions (269).

397. Thus the dominion of the vis nervosa is in reality as

214 ANIMAL FORCES. [ii.

extensive as that of the cerebral forces, and it would be difficult
to discover a movement which occurs as a sentient action, which
may not be also effected by the vis nervosa, although, in many
cases it is not practicable to show this by satisfactory experi-
ments. The greater number of movements take place by means
of muscles or muscular tissues, whether they be sentient or
not (379). That, however, which a muscle can effect when
stimulated by the cerebral forces, it can also effect very easily
solely by means of an unfelt internal or external impression
on its nerves (364, i), for in either case it is stimulated to the
same movement (356). It is not surprising, therefore, that
suitable impressions on the motor nerves can act as the primary
iucitants to all nerve-actions independently of sensation or
thought, and maintain the whole machinery of an animal body
in continued working and reciprocal functional activity, just as
is effected by external sensations and their sensational concep-
tions by means of internal impressions on the brain. For we
must remember that an impression not only develops the same
movement as it develops when felt, or as when excited by con-
ceptions ; but that, just as from external sensations and their
sentient actions, other sensational conceptions and their sen-
tient actions are produced and combined together, whence the
connected acts of the cerebral forces arise, so also unfelt external
impressions cause unfelt internal impressions, from which some-
times other external impressions originate; all which have
unitedly their special nerve-actions, constituting connected and
combined acts. To show this more distinctly, and to render it
by successive proofs more probable and obvious, how an animal
body can be regulated and excited, as well to automatic as to
what are usually volitional movements, independently of mind,
as regularly and connectedly as if directed by thought and sen-
sation, we must now consider the relations of the two kinds of
vis nervosa to each other ; and thus facilitate a comprehension
of this important matter, which will, for the first time, be placed
in its proper light in the succeeding Chapters.

398. Either of the two kinds of impressions may reciprocally
excite the other, without the intervention of the conceptive
force ; and both can excite the same or other movements, either
consentaneously or consecutively; and from their reciprocal
connection whole series of acts may take place as the result of

CH. I.] RELATIONS OF IMPRESSIONS. 215

a single impression, and be combined together by the proper
animal force of the body ; although there be neither sensation
nor thought, even although the animal possess neither brain
nor mind, or, if it possess mind, without the mind in any way
influencing the acts. Consequently, the general principles that

I we shall lay down as to the connection and reciprocal influence
bf the two kinds of vis nervosa with and on each other are
equally valid, whether or no external impressions be felt or
pternal impressions be excited by conceptions.
« 399. An external impression is changed into, or develops an
internal impression, whenever its course which is naturally
towards the brain from the terminating fibrils, is so reflected
or turned back, that it returns in the direction from the brain
downwards to the branches and terminations of the nerves (32,
121). This usually takes place in the brain in animals endowed
with cerebral forces, by means of the external sensation of the
external impression (129). But since the external impression
without either being felt, or without either the presence of the
brain or of mind, causes the same movements as are excited by
the internal impression of its external sensation (358), it must
become a non-conceptional impression without this transition
into a sentient action taking place, because it is turned back
and reflected in its course to the brain, before it forms the
material external sensation in the latter. There are grounds
for supposing that this can take place in the brain itself (373,
376). In the nerves, however, there is no place in which it can
occur, except the ganglia of the motor nerves (14), and at their
separation into branches and fibrils (48). According to all
probabihty, these ganglia and points of division of the nerves,
perform in the motor nerves the office of the brain in relation
to the external impressions, since they deflect these from their
course upwards, and communicate an internal impression, either
to other nerves and their branches, or to different fibrils in the
same nerve, conducting in the direction from the brain down-
wards ; whereby these twigs and fibrils are suitably stimulated,
and such muscular movements excited, as would have been
caused if the external impression had reached the brain and
had been turned back or reflected from thence by the inter-
vention of an external sensation (364, ii). If this reflexion of
the external impression be made upon the same efi'erent fibrils,

216 ANIMAL FORCES. [ii.

as transmit internal impressions, then the nerve-actions produced
by the two kinds of impressions are the same, and also identical
with the direct sentient actions of the external sensations (188).
If, however, other nerves, or nerve fibrils, be the channel of the
reflexion, other nerve-actions are excited, which accord with
the sentient actions of the external sensation produced by th(
impression so reflected (97, 124; compare also 435, 436).

400. In so far as an external impression can excite a non-con-
ceptional internal impression, it may also induce all such nerve-
actions as can be produced by the latter. Now, these are in
fact the same as sentient actions (363) . Consequently, an external
impression although unfelt, can induce the same movements
which, when felt, it induced as sentient actions (364, i). In the
animals destitute of brain, as sea-anemones, tape-worms, &c.,
and in microscopic animals, polypes, &c., external impressions,
although unfelt, can be the incitants of the machines, whereby
they are incited to all those movements which arise as sentient
actions from sensation, when the impressions are felt by these
or other animals (366). If, therefore, brainless animals like
those alluded to, are so formed by nature, that all their external
impressions are reflected, and changed into non-conceptional
internal impressions, in the plexuses, ganglia, and points of
division of the nerves, and which move their Hmbs just as they
would have been moved by sentient actions, it ought not to
be matter for surprise, that such animals although without
thought or sensation, appear to act as designedly, spontaneously,
thoughtfully, and volitionally, as animals really endowed with
mind.

401. A non-conceptional impression can develop obvious
animal movements in the purely sensitive nerves (377). Still
more can it put muscles into action by means of the motor
nerves (360). These muscular movements in the healthy con-
dition of the individual (225), are often felt, and consequently
cause an external impression on the nerves of the muscles (35),
and which, even if not felt, can excite the same movements
as if they were. In this way non-conceptional impressions
can produce external impressions, which, although not felt,
still imitate in the mechanical machines the sentient action of
their external sensation. Thus, if the spinal cord of a headless
frog be irritated with a needle, the internal impression thus

!H. I.] RELATIONS OF IMPRESSIONS. 217

)roduced acts in the same way as a volition^ and the animal is
jxcited to raise itself up. Whilst the muscles are contracted
this end^ their nerves have an external impression commu-
licated to them by the movement, which irritates them and
rther muscles to new movements_, so that the animal either
)laces itself upright, or balances itself, or turns round, retreats,
lakes a spring, swims, &c., according as the irritation of the
jpinal cord has excited the first movement.

402. To determine more definitely the relationship which the
two kinds of impressions bear to external and internal sensations,
re will still further consider their relations. An external im-
)ression is necessarily required for all external sensations (35),
id, consequently, constitutes a portion of them, but only in so far
it is felt, for the entire external sensation is in the mind — is
conception (34) . Taken alone, it is a portion of the material
external sensation, but only in so far as it forms therewith a
material idea at the origin of the nerves which have received
it (34). Popularly, and indeed in books also, external sensation
generally, and in its widest signification, is termed feeling
[Gefiihl], and attributed to the five senses, for it is said that
the eye feels the rays of light, the ear feels the undulations of
the atmosphere, &c. It is also customary to apply the term
sensation and feeling to animal bodies, for it is said that the
hand, the flesh, a nerve, feels and has sensation. According
to this established signification of the terms, it may be said
that the external impression is an element in feeling (the
material external sensation), and since it produces the same
phenomena, whether it reaches the brain to form material
ideas in it or not, the name is derived from a part, and the
external impression thus becomes to be designated the external
feeling [Gefiihl] of the nerves (32). In this way, the external
impression and the material external sensation in the brain
may be distinguished by convenient terms, both of which are
figurative, the latter being termed sensation [Empfindung], the
sentiment of Buff'on ; the former, the external feeling of the
nerves — sensation of Buff'on. Thus it is said, that the
tongue, the hand, the ear, have sensation, whilst a decapitated
animal, or an excised heart, or portion of intestine, so long as
it is excited to motion by a purely external impression, is said
to have feeling left in it, or that the acephalous embryos, which.

218 ANIMAL FORCES. [ii.

are born destitute alike of head and brain, but are moved,
nevertheless, by external impressions, have feeling ^ &c.

403. The external feeling of the nerves, or what is identical
therewith, the external impression, is that animal force of the
nerves, the properties of which have been already stated (32,
34, and 364, iii). According to the laws and principles pre-
viously established, it is in no degree mental, although it excites
external sensations, being neither conception nor sensation
[Empfindung], but seated externally to the mind in the nerves
(98, i, &c.) Neither is it a sentient action, but a property
independent of the conceptive force, peculiar to and innate in
the nerves, of being excited to this wonderful movement by an
irritation of their medulla, which is the case with no other
bodies, nor with any purely mechanical machines, and is
wholly independent of the physical and mechanical laws of
motion ; — a movement which penetrates the brain, and awakes
the soul to sensations, and at the same moment puts the ma-
chines of the body into motion, in a way that no other force
in nature can attain to.

Note. — So important an animal force merits well to be
specially distinguished as well from sensation, which is a pro-
perty of mind, as from the physical and mechanical forces of
inorganic machines. I have termed it for the reasons previously
stated (402), the feeling of the nerves, but the expression is so
new, that although quite correct, it may lead the reader to mis-
apprehend its meaning and application. I have, therefore, in
this work used the term external senselike (sinnlich) impression
in its stead.^

404. If this difference between external feeling (the external
impression) and external sensation had been better observed,
that erroneous proposition of the ancients (renewed by Whytt)
would have been long ago forgotten, which propounded that
the soul was diffused throughout the entire organism, because
in sensation the mind determined and fixed the point where
the nerves received an external impression, or in other words,
where it felt. Even a materialist cannot defend so fundamental
an error. If the mind be that which has self-consciousness,
or which forms ideas, the nerves can constitute no part of it ;

' The reader is particularly referred to the note to § 31 for an explanation of this
term. — Ed.

CH. I.]

NATURE OF IMPRESSIONS.

219

for they at least, can neither conceive nor perceive, if we grant
khat the brain can ; nor can sensation [das Empfinden] be con-
nived to be a property of the nerves, by those who maintain
fchat the brain is the soul. From the point of impression at
the termination of the nerves to their origin in the brain, the
external impression (external feeling) is nothing more than a
ddden movement in the nerve, which, at the point where it
forms a material idea, is only first perceived, conceived, felt,
)bserved by the soul (80). If, therefore, the materialist main-
lins, that it is the materies (Stoff) of external sensation, still
it does not become an external sensation until it enters this
)oint of sensation [Fiihlpunkt] in the brain ; and it cannot be
[antecedently to this, while in the trunk of the nerve from whence
puts the animal machines which it can regulate into motion,
[either an external sensation or sentient moving force ; but is a
[pure vis nervosa [eine blosse Nervenkraft] , and all its operations
:e purely nerve-actions and not sentient actions from external
sensation (98, i).

405. The distinction between internal impressions with con-
sciousness and without, is equally as great as that between an
external impression and external sensation. The conceptional
internal impression, which operates in the mechanical machines,
is a material idea at the point of origin of a nerve in the
brain, where the mind felt in virtue of its self-consciousness
[Selbstgefiihl] ; (80) and so soon as this hidden movement at
the origin of the nerve (the material idea) passes onward from this
[point of consciousness [Fiihlpunkt der Seele] over to the nerves,
[to the end that they may put the mechanical machines into
motion, the internal impression becomes nothing more than
what the external impression is before it enters the point of
consciousness in the brain ; it is therefore neither a sensation
nor conception, but a hidden movement in the nerve, which
continues downwards from the brain towards the terminations
of the nerves, and puts the mechanical machines into motion
to which they are distributed. In so far as a conception was
the basis of this animal movement, and in so far as the impres-
sions passed from the brain downwards from the point of con-
sciousness, at which the mind perceived the conception of this
material idea, to that extent the movement is a sentient action
(97) ; and the internal impression (the material idea) is an

220 ANIMAL FORCES. [ii.

animal-sentient force. But if an irritation of the medulla of
the nerve constituted the internal impression, and if it did not
depart from the point of consciousness, that is to say, from the
locality of the material idea of a conception, then it is not an
animal-sentient force, and the resulting movements, although
similar to sentient actions, are not such, but nerve-actions of a
vis nervosa. This may be termed the internal feeling of the
nerves, to distinguish it from internal sensations (80, 121).

406. This internal feeling of the nerves, or what is identical
therewith, the internal impression not produced by concep-
tions, is that animal force of the nerves, in virtue of which
they receive in their medulla a certain impression, not mental
in its origin, and communicated to them in the direction
from above downwards ; transmit the impression thus received
in the same direction to their minutest fibrils ; and excite in
the mechanical machines with which their fibrils are incor-
porated, the same movements as would have occurred if the
impression had originated from conceptions. It is a property
peculiar to and innate in the nerves, in virtue of which a
stimulus applied to their medulla in the direction from above
downwards excites hidden movements in them, which no other
bodies and no purely mechanical machines could acquire from
such a stimulus, and which are not subject to the physical
and mechanical laws of motion. These hidden movements
are propagated by the nerves to the mechanical machines to
which they are distributed, if no hindrance arise, and move
them in the same way as they are usually moved by con-
ceptions.

407. According to these views as to the distinction between
the cerebral force and the internal feeling of the nerves, it
follows, that it is manifestly erroneous to say (as is said in our
elementary works), that the animal movements excited by the
internal impression are mental, or at least, cerebral. Hence
have arisen the erroneous views, which have had so injurious
an influence on pathology and therapeutics ; to the effect that
the phenomena of fevers, spasmodic diseases, epilepsy, paralysis,
and all nervous diseases in general, depend upon some aff^ection
of the brain, and that they must be cured by remedies which
act upon that viscus. On the contrary, an internal impression
excited in nerves far distant from the brain by various irritating

CH. 1.]

NATURE OF IMPRESSIONS.

221

jents in the body, especially by reflected external impressions
rhich are not felt, may induce all these affections quite inde-
mdently of the brain, and must be cured by the removal of
lese agents.

It is manifest, too, with what justice we have controverted
le doctrine of Haller, that the motor force of the nerves can
leither arise nor continue independently of the brain, and how
)rejudicial such views must be to pathology and the practice of
nedicine, especially when advocated by so eminent a physio-
logist. It has simply escaped his notice, however, for it could
be shown by a hundred passages in his writings that the truth
was known to him.

CHAPTER II.

ON THE VIS NERVOSA OF EXTERNAL IMPRESSIONS.

408. After having considered the two kinds of vis nervosa in
general (355), we will consider them separately, and, firstly, the
vis nervosa of the external impressions, generally and specially.

SECTION I. ON THE VIS NERVOSA OF EXTERNAL IMPRESSIONS

IN GENERAL.

409. An impression passes upwards to the brain, along the
nerves, from the point of impression. If it reaches the cerebral
origin of the nerves, it develops there an external sensation,
and the actions which it thus produces in the body are sentient
actions from external sensations (32, 34) . On the other hand,
all actions which it produces before it reaches the brain, or in
other words, before it becomes an external sensation, are nerve-
actions of its vis nervosa (98, i, and 353). It is the latter which
we have to consider here.

410. When a nerve is irritated with a needle, it receives
both an internal and external impression ; if, for example, it be
a motor nerve, the latter acts on the muscles above the point
irritated, and the former (or the non-conceptional internal im-
pression) on the muscles situated below, or in a direction from
the brain. Both kinds of movement are equally nerve-actions.

411. If when, as in many external sensations, the irritation
is so applied that the nerve is mechanically concussed below
the point of irritation, and this concussion of the lower portion
of the nerve acts as another external impression, and thus
develops movements in the parts below, they will be the same
as those induced by the first irritation (37).

412. Since the external impressions that are made at the
same time on several nerves, do not hinder or confuse each
other in their course to the brain, but pass along the same
nerve, or through the spinal cord, unmingled with each other
(39) ; it follows, that they can produce their corresponding

cii. II.] VIS NERVOSA OF EXTERNAL IMPRESSIONS. 223

nerve-actions, without the one kind interfering with the other.
Experiments on decapitated animals establish this fact.

413. It is as difficult to discriminate the various kinds of
impressions from their nerve- actions as from their external sen-
sations (40, 41). An irritant may often act when we cannot
detect it, or when we think it not an irritant ; and hence it is
that the phenomena of idiosyncrasies are so inscrutable (52).
The heart is more stimulated by blood than by acrid irri-
tants, the urinary bladder by water, the intestinal canal by air
(Haller's 'Physiology,' §402). An irritant which a priori
would be expected to be more active than another apparently
less irritating, is in fact less active : many parts that remain
unchanged when the most acrid chemical spirits are applied
to them, are excited to convulsive movements on being irritated
by the point of a needle. It is in fact impossible to infer from
mechanical or physical laws, what nerve-actions will follow on
certain kinds of irritants ; the laws of their action can only be
known by experiment and observation.

414. It is not every impression on the nerves that is adapted
to their structure, but only that which excites animal actions
(31, 32) ; nor is it adapted if it be not made so as to excite that
hidden movement in the nerves, which when propagated to the
brain, excites external sensations ; or excites movements in the
mechanical machines when propagated to them. We have
already discussed the former (42, et seq.) : we will now treat of
the hidden movements in the latter, as disclosed by nerve-
actions, and inquire under what circumstances they take place.

415. i. If, at the point where a nerve receives an external
impression, it be completely incorporated with a mechanical
machine which is capable of performing certain movements at
that point, as in muscles for example (161), it excites these
directly to perform their animal movements ; and the nerve-
action thus excited requires nothing more than the external

I impression, whether it proceeds further or not. Thus a mus-
cular fibre in an excised muscle contracts immediately at the
point where a point of a needle irritates it, or a particle of salt
is dissolved upon it.
ii. If a nerve causes nerve-actions, by means of an external
impression in parts remote from the point of impression, or even

224 ANIMAL FORCES. [ii.

primarily received the impression, or through its own efferent
fibrils (127), the impression is transmitted along the nerve
upwards to the brain ; but ere it reaches there, it is turned
from its course, and so reflected downwards, that it excites (as
an internal impression) the nerve of the other remote parts, or
the nerve-twigs or efferent nerve-fibrils of the part receiving
the impression ; and this internal impression, which is nothing
else than the reflected external impression, thus reaches the
mechanical machine which has to perform the nerve-action.
This is proved by undoubted experiments. If the toe of a frog
at rest be pricked, the external impression thus made goes to
the brain. From thence it is reflected upon the limbs, and
the animal rises up and springs forward. But if the head be
cut off, and the toe be again pricked, the same motions take
place (357). In this case, the external impression on the toe,
must pass upwards towards the brain, although it cannot reach
it, for if the nerve be divided in the thigh, so as to prevent
its transmission, the motion does not take place. Further, it
is obvious that it is reflected on the nerves of the limbs, as an
internal impression, and along their twigs to their muscles,
because no other part of the body, except this single toe
which was pricked, receives an external impression. Again,
supposing while one toe is pinched, that the nerve of the other
leg be divided ; in this case, the movements will be repeated in
all the parts except that whose nerve is cut through. This
explains what takes place in similar circumstances, when an
impression is made on the spinal cord, and spasms and con-
vulsive movements are excited in all parts below the point of
irritation, except those the nerves of which are cut through.
The reflected external impression passes as an internal im-
pression to, and only excites movements in those muscles to
which it can be transmitted from the point of reflexion.

iii. Examples of this class of nerve-actions are to be met
with daily, which sometimes are mistaken for sentient actions
(which they often accompany), sometimes for special operations
of unfelt external impressions acting through the brain, some-
times for inexplicable sympathies. Numerous instances of this
kind may be found in Haller^s ' Physiology,' vol. iv, p. 529,
and B. 10, Absch. vii, ^ 30-31.

416. As the brain secretes the vital spirits, and as in

II.] VIS NERVOSA OF EXTERNAL IMPRESSIONS. 225

mimals endowed with brain, it is requisite that the nerves be
supplied with these, as the medium for the transmission of
impressions, the brain must be considered as being necessary
at least to the continued production of nerve-actions; unless
the animal be so constituted, that the vital spirits are secreted
in the medulla of the nerves themselves, or in their ganglia,
as is the case in avertebrate animals (362). Compare also
§ 673. This is one of the reasons why in animals endowed
with brain, the vis nervosa is abolished so soon after de-
capitation ; for the vital spirits gradually flow out of the nerve-
medulla, and are not re-produced. So long, however, as a
sufficiency of vital spirits remain in the nerves, their vis nervosa
continues to act with vigour, thus establishing its independence
of the brain. In many animals, the vis nervosa is retained after
decapitation for days and weeks, and in turtles for half a year.
The destruction or removal of the brain, which destroys con-
sciousness, hinders therefore the continuance of the vis nervosa,
but only so far as it prevents the influence of the blood in the
muscles (161) ; or, in other words, in proportion as the nerves
thereby become gradually more feeble and dead, but not because
the co-operation of the brain is a part of the vis nervosa,

417. Those portions of animals which are supplied with
nerves highly susceptible of impressions (160), are endowed
with more acute external feeling, and a stronger vis nervosa
from external impressions (403) than others ; as for example,
the heart, stomach, and intestines. Structures with few nerves,
or nerves little irritable, are endowed with a feebler vis nervosa
from external impressions ; and those to which no nerves are
distributed, have neither external impressions, nor vis nervosa
(390). Thus bones, tendons, cartilages, and ligaments, however
they may be irritated, display no traces of movement. A part,
to possess the vis nervosa of external impressions must have
nerves that can receive an impression, fully incorporated with
it ; the more numerous such nerves, the more varied the im-
pressions, and the more susceptible they are to these impressions,
the more vivid its external feeling, and vice versa (44, 47) .

418. When an external impression in a nerve distributed to
a mechanical machine, excites a nerve-action in the latter at
the point where the impression is received, it is termed,
whether the impression be transmitted onwards or not (415, i), .

15

226 ANIMAL FORCES. [ii.

in so far as it is independent of that transmission^ its direct nerve ,
action. The conditions requisite to the production of this are — •

i. That the mechanical machine be endowed with nerves
(160, 417).

ii. That its nerves be so touched, that an external impression
be communicated to their medulla (414).

iii. That the mechanical machines be capable at the point of
impression of such movement as the impression can excite.

419. The direct nerve-actions are to be distinguished from
the indirect, which are induced either remotely from the point
of impression, or, if they arise in the machines whose nerves
are irritated, are not excited through those nerves, but through
some other, or else through the efferent fibrils of the irritated
nerve (127) . The conditions under which they arise, are more
numerous than the preceding, and to understand them the
following must be premised.

420. Take a nerve which pursues a direct course from
the brain to a limb, and penetrates tissues, without giving
off a single branch to any organs or structures in its course,
having neither ganglia nor plexuses, and instead of ending in
numerous fibrils, gives off one only to a simple muscular fibre.
If the latter be irritated with the point of a needle, and the
nerve thus receive an external impression, the fibril contracts,
and so a direct nerve-action is produced, whether the im-
pression be transmitted upwards or not (161, 204). But sup-
pose it to be so transmitted, what then happens ? Since there
are no ganglia or plexuses, in which the impression can be
reflected, and since there are no branches whatever given off,
the tissues it penetrates cannot be excited to action; but the
impression must go on to the brain, in which, if it reach the
brain, it causes sensation, and can then be reflected from the
brain as the internal impression of an external sensation, and
thus again move the fibrils it moved before (188, 127). This
result is, however, a sentient action, and not a nerve-action.

421. When, therefore, an external impression on a nerve ex-
cites, in addition to its direct nerve-actions, a movement in remote
machines, or in the same machine, to which it is distributed by
fibrils of nerves distinct from that which received the impression^
or by efferent fibrils ; or, in other words, when it develops indirect
nerve-actions, it follows that either the nerve itself is deflected,

KJJ.

I

tf

CH. II.] NERVE^ACTIONS, EXTERNAL IMPRESSIONS. 227

from its course, or it must have ganglia, plexuses, or points of
division, in which the impression itself may be deflected in its
course upwards. In this case, the impression is reflected either
in the nerve itself, or on its eff'erent fibrils, or in the ganglia
and plexuses, on altogether diff'erent nerves, and thus it passes
downwards, as a reflected internal impression, but unfelt, and,
as such, can excite nerve-actions in those machines suppliied
with the nerves, along which it is reflected.

422. The conditions, then^ which are requisite to the pro-
duction of indirect nerve-actions by an external impression,
are —

i. The external impression must be transmitted upwards, to
that point of the nerve where it is reflected, and changed into
a non-conceptional, internal impression j as^ for example, to
that point where the efferent fibrils of the nerve are excited by
the external impression, or where the nerve-fibrils are given off
which subserve to the required nerve-action ; or to the ganglia,
or to the plexuses which contain them (415, ii).

ii. Reflexion of the external impression, or its change into a

n-conceptional impression, must actually take place there,
'y in other words, must duly affect the efferent or other fibrils
bove mentioned (121).

iii. This new internal impression must also be transmitted
to, and reach, the mechanical machines to which the fibrils are
istributed (128, 415).

The indirect nerve-actions of external impressions are, con-
sequently, no other than nerve-actions of non-conceptional in-
ternal impressions, originating from external impressions turned
back from their course towards the brain, and unfelt.

423. Although this reflexion of external impressions fre-
uently takes place, and always in certain circumstances or-

ined by nature (48), yet it does not follow that it takes place
solutely in every case. On the contrary, it is often seen
at an external impression, which excites in certain machines
ct or indirect nerve-actions, excites also, at the same time,
the same movements in other machines regulated by other
nerves ; nay, is even felt, and produces them as sentient actions
of the internal impression of the external sensation (363, 364, ii),

424. An indirect nerve-action from an external impression
cannot arise, or is prevented, —

228 ANIMAL FORCES. [ii.

i. If the meclianical macliines which ought to be its seat,
are not endowed with nerves.

ii. If their nerves be not irritated, or only so irritated that the
nerve-medulla does not receive thereby an external impression
(418, ii). Something more than mere irritation is required to
this end, as a strong excitant fails to excite the nerve-actions,
if- it be not such an one as stimulates the nerve suitably.
(Compare 413, 414.)

iii. If the mechanical machines be unfit, at the point of
impression, to manifest the nerve-actions to which they are
stimulated (418, iii). In such cases, the impression has no
direct action ; but leaving the machines unchanged, acts upon
them indirectly, and causes an indirect nerve-action, or, if it be
felt, a sentient action. Thus, a stimulus applied to a muscle,
excites no contraction, if it be already affected with spasm,
although it may be felt, and excite spasmodic movements in
many other muscles. (See §§ 208, 464.)

425. An indirect nerve-action from an external impression
cannot arise, or will be prevented, —

i. If the external impression do not reach to the point,
where it can be so turned as to be reflected (422, i), as when
the nerve is tied, or divided.

ii. If the external impression, although it reach this point,
be not changed into a non-conceptional impression, or, in other
words, at least partly deflected from and hindered in its course
to the brain ; as when there is induration, or other disease, of
the ganglia, or plexuses, or of points of branching.

iii. If the transmission of the reflected impression downwards
to the machines be prevented, as by ligature ; it being under-
stood that the machines themselves are capable of the actions
(422, iii).

426. Since we can prevent the action of irritants and of ex-
ternal impressions, and hinder their course, reflexion, and trans-
mission downwards, so also nature herself regulates them ; and
the impressions do not act blindly and necessarily, being pre-
vented in various ways, and guided so as to excite the mechanical
machines for specific objects, just as various external sensations
are prevented by various means, to the end that the conceptive
force be not excited by every irritant applied to the body
(47 — 51). It is of importance to comprehend all the modes

[CH. II.] NERVE- ACTIONS, EXTERNAL IMPRESSIONS. 229

which, in the natural condition, the nerve-actions of external
ipressions can possibly be prevented, and we will therefore go
[through them.

427. All those natural obstacles which hinder external im-
jressions arising, prevent them also from developing direct
lerve-actions (47, i, ii, iii).

i. If a part be not supplied with nerves, nerve-actions cannot
ike place in them : of this kind are bone, cartilage, 8zc.

ii. If the nerves of a part be so protected by nature, by

leans of membranes, mucus, &c., that they cannot receive

irious impressions, they cannot excite the corresponding nerve-

jtions, although they may be moved by internal impressions,

md manifest, through these, either sentient actions or nerve-

ictions.

iii. If a nerve is naturally susceptible of certain impressions
mly, these alone can excite the direct or indirect nerve-actions,
id none others (424, ii ; 47, ii) . Various insects, as spiders,
5ndure the application of very acrid irritants, from which other
limals would experience violent inflammation and convulsions,
md yet feel the slightest irritation of another kind (413, 414) . It
often observed, in animals endowed with sensation, that some
lerves are only susceptible of certain impressions for a 'given
jeriod, consequently the nerve-actions dependent thereon cease
soon as the period of susceptibility terminates (265). The
)henomena of idiosyncrasy belong to this class.

iv. If a mechanical machine be endowed with nerves, and

'^et is naturally incapacitated for animal movement at the point

[of impression, no direct nerve- actions can arise therein (424, iii) .

^he liver, spleen, &c., are incapable of motion at the point

firritated, namely, the substance of the viscus, and therefore no

external impression excites movement in them.

428, V. If the external impression be too feeble to reach a
point of reflexion, to be there changed into an internal impres-
sion, it may excite a direct, but not an indirect nerve-action,
although the body be in the natural state (425, i). Thus, in
a decapitated animal, a slight irritation of a muscle excites a
gentle contraction of its fibres, without any of those convulsions
resulting in other parts, which a more powerful irritation gene-
rally produces.

vi. Doubtless there are cases in which, in the natural state

230 ANIMAL FORCES. [ii.

of the body, a certain external impression is not reflected in
its course to the brain, or changed into a non-conceptional
impression, and in which direct actions result, but not those
indirect actions as would have occurred had not the reflexion
been prevented (425, ii). There are numerous instances of
this kind, in which the impression is naturally not felt, and
not transmitted to the brain, and which render it probable that
there are secondary points in the nerves, whence it must be
reflected, and sent in a certain direction, where it is to be
changed into a non-conceptional internal impression. A great
number of external sensations, and also of unfelt external im-
pressions on the stomach and intestinal canal, are never com-
municated to the muscles of the limbs, although these two
kinds of nerves are in close connection : there are also impres-
sions of this kind, which are not felt (48), yet excite the most
violent convulsions. Here we can only say, with reference to
the greater number of these impressions on the nerves of the
stomach and intestinal canal, that the points where the latter
come into contact with the nerves of the muscles, are not duly
excited, or do not reflect the external impression. Since many
of these impressions are, in fact, felt, it is certain that they
reach- the brain, and if they had been reflected, they would
also have excited the muscles to action; unless it be that the
impressions actually reflected do not reach the muscles, being
interrupted (as shown in the next section) in their course be-
tween the point of reflexion and the mechanical machines.
In the examples above quoted, this is neither demonstrable
nor probable.

429, vii. Wlien an external impression on its way to the
brain is actually reflected and transformed into a non-concep-
tional internal impression, but is not transmitted back again
along the nerve which received it, or on account of a natural
deflection by means of intervening ganglia, or plexuses, or is
reflected upon a certain other nerve, the nerve-actions which
usually result from it, do not take place, but those mechanical
machines are put into motion in connection with the nerve
along which the impression is deflected (425, iii). This case
often occurs naturally (137), but the proof is difficult. When
an external impression has caused an external sensation, we
know that it has reached the brain, and that the cerebral

lilt

CH. II.] NERVE-ACTIONS, EXTERNAL IMPRESSIONS. 231

origin of the nerves has received the internal impression of the
conception ; and if the ordinary sentient actions do not result,
we conclude that the internal impression cannot have reached
the mechanical machines (137). But with regard to the non-
pnceptional internal impressions, we have not the direct proof

brded hy sensation, but only secondary evidence, when their

direct nerve-actions remain unperformed, whether they be
"reflected at the point of reflexion [Reflexionspunkte] of their
nerve ; and, consequently, whether the cause of the failure is in
their course to the mechanical machines or not. We can only
incidentally conclude in a case of this kind, that the reflexion
has taken place, if another organ situate below the point of
reflexion, and receiving its innervation from the same nerves,
is excited to action by the same external impression which
ordinarily excites the other organ, but now fails to do so. It
is difficult to adduce instances, hut reasoning from analogy,
(compare §§ 138, 360,) it is probable that the reflexion takes
place, and it is the transmission downwards of the reflected
impression that is arrested.

430. Just as habit enfeebles and prevents many sensations
and their sentient actions, in like manner it influences nerve-
actions from external impressions, as follows :

i. The terminating fibrils may be so changed by the frequent
repetition of an external impression, that they are no longer
capable of the irritation requisite to the production of the im-
pression j and, consequently, no nerve-actions result from the
application of the stimulus.

ii. The sensibility to certain stimuli only, may be destroyed
by frequent repetition of them, whilst with regard to others it
is unaltered (51, ii), and thus the former are no longer able to
excite nerve-actions (427, ii, iii).

iii. The frequent repetition of the same external impression
on the same part of a nerve, may so enfeeble it, that whereas
previously it could reach the point where it was reflected, and
thereby excite indirect nerve-actions, after long habit it cannot
reach that point, and thus its indirect nerve-actions cease,
while its direct continue (428, v) .

iv. Frequent repetition of the same external impression on
the same nerve, can so afi'ect the point of reflexion, that re-
flexion and transformation of the impression no longer take

232 ANIMAL FORCES. [ii.

place (137, iv) ; and thus, althougli its direct nerve-actions con-
tinue, the indirect no longer occur (428, vi).

V. Lastly, in consequence of this frequent repetition of an
external impression, the reflexion ' and transformation may-
take place so imperfectly, that it is not transmitted as a non-
conceptional internal impression, with sufficient force to reach
the accustomed mechanical machines (138) ; and thus the
indirect nerve-actions cease, although the ordinary direct
actions, or other direct actions still occur (429)

431. That continued-frequent repetition, or habit , has con-
siderable influence on nerve-actions excited by external im-
pressions, as well as on external sensations and their actions,
is proved not only by the analogy of all experience as regards
the latter (51), but also by experience in all instances in which
the external impression is not felt. The habituation to various
foods, poisons, &c., are examples of this kind. The movements
excited by these, until a person is habituated to them, are
usually nerve-actions of their external impressions, and con-
tinue to be such, although they may be felt (364, ii) ; but these
movements often cease from constant repetition of the stimulus.

432. The organisms of those animals, whose organs beiag
well supplied with nerves, have, as compared with other
animals, a vivid sensibility (417), are termed irritable organisms
(animals) : those which are the contrary, are inirritable. Sen-
sibility [empfindlichkeit] may co-exist with irritability, and
insensibility with inirritability ; but irritability does not always
imply sensibility, because a very irritable organ, as the heart
or stomach, may be endowed with a less sensibility than a less
irritable one, as the tongue. But as sensibility implies irrita-
bility, the latter enters also into the temperament^ or corporeal
constitution (52), and like the former, is influenced by habit,
and thus forms the basis of all the peculiarities of idiosyncrasy
(Haller ^Elem. Phys/ tom. iv, p. 576).

Note. — That which Haller terms vis insita [angeborne
Kraft], is really only a part of the same property of animal
organisms, and has the same relations to sensibility and habit ;
for, according to our views, it is nothing else than the vis
nervosa of external impressions exciting direct nerve-actions.
Let the reader compare Mailer's ^ Physiology,' § 400, with
other parts of his works, and with our own views, and it will

CH. II.] NERVE-ACTIONS, EXTERNAL IMPRESSIONS. 233

be seen that the latter afford a ready explanation of all the
phenomena which he refers to the vis insita.

433. When an external impression is felt, it is also felt to be
either pleasing or displeasing (187). This difference lies in the
impression itself (186) ; consequently, the external impression,
which when felt is pleasing, is totally different in its nerve-
actions, and is of quite another kind, than the impression
which when felt is displeasing (189). Now since the nerve-
actions of an external impression are the same, whether it be
felt or not (364, iii), it follows that the impression which can
cause a pleasing sensation will excite the same animal move-
ments as the pleasing sensation itself will excite ; and so in
regard to the external impression of a displeasing external sen-
sation. Consequently, external impressions produce, as nerve-
actions, the same movements which their external sensations,
accompanied with sensual pleasure and pain, would develop as
sentient actions (186, 80).

434. By means of the same force, an external impression
also produces the sentient actions of smarting, or tickling,
although not felt, provided it occur under the circumstances
when it would have caused titillation or pain (80). It cannot,
consequently, be inferred from the occurrence of those move-
ments which usually accompany an external sensation, par-
ticularly tickling or smarting, that the latter are felt, but only
that there is that present in the external impression which
can cause tickling or smarting. If an acephalous foetus,
or the headless trunk of a worm or insect, be irritated, the
same movements result as would have been considered the
direct and incidental sentient actions of the irritation, if it had
been felt, although this is impossible (25, 34). If it be so
irritated, that pain under ordinary circumstances would have
been caused, then those movements result which are the
ordinary direct and indirect sentient actions of pain. The
injured part contracts, is congested with blood, and swells and
inflames, and the animal writhes, tries to escape, leaps, flies,
defends itself, and exhibits all the signs of suffering, although
it is incapable of sensation. Titillation has a similar effect
imder similar circumstances, so that decapitated animals may
be excited to the performance of sexual acts, by the external
stimuli appropriate thereto (274, 396).

234 . ANIMAL FORCES. [ii.

435. If we would compreliend more distinctly how the
nerve-actions of an external impression can resemble all the
sentient actions, whether direct or indirect, of its external sen-
sation, we must take into consideration that the direct nerve-
actions in the part irritated result immediately from the appli-
cation of the external impression, and before it can be felt ; to
this class the internal impression is not required. With regard
to the indirect nerve-actions of external impressions, the matter
is as follows :

436. When an external sensation, either from sympathy or
natural deflexions, develops direct sentient actions, or excites
incidental sentient actions by means of subordinate concep-
tions, imaginations, foreseeings, desires, &c., through other
branches of the nerve which has received the external impres-
sion, or by means of nerves quite different (131), it is requisite
to these series of phenomena, that the external impression be
changed into a conceptional internal impression before it can
suitabl}^ excite the cerebral origin of the nerve, or be reflected
in its course downwards on the other branches or nerves, as
an internal impression (123, 124). If the same nerves be
suitably excited in the same manner, by a reflexion or turning
back of the (External impression, exactly the same phenomena
are excited, as if they had resulted from secondary sensational
conceptions, foreseeings, desires, &c.

437. It is thus we comprehend, how it is possible for head-
less animals to exhibit on a stimulus being applied (as proved
by experiment), the same adapted movements as are produced
by sensation, and by the ideas, foreseeings, desires, &c., resulting
therefrom ; as when a fly deprived of its head, flies away if
irritated, or as when a headless snake quickly withdraws its
body from whatever comes in contact with it, or a headless
fish strikes the boiling water it is put into with its tail, &c.

438. It appears really wonderful that a blind external im-
pression is so reflected on other nerve-fibrils in its way to the
brain, as to produce those movements which the mind produces
in virtue of its sensational volitions. The wonder arises,
however, from our ignorance of the laws of animal nature, and
from our prejudice in concluding that all which results from
sensation, can result in no other way. The nerve- actions pro-
duced by external impressions, are referred by the mind to

cu. II.] NERVE- ACTIONS, EXTERNAL IMPRESSIONS. 235

ieir external sensations, and to the pleasure or pain they excite,
or to the secondary conceptions they produce. There must be
then a sub-element [Merkmal] for the mind in the external
sensation of an external impression, so that it feels co-ordinately
the reflexion of the latter, and also the force required for
the resulting indirect nerve-action; and it is thereby led by
the sensational secondary desires to eff'ect the movements
volitionally, which then take place the more readily, because
the mind can of itself satisfy the desires for volitional movements
(283). In this way, the indirect nerve-action becomes at the
same time the incidental sentient action of the external sensa-
tion excited by the same external impression (97, 221). But
having observed, that adapted motions excited after decapitation
were always previously volitional, we are led to presuppose
that they must be volitional in their nature, and, therefore,
always volitional ; and are astonished when we find that they
can take place independently of the will. It is so in every
instance ; but it is those motions only that excite astonishment,
which from their nature we have always been accustomed to
consider as wholly dependent on the will. "We are little sur-
prised at seeing a muscle in a decapitated animal contract when
irritated, because we often feel the irritation without at the
same time feeling or observing the contraction; but when we
see the animal rise up and leap away when strongly irritated, we
are surprised, because a similar sensation was always previously
connected with the determination to escape, made by a sensa-
tional act of will. If the movement to escape were not always
connected with the painful sensation in the uninjured animal,
we should see it produced in the decapitated animal without
thinking it resembled a volitional movement, and without being
surprised.

439. It is clear from the preceding statements (366, and
398 — 401), that brainless animals, although without sensation,
because not endowed with mind, nevertheless by means of ex-
ternal impressions which operate incessantly in them, perform
all the acts and manifest all the activity of the sentient animal ;
everything, in short, that is effected sensationally and voli-
tionally they effect by means of the organic forces of the
impressions ; and since they can act as orderly, judiciously, and
rationally as it were, as if they thought, it has been inferred

236 ANIMAL FORCES. [ii.

erroneously, that the apparent voluntariness of these acts
depended on sensational conceptions, even although they might
be only external sensations. That which is termed voluntary
motion, we term so only in ourselves ; the voluntariness is not
in the movements — which remain the same whether sensational
conceptions produce them or not — but simply in this, that we
produce them by spontaneous sensational conceptions. But
who has proved that animals thus produce their movements ?
or who can demonstrate, in the face of ocular proof to the
contrary, that these movements can be effected by no other
animal force than conceptions (400) ? That these animals act in
this way according to the preordained objects of nature, especially
in the instincts, is undeniable (262) ; but of these objects even
the greater number of thinking animals themselves know nothing
(265). They are the objects of nature, not theirs (266); and
nature has so provided when their adapted acts should take
place, or their instincts ought to be in operation, that certain
external impressions are imparted in a naturally necessary
manner, which pass along their nerves, and are so reflected
and changed into internal impressions (399), that the animal
must perform those apparently adapted and volitional movements;
and which are intended also for the gratification of an instinct,
if it exist, but which are nevertheless just as fully eflPected
without it (269). Thus it is from erroneous views that our
astonishment arises, inasmuch as we think that these acts
cannot be developed by any other animal force than the con-
ceptive force of the mind. For the same reason we erroneously
infer, that because the acts of bees, ants, flies, polypes, and other
insects and worms, are regulated to ends and in agreement with
preordination of nature, they are dependent upon the conceptive
force (266). It is quite possible, however, that the external im-
pressions manifestly provided by nature for the instincts in a
preordained manner, and which excite the organs according to
a pre-established order of sequence, cause in them all those
wonderful and apparently voluntary acts, without a conception
being at all necessary thereto (286, 292, 293).

440. We know as little how and wherein external impressions
on the nerves diff'er from each other as we know with regard to
the various external sensations which they excite (413). An ex-
ternal impression produces as nerve -actions the same movements

4

H. II.] NERVE-ACTIONS, EXTERNAL IMPRESSIONS. 237

hicli it would excite if it were felt and caused a painful or
pleasing sensation; but we know no more in what it differs
from an impression which produces the contrary effect, than in
what sensations themselves differ (190). Nevertheless, it is very
probable, that the external impression which would have excited
pleasing sensations, operates upon the nerves connaturally or in
a way that is in accordance with their normal and appointed
functions ; while on the contrary, those which would have caused
a painful sensation, act upon the nerves contra-naturally
[widernatiirlich] ; consequently, the resulting nerve-actions
themselves are either connatural or contra-natural (191, 195).
Experiment supports this view. If a decapitated animal be
irritated, so that in its ordinary state the irritation would have
caused pain, it fights with its natural weapons, as if the pain
were really felt; a headless wasp stings, a headless earwig
attacks with its nippers, &c. All these movements are violent,
convulsive, and contra-natural, just as they are in the ordinary
state of the animal. An acrid irritant causes a convulsive con-
traction in the excised intestine of an animal, just as usually
occurs in the painful colic excited by ths same acrid poison.
Gentle stimuli, on the contrary, excite in headless animals
gentle movements only; when a decapitated cricket receives
the external impressions which ordinarily excite the insect to
the act of sexual congress, a disordered and half- convulsive
manifestation of the sexual instinct is excited, which borders
closely on a contra-natural state, because its sensational stimulus
is a titillation of the sexual organs (274). It chirps incessantly
with its wings, and allures to se:8;ual congress with unusual
energy and activity.

441. Consequently, just as external impressions follow upon
each other, so also the same movements result as nerve-actions,
which take place as sentient actions, when the external im-
pression excites pleasing or unpleasing external sensations, pain
or tickling ; and these nerve-actions are in like manner, either
in accordance with the natural destination of the mechanical
machines, or opposed thereto.

442. It is not necessary that an external impression shall
always develop indirect nerve-actions in the mechanical ma-
chines supplied with fibrils from the nerve which received the
impression, or from others in connection with the latter, for

238 ANIMAL FORCES. [ii.

the same reasons as laid down in § 201 with reference to
external sensation.

443. The nerve-actions of an unfelt external impression may
be felt, and induce external sensations (184). This constitutes
in sensational animals, a new link between the nerve-actions of
external impressions and the sentient actions of external sen-
sations. A loaded state of the stomach, worms, or poisons
cause therein external impressions, which usually are not felt.
These have their direct nerve-actions in the stomach, producing
in it a contraction and contra-natural movement, and this
nerve-action it is which we feel, when we say that we are ill.
Vomiting follows upon this external sensation, as its sentient
action, and as the result of a nerve-action of an unfelt impres-
sion. So the headaches accompanying disorder of the stomach,
are felt nerve-actions from unfelt external impressions (419).
Examples of this kind are of daily occurrence.

In specially considering the nature of the nerve-actions in
the different mechanical machines, it must not be forgotten
that the latter are by nature peculiarly adapted to certain
movements, and to none other (193).

SECTION IT. THE VIS NERVOSA OF AN EXTERNAL IMPRESSION IN

SPECIAL RELATION TO DIRECT NERVE-ACTIONS.

444. The nerve-actions, produced indirectly by an external
impression, are really nerve-actions of a non-conceptional
internal impression (422). As these will be considered in the
next Chapter, our inquiry as to the vis nervosa of an external
impression need not extend beyond the direct actions it produces
in the mechanical -machines (418).

415. Muscular fibre of all the tissues is most eminently that
in which an external impression excites direct nerve-actions.
The structure is peculiarly adapted to the latter, since the
fibrilli are easily excited to movement at any point of their
length, when the two ends either approach or separate from each
other (161). An external irritation which duly excites the nerve-
medulla distributed through the muscle can therefore very
readily impart an obvious movement at the irritated point, and
produce a direct nerve-action (418). An external impression
cannot so easily excite motion in other mechanical machines.

I

H. II.] EXTERNAL DIRECT NERVE-ACTIONS. 239

ot constituted of longitudinal fibrils like those of muscles
(161), although supplied with nerves ; as the substance of the
liver, the osseous medulla, the glands, and the membranes not
made up of sensitive muscular tissue, as the mucous. When
such a tissue is irritated, no immediate movement results;
nevertheless, an external impression is transmitted along the
nerves, and felt or reflected in its course upwards, and can
produce indirect nerve-actions and sentient actions of external
sensations in the same or other mechanical machines (424, iii).
Note. — This peculiar capability of muscular fibre for direct
nerve-actions, as compared with other machines, has probably-
been the principal source of the erroneous doctrine, that the
animal motor force of an external impression, or, in other
words, their irritability, is a property peculiar to the tissue,
and independent of the nerves. It is probable, however, that
it is not the only seat of direct nerve-actions, as wiU be shown
subsequently (463).

446. When many muscular fibres are united together, so as
to form bundles, the motion excited in one readily extends to
others, and puts the whole bundle into action ; or, if a viscus
be made up wholly of such bundles, the whole machine may be
thus excited to action, as is the case with the heart, stomach,
intestines, &c. This compound and communicated action is as
much a direct nerve-action, as if only one fibril had been
excited to contract; consequently, when the motions of the
heart, or of portions of intestine, are renewed after their
removal from the body, by pricking with a needle, direct
nerve-actions are produced. {Vide Haller's 'Elem. Physiol.,^
tom. iv, p. 467.)

447. Nevertheless, it is not advisable thus to consider them.
For, firstly, the movements excited in the fibrils connected with
those primarily irritated, is only a mechanical result. Secondly,
it may be considered as a nerve-action, the direct result of an
internal, or the indirect nerve-action of an external impression,
and this may take place as follows. The nerve entering a
muscle is distributed to every fibril of it, otherwise every
portion would not be sensitive (35). Consequently, there must be
numerous points of division of the nerve in the substance of
the muscle, at which an external impression on its way upwai'ds
can be reflected, and changed into a non-conceptional impression

240 ANIMAL FORCES. [ii.

(48). This reflexion of the impression can excite indirect nerve-
actions in all other parts of the muscle. It is difficult to decide
which of these two modes of action takes place, when an entire
muscle, or muscular viscus, is excited to movement by the
irritation of a single point ; but it is necessary for the sake of
establishing the correctness of the doctrine, that the possible
distinction be known.

448. The motion of which a muscular fibril is capable, is
alternate cqntractiop and relaxation. According to the views
stated in the previous paragraph, irritation of a single fibril
may excite entire muscles, or bundles of fibrilli, into action,
and by means of the latter, entire viscera and limbs be put
into motion. When an impression produces this motion it is
animal, whether it arise from a conception, or from an irritation
applied to the nerves of the fibrilli (161 — 163, 193). Thus, in a
decapitated animal, an external impression produces contrac-
tions, spasms, &c., in a muscle, by a direct nerve-action, and
thereby puts those limbs into movement to which it is attached,
just as a volition would. And thus, many movements which
are or may be sentient actions, result from the direct nerve-
actions of external impressions on the muscles ; as when the
irritated muscle moves a limb by its contractions, or closes a
cavity, or, as in the intestines, causes peristaltic movements and
numerous writhings.

449. Neither the mind, nor internal impressions on the
brain or nerves, are necessary to direct nerve-actions in the
muscles. They occur, although the brain be compressed, or
even the head removed from the body, and although the nerve
going to the muscle be divided, or the muscle itself excised.
All these are points of distinction between direct nerve-actions
and sentient actions generally, but especially those of external
sensations (164, 204).

450. Although, therefore, after the functions of the brain are
arrested, or the nerve divided or tied, the muscle is excited to
motion neither by the cerebral force, nor by any other internal
impression above the point of division, but remains paralysed
(415, ii) to all impressions, still the nerve itself retains the
power of producing direct nerve-actions in it, by means of an
external impression.

451. It is not every irritation that excites direct nerve-

I

II.] EXTERNAL DIRECT NERVE-ACTIONS. 241

actions in a muscle (424); nor is it to be inferred, that because
certain irritants fail to excite movement in a muscle, it is de-
fective in the vis nervosa of an external impression; or because
it is excited to movement by some, it must necessarily be so
excited by all. Every muscle, like the nerves, has its own
special external impressions, which directly irritate it rather
than others, and that whether they be felt or not. And the
same irritant of the nerves in a muscle may cause an external
impression, be transmitted upwards, be felt, or be reflected
downwards, and consequently produce sentient actions, or in-
direct nerve- actions, and all without having produced a direct
nerve-action in the muscle itself (424, iii).

452. Those external impressions on the muscular fibre which
can excite an agreeable external sensation, excite the muscles
to movements in accordance with their healthy functions, as
the sensations themselves would ; on the other hand, those
which would be painful to the animal under ordinary circum-
stances, excite the irritated muscle to spasmodic and convulsive
actions, and convulse the limbs (204, 440) . Thus acrid, irritant
poisons, excite violent writhings in an excised portion of intes-
tine, and render an excised muscle hard, and permanently
contracted; the excised heart beats irregularly, if strongly
irritated, &c.

4<53. The direct nerve -actions of an external impression on
the muscles are the same as the direct sentient actions of its
external sensation, and can cause the same series of movements
which these latter excite by their pleasure and pain, and the
resulting sensational conceptions as incidental sentient actions ;
so that external impressions may thus excite a whole chain of
apparently volitional acts, without one of them being felt, or any
conception whatever excited (437-8). Hence an animal may,
by external impressions only, perform all the organic and appa-
rently volitional movements necessary to its existence, without
having either brain or mind, if its body be so constituted (as is
quite possible) that all external impressions on its nerves can
produce their direct and indirect nerve-actions, without having
to excite material ideas in the brain, or conceptions in the
mind, connected therewith.

454. Although muscular movements be, for the most part,
excited volitionallv, either by external sensations or volitional

16

242 ANIMAL FORCES. [ii.

conceptions (163), still an infinite number of instances are ob-
served in the natural state, in which they take place solely
by means of the vis nervosa, and, in particular, that of external
impressions. A limb is often moved, not only against our
wish, but often without any feeling of the irritation that causes
the involuntary movement. It often happens that an impres-
sion in the intestinal canal, which is not felt, causes, in virtue
of an indirect nerve-action, the most violent movements of the
limbs; as is proved by epileptic paroxysms dependent on worms,
and the presence of which, in the intestinal canal, is not indi-
cated to either the physician or patient, by any peculiar phe-
nomena (470). Thus, also, an irritant poison causes spasmodic
action of the intestines, which is only indicated by the rumbling
of flatus, but not felt. So, also, the stimulus of light causes
contraction of the iris, as an indirect nerve-action, without any
accompanying sensation. Consequently, there are many move-
ments considered to be sentient actions of external sensations
only, which are nevertheless, at the same time, direct or indirect
nerve-actions of an external impression which is felt; and in
this way may be explained many movements made during sleep,
particularly by somnambulists, and those habitual voluntary
movements which are induced by external impressions that are
not felt. But the principal point is, that on this depends the
secret of the instincts in those animals which probably do not
feel the sensational stimuli of the instincts ; as, for example,
animals in utero, or in ovo, which already know how to aid
their birth before they seem to have felt anything; or animals
which are stimulated to undertake movements the most skil-
fully adapted to their preservation, without having been taught
by experience (269) ; or animals which, during their whole life,
do nothing that shows the least trace of ideas, and, conse-
quently, of external sensations, as polypes and oysters, &c.
In all these examples, the external impressions which are ordi-
narily the sensational elements of the instincts, seem to act as
a vis nervosa in producing the movements of the so-called in-
stincts; and many of these are undoubtedly true, direct, nerve-
actions, although it is equally certain that others are indirect.
In animals which gradually learn to feel, and to form volitions,
these external impressions become, in time, to be external sen-
sations, and the movements, hitherto nerve-actions, become to

CH. II.] EXTERNAL DIRECT NERVE-ACTIONS. 243

be also sentient actions, as has been already shown in detail,
in Part I. (Compare §§ 269, 285—293, &c.)

455. The heart is a muscular viscus, which can be excited
into direct nerve-actions by an external impression (357), applied
either externally or internally; and even when it has been re-
moved from the body, and its action has already ceased for a
lengthened period. (Haller*s ' Physiology/ § 102.)

456. Since the cardiac movements, thus excited, are neces-
sarily independent of the mind or the brain, and are, therefore,
in no respect sentient, they are direct nerve-actions excited by
an external impression, and would still be such if they were
also felt, and occurred (as they sometimes do) as sentient
actions of external sensations (452, 512).

457. The external stimuli which more especially excite direct
nerve- actions in the heart, are the blood and other fluids, and
the air itself, if in contact with the inner surface. (Haller^s
' Physiology,' § 101, and 'Opera Minora,' tom. ii, pp. 389, 390.)
Various stimuli, applied externally, have also the same effect ;
the heart is, indeed, the organ which, of all others, possesses
the greatest irritability (Haller's ' Physiology,' § 102) ; or, in
other words, which is the most readily excited to violent, direct
nerve- actions, by the greatest number of external impressions.

458. Just as painful or pleasing sensations excite the heart's
action contrarily to, or in accordance with, its natural func-
tions (211, 204), so, also, are the nerve-actions, when excited by
those external impressions, which, if felt, would excite painful
or pleasing sensations (452). An excised heart is irritated to
convulsive movements, if the irritant be violent, or such as
would have been painful. Now, inasmuch as the circulation
of the blood is closely connected with the motions of the heart,
it may be either in accordance with the well-being of the
organism, or opposed to it, just as the external impressions on
the heart differ; and it thus appears that an abnormal com-
position or temperature of the blood renders the stroke of the
heart contranatural, in fevers and other diseases.

459. The ordinary and natural stimuli, or the external im-
pressions of the heart, are not felt by animals (167); conse-
quently, their transmission beyond the heart is not necessary
to the excitation of its action, although it seems to be necessary,
in many animals, to the more certain maintenance of the

244 ANIMAL FORCES. [ii.

movements. (See § 515.) It follows^ therefore^ that the heart's
action is, for the most part, purely a nerve-action of an external
impression, and direct, although, at the same time, a sentient
action also (167), especially of external sensations, and, therefore,
may be also an indirect nerve-action (421 — 423) . Consequently,
in animals without either sensation or brain, the movements of
the heart may go on just as in sentient animals, and be either
connatural or contranatural, according to the nature of the
external impressions exciting them; and the change thus in-
duced in the circulation may induce the same movements,
which, when the animal felt it, constituted incidental sentient
actions of the external sensation exciting the movements (453).
460. The pulse, or the contraction and dilatation of the
arteries, and the entire circulation of the blood through the
blood-vessels, are, for the most part, nerve-actions only, although
they may sometimes be also sentient actions (167, 205), and
indirect nerve-actions. They may take place independently of
the brain or of sensation. The action of the arteries, inde-
pendently of the heart, seems to be rather mechanical than
animal. They are endowed with the force of contractility, as
is shown when they contract on a finger inserted into them,
and when they contract again, so soon as they are distended
with the blood sent from the heart. This force is, in all pro-
bability, purely mechanical, for the arteries are always con-
tracted in the corpse ; and if fluids be injected, so as to distend
them, they contract again so soon as the pressure is withdrawn.
They have also a natural elasticity, for they retract very consi-
derably when divided. (Haller's 'Physiology,' § 33.) But they
have no sensibility, if their nerves be not irritated, which, how-
ever, are certainly not distributed to their fibrous tissue : even
Haller himself denies that they have any visible irritabihty.
{' Physiology,' § 32, and 'Opera Minora,' torn, i, pp. 377, 418.)
Nevertheless, they are surrounded with muscular fibres and
nerves, that have both properties. It appears, however, that
these are supplied by nature, to the end that their ordinary me-
chanical stroke may be changed by means of direct nerve-actions,
when certain external impressions, which are unusual or contra-
natural, are received. This is observed, when an artery, being
so wounded, that its nerves or muscular fibres are injured, be-
comes inflamed at the spot, and pulsates strongly. Probably

CH. II.] EXTERNAL DIRECT NERVE-ACTIONS. 245

the alteration of the pulse, when the blood is at a higher tem-
perature, or has undergone a morbid change, is connected
therewith, the nerves and muscular fibres being irritated by the
morbid blood, so that the arteries contract more forcibly and
quickly; which action must be a direct nerve-action, excited by
an external impression of an unnatural kind. The reader is
recommended to take into consideration the proofs of the irri-
tability of arteries, adduced, from his own researches, by
Verschuir, in his excellent dissertation, " De Arteriarum et
Venarum vi irritabili/^ &c. — Groningen, 1766. However,
whether the natural movement of the arteries be simply me-
chanical, or whether it be a direct nerve-action of external
impressions received from the in-streaming blood, in either
case it is independent of the brain or the mind. Lastly, since
every assistance which is given to the circulation in the blood-
vessels of the muscles by muscular action (169), maybe as often
the result of a direct nerve-action of an external impression on
the muscles as of a sentient action; it may be asserted, that
the entire circulation of the blood, and the functions, and
changes in organs mechanically connected therewith, may be
carried on without the co-operation of either the brain or the
mind, and, in fact, are so carried on, even in animals endowed
with consciousness.

461. This is proved by experiment. In animals which do
not bleed to death immediately after decapitation, the beat of
the heart and the pulse, and the entire circulation (so far as
the great disturbance of the organism admits of) goes on un-
interruptedly for a considerable period (Haller ^ Opera Minora,^
torn, i, p. 425), and are altered by external stimuli, especially
by the various qualities of the blood. The arterial pulse, in
cases of suffocation, when life is restored by artificial means,
returns only after the hearths action is established, and is first
felt in the vessels nearest to the heart. In the dying and in
syncope, the pulse continues in the latter vessels, when it can
be no longer perceived in the more distant.

462. The arterial capillaries, as has been already shown
(207), are capable of special movements, which although some-
times sentient, belong properly to the class of direct nerve-
actions, excited by external impressions on the nerves which
surround these vessels. They consist in this, that an external

246 ANIMAL FORCES. [ii.

impression on these capillaries, attracts the contained fluids to
them, which are thence in many cases effused, but in many
other cases rendered motionless, and thus redness, swelling,
and inflammation are caused. That this is a purely direct
nerve-action of external impressions is proved by the fact, that
if a portion of the body be struck after decapitation it becomes
congested, just as if the animal had felt the blow. And we
often perceive similar effusions, redness, congestions, swellings,
and inflammations, take place in sleep, syncope, convulsions,
delirium, &c., without the external impression having been felt
that caused them, so that the principle that at each external
sensation a flow of fluids to the irritated part takes place pro-
portionate to the external impression, must have a wider appli-
cation, and be extended to every external impression, whether
it be felt or not (218).

463. The question has been raised, whether this direct
nerve- action in the capillaries takes place through muscular
fibrilli, or through the irritation of the nerves. Without
attempting to solve this difficult problem, it is sufficient to ob-
serve, that it may be analogous to the sentient actions de-
scribed § 147; that is, an external impression on the capillaries
causes a slight movement, whereby it immediately induces a
closure of their mouths, and so the other phenomena described
(207) result.

464. The flat muscles and muscular membranes, are capable
of direct nerve-actions independently of the brain and of mind,
just as other muscles : this has been fully established by ex-
periments with reference to the diaphragm. '^ Caro diaphrag-
matis per integram horam tremuit, et mansit irritabilis, cum
intestina jam quievissent,'^ &c. (Haller, ' Opera Minora,' tom. i,
p. 368: Exp. 181, 182, 194).

Those tissues which have no muscular element, as the skin
and mucous membranes, are not capable of movements from
external impressions at the point of irritation, although they
be felt (208, 445) ; but since they contain numerous blood-
vessels and glandular structures, which are capable of direct
nerve-actions, it follows that these membranes, however little
irritable they may be of themselves, will still exhibit certain
movements, which will sometimes occur in them at the irritated
spot, as sentient actions (208). When a painful irritation of

( H. II.] EXTERNAL DIRECT NERVE-ACTIONS. 247

the skin causes redness, it is the sentient action of an ex-
ternal sensation at the irritated part; but when the same takes
place after decapitation, it is the direct nerve-action of an
external impression on the terminations of the capillaries of
the skin (462) . When an irritation of the mucous membrane
of the nares, causes a flow of mucus, a sentient action of an
external sensation takes place; but if the same occurs after
removal or destruction of the brain, it is a direct nerve-action
in the capillaries, or the glandular tissues of the mucous
membrane.

On account of the deficiency of nerves in the insensible
fibro-serous tissues of the thorax and abdomen (208), no other
nerve-actions occur than those produced in the sensitive nerves.
Thus a repelled transpiration from cold excites the capillaries
of the pleura to contract, and thereby induces congestion and
inflammation, although no sensation is excited by this external
impression ; for the pain results from the inflammation (208,
note) .

465. Although the broad muscles and muscular tissues are
sensitive (171), and an external impression excites their natural
functions as sentient actions (as, for example, when an irritation
causes spasmodic action of the diaphragm) ; yet it often happens
that the excited functions are the direct or indirect nerve-
actions of the same external impression, or even mechanical
results of the direct nerve-action (447, 464). Thus, the
external irritation which excites the diaphragm to motion, and
that which irritates the muscular tissue of the glands, when
they pour out their secretions, are very seldom felt. It is the
same with the indirect nerve-actions in the membranes devoid
of muscular tissue ; although they sometimes arise from ex-
ternal sensations, yet general observation shows, that small
suff'usions, inflammations, congestions, induration, effusion, &c.,
take place in the pleura, peritoneum, &c., which necessarily
result from external impressions on those tissues that are
altogether unfelt; just as occurs in various diseases, namely,
erysipelas, catarrh, cough, pleurodynia, cutaneous eruptions, &c.

466. The large muscular viscera, particularly the oesophagus,
stomach, and intestines, are not only directly excited by ex-
ternal impressions, but in virtue of their peculiar structure, and
by means of their direct nerve-actions, are so excited through-

248 ANIMAL FORCES. [ii.

out their whole extent (446), that_, like the heart, they move
actively on being irritated, when separated even for a lengthened
period from the body (357). See Haller's ' Physiology,' § 402,
and ' Opera Minora,' torn, i, pp. 384, 199, 390, &c.

467. The co-operation of neither the cerebral forces nor the
mind is necessary to the natural functions of the oesophagus,
stomach, and intestines, excited as nerve-actions by external
impressions ; they can take place in animals deprived of both
(418).

468. The oesophagus and gastro-intestinal canal are directly
excited by numerous external stimuli. Food of various kinds,
air, medicines, poisons, injuries, &c., excite contractions at the
point of irritation, which are propagated to their whole extent
as a result of the direct nerve-actions of the external impression
(446). Those excitants, which can excite an agreeable external
sensation, produce only natural movements in these viscera :
those which would excite pain, excite convulsive contractions,
as in muscles (compare § 452).

469. In accordance with these views, it follows that the
entire process of digestion, considered as an animal function,
is the result of the nerve-actions of the external impressions
derived from the food in contact with the digestive organs, and
it may, therefore, take place quite independently either of
brain or mind. The movement of the chyle in the chyliferous
ducts belongs also to this class of functions. See Haller's
' Opera Minora,' torn, i, pp. 378-9.

470. The ordinary stimuli of the vermicular motions of the
alimentary canal, are not felt or propagated beyond its tissues.
We feel nothing of the food after it has passed beyond the
tongue : the violent irritants, which excite spasmodic action
and convulsive movements, are so little felt, that their presence
is only inferred from the rumbling of flatus, or from their
indirect nerve- actions, or from the external sensations excited
thereby in widely distant parts (212); as when w^orms in the
stomach or bowels excite convulsions, paralysis, pleurodynia,
frequent nausea and vomiting, &c.

471. The functions of glandular secretion and excretion
are, for the most part, regulated by physical laws (159); but
since a gland is a tissue compounded of blood-vessels and
nerves, these functions must depend upon the influence of the

I

CH. II.] EXTERNAL DIRECT NERVE- ACTIONS. 249

vis nervosa, and are, consequently, animal (6, 9). It has been
already shown, that they are sometimes sentient actions, espe-
cially of external sensations (172, 209). Can they occur also
as nerve-actions ? Experiments, as to this point, are not
decisive ; but, it has been observed, that the glands of excised
portions of the intestines may be excited to pour out fluid, which
act is undoubtedly a nerve-action (Haller, ' Opera Minora,^
torn, i, pp. 390, &c. " Humorum a purgante medicamento
copiosior adfluxus,^^ p. 401.)

472. Granting, however, that the doctrine is not proved by
direct experiment, the principles already established as to the
action of external impressions on the blood-vessels and their
terminations (4G0 — 463) and on muscular fibre (which also
enters into the composition of several secreting organs, § § 448,
454), sufficiently prove that secretion and excretion may be
simply direct nerve-actions of external impressions.

473. An additional proof, that secretion and excretion in
animals endowed with mind, are nerve-actions of external im-
pressions, is found in the fact that they are rarely sentient
actions of external sensations, and, consequently, the external
stimuli are not usually felt ; and as nerve-actions can only
occur in so far as the functions of the capillaries and the action
of the muscular fibres and muscles are directly excited (472),
it follows that secretion and excretion from glands are nerve-
actions of an external impression acting directly on their nerves
{vide Haller's 'Physiology,^ § 233). Hence we conclude that
the whole of these phenomena may take place perfectly in
animals unendowed with brain or mind, and difi*er in being
either in accordance with the objects of nature or opposed
thereto, just as in animals endowed with consciousness. (Com-
pare Haller^ s ' Elements of Physiology,^ tom. iv, p. 575.)

474. The viscera are compound mechanical machines, made
up of muscular fibres and coats, muscles, vessels, glands, or
secreting vessels, which are, in fact, the mouths of capillaries;
consequently, the statements already made (445 — 473), apply
equally to them in every respect. We need only mention a
few experiments to establish this truth.

475. As to the heart {vide §§ 455 — 459), the alimentary canal
(^ 466 — 470), the diaphragm (§§ 464, 4^66), ffla?idular struc-
tures (§^ 471 — 473), fibrous tissues (§§ 460, 461), muscular

250 ANIMAL FORCES. [ii.

structures (§§ 448 — 454). The lungs have mechanical functions
(Haller's 'Phys/ §263*), in which their nerves have httle share ;
neither are they endowed with much sensibiUty or irritability.
[Ibid. § 245.) Yet the bronchial tubes, far into the lungs, are
supplied with muscular fibrilli, a very sensitive membrane, and
numerous glands. Hence, external impressions excite many
direct nerve-actions, as spasmodic contraction of the tubes, and
a flow of fluids from the irritated glands and the mouths of the
capillaries. Respiration is carried on by means of the muscles
of the thorax, back, abdomen, and diaphragm; but many
changes are caused in it, as in singing, speaking, coughing, by
means of the upper portion of the air-tubes which are regulated
by muscles, and by the mouth, lips, tongue, and nose, all
which are muscular structures. Now, since all these organs
are usually moved by means of direct nerve-actions of external
impressions, it follows that the whole function of respiration
may take place independently of either the brain or mind
{Vide Haller^s experiments, 'Opera Minora,' tom. i, pp. 368,
&c.), and be either connatural or contranatural (454), although
it may be, at the same time, a volitional act, and the result of
an instinct ; or, in other words, an incidental sentient action of
external sensations (221, 285). It is thus that unfelt external
impressions re-excite this highly complex process, in cases of
suspended animation, by stimulating the nose, air-passages, and
respiratory muscles. It is not to be forgotten, that some of
these act as internal impressions, producing indirect nerve-
actions. (Compare § 525.)

476. The liver is only capable of the nerve-actions, which
are produced through the nerves that accompany its blood-
vessels. Experiments are not easily instituted on this viscus.
The irritability of the gall-bladder is somewhat doubtful.

477. Various remedies, and articles of food, act quickly, in
increasing the secerning function of the kidneys. The external
impressions they cause on the kidneys are not felt ; the func-
tion, therefore, is a nerve-action, and the doctrines already laid
down with regard to secretion and excretion are applicable to
the kidneys.

478. The urinary bladder is opened, contracted, and shut,
by muscular fibres ; consequently these processes may be and
are nerve-actions of external impressions, inasmuch as the latter

CH. n.] EXTERNAL DIRECT NERVE-ACTIONS. 251

e often not felt^ although usually the natural functions of the
bladder are volitional, and therefore sentient actions.

479. The spleen, being composed of vessels, is in the same
^^ategory with the liver.
^B 480. The organs of the senses (considered as mechanical
^fciachines, and not as organs of sensation), being supplied with
^fcauscles, are, to that extent, capable of nerve- actions : the spas-
^Biodic affections of the tongue and of the muscles of the orbit,
horripilation, and, in lower animals, twitchings of the ears, are
manifest examples of these. Are not the actions of the iris in
contraction and dilatation, and the tension of the muscles of
the ossicula auditus, although usually sentient actions, caused by
external sensation, at the same time also nerve-actions caused
by the same external impressions ? It is difficult to decide the
question. (Compare Haller's ' Physiology,^ §§ 494, 496, 513.)
481. The functions of the sexual organs in mammalia, and
in animals of a similar organisation in this respect, are usually
sentient actions ; but, nevertheless, there are some reasons for
thinking, that the cerebral forces only co-operate, and that they
may be induced by the vis nervosa alone, as direct nerve-actions
of external impressions. Erection of the penis will take place
in sleep, or in disease, without any external sensation, and is,
therefore, a direct nerve-action. The uterus is endowed with
as much irritability as the intestinal canal : and, lastly,
Bibiena^s experiments, lately instituted, show that butterflies
and silkworm-moths copulate, and deposit their eggs, after de-
capitation ; and thus a natural instinct is fulfilled by nerve-
actions alone. (Compare § 269.)

CHAPTER III.

ON THE VIS NERVOSA OF INTERNAL IMPRESSIONS
(WITHOUT CONCEPTIONS).

SECTION I.

482. Every internal impression is transmitted along the
nerves, in a direction from the brain downwards^, and is a mo-
tor force not subject to physical or mechanical laws (32, 121).
If it be caused by conceptions at the cerebral origin of the
nerves, the movements it excites are sentient actions (122),
but if it be not caused by conceptions, then the movements it
excites are nerve-actions of its vis nervosa, and it is of these we
propose to discourse.

483. Non-conceptional impressions, that is to say, internal
impressions not caused by conceptions, consequently not origi-
nating from a material idea in the brain (123), can take place
at any point of a nerve, even at its cerebral origin, but always
excepting the terminal fibrils, for it would then be an external
impression (32, 121). Consequently, the indirect nerve-actions
of external impressions are nerve-actions of non-conceptional
internal impressions (422).

484. Since every internal impression on the nerves is pro-
pagated downwards only (141) — if made on a nerve between its
origin and termination, it cannot be transmitted as an internal
impression upwards to the brain, nor can it excite any animal
actions in the parts situate above the point of impression; and
if such result, they must be considered as being excited by a
concurrent external impression, transmitted upwards to the
brain, and consequently are either sentient actions of external
sensations, or indirect nerve-actions of the external impression;
although, in the latter case, nerve-actions of another internal
impression (419, 422). Supposing the trunk of a motor nerve
is irritated by a needle, its medulla receives an external im-
pression, which is transmitted upwards, and, if it reaches the
brain, excites sentient actions by means of an external sensa-

CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 253

tion ; or is reflected downw wards, and develops indirect nerve-
actions of the external impression ; or else, both results take
place : at the same time, however, the irritation made by the
needle is transmitted downwards to the terminating fibrils of
the nerve, as a non-conceptional internal impression, and excites
nerve-actions in the parts to which the terminating fibrils are
istributed.

485. An internal impression, unconnected with conceptions,
acts downwards from the point where the impression is made
along the twigs and branches of the nerves, and if there be no
obstacle to its course, operates in those mechanical machines
connected with the fibrils. It may also (as when produced by
conceptions) be communicated to other nerves and to other
mechanical machines, if the fibrils be interwoven in ganglia
beneath the point irritated (124).

486. As the action is the same in the mechanical machines,
whether the internal impression be produced by conceptions or by
other irritants, so also is its transmission; so that, just as internal
impressions from conceptions are transmitted along the trunks
of the nerves to the terminal fibrils, without being commingled
with each other, although passing along the same trunk, as, for
example, the spinal cord, or principal branch of a nerve (125),
so also the non-conceptional internal impressions have their
independent course, and are not confused by or commingled with
each other ; whence it is inferred, that every internal impression
takes place in a special fibril, running an independent course to
a distinct mechanical machine, as has been previously shown (125).
If we knew which particular fibrils were excited by a certain
conception, when it produced a certain movement of a mecha-
nical machine, as a sentient action, we might be able to excite
the same movement as a nerve-action, by irritating the special
fibrils, and thus causing an internal impression, either in the
spinal cord or in the branches given off from it. It is not
possible, however, to perform this experiment, because we can-
not distinguish the various efferent fibrils on which a special
conception acts; and because the irritation of a single efferent
fibril would probably require much more delicate instruments
than we possess.

487. The non-conceptional internal impressions will be as
little interrupted in their course to the terminal fibrils, by ex-

254 ANIMAL FORCES. [ii.

ternal impressions taking the opposite direction, as the concep-
tional internal impressions (126), because it is indifferent
whether the stimulus be a material idea, or some other irritant
in the brain, or on the course of the nerve ; and because the
apparent reason of this phenomenon, namely, the natural dis-
tinction between the afferent and efferent nerve fibrils remains
the same (126, 127). Experiments confirm this doctrine.

488. The doctrine laid down in § 126, as to the existence
of two kinds of fibrils in each nerve, ^ the one transmitting ex-
ternal impressions upwards, and the other internal impressions
downwards, enables us to explain how it may happen, that in
a natural or contranatural condition of the nerve, certain me-
chanical machines may be excited into action by the one, and
not by the other ; although it may be excited to action by both
kinds of impressions. For example, the terminal nerve-fibrils,
in a mechanical machine, may not be duly excited by certain
external excitants (424), or a natural or contranatural impedi-
ment may take place in the fibrils which have to transmit the
external impression upwards (425), and, consequently, neither a
direct nor indirect nerve-action results (427 — 431). But, if
there is no such impediment in the efferent fibrils of the same
nerve, a nerve-action may take place in the mechanical machine
from an internal impression on the medulla of the nerve, and
vice versa. Except on the hypothesis of such a difference in
the nerve-fibrils, it is very difficult to understand phenomena
of this kind. That such phenomena really take place is un-
doubted ; for a limb which has become insensible to all external
impressions, and never once manifests nerve-actions, as in the
case of a paralysed limb, which neither feels nor even contracts
when scourged with nettles, may be stimulated to contractions,
independently and even in spite of the will, by irritation of the
trunk of its nerve; or when some internal agent causes a
morbid change in it ; and these contractions are manifestly
nerve-actions of a non-conceptional internal impression. Again,
there are instances in which the limb is not moved either by
conceptional internal impressions, or other internal stimuli of
the nerves, although it is sensible of external impressions on
the terminal nerve-fibrils, and nerve-actions are produced

' See note to § 126, with reference to this point. — Ed.

CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 255

thereby. This, it would appear, is the normal condition of
the heart ; for it is not only not sensitive, but is excited to the
most violent movements by external impressions on its nerves
(455, 456). It is also excited to movements by the internal
impressions of some conceptions (167, 211). Nevertheless, the
will exerts no influence over it; and the internal irritation of the
trunks of its nerves never causes, so far as has been observed,
any internal impression in them, and develops no nerve-actions
in it; on the contrary, the hearths action remains unchanged, and,
if separated from the body, is not re-excited thereby, although
this readily results from an external irritation. {Vide § 515,
and Haller^s 'Physiology,' § 101.) If it be conceded that,
from natural impediments, the efferent fibrils of the cardiac
nerves transmit only few kinds of internal impressions, and are
capable only of certain conceptions, being at the same time
incapable, for the most part at least, if not wholly, of other
kinds, and particularly of non- conception al internal impressions;
whilst, on the other hand, the afferent fibrils are readily sus-
ceptible of an infinite number of external impressions, we can
thus comprehend the phenomena, without having recourse to
the erroneous doctrine that the cardiac movements result from
an animal motive force innate in the muscular fibre, and inde-
pendent of the nerves (380 — 388).

489. The ordinary natural stimuli of the nerves causing in-
ternal impressions, are, — I, the conceptions which produce
sentient actions (121, 123) ; and, 2, reflected external impres-
sions (399), which excite indirect nerve-actions of external
impressions, and, consequently, nerve-actions of non-concep-
tional internal impressions (399, 421-2). Both can effect the
same movements in the mechanical machines, or one only, as
well as both (360, 364). These movements may be nerve-
actions, excited by reflected external impressions only, and be
as connected and adapted as if they were sentient actions ex-
cited by conceptions (438). Nature has endowed sentient
animals with both kinds of stimuli, but to those which exhibit
no conceptive faculty, she has only given the last mentioned ;
and she thereby attains, in both, the same end, namely, to
impart to them internal impressions, which, together with the
direct vis nervosa of the external impressions, constitute the
proper natural incitants of the animal movements of the me-

256 ANIMAL FORCES. [ii.

chanical machines. For all conceptions are primarily produced
by external sensations, that is, by means of external impres-
sions (65); and by means of these identical impressions, when
reflected ere they reach the brain, can those movements be
excited, as simply nerve- actions of non-conceptional impressions,
which are sentient actions of conceptions; or they may act
concurrently with conceptions (421-2). This great truth will
be amply established, by what will be laid down in this and
the following chapter, as to the vis nervosa of non-conceptional
internal impressions.

490. Nevertheless, there are other irritants that act as non-
conceptional impressions. When the medulla of a nerve is
irritated, as by pricking, pinching, cutting, &c., the same move-
ments take place in the mechanical machines to which the
nerve is distributed, as if a conceptional internal impression j
had produced them; or as if they were the indirect nerve-action
of an external impression. Thus, a decapitated frog retracts
its leg when its spinal cord is irritated, just as it did when,
during life, it willed to make a spring, and as also, if decapitated,
when its toe is pinched (359). So also a muscle contracts, when
its nerve is cut through. (Haller^s ' Physiology,^ §§ 403, &c.)
Suppose that instead of this artificial irritation, some materies
so irritates a nervous trunk in the direction downwards from
the brain, that the muscles which the nerve regulates are
thereby put into motion; the resulting movements are then
nerve-actions of a non-conceptional internal impression, which
are not in the first place indirect nerve-actions of an external
impression, but are produced by 2i primary internal impression.
Such irritants, while exciting movements in a direction down-
wards from the brain, may be also felt ; but in this case
sensation contributes nothing to the movements which are j
excited at the same time by the primary internal impression. %

491. Observation teaches, that this class of nerve-actions
occurs, but the most distinct are usually contra-natural. Various
contractions, spasms, convulsions, and cramps of muscles and of
limbs, occur in disease, without being induced by a conception
or an external sensation, or even by an external impres-
sion on the motor nerves, and are therefore neither sentient
actions, nor indirect nerve-actions of external impressions,
and have no other origin, than that some acrid irritant matter

tf

III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 257

18 applied to the trunk of the nerves, and develops in them
primary internal impressions, which cause these nerve-actions.
Movements of this kind are observed_, for the most part, in
persons in whom the whole mass of humours is acrid, so that
when they come into contact with the medulla of the nerves,
they stimulate it. Of this class also are the movements which
occur if the trunk of a nerve be ulcerated, and the limbs to
which it is distributed are moved in various contra-natural
ways ; or when a tumour, a foreign body, &c., irritates the
nervous trunks, and thereby excites the muscles to contra-
natural movements. Examples of primary non-conceptional
impressions will be given subsequently, (515, 525, 532, &c.)

492. We are as ignorant what peculiar irritation of the me-
dulla in the nervous trunks must be excited, to produce a certain
kind of internal impression and thereby certain definite nerve-
actions, as we are with reference to external impressions (413).
Thus much is known, however, that it is not every irritation
or impression on the trunk of a nerve that is effective
[sinnlich] ; or, in other words, it is not every irritation,
although directed from the brain downwards, that causes in
the nerve itself that mysterious movement which is propagated
downwards in the nerve, and puts the mechanical machines to
which it is distributed into motion. Every irritation which is
adapted to act on the nerves [or is sinnlich], develops animal
actions (121), and all others act simply as physical or mechanical
forces (7) . We have in the heart an example, in what a minor
degree many nerves receive certain internal impressions (488);
it is also known that nitric acid applied to a nervous trunk
corrodes the medulla, but does not excite the muscle to which
the nerve is distributed, although irritation of the same nerve
with a needle will throw the muscle into convulsions (Haller,
' Opera Minora,^ torn, i, p. 364). The action of impressions can
be learnt only by experiment and observation.

493. Just as a conceptional internal impression on a tied or
cut nerve does not pass beyond the injured point (128), so
also no other internal impression made above the injured point,
nearer the brain, passes beyond the ligature or section, to excite
nerve-actions in those parts only which are supplied with twigs
from the trunk between the point of irritation and of injury.
But if an internal impression be made on the nerve below the

17

258 ANIMAL FORCES. [ii

<

ligature or section, it is transmitted to all the terminal fibrils,
and nerve-actions are excited in all the organs supplied with
twigs given off from the trunk below the point of injury, provided
there be no impediment to the course of the impression (359).
These are principles well known to physiologists (Haller^s
'Physiology/ §§367, 403).

494, i. Non-conceptional internal impressions excite nerve-
actions only, when duly transmitted from the point of irritation
to the mechanical machines (493). Consequently, the brain
may be destroyed, or even the head wholly separated from the
body, and yet an internal impression made on the spinal cord,
or the trunk of a nerve, will develop nerve-actions in those
mechanical machines which receive their nerves from the cord,
or from the nervous trunk from below the point of irritation,
provided there be no impediment to its transmission downwards
(483) . Thus, a frog, although headless, will leap forward, when
its spinal cord is irritated with a needle, so that the brain and
the conceptive force are as little necessary to the nerve-actions
of internal impressions as of external, with the condition, how-
ever, that the vital spirits be present in the nerves as stated
in § 416.

ii. Nevertheless, there are cases in which the existence of the
brain and its uninterrupted connection with the limb are neces-
sary to the nerve-actions of internal impressions, although the
cerebral forces and the mind do not come into action. In the
natural condition of the animal, certain functions are per-
formed by both kinds of vis nervosa acting at the same time, so
that ordinarily they are both direct nerve- actions of external
impressions and nerve-actions of non-conceptional internal
impressions. The heart, diaphragm, and muscular system
generally, will be subsequently referred to, as exhibiting ex-
amples (575, 524, 514). In instances of this kind, a shock
may easily injure, enfeeble, or interrupt the functions so com-
pounded, by causing one of the two kinds of vis nervosa to cease
to operate ; although the other is able of itself to restore the
disturbed functions, when after this interruption its influence
on the mechanical machines be renewed. Consequently, if
the trunk of a nerve distributed to a mechanical machine, the
natural function of which is at the same time both a direct
nerve-action of an internal impression and a nerve-action of an

CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 259

internal impression, be tied or divided, the function may cease
or be interrupted, because the co-operation of the internal im-
pression ceases ; although the same function can be renewed, if
an external impression be made, or a new internal impression
be communicated to the nerve below the ligature or section.
If, however, the usual non-conceptional impression stimulus be
applied to the nerve near its cerebral origin, whether directly,
or whether as an external impression reflected and changed
there into a non-conceptional impression, then the presence
of the brain and its unbroken connection with the nerves of
the machines are requisite to the continuance of the natural
functions of the latter; although they may be renewed by a
renewed impression, or by the renewal of one or of both im-
pressions. Thus, a muscle is enfeebled, or the natural move-
ments of the heart, diaphragm, &c., interrupted, so soon as the
connection of their nerves with the brain is broken ; yet their
functions can be renewed so soon as one of the two kinds of vis
nervosa communicates a new impulse, and the heart receives an
external impression below the ligature, or the diaphragm an
internal impression, or the muscle either or both.

iii. Nevertheless, the brain and the conceptive force are
necessary to these movements of the non-conceptional internal
impression, when, to continue in their natural order, they must
be at the same time sentient actions ; for the removal of the
brain interrupts this natural order, although it does not abolish
it irreparably.

iv. That the brain is necessary to the prolonged continuance
of the nerve-actions of non-conceptional internal impressions,
in so far as its medullary substance supplies vital spirits to the
nerves, has been already stated ; it is also necessary in those
cases, in which the nerve-action depends on an internal im-
pression made near to or at the cerebral origin of the nerve,
but not by conceptions. But it is manifest, that in none of

i these cases, the action of the cerebral forces or of the conceptive
force is necessary to nerve-actions, and that even in the in-
stances mentioned in par. iii, neither contributes to the sole
production of the movements as nerve-actions.
495. When an internal impression is not a primary, but a
reflected external impression, it causes nerve-actions, as if it
■■■——-—

260

ANIMAL FORCES.

[II.

the brain and the conceptive force. When a decapitated frog
leaps from pinching of its toe, the action is a nerve-action of
an internal impression derived from a reflected external im-
pression .(419j 415, ii). The external impression in this case
can pass uninterruptedly from the point of irritation in the toe
to the point of injury in the spinal cord, where it is reflected,
and passes uninterruptedly back again, and thus the same
nerve-action is caused by it, as if a primary internal impression
had excited the spinal cord (494).

496. A non-conceptional internal impression can excite nerve-
actions under the following conditions only :

i. The medulla of the trunk of the nerve must receive an
internal impression in one direction downwards from the brain,
independently of any conception (121, 4SS).

ii. This internal impression must be transmitted downwards,
along the trunk and its branches through the efferent fibrils, to
the mechanical machines which have to perform the nerve-action.

iii. The mechanical machines must be capable of performing
that nerve-action, which the received internal impression can
effect in virtue of its nature ; just as is necessary in sentient
actions excited by conceptional internal impressions (130, ii,
129, iv).

The conditions under which those nerve-actions of internal
impressions take place, that are caused by a reflected external
impression, have been already stated (419, 422).

497. The nerve-actions of non-conceptional internal impres-
sions are quite independent of the brain and the conceptive
force ; nevertheless, at another time, or in other animals, they
may be sentient actions of impressions caused by conceptions
(364, i); and this applies especially to indirect nerve-actions of
external impressions (423). Thus, the volitional movement of
a limb (a sentient action) may occur as the nerve-action of a
primary internal impression, when an acrid humour irritates the
trunk of the nerve going to the limb ; and although this acrid
humour, as in gouty diseases, may cause pain, yet this external
sensation of pain is not the motor force of the limb, but the
concurrent internal impression (484). See a previous paragraph
for examples of this class (423) .

498. A nerve-action of a primary internal impression cannot
take place, or will be prevented :

I

CH. HI.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 261

i. If an irritation, although applied to the medulla of a nerve

the direction downwards from the brain, excites no internal
impression therein. Thus, in disease, there are often traces of
putrid humours collected about the points where the trunks of
nerves occur, without any motions resulting in the muscles;
either because the putrid fluids do not penetrate to the medulla
of the nerve, but remain externally to it, or else because they
are of a kind which excites no internal impression in it (492) .

ii. If the transmission of a primary internal impression is
prevented by some impediment, so that it cannot reach the
mechanical machines which it regulates (496, ii). Thus, an
acrid humour in the axilla may irritate the nerves, which regulate
the forearm and hand, and so excite convulsive movements
therein. But if there be a tumour at the elbow-joint com-
pressing the nerves, or if some external pressure be made on
them (as when a limb goes to sleep), then the transmission of
the primary internal impression from above downwards is
prevented, and no nerve-actions take place.

iii. If the mechanical machines are rendered incapable of
the requisite nerve-action. Thus, when an acrid humour irri-
tates the nerves, a bandaging of the muscles of the convulsed
limb, will prevent their action, and so the patient may obtain
sleep and rest. (Compare also § 425.)

499. There must be natural obstacles to the development of
the nerve-actions of non-conceptional internal impressions, as
well as of sentient actions (136 — 138). Those already enume-
rated as preventing the indirect nerve-actions of external im-
pressions, act also in preventing the nerve-actions of primary
internal impressions (428, vi; 429). The following is a short
statement of some others.

500. A natural impediment to the production of certain
nerve-actions from primary internal impressions, occurs —

i. When a nerve, by nature, is but slightly or not at all
susceptible of certain primary natural stimuli (492, 498, i) ;
consequently, if it do receive an impression, the latter is too
weak to be propagated to the mechanical machines. It is quite
certain that there are stimuli, which, when applied to the
medulla of the nerve in its normal condition, do not excite
nerve-actions. The nerves are in close relation with many
tissues, and their medulla is penetrated by capillaries and fluids.

262 ANIMAL FORCES. [ii.

all which must often necessarily act as active stimuli, but they
seem to act as such, for the most part, extraordinarily and
abnormally only, otherwise they would incessantly stimulate
our limbs to movements.

ii. When certain internal impressions on the nerves are not
naturally transmitted to certain mechanical machines (498, ii).
This hindrance is principally constituted by the ganglia and points
of division of the nerves (137, 429), which sometimes so receive
internal impressions of a certain kind, that they go forwards ;
but also, sometimes, so that the nerves are not excited inter-
nally by them, and consequently the impressions have no in-
fluence on the mechanical machines innervated by the nerves.

iii. When the mechanical machines are as yet naturally
incapacitated for the animal movement which a certain internal
impression can communicate to it, or becomes so incapacitated.
This impediment is observed in young animals, or in the very
old, which are excited to certain movements simply by their
blind instincts, in virtue of the vis nervosa (439) .

501 . Habit, and the frequent repetition of internal impres-
sions, can act as impediments to this class of nerve-actions, in
the way already laid down (430, 431).

502. Since the nerve-actions of non-conceptional impressions
are, for the most part, indirect nerve-actions of external im-
pressions (which determine the sensibility of animals), the
vis nervosa of internal impressions has also its influence in
determining the irritability and vital constitution of animal
bodies.

SECTION II. ON THE VIS NERVOSA OF INTERNAL IMPRESSIONS

IN PARTICULAR.

503. Nerve-actions of internal impressions, whether the latter
be primary internal impressions, or reflected external impres-
sions changed into internal, can be developed in all the organs
that are capable of sentient actions ; for the whole diff'erence
of the two consists in this, — that in the development of the
latter, the nerves are excited by conceptions, and solely at their
origin in the brain ; of the former, by other stimuli applied to
the whole nervous system, except the terminal fibrils (121, 483).
Both kinds of stimuli consist in the same changes in the nervous

CH. 111.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 263

system [the animal machines] ; both kinds of impressions are
transmitted in the same way through the nerves, and move the
mechanical machines with which they are incorporated (360).
We have now to show, by facts, in what structures this class of

trve-actions are produced in the normal condition.
504. Conceptions act on the brain and nerves, so as either
put mechanical machines into motion or not (117). In the
latter case, they are manifested specially in the brain " and
sensitive nerves. It is already established by experiment, so
far as the difl&culty of investigating this profound subject will
allow, that there are also other stimuli than conceptions, which
excite nerve-actions in and limited to the brain itself, by means
of their internal impressions (374). It has also been shown
(377, 378), that internal impressions not caused by conceptions,
excite in the purely sensitive nerves, as nerve-actions, the same
changes which the internal impressions of conceptions produce,
as sentient-actions, inasmuch as both induce imperfect external
sensations (148, 377). Hence it follows, that the internal im-
pressions not caused by conceptions, are subject to the same
law of deflexion, and excite the same changes in the nerves, as
the internal impressions derived from conceptions {vide § 151).
The question is, however, so recondite, that it is difficult to
institute experiments in regard to it.

505. Conceptions act on the mechanical machines (155)
either directly through the brain, or through the nerves. Now,
as non-conceptional internal impressions develop changes in the
brain, they can also thereby put mechanical machines into
motion. It is properly, however, the vessels, and especially the
blood-vessels, that experience this change (156 — 159), enabling
them to alter the cerebral circulation and the vital movements
generally. It is not, however, possible to show clearly, that
non-conceptional internal impressions cause the same changes
in the cerebral capillaries, since it is impossible to determine
whether a certain stimulus of the brain acts through the nerve-
fibrils in the brain, according to § 132; or directly on the
membranes and mouths of the capillaries of the brain, accord-
ing to § 392 ; or whether in either of these two cases it acts
as an external impression by means of direct or indirect (418,
419) nerve-actions, or through the sentient action of an external
sensation (132) ; or (much more probably) as a primary internal

264 ANIMAL FORCES. [ii.

impression not induced by conceptions (490). The obscurity in
wbich these changes in the brain are involved, is an apology
for the want of experiments. (Compare § 159.)

506. Except in the example stated, § 504, non-conceptional
internal impressions act on the mechanical machines, only so {
far as the latter have nerves incorporated with them. Their
nerve-actions, as well as the sentient actions of the conceptional
impressions, are effected through the nerves (160).

507. The laws of action on the muscular system of the im-
pressions derived from conceptions, are applicable to the in-
ternal impressions not derived from conceptions, whether they
be primary or reflected in their origin (161, 162, 204). The
primary are illustrated § 498 ; those from a reflected external
impression §§ 415, 495.

508. Since non-conceptional impressions act on the muscular
system, they must also excite movements of the limbs. Examples
of this kind are seen, when a decapitated man, either from the
primary internal impression of the sword- stroke in his spinal
cord, or from the reflected external impression of the injury,
makes those movements, which a conception of danger, or an
external sensation of the injury, would have led him to make ;
or when an animal, decapitated while moving, still goes on, and
continues its former sentient actions in the muscles of locomo-
tion, as nerve-actions, &c.

509. A nerve-action in a muscle from an internal impres-
sion implies the transmission of the impression along the nerve,
in the direction from the brain downwards to the muscle which
is excited to movement. If the movement be the indirect
nerve-action of an external impression, it implies that an ex-
ternal impression, is reflected in its course upwards to the brain,
and transmitted from the point of reflexion downwards, as an
internal impression, to the muscle excited to movement (422,
496).

510. The same nerve of a muscle may receive external im-
pressions, at the same time that internal impressions on it
excite muscular action, and this external impression may be
either felt, or develop nerve-actions, without the two antago-
nistic impressions impeding each other^s action (487).

511. When a nerve is tied, divided, or compressed, an in-
ternal impression (whether primary or reflected in its origin) if

CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 265

applied above the point of injury, cannot excite a nerve-action
in the machines to which the nerve is distributed. Nevertheless,
the brain and conceptive force are not necessary to nerve-actions,
although in many cases nerve-actions cannot take place without
the brain; not, however, because the cerebral forces or the
conceptive force are requisite, but because it contains the
origins of the nerves, and without it non-conceptional impres-
sions cannot be applied to that portion of the nerves. If the
brain be excited by some general stimulus, in which the roots
of all or the greater number of the motor nerves participate, its
influence must be extended to the greater part or the whole of
the muscular system, as occurs with internal impressions caused
by conceptions (164, v). The same doctrine applies to the
spinal cord. Consequently, in experiments made on animals
when the brain and spinal cord are irritated mechanically, some-
times partial, sometimes general convulsions are excited (359).

512. The nerve-actions from the two kinds of internal im-
pressions are liable to the impediments that have been already
indicated (428 — 431, &c.), and hence it is not every internal
impression which can excite nerve-actions in the muscles (50Q).

513. Unfelt external impressions in the muscles can be
reflected in the muscles themselves, and then cause nerve-
actions in them by means of internal impressions (447); so
that various movements of the limbs and the viscera, which
appear to be nerve-actions of external impressions only, are at
the same time nerve-actions of an internal impression induced
by external impressions (448, 423). The excited motion of the
heart and intestinal canal may be taken as examples (446).

514. A direct nerve-action of an external impression may
at the same time, or at another time, or in another animal, be
indirect, or the nerve-action of internal impressions, or a sen-
tient action of external sensations, or of other conceptions, nay,
may even be volitional; and vice versa. Consequently, those
go too far who maintain that the irritability of muscles is their
only or principal motor force. It would rather appear, that
although the greater number of muscular actions can be directly
excited by external impressions, in the natural condition of
animals endowed with a brain and conceptive force, yet
internal impressions, whether primary or originating in a re-
flected external impression, may co-operate therewith ; so that the

266 ANIMAL FORCES. [u.

muscular movements may be either sentient or nerve-actions
only, or both at once. It is this common action of the two
kinds of vis nervosa in the muscular movements of animals
which renders the presence of the brain and its uninterrupted
connection with the muscles, necessary to the development of
many nerve-actions ; the co-operation of the cerebral forces or
of the conceptive force being unnecessary (494, ii). Haller
referring to the instinctive acts of animals, observes that the
causes of muscular action in these instances depend on a law
given by God, and not on the mind (^Physiology,' § 408).

515. External sensations and other conceptions in many
ways change the action of the heart by means of their internal
impressions (167, 211) — that action being for the most part an
indirect nerve-action of external impressions on the heart (457,
459). Can internal impressions not caused by conceptions also
exercise a motor power over it ? It is a priori probable, for
the heart is a muscle. It is much more probable, however,
from another consideration deduced from experiment, namely,
that when in animals endowed with brain the cardiac nerves
are tied, the movements of the heart cease, even although all
the nerves are not tied at the same time (Haller's ' Physiology,'
§ 100). Consequently, although the natural movements of the
heart be a direct nerve-action excited by external impressions, yet
it must be maintained by a co-operating internal impression, and
this must depend either on conceptions or other stimuli. Now,
although the ordinary natural stimuli of the heart's action be
unfelt, they are not the less sentient actions of other conceptions
(457 — 459). Perhaps the natural motion of the brain, which
synchronises with the respiratory movements, may be enume-
rated amongst these, although that motion is itself dependent
on the heart's action, and acts by communicating non-concep-
tional internal impressions to the cerebral origins of the cardiac
nerves ; yet, on the other hand, the heart beats in the foetus
in utero, or in the embryo in ovo, and also in animals which
have no respiratory movements. Or the heart's action may be
influenced by primary internal impressions, communicated to
the cardiac nerves by the arteries of the brain (505). In this
way we may understand why the connection of the brain with
the heart, is necessary to the movements of the latter, without
the cerebral forces being requisite. But reflected external im-

CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 267

pressions may constitute this co-operating force in the action of
the heart ; the external impressions being reflected downwards
in the ganglia on their way to the brain^ or changed into internal
impressions in the spinal cord, and so acting reflexly in the
heart ; for it is quite certain that external impressions made on
the cardiac nerves are transmitted upwards to the brain, be-
cause they are sometimes felt (35). The object of nature in
thus providing that internal impressions shall co-operate in the
natural movement of the heart, although external impressions
alone may fully efi'ect it (457), seems to be simply this, that
the continuance of an action so important to life may be the
more certainly maintained, and in the less danger of being
interrupted than it would otherwise be, if wholly dependent
upon the usual external impression, namely, the stimulus of the
inflowing blood on the heart. When this ceases momentarily,
or acts only feebly, as in syncope, still the heart is not left
without a stimulus to its continued action. Observation seems
to corroborate this opinion, for the enfeebled or interrupted
stroke may be restored or invigorated in a moment by the ex-
ternal impression of irritating vapours on the nerves of the
nose, and which are reflected upon the cerebral origin of the
cardiac nerves. It is not probable, that any other end is
gained from this co-operation of internal impressions, for they
only strengthen the motion of the heart, and if it be interrupted,
a slight irritant re-excites it, as has been shown by experiments,
when by means of an irritation (a non-conceptional internal
impression) applied to the eighth pair, to the brain, or to the
spinal cord, the stroke of the heart has been rendered stronger
(Haller's ' Physiology,^ § 100), although by no means able to
maintain it continuously. Farther, although the ligature or
section of the cardiac nerves enfeebles the heart's action, it
never quite abolishes it (Haller, loco citato) ; whilst a slight ex-
ternal impression (its principal excitant) will re-excite the
movement.

516. Without, however, entering further into this obscure
part of the subject, we conclude that the heart is susceptible
of nerve-actions from non-conceptional internal impressions,
although the principal motive force consists in unfelt external
impressions (459). Additional proofs will be found in § 519.
Further researches are much to be desired, for the properties

268 ANIMAL FORCES. [ii.

of the cardiac nerves are peculiar, and the action of impressions on
the heart differs from that on other muscles. The number of the
cardiac nerves, their origin from such different points, their in-
tricate combination, and their ganglia and remarkable plexus
all merit the closest attention. Probably, the results of external
impressions would be very different, according as the nerves
were irritated, or tied, or divided, above or below the ganglia
and plexuses and points of division into branches ; and that the
different results observed when the cardiac nerves are imtated
— the hearths action being sometimes increased, sometimes un-
altered— may be dependent upon some such difference in the
mode of experimenting (Haller^s 'Physiology,^ loco citato).

517. Since the heart is compounded of several muscles, and
since these can be excited to action independently of each
other, as has been shown in excised hearts, it is more probable,
that the stroke of the heart, or the combined action of all the
muscular structures, is an indirect nerve-action of external im-
pressions, they being reflected in the heart itself (513), than
that it is simply a mechanical result of their direct nerve-
actions (447); for in the latter case, the whole heart must be
excited to action by an external impression which acts only on
certain of its fibres — a conclusion opposed to the results of ex-
periments (Haller's 'Physiology,' § 101).

518. Although the preceding propositions are well founded,
still many a change in the heart's action is either a sentient ac-
tion, or at the same time both a sentient and a nerve-action; and
consequently, it is erroneous to infer, because the heart's action
is usually a direct nerve-action of external impressions, or in
other words, a result of irritability, that it is always such,' or
such only, or such in all animals. Lastly, in so far as the
circulation is dependent on the heart, each kind of impression
contributes something thereto, so that the whole of the circula-
tion derives some stimulus to its continuance and maintenance
from every kind of animal motor force, although the customary
and principal stimuli consist in unfelt external impressions (459).

519. The arterial pulse, in so far as it is dependent on the
heart's action and the circulation, may be a nerve-action of
every kind (518). Many of the stimuli used in cases of
suspended animation to restore life by re-exciting the action of
the heart, the circulation, and the pulse, act as non-concep-

CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 269

tioiial internal impressions ; although it may be easily conceived
that these re-excited movements are simply direct nerve-actions
of external impressions on the heart, arising from inflation of
the lungs, and from the various stimuli applied to the throat,
stomach, intestinal canal, &c. But as these stimuli are applied
to the nerves adjacent to the heart, and which have a much
less degree of irritability than the cardiac nerves, they must be
applied strongly and for a lengthened period, before the external
impressions they receive are transmitted upwards to the points
of reflexion, and hence sent downwards ; and when the result
follows, the heart makes only a few strokes and then stops, so
that the stimuli must be renewed continually to keep up its
action. But if the heart be excited by stimuli applied directly
to its nerves, all this takes place more readily and actively.

520. The changes in the pulse, resulting from the action of
the muscular fibres and nerves of the arteries, independently of
the heart, are direct nerve-actions from external impressions
derived from the blood, as in the case of the heart (460) . Why
should not these impressions on the muscular fibrils be pro-
pagated to the nerves, and, although not felt, nevertheless, at
least in some cases, be reflected so as to change the circulation
by means of indirect nerve-actions ? The possibility of this is
hardly doubtful, yet it is as difficult to demonstrate by experi-
ments, since the phenomena of direct nerve-actions from ex-
ternal impressions on the blood-vessels are scarcely perceptible
(460). As conceptional internal impressions, and particularly
those of external sensations (147, 151), excite changes in the
pulse and circulation, the same may result from primary in-
ternal impressions, or from external impressions reflected be-
fore they are felt (360, 503).

521. Lastly, in so far as muscular action changes the pulse,
all those non-con ceptional internal impressions which excite
muscular action will influence the pulse. Every effort, or bodily
movement, whether convulsive or volitional, accelerates the
circulation, and often the causes of the movements are neither
felt nor perceived.

522. The mouths of the capillaries are as subject to changes
from non-conceptional internal impressions, as from external
impressions, whether felt (207), or uufelt (462). The action of
certain remedies on the capillaries proves this : as Avhen certain

270 ANIMAL FORCES. [ii.

haemorrhages are cured by external applications. Sleeping with
a pillow of oak-chips beneath the loins, or having a decoction
of gall-nuts applied to the abdomen, cures a haemorrhage from
the hsemorrhoidal veins ; cold water to the forehead or nape of
the neck, cures a bleeding from the nose ; a blister applied
externally, relieves inflammation of the subjacent parts, &c.
The external impressions made by such remedies on the nerv^es
they are brought into immediate contact with, are in many
cases transmitted upwards, since they are felt; but in other
cases in which they excite no external sensation they must
be reflected downwards on the nerves distributed to the capil-
laries, and excite contraction of their bleeding mouths.

523. That the diaphragm may be excited to action by non-con-
ceptional internal impressions made on its nerves, has been proved
by experiments. (Haller, ^ Opera Minora,' tom. i, pp. 365, 199.)
Further, the irritants, which when applied to the nose, excite
sneezing — a convulsive action of the diaphragm — as the sen-
tient action of an external sensation (208), contribute much to
the restoration of life in cases of suspended animation; and
since they are not felt for some time after the action of the
heart and lungs is re-excited, it follows that they act in virtue
of a reflexion of their external impressions on the trunk of the
phrenic nerve, and thus excite the movements of this muscle as
their indirect nerve-action. Consequently, we can infer that
the same movements will result from non-conceptional internal
impressions.

524. The ordinary and natural movement of the diaphragm,
does not arise from external stimuli that are felt, although it is
very much influenced by such (208) ; nor is it ordinarily a sen-
tient action from external sensations ; and inasmuch as it takes
place without our consciousness, and even without any know-
ledge on our part of its existence, it is not a sentient action
from other conceptions, although these can change it volition-
ally (171). Consequently, the usual stimulus to the continued
natural movement of the diaphragm, acts by means of non-con-
ceptional impressions, and it is either a direct nerve- action of
the latter, or of external impressions (356) : if from the non-
conceptional, it may be either from primary internal im-
pressions or reflected external impressions (419, 483). Granted
that it arises from external impressions, still as in the instance

cH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 271

of the heart's movement, the co-operation of an internal im-
pression is necessary to its maintenance, and probably with the
same object (515), for so soon as the phrenic nerve is tied, the
movement of the diaphragm is interrupted (171).

525. Although the motion of the diaphragm is influenced
by volitional conceptions and external sensations, still its
natural action in respiration is a nerve-action. Nevertheless,
while the cerebral forces and the mind are not requisite to that
action, the connection of its nerves with the brain is, inasmuch
as non-conceptional internal impressions co-operate in exciting
it. This doctrine is equally applicable to the respiratory move-
ments, in which the diaphragm plays so important a part. The
morbid changes in the respiratory movements arising from
contra-natural nerve-actions in distant parts, especially the ab-
domen, sufficiently prove this influence of the vis nervosa of
non-conceptional internal impressions on the nerves of the
thoracic muscles, and of the structures subservient to respira-
tion.

526. We can hence confirm the proposition already mooted
(285) as to the respiratory function ; namely, that at first in the
newly born, it is a nerve-action of external impressions, or at
the most a sentient action excited by obscure external sensa-
tions (525) ; that subsequently it continues both as a sentient
action excited by an instinct originating in those obscure ex-
ternal sensations (364, 285), but being also, from the habitual
recurrence of those stimuli, a direct or indirect nerve-action of
external impressions (51), occurring mechanically (475) ; and is
continually changed into a sentient action by new instincts, or
volitional conceptions, constituting the acts of laughing, weep-
ing, sighing, singing, speaking, &c. (285). According to all
probability, this is the true nature of the respiratory move-
ments in animals endowed with consciousness. In those not
so endowed, their mechanism is altogether diff'erent, and they
consist solely of nerve-actions.

527. The skin and mucous membranes have not a structure
capable of movements from external sensations, and, conse-
quently, cannot manifest nerve-actions from non-conceptional
internal impressions. Their vessels, and the glandular struc-
tures imbedded in them are, however, capable of their proper
nerve-actions. (Compare §^ 520 — 522.)

272 ANIMAL FORCES. [ii.

528. The functions of glandular structures generally must
be comprised in the same proposition, except in those cases in
"which secretion or excretion is effected by means of muscular A
tubes, or the action of adjoining muscles (172). Since secretion

is effected by the action of stimuli on the mouths of the capil-
laries, the general views already stated are applicable to it.
Thus, by means of the vis nervosa of non-conceptional internal
impressions, certain external impressions of food and poisons in
the stomach which are not felt, excite a flow of saliva and a
discharge from the bronchial tubes, as an indirect nerve-
action (419).

529. The glands, whose functions are regulated by muscular
action, are subject to laws previously stated (172, 473).

530. Although the glandular system is excited to the per-
formance of its functions by cerebral forces (172, 209), as well
as by the vis nervosa, yet the latter is the most general and
most usual excitant. Many glandular functions go on in de-
capitated animals, so long as they possess vis nervosa and the
functions are not interrupted by deep sleep, syncope, &c. They
are observed, too, in many animals not endowed by nature
with cerebral forces.

531. The oesophagus, stomach, and intestinal canal, are
capable of nerve-actions from non-conceptional internal im-
pressions. Vomiting, from injury of the brain, is an illustrative
example (490) ; colic or diarrhoea, produced by the application
of poisons externally to the umbilical region, is another ; ver-
micular action excited by puncture of a portion of the intestinal
canal, another (513).

532. Although the movement of the digestive apparatus is
usually a direct nerve action of external impressions, and con-
sequently requires neither the cerebral forces, nor the concep-
tive force (466, 467), nevertheless, not only conceptional internal
impressions often change it (170, 174, 206, 212), but it also
requires the co-operation of non-conceptional internal impres-
sions for its continuance, just as is required in the movements
of the heart, diaphragm, and other parts; for the moving
power of the stomach is abolished, when the trunk of its
nerves is tied. Hence the continued connection of its nerves
with the brain is necessary to the movement of the digestive
apparatus, although independent of the cerebral forces and

CH. III.] VIS NERVOSA OF INTERNAL IMPRESSIONS. 273

the conceptive force. External impressions on the stomach
and intestines are the principal motor forces, and the peri-
staltic motion may be excited in those viscera when separated
from the body. The point whence the co-operating internal
impressions proceed, as well as the natural stimuli which cause
lem, are as yet unknown.

533. The entire process of digestion, although peculiarly a
direct nerve-action of external impressions, is changed in
various ways by non-conceptional internal impressions. It is
by no means correct to conclude, that because a certain altera-
tion in the digestive process is usually a direct nerve-action of
external impressions, it cannot originate in other animals from
primary non-conceptional impressions, or even that it may not
be a sentient action. It is also a great mistake, to refer all
such changes to the great irritability of the intestinal canal.

534. The muscular fibres of the lungs are as capable of
nerve-actions from non-conceptional internal impressions as
muscular fibres generally ; and since their capillaries and glan-
dular tissues are in this respect under the same general laws,
as the skin and glands at large, no further illustrations are
here necessary.

535. The capillaries of the liver, like those of the lungs,
and probably the ductus communis choledochus, are influenced
by non-conceptional internal impressions. Is it probable that
the animal poisons, introduced by the fangs or stings of en-
raged or poisonous animals, thus excite, by means of reflected
external impressions, contraction of the gall- duct and jaundice,
just as they excite spasmodic nerve-actions of the oesophagus
and the muscles of deglutition? or are they the direct nerve-
actions of the external impressions, derived from the poisons
introduced with the blood into the viscus ?

536. The kidneys are liable to the same changes in function-
as the liver. Is the change in the urinary secretion which
occurs when cantharides are simply held in the hand, but not
so as to excite any manifest external sensation, a nerve-action
of a reflected impression ? or is it not rather a direct nerve-
action, excited by the poison itself being carried to the kidneys ?
The latter is the more probable.

537. The urinary bladder is capable of many sentient
actions (176), and, consequently, of many nerve-actions from

18

274 ANIMAL FORCES. [ii.

non-conceptional internal impressions, although it is excited
for the most part by unfelt external impressions. This is
shown by the development of various spasmodic phenomena
involving the bladder.

538. The nerve-actions of non-conceptional internal im-
pressions in other viscera, as the spleen, pancreas, are either
the same as those of the glands, blood-vessels, &c., or else
experimental researches have not thrown light on the subject.

539. The organs of the senses are the seat of the same
nerve-actions, as the muscular system generally; it is there-
fore not necessary to give special illustrations.

540. The sexual functions in animals not far removed from
quadrupeds, are undoubtedly, for the most part, nerve-actions.
The seminal emission, which takes place in epilepsy, and in
which all sensation and consciousness is abolished, is of this
nature, as also the sexual congress of decapitated animals
before alluded to (481).

CHAPTER IV.

RELATIONS OF THE ANIMAL-SENTIENT [CEREBRAL] FORCES, AND
OF THE VIS NERVOSA TO EACH OTHER.

JECTION I. ON THE SUBSTITUTION [eRSETZUNg] OF NERVE-
ACTIONS FOR SENTIENT ACTIONS.

541. When an internal impression, caused by conceptions,
levelops sentient actions in the mechanical machines by means
)f the nerves, the material ideas must, firstly, be suitably in
contact with the cerebral origin of the nerve which regulates
the machine ; secondly, the internal impression must go un-

jinterruptedly downwards along the same nerve to the machine

itself; and, thirdly, there must be no impediment in the latter,

^hen duly excited, to its performing the movements, which

'e in accordance with its structure (129, 130). When an

iternal impression, not derived from conceptions, develops

lerve-actions in the mechanical machines, it acts under the

fsame conditions (422, 496) ; only it is not necessary that it be

lade at the cerebral origin of the nerve, or by means of

laterial ideas there, but it may be made at any point of the

lerve, provided it can go uninterruptedly from the point of

impression to the mechanical machine, which it moves (493).

In either case, the movement excited is the same, whether it

he a sentient action or a nerve-action (360).

542. When an internal impression, from external sensations,
|; develops direct sentient actions by means of the nerves, and,

even, at the point where the external impression of the sen-
sations has taken place, it must be reflected, and sent downwards
.along the same nerve which received the external impression
(188). When an internal impression, by means of an indirect
nerve-action of an external impression, causes movements at
.the point where the external impression has taken place, it
-produces the same movements as nerve-actions (422), which, as
sentient actions, were produced under the circumstances just
mentioned; these are also produced by a reflected external

276 ANIMAL FORCES. [ii.

impression (399, 422, 360), and may likewise result as direct '
norve-actions, from the vis nervosa of external impressions
(435). These principles have already been fully established
by the details of experiments on decapitated animals, and by
an analysis of the phenomena of muscular contractioD. Com-
pare §§ 201, 357, 445, 453, &c.

543. When an internal impression, from external sensations,
excites direct sentient actions in mechanical machines, which
have not received the external impression, it is reflected at the
cerebral origin of the nerve along fibrils which were not
impressed (188, 129, iv). If a non-conceptional impression, by
means of a direct nerve-action of an external impression, de-
velops movements in another machine than that duly im-
pressed by the external sensation, or excites them in the same
machine by means of other fibrils, it operates exactly as in
the preceding case. A non-conceptional primary internal im- i
pression produces the same effects under conditions already |
stated (436, 496). If, therefore, such an impression excite a
nerve-fibril, in the same way as it is excited by the internal
impression of an external sensation, then the same changes
take place, as a nerve-action, that usually accompanied the
felt external impression, and constituted a sentient action of
the external sensation.

544. When external sensations excite incidental sentient
actions, the material external sensation impresses the origins
of other nerves in the brain, which have not received the
external impression (124, 131), since it causes material ideas
in the brain for other conceptions (97). Consequently, the
incidental sentient actions of external sensations differ only
in the mode of causation, from those of other and spontaneous
conceptions (219, &c.), and are not really different. But
just as in a similar manner felt external impressions, acting
through nerves indirectly, induce sentient actions of spon-
taneous conceptions, so also unfelt external impressions induce
nerve-actions of non-conceptional internal impressions, con-
stituting the same movements which the spontaneous sensa-
tional conceptions caused by sensation would develop ; provided
only, that the unfelt external impressions be so deflected from
their course before they reach the cerebral origin of their
nerve, as to impress the same nerves as the spontaneous con-

CH. IV.] SUBSTITUTION OF NERVE^ACTIONS. 277

ceptions would have impressed, and in the same way ; and
provided also, that they be transmitted thence as non-concep-
tional internal impressions to the same mechanical machines,
as the spontaneous conceptions would have set in motion (436).
It has already been demonstrated, that the bodies of animals
may be so constituted, that external impressions, while being
transmitted to the brain, are reflected here and there upon
other fibrils of the same nerve, or upon other and different
nerves, and thereby cause an indirect nerve-action; that a
part [Merkmal] of this reflexion may be present in the
external sensation caused by the external impression, and
induce the conceptive force acting with the sensation to form
a certain spontaneous conception, foreseeing, imagination, &c.,
of which the indirect nerve-action, excited as aforesaid, is the
ordinary sentient action; and that thus the same animal
movement may be at the same time both an indirect nerve-
action of an external impression, and the sentient action of a
volitional or incidental spontaneous conception, connected by
the mind with the sensation of the external impression (438,439).
There are phenomena which accord with the view of the
constitution of animal bodies, and render it probable ; but this
probability is rendered much greater, when it is recollected
that in each kind of spontaneous sensational conceptions, (all
which are proximately induced by external sensations) (66),
phenomena are actually observed, that indicate that their sen-
tient actions are not solely developed by primary non-concep-
tional internal impressions, but that also in virtue of their con-
nection with the impression from whence the sensations which
excite them originate, they are excited as indirect nerve-actions
of those external impressions. This will be subsequently shown
more distinctly.

545. The material ideas of the sensational conceptions
arising out of external sensations, namely, imaginations, fore-
seeings, imperfect external sensations, &c. (67, 73, 148), are
simply imperfect material external sensations, which the cere-
bral force produces of itself, without the assistance of external
impressions derived from external stimuli (228, 239). Their
sentient actions are those of the external sensations to which
they refer, only they are less complete (229, 240, ii, iii).
Now, since unfelt external impressions and non-conceptional

278 ANIMAL FORCES. [ii.

internal impressions imitate tlie complete sentient actions of
external sensations, so also their nerve-actions resemble the
sentient actions of all other sensational exceptions : and inas-
much as the dominion of the vis nervosa extends over all
the mechanical machines capable of any sentient actions, it
follows, that all the sentient actions of imaginations and fore- «
seeings are imitated by the vis nervosa only. This view is ■
supported by observation. A gouty person dreams that he
has an attack of gout, and this foreseeing is accompanied by
the sentient action of retraction of the limb : in this case, the
obscure external sensation caused by pressure of the toe
against the bed-post, induced the foreseeing. But if the toe
of a decapitated frog be pinched, it makes the same movement,
although the irritation is quite unfelt. The same movement
is a sentient action in the one case, and a nerve-action in the
other.

546. By the same cause that a sensational conception is
rendered agreeable or disagreeable, but especially by means of
the impressions of sensational pleasure or suffering, its sentient
actions are also so ordered, that at the same time they cause
changes in the vital movements (251); and these changes are
connatural, if resulting from a moderate sensational pleasure,
and contra-natural, if from an immoderate sensational pleasure,
or from sensational suffering (252). The vis nervosa can
induce similar changes. Examples of this kind are afforded
by changes in the heart's movements — especially in the
circulation through the thorax — and in the mechanism of re-
spiration (519, 520, 525).

547. A change is caused in the vital movements — a sentient
action — by external sensations, in so far as they are pleasant
or unpleasant, or cause titillation or pain (80, 250). Now, the
cause why an external sensation is pleasing or unpleasing, con-
sists in a difference in the external impression itself, and this
difference exists whether it be felt or not (189). Consequently,
the vis nervosa of external impressions alone causes those
changes in the vital movements, which were caused when its sen-
sation was titillation or pain. For illustrations, see §§ 433, 434,
but the number might be readily increased.

548. Spontaneous sensational conceptions, imaginations, fore-
seeings, &c., are only portions of external sensations (228, 239),

( H. IV.] SUBSTITUTION OF NERVE-ACTIONS. 279

and, consequently, the pleasing or unpleasing internal feelings
they excite in the mind, depend on the difference in the nature
of the external sensation to which they are related. Now,
since sensational pleasure or pain depends on a difference in
the nature of the impressions which are felt (80), so also the

Ileasure or pain excited by all spontaneous sensational concep-
fons, differs accordingly as the external impressions differ that
Kcite the external sensations to which they are related (88).
jhe sentient action of sensational pleasure or pain is either a
Dnnatural or contra-natural change in the vital movements
^51, 252) ; and an imagination, foreseeing, &c., in so far as
; is agreeable or disagreeable, produces also a connatural or
Dntra-natural change by means of its internal impressions of
pleasure or pain, just as the external impression whereon it
depends produces change by means of its vis nervosa alone
(546, 547). The imagination or foreseeing of a titillation or
pain, changes the vital movements in the same way, but less
perfectly, as the titillation or pain itself. From hence we
conclude, that the vis nervosa of the external impressions, by
which the pleasure or pain in the imaginations, conceptions, &c.,
is indirectly excited, can of itself excite vital changes, which
constitute the sentient action of the imaginations, foreseeings,
&c., themselves. In the example already given of the dream-
ing gouty patient, we have an illustration of this view; de-
capitated animals and acephalous foetuses seem also to be as
much distressed by violent external impressions merely, as they
would have been if those impressions had been felt, so that the
heart palpitates, and the pulse is manifestly quickened. This
doctrine will be also fully illustrated, when we consider the
relations of the instinctive and emotional acts to the vis
nervosa.

549. From the preceding considerations (542 — 548), it
follows, that the actions of external sensations, or of imagina-
tions, or foreseeings, or of their sensational pleasure or pain,
may at the same time be both sentient actions and nerve-
actions, or may at another time be nerve-actions only ; or in
other animals, they may be solely nerve-actions resulting from
impressions independently of the co-operation of the cerebral
forces, so that neither head, nor brain, nor mind, is absolutely
necessary to their development; nay, if there be animals altogether

280 ANIMAL FORCES. [ii.

devoid of cerebral forces, and so constituted that the impressions
made on their nerves, are communicated to the mechanical ma-
chines, as they are when felt, or produced by spontaneous sensa-
tional conceptions, these animals can perform all the sentient
actions of pleasurable or painful sensations, imaginations, fore-
seeings, &c. (437 — 439); and the actions themselves vj^ill have
all the favorable or unfavorable influence on the economy, which
they would have had if they had been true sentient actions.

550. The efiPort of the conceptive force, arising out of the
pleasurableness or painfulness of sensational foreseeings, is
termed desire or aversion (81, 89); and by it the cerebral forces
are strained to develop fully the material idea of a certain fore-
seen conception (83). Ail the sentient actions of the sensational
desires and aversions are compounded of those of a sensational
foreseeing and of its pleasure or pain (255). Now, since all
these sentient actions can be caused also by the vis nervosa
(549), it follows that the sentient actions of the sensational
desires and aversions can be caused in like manner.

551. The blind instincts and emotions are sensational desires
and aversions dififering from the latter only in this, that they
manifest a higher degree of intensity, that they are wholly
sensational, and that the mind has only an obscure and confused
knowlege of their objects (90) ; their sentient actions diff'er also
in attaining a high degree of intensity, often bordering on the
contra-natural (256). Now, since the vis nervosa can of itself
cause the actions of the sensational desires and aversions, it
follows, that it can also cause those of the sensational instincts
and emotions.

552. Nature leads animals by means of sensational instincts,
to perform the acts necessary to self-preservation and self-
defence, to the propagation of the species, and to the care of
their young, by means of external impressions which she places
in their way at the proper time, if necessary (262 — 265) ; and
which impel even rational animals by very obscure sensations
to the fulfilment of these duties (266 — -269). Hence it is so
much the less surprising, that external impressions so wisely
prepared beforehand and produced by nature, can excite the
sentient actions of the natural instincts, as nerve-actions ; and
attain to and accomplish their object without their being felt,
and without the cerebral forces taking any share therein (89).

IH. IV.] SUBSTITUTION OF NERVE-ACTIONS. 281

I

^^Wut direct sentient actions of the instincts are none other than
l^^bianges in the vital movements arising from pleasure and pain,
combined with those movements which take place more com-
pletely during the satisfaction of the instinct, and which are
properly the sentient actions of a foreseeing (271, 272). To
these may be added a number of incidental sentient actions of
the instincts, which the vis nervosa can develop as regularly
and as providently as those of the instincts themselves (436 —
439). Lastly, the sentient actions of the satisfaction of the
instinct, are simply those of the foreseeing and of the actual
sensation, or of other sensational conceptions (275, 276), and
these also can be developed by the vis nervosa. We will de-
monstrate these views with reference to some of the principal
instincts.

553. The external impressions on the stomach, which excite
the instinct of hunger, excite an unpleasant external sensation
in the stomach of faintness, which, being a painful sensation,
changes the vital movements contra-naturally, and otherwise
stimulates to the performance of their functions, all the me-
chanical machines which co-operate in the mechanism and func-
tion of digestion (281). Incidental sentient actions accompany
these direct sentient actions of the instinct, as, for example,
that the animal shall go out to seek food, seize it, and carry it
to the stomach. Satiety, or the satisfaction of the instinct by
these means, is an external sensation in the stomach, which has
also its peculiar direct and incidental sentient actions, subser-
vient to the whole process of digestion. AU these actions may
be excited by the vis nervosa only, especially in those animals
whose organisms are so constituted that the vis nervosa can
take the place of the cerebral forces (439) . A headless tortoise
lives several months ; it cannot possibly feel the sensation of
faintness from emptiness of the stomach, yet the external im-
pressions must change the vital movements contra-naturally
like that painful sensation, because it becomes feeble and faint
from starvation. The digestive organs must be excited to the
movements which are requisite to digestion, by the external
impressions of emptiness, just as by the instinct, since the
bowels are moved peristaltically, and the digestive fluids are
secreted, so long as life continues (468). The most convincing
proof, however, of the general principle is, that those movements

282 ANIMAL FORCES. [ii.

are excited as nerve-actions, which usually are volitional; for
the animal raises itself, and creeps about to seek food. In
animals in whom the existence of a conceptive force is more
doubtful, the same thing is observed, for it appears from
Schaffer's experiments, that decapitated snails can obtain food,
and satisfy the instinct of hunger. (Schaffer, Versuche mit
Schnecken.) He placed headless snails under a glass, with
some bean-leaves ; on the following day he observed traces,
showing that they had crept about; on the fourth day, the
leaves were eaten into holes ; by the end of the month a new
head had grown.

554. It must be remembered, however, that direct proofs of
the production as nerve-actions of sentient actions, by the vis
nervosa only, are not always possible. In many cases, de-
capitation arrests certain functions, which although purely
nerve-actions, require some influence from the vis nervosa pro-
duced in the head and cerebrum. (Compare §§ 515, 524, 532.)
Again, when the head is separated, many nerve-actions cannot
possibly take place, because the organs in which they ordinarily
occur as sentient actions, are removed with the head. Thus,
the flow of saliva cannot be excited in a headless animal, by
the sensational stimulus of hunger. Further, the proof in
many cases can only be indirect, or an inference, as in the ex-
ample of the headless tortoise just mentioned, which, after long
fasting, crept about as if in search of food. Certain actions
result from certain stimuli previously to decapitation ; the same
results follow on the same stimuli after decapitation ; hence
we conclude, that in both cases the actions result equally from
the stimuli.

555. The external impressions that develop the instinct to
voluntary movements, excite unpleasant external sensations of
weariness, lassitude, indisposition, &c., which, being strong sensa-
tional painful feelings cause the vital movements to be feverish,
and stimulate the muscles of voluntary motion to perform their
proper functions, so that they jerk, move the limbs, and produce
complete movements. When the instinct is satisfied by the
performance of the movements, the agreeable sensation thence
resulting has also its peculiar results in the economy, and in-
duces a general healthy tone of the system (283). The instincts
for particular kinds of movements, as walking, sighing, laughing.

(II. TV.] SUBSTITUTION OF NERVE- ACTIONS. 283

yawning, crying, singing, striking, swimming, spinning, building,

&c. (284), have, as their inducements, various external sensations,

imaginations, foreseeings, and other instincts ; and it is an esta-

)lished fact in the whole animal kingdom, that all the actions

these instinct for voluntary movements may be produced by

le vis nervosa only. Various experiments and observations

lade on decapitated frogs and other animals already detailed,

rove this amply. An acephalous child retracts its limbs when

winched or burnt, exactly as an ordinary child would have done.

[t is related, that a decapitated man, being thrust through the

)reast with a sword, threw his arms together, — a movement

^bich under ordinary circumstances would have been the sen-

ient action of the instinct of self-preservation. The movements

ide by a decapitated man, immediately after decapitation, are

Tor the most part volitional in character. He struggles violently

dth his arms, that he may free bis hands from their bonds, and

10 be able to use them to save himself. He grasps with his

lands, and endeavours to turn, to stand on his feet, &c.

Jimilar movements in great variety may be seen daily in

lecapitated animals, as turtles, snakes, snails, flies, centipeds,

:c. Many of this class of movements, as singing, sighing, &c.,

jannot, however, be excited as nerve-actions, because decapita-

ion renders the experiment impossible, the organs themselves

)eing removed.

556. From the preceding and other considerations already

idduced (435 — 439), it is extremely probable, that these actions

)f the instincts, ordinarily voluntary movements in all animals

'^hich feel true instincts, often take place as pure nerve-

|actions (269); that they are sometimes of the one kind, some-

Itimes of the other (286) ; and, consequently, that animals which

[are endowed with neither sensation nor true instincts, being

Simulated solely by unfelt external impressions, can apparently

[act volitionally, and as if endowed with sensation. Respiration

pas already been quoted as an example of this kind (285, 526).

iWhen the instinct of an animal excites it to walk or run

[Toluntarily in a certain locality, the muscles of the legs

[are only sentiently excited at first to the suitable movements,

id, subsequently, an external impression is sufiicient to

^excite the same movements. Thus there are examples of

^persons who continually traverse the same streets, who fall fast

284 ANIMAL FORCES. [ii.

asleep on tlie way, are conscious of nothing, observe nothing
that they meet, and yet reach their destination. If it be
advanced, that these movements depend on obscure sensations,
(which, however, is not the case,) there are innumerable illus-
trations in lower animals, that are unanswerable. A frog uses
its legs quite differently, when it swims than when it leaps.
If, when decapitated, it be pinched, it leaps away, not because
an external sensation excites an instinct, but simply in virtue
of the nerve-action of an external impression. If, in leaping,
it falls into the water, it then uses its legs to swim, not because
the external sensation of the water excites the instinct to swim,
but because the external impression from the contact of the
water excites the movement as a nerve-action. This being
undoubted, why should it be presupposed that a living frog
leaps or swims only in consequence of the excitement of the
instinct by external sensations ? It is clear that it may do
both without external sensations, and without the development
of the instinct. Thus, it is manifest, that the movements are
probably often nerve-actions only, which we constantly suppose
to be sentient actions, because they are such in ourselves and
in other animals.

557. We can manifestly see from these considerations, what
truth there is in the inference made from the performance of
volitional motions of animals, especially of those which are
instinctive, as to the existence of mind, and of sensations, and
volitional conceptions. If the most voluntary instinctive ac-
tions of animals really sentient and endowed with true instincts
can be excited by means of mere external impressions, and can
go on after their organism has been subjected to so great an
injury as decapitation, — or if volitional movements can be
excited and regulated under such circumstances, by various
and successive external impressions, just as if they were felt,
and so excite new instincts into operation (555, 556), it were
altogether unreasonable to infer from the apparently voluntary
movements of many animals, whose whole conceptive force is
of doubtful existence, that those movements in them are sen-
tient actions of true instincts, and the results of external sen-
sations; or to accept these as the sole decisive proof, that
they possess conceptions. When we consider how carefully
nature has provided, that in the apparent instincts of animals.

en. IV.] SUBSTITUTION OF NERVE-ACTIONS. 285

the external impressions shall be applied in such order, and

with such energy, that in a like order and with proportionate

vigour, those voluntary movements are excited, which we con-

jsider as the sentient actions of the instincts (265), remembering

the same time how closely these are related to the ordinary

lerve-actions caused by these impressions, it can hardly be a

latter of surprise, that the latter take place as regularly and

adaptively, as if they were sentient actions. Our astonish-

lent, as we have already shown, arises from our erroneous

►Delusions (438). Is not that which appears to be performed

laptively, volitionally, and in a definite order, by a worm

dthout a head or brain, by an insect, or by any other animal

^hose structure is widely different from that of sentient beings,

Ithough in such we can scarcely trace vegetative life — is not

the whole life of an oyster, a sea-worm, a polype, a snail,

spider, a flea, an ant, a bee, &c. — is not the whole of their

lets, or part of them, solely an operation of the vis nervosa ?

[ay, are they not such even in sentient animals ? We know

)f no reason why it should be doubted, that such is the case

dth those animals whose organisms are not constructed to be

le seat of mind, like the bodies of sentient animals, but are

lanifestly so formed as to lead to the conclusion, that the

lervous ganglia, so numerous in many, perform the office of

brain, and that the external impressions which nature sup-

)lies, are so reflected from them to the limbs, that the latter

ire excited thereby to perform those movements, according to

the pre-ordained intent of nature, which, in sentient animals,

khe material ideas of the instinct develop in like manner by

leans of the cerebral force.

558. The external impressions, which cause the sensation of

[weariness, lassitude, and fatigue, whence the instinct for repose

ind sleep arises, develop the sentient actions of this instinct, as

[nerve-actions ; namely, a relaxation in the activity of the cerebral

forces, and the weakening of their action on the mechanical

lachines (287, i), without the instinct itself being excited, and

dthout being felt. A sudden pressure on the brain arrests

[in a moment the operation of the cerebral forces, without the

^nstinct for sleep being previously developed, and all conceptions

[and sentient actions suddenly cease. Opium, when taken,

texcites this instinct, and not only changes the vital movements

286 ANIMAL FORCES. [ii.

thereby, but the sentient actions gradually cease, in conse-
quence of the brain being rendered unfit for the performance of
its functions, and no material sensations being excited in the
brain. Opium acts on the nerves, as on the brain, and renders
the vis nervosa as inefficient as the cerebral forces. When
opium is applied to the nerves of a decapitated animal, it
changes and arrests the movements of the heart, but somewhat
more slowly than if taken. According to Whytt, a muscle
suddenly loses its irritability, if opium be applied to its nerve.
But the power of the vis nervosa to excite indirect nerve- actions,
as well as the direct, is abolished by opium, since all the nerves
of the body are rendered insensible, as well as those with which
it comes in contact; so that external impressions are neither
transmitted upwards along the nerves, nor reflected downwards.
Very frequently, not a particle of opium or other narcotic
poison, reaches the brain in narcotization ; for it acts when it
has scarcely come in contact with the stomach, and even when
applied externally, or when the heart is excised, and, conse-
quently, the circulation of the blood arrested (Whytt). It is
often impossible, that narcotics can excite sleep by causing ex-
ternal sensations, since their impressions on the stomach and
intestines are rarely felt (470), for they deprive the terminal
points of the nerves with which they come in contact, of both
their sensibility and vis nervosa at the same time, and thus, in
a moment abolish the most violent external sensation of a
nerve, namely, pain. It would appear, that Whytt (whose
experiments we have just quoted) was correct in concluding,
that the sleep which opium induced, was much more probably
the result of a diminution of the general sensibility of the
nerves caused by it, or in other words, of the cerebral forces
and the vis nervosa, than of the excited instinct for sleep ;
although when the opium acts at the same time on the brain,
this instinct may be developed.

559. The war-instinct, by which animals are motived to use
their natural weapons when exposed to danger, is really only
another form of the instinct to voluntary movement ; and, con-
sequently, its sentient actions may, under suitable circumstances,
be nerve-actions, excited by the same external impressions,
which, when felt, excite the instinct. Insects, as the earwig
and bee, thus use the natural weapons, placed in their abdomen,

'cii. IV.] SUBSTITUTION OF NERVE-ACTIONS.

287

Fter being decapitated. A horse with his head shot off by a
jannon-ball kicks when it is struck down, just as it usually
loes when its war-instinct is otherwise excited. Examples of
ithis kind are numerous.

560. It scarcely requires proof, that the sentient actions of
the instinct of propagation may take place as nerve-actions

'om external impressions only. Crickets allure to sexual
[congress, after decapitation, by the vibration of their wings;
land Kedi, Bibiena, and others, have observed that butterflies,
[after having copulated but once in their lives, repeat the func-
ition perfectly when decapitated, and the females after sexual
jcongress, deposit their eggs as carefully as if excited thereto by
[their instinct.

561. The preceding statements fully estabhsh the general
[fact, that all this class of sentient actions are only animal
imovements, which may be produced as perfectly by the vis

wsa only, as by the cerebral forces ; in many animals they
[are the preordained and adapted results of external impressions
^made by nature on the nerves for the express purpose ; in many
)thers, are at the same time sentient actions, being produced
|by the co-operation of the cerebral forces, and in this class are
-at one time excited as nerve-actions only, at another as both
sentient actions and nerve-actions ; and in newly-born animals,
which are insensible to the external impressions of the instincts,
are developed as nerve-actions only. Further, the acts which
btake place in connection with its principal and secondary
/instincts, characterise an animal, and determine its sensational
-character and leading propensities (295), constitute no proof
^that such animals are controlled by true instincts, or are en-
dowed with the sensational faculty or with mind (437 — 440).

562. The instinctive passions originate like instincts from
obscure sensational stimuli; differing only in this, that the
latter are perceived during their continuance (298). Their
sentient actions are the same as those of the instincts, but the
incidental sentient actions are developed rather according to
psychological laws (297). But inasmuch as they arise in the
instinct itself, and, consequently, in close connection with the
external impressions which excite it, and since the sentient
actions of the instinct are excited by the vis nervosa only, and

, can take place in the same order as if excited volitionally (552),

288 ANIMAL FORCES. [ii.

it appears that the incidental sentient actions of the instinctive
actions, stand in the same relation, and may be equally excited
by the vis nervosa. All the actions which a sentient animal
performs under the influence of the instinctive passions (299 —
303, &c.), may be excited in another animal by the vis nervosa of
external impressions in the order and succession preordained
by nature. Decapitated insects supply illustrative examples.
In many animals these actions take place naturally as nerve-
actions.

563. That the sentient actions of the passions can be excited
as nerve-actions, by means of non-conceptional internal im-
pressions, does not admit of doubt (503). All the passions
modify the circulation, the action of the heart, the respiration,
and the vital movements in general (307, 310). Internal im-
pressions do the same in a thousand instances, simply by means
of the vis nervosa (515 — 521, 525). The other sentient actions
of the passions are often volitional movements, often changes
in the natural functions of the viscera (307 — 325), and these
also can be produced by the vis nervosa of internal impressions
(508, 532 — 540). But an important question arises, whether the
sentient actions of a passion, considered as incidental actions
of the primary external sensation, can be excited by the vis
nervosa of the external impression proper to the latter, according
to the doctrines stated, § 544.

564. Animals not endowed with reason are peculiarly main-
tained in the performance of their natural functions by the
blind instincts ; and it is only the most skilful in which we see
the latter attain to the stage of instinctive passions, because
their brain is capable of containing a greater number or a
greater development of material ideas (26); for it is certain,
that a more perfect conceptive force which can form wholly
pure conceptions and a higher degree of sensational perceptions,
are necessary to the development of the passions in general
(305), and these are possessed only by the more perfect animals.
A true passion never results so directly from external sensations,
however pure [klar] they may be, as the natural instincts and
instinctive passions (276, i, 298). The former usually require
entire series of other pure [klar] sensational conceptions, often
only distantly related to external sensations, which the mind
connects together according to psychological laws, and of w^hich

CH. IV.] SUBSTITUTION OF NERVE-ACTIONS. 289

a very imperfect and obscure conceptive force is not capable
(89^ 108). It is only necessary to compare an instinct and a
passion, ia one point, to be assured of this. Any painful external
sensation immediately excites the war-instinct, and the move-
ments proper to the instinct as instantaneously follow, even in
man himself, and before the cause of the sensation is known.
Between the external sensation exciting the instinct and its sen-
tient actions, no traces of conceptions can be discovered, con-
sequently there are no material ideas of imaginations, foreseeings,
&c., produced by the external sensation ; so that there appears
to be a direct transition [Uebergang] of the latter into the
instinct itself, and the material ideas proper to it to take effect
in the sentient actions of the other. So that it may in some
degree be asserted, that in the instincts the brain turns back
[umwendete] the felt impression, and reflects it on the nerves
appropriate to the sentient actions of the instinct, just as an
unfelt external impression is reflected in the ganglia, and this
without the material ideas of the conceptions necessary to the
instinct becoming an object of special thought, they being too
little developed; and without its sentient actions being obviously
excited and connected with each other, according to psycho-
logical laws. If, on the contrary, a man be excited to anger
by a pain inflicted by another, between the passion which
excites to combat, and the painful sensation, a number of
connected sensational conceptions arise, which are psychological
and volitional in their character. He perceives clearly that an
injury has been done him; he resolves to retaliate on the
offender; is undecided as to the means by which he should do
this; chooses that which comes first to hand, and by a con-
tinually repeated and magnified conception of the injury, is
more and more irritated against his enemy. Just as these
sensational conceptions, excited by the external sensations, are
developed in the mind, and excite the instinct (94), so also are
the material ideas which produced the material external sensa-
tion developed in the brain ; so that in this case there is not
that apparently direct transition of the external sensation into
the passion itself, and of the material ideas of the former into
the sentient actions of the latter. To comprehend the sentient
actions of the passion, in their connection with the external
impression which first excited it, the course of all the sensational

19

290 ANIMAL FORCES. [ii.

conceptions and their sentient actions must be traced as far as
the outbreak of the passion and its sentient actions, so that it
may be noted how they are developed from each other, according
to psychological laws (108).

565. Amongst those sensational conceptions induced by an
external sensation, and which must be generally developed ere
they form the passions (94), there are in many passions some
which are incidental and as little related to the primary sensa-
tion, as conceptions of the understanding; and, consequently,
are not really produced by the external impression which
excites the sensation, but are excited in successive series, accord-
ing to psychological laws. But since these conceptions are
nevertheless the incitements [Triebfedern] of the passion which
they excite into activity, it follows that the sentient actions of
the passion so excited are not really produced by the primary
material sensation, and, consequently, not by its external im-
pression; and therefore cannot be developed either as its
sentient action or nerve-action. An example will illustrate
this. An individual sees another who resembles a deceased
friend. This constitutes the primary external sensation of all
that follows. In accordance with psychological laws the mind
perceives the resemblance, and this is the first intermediate
conception which is not connected with the sensation according
to the laws of the vis nervosa. Thence arises the imagination
of the deceased friend, which has only, in common with the
sensation, those sub-impressions of the two persons in which
they are alike. Next arises the recollection of the death of the
friend, and all its accompanying circumstances, with which the
primary sensation has nothing in common. Lastly, the fore-
seeing arises, that death has cut off all possibility of future
converse with him. This foreseeing is painful, and the mind
endeavours, according to psychological laws, to develop the
conception antagonistic to this painful one. In the effort of
the conceptive force to effect this, consists the passion of sorrow,
which was excited by the sight of the individual. All the
conceptions thus excited are as far removed from the primary
sensation, as many an abstract conception induced by sensations,
consequently, the sensation has really contributed nothing to
the sentient actions of the sorrow. But the vis nervosa of the
external impression of the sensation can only develop as nerve-

CH. IV.] SUBSTITUTION OF NERVE-ACTIONS. 291

actions, those movements which its external sensation would
have, or had, excited as its sentient actions (542, 543). Con-
quently, the vis nervosa of the external impression which induced
the emotion of sorrow, cannot excite as nerve- actions, the sen-
tient actions of the emotion. The same doctrine applies to
many other passions.

566. Nevertheless, all passions are not excited so remotely,
and with the intervention of so many purely psychological con-
ceptions ; for there are some which, from their closer connection
with external sensations, are similar in their origin and de-
velopment to the instincts. With regard to this class, it must
often remain doubtful, whether they belong to the passions, or
to the instincts, or instinctive passions. Thus fear, alarm, and
terror (313, 318), which an external stimulus excites in us,
without an intervening series of irrelevant and purely psycho-
logical conceptions, is usually rather a form of the instinct of
self-preservation (299) : the anger and revenge of the dog rather
a modification of self-defence (326). The affection of many
animals for their ofPspring, which sometimes (as in monkeys),
appears to be a passion, is but a form of the instinct to tend
offspring (303) ; the frolicsomeness and cheerfulness of many
animals rather an iiistinctive passion for enjoyment (299). The
sentient actions of emotions of this class do not differ from
those of true instincts, except in being accompanied with the
sentient actions of some other conceptions, which the conceptive
force intermingles according to its own laws (297 — 304). Now,
since all these may be excited by the vis nervosa only (549, 552),
no repetition of proofs from observation (compare 553 — 562) is
necessary to demonstrate, that the same external impressions,
which, when felt, excite the sentient actions of these instinctive
passions, will also excite them by means of the vis nervosa only,
as nerve-actions. We will, however, analyse the emotion of
terror. In this, the external impressions cause a painful
external sensation; or such a sensation as induces a strong
sensational unpleasantness [Uulust] , because it excites a sudden
secondary sensational conception : as, for example, when an
individual hears a noise, he immediately imagines it to be
thunder, or, if he receives a blow, he conceives it to be given
by a robber. This disagreeable sensation changes the vital
movements contra-naturally, and violently (314, 318), and puts

292 ANIMAL FORCES. [ii.

those machines into motion, which must act in flight and
defence from the foreseen danger (315, 319), whence all the
other phenomena result (316, 320). All these sentient actions
may be excited as nerve-actions, in decapitated animals, insects,
or frogs, or in a decapitated man, or in an acephalous foetus.

567. Not even the same kind of passions arise always from
external sensations in the same way, but sometimes directly
from them, sometimes with the intervention of many psycho-
logical conceptions. When a dog is frightened by a sudden
blow, so that it excites its muscles for the purpose of running
away, it connects with the external sensation of the blow, the
foreseeing excited by frequent experience, that many more
blows will follow, and thus the emotion of fear arises, without
the intervention of other conceptions. This sentient action of
fear can be developed by the vis nervosa only of the same ex-
ternal impression, and would be manifested if the animal were
decapitated (555). If, on the other hand, fear is excited in a
man by a sudden blow, it may arise from a sensational concep-
tion, which has little in common with the sensation. He judges,
for example, that the blow must have been inflicted by a man :
he looks about, and sees no one. This excites surprise and
thought, and he now concludes from probabilities : firstly, he
thinks it may have been from a concealed robber, and thus fear
incites him to those sentient actions which can protect him :
then he conceives it was a ghost, and fear incites him to run
away : lastly, he attributes the blow to some missile, and fear
incites him to hide himself, &c. The impression of the blow
could not possibly excite all these various kinds of sentient
actions, since so many volitional conceptions influence them ;
the external sensation only excites the will into action.

568. We conclude, therefore, from the preceding statements :
i. That the sentient actions of the passions generally may
be excited by means of the vis nervosa only (563) ; but that
the same external impressions, which by means of their corre-
sponding external sensation induce the passions, however
remotely (66, 90), can only excite by the vis nervosa the move-
ments constituting the sentient actions of the latter, in so far as
these actions, although always incidental to the external sensa-
tion excited, are not produced by intermediate conceptions, in-
duced by other sensations differing altogether from it, and only

CH. IV.] SUBSTITUTION OF NERVE-ACTIONS. 293

in so far as the movements are at least in part dependent
on it.

ii. That the reason why the sentient actions of the instincts,
although only incidental, are much more frequently excited as
nerve-actions by the vis nervosa of the external impression
only, than those of the passions, is this : namely, that the ex-
ternal sensation which excites an instinct, being seldom or
hardly an object of consciousness to the animal, is in closer
relation with the sensational volition of the conceptive force
than in the passions ; in which other sensational conceptions,
altogether foreign to the primary external sensation, are so
widely removed from it, that the sentient actions are quite
incidental and excited by them according to psychological laws.

569. Although the vis nervosa can excite the sentient
actions of the passions generally, it cannot imitate the opera-
tions of the cerebral forces, in the order in which they are
developed psychologically, from the primary external sensation
to the outbreak of the passion, unless the latter, like instincts,
depend directly, or for the most part, on the sensation. Now
since the other results in the animal economy, which peculiarly
characterise each passion, are caused by the sentient actions of
the passion, by means of the natural connection of all the
forces of the animal body, they can be induced by the vis
nervosa of the external impressions which excite the passion
only under the same conditions. Thus, the sentient actions of
joy, namely, the quicker and more vigorous action of the heart,
the half-convulsive movement of the diaphragm in laughter,
and the volitional movements of dancing, singing, &c., may all
be induced by the vis nervosa only, as has been already fully
shown. But if the attempt be made to trace the greater
number of the joyous emotions to their primary sensations,
and to deduce their sentient actions and their other animal
movements from their impression alone, as for example, from
the nerve-actions caused by wine, or by music, or by a look,
or conversation, observation will not afford an instance in which
these flow directly from the external impression, except in
those cases in which the emotion arises directly from external
sensation, like the instinct for pleasure. Such is the case when
a chrysalis writhes and turns about if placed in the sun, as if
from the pleasurable sensation of warmth ; or when a torpid

294 ANIMAL FORCES. [ii.

newly-born child, after being washed with wine, moves its
limbs, having its circulation accelerated, &c., just as would
have followed from the taking of wine; or when a headless
butterfly is excited to copulation, by the fluttering of the
female, just as if the sexual sensation had been excited in it.

570. Who can doubt, that the sentient actions of sorrow
(310, 312) may be induced by the vis nervosa only ? Yet if
we were to trace them back in the majority of cases to the
primary sensation, and attempt to deduce them from their
external impressions only, namely, from the nerve-actions of
black bile in the stomach and bowels, of imperfect digestion,
&c., in the order in which they arise, together with their
material results in the economy, such as diminished transpira-
tion, weeping, wailings, &c., we should find no examples in
which it could be done, except in instances in which they
arise directly from the external sensation. In this way, a child
cries from the first external impression of the air, as if suffering
pain, a decapitated man clasps his hand, when wounded, as if
lamenting, &c.

571. The sentient actions of all kinds of fear, anguish,
despair, and terror (314 — 320), may also be excited by the
vis nervosa solely ; still, as in the preceding cases, they cannot
be traced directly back in the order in which they arise to the
primary sensation, and thence to the external impressions
causing them, except in the instances in which they arise (as
in instinctive actions) immediately from the external sensation,
and of which illustrations have been already given (566).

572. Lastly, the sentient actions of all kinds of anger and
revenge (323 — 325), may be excited by the vis nervosa only;
still, as in the preceding instances, they cannot be traced back
to their primary exciting impression, except when they are
instinctive in their nature, and arise directly from an external
sensation.

573. In investigating the sentient actions of all the other
passions, and other desires and aversions, the material ideas of
all the intervening sensational conceptions must be considered
(111, 568, i, ii). The sentient actions of the true passions
(306, 309), can never occur in decapitated animals, solely by
means of the vis nervosa, or in those not endowed with mind,
or capable at most of only feeble and obscure external sensa-

I

(II. IV.] SUBSTITUTION OF NERVE-ACTIONS. 295

tions. The apparent instances adduced to the contrary, are
really only examples in which the sentient actions are instinctive
in their nature, and have arisen from direct external sensations.

574. The material ideas of the conceptions of the understanding,
are not excited like those of sensational conceptions by external
impressions (66) ; consequently, they cannot be excited by
the vis nervosa of the latter, in the order in which they are
developed psychologically. But as all material ideas, and, con-
sequently, those of the intellectual conceptions are internal
impressions on the cerebral origin of the nerves (121), it follows
that their actions may be developed by the vis nervosa of non-
conceptional internal impressions (360). Still, as they manifest
no visible direct sentient actions (330), except in so far as they
are either at the same time sensational (and then the vis nervosa
can excite them) or incitements of the mind, and excite the
will, it follows that no direct actions of the intellectual con-
ceptions can be induced as nerve-actions by the vis nervosa
acting through the nerves.

575. The incidental influence of the understanding on the
animal economy arises in various ways (331), and can only be
replaced by the vis nervosa acting alone, in so far as it consists
in sentient actions from sensational conceptions, or from plea-
sure or pain of the desires and aversions, whether sensational
or intellectual (574). In so far, however, as the eflPort of the
intellectual power involves and disorders the entire organism
(331, 332), and an abuse of the cerebral forces must necessarily
have this effect, — to this extent the effects of the abuse of the
vis nervosa are identical, whether the latter co-operate with the
former or not (356 — 360). For example, just as study en-
feebles the body, wastes it, and disorders its natural functions,
so also does an excessive indulgence of the sensational instincts
(261, iv). Thus, an abuse of the sexual instinct has the same
injurious effect as excessive study.

576. The gentle influence which the intellectual conceptions,
in so far as they are agreeable, or the contrary, have on the
vital movements (333), may be exercised by non-conceptional
internal impressions ; and in this way the movements of the
muscles which the intellectual desires and aversions, and
their satisfaction, develop as direct sentient actions (340),
are often incidentally mere nerve-actions of impressions

296 ANIMAL FORCES. [ii.

(342, 445, 507). But since the mind produces all these kinds
of motives [Bewegungsgriinde] and desires of the will, according
to purely psychological laws, and independently of external
impressions (333, 341), the movements resulting cannot be
induced like the sentient actions of sensational conceptions,
feelings, and desires, by the vis nervosa ; and, although those
movements which are excited by the will, in intellectual beings,
may and do occur in decapitated animals, or in purely sen-
sational animals, still they are induced by impressions, and not
psychologically.

577. The incidental influence which the will exercises, by
means of its acts on the animal economy (compare 336, 337, 343),
can be exercised also by the vis nervosa, in so far as that in-
fluence consists in sentient actions directly dependent on the
internal impressions of sensational conceptions, incitements,
and desires.

578. The intellectual conceptions (330), the motives con-
tained in them (333), and all desires and aversions of the will
(339), in addition to their remote connection with sensation
(65), possess a special connection in virtue of the sensational
conceptions, incitements, and desires, intermingled with them.
Hence all their sentient actions have a sensational character, and
to this extent can sometimes be induced by the vis nervosa of
external impressions, although always very imperfectly. When
the external sensation of a tune excites our instinct to dance,
the desire of the will to dance a rhythmical dance is combined
with the instinct, and by dancing we satisfy that desire. In so
far as this free-will act is a sentient action of the instinct, it can
be excited purely as a nerve-action of other impressions : those
affected with chorea St. Viti, for example, dance involuntarily
and convulsively, even when sleeping, but certainly not ryth-
mically, since this is an action of the will.

579. The following conclusions may be drawn, as to the
substitution of nerve-actions for sentient actions. All move-
ments which can be sentient actions may be excited, either
as nerve-actions only by the vis nervosa alone, or as the latter
at the same time that they are sentient actions (503); and so
far as it is possible to illustrate the question by observations and
experiments, the latter establish this principle without exception.
If, however, the sentient actions be considered in reference to

CH. IV.] SUBSTITUTION OF NERVE- ACTIONS. 297

their exciting cause, namely, the conceptions of the mind, and
in connection with the order in which they are developed, and
succeed each other, we find there are two kinds :

i. Certain conceptions, namely, the sensational, are induced
in the mind by external impressions corporeally and necessarily
(65, 66), and are developed by the mind, so as to succeed
each other only in the same order as the external impressions
succeed each other, and determine the conceptions to act,
according to the laws of the vis nervosa. These sensational
conceptions are — the external sensations, imaginations, fore-
seeings, &c. — the sensational incitements they contain, and the
sensational desires and aversions, particularly the instincts
and passions. External sensations, together with sensational
pleasure and pain (80), and the blind instincts (263), are the
most directly induced of all these by external impressions, and
are developed and succeed each other just as the impressions
succeed each other, according to the laws of the vis nervosa, and
develop their material ideas in the brain; and the sentient
actions of these sensational conceptions are also developed in
like manner, (542, 543, 547, 552, &c.) The remaining sensa-
tional conceptions, incitements, and desires, namely, the
imaginations, foreseeings, &c., with their sensational pleasure
and pain (66, 80), and the passions (305), are somewhat more
free from the natural and necessary influence of external im-
pressions, and are developed and succeed each other more
according to psychological laws ; nevertheless they are not to be
confounded with recollections, expectations, &c. (238 249),
considered as simply imperfect external sensations, and not
directly dependent on external impressions. Hence the sentient
actions of imaginations, foreseeings, &c., are in fact those of the
external sensations to which they are related (237, 247), and as
such (as experience teaches) may be induced by the vis nervosa
only (545, 547). It is only the sentient actions of the higher
passions, and of the higher sensational desires and aversions,
which are formed and developed rather according to psycho-
logical laws than the laws of the vis nervosa, and which cannot
be induced by it as nerve-actions (573).

ii. The other class of conceptions is the intellectual. This
comprises those perceptions which are not sensational, the
motives they contain, and the desires, aversions, and satisfactions

298 ANIMAL FORCES. [ii.

of the will. Their material ideas are formed, and connected
with each other, in the brain, solely according to psychological
laws, and their sentient actions are developed and succeed each
other independently of external impressions : consequently,
they cannot be induced by the vis nervosa as nerve-actions,
except incidentally, and then not in the same sequence as that
in which the mind develops them (574 — 576).

iii. This difference in the two classes of conceptions, as
regards their relations to external impressions, has led eminent
men into the singular error of placing the seat of the first class
in the body, and that of the second in the mind. The occasion
of the error is so obvious, that further explanation is not
necessary. All that is conception, consciousness, thought, is in
the mind [in der Seele]. External sensations are conceptions
of external impressions on the nerves; all sensational concep-
tions are only repetitions, or anticipations of these ; the feeling
of that which is pleasing or displeasing in a sensational con-
ception constitutes sensational pleasure or pain [Unlust] ; hence
are developed sensational desires, instincts, and passions ; and
although all these take place from the impulse of external im-
pressions, still it is always in the mind that these conceptions,
pleasures, and desires, are forcibly developed. They are as
certainly sentient as the most voluntary sensational conceptions
and desires, or the most abstract ideas, and the noblest motives,
passions, and conclusions of the will. But the external im-
pressions which excite sensational conceptions, pleasures, and
passions in the mind, can, nevertheless, if they do not develop
these, excite, by means of their vis nervosa, the same movements
in the animal economy, and in the same order and series, as if
they were excited as sentient actions. In cases of this kind,
the organism performs the sensational acts of desires, of instincts,
of passions, without these being really in the mind ; but how
can it be inferred from hence that they are present in the
body ? There is a force, it is true, which imitates their work-
ings, whether it co-operates with them or not; but the crude
matter cannot feel pleasure and disgust ; or desire, or shun
anything.

CH. IV.] SUBSTITUTION OF SENTIENT ACTIONS. 299

SECTION II. ON THE SUBSTITUTION OF SENTIENT ACTIONS FOR

NERVE-ACTIONS.

580. There are three principal kinds of nerve-actions in the
mechanical machines : firstly, those of primary internal impres-
sions, not caused by conceptions (419); secondly, those of
unfelt reflected external impressions ; and thirdly, those of direct
external impressions (418).

581. The nerve-actions of primary non-conceptional internal
impressions may be excited by the impressions of conceptions,
since the two kinds develop the same animal movements (541).
The non-conceptional internal impressions may be divided into
the contra-natural, to which class the experimental belong, and
the natural. The experimental internal impressions are those
made on the brain, spinal cord, or nervous trunks, by various
stimuli in experimental researches. There is no nerve-action
caused by impressions of this class, which is not induced also
as a sentient action ; and it is because we know them as the
latter, that they surprise us so much when excited artificially
(486). Nerve-actions are often excited in the usual condition
of an animal, by contra-natural internal impressions, as when
the cerebral origin of the nerves, the spinal cord, or the trunk
of a nerve is irritated by stimuli, which are not conceptions,
and so cause nerve-actions; as, for example, when efiused
fluid in the brain partly paralyses, partly causes spasmodic
action in the extremities ; or when an acrid humor is determined
to the spinal cord ; or it has been injured ; or a tumour or growth
on nerves causes contra-natural movements in the parts regu-
lated by the afi'ected nerves. These are also similar to move-
ments which occur as sentient actions in the natural condition,
or at least, as contra-natural sentient actions. Thus, a fright
will paralyse or convulse the limbs, as much as a paralytic
stroke from effusion; the convulsions excited by an acrid
humor determined to the nerves are excited also by anger or
anxiety; and the most violent convulsions may accompany
intense passion in sensitive persons, &c.

582. When reflected unfelt external impressions produce
nerve-actions, they act in the same way as internal impressions,
and the same animal movements are excited. Consequently,
the observations made in the last paragraph apply equally to

300 ANIMAL FORCES. [ii.

them. But the question arises, whether the unfelt external
impression, which, by its reflection causes an indirect nerve-
action, can, when felt, excite the same movement as a direct or
indirect sentient action of its sensation ? It is not easy to
answer this question without going into details.

583. When the toe of a decapitated frog is pinched, it
places its limbs in a position for leaping, and actually leaps, in
consequence of the indirect nerve-action caused by the external
impression on the toe (415, ii) ; and the question arises whether
the same impression, when felt, would cause the same leap as
a sentient action of the pain caused, either indirectly or
incidentally, in consequence of the excitement of an instinct ?
Probably it is so, for a healthy frog leaps when it feels the pain
caused by pinching its toe ; but in this case is the leap neces-
sarily a sentient action caused by the pain? for although it
may take place as such at the same time that it occurs as a
nerve-action (364), still it does not follow, that in the case of
the healthy frog, the leap is so produced. How can it be shown,
experimentally, whether it occurs from the sensation of the ex-
ternal impression, or from the impression only? Everything
which prevents the action of the external impression, also
partly prevents its being felt, and if felt, partly prevents the
same movement being excited as a sentient action of the sen-
sation. Other difficulties might be mentioned, and, in fact,
there is only one means of solving the problem.

584. The sensational conceptions, namely, imaginations,
foreseeings, &c., are imperfect external sensations, which are in
relation to an external impression ; and their sentient actions
are the same as the actions of the external sensations, but are
imperfectly so, since the external impression and all its nerve-
actions are wanting (68 — 74). Now, if an imagination or fore-
seeing of a sensation excites imperfectly as sentient actions, the
same movements which the external impression of the sensation
usually excites, as its indirect nerve-action, the conclusion is
obvious, that the sensation of the impression itself will produce
the same animal movement ; particularly, as in the normal con-
dition it always accompanies sensation, which would not be the
case if it were always a nerve-action only of the external im-
pression. Now, the former proposition is established by ob-
servation ; and the latter must be true, since it does not appear

CH. IV.] SUBSTITUTION OF SENTIENT ACTIONS. 301

that any objection can be raised. If a frog could dream, and
dreamed of a pinching of its toe, the imagination would certainly
induce it, if not to take a leap, at least to place its limbs in the
necessary state of preparation for leaping. Animals endowed
with sensational conceptions and instincts afford a thousand
proofs of this doctrine, since all their imaginations and fore-
seeings express, although imperfectly, the sentient actions of the
sensation to which they are related; while many of these actions
are at the same time nerve-actions of the external impression
which causes the sensation (543, 545). A person dreams that
his finger is touching red hot iron, and withdraws his whole
arm, as if he really touched it. This retraction is the imper-
fect sentient action of the imagined sensation, and may occur
as a nerve-action, being analogous to the retraction of its foot
by a decapitated frog, when its toe is pinched. Illustrations
of this kind could, in fact, be multiplied to any extent in support
of the proposition, that the indirect nerve-actions of external
impressions are, when the latter are felt, at the same time
direct or incidental actions of the sensations of those impressions;
and that the feeling itself is nothing superfluous in the pro-
duction of these movements, which the impressions themselves
can excite as indirect nerve-actions.

585. The direct nerve-actions of an external impression, or
in other words, the movements of irritability (432), can, in
general be replaced by sentient actions. Since they take place
principally in muscular fibres (445), which are moved by all
cerebral forces from external sensations to free-will acts in-
clusive, the movements of the muscles are the same, whether
they be nerve-actions or sentient actions (161-162); and no
result of irritability can be mentioned, which cannot be a
sentient action. Innumerable illustrations might be advanced
(445_448, 204, 229, &c.)

586. But since the direct nerve-actions of external impres-
sions are developed at the point where the impression is made
when it is not transmitted to the brain, or, if transmitted along
the nerves, before it reaches the brain — the question arises,
whether the impression can produce, when felt, the same direct
nerve-actions it produced when unfelt ? This question offers
the same difficulties as that mooted in a previous paragraph,
regarding indirect nerve-actions.

302 ANIMAL FORCES. [ir.

587. The answer must, as in the preceding paragraph, be
deduced from a consideration of the sensational conceptions,
and mutatis mutandis, the line of argument is the same. When
we imagine that we have swallowed an emetic, and the imagi-
nation excites retching and vomiting, as if an emetic had been
really taken, the conclusion is obvious, that the felt external
impression on the stomach of such an emetic, or its felt nerve-
actions (413), must have produced the same movement, namely,
vomiting, as a sentient action of the external sensation at the
irritated point, which the same external impression had excited
there at the same time, as a direct nerve-action. This occurs
also when purgation takes place, simply from dreaming that a
purgative has been taken; when we shiver from the imagination
of intense cold; when suffusion and blue marks take place, at the
spot where we dream that we have received a blow, pinch, &c.

588. Although the direct nerve-actions of external impres-
sions, or in other words the results of irritability (432), do not
require the co-operation of the cerebral forces for their produc-
tion, still, in cases where the impression is felt, they may occur
also as sentient actions of the sensation. Consequently, it
would be erroneous to conclude, that a result of irritability
could not be at another time a sentient action of the sensation
caused by the irritant, or that it may not depend on sensibility.
This conclusion can only be made when the external impression
which causes the movement is not felt nor cannot be.

589. We conclude therefore, that all nerve-actions of non-
conceptional internal impressions can be altogether replaced by
sentient actions, that is to say, induced by internal impressions
caused by conceptions (581). With reference particularly to
those excited directly by external impressions, it may be stated,
that they are developed as sentient actions by the external
sensation of the external impressions which excite them (584,
588).

SECTION III. THE RECIPROCAL CONNECTION OF THE ANIMAL-
SENTIENT [cerebral] FORCES WITH THE VIS NERVOSA IN
THE NATURAL STATE.

590. When an external impression is not felt, and a primary
internal impression is not excited by conceptions, the movements

CH. IV.] RELATION OF CEREBRAL & NERVE FORCES. 303

resulting from either are only nerve-actions, since they cannot
be also at the same time sentient actions (97), and there are
no other animal forces than the vis nervosa (356), inasmuch as
in this case it does not signify, whether the unfelt external im-
pression can be felt or not ; or whether the primary internal
impression not caused by conceptions can be caused by con-
ceptions or not. It follows, that no combined action of the
cerebral forces and vis nervosa effects these animal movements,
even in sensational and thinking animals, and a fortiori in those
which have no sensational faculty, and, consequently, no mind.
Since the latter class, in common with all animals, without
exception, are endowed at least with the vis nervosa, it alone
must be sufficient for all the objects of their existence. According
to this view, the acts of all anencephalous [hirnlosen] animals
(to all which, as far as can be observed, they are excited by
external impressions), are partly direct nerve-actions, partly
dependent on the reflexion of the impressions in the ganglia
and plexuses, and thereby are rendered similar to sentient
actions and volitional acts (438-439) ; while, on the other hand,
their vital movements and the indispensable functions of their
mechanical machines, are maintained by non-conceptional im-
pressions, as occurs in sensational animals (515, 519, 525, 532).
These views apply also to the acts of sensational animals, in as
far as the impressions which excite them are unfelt, or not
induced by conceptions, for as they all possess the two kinds
of vis nervosa, the acts must necessarily be nerve-actions, inas-
much as the mind cannot act (353, 356).

591. When an external impression is felt, the resulting
animal movements are both nerve-actions of its vis nervosa and
sentient actions of its external sensations. The first — because
they equally result, even if the sensation be wanting (542 — 547):
the last — because the sensation of an external impression
excites material ideas at the cerebral origin of the sensitive
nerves; the internal impression thus caused is transmitted down-
wards, and excites movements in those machines to which the
nerve is distributed, and these are the direct sentient actions of
the external sensation, and identical with the direct or indirect
nerve-action of the external impression, which gave rise to the
sensation (418, 419, 358). But since the transmission of the
internal impression, caused })y a material external sensation.

304 ANIMAL FORCES. [ii.

may be prevented by natural obstacles, and thus the movements
may never take place (136 — 139), it follows that animals may,
in the natural state, exhibit direct or indirect nerve-actions of
external impressions, which never occur as sentient actions of
their external sensation, and never can. Direct physiological
illustrations are almost impossible, for the reasons stated, §§ 583
and 586, and the proofs can only be argumentative. The
morbid condition affords an illustration in those cases in which
a limb, still possessed of sensation, cannot be excited to those
movements by external impressions, of which in a natural con-
dition it is capable (127).

592. When an internal impression depends on sensational
conceptions, as imaginations, foreseeings, feelings [Reizungen],
desires, aversions, instincts, instinctive emotions, and various
passions, the movements it excites are both sentient actions of
the conceptions and nerve-actions of the external impression
that causes the external sensation upon which they depend.
They are nerve-actions, because they can be excited when there
is no sensation; they are sentient actions, because all these
sensational conceptions develop no other sentient actions than
movements that are identical with those excited by the external
sensation itself. The probable object of nature, in thus uniting
the action of the cerebral forces and of the vis ne^^vosa, in the
movements of external sensations, and of sensational conceptions,
desires, and aversions, has been already referred to (184, ii,
370, 371).

593. When an internal impression arises from the higher
passions, from intellectual conceptions and motives, and from
desires and aversions of the will and their satisfaction, the
movements it excites, in so far as these intellectual conceptions,
&c., are unmingled with sensational conceptions, are solely
sentient actions, and there is no combined action of the cere-
bral forces and the vis nervosa in their production. They are
not dependent on any external impression, and consequently
cannot be nerve-actions induced by the vis nervosa, and the only
other animal forces are the cerebral (353 — 356). Nature has
granted this higher species of conceptions to the most perfect
animals only, whose souls are not simply sensational [Sinnlich] ,
but spiritual [Geister], (Baumgarten^s ^ Metaphysics,^ §' 590).

594. Those err who conclude, that because an animal per-

CH.iv.] RELATION OF CEREBRAL & NERVE FORCES. 305

rms animal acts, it must necessarily therefore be endowed with
cerebral forces, or with a soul, or with will ; for it is undeniably-
possible, that the vis nervosa alone can cause the greater num-
ber of the animal acts (590). The majority of philosophers
have been led by this error to consider all animals without
exception as endowed with souls ; but it is highly probable, that
many have neither consciousness nor feeling.

595. It cannot be correctly inferred, that, because in a
sensitive or thinking animal, movement is excited in virtue of
irritability, or by the vis nervosa of external impressions gene-
rally, it cannot be a sentient action of the external sensation
caused by the impression ; or, vice versa, that because it is a
sentient action of the external sensation of an external im-
pression, it cannot be a nerve- action of the impression only.
The first is the error of some recent writers, who, since Haller
recognised the agency of the vis nervosa of external impressions
in exciting direct nerve-actions, and taught it under the term
irritability, wished to maintain, that all animal movements not
resulting from volition are dependent on irritability, and
erroneously deny those dependent on sensation. The latter
error is that of the Stahlians, when they maintain, that in ex-
ternal sensations the body is purely passive, and does not co-
operate by means of its own proper forces.

596. It cannot be correctly inferred, that because in a
sensitive or thinking animal the movements which accompany
the sensational conceptions, incitements, desires, aversions, &c.,
are sentient actions, for this reason they cannot be nerve-
actions j and vice versa, that they cannot be sentient actions of
these sensational conceptions (592). From this error, taken in
connection with the second mentioned in the preceding para-
graph, the old error has probably arisen, and which the author
of the article '^Sensibilite,^^ in the 'Dictionnaire Encyclopedique'
has lately reproduced, namely, that there are two kinds of souls
in reasoning animals, the one being the rational soul, by which,
sentient actions are developed according to psychological laws;
and the other a sensational soul, by which the sentient actions
of the external sensations and other sensational conceptions are
developed according to the laws of the vis nervosa. We have
shown, however, that to the action of the latter no soul is
necessary.

20

306 ANIMAL FORCES. [ii.

597. Lastly, those also are in error, who conclude that
because an animal performs movements, which are effected by
the cerebral forces alone, without the co-operation of the vis
nervosa, all its animal forces are actions of the cerebral forces
(590, 593). This is the error of the Stahlians, who consider
all animal movements to be sentient actions, nay, to be medi-
tated acts of a will, of which the soul is necessarily unconscious.
The old error, lately renewed by Whytt, is also connected with
this erroneous supposition, namely, that the souls of animals are
distributed throughout their bodies by means of the nerves,
because animal movements, which are usually sentient actions,
can be excited in decapitated animals, thus assuming that no
other force than the mental can effect this.

PAET III.

ANIMAL NATURE CONSIDERED AS A WHOLE.

INTRODUCTION.

598. The cerebral forces and the vis nervosa are essential
constituents of the proper animal nature of animal organisms
(6, 356)^ and in the more perfect animals are in close connection
(591 — 593). The aggregate of those animal forces, which act na-
turally in connection in an animal body, constitute its whole
animal nature, and this whole is now to be considered; its two
essential constituents even in the most perfect, having been dis-
cussed in the two preceding parts.

599. The arrangement of this part is as follows : — first, the
character of the whole animal nature of an animal will be
sketched ; secondly, the existence of distinct classes of animals
will be proved ; then the origin of animals according to their
nature will be considered ; next, animal life and its natural
periods up to its full development ; then the system of forces
necessary to animal life, or how they act with and through each
other for its maintenance and perfection ; and, finally, old age
and death will be treated of in succession.

I

CHAPTER I.

ON ANIMAL NATURE IN GENERAL.

600. An organism, which, in its entire and natural condition^
is regulated by the animal moving forces of its own proper
animal machines, is termed a living animal organism^ an animal
endowed with life, an animal in the widest sense. In deter-
mining the general characteristic distinction of plants and
animals, by which we decide whether an organism belongs to
the one or the other division, we have to determine whether it
is moved in its natural condition, according to the known
physical or mechanical laws of gravity, of the force of attrac-
tion, of elasticity, of the mechanism of its structure, &c. ; or,
according to peculiar laws : — whether a touch, or an external
impression upon it, excites it to the movement that we should
be led to expect from the known physical and mechanical laws
of motion, or whether a movement is excited thereby, which
compels us to recognise the phenomena of a peculiar force put
into action by this external impression ; and which regulates it
according to other and widely different laws. It is not denied
that this distinction is always somewhat indefinite, still it
exists in nature, and we universally form a judgment thereon ;
but we only become more definite, when we have become
acquainted with the laws of the animal moving . forces. If
some persons distinguish animals from plants by their volun-
tary movements, others by their instinctive actions, and others
by their external sensations, it all comes to the same thing;
inasmuch as we recognise a moving force in animals differing
altogether in its nature from physical and mechanical forces,
and acting according to altogether different laws. But these
distinctions are wholly deduced from the phenomena of the cere-
bral forces, while the nerves themselves possess peculiar animal
forces, which are not taken into consideration; so that they who
adopt this as an universal distinction, are at a loss when they
come to decide, whether a certain organism which cannot

310 ANIMAL NATURE AS A WHOLE. [iii.

possibly be endowed with cerebral forces^ be a plant or an
animal. Hence the confusion of ideas, caused by the researches
on decapitated animals, moved solely by the vis nervosa, — by
the phenomena of anencephalous infants bom alive — and by
animals so constituted by nature, as to live without head or
brain, and which manifest no traces of mind; regarding all
which no definite opinion can be stated. If, however, the above
general distinction be adopted, no difficulty arises in such cases ;
for, although entirely without conceptions, all these organisms
are regulated by external impressions, in a way wholly different
from plants, and according to wholly different laws. Now,
since we recognise the existence of the vis nervosa of external
impressions in animal machines [the brain and nerves], and
know that it is adapted to sentient animals, and excites in them
the same movements, according to the same peculiar laws as
external impressions excite in these organisms; and since we
find machines in the latter, which are very similar to the
animal machines [brain and nerves] of sentient animals, we
can positively decide, that all these organisms are moved
animally by nature, by means of animal machines, and that
they also belong to the class of animal bodies.

601. Still, as has been said, the line of distinction is always
indefinite, and the limits of the animal and vegetable kingdoms
run so into each other, that they cannot be defined. The
fault, however, is not in the want of grounds of distinction,
but in the difficulty of discovering them in many cases. The
movements excited in the sensitive plant by a touch, leads us
to the conclusion that it is a zoophyte; so fixed is the principle
in us, that an organism must be an animal which is moved by
certain impressions — not according to physical and mechanical
laws — but according to the laws of movement in animals. But
these movements are neither sentient actions nor nerve-actions,
for upon investigating the structure of the leaf, it is found that
the closing of the leaves is simply a mechanical action, excited
by a touch.

602. The question may arise, however, whether a body may
not be animal in its nature, and yet not be an animal ; as, for
example, in the case of a decapitated animal. A man, deprived
of his limbs, is not the less a man ; and so if the vis nervosa
continue in a mutilated creature, it is still an animal. Besides,

cu. I.] ANIMAL NATURE IN GENERAL. 311

our definition is based on the condition, that the organism be
entire, and in its natural state. A decapitated animal is a
living animal body, and not a living animal.

603. A living animal is regulated in its natural state by the
animal moving forces of its own animal machines. These are
the analogues of our nerves and our brain, at least we know
of no other; and their animal forces are the impressions of which
they are susceptible, when touched, or when a movement is
communicated to them (31, 32, 121). Further, every living
animal is regulated, either by the vis nervosa, or by the cere-
bral forces, or by both (356) . If by cerebral forces, then it is
by means of external sensations and conceptional impressions
(65, 121), and, consequently, also by the vis nervosa of the
external and internal impressions (35, 32, 358, 360). That the
vis nervosa alone regulates living animals is fully proved in the
Second Part. Now, since the cerebral forces imply the action
of a conceptive force, or mind, it follows that the animals
endowed with the former have also the latter, or are sentient
animals; while those which are regulated solely by the vis
nervosa are insentient, or simply living animals.

604. Every insentient animal must possess nerves, or their
analogues, to which the vis nervosa is adapted by nature. But
since their external impressions are not felt, and their internal
impressions never produced by conceptions, and as they require
no animal sentient forces, it follows, that in so far as the brain
is the seat of the latter, and of mind, or the conceptive force, it
may be entirely wanting, and yet they may perform all the
acts necessary to their existence.

605. Every sentient animal must not only be endowed with
mind, or the conceptive force, but also with the vis nervosa
and nerves, and with the cerebral forces and a brain : if the
soul be spiritual, that is to say, if the animal be endowed with
understanding and will (574), it is termed a reasoning animal,
but if the soul be simply sensational, then the animal is a
sensational or unreasoning animal (a brute) .

606. Insentient animals are moved solely by means of the
nerves; and if, also, in sentient animals, the cerebral forces do not
act, still the greater number of their vital movements, natural
functions, and sentient actions, can be produced by the vis
nervosa ; and when in such the brain does co-operate, it is by

312 ANIMAL NATURE AS A WHOLE. [in.

means of its vis nervosa (373, 374), and not by the animal-
sentient forces. But, on the other hand, when the latter act
on the body, they are excited into action by the conceptive
force (Baumgarten's ^Metaphysics', § 554).

607. The vis nervosa is distributed to every portion of a
nerve (31). The seat of the animal-sentient forces is in the
brain, or the nerves dependent on it (25). The seat of the
animal-moving forces in insentient animals is in their nervous
system, and this is the case with sentient animals, in so far as
they also possess the nature of the insentient. But the seat of
the animal-moving forces of sentient animals, peculiarly as such,
is in the brain, the seat of mind (10).

608. All the animal movements of an insentient animal Eire
dependent on the vis nervosa, and all the animal acts take
place according to its laws of action. This is the case also with
sentient animals, in so far as their movements are dependent
on the vis nervosa; but in so far as they are sentient actions of
those conceptions which the conceptive force forms and de-
velops in the mind, according to psychological laws, indepen-
dently of the vis nervosa, they flow from the cerebral forces,
which the conceptive force regulates (6). But if the movements
be both sentient actions and nerve-actions, they follow the
laws of both kinds of forces acting in co-operation (Part II,
Chap. IV, Sect. in. Compare also § 579).

609. Insentient animals are moved animally by the vis ner-
vosa of external or internal impressions, according to their
nature (31, 32, 121). The external impressions act upon them,
either by means of direct nerve-actions (418), or indirect; when
they are reflected in the ganglia, or points of division of the
nerves, along which they pass upwards upon other nerves, and
thereby put the organs to which the latter are distributed into
motion (419, 421). Nature herself causes in insentient animals
such external impressions as are necessary to the maintenance
in them of those animal acts on which their preservation and
the objects of their existence depend; and to this end their
animal acts are as adaptively excited, arranged, and connected
with each other, as in sentient animals by means of their
natural instincts (435 — 439), although neither the sentient nor
insentient act from consciousness (266). The natural primary
internal impressions, in insentient animals, excite those move-

CH. I.] ANIMAL NATURE IN GENERAL. 313

ments which either cannot be caused by external stimuli, or
else require the co-operation of others that they may go on
uninterruptedly; their continuance being necessary to the main-
tenance of life in the animal. Consequently, they are to be
particularly observed in the vital movements and in the viscera,
the functions of which are the most necessary to the preserva-
tion of the animal (515, 525, 532). The stimuli to the move-
ments thus induced, being deeply hid in the interior of the
medulla of the nerves, and traceable to no external cause, we
infer erroneously that the movements themselves are the re-
sult, either of obscure sensations, or of other and volitional
conceptions.

610. The movements necessary to existence, preservation,
and other objects of nature, in insentient animals, are effected
wholly in them by means of the vis nervosa, and in some degree
in the same way as in sentient animals; so that they are capable
of movements, which experience and observation prove may be
effected without the co-operation of the cerebral forces ; that is
to say, they are capable of muscular action, and the appa-
rently voluntary movements, the movements of the heart, and
the circulation of the fluids ; the arterial pulse ; the flow of
humors to an irritated part ; the movements of the diaphragm ;
the animal mechanism of respiration ; digestion and peristaltic
action ; glandular secretion and excretion ; and the animal
functions of the lungs, — of the liver in the secretion and excre-
tion of the bile, — of the kidneys and urinary bladder in the
secretion and excretion of urine, — and of the sexual organs in
the propagation of the species (445 — 481, 507 — 540) .

611. Insentient animals can also excite, by the vis nervosa
alone, according to its animal laws, all those animal movements
which are excited in sentient animals by means of the animal-
sentient forces of the sensational faculty [Sinnlichkeit] ; de-
veloping them in the same order, connecting them with each
other in the same way, and just as consecutively as when the
movements constitute sentient actions of sensational concep-
tions; that is to say, the vis nervosa excites the same move-
ments in insentient animals, as constitute the sentient actions
of external sensations (433, 439) ; of imaginations and of fore-
seeings; of sensational desires, aversions, and instincts; namely,
of the alimentative instinct, of the instincts for volitional move-

314 ANIMAL NATURE AS A WHOLE. [in.

ments, for repose and playfulness, for combat, for self-defence,
for propagation of the species and care of offspring ; and of the
instinctive emotions, as rapacity, revenge, lasciviousness, and all
the passions closely allied to them (542 — 573). On the other
hand, the sentient actions of sentient animals, which arise as
free-will movements, from desires, aversions, and passions, de-
veloped in the mind according to psychological laws (564 — 573),
or from pleasing or displeasing conceptions of the understand-
ing, or from desires or aversions of the will (564, 576), cannot
be developed in insentient animals by means of the vis nervosa,
unless there be a sensational element in the conceptions them-
selves (578).

612. Since sentient animals are endowed with the vis ner-
vosa, in common with the insentient, and which sometimes acts
in them alone, sometimes in connection and in harmony with
the cerebral forces, they are capable, under certain conditions,
of all those movements of which insentient animals are capable.

613. Sentient animals are moved according to their nature,
not only by the vis nervosa, but by the forces of material ideas
in the brain. These material ideas are those either of external
sensations, and other sensational conceptions and desires, or of
intellectual conceptions : the former are regulated according to
the laws of the vis nervosa, the latter according to the psycholo-
gical laws of the conceptive force. By means of these cerebral
forces of conceptions, the movements iu sentient animals in the
natural condition are developed, arranged, and changed, in ac-
cordance with the conceptions in their mind : this, however, is
so done, that in purely sensational animals, and in the reason-
ing animals also, in so far as their sensational conceptive force
acts, the conceptions are caused and connected in the mind by
means of the vis nervosa of external impressions. On the other
hand, they arise and are linked together in rational animals,
when the conceptive force acts solely according to psychological
law (60, i, 579, i, ii).

614. Purely sensational animals are capable of all the vital
actions just enumerated in § 600 (compare 161 — 179, 207, &c),
in virtue of the cerebral force of the sensational material ideas,
which external impressions excite and connect in the brain, and
which develop the vital actions as sentient actions.

615. Purely sensational animals perform as sentient actions,

CH. I.] ANIMAL NATURE IN GENERAL. 315

by means of various external sensational conceptions, and
enumerated in § 611, those animal movements which, although
they can be, and often are, in unreasoning animals, mere nerve-
actions, can, nevertheless, be developed, arranged, and modified
by the cerebral forces solely (581 — 592).

616. Reasoning animals, in addition to the preceding, are
capable of performing as sentient actions all movements vrhich
the higher emotions, intellectual pleasure or suffering, and
the desires, aversions, and satisfyings of the will develop
through the free-will movements; and this by means of the
cerebral force of the material ideas connected with the under-
standing and the will. And since these animal monements are
neither sensational actions, nor nerve-actions (336, 593), they
are the peculiar privilege of reasoning animals, and distinguish
them from all others.

617. The animal nature (1) of an insentient animal is the
aggregate of its two kinds of vis nervosa : that of a sentient
animal is the aggregate of its two kinds of vis nervosa and its
cerebral forces ; and implies also the animal nature of the
insentient. The animal nature of a purely sensational animal,
is the aggregate of its two kinds of vis nervosa, and of the
cerebral forces of its sensational conceptions, desires, &c. The
animal nature of a reasoning animal is the aggregate of the
cerebral force of sensational and intellectual conceptions and
desires, &c., and presupposes the nature of the sensational
animal, which includes that of the insentient animal.

618. The animal natures of all other animals are conjoined
in a reasoning animal, as well as the two essential principles
[principien] of all animal movements, namely, the vis nervosa
and the cerebral forces. The physician need not seek to explain
the mode in which the vis nei^vosa excites sensational concep-
tions and desires, and in which these, together with those of the
intellect, excite animal movements, for it is inexplicable : con-
sequently he need not investigate psychological explanations of
the union of body and soul; or the hypothesis of physicians as
to the nature of the vital spirits, of the medulla of the brain and
nerves, and of material ideas ; his business is with general facts,
from whence he must deduce his principles of theory and prac-
tice. The whole physiology of animal nature must be based
upon the following general principles :

316 ANIMAL NATURE AS A WHOLE. [in.

i. The nerves receive external impressions in a manner
peculiar to themselves ; that is^ according to their peculiar laws,
which accord with neither the physical nor mechanical laws of
any other bodies, than animal bodies ; these impressions are
transmitted along the nerves to the brain, and laterally by means
of branches or ganglia to other nerves, and thereby become
animal-motor forces of the mechanical machines with which the
nerves are incorporated, as well as animal-sentient forces by
means of the brain, for the development of external sensations
and sensational conceptions, desires, aversions, instincts, &c.,
which are developed and connected with each other in the mind,
according to the animal laws of the vis nervosa of the external
impressions.

ii. The conceptions of the mind communicate internal im-
pressions to the brain, which it receives in a peculiar manner,
according to the laws of its own peculiar animal-sentient forces,
and transmits along the nerves, whose cerebral origins these con-
ceptions excite, to the mechanical machines in which the nerves
are distributed, or along their branches, or by means of their
ganglia along other nerves going to mechanical machines, and
thereby the impressions become motor animal-sentient forces of
these machines, and are developed and connected with each
other in them, according to the psychological laws of the con-
ceptive force ; but which are themselves nevertheless necessarily
regulated in the sensational conceptions, by the animal laws of
the vis nervosa of external impressions.

iii. The vis nervosa of external impressions can produce all
the sentient actions which sensational conceptions excite, even
if the conceptions themselves do not ensue.

iv. The animal-sentient forces can reproduce the nerve-
actions of impressions, when the impressions themselves do not
actually take place.

V. Lastly, the movements excited by unfelt external im-
pressions are purely nerve-actions : those excited by the higher
passions, intellectual conceptions, desires, aversions, and satis-
fyings of the will, are purely sentient actions, and all others are
excited by the combined operation of the animal-sentient forces
and the vis nervosa.

CHAPTER II.

THE PRINCIPAL GENERA OF EXISTING ANIMALS.

619. Man is an example of a reasoning being, and all the
principal forms of existing animals are combined in him, namely,
the insentient, the sensational, and the reasoning; he is also
capable of all the animal functions proper to these.

620. The nature of a reasoning being implies the presence
of the natures of merely sensational and insentient animals, but
the last two do not necessarily require the former. There is a
great number of sentient but purely sensational beings, endowed
with neither understanding nor will; and even a reasoning being
may, by poisons or disease, or in the early periods of life, exist
only as a purely sensational animal, without any use of the
reason or the will, and usually capable only of those functions,
of which purely sensational and insentient animals are capable
(612—615).

621. A sentient animal may be entirely deprived of its animal
sentient forces (for by separating the head from the body, the
brain and soul are removed), and yet may live for some time as
an insentient animal, and continue all those functions of which
as an insentient animal it is capable. But do true insentient
animals exist ? We will state the arguments for the affirma-
tive and negative, leaving the reader to decide.

622. It is unquestionable that every animal does not require
to have a soul : the definition that an animal is a whole com-
pounded of soul and body is a petitio principiij for no one has
ever proved that a soul is requisite, and we therefore base one
false proposition upon another. Many eminent men have
doubted, whether unreasoning animals possess a soul; although
like others they have been educated in the dogma, that body and
soul constitute an animal.

623. It is incontrovertible, that the nature of an insentient
animal can only be requisite to the existence and continuance
of an animal absolutely; firstly, because all the processes

318 ANIMAL NATURE AS A WHOLE. [iii.

required for the life and preservation of an animal organism, can
be effected by the vis nervosa only; nay, even the greater num-
ber of the actions of sensational conceptions, desires, instincts,
&c., may be induced by it, simply as nerve-actions ; secondly,
because experiments on decapitated animals prove it.

624. As to a large class of animals, it has never been proved
that they are endowed with animal-sentient forces, and it is
highly improbable that they are :

i. Because we can detect no traces of mind or a conceptive
force with which their animal forces can co-operate (6). If
those movements of sensation and volition, which occur in de-
capitated animals, as results of the vis nervosa solely, are all
that can be adduced as proofs of the existence of an external
sensation, then an oyster, a sea- worm, a snail, a polype, do not
manifest, during their whole existence, a single movement
which renders the existence of conceptive force in them at all
probable.

ii. Because many animals, unlike those undoubtedly sentient,
have not a head distinct from the body (15, ii). We may con-
clude from analogy, with some probability, that since all animals
to which we can undoubtedly attribute the possession of a con-
ceptive force and consciousness, have heads distinct from the
body, it follows that the former must be governed by forces alto-
gether different from the latter ; and since these are regulated
by animal-sentient forces, the others must be governed by the
vis nervosa, for there is no other force (356). The relations of
mental endowments to the cerebral development is specially
noticed by Haller. ('Physiology,' vol. iv, p. 634<.)

iii. Because, although all animals possess the analogues of
nerves, the most numerous genera have nothing analogous to a
brain, even when they have a head distinct from the body; or,
indeed, a part which in movements all others are accustomed to
follow. This principle is of very great importance. In those
animals undoubtedly endowed with sensation, there is a distinct,
complete brain, the seat of mind (10) : all observations establish
this doctrine — none are opposed to it — none render it even
doubtful. Yet this undoubted dwelling-place of the soul is not
a necessary portion of many animals; nor necessary to the per-
formance of numerous acts, performed in virtue of the vis
nervosa, by animals after decapitation, in the same order, with

cH.ii.] PRINCIPAL GENERA OF EXISTING ANIMALS. 319

the same connection, and from the same external impressions,
as before decapitation. A single series of experiments, having
such results, would be sufficient to refute the proposition, that
to every animal life a body, soul, and brain are necessary. Yet
nature presents millions of such examples : the whole creation,
nay, every drop of water is full of them ; numerous genera of
animals exhibit no trace of a brain, or its analogues ; all their
acts, as in sentient animals, can be simply nerve-actions ; their
bodies are so constructed, that these acts can take place with-
out any co-operation of a conceptive force. Their souls must
be extended, and be everywhere present in their bodies, since
polypes may be cut into pieces, and each piece becomes a new
animal. Contrary to all analogy, there must be consciousness
in various parts of their organism, or they must consist of many
souls. How opposed is all this to sound theory and to com-
mon sense !

iv. Because, although some trace of a brain, or its analogue,
be found in animals, as in worms, snails, crabs, spiders, mites,
caterpillars, lice, ants, fleas, bees, and other insects and worms,
no indications of animal-sentient force can be detected in them.
In none of the animals undoubtedly sentient is the brain ever
the organ of the animal- sentient forces only; but it is endowed
also with the vis nervosa necessary to all animal life, even of an
insentient animal, since to it belongs the function of separating
the vital spirits from the blood, and distributing them to all
parts of the nervous system, for without these the mere vis
nervosa cannot act in any animal (21, 22). It is true, that this
is only the function of the cortical substance of the brain (159,
374) ; but who has proved that in the animals in question, the
brain consists of any other than this cortical substance ? More-
over it is probable, that the medullary substance of the brain,
even in sentient animals, possesses the vis nervosa, in virtue of
which, like the ganglia and spinal cord, it reflects external im-
pressions, receives non-conceptional internal impressions, and
by means of both moves the mechanical machines (373). It is
extremely probable, that the structure considered to be brain
in these animals is either only cortical substance, or only a
general ganglion, — an addition to the spinal cord, in which the
vital spirits are separated from the blood, and thence trans-
mitted through all the nerves ; in which also, as in the spinal

320 ANIMAL NATURE AS A WHOLE. [iii.

and other ganglia/ unfelt external impressions are reflected,
in accordance with the objects of nature, upon those nerves
through which the nerve-actions appropriate to the impressions
are induced, and in which certain non-conceptional internal
impressions (internal stimuli of the nervous fluid) induce or
maintain, by means of the mechanism of the animal, various
animal movements necessary to its existence, well-being, &c.;
but which cannot be induced, at least solely, by external im-
pressions. Such a brain could be no more the seat of mind,
than the spinal cord or the ganglia. Haller, quoting the ob-
servations of Swammerdam and Lyonnet, as to the great
simplicity of structure of the small ganglion in lobsters and
caterpillars, termed a brain, and its great similarity to the other
ganglia, adds, that even in fishes and cold-blooded animals, the
brain appears to be only an appendage to the spinal cord.
('Physiology,^ vol. iv, p. 6.)

V. Because, all the proofs which are adduced to show that
certain nerve-actions in sentient animals are not sentient actions
(129, 130), are equally valid here. All the conditions necessary
to sentient actions are wanting in animals without a brain, or
with a brain of the kind just referred to, and in which no ma-
terial ideas are produced. There is medullary substance in all
the nerves ; the spinal cord is for the most part made up of it,
and yet in neither are the material ideas of conceptions ever
formed.

625. All these grounds taken together, render it extremely
probable, that such animals are constituted insentient by nature,
and endowed with vis nervosa only, so as to be fitted for all the
objects of their existence. We will deduce no arguments in
favour of this doctrine, from the nature of the soul, so totally
unknown to us, nor will we answer any objections brought
against it from the same source, for what can be adduced where
we are so completely in the dark ? There is the same difficulty
in explaining how a pure soul develops animal movements,
whether the body through which it operates be a skilfully con-
structed mechanism, or mere matter. Nature has prescribed
this law to them, on grounds entirely unknown to us, and it
remains with her, whether all or only a few animals be endowed

' Compare note to § 35. — Ed.

cH.ii.] PRINCIPAL GENERA OF EXISTING ANIMALS. 321

with mind. We can only infer the true condition of animals,
in this respect, from their organisms and their acts. We have
conclusively shown, that animals unendowed with mind perform,
by the vis nervosa only, in the highest degree of completeness,
those acts (with certain exceptions) which are performed by
sentient animals. Consequently, nature was not obliged to
render all animals sentient, if she were willing to be satisfied with
those which could sufficiently perform the natural functions of
alimentation, defence, and propagation of the species, although
not capable of the more perfect acts of sentient animals. If, then,
there are animals defective in the higher order of passions, in
reason, and will ; animals, which do not possess the organ of the
conceptive force peculiar to sentient beings; whose whole life is so
uniform, simple, and unvaried, that they do not possess even the
vis nervosa, so perfectly as sentient animals possess it after de-
capitation ; animals, which can continue in life, almost as per-
fectly, when that is removed which is considered the machine (if
the phrase may be allowed) of the conceptive force, namely, the
entire head wherein their mind must dwell (621 — 624) as before;
we are necessarily led to the conclusion, that it has pleased
nature not to place a considerable portion of the animal creation
in closer connection with a thinking essence, or to endow it
uselessly with mind. Still it would be well to notice the op-
posing arguments, few of which, however, are of much weight.

i. The objection that the definition of an animal includes the
idea of the existence of mind, has been answered already (622).

ii. But it is advanced, " that all animals feel when they
receive external impressions, and since external sensations are
conceptions, they must therefore have mind.'^ To this we reply,
that we have no knowledge that they feel external impressions,
but only that the latter induce animal movements. It is
allowed, that all direct and incidental sentient actions of ex-
ternal sensations may be excited in animals endowed with
mind, by the vis nervosa of their external impressions, both
during Kfe and after decapitation (542 — 544) ; and, in fact, it
is more difficult to prove, that these movements are sentient
actions of the external sensations of the impressions, than that
they are nerve-actions of the impressions solely (582 — 588) .

iii. It is also objected, that " many insects, worms, &c.,
which must be considered unendowed with mind, have never-

21

822 ANIMAL NATURE AS A WHOLE. [iii.

theless organs of sense, particularly organs of vision; and,
since tliese nerves are purely nerves of sensation, these animals
must possess a conceptive force /^ But are the organs of the
senses in these animals analogous to ours ? Are they — like ours
— without ganglia ? Or is it not, that their brain can reflect
external impressions in the same way as the ganglia? (624, iv).
We see in the senses of taste and touch external senses, the
nerves of which are also motor nerves, and accomplish, by
their vis nervosa alone, all those movements which they can
excite as sentient actions (Haller's ' Physiology/ vol. iv, pp. 615,
sqq.). Now, since the organs of the senses in insects and
worms are very different from those of animals endowed with
mind (15, ii), it is possible that their nerves are altogether
motor, like the nerves of touch in sentient animals, and thus
they may regulate an animal without there being any sensation.
It cannot be maintained, that the organs of the senses are con-
stituted for the sole purpose of exciting certain special kinds of
external sensations — as the eye for seeing, the ear for hearing,
&c. Their proper function is to render the nerves capable of,
receiving certain external impressions, which could not be
received without the aid of such machinery (55, 42) . If these
impressions are felt, the nerves certainly develop a particular
kind of external sensation ; but if they act as motor nerves,
they excite a particular class of movements only, for they are
the same that the sensation caused by the impression would
excite (358), and this is their function in animals not endowed
with mind. In cases of this kind, the animal would not see
with its eyes, nor hear with its ears, nor smell with its nose,
but only have the same animal movements excited by the special
external impressions, as would result if they were actually felt
(542 — 544). The external impression of light in the eye, which
sentient animals perceive, and through which they are excited
to a thousand volitional movements, can imitate the actions of:
the instinct to volitional movements in insentient animals, and
excite them directly as nerve-actions (555). Impressions on
the ear can excite as nerve-actions the actions of the instincts
of self-defence, sexual congress, &c. (559, 560, 566). So also
the actions of the instinct for food may be excited in insentient
animals as nerve-actions, by external impressions on the nerves
of taste and smell (552, 553).

CH.ii.] PRINCIPAL GENERA OF EXISTING ANIMALS. 323

iv. But it is further objected : — all these animals appear to
be moved and excited by external sensations, and to act voli-
tionally, rationally, and designedly. Ants like sugar, bees
Hke the juice of certain plants, and each species of insects and
worms has its peculiar food, which they seek, avoiding others.
They are guided by certain sounds, as when they are allured
by sexual intercourse (in the case of crickets), or when bees
would swarm ; they fly away when they see any thing unex-
pectedly; they smell the odour of their food, and go towards it.
In these actions, an effort to satisfy an instinct is shown, which
is directed volitionally, and an animal that so acts must be sen-
tient. The argument has much plausibility; it has, however,
been demonstrated already, that external impressions will excite
voUtional acts simply as nerve-actions, whether the animal feels
them or not, and independently of any reference to the gratifi-
cation of any desire or instinct (263 — 269, 552, 561). The
phenomena manifested by newly-born and decapitated animals,
some of which have been already stated (555, &c.), amply prove
that such apparently volitional acts may take place, under cir-
cumstances which altogether exclude the idea of mind. What
in them appears to be volitional, only appears so, because we
draw conclusions as to other animals from the nature and work-
ing of our own minds (436 — 439) . What appears to be designed,
arises from the preordination of nature, and in no case enters
into the minds of even sentient animals (266, 609) .

V. But it is further objected, — that these animals act de-
signedly and volitionally, without the incitement of external
impressions, and consequently they must be under the influence
of conceptions. The answer is, that the movements alluded to
result from primary internal impressions not caused by con-
ceptions (609), and it would be indeed difficult to show, that
these animals had such, independently of external impressions.
(Compare § 553.)

vi. It is further objected, that many of these animals, as
bees, ants, &c., act socially and in combination, for the purpose
of attaining certain objects. They assist each other in their
labours, get out of each other^s way, take each other's burdens,
appear to apprize each other of danger, combat their common
enemies, &c. This is really the most weighty argument that
can be advanced in support of the doctrine, that these animals

B2i ANIMAL NATURE AS A WHOLE. [iii.

are endowed with mind. Granted that bees, ants, and other
social animals, are endowed with mind, and have external sensa-
tions, and other conceptions, and true instincts, all their social
acts would be sentient actions of their sensational instincts, and
these are almost the direct results of external sensations (276, i,
579, i). These social acts are, therefore, either direct or
incidental actions of the sensations of their external impressions.
Now, it is indubitable, that all such may be also nerve-actions
of the impressions only, and consequently, these social acts may
be excited solely by the vis nervosa, even if the animals be
endowed w^ith mind. That this actually is so in other animals
is fully established by observation (555 — 557) ; how then can
we infer the existence of mind from these social acts ? If the
acts of an animal are required to follow each other, or other
acts, in a certain order, the impressions which excite them must
be received in the same order, and the former will result,
whether the latter be felt or not. Which method nature has
adopted in social animals must be determined by the question,
whether they are endowed with mind or not ; but it would be a
perversion of the argument to say, that because the acts may
occur in two ways, they therefore are dependent on mind. The
probability is, that these animals are not endowed with mind,
because they have no brain, or at least not a brain, constituted
like those of animals undoubtedly endowed with mind. If it be
replied, that bees and ants no longer perform social acts when
deprived of their heads, it must not be forgotten that the eyes of
the insects are removed at the same time, and that it is by means
of the eyes that all these external impressions are received which
excite social acts. They yet can and do perform former move-
ments, although headless, but not in a definite order, and in rela-
tion to and in connection with the labours of others, because the
impressions which excite them are merely accidental, whilst
previously the impressions were made through the organs of
vision, in a given order predetermined by nature. The won-
derful concord in the acts of these social animals, is much more
probably a result of that wisdom which is manifested in the
sensational instincts of the whole animal kingdom, and in virtue
of which animals, even the sensational and thinking, perform
acts according to a design and preordination of nature (561,
263 — 270). When the acts of republican insects are considered

CH.ii.] PRINCIPAL GENERA OF EXISTING ANIMALS. 325

from this point of view, it is readily seen how the operation of
the mysterious and God-like element of the instincts (263), may
lead us to erroneous conclusions in attributing them to mind
and external sensations.

626. An argument for the existence of animals endowed
with mind may be drawn from analogy. In the scale of crea-
tion, nature ascends by successive degrees of perfection. From
physical bodies she constructs natural mechanical machines, as
elastic matter, capillaries. To these, by means of the intimate
connection and combined action of many mechanical machines
for a common object, or in other words, by means of organisa-
tion, she communicates organic forces, and thus from them she
forms organised bodies, such as plants and growths. Organised
bodies are undoubtedly capable of three successive degrees of
perfection. If by means of animal machines, they be endowed
with the vis nervosa, they attain the grade of insentient
animal (609 — 611). If to this a brain be superadded, and
the vis nervosa determine and act in accord with a conceptive
force, it becomes then a purely sensational animal (605, 620) ;
and when in this class the conceptive force attains to that per-
fection, that it regulates itself and its body independently of
the vis nervosa, then it is a rational animal, such as is man
(619). If there were no insentient animals, the scale of nature
would be defective in that one point. Now this is very im-
probable, and, consequently, it is in accordance with a perfect
creative scale, to consider microscopic creatures, conchifera,
and insects, as insentient animals.

627. There are degrees of perfection in every genus of
animal. A mathematician and a hottentot, equally belong to
the class of rational beings. Both comprehend the multipli-
cation table, both can think of God, and distinguish between
right and wrong ; both in short are capable of ideas and acts,
to which the most intelligent monkey can never attain. But
what a difference between the two, and how much the one is
more nearly allied to the brute than the other ! A bee, an ant,
a cheese-mite, are in the same class of insentient animals as a
snail, an oyster, or a microscopic animal, but how intelligently
and perfectly the vis nervosa acts in the former, how imper-
fectly and awkwardly in the latter ! Those are nearly allied
to the sensational animals, whose actions they imitate so

326 ANIMAL NATURE AS A WHOLE. [iii.

closely, these are little above the sensitive plant. Yet the line
of demarcation is never passed. The monkey never acts from
general principles, or ever meditates on an abstract truth. All
its actions are such as a man might perform independently of
his reason and will, in virtue of the high perfection of his sen-
sational perceptions and sensational will. However cleverly
the ant or bee acts, it so acts independently of perception or
sensation ; and its actions are those which a sensational animal
could perform after decapitation, and, therefore, independently
of mind, and in virtue of the high perfection of its vis nervosa.
However animal-like the movements of the sensitive plant
may be, they do not take place according to the laws of im-
pressions on the nerves of sentient animals.

Note, — The question as to the existence of insentient
animals, must not be considered as quite decided, and it has
no very important bearing on the other doctrines of proper
animal physiology. Animals placed in this class must be con-
sidered to be those which either have no brain at all, or else a
brain of very simple construction, widely different from the
brain of undoubtedly sentient animals, and which is capable
only of those movements that sentient animals can execute
after decapitation, and independently of their animal-sentient
forces.

CHAPTER III.

ON THE ORIGIN OF ANIMAL NATURE.

628. The commencement of animal nature is termed its
generation ov procreation. (Baumgarten^s 'Metaphysics/ § 311.)

Consequently, an animal in the widest sense of the term is
[produced so soon as au organised body is capable of being
[moved by means of the animal-motor forces of its proper animal
lachines. No animal can thence arise, not even the insen-
ient, unless provided at least with nerves and vital spirits, or
[their analogues, of which the vis nervosa of impressions is a
[peculiar property (1 5, 604) . No insentient animal can become
I sensational, unless furnished with brain and its vital spirits, or
an analogue, and of which the animal -sentient forces (10), are
a peculiar property. A sensational animal can only become a
rational animal when it attains to the power of regulating its
jbody by intellectual conceptions and volitions (76,574, 96).

629. Every animal springs from one like itself. The mi-
nutest, with few, if any, organs and functions, and a very brief
life, are generated after a very simple mode. They are pro-
duced without any difference of sex by fissiparous generation.
In others, the mode is oviparous, and of these a large class is
hermaphrodite, the same individual containing both male and
female organs. In a larger class, the two sexes are distinct.
The females of cold-blooded animals deposit their ova, and then
they are fructified by the male ; in warm-blooded animals, the
ova are fructified in the uterus, and may be incubated either
within or without that viscus ; in some genera and species of
animals either method is followed, and they are both oviparous
and viviparous.

630. The generation of an animal always takes place by one
similar to it, and by which the essential constituents of its
animal nature are communicated to it. The origin of an animal
machine and its vital spirits, whether it be nerve or brain, is
one of the hidden secrets of nature, of which we are totally
ignorant.

328 ANIMAL NATURE AS A WHOLE. [iii.

631. The organs of generation are very different in different
animals. In the higher classes in which there are two sexes
the instinct of propagation of species is requisite, its satisfac-
tion (or copulation) having no other natural object than the
fertilization of the ovum. The objects aimed at in the various
modes of generation are concealed from us, but in animals
endowed with mind, the intent of the difference of the two
sexes seems to be this, that the sexes may be led to associate
in protecting their offspring, and providing for their various
wants.

633. So far as our observations on the development of the
ovum extend, we find that the new animal is a portion sepa-
rated from the parent, duly furnished with both animal and
mechanical machines necessary to its existence and develop-
ment. With regard to those animals which produce their
young like themselves, we find that their offspring is furnished
with all the essential animal structures, so soon as separated
from the parent.

633. The whole process of generation is a masterpiece of
nature, and animal bodies are constructed most skilfully to this
end, so that even the most intelligent animals do not possess
the least knowledge of the varied arrangements and plans of
nature in carrying it on (289, 290). This is not the place,
however, for details.

634. The period of development comprised between the
time of conception and of birth, is a period of imperfection,
and, consequently, no animal can be expected to have the full
use of its natural animal forces ; it is for this reason that insen-
tient animals and even sections of polypes are inactive during
this period, until full development be attained. In the more
perfect animals it is different after the appearance of the
pundum saliens, for this movement is a direct nerve-action of
the external impression of the blood on the heart (459), and,
consequently, sentient animals have at least the use of the vis
nervosa to some extent, and, therefore, possess the nature of
living organisms. The intestines of the chick in ovo are not
irritable during the first fourteen days, but subsequently they
become more and more irritable every day. (Haller^s ' Opera
Minora,' p. 401, tom. ii, pp. 364, 398.) As development ad-
vances, (in man about the fourth month,) the foetus is excited

cii. iii.J ORIGIN OF ANIMAL NATURE. 329

by external impressions to movements, which are usually sen-
sational voluntary [Willkiihrlich] ,^ but are probably only nerve-
actions, since, besides that there is no proof of senations being
felt by the foetus in utero, the brain seems to be unfit for the
operation of the animal-sentient forces, inasmuch as its natural
movement is dependent on respiration (24). So that the foetus
is analogous to an insentient animal in its nature, and becomes
sensational at the moment of birth.

635. Since an animal is procreated by one like itself, so the
structure of the two are in accordance ; a resemblance in inci-
dental peculiarities of structure may accompany a similarity in
outward form, and as the embryo, whether in uiero or in the
shell, receives all its fluid elements from the female parent,
peculiarities in the condition of the fluids, as well as of the
sohds, may be thus communicated from parent to ofi'spring;
hence the hereditary predispositions to various states and condi-
tions of health and disease.

636. Original defects in the structure of the germ, an un-
natural condition of the fluids which nourish it, violent move-
ments of the latter in the germinal tissues, injuries to its
structure by external force, the unnatural connection in growth
of two or more germs, and many other incidental causes, give
rise to various monstrosities (Haller, ^Oper. cit.,' tom. iii). In
some of these ways, violent emotions or sensations of the mother
may influence the foetus, and to this extent the former can act
upon the latter; but the doctrine of a harmony between the
sentient actions of the mother and foetus is fabulous.

637. Merely organised natural bodies can never be developed
into living or sentient beings, as Needham erroneously taught.
The existence of an animal pre-supposes that it originated from
an animal germ, and that this was secreted by an animal
similar to itself, (Compare Spallanzani and Haller.)

» See note to § 283.— Ed.

CHAPTER IV.

ON ANIMAL LIFE.

638. The continuance of animal nature is animal life, (The
life of an animal^ as such, Baumgarten's 'Metaph./ § 311.) So
long as an animal force operates in the animal, and there is the
smallest animal action left, so long the animal lives (5, 6).

639. The continuance of the animal nature of an insentient]
animal may be termed simply animal life, just as the vi
nervosa is termed a simply animal force. This mere animt
nature implies the existence of the organic nature, and the
existence of the latter implies the existence of the mechanical
and physical natures : consequently, the entire nature of an
insentient animal (598) is made up of these; but since the
last mentioned may continue independently of animal life, it
may cease, or in other words, the animal may die, and yet the
organic, mechanical, and physical nature remain. Consequently,
the continuance of the vis nervosa is solely necessary to animal
life, and so long as there are the minutest traces of the vis
nervosa, life remains.

640. The continuance of the animal nature of a sentient
animal, and especially of a purely sensational animal, may be
termed sensational life. Such an animal nature implies the
existence of the animal nature of insentient beings, and con-
sequently it is a whole, compounded of the two animal natures.
But a sentient, and particularly a sensational animal, may lose its
sensational life, and still be a living creature (603) ; or in other
words, it may die sensationally , and still live. Consequently, so
long as it retains in the slightest degree that animal sentient
force which characterises it, so long it remains sentient, and
exists sensationally. Again, sensational life only continues so
long as the soul is in such connection with the body, that it per-
forms any one of its movements as a sentient action : when this
connection is broken, mere animal life may still continue (621).

641. The continuance of the animal nature of a reasoning
being may be termed its spiritual life [geistiges Leben] : this

CH. IV.] ANIMAL LIFE. 331

animal nature implies the existence of the sensational animal

nature, and is consequently compounded of these two — the

intellectual and sensational. But inasmuch as sensational life

;an continue independently of the intellectual (620), it follows

lat a reasoning animal may lose its intelleccual life, and yet

>ntinue to be a sensational animal : — it may die mentally, and

ive sensationally, or merely animally. So long as the higher

limal-sentient forces continue in action in the slightest degree,

lental life continues. As this life depends on the intimate

lion of the soul and body, when this union is broken, that is

say, when reason and will are abolished, mental life ceases,

mt sensational life may still go on (620).

642. All these differences in the liie of animals exist in
lature (638 — 641) ; but their nomenclature does not accord

with the terms in ordinary use, so that their specific designa-
tion enables us to analyse our ideas more correctly. Ordinarily,
sensational life and intellectual life (made up of the sensational
and natural) are both designated by the term proper animal
life, or the life of an animal (Baumgarten^s 'Metaphysics/
§§ 575, 576), which can only be understood to mean, the actual
continuance of the union of soul and body. This idea is too
narrow, and is founded on the erroneous notion, that every
animal is endowed with a soul, and consequently excludes the
idea of mere animal life (639) ; but since insentient animals
may exist, the definition must include these, and thus various
errors will be avoided : as for example, that decapitated animals
still possess souls, or that the soul is extended throughout the
body, or that a sentient animal must have several souls, or that
all animal movements are sentient actions, &c.

643. If, therefore, the usual phraseology be adopted, sentient
animals alone (640 — 642) possess proper animal life, and there
remains a special class of animals, intermediate creatures pos-
sessed of mere animal life solely (639). We would designate
the aggregate in sentient animals of the two kinds, namely,
of the proper animal life and the mere animal life — complete
[ganze] animal life, or the continuance of their complete animal
nature (598). We should not, consequently, infer that an animal
had lost its complete animal life, because its proper animal life
— the connection of body and soul — had ceased ; nor that no
sentient actions could take place in it; otherwise we should

332 ANIMAL NATURE AS A WHOLE. [in.

fall into the error of those who thus argue (Baumgarten^s
' Metaphysics/ § 576), and say — contrary to the ordinary
meaning of terms — that a tortoise, which crept about for six
months, deprived of its head; or that a headless butterfly,
which had sexual intercourse, and deposited its ova ; or that a
snail, similarly mutilated, which sought about for food, and had
its head regenerated ; or that a lizard that ran about in the
grass for several days after decapitation, &c., was a dead
animal, or a corpse.

644. The life of every animal is divided into four periods.
The first is the period of development^ and extends from the
moment at which the germ is separated from the parent, to the
time when it is so far developed as to be capable of an inde-
pendent existence. In the majority of animals this occurs at
birth.

645. The second period is i\LQ period of growth, and extends
from the moment of birth to the time when the animal is fully
developed, and fit for the performance of the entire range of
its functions, and of those duties which nature has assigned it.
During this period the animal is unfit for many functions which
it performs afterwards, when fully developed.

Qi^Qt. Neither nutrition nor growth are purely animal func-
tions, nor do they involve animal machines only, but are effected
by the common action of the forces of all parts of the entire
nature of an animal, — the physical, mechanical, organic, and
animal — and in sentient animals — the animal-sentient forces —
all acting in wonderful union to that end.

Note. — The laws of nutrition and growth are laid down in
physiological works, and we refer to them here only in so far
as they bear on proper animal nature, and influence the proper
animal machines, and the proper animal forces.

647. Neither the nerves, nor, in sentient animals, the brain,
are fully developed at first, or are fully capable of the vis
nervosa, or of all the animal-sentient forces. Innumerable
facts show, not only that the nerves continue to grow after
birth, but are developed in new growths. This is most clearly
seen in insentient animals, as in insects ; in the metamorphoses
they undergo during the various stages of their development ;
and in animals in which entire limbs, or entire segments of the
body, have been reproduced after mutilation.

cH. IV.] ANIMAL LIFE. 333

^

648. In fact, we see that all animals perform more numerous
and perfect acts as they approach the period of perfect de-
velopment. Many animals, especially the insentient, act from

e beginning with great skill and adaptiveness, but they can-
t perform those movements which belong to a more perfect
stage. A caterpillar acts principally from the instinct for nutri-
tion ; it must undergo several changes, before it is capable of the
animal act of spinning : it is only when fully developed into a
butterfly, that it can perform the acts necessary to propagation
of the species. No signs of a desire to perform motions of
this kind are manifested before the organs requisite to their
performance are developed. (Compare Spallanzani, ' Phys.
Abhand.,^ p. 167, for examples in the infusoria.)

649. The brain is always imperfect at first in sentient animals.
During the period of growth, it becomes larger and firmer, and
receives a movement from the respiratory act, which it had not
before, and which seems to have an influence on the actual use
of the cerebral forces. The nerves also increase in sentient
animals after birth, not less than in the insentient, and parts
become sensitive and irritable which were not so formerly.

650. In sentient animals, as w ell as in insentient, we observe
a progressive development of the animal forces ; although from
the moment of birth many of these display a readiness in the
use of the vis nervosa, and a perfection in the instincts necessary
to their maintenance, so as greatly to surpass man in these
respects. Still many of their sensational and motor faculties
are so imperfect, that the earliest portion of their existence is
only the vague dream of an almost continuous sleep.

651. Since it is during the period of growth that the nervous
system and its forces are developed, it is at that time that they
determine the temperament of the animal (52, 502), together
with its animal and even moral character, if capable of such
(65, 295, 344). Now, as every genus and species of animal
has originally the capabilities of its parents, and these only be-
come more perfect and fixed during the period of growth, it
follows that every genus and species have each their special
characteristics. These capabilities and endowments may be
changed in numerous ways, by habit, education, and accidental
modifications of development (52, 431, 501).

652. The third period, or that of propagation of the species.

334 ANIMAL NATURE AS A WHOLE. [in.

is the perfect or adult stage of life. In some animals it is ex-
tremely short, in others prolonged; but without it no animal
is complete, and so soon as it terminates, the animal begins to
decline. This period is also the great object of natiu-e in the
animal creation, and to this there is no exception from man to
the simplest animalcule.

653. In sentient animals the propagation of the species
takes place by means of the satisfaction of the instinct for
sexual congress (289) : in insentient animals which propagate
by copulation, this instinct is replaced by nerve-actions. It has
been already illustrated fully (274, 289, 290, 481, 540, 560) ;
and we have only to consider here the changes which take
place at this period in animal nature.

654. All animals are not bom with sexual organs : some
only acquire them after undergoing a succession of transforma-
tions, as insects. But these organs in those animals which
possess them at birth, as well as the body generally, undergo
such great changes, as the period of propagation of the species
approaches, that the period itself becomes of the greatest and
most general importance. The whole body is invigorated, the
seminal fluid is secreted, and often communicates its odour to
the whole animal ; smooth parts become hairy, horns grow, the
voice alters, &c. In the female equally important changes
take place.

655. It is a necessary result, that great modifications of
the nervous system accompany these important changes in the
animal. The nerves of the whole body, and particularly of the
sexual organs, become susceptible of new impressions, and in
sentient animals this occurs so extensively, that it appears as
if a wholly new sense of feeling had been developed. A look,
a tone, an odour, a touch, which the sentient animal had ex-
perienced a thousand times before, without any other than
ordinary results, cause an emotion during this period, which
excites the instinct to sexual congress, while the sexual organs
themselves undergo analogous changes (274, 289). The external
impressions of these sensations in sentient animals excite the
same unusual operations in the insentient (481). Without
exciting a sensation, they are so reflected as to act upon the
sexual organs, as if they had excited a sensation (540). That
external impressions are so reflected on the nerves of the sexual

CH. TV.] ANIMAL LIFE. 835

organs, even when these are not directly irritated, and act as
though they were felt, is shown by the fact that the fluttering
of the wings, whereby the female butterfly allures the male to
sexual congress, irritates the nerves of the decapitated male
butterfly generally, and not those of the sexual organs in par-
ticular, as any other fluttering would ; yet it has the same
eff'ect on the sexual organs of the male as if they felt it, and it
was reflected as a conceptional internal impression. It is
shown, however, that this reflexion of the external impressions
on the sexual organs, purely by means of the vis nervosa, takes
place for the first time at this period of propagation, and be-
cause the route thereto is as it were laid down, from the fact,
that the external impressions made by the fluttering of the
female on the decapitated male butterfly, are not thus reflected,
unless they have copulated at least once before decapitation
(560).

656. The internal impressions caused by conceptions in sen-
tient animals, or independently of conceptions in the insentient,
manifest, at this period, the same new powers of action on the
sexual organs as external impressions. The remembrance of
a sensation, that in the child would excite no attention what-
ever to sexual congress, now becomes a sensational excitant of
the instinct, and it is probable that the mind repeats the for-
mer pure sensation, increased by new sub-impressions [Merk-
male] that excite this new instinct, and from which the former
sensation was entirely free. This also appears to be imitated
in insentient animals by the vis nervosa, when the female of
insects, if decapitated at the period of sexual excitement, not
only continue the sexual functions, without any apparent ex-
ternal excitement, but frequently recommence them after a
period of repose, fluttering with their wings, to call as it were
the male to sexual congress.

657. In reasoning animals this period of life is not distin-
guished by all these new movements in the vis nervosa and in
the cerebral forces, as is the case in sensational animals, but
the understanding and will attain to new and higher powers.
Every one is aware that these attain the greatest perfection
of which they are capable, with adult age. The brain also
acquires a higher and more perfect development, in accordance
with the greater perfection of the mental powers.

336

ANIMAL NATURE AS A WHOLE.

[III.

658. As this period of perfection of all the functions is
attained sooner in some animals than in others, and continues
for a shorter period, it determines the duration of life in
different classes of animals ; and in this there is the greatest
difference, the period in which the sexual organs are active,
varying from a day to a hundred years. The interval between
the cessation of sexual activity and death, seems only to be an
addition to life, — a something given over and above ; and we
will term it the period of decline. But before entering on the
consideration of this period, we must consider the whole plan
of perfect animal life, the proper knowledge of which is the
great object of this system of physiology.

CHAPTER V. -

THE SYSTEM OF THE FORCES OF ANIMAL LIFE.

659. The mode and method by ,whicli, in the perfect con-
dition of animal life, tlie animal forces act with and by each
other, and are co-ordinate and subordinate, is termed the system
of the forces of animal life.

660. The order in which a watchmaker constructs a watch,
when at one time he forms a wheel, at another a chain, now the
hands, the face, and the spring, and then connects these separate
pieces, and inserts the spring, cannot enable a spectator to dis-
cover how each of them will contribute its share to the perform-
ance of the whole machine, although well known to the master-
workman, who has worked according to a previous plan. But
when the watch is put together, wound up, and set in motion ;
in short, when the mechanism is completed and finished, the
spectator can understand how all the separate pieces and the
motor powers co-operate with each other, so as to attain the
intent of the machine, namely, to divide the time accurately.
Hitherto, we have seen how the machines and forces of the
animal are more and more developed, as it approaches the period
of maturity. It is at that period that the complete machine
can be investigated in all its relations, and the connection
of all its machinery and forces, as a system, be comprehended.

661. The animal functions of animals are effected generally
by means of the nervous system and the vital spirits it contains.
These do not constitute the only parts which develop animal
movements, but in virtue of their relation, are the first that are
capable of them. Then all animal functions take place in virtue
of impressions on the animal machines (356). It is necessary
to the reception of an internal or external impression by a
nerve, that it be communicated to it in a certain direction, that
it be impressed on the medulla of a nerve, and be propagated
therein by means of the vital spirits (32, 121) ; and if the
brain is to receive impressions from conceptions or other causes
of irritation, they must take place in virtue of a current
[Antrieb] of the vital spirits in its minute tubes (28, 121). But

22

338 ANIMAL NATURE AS A WHOLE. [m.

all these conditions cannot possibly be coincident in an isolated
portion of the brain, or of a nerve, since they are dependent
on the connection of the whole, and imply the existence of
the natural structure of the animal machines.

662. Hence it follows, that although the nerves and brain
[the animal machines] daily receive new elements by nutrition
and growth, and wear away by daily use, still they can continue
their functions, so long as this increase or change of their
elements neither alters their structure, so as to render them
incapable of their functions, nor prevents the action of the ani-
mal-motor forces, for their individual constituent parts have no
share in these functions, except under these conditions. Indeed,
so far from the gradual and imperceptible growth and change,
which the brain and nerves undergo from continued use, ren-
dering them unfit for their functions, and preventing the action
of the animal-motor forces, they are the rather rendered more
and more capable of new functions (644 — 648). All plants
which daily lose old elements and receive new, their organic
functions going on uninterruptedly, are illustrations of these
views; the heart in animals, considered as a mere mechanical
machine, is another, for although the heart of the old man con-
tains not one of the constituents which made up the heart of
the child, the general change of all its constituent parts has in
no degree interfered with its functions, they having gone
on without a moment^s interruption. Thus also it is with the
brain and nerves.

663. The structure of the brain and nerves renders them
capable of their proper and natural functions, and is necessary
to animal life in general, but it does not excite those functions.
This is the case with all machines, whether mechanical, organic,
or animal. A watch or a mill does not go merely because its
machinery is complete in all its parts, but the action of the
motor force appropriate to the machinery is requisite. The
whole body of the animal is so constructed in its perfect state,
that it can perform all the movements to which nature has des-
tined it, but it is endowed with true animal life, solely in virtue.:
of the animal forces which put it into motion ; and so soon as
these cease to act, animal life ceases, although its nervous struc-
ture has undergone no change whatever (638).

664. There may be also such a condition of the animal, that

CH. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 339

the nervous system cannot, either wholly or in part, perform its
functions, independently of any defect of structure; as, for
example, before the animal has an independent existence. It
is also a mistake to refer the true animal functions solely to
the structure of the animal, since that only renders the func-
tions possible. But while the accomplishment of the functions
by the animal forces implies the existence of the requisite
structures, the absence or injury of the structures, and every-
thing which renders them incapable of performing their func-
tions, interrupts life, and brings it to a termination. Thus, if
the brain be removed or destroyed, sensational life ceases ; and
animal life would cease too, if all the nerves were destroyed, or
all the vital spirits, or their circulation through the nerves en-
tirely arrested, or any means used by which the nerves were
rendered unfit to receive any impression, although the same
impressions may still be made, which make ordinary circum-
stances constitute true animal motor forces (356).

665. The animal forces, which give vitality to the whole
animal kingdom, are all those impressions of which animal
machines are capable, in virtue of their proper animal structure.
These impressions have been already fully considered, as well
as their co-ordinate and reciprocal action (31, &c., 121, 356,
590, &c.) We must, however, note more specially their mutual
subordination, or their dependence on each other.

666. An animal function (the action of an animal force)
which is based on another, is subordinate to it (Baumgarten^s
'Metaphysics,^ § 25). Consequently, this subordinate function
implies another animal function and force, namely, that to
which it is subordinate. Now, as many animal functions are
based on others, as, for example, sentient actions or imagina-
tions, these latter on sensations, and sensations on external
impressions, there is doubtless a subordination of animal forces
in animal life; and if they can act in the natural condition in
no other way than subordinately, it is a natural subordination}

667. There are certain animal forces which are not naturally
subordinate to any others, namely, — i. External impressions
when not in themselves animal actions ; for the nerves receive

' The term natural has here and elsewhere a peculiar meaning, and refers to the
mode of action of the organism, as resulting necessarily from its organisation. See
note to § 27.— Ed.

340 ANIMAL NATURE AS A WHOLE. [in.

impressions without a previous animal action being necessarily
implied (33). ii. Primary internal impressions, independent of
conceptions, with the condition just stated. In these no pre-
vious animal action is necessarily implied (490). iii. The in-
ternal impressions, arising from those conceptions, desires,
aversions, &c. that are mental, and not sensational in their
nature, when considered independently of their remote sensa-
tional origin, since in these the brain receives impressions from
conceptions formed solely according to psychological laws, and
not necessarily in dependence on any other animal action {76).

668. All the remaining forces are naturally subordinate to
others, as for example, — i. The internal impression developed
from unfelt and reflected external impressions ; for in this case,
the internal impressions on the nerve implies the reflexion of
an external impression (421). ii. The internal impression from
external sensations and sensational conceptions, desires, in-
stincts, &c. ; since these are dependent on animal- sentient
forces excited from without (66). iii. All those mentioned,
§ 667, if the condition there stated as necessary be wanting.

669. The animal forces which are naturally subordinate to
others, are, — i. Unfelt external impressions, which, by being re-
flected, excite internal impressions, ii. Those external impres-
sions which excite sensations, sensational desires, aversions, &c.
iii. Internal impressions not connected with conceptions, in so
far as they are reflected on other nerves in their course down-
wards (500) : and iv. The internal impressions of conceptions,
but with similar conditions (137).

670. Those animal forces which are not naturally subordi-
nate to any other, are all those just mentioned, when the
conditions are not present ; or, in other words, when unfelt ex-
ternal impressions cause unfelt direct nerve-actions simply (418,
443) ; or if, when they excite no direct nerve- actions (445), are
prevented naturally from being transmitted along the nerve,
and are either reflected (426, 199), or felt (47, &c.), or, in so
far as internal impressions not dependent on conceptions, or
those of conceptions, are not reflected on other nerves in their
course downwards (485, 124).

671 . The animal machines of an animal are all in connection
with each other, and constitute a special system of animal ma-
chines. In those endowed with brain, the nerves are only

CH. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 341

prolongations of it, and the current of the vital spirits passes
upwards and downwards in both (21) ; in others, all the animal
lachines are in general connection, by means of ganglia,
)ranches, and plexuses. Nevertheless, every portion of the
lystem of animal machines is of itself capable of animal forces
(31). The brain receives its own impressions at points quite
.different from those at which the external impressions which
are felt are received (124) ; as well as those from other con-
ceptions (130, i). In like manner, every nerve, every portion
of the system of nerves, has the capability of receiving both
internal and external impressions, and when there are no na-
tural obstacles present, of transmitting them to other branches,
or other nerves, either through the ganglia or plexuses, or com-
municating nerves, or through the brain itself, by means of
conceptions (31, 32, 121). But if the action of an animal force
in this system of animal machines shall have another subordinate
to it, it must excite another animal force either in the same
portion of the system — as when an external impression excites
an internal impression in the same nerve, or vice versa; or else
it must excite an animal force in another portion — as when an
external impression on one nerve excites either an internal or
external impression in other nerves, or other branches, &c.

672. This natural subordination of the animal forces does not,
therefore, occur in each and every point of the system of animal
machines, but (as experience proves) certain points are destined
by nature to this end ; these may be termed the natural con-
necting points of the animal forces, inasmuch as in these the
forces communicate and combine with each other. The external
impression continues its course along the nerve, until it arrives
where a branch is given off, and which receives it as an internal
impression, and thereby other animal actions may be produced ;
or until the nerve is intermingled with others in the ganglia
or plexuses, where its external impression can be received, and
act as an internal impression (421) ; or in sentient animals,
until the external impression reaches the origin of its nerve in
the brain, and there, by means of a conception (sensation),
excites the animal-sentient force to send it back again along
the nerve (35, 121, 124) ; or until one of its nerve-actions
excites external impressions, which cause corresponding sensa-
tions and sentient actions (184, i, 443). An internal impres-

342 ANIMAL NATURE AS A WHOLE. [in.

sion, whether arising from conceptions or other stimuli, con-
tinues its course onwards in the system of animal machines
from the place of its origin, whether that be in the brain, or in
a ganglion or plexus, or at the point of division of a nerve, or
any other point of the nerve-medulla, without putting any other
animal force into action, until it is conducted along other
branches or nerves (which duly receive it), either in a ganglion,
a plexus, or point of division, and thus excites animal actions
(124, 485) ; or until its own action excites external impressions
in the nerves, which again have their peculiar course and
operation (225).

673. Those portions of the system of animal machines which
combine several natural connecting points of the animal forces,
are termed centres of the animal forces. A number of animal
machines are put into action, by means of these centres, when
external or internal impressions reach them. We will mention
the principal of these centres. The brain deserves the name in
a two-fold manner. Firstly, in its relation to the vital spirits,
of which it is the secreting organ, partly sending them to all
other animal machines, or communicating internal impressions
not caused by conceptions : partly receiving them back again
from the machines, or having external impressions commimi-
cated to it from the latter (11, 17, 18, 31). Now, although
many insentient animals have no proper brain, still all must
have animal machines performing this function, because there
can be no animal life without the intervention of the vital
spirits, and consequently without their secretion and circula-
tion. The ganglia and plexuses are probably, in this respect,
the analogues of the brain ; and in those animals, a mere section
of which has an independent existence, as polypes, or in those
in which the head and brain may be removed without injury
to life, since they are reproduced, as snails [vide Spallanzani),
either the whole nerve-medulla of the entire system of animal
machines, or a special portion in each limb, has the same func-
tion as ganglia and plexuses; so that animals of this class
possess several analogues of the brain (362, vide Haller's
'Physiology,' part iv, vol. x, sect, vii, § 36). Now, although
a brain of this kind may not be so constituted, as to be also
capable of the animal-sentient forces, as in sentient animals,
still it possesses so much of the structure of a brain, as to be

CH. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 343

an animal secreting organ, and consequently may be very pro-
perly termed a brain ; and thus the unnecessary multiplication
of terms be avoided. Many eminent men, seeing that the
ganglia are supplied with numerous capillaries, have concluded
that they have some beneficial function with reference to the
nerves. {Vide Haller, vol. cit. sect. 10, § 32.)

In the second place, the brain merits the designation of
centre of animal forces, inasmuch as it is so constructed in
sentient animals, that it is adapted to the animal-sentient
forces ; and external impressions which are felt, are generally
so reflected in it by the intervention of conceptions, that they
put internal impressions from external sensations and sensa-
tional conceptions into action (34, 66) ; the operation of which
can be extended throughout the animal machines [nervous
system] of the whole body. (Part I, Chap. III.)

Another centre of animal forces found in all animals is the
hearty and which is specially adapted to be such by the number
of its nerves and the varied composition of its plexuses (516).
When it is remembered that all conceptions, in so far as they
are pleasant or disagreeable, modify its movement (250) ; that
a great number of animal actions in the entire economy of
the organism are thus developed, as is particularly shown in
the sensational instincts and passions (258) ; that its natural
movement is maintained by means of unfelt external and in-
ternal impressions (459, 515) ; and that by means of the circu-
lation the greater number of the processes necessary to the
preservation of the individual are maintained, there can be no
doubt as to the importance of this centre of animal forces.
Although such a heart as the larger animals possess is not de-
veloped in all animals, still there is always a machine which
regulates the circulation of the fluids, and to which the term
heart may be very fairly assigned. The region of the diaphragm
and of the stomach is not unreasonably considered to be a
centre of animal forces, because numerous nerves meet and
unite there (171, 174) ; and because it is observed that the
impressions reaching there develop nerve-actions and sentient
actions in most parts of the body {vide § 688). Lastly, the
sexual organs occupy an important position amongst the centres
of animal forces (687) .

674. We know of no animal with a general centre of animal

344 ANIMAL NATURE AS A WHOLE. [in.

forces, that is to say a centre wherein all the natural connect-
ing points of the animal forces are collected together, since in
all, there are found, at very distinct portions of the nervous
system, larger and smaller ganglia, plexuses, and general points
of division of nervous trunks into branches. If, however, those
centres of the animal forces ought to be termed general, which
are common to all animals without exception, then there are
many such (673) ; or if by the expression is meant a certain
portion of the animal machines [the nervous system], the
injury, destruction, or removal of which terminates life, then
there certainly are such general centres, as we shall shortly
show (675) ; but those are in general in greatest number which
are mutually subordinate to each other.

675. The heart and brain are essential to animal life in all
animals, the latter as the secreting organ of the vital spirits,
the former as the first cause of the circulation. Both are the
most important and the first visible portions of the germ. It
is true, that the brain in the embryo of sentient animals has
no apparent function, for its natural visible movement seems
to be requisite to the action of its animal-sentient force, be-
cause it only occurs with respiration, and consequently not
before birth (24) ; anteriorly to which no animal-sentient force
can be shown to be in operation (634). On the other hand,
the secretion of the vital spirits is an invisible function (28),
and in so far as it is animal is a pure vis nervosa (374, 159),
which may without doubt be active in utero. The heart, or its
analogue, manifests a distinct movement in the earliest stage of
development of the embryo : these two centres must conse-
quently be considered to be the primary and essential portions
of the system of animal machines. We therefore term the
secreting faculty of the brain and the natural force of the
heart, the primary vital forces. We exclude from this desig-
nation the animal-sentient force of the brain, which is not com-
mon to all animals, and understand solely the two mentioned,
the one being that on which all animal forces depend, without
exception; and the other that on which the circulation, the
secretions, and nutrition are dependent

676. It may happen, that before birth an animal receives its
fluids from its mother, elaborating none by its own forces, and
secreting none until it has an independent existence. The vital

CH. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 345

spirits is the only one of these secretions absolutely necessary
to the action of the other animal forces in the economy (21);
and as they are secreted from the blood, this primary vital force
of the adult and perfect animal is dependent upon the cardiac
force. But the influence of the vital spirits on the heart keeps
up its continuous action, by means of its unfelt external impres-
sions (515, 532, note) ; and unless the cardiac nerves be filled
with the vital spirits, they cannot respond to the impressions
made on them by the blood, and consequently cannot excite
its whole motor force (665, 457). The two primary forces are
therefore reciprocally subordinate to each other : neither can
continue uninterruptedly, independently of the other, and if
the one ceases, so must also the other. Therefore, if there be
a common point of union of the two forces in an animal, that
point is also the general centre of the animal forces in the sense
already referred to (674). According to Lorry's observations,
this point is situate in that part of the meduUa oblongata cor-
responding to the second cervical vertebra. Animal life sud-
denly ceases if this portion be injured, destroyed, or removed.
( Vide Haller's ^ Physiology,' part iv, vol. x, sect. 7, § 36.)

677. The objections to this doctrine of the reciprocal sub-
ordination of the two forces to each other are easily met.——
i. It may be advanced, that in the germ one of the forces must
necessarily begin to act before the other, and consequently
either the heart can act independently of the vital spirits, or
the latter may be produced independently of the heart. As
to the former objection, we answer, that both may commence
at once; as to the latter, the assertion is only applicable to
animals enjoying an independent existence, inasmuch as the
fluids may circulate before birth in virtue of extraneous forces,
and not of those proper to the germ (Haller's ' Physiology,'
§ 891).

ii. It is objected, that in sentient animals the heart's action
will continue for some time after decapitation. The reply is, that
the vital spirits do not drain away immediately after removal
of the brain ; and so long as the cardiac nerves respond to im-
pressions, so long are the vital spirits retained in them (515).

iii. It is further objected, that the brain can perform sen-
tient actions after the heart has been removed from the body.
This may occur for a short time, but only so long as the brain

346 ANIMAL NATURE AS A AVHOLE. [iii.

contains the blood sent to it from the arteries, which can con-
tinue to act for a short time after excision of the heart.

iv. Another objection is, that insentient animals exist with-
out either brain or heart. According to all probability, in
these the vital spirits are not secreted in what is ordinarily
termed a brain, but from the nerve-medulla at 'several points of
the nervous system, and consequently the organs of these
animals retain their whole animal life until either their fluids
are exhausted from the want of nutrition, or can no longer
contribute the material of the vital spirits (362, 416). Animals
of this kind, which are not only nourished by what may be
termed the head, but also by several organs, or by the entire
surface of the body, can perfectly retain their whole animal
life, and each separate portion of their body must be considered
as a whole, having the two centres of primary vital forces, in
which an analogue of the brain secretes vital spirits, and acts
in reciprocal subordination with an animal machine, the
analogue of the heart having the function of carrying on the
circulation [vide § 699).

678. The proper motor force of the heart in the natural
adult condition of an animal, is the external impression which
the in-flowing blood, or some other general fluid, excites in its
nerves, and whereby the movement of the heart is peculiarly a
direct nerve-action (456) ; but at the same time it is continued
in its natural order by the internal impression, which the
influence of the vital spirits makes on the nerves. The life of
the heartj therefore, continues, — i. So long as its nerves are
capable of responding to external impressions, especially those
made by the blood, ii. So long as these external impressions
actually act upon them. These two conditions are alone neces-
sary. But since the cardiac nerves lose this capability, if the
continued flow of the vital spirits into them be interrupted, or
the secretion arrested, the vitality of the heart is extinguished as
soon as the supply of vital spirits contained in them is exhausted,
and this is the reciprocal subordination of the two forces.

679. The primary vital force of the cortical substance of the
brain (362), (not the animal-sentient force, 375), in the perfect
condition of an animal, is the impression made by the in-
streaming blood on its secretory vessels, whereby they are sti-
mulated to perform their proper function, in so far as it is

CH. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 347

I

nimal, namely, to secrete and transmit the vital spirits (374).

t is naturally subordinate to the animal force of the heart, and
continues so, firstly, so long as the blood continues to flow
through the vessels in virtue of the hearths action ; and secondly,
so long as the vessels respond to the impressions made by the
blood circulating through them. These two conditions are
alone requisite to the maintenance of this natural vital force
of the brain (663, 664). But when the secretion of the vital
spirits is arrested, or their flow to the cardiac nerves cut ofi",
then the hearths movements are easily interrupted, and at last
stop, so that when the circulation of the vital spirits in the
cardiac nerves ceases, (which may result from the interruption
of all the cerebral functions, of the connection between the heart
and brain, &c.,) this primary vital force of the brain ceases.

680. All other animal forces are naturally subordinate to
these two primary vital forces, in so far as the operation of all
in the animal machines presupposes the influence of the vital
spirits which render the animal machines fit for their func-
tions, and which they cannot be, without the natural subordina-
tion of both j and again, in so far as every animal machine is
nourished and developed by the circulation of the blood, their
natural functions are eff'ected also by it.

681. In especial, the natural functions of all parts of animal
organs are naturally subordinate to the combined action of the
two primary vital forces of the heart and brain, as may be
easily shown. This is manifest with reference to the animal
force of the arteries, in forwarding the general circulation of
the fluids, since they become fit for their function in virtue of
the vital spirits, and are dependent on the heart for receiving
the impressions which excite their stroke (460).

682. The animal forces of the capillaries and their termina-
tions stand in the same natural subordination, whereby they
excite a flux towards parts duly irritated (207). The circula-
tion must supply the fluids which constitute the flux, and it
is through the vital spirits that they are rendered capable of
responding to stimuli (462, 463). But a co-operating or co-
ordinate force is necessary to this flux, and the subordination
of this animal function is also conditional, inasmuch as it only
results when an external impression takes place at the same
time on the capillaries, or their mouths (207, 462).

348 ANIMAL NATURE AS A WHOLE. [in.

683. The natural subordination of excretion and secretion
to the two primary vital forces is less direct, because they
imply the action of the arteries, for the latter must carry
those materies, the external impressions of which excite them
to the functions of secretion and excretion, and subserve
thereto (472).

684. The movements of muscular fibrils, of membranes, of
muscles, and of muscular viscera and organs (162), are also
subordinate to the two primary vital forces. The influence
both of the vital spirits and of the blood is necessary to the
natural actions of all these. Although the subordination is
more direct than in the glandular system and excretory viscera,
co-ordinate forces are required, inasmuch as all muscular action
requires also an internal or external impression (162, 448).

685. The function of respiration in breathing animals,
being effected by muscular tissue, follows the law of subordina-
tion of muscular action in general.

686. Lastly, all compound functions of the viscera are
subordinate to the primary vital forces, in accordance with the
preceding laws. The functions of the sexual organs, whether
male or female, — as copulation, &c., include those of arteries,
capillaries, muscles, glands, &c., and are subordinate, according
to the age and conditions of the constituent parts.

687. But even these compound animal functions, as respira-
tion, digestion, generation, have a number of functions subor-
dinate to them, inasmuch as their effects extend through the
entire animal economy. This is very remarkably the case
with the function of generation, which, in those which have
sexual congress (633), puts animal forces into operation that
are subordinate to it in a wonderful manner.

688. The diaphragm and the stomach (which forms with
the intestines one canal) stand in very close relation to each
other, and attentive observers have recognised the region in
which they are situate, as a very general centre of animal forces ;
not only because many nerves meet and communicate there,
but because many phenomena prove it to be such. Violent
injury of this region causes great general changes in the body,
and diseases of these parts derange many animal functions.
Thus, worms and mucus in the stomach excite convulsions of
the extremities ; colic induces paralysis ; bad digestion causes

cii. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 349

hypochondria; inflammation of the diaphragm induces fatal
delirium and nervous attacks, &o.

689. There are many other subordinations, but it is not
possible to give all in detail in this general sketch ; it is easy,
however, to deduce them from the general principles laid down.

690. The natural subordination of all animal forces we have
considered hitherto, has been considered with reference, it is
true, to the most perfect type of animal organisation; but,
nevertheless, it is applicable to every species of animal, whether
sentient or insentient, provided only that they have some of
the organs belonging thereto ; for, in the Second Part of this
work it has been shown, that the animal functions in question
may be performed as well by the vis nervosa only, as by the
animal-sentient forces; or by both acting conjointly. But in
sentient animals, the brain is a special organ and centre of the
animal sentient forces, and of this we have now to treat.

691. The brain is not capable of an animal -sentient force,
without vital spirits (21, 22). Further, its animal-sentient
forces are subordinate to the primary vital forces, as regards the
secretion of the vital spirits. The proper animal-sentient forces
of the brain are the material ideas of conceptions (25), which
are always induced primarily by means of external impressions
(65), although some of them, namely those of intellectual con-
ceptions, desires, &c. are impressed on the brain by the mind,
without their being more immediately dependent on external
impressions (579, ii.)

692. As the animal-sentient forces of the brain depend upon
external forces that are felt, and all sentient operations in the
system are effected through them (97, 6), it follows that the
brain, in so far as it is adapted to them, is the centre of the
animal-sentient forces (673) ; although the latter are themselves
naturally subordinate to the primary vital forces.

693. Proper animal life endures so long, as, i. The natural
functions of tbe primary vital forces continue, at least in some
degree, namely, the secretion of the vital spirits in the brain,
and the circulation of the blood (640, 641). ii. So long as the
brain is not prevented receiving external impressions, or internal
impressions from certain conceptions, iii. So long as external
impressions, or sensational or intellectual conceptions, induce
material ideas in the brain (663, 664.)

350 ANIMAL NATURE AS A AVHOLE. [i"-

694. Proper animal life, or in other words the connection
of body and soul, ceases,

i. When the primary vital forces cease, that is to say when
the circulation is altogether arrested, so that no blood is sent
to the brain, and that already sent is no longer retained in it ;
or when the functions of those portions of the brain which
secrete the vital spirits is altogether abolished, so that no more
is secreted, and that already circulating in the nervous system
is used up or destroyed.

ii. When, although the circulation of the blood and secretion
of vital spirits go on, the brain itself is so changed, that neither
an external impression, even if it reach the cerebral origin of
the nerves, nor a conception, can produce a material idea in it.
This takes place, when the brain is entirely removed or de-
stroyed, or so under the influence of poisons, that its functions
are abolished, — circumstances which change the animal into
an insentient animal machine.

iii. When an animal no longer has in the slightest degree,
either an external sensation, or a sensational or intellectual
conception, or when neither these, nor external impressions,
develop any material ideas whatever ; for under these circum-
stances the soul has no connection with the body, whether it
have an independent existence or not, and, consequently, the
life of the sentient-animal terminates (610).

Note. — In these conditions consist the first principles
of our knowledge of the causes of death; of the fatality
of wounds, poisons, and other injurious agents; and the
question of life or death in disease and in doubtful cases,
(vide § 710, &c.)

695. All natural functions are subordinate to the animal-
sentient forces, in so far as they are sentient actions and forces
of other sentient actions subordinate to them; and result (sub-
ject to the general conditions of proper animal life) from all
conceptions, in so far as they are excited by external impres-
sions, or the sensational or conceptive force.

696. In particular, all the sentient actions enumerated
§ § 97 — 100, and considered in detail in subsequent chapters ;
and all those developed in the tissues and organs, considered
§§ 160 — 179, and in the capillaries (207), are subordinate to
the animal-sentient forces.

N

H. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 351

697. So soon as the connection of body and mind is abolished,
and, consequently, proper animal life ended, all these animal
operations cease to be sentient actions, although, in conse-
quence of the maintenance of mere animal life, they may still
be produced by the vis nervosa only. (Part II, Chap. IV, sect, i.)
They may be produced, however, in virtue of the natural co-
ordination of the forces of the mind and the nerves, by both
acting at the same time in parallel subordination. (Part II,
Chap. IV, sect, ii, iii.) But as the animal-sentient forces are
subordinate to the primary vital forces towards the close of
mere animal life, the animal functions cannot be produced by
the former, but all proper animal life must cease at the same
time (640).

698. Thus then, in tbe perfect condition of the animal, all
its animal forces are both subordinate and co-ordinate in the
most wonderful manner ; whence in the system of all the forces
of the complete animal nature, the concurrence of merely
physical, mechanical, or organic forces come into consideration ;
as, for example, of the commingling of fluid elements, of rigidity
or flexibility, shock, compression, elasticity, &c., to which the
action of the animal forces is often incidentally, naturally, or
contra-naturally co-ordinate and subordinate. All animal
operations are naturally subordinate to impressions, through
which the primary vital forces are maintained in activity, but
only so long as animal life remains (678, 679). It depends on
these forces whether an animal life can exist and continue in
perfection, be the animal endowed with mind or not, and that
a thousand impressions on every part of the nervous system
(which act with them in a co-ordination, partly fixed by nature
and naturally necessary, and partly incidental) can develop at
one time whole series of natural and subordinate animal pro-
cesses, from distinct centres of animal forces (673, 687 — 689);
at another one such process only, but all subservient to the
preservation of the animal and the attainment of the ends
designed by nature (674,681 — 686). In animals endowed with
mind, the animal- sentient forces are subordinate to the primary
vital forces, the former being, in fact, impressions of a peculiar
kind (356) which act through the brain, (the centre of the
animal-sentient forces,) by means of the production or operation
of conceptions and material ideas, and which can thereby

352 ANIMAL NATURE AS A WHOLE. [in.

develop the same series of subordinate or single processes, pro-
duced by the other impressions necessary to the preservation of
the animal and the attainment of nature's objects ; and with
the same partly necessary and natural and partly incidental
co-ordination (696). All this takes place, in order that these
processes may be caused also at the same time by sensation,
perception, volition, effort, desire, aversion, reflection, and choice
and satisfaction of the animal, and thus it be rendered more
perfect, and capable of a more independent carrying out of its
proper objects (370, 371).

699. The doctrine, as to the general subordination of all
animal forces to the primary vital force of the brain, may excite
doubts which require a solution. In this entire work, we have
taught that the most essential and the greater proportion of the
animal processes necessary to life, may go on perfectly, even in
sentient animals, not only absolutely, but also in their natural
connection, without the assistance or co-operation of the brain ;
and that it is possible animals may and do exist, that have
neither brain nor head, nor conceptive force, and yet can
perfectly perform all the functions necessary to their animal
life, by means of the vis nervosa only. How can t)iis agree
with the doctrine, that the brain is the centre of all the animal
forces of animals ? and that the secretion of vital spirits in it,
and their circulation through the whole system of animal
machines, is a primary vital force of all (675)? The animal
machine which secretes the vital spirits, is not in all animals
the same as that which is capable of animal-sentient forces,
although the term brain has been applied to both kinds (673).
All animal functions require the primary vital force of the
brain, because it is necessary to the secretion and transmis-
sion through the nerves of the vital spirits ; but all do not
require the animal-sentient forces, inasmuch as they can be
replaced by the vis nervosa only. In those animals not en-
dowed with animal-sentient forces, the secretion and diffusion
of the vital spirits is necessary to their animal processes ; and,
consequently, a brain endowed with a primary vital force is also
necessary, since all the processes are subordinate to it (680,
690). But this brain may be diffused throughout the body, and
every part may have its own brain ; and their animal processes
may be in subordination to the primary vital force of this

CH. v.] SYSTEM OF THE FORCES OF ANIMAL LIFE. 353

diffused brain (677, iv). If, however, the nerve-medulla in the
head secretes and transmits the vital spirits only, then life
ceases with the removal of the head, except in so far as vital
spirits already secreted and transmitted may still remain in
the nerves (661, 677, ii); until these are exhausted, various
processes may go on in the body in their natural co-ordination,
although no sentient actions can take place in sentient animals.
The functions of the brain may be compared with a fountain
supplied from a brook, which waters flowers and plants : the
latter are the nerves ; the fountain represents the animal-sen-
tient force, and the brook the primary vital force. The fountain
may be removed, and still the flowers may flourish, provided
the sources of the brook be not cut off", but the flowers and
plants live only so long as the supply of water already in the
garden holds out.

23

CHAPTER VI.
ON OLD AGE AND DEATH.

700. After an animal has attained its growth, and all its
natural transformations being completed, it has remained for a
period in its state of full development, everything in its nature
tends to decline. Its fluid elements are used up, and become
more inspissated and earthy ; its solid constituents are partly
destroyed, partly rendered harder and denser; its canals are
filled up and ossified. All this occurs from natural causes
existing throughout the organism, and for the most part in
virtue of physical and mechanical forces. The consideration
of these belongs to the physiology of mechanical nature; we
have only to discuss the decay of the proper animal forces.

701. In old age, the brain and nerves appear to dry up, and
become flaccid ; the nerves even of the organs of sense become
hebete from constant use and the growth of impediments to
their functions, so that external impressions are less felt, and
external sensations are less readily excited. Hence the dimi-
nished activity of the sexual instincts and desires, the diminished
muscular energy, the insensibility and dullness of age. Internal
impressions following the same rule as external, the mental
powers become enfeebled, the memory fails, the judgment is
impaired and becomes slow and undecided. Hence the appear-
ance of greater wisdom and prudence than the old really
possess, &c.

702. Since every kind of animal force decays, whether
manifested in the insentient, the merely sensational, or the
reasoning animal, destruction naturally impends over aU animals,
and every animal is naturally mortal. The natural necessity
of this interruption of animal life is not only shown by the
laws of the economy, but also by the operation of remote phy-
sical and mechanical causes, which partly destroy — insensibly
and gradually — the structure of the animal machines, partly inter-
rupt the natural action of their forces, as well in themselves as
in the mechanical machines, in a way not known. The subject
belongs, however, to the physiology of the mechanism of animal
bodies (Haller's 'Physiology,' § 31).

CH. VI.] OLD AGE AND DEATH. 355

703. The termination of animal life is death, which there-
fore occurs when no animal force whatever exercises the slightest
action on the organism (638).

704. The spiritual death of a reasoning animal is the end of
its intellectual life, and takes place when not a single higher
animal-sentient force exercises the slightest action in the
organism. In this kind of death, sensational life and the
union of body and soul may still continue (641).

705. Sensational death comprises also spiritual death, and
takes place when not a single sensational force exercises the
slightest action in the organism. It has been termed peculiarly
the death of the animal, or the deprivation of life, since it
completely destroys the connection of body and soul (640);
mere animal life may, however, continue.

706. Complete death takes place when not one of all the
animal forces any longer acts in the slightest degree, or when
the vis nervosa has ceased to act. The popular mistake as to
this kind of death has been already noticed (643) ,

707. Natural death occurs from the natural death of the
animal forces, after the animal has attained its full growth and
perfection, and takes place necessarily. Few animals, and least
of all mankind, die a natural death, and death occurring under
other circumstances is termed accidental, the causes of which
may be found in Haller^s ^ Physiology,' § 959.

708. Animal death in the strict sense, or the separation of
the soul from the body, whether accidental or natural, takes
place, either when the natural functions of the primary vital
forces altogether cease, others being subordinate to them, or
when the animal-sentient forces are abolished. In the former
case, it results in consequence of the entire death of the animal,
which includes the separation of the soul and body; in the
latter case, mere animal life may continue after such separation
(640). We will consider the modes in which it may occur.

709. 710. The union of body and mind is sundered when
the animal ceases wholly to exist. An animal wholly ceases to
exist when its vis nervosa is abolished, together with all its
natural effects in the economy. No portion of the animal
machines is susceptible of vis nervosa without a suitable
structure, and without vital spirits (661, 663); and cannot
be supplied with the latter independently of the primary
vital force of the brain or nerves, by which the vital spirits

356 ANIMAL NATURE AS A WHOLE. [m.

are secreted and diffused (678); and the brain cannot be
active if the heart do not, in virtue of its primary vital
force, transmit the blood to it, so that the vital spirits may
be secreted. Further, the primary vital force of the heart is
inoperative, if the vital spirits do not flow to it, and if external
impressions be not duly received by it (678, 679).

711. Firstly, complete death may take place when the heart
wholly ceases to act, and all the functions dependent on the
circulation are entirely abolished; so long, however, as the hearths
action continues, in however slight a degree, the animal still
lives ; or so long as the arteries maintain the circulation, which
may occur longer in the capillaries than in the larger vessels,
independently of the direct action of the heart ; or so long as
there is blood remaining in the brain, from which vital spirits
may be secreted ; or, so long as vital spirits remain in the nerves,
and render them capable of duly receiving impressions. It is
thus we can understand, why certain animals survive after the
heart's action has ceased, or even when that viscus has been
entirely removed from the body.

712. Secondly, complete death may result from whatever
destroys the primary vital force of the brain, or of its analogue,
and prevents the secretion of the vital spirits, and their diffu-
sion through the entire system of animal machines; so soon
as the functions dependent thereon are quite abolished, the
animal is perfectly lifeless. If, however, the primary vital
force of the brain continues to act in the slightest degree, or
if there be any vital spirits remaining in the animal machines
after the removal or destruction of the brain, so that they are
capable of duly receiving impressions, the animal is not
absolutely dead.

713. Thirdly, death is complete, when either both the primary
vital forces are abolished at once, or when the one is so arrested,
that the other is destroyed. So soon as the operations of one
or both cease entirely, the animal dies absolutely, because they
are mutually subordinate to each other. But if the centres of
one of these vital forces be removed from the body or destroyed,
without the other being entirely abolished, then death is not
complete. Such is the case in those animals in which the
arterial system keeps up the circulation for a lengthened period,
after removal of the heart ; or in those in which several points
of the nervous system secrete vital spirits, and thereby maintain

CH. VI.] OLD AGE AND DEATH. 357

the action of the heart after removal of the head ; or in those
in which the vital spirits remain for a lengthened period dif-
fused through other portions of the nervous system. Thus,
merely animal life may continue after the removal of both the
heart and the brain.

714. Fourthly, an animal is absolutely dead, when its entire
system of animal machines is rendered wholly incapable of per-
forming its functions (639) . But so long as the structure of that
system is not completely destroyed or changed, or the vital spirits
contained in it exhausted, so long, in short, as any portion of the
system retains the property of duly responding to impressions,
the animal is not absolutely dead. It is thus we understand,
how animals may be frozen, and yet retain animal life. (Vide
Spallanzani.)

715. The destruction, division, or injury of portions of the
system of animal machines, and the exhaustion of the contained
vital spirits, are necessarily followed by the complete death of the
whole organism, when the primary vital forces of one or both
centres of animal forces are abolished (711 — 713). Hence
mortification, or the loss of entire limbs, only causes death,
when it involves one or other of these centres.

716. Lastly, death is absolutely complete, when those im-
pressions are no longer made on the animal machines which
maintain the primary animal functions. Thus, if the heart
becomes empty from haemorrhage, its movements cease, the
natural stimulus derived from the blood being wanting. Death
will not take place, however, so long as either of the primary
vital forces are kept active, in some degree at least, by
supplying the defective impressions : and this is the art of
restoring persons to life apparently dead ; for all animals,
whether sentient or insentient, which perish suddenly, as those
drowned, frozen, strangled, stunned, suffocated, &c., die from a
want of those natural impressions that excite the primary vital
forces to the performance of their functions.

717. Sentient animals may die in any of the modes in which
absolute animal death occurs, but none of these are necessary
for proper animal death, or the disseverance of soul and body,
because animal life may continue after the latter has taken
place (708), just as it existed in the earliest germ independently
of mental life (634); and a sentient animal may thus be capable,
after death in the ordinary sense has taken place, of those

358 ANIMAL NATURE AS A WHOLE. [in.

animal functions which insentient animals perform as perfectly
as sentient (609 — 611). Hence we can comprehend the asto-
nishing persistence of mere animal life in many animals after
decapitation, which, inasmuch as 'they have a head and a brain,
and seem to feel, may be considered to be very imperfect sen-
sational animals, such as turtles, frogs, &c. It cannot be
doubted that poisons may possibly be administered, which shall
put an end to proper animal life alone, and only dissever the
connection between the soul and body, so that a mere Uving
machine is left, which, if supplied with nutriment, will continue
to live on, and, like an anencephalous infant, be excited to
movement without having the least sensation or any conception
whatever. But the bodies of sentient animals are not con-
structed by nature so as to be capable of this continued animal
existence, but require, for their preservation and perfection, the
co-ordinate action of both the animal-sentient forces and the
vis nervosa.

718. The separation of soul and body may occur : i, from
everything which completely interrupts the functions of the
brain (708), so far as it is the centre of the animal- sentient
forces (692) . The interruption must be, however, complete, as,
for example, by the entire separation of the head from the body,
the destruction of the brain, every injury which absolutely stops
the formation of material ideas in it &c., but the injury or
removal of portions only is not sufficient.

719. No one knows how the structure of the brain is adapted
to material ideas, how these ideas are formed in it, or what is
their nature, or how the vital spirits assist in forming them, or
in what the animal-sentient force of the brain differs from its
primary vital force (679, 692). It is only possible to suppose,
with great probability, however, that the gray portion is the
seat of the latter, and appropriated to the secretion and diffusion
of the vital spirits ; while the white matter is the seat of the
animal-sentient forces ; and that the distribution of the vital
spirits through the entire system of animal machines is a
continuous and slow movement, whilst that by which material
ideas are produced and their sentient actions excited, is
altogether different, being extremely rapid, not continuous,
and dependent on the stimulus of impressions (11). {Vide
Haller^s 'Physiology,^ § 383.) It is known, that the animal-
sentient forces are active at the origins of all the nerves in

CH. VI.] OLD AGE AND DEATH. 359

the brain (124, 130, i), but it is not known, whether there
be one point only in the whole brain appropriated to con-
sciousness and the conceptive force, and which can be termed
the seat of the mind. (Consult Haller's ' Physiology,' § 370,
sqq.) The difficulties in the way of a correct theory, render
it impossible to give any details as to the modes in which
the separation of body and soul may take place.

720, ii. The separation of the soul and body may occur inde-
pendently of entire animal death when the conceptive force ceases
to act ; that is to say, when those impressions are absolutely
wanting, which the brain can duly receive in virtue of its animal-
sentient forces. If the soul be considered as a substance distinct
from the body, cases may be imagined, in which it may separate
itself from the body, the animal-sentient forces of the brain
being altogether unaffected, as is supposed to occur in the trans-
migration of souls. But it is fixed by the eternal laws of
nature, that no conception can occur without the co-operation
of the animal-sentient force, and no material ideas arise in the
brain, without the co-operation of the conceptive force. Con-
sequently, all possible modes of dissolution in the ordinary
acceptation of the word, are comprised in those stated, § 718.

721 — 726. Dissolution of the connection between body and
mind must take place, whenever complete animal death occurs,
and will be caused —

i. By whatever entirely arrests the action of the heart (711),
and thereby arrests the functions of the brain and its animal-
sentient forces (718). But so long as interruption of the cardiac
action fails completely to effect this, the animal is neither
absolutely nor mentally dead. ii. By whatever abolishes the
primary vital force of the brain, and, consequently, the secre-
tion and distribution of the vital spirits, so that the action
of the animal-sentient force is quite arrested (712). iii. By
whatever abolishes both the primary vital forces at once, or by
abolishing one destroys the other, and thus complete animal
death takes place (713). iv. By whatever at once renders the
whole system of animal machines unfit for its function, and,
consequently, for the animal-sentient forces (714). If this
occurs gradually, the dissolution of the connection of body
and soul, may precede complete animal death. In death
by lightning, both take place at the same time. If the
animal machines be only rendered partially unfit for their

360 ANIMAL NATURE AS A WHOLE. [iii.

function, separation of the body and soul can only take place,
when those parts of the brain are involved which constitute
the centre of its animal-sentient forces. But inasmuch
as these are scattered throughout the brain, often injury
of the cerebral medulla only destroys a certain class of animal-
sentient forces, and others not naturally subordinate to them,
remain uninjured. Thus, it is possible in injuries of the head,
or in old age, that one kind of external sense, or the memory,
understanding, judgment, &c., may be enfeebled or abolished,
while other faculties are unaffected, v. By whatever entirely
prevents those impressions, which put the primary vital forces
into action, or maintain them in action, in so far as the animal-
sentient forces of the brain (which are subordinate to them)
are abolished (716).

727. All these various kinds of death are usual in nature.
Often mental death precedes mere animal dissolution; often
both occur at the same time ; but in every case, traces of mere
animal life remain after the soul is separated from the body.
When all conceptions are abolished, and all sentient actions have
ceased, the body still manifests signs of the vis nervosa ; peri-
staltic motion continues, the heart makes a few feeble strokes
(the right ventricle retaining the power of motion the longest),
and the muscles are still irritable. Even when all other tissues
are no longer capable of stimulation, the heart's action may be
renewed by external impressions, so that to this extent we may
consider with Haller (Physiology, § 961), that the moment the
heart loses its irritability is the moment of complete animal
death. That the moment of interruption of the heart's action
is not that moment, is manifest from what has been already
stated (711 — 721). Undoubtedly, every trace of the vis nervosa
disappears as soon as the parts become cold, or deprived of
moisture.

728. After absolute death comes the end of the remaining
part of the entire nature of the dead body, that is, of the
organic, mechanical, and physical forces, and is termed putre-
faction. It resolves all the animal machines, — the brain and
nerves, — together with all the other components of the animal
organism, into their primary elements.

END OF "PRINCIPLES OF PHYSIOLOGY."

DISSERTATION

ON THE

FUNCTIONS OF THE NERVOUS SYSTEM

BY

GEORGE PROCHASKA, M.D.

A DISSERTATION

TUNCTIONS OF THE NERVOUS SYSTEM.

INTRODUCTION.

The nervous system^ in which term we comprise the cere-
brum, cerebellum, medulla oblongata, and medulla spinalis, and
the nerves thence distributed throughout the whole body, is of
all organs of the animal economy the most important. It is
the seat of the rational soul, and the link by which it is united
to the body ; it is the instrument by which the soul, so long
as it is united to the body, produces its own actions, termed
animal, and by which it acts on the rest of the body, and the
body in turn acts upon it. But, however great may be the
importance of the nervous system in these respects, it is of fur-
ther importance, because it possesses in addition the singular
faculty of exciting in the human body various movements with-
out the consciousness or assistance of the soul; nay, plainly against
its will it can and does excite them without intermission through
the whole of life. The nervous system also influences other
functions of the human body, as digestion, nutrition, and secre-
tion, which functions do not remain long undisturbed if the
nerves be injured. I say nothing of the share which the
nervous system is well known to have in almost every disease.

Prom all this it is manifest how valuable results would follow
on sedulous inquiry into the structure and functions of the
nervous system, inasmuch as much light might be expected
to be thrown on medical art; nor ought it to be lightly
esteemed as to its results, with reference to those who desire to
know themselves. For he who desires to understand more
thoroughly his own mind, — the nobler portion of himself, — can
understand it only from its operations. But these are never

36 1 INTRODUCTION.

so pure and so unmixed, that the nervous system, — the imme-
diate instrument of the mind, — has no part in them ; and
consequently it is necessary that the structure and functions
of the nervous system should be well understood by those who
would determine what should be ascribed in animal actions to
the operations and structure of the nervous system, and what
should be clearly assigned to the immaterial soul alone.

After all the earnest attempts of the greatest philosophers
and physicians from the earliest ages, to explain the functions
of the nervous system, we can hitherto only say with Haller,^
it is but a little that we certainly know, that much remains
unknown, and if we may judge of the future by the past, that
no httle will remain unknown for ever. Nevertheless, I do
not think all hope should be abandoned, especially if we should
be able to detect and remove the cause of that slow progress
hitherto made ; and this, in my opinion, partly consists in the
difficulties of the subject, which nothing but great labour can
overcome; and partly in the love of hypotheses, which
have been devised to explain the functions of the nervous
system. Many, content with these false resemblances of truth,
neglect to inquire into the truth itself, and they who do inves-
tigate, unless they discard the prejudices which spring from
hypothesis, often fail to perceive the truth, even when it is
plain before them.

I have therefore entered on this attempt, to explain the
natural functions of the nervous system, without any hypothesis,
and by simple facts only; and should the attempt be approved,
and by additions and emendations be rendered more complete
(and these I well know my labours to stand in need of), it
may be readily and usefully applied to an explanation of the pre-
ternatural functions of the same system. I have taken certain
observations and experiments of celebrated men as a founda-
tion ; I have spoken doubtfully of what was doubtful, and I
have preferred to acknowledge my ignorance of what was inex-
plicable, rather than with the itch of explaining everything to
have recourse to improbable hypotheses. How nearly I have
attained to the truth in other respects let the indulgent reader
decide.

' Elem. Physiol., torn, v, p. 529.

CHAPTER I.

THE PRINCIPAL OPINIONS OF AUTHORS, REGARDING THE USES AND
FUNCTIONS OF THE NERVOUS SYSTEM, CONCISELY STATED.

SECTION I. THE OPINIONS OF ARISTOTLE.

It is remarkable how widely Aristotle with many others of the
philosophers and stoics have erred in assigning a use for the brain,
having described it as an inert viscus, cold and bloodless, an organ
sui generis, not to be enumerated amongst other organs of the
body, seeing that it is of no use except to cool the heart. He
thus explained how the brain might be the refrigeratory of the
heart :^ — Inasmuch as vapours arise from the waters and earth,
and when they reach the cold middle region of the air are con-
densed into water, which, falling upon the earth, cools it ; so
also, the hot spirits carried from the heart to the brain with
the blood, and there being cooled, are condensed into water,
which again descends to the heart for the purpose of cooling it.
He placed the seat of the rational soul in the heart, where it
can exercise all its functions, and he therefore made the nerves
(of the use of which, in sensation and motion, he was not igno-
rant) to arise from the heart. This opinion of Aristotle as to
the heart being the seat of the soul, appears to be preserved, even
to our own days, in the popular modes of expression, as when a
man of a good disposition is said to have a good heart, and the
writers on moral science speak of '^ the cultivation of the heart.''

It would appear, that anteriorly to Aristotle, Hippocrates
had formed a more correct opinion as to the functions of the
brain, for in his book ^ de Insania/ he observes, that that man
is sane whose brain is undisturbed ; although, in another book,
' de Corde,' referred, however, to the spurious works, he places
the mind of man in the left ventricle of the heart. Plato, the
preceptor of Aristotle, also thought differently, for he recog-
nised three distinct faculties of the mind, having three distinct
seats : one was the concupiscent, whose seat was in the liver ;
the second, the irascible, seated in the heart ; the third, the

I

De Animal, partib., lib. ii, cap. vii.

366 FUNCTIONS OF THE NERVOUS SYSTEM, [ch. i.

rational, seated in the brain. In this doctrine he was followed
by Galen, Vesalius, Fernelius, and others, who hence acknow-
ledged three spirits : the natural, which pass from the liver with
the blood ; the vital, which are carried from the heart to every
part of the body through the arteries; and the animal, which
are transmitted from the brain through the whole body by
means of the nerves.

SECTION II. THE OPINIONS OF GALEN.

Erasistratus and Herophilus abandoned the doctrine of
Aristotle their master, as to the functions of the brain ; the
former taught, when young, that the sensory nerves arise from
the meninges, and the motor from the cerebrum ; but when
old, he taught that both classes of nerves arise from the me-
dullary matter of the brain ; that the animal spirit was from
the head, the vital from the heart. Herophilus maintained,
that the ventricle of the cerebellum, the calamus scriptorius, is
the chief of all the ventricles of the brain, and that the nerves
of volition spring from the brain and medulla spinalis. The
most important doctrines, however, are those laid down by
Galen in the books de placitis Hippocratis et Platonis and de
usu pari'ium, and which it will be well to notice more in detail.

In the first place, Galen refutes the doctrines of Aristotle,
by showing that the refrigeration assigned to the brain is
abundantly effected by the respiration ; that he himself had
always found the brain of animals hot to the touch ; and that
it must be so, is proved by the numerous blood-vessels dis-
tributed over the pia mater and throughout the brain. More-
over, in contradiction to the assertion of Aristotle, that all the
organs of the senses are not centered in the brain, he shows
that nerves are given off to both ears, to both sides of the nose,
to both eyes and their motor muscles, and not only four to the
tongue, but also nerves to the pharynx, larynx, gullet, and
all the viscera, as well as all parts of the face. Consequently
he asks, if the brain be only a refrigeratory, of what use are the
various parts of the brain, as for example, the choroid bodies,
the retiform plexus, the pineal gland, the pelvis, the infundi-
bulum, the fornix, the processus vermiformis, the two meninges,
their processes to the spinal marrow, and the branches of the
nerves? It would have been suflBcient for the purposes of

SECT. II.] OPINIONS OF GALEN. 367

refrigeration, if the brain had been made Hke a rude and form-
less sponge, nor need there have been so much artificial con-
struction as is found in the brain.

Subsequently, when he is about to indicate generally the
use of the cerebrum and cerebellum, he observes that the brain
is of the same substance as the nerves, but softer, as it neces-
sarily should be, inasmuch as it receives all the sensations, per-
ceives all the imaginations, and then has to comprehend all the
objects of the understanding, for what is soft is more easily
changed than what is hard. Since double nerves are necessary,
the soft for sensation, the hard for motion, so specially also the
brain is double, the anterior being the softer, the posterior the
harder, which is also termed parencephalis. These two cerebra
are, therefore, separated from each other by nature, because it
would not be at all safe, that the soft should be exposed to the
contact and pressure of the hard.

The use of the anterior or superior ventricles, he says, is as
follows : Firstly, to receive air through the nostrils, the ethnoid
bone, and the mamillary processes, and mixing this with the vital
spirit brought into the ventricles through the arteries from the
heart, to prepare the animal spirits transmitted from the brain to
the nerves for the purposes of motion and sensation. Moreover,
that the brain had a double movement : — a diastoHc, by which
it receives the air and vital spirit into the ventricles ; and a sys-
tolic, by which it distributes the animal spirits to the nerves.
Secondly, by the same entrance, sensible objects, and objects of
the faculty of smell, are introduced. Thirdly, the excrementa from
the bodies contained in the ventricles collect there, the accumu-
lation of which excites apoplexy, unless a suitable outlet be pro-
vided ; this, however, is double, the one through the meatus of
the nostrils, the other through the infundibulum, or pituitary
gland, with its two ducts opening into the palate and cavity of
the mouth. The superior ventricles are double, in the same
way as other parts are ordained to be double by nature, for the
purpose, doubtless, that if the one suffers, the other may serve j
for this reason, also, the brain is double, and every sensorium is
double. He mentions the case of a youth he saw at Smyrna, to
prove the usefulness of double ventricles : this youth had one
ventricle wounded, and was thought to have escaped death by
the help of God, but Galen says that he certainly could only have
lived a short time, if he had been wounded in both ventricles.

368 FUNCTIONS OF THE NERVOUS SYSTEM, [ch. i.

The animal spirits, he says, are transmitted from the
anterior ventricles to the fourth through the opening, now
termed the aqueduct of Sylvius. But he afterwards says,
[lib. 8, de usu partium,) that the animal spirits are not contained
in the ventricles only, but are diffused throughout the whole
substance of the cerebrum and cerebellum.

The use of the fornix, to which also the corpus callosum
belongs, is the same, he says, as of the arches of buildings;
namely, to support commodiously and safely the whole of the
superjacent part of the brain.

The eminences, termed nates and testes, and the vermiform
process of the cerebellum, serve to open and shut the passage
by which the animal spirits are transmitted from the anterior
ventricles to the posterior ventricle. Some have attributed this
function of a janitor to the conarium [pineal gland] also, but
erroneously, since it is not a portion of the cerebrum, but
merely a gland, and hence, doubtless, the conarium has the
same functions as other glands, namely, to support the ramified
veins amongst which they are introduced.

He agrees with Erasistratus in the opinion, that the plexuses
and convolutions are larger in man than in other animals, but
he does not admit that the intellect of men depends on this,
because asses also have a brain much convoluted.

Although Galen asserts passim, that the function of the
nerves consists in transmitting the animal spirits from the
brain to the other parts of the body, for the purposes of sen-
sation and motion, because parts are deprived of motion and
sensation when the nerve is cut, tied, compressed, bruised, or
aflPected with scirrhus, still he does not appear to have been
quite certain as to the correctness of his doctrine, since he
raises some doubts in the seventh book de Placitis Hipp, et
Platonis. Firstly, whether the nerves contain animal spirits
like the cavities of the brain ? Secondly, whether this
spirit is innate in the nerves, and when a limb is to be moved,
is excited only when acted upon by the spirit contained in
the cerebrum? Thirdly, whether this spirit be innate in the
nerves at all, but rather when we seek to move a limb,
whether it does not flow from the brain into the nerve?
Fourthly, whetlier the matter of the spirits flows into the
nerves from the brain in any way ? or is it not rather its force,
virtue, or faculty, just as the substance of the sun remaining

SECT. III.] FOLLOWERS OF GALEN. 369

motionless, its light-giving property is poured forth into the
ambient air ? He observes, however, that he cannot decide ab-
solutely on these questions, but only proposes them for general
discussion.

SECTION III. THE FOLLOWERS OF GALEN.

The Arabs distributed the animal functions amongst the
ventricles of the brain, so that one of the anterior ventricles
they made the seat of common sensation, the other of the
imaginative faculty, the third ventricle was the seat of the
understanding, and the fourth of memory. This was also the
doctrine of Benivenius, who, in confirmation of it, relates
the case of a certain thief, often caught stealing, who never
remembered his previous offences ; after death it was found
that he had no cerebellum. This doctrine was also main-
tained by Duns Scotus, Thomas Aquinas, and other theo-
logians ; and although disavowed by Vesalius and other phy-
sicians, was again adopted by others.

The Italian and other anatomists who flourished after the
Arabians and the revival of learning, scarcely deviated from
Galenas views in assigning the function of the nervous system,
and in particular of the encephalon. Berengarius, Massa,
Fernelius, Vesalius, Stephanus, Fuchsius, Columbus, Valverda,
Fallopius, Goiter, Vidus Vidius, Varolius, Felix Platerus,
Piccolhomineus, Laurentius, Riolanus, Spigelius, Cartesius,
&c., agree with Galen passim^ although some have their
peculiarities. Fernelius followed the doctrine advocated by
Erasistratus in his youth, that the sensory nerves arise from
the membranes and the motor from the substance of the brain.
Vesalius was not anxious to determine whether the animal
spirit is conducted through certain channels of the nerves, or
along the sides of the nerves, or whether the vis cerebri reaches
the parts merely by the continuity of the nerves. Fallo-
pius denied that the brain is moved by a systole and diastole,
since he had never witnessed the movement, either in animals
or in wounded men. Columbus said that the use of the cir-
cumvolutions of the brain was for the sake of lightness, so that
it might the more readily be agitated by systole and diastole ;
and that the animal spirits derived from the air drawn in
through the nostrils and commingled with the vital spirit, arise

24

370 FUNCTIONS OF THE NERVOUS SYSTEM, [ch. i.

into the upper ventricles from the motion of the brain and of
the plexus choroides ; this he published as his own discovery,
for which he was reproved by Piccolhomineus. Des Cartes
maintained that the animal spirits were secreted from the
brain through pores opening into the ventricles, and that
there accumulating, the slightest disturbance of them excites
the soul seated in the pineal gland ; and contrarily that the
animal spirits in the ventricles are moved by the will acting
through the pineal gland, and distributed thence through the
nerves to all parts of the body.

SECTION IV. THE ANIMAL SPIRITS ARE DISLODGED FROM

THE VENTRICLES.

Caspar Bauhin was amongst the first who denied that the
ventricles are the laboratory and storehouse of the animal spirits_,
and who taught that these are generated in the substance of
the brain, and dispensed directly from thence through the
nerves to the organs of sensation and motion. He maintained
that the ventricles are more properly accidental structures,
which have no other use than to receive the excreta and
residuum formed in the nutrition of the brain and in the pro-
duction of the animal spirits, and to pass them away through
the infundibulum to the fauces. Platerus, Varolius, Spigelius,
Moebius, &c., were also of this opinion.

Caspar Hoffmann, Professor at Altorf, more particularly
opposed the ancient doctrine as to the use of the ventricles in
preparing and retaining the animal spirits, and used six leading
arguments against it, which he considered to be wholly irre-
fragible. 1 st. That all the nerves of the body and cerebrum arise
from the spinal cord, either within or external to the cerebrum.
2dly. That if it be necessary to the action of the spirits that they
be under the control of the mind in the vessels, what compels
them into the straits of the nerves after having entered into
the ocean of the ventricles ? 3dly. That the ventricles are lined
internally with the pia mater which prevents ingress and egress.
4thly. That since the two superior ventricles open into the third,
and the third into the infundibulum, and this into the palate^
who will say that the spirits might not pass out by this way ?
5thly. That the ventricles are not continuous with the nerves,
but with the body. 6thly. That the ventricles have already a

sECT.iv.] ANIMAL SPIRITS NOT IN THE VENTRICLES. 371

function incompatible with that of the spirits, namely, to collect
and excrete the effete matters. These arguments, whatever
validity they might have, were sufficient to lead many from the
doctrines of Galen, and to convince them that the ventricles of
the brain are not the factories and storehouses of the spirits,
but only established for the collection and expulsion of the effete
matters. Riolanus the son,^ endeavoured to remedy this neglect
of the doctrine, and tried to weaken and explode the arguments
of Hoffmann, and while he defended the doctrine of Galen, he
in some measure adopted that of Aristotle. He taught that
the animal spirits are generated from the vital in the ventri-
cles of the brain alone, and diffused thence through the whole
cerebrum ; that the air inspired through the nostrils does not
enter the ventricles, nor is it mixed with the spirits, but being
diffused round the dense membrane [dura mater] cools the
brain, as the inspired air cools the lung ; and that the convo-
lutions are so constructed for the sake of lightness and the
distribution of the arteries. He more particularly blamed
Hoffmann, and charged him with ignorance, because that by
his new dogma he unsettled both the whole pathology and
therapeutics of the brain, for he fixed the seat of epilepsy
and apoplexy in the whole substance of the brain, and not in
the ventricles, as Galen taught. And this argument is that
with which physicians are accustomed to meet new dogmas,
when opposed to their own, even if true, lest they should be
compelled by shame to unlearn when old those things which they
have learnt in youth. Harvey was met with almost a similar
argument, and considered as an audacious man, a disturber of
medical peace, and a seditious citizen of the medical republic,
who first dared to unsettle the doctrine established by unanimous
assent for many ages, confirmed by the writings of so many
physicians, and handed down, as it were, from generation to
generation, as if no one knew any thing for so many ages.^

Wepfer fully refuted Riolan in his 'Auctarium Historiarum
Apoplecticorum et Exercitationis de loco Apoplexia affecto,^
and duly interred the doctrines as to the use of the ventricles
in producing and retaining the animal spirits.

' Enchirid. Anat.

' In Zacchar. Sylvii praefat. ad Harveii Exercit. Anat. de Circulatione Sanguinis.
Vide Biblioth. Anatom. Mangeti.

372 FUNCTIONS OF THE NERVOUS SYSTEM, [ch. i.

SECTION V. ANOTHER OFFICE ATTRIBUTED TO THE VENTRICLES

OF THE BRAIN BY GALEN, IS ALSO SHOWN TO BE ERRONEOUS.

After it had been fully decided, tliat llie animal spirits are
not generated in the ventricles of the brain, nor generated in
the brain, to be collected in the ventricles, still all believed
in this use of the ventricles at least, that they are cloacae,
and receptacles appointed to receive the effete matters which
flow towards the ventricles after the secretion of the spirits
and the nutrition of the brain. They asserted that the finer
portion of these excreta escape through the sutures of the
cranium, but that the denser portion trickle down partly
through the mamillary processes and cribriform bone into the
nostrils, partly through those peculiar ducts pointed out by
Galen and Vesalius, which lead from the pituitary gland through
the sphenoid bone to the fauces. It then became the theory
of the day, that these effete matters passing down continually
formed the mucus of the nostrils and fauces; coryza and catarrh
were said to be caused by these effete matters trickling down
more freely and in larger quantity, and that the brain in those
affections purged itself from humidities, which if left to ac-
cumulate in the ventricles, induce cold in the head, vertigo,
headache, epilepsy, apoplexy, &c.

Conrad Victor Schneider, professor at Wittenberg, whom
Haller has praised in the highest terms,^ essayed to refute these
errors in the happiest manner by means of anatomy. In his
tract 'De Osse Cribriformi,^ he combats by dissection two
epidemic errors, as Haller terms them, the one which taught
that odoriferous particles enter the ventricles of the brain, and
there excite sensation ; the other, that the effete matters
descend from the brain through the cribriform bone ; for the
olfactory nerves are not hollow in man, as they are in brutes.
In his work ' De Catarrhis/ he fully demonstrates by anatomy,
that nothing could pass from the nostrils into the ventricles
of the brain, neither air nor fumes, because all the foramina
of the cribriform bone are closed, and the dura mater adheres
strongly everywhere to the bones and also to the cribriform
plate; that nothing could pass down to the fauces through
the infundibulum, through the pituitary gland, or through its
» Bibl. Anat., torn, i, p. 413.

SECT, v.] ANOTHER OFFICE OF THE VENTRICLES. 373

imaginary ducts ; that no vapours could exhale from the ven-
tricles through the sutures of the cranium ; that catarrhs never
collect in the ventricles of the brain, but have their seat in the
pituitary membrane of the nares and fauces, which, from being
more exactly described by him, was called the Schneiderian
membrane. In confirmation of this, he states a case of coryza
equina, in which both the anterior and posterior portion of the
pituitary membrane was affected, but the mamillary processes
of the brain were perfectly healthy.

This demonstration by Schneider, however lucid, could not
convince every one, and there were still some who preferred
the old doctrine; amongst these, were Diemerbroeck, Bartholin,^
and Otto Horstius.^ Lower,^ Willis and others, were convinced
indeed, that nothing could pass from the ventricles to the
nostrils, or trickle through the infundibulum and pituitary
gland to the fauces, but they thought, nevertheless, that the
serum of the ventricles passed through the infundibulum to
the pituitary gland, and hence through peculiar ducts to the
jugular veins, where it was mixed with the blood. With these
Adolphus Murray may be classed,* who found the infundibulum
hollow, and transmitting a serous fluid from the ventricles ; but
what change this serum underwent in the pituitary gland he
found it difficult to say ; yet he affirms that he once found two
ducts, which arose on each side of the pituitary gland, and
terminated in the cavernous sinus. He therefore thought it
possible, that the superfluous serum of the brain might pass off
by this route ; but on his repeating the experiment, he did not
succeed in finding these ducts. The opinion of Haller as to
this controversy,^ whether the infundibulum be hollow or
solid, is, that we must agree with Murray, who found it
hollow, but that he strongly suspected the two ducts passing
from the pituitary gland to the cavernous sinuses were only
veins ; nor, in fact, do the ventricles require a special outlet,
by which the serum may be evacuated, because in every part
of the body a secreted vapour is reabsorbed by its proper veins,

' Anat. Reform.

^ Presid. Slevogtio defendit. Vid. Halleri disput. Anat., torn, ii, p. 849.

^ Tract, de Corde, Capite de Catarrhis.

* Dissert. Inaug. de Infundibulo Cerebri, &c. Upsal, 1772.

De Usu et Fabrica Part. Corp. Human., tom. viii, p. 92, &c.

374 FUNCTIONS OF THE NERVOUS SYSTEM, [ch. i.

and just as the fluid of the pericardium, thorax, abdomen,
scrotum, generated from the arterial exhalation, does not require
special excretory ducts, but is absorbed by the absorbent veins,
so also beyond all doubt, is it with the fluid of the ventricles
of the brain. Haller conjectures, with probability, that the
pituitary gland is an appendix of the brain, as in fishes he
has seen filaments like those of nerves to pass out of it.

SECTION VI. IT IS PROPOSED, WITH OTHER SPECIAL FUNCTIONS

OF THE NERVOUS SYSTEM, THAT THE CORTICAL PORTION OF
THE BRAIN BE SUBSTITUTED FOR THE VENTRICLES AS THE
PART WHERE THE ANIMAL SPIRITS ARE SECRETED, AND
THAT THE MEDULLARY MATTER HAS THE FUNCTION OF
COLLECTING AND DISTRIBUTING THEM TO THE NERVES.

The animal spirits, being ejected from the ventricles, were
placed in the cerebral substance ; so that Malpighi, "Willis, and
Sylvius de le Boi, were unanimous that they are secreted in the
cortical substance of the brain ; that, when secreted, they are
received into the medullary substance, and distributed thence
through the nerves to the whole body ; and this doctrine is
maintained by many physiologists and pathologists to the pre-
sent day. The faculties of the mind, such as perception, imagi-
nation, understanding, and memory, were banished from the
ventricles together with the vital spirits, and were located by
some in the solid mass of the brain ; by others were afl&rmed
to be properties of the immaterial and rational soul alone, and
in no wise dependent on the body. Lest I should weary the
reader by a lengthened enumeration of the almost innumerable
authors of this opinion, I will only adduce the doctrines of
Malpighi and Willis, and then state, in general terms, how far
their successors followed these celebrated men, and how far
they departed from their doctrine.

Marcellus Malpighi, in his letters to Fracassatus, ' De Cerebro
et Cortice Cerebri,^ maintains that the cortical portion secretes,
by means of a glandular structure, which he pretends it con-
tains, a coagulable serum from the arterial blood, and that it
is necessary to sensation and movement, that this fluid be
transmitted from the cortical to the medullary matter. It
does not seem possible to him, that there can be a reflux of
this serum in the nerves to the brain so as to cause sensation,

\

SECT. VI.] SUBSTITUTION OF BRAIN FOR VENTRICLES. 375

since the new serum perpetually secreted resists the retrograde
movement.

He confirms the ancient opinion of Plato, that the brain is
an appendage to the spinal cord_, in which medullary fibres,
collected together, radiate towards the brain, until they end in
the cortical portion, just as the fibres in the stem of a cauli-
flower radiate into the leaves. Confirmatory of this doctrine
are the small brain and large spinal cord of fishes. Fracassatus
also adopted this opinion, and Thomas Bartholin, in his ' Ana-
tome quartum renovata,' says this opinion is both new and
peculiar, and that by it he can understand how fishes, on
account of their small brain, are dull as to sensation, but agile
as to movement, from their large spinal cord ; especially since in
the incubated egg also the anterior part of the brain is developed
at a much later stage than that in which if the chick be touched
it contracts. It is well known, however, that Plato had already
stated, that the spinal cord is first formed, and the brain is an
appendix to it.^

Thomas Willis, a celebrated member of the chemical sect,
advanced, with some ingenuity, many new hypotheses as to the
uses of the nervous system ; with these he commingled some
ancient doctrines, as for example, that serous effete matter in
the ventricles trickles partly through the olfactory nerves into
the nostrils, partly through the infundibulum to the pituitary
gland, and thence by peculiar ducts to the veins which return
the blood to the heart from the brain ; he also agreed with Galen
in considering the use of the fornix to consist in supporting the
hemispheres. His own peculiar doctrines chiefly are : that the
cerebrum subserves to the animal functions and the voluntary
motions, the cerebellum to the involuntary ; that a perception
of all the sensations takes place in the ascending fibres of the
corpora striata, and that through the descending, voluntary move-
ments are excited ; that the understanding is seated in the corpus
callosum, and memory in the convolutions, which are its store-
houses ; that the animal spirits are generated in the cortex of
the cerebrum and cerebellum from the arterial blood ; that they
collect in the medulla, are variously distributed and arranged
to excite the animal actions, and distil through the fornix
as if through a pelican : that the animal spirits secreted in

' Ilaller, Bib. Anat., torn, i, p. 30.

376 FUNCTIONS OF THE NERVOUS SYSTEM, [ch. i.

the cerebellum are ever flowing, equably and continuously,
into the nerves which regulate involuntary movements; but
those of the cerebrum tumultuously and irregularly, according
as the animal actions are vehemently performed or quiescent.
To excite sensation, the spirits flow along the nerves to the
brain. He distinguishes between a thick nervous fluid, suit-
able to nutrition, and the extremely volatile animal spirits,
subservient to sensation and movement, and commingled in the
preceding as their vehicle. He maintains, that there are two
souls in man, the one rational, the other corporeal ; the latter
alone is given to brutes. The corporeal, or brute soul, consists
partly of a fiery or sulphureous element, which is located in
the blood; and partly of an ethereal element, which is the
animal spirit secreted in the cerebrum. That the corporeal soul,
thus composed, forms a foetus from the semen of the parents
like to the parents, increases with the body, preserves the body
until death, causes the perception of sensations in the corpora
striata, and thence reflected, excites desires and voluntary
movements; in the corpus callosum excites imagination, and
in the convolutions memory. It diff'ers from the rational soul
in this, that the latter uses the corporeal soul as the instrument
whereby it performs all things more quickly and readily in man
than they are done in brutes, and because in virtue of the
rational soul man is rendered capable of contemplating things
not belonging to the senses, as God, angels, himself, infinity,
eternity, &c. He explains the unity of the nerves by their
communications and connections with each other, or their anas-
tomoses, as anatomists term them : and he also explains, that
the union of the cerebrum and cerebellum is attained by the
tubercula quadrigemina, or nates and testes. As to the loops
of nerves with which the arteries here and there are encircled,
he states their use to be, to relax or close the arteries, and
thus during various emotions of the mind to admit the blood
in greater or less quantity to certain parts. He decided that
the pineal gland is not the seat of the soul, but a lymphatic
gland, having no relation with the substance of the brain,
which absorbs lymph, aud carries it ofi* again through other
vessels, and keeps the plexus choroides expanded.

His successors, especially of the school of Boerhaave, em-
braced some of these doctrines of Willis, but some were exploded.

i

sECT.vi.] SUBSTITUTION OF BRAIN FOR VENTRICLES. 377

For example, it was shown by anatomy, that all the nerves are
not of involuntary motion which arise from the cerebellum, as the
fifth pair of cerebral nerves is wholly derived from the medulla
of the cerebellum, the pons varolii. Ruysch, in opposition to
Malpighi, earnestly endeavours to prove, by his injections, that
the cortex of the brain is not glandular, but consists of parallel
vessels : however, Albinus clearly showed, that it was not alto-
gether vascular. Mayow attempted to show, that the animal
spirits consist of nitro-aerial particles ; Boerhaave, that they
consist of a very refined aqueous fluid, having also a nutrient
property, which was disputed afterwards by Haller. Some
thought they are aether, some electron ; Vieussens placed the
seat of imagination in his centrum ovale ; Lancisi and Peyronie
maintained, that all sensation is felt and motion excited in the
corpus callosum. Meyer placed the seat of memory in the
cortical matter, sensation at the origin of the nerves, and
abstract ideas in the cerebellum ; many, however, acknowledged
that it was not possible to determine the seat of the mental
faculties with any accuracy, although there could be no doubt
that nature had not formed so many and so various divisions of
the cerebrum and cerebellum without an object. Haller thought
that the only prospect of attaining to any knowledge of the
uses of these portions (if it were possible) was in diligently
availing ourselves of every opportunity for dissecting fatuous,
oblivious, or maniacal persons, or in accurately comparing the
cerebra of animals whose faculties are well known with the
human brain, &c.^ Meckel, Gasser, and others agreed with
WilHs in affirming, that the consentience of the nerves is
effected by the communicating branches; Whytt, Kaauw,
Astruc, objected to this doctrine, and maintained that con-
sentience takes place in the sensorium commune only, and
Haller adopted this opinion. Haller, and some of his dis-
ciples, amongst whom the celebrated Meckel, also conjectured
that the nervous loops had the function attributed to them by
Willis, but Haller subsequently retracted this opinion, being
taught by his own experiments, that nerves when torn or
irritated do not contract in the least. Vieussens, Ridley, Nuck,
and others, following Willis (and this indeed was the opinion of
Galen) classed the pineal gland with the lymphatic glands.

' Elem. Phys., torn, v, p. 529.

378 FUNCTIONS OF THE NERVOUS SYSTEM, [ch. i.

Nuck plainly subscribes to this doctrine in his ' Epistola Ana-
tomica de novis inventis/ but, however, in the present day we
are certain, that the pineal gland is really a part of the cortical
substance of the brain, connected by two medullary peduncles
with the thalami nervorum opticorum, and, consequently, not a
lymphatic gland.

The ganglia of the nerves were known to Galen, Fallopius,
Eustachius, and Willis, but their function was first taught by
Vieussens ; who considered them to be receptacles of the animal
spirit, in which it could be nourished, preserved, and rectified,
by the arterial blood flowing through them ; others, however,
amongst whom was Winslow, looked upon them as little brains,
from which fresh animal spirits are secreted, and new nerves
given ofi^. Lancisi assigned to them a muscular coat, by which
the animal spirits contained in them might be impelled for-
wards; Tarin considered them to be accidental callosities;
Meckel and Zinn were of opinion that they divided the larger
nerves into smaller, and gave them another direction. Johnstone
maintained that ganglia were peculiar to those nerves not sub-
ject to volition. Various objections were raised against this
doctrine, especially by the illustrious Haller, and Haase, but
Tissot and Pfeffinger approved of it. There will be an oppor-
tunity of discussing this again; and since Tissot has fully
treated of the matter in his work on the nerves, I will not
abuse the patience of the indulgent reader by the repetition of
things well known.

SECTION VII. THOSE WHO HAVE DENIED THE EXISTENCE OF

ANIMAL SPIRITS.

The existence of the animal spirits being received, from the
most remote period, descending by tradition, as it were, no one
proved or attempted to prove it as it ought to be. Celebrated
men began, however, to call in question the existence of these
animal spirits, especially since the doctrine seemed to be a gra-
tuitous assumption ; amongst whom were Argenter, Alexander
Benedictus, Quercetanus, Nymman, Fernel, Avicenna, Felix
Plater, Helmont, Cabroli, Back, Bidloo, Lister, Brini, Parisinus,
and many others : of these some attempted to substitute for the
discarded hypothesis one not more demonstrable, namely, that

SECT. VII.] EXISTENCE OF ANIMAL SPIRITS DENIED. 879

the nerves acted as solid tense-cords, alternately contracting
and relaxing, or only oscillating. But it was easy to demon-
strate to these, that the nerves are soft, pulpy, and not tense-
cords, and therefore unsuitable to the functions assigned to
them : this hypothesis being rejected, the authority of the
other, as to the animal spirits, increased. In the next place,
opponents of the animal spirits were found in the Stahlians, who
maintained that all the functions of the nerves depended directly
on the soul, and who rejected the animal spirits (whose exist-
ence was not proved) as useless. But the defenders of the
animal spirits silenced these opponents also, not by proving the
existence of the spirits, but because they overturned the foun-
dations of the Stahlian doctrines, which, it appears to me, Haller
especially accomplished. After this second victory over the op-
ponents of the animal spirits, some distinguished men of the
mechanical school attempted to prove their existence by various
and far-fetched arguments ; the principal were Boerhaave,
Haller, and Tissot, the latter plainly endeavouring to establish
the hypothesis as a truth. Notwithstanding the authority of
these great names, the love of truth excited distinguished men,
who advanced doubts as to this hypothesis of the animal spirits,
and who showed that the arguments adduced in its favour
proved nothing when carefully analysed, and that the whole
hypothesis was altogether devoid of truth. Of these the illus-
trious Caldani, so highly esteemed by Haller, on account of
his great merit in medical art, led the way ; and whose argu-
ments have, I think, the greater weight, because, although a
most dear friend to Haller, yet led by the love of truth, he did
not hesitate, in this case, to think and act in opposition to him.
Afterwards Metzger,^ Azzoguidi,^ Mayer,^ Michelitz,^ Marzari,^
and Fiorati, in the notes to his Italian edition of ^ Tissot on
the Nerves,' joined their arguments to undermine and entirely
overthrow the hypothesis; and if we consider these with a
mind free from prejudices, we cannot but forget the hypothesis
as we would a dream, and be excited to inquire after truth in
another way than through hypotheses and conjectures.

* Adversar. Med.
« Instit. Med.

^ Abhand. vom Gehirn, Ruckenmark, und Ursprung der Nerven.

* Scrutin. hypoth. Spirit. Anim.

* Dissertazioni Accadem. delle Ipotesi, &c.

380 FUNCTIONS OF THE NERVOUS SYSTEM. [cH. i.

SECTION VIII. THE FUNCTIONS OF THE NERVOUS SYSTEM ARE

EXPLAINED BY THE VIS NERVOSA.

At length we abandon the Cartesian method of philoso-
phising in this part of animal physics also, and adopt the
Newtonian, being persuaded that the way to truth through
hypotheses and conjectures is tedious and altogether uncertain,
but far more certain, more excellent, and shorter, through the
inductive method. Newton designated the mysterious cause
of physical attraction by the term vis attractiva, observed and
arranged its effects, and discovered the laws of motion ; and
thus it is necessary to act with reference to the functions of
the nervous system : we will term the cause latent in the pulp
of the nerves, producing its effects, and not as yet ascertained,
the vis nervosa : we will arrange its observed effects, which are
the functions of the nervous system, and discover its laws ; and
thus we shall be able to found a true and useful doctrine, which
will undoubtedly afford a new light, and more elegant character
to medical art. The illustrious Haller has already used the
phrase vis nervosa, in designating the agent which the nerves
employ in exciting muscular contractions ; but the celebrated
and ingenious J. A. Unzer has thrown the greatest light on
the subject -^ for although he continues the use of the term
animal spirits, that he may the more conveniently and intel-
ligibly express himself, yet, as he himself observes, his whole
system is complete without them.^

• Vid. Grundrisz eines Lehrgebaudes von der Sinnlichkeit der thierischen Korper,
&c. 1768. Also, Erste Griinde einer Physiologic der eigentlichen thierischen Natur
thierischer Korper, 1771.

^ Prochaska thus explains in what sense he uses the term vis nervosa, in the
" Address to the Reader," prefixed to the edition of this dissertation, pubUshed in
his ' Opera Minora,' part 2. (Vienna, 1800.) "I had already (in 1780) published
this dissertation, in the third fasciculus of my * Adnotationes AcademiccB ;^ at which
time many philosophers, and the distinguished Tissot himself, still used the hy-
pothesis of a nervous fluid, to explain the functions of the nervous system in accord-
ance with the opinion of Boerhaave. Convinced of the insufficiency of this hypothesis, I
resolved to use the inductive method in this dissertation, and explain those functions
by facts only ; using the term * vis nervosa' to designate that agent (as yet unknown)
by which the nervous system is rendered fit for the performance of its functions,
and which I have used more extensively in my pubUc lectures, and in my institutes
of human physiology (' Lehrsatze aus der Physiologic des Menschen,' 1797)." — Ed.

CHAPTER II.

THE NERVOUS SYSTEM IN GENERAL.

SECTION I. WHAT PARTS IT INCLUDES.

The nervous system, as well in man as in the animals in
any way d:'elated to him, comprises the cerebrum, cerebellum,
medulla oblongata, medulla spinalis, and all the nerves dis-
tributed thence to every part of the body. These divisions are
manifestly dissimilar in structure; those portions whose functions
are more numerous and complicated seem to require a more
composite and complicated structure than those whose functions
in the animal economy are of a simpler kind ; in particular,
the brain of man is larger and of a more complex structure
than the cerebellum, and other portions of the nervous system.
This large cerebrum is divided into two hemispheres, united
in the middle principally by the corpus callosum : the gray cor-
tical matter entirely surrounds the white internal medullary
matter, which is in much greater quantity in the cerebrum than
in the cerebellum : the external surface appears as if divided
into convolutions, having a resemblance to the intestines. The
cerebrum has three cavities, or ventricles, in the two superior
of which are seen the plexus choroides, then the corpora striata
and thalami nervorum opticorum ; behind these, are the pineal
gland and corpora quadrigemina. The septum lucidum divides
these ventricles, beneath which is the fornix divided posteriorly
into two crura, termed pedes hippocampi and cornua am-
monis. In the third ventricle, are the anterior and posterior
commissures; also, posteriorly, the opening into the fourth
ventricle, which is in the cerebellum, and, anteriorly, the orifice
into the infundibulum, which is inserted into the pineal gland.
Posteriorly to the infundibulum, are seen the corpora mamil-
laria, and here are also situate the two great crura cerebri into
which all the medullary matter from both hemispheres seems
to be collected. The cerebellum is much less than the cere-
brum, and presents on its surface highly-curved and slender
convolutions; its medullary matter is much less in proportion to

382 THE NERVOUS SYSTEM IN GENERAL, [ch. ii.

the cortical than in the brain, and gives off its medulla, partly
upwards to the corpora quadrigemina, and partly downwards to
the medulla oblongata, but principally to the pons varolii of
which it constitutes the greater portion. Beneath the pons
varolii the caudex medullaris takes its origin, and passes through
the occipital foramen. It has been specially designated the me-
dulla oblongata by late anatomists, and consists of the anterior
and posterior pyramids, with the olivary bodies between them,
in which the cortical matter is so peculiarly interwoven, that a
transverse section of an olivary body presents serpentine lines,
having somewhat the appearance of a small tree. The composi-
tion of the medulla oblongata is of a simpler character ; it is a
thick nervous cord, occupying the cavity of the vertebral column:
on its anterior surface there is a groove (some call it a fissure)
which divides it perpendicularly into two columns, internally
in its centre there is, as some think, something of a cortical
substance. The origin of the nerves of the brain, and of the
medulla spinalis, is different as to situation and size, more
simple in some, in others compounded of many roots ; of these
are some which are enlarged near their origin by a ganglion,
as in the fifth pair of cerebral nerves, and in all the spinal
nerves, but others more distantly, as is particularly the case in
the intercostal nerves. As to other points, all the nerves
passing out from the cranium and vertebral canal are furnished
with a double investing membrane, and contain a continuation
of the medullary substance of the brain and spinal cord, but
are of a firmer consistence. In their course to various parts,
the fasciculi of which they are composed enter into remarkable
plexuses and connections, until they terminate variously in
various parts ; in the eye, the optic nerve expands into a mem-
brane ; in the ears, in the Schneiderian membrane, in the pa-
pillae of the tongue, in the skin, in muscles, and in various
secreting viscera they probably terminate differently ; but as to
this point nothing is known, for they escape the most acute
vision.

All these portions of the nervous system, which I have only
cursorily enumerated for the sake of brevity, and of which
anatomy furnishes an accurate description and delineation, ^

• Monro, Winslow, and Haller, have published most accurate descriptions of the
nerves ; and their works are so well known and received with such general approval,

SECT. I.] PARTS INCLUDED IN THE NERVOUS SYSTEM. 383

abundantly shows how wonderfully and diversely the machine
of the nervous system is constituted, and how skilfully pro-
tected j and if it be compared with any other part or organ of
the body, testifies that nature nowhere else has adopted such a
variety and number of parts, nowhere else framed such sin-
gular forms, nowhere else used such a delicate and fragile ma-
terial, no other structures so skilfully protected as that system ;
whence it follows that its functions in the animal economy
must be of the highest importance, and at the same time the
most complicated. However composite the machine of the
nervous system may be, I think it may be divided into three
portions, just as its functions are most conveniently arranged
in three divisions : namely, in the first place, the animal organs,
or the organs of the mental faculty, the cerebrum and cere-
bellum ; secondly, the general sensorium which appears to con-
sist of the medulla spinalis and medulla oblongata, together
with that portion of the medulla of the cerebrum and cere-

that it would be superfluous to quote them. Besides these, a most accurate de-
scription of the nerves of the humau body, containing all the recent discoveries
appropriately arranged, may be read in the new Latin edition of the * Institutiones
Neurologicse,' 1781, by Martini, President of the Royal Academy of Sciences of
Sweden, and formerly Professor of Anatomy and Surgery. They who desire to see
correct delineations of the nervous system, may consult, for this purpose, the 17th
to the 23d inclusive of Eustachius's plates, and the ' Anatoraica Adversaria' of Tarin
(Paris, 1750). Mayer, the celebrated anatomist and professor of Frankfort, in his
work entitled * Anatomisch-Physiologische Abhandlung vom Gehirn, Ruckenmark,
und Ursprung der Nerven' (Berlin, 1779), as also in another on the vessels of the
human body, has published most beautiful and accurate views of the cerebrum,
medulla oblongata, and medulla spinalis, together with the origin of the nerves.
Consult also the excellent work of S. T. Soemmering, * De Basi Encephali et Ori-
ginibus Nervorum Cranio Egredientium ' (Gottingse, 1778). The celebrated Meckel,
in his 'Tractatus de quinto pare Nervorum Cerebri' (Gott., 1748), and his tract 'De
Nervis Faciei' (Berolini, 1755), has dissected the most minute filaments with inimitable
skill, and most admirably depicted it. Neubauer, Professor at Jena, snatched away
by premature death, published (1772) a work entitled * Sectio prima Nervorum Car-
diacorum,* which could only have come from the hands of one equally skilled as an
anatomist and draughtsman ; also Camper's * Demonstrationes Anatomico-Patholo-
gicae ;* Lobstein's * Dissert, de Nervo Spinali ad par Vagura Accessorio ' in Sandifort's
Thesaurus, 1 : George Asch's ' Diss, de primo pare Nervorum Spinalium ; Wrisberg's
'Observ. Anatomicae de 5to pare Nervor. Cer.' (Gott., 1777); Boehmer's ' Com-
mentatio de nono pare Nervor. Cerebri (Gott, 1777). To these might be subjoined
my tract ' De Structura Nervorum ' (Viennae, 1 779). Consult also Ludwig's * Dissert,
de Cinerea Cerebri Substantia' (Lipsiae, 1779), and the beautiful plates of the nerves
lately published by Walther, Professor at Berlin.

384 THE NERVOUS SYSTEM IN GENERAL, [ch. ii.

bellum, from which the nerves directly arise ; and, thirdly, the
nerves distributed from the general sensorium to all parts of
the body.

SECTION II. HOW THE NERVOUS SYSTEM IS CONSTITUTED IN

OTHER ANIMALS, AND HOW FAR IT EXTENDS THROUGH THE
WHOLE ANIMAL KINGDOM.

That the nervous system is not constituted in all animals as
in man, is proved by the observations of eminent men; but
all the differences which the almost innumerable species of
animals present, have not as yet been fully investigated : to
observe and tabulate all would require almost an age, although
much light might be hoped to be thrown by them upon the
functions of the nervous system. Many of the able observers,
who have undertaken the investigation of these differences by
means of comparative anatomy, have directed their attention
solely to the cerebrum, and the sum of their observations has
been set forth by Ludwig, in his dissertation ' De Cinerea Ce-
rebri Substantia.' For the sake of brevity, I will only glance
at the more manifest differences derived from the trustworthy
observations of distinguished men.

Man has the largest brain ; all other animals have less, except
certain apes, in which the brain is not less proportionally than that
of man.^ In fishes and animals of cold blood, the brain is so
small, that some writers have not hesitated to look upon it as only
an appendix to the spinal cord. There is a great difference in
the structure and composition of the brain of animals : in many
the olfactory nerves are thick and hollow, and termed mam-
millary processes, while the contrary is observed in man ; the
convolutions are absent in dormice and birds ;^ in birds and
fishes, the thalami nervol'um opticorum are hollow and distinct
from the cerebrum ; birds and many fishes have no true corpus
callosum, or fornix, or pineal gland; according to the obser-
vations of Haller,^ birds and fishes have bodies similar to the
corpora quadrigemina, but of simpler character than those of
quadrupeds. Other divisions of the brain, as the medullary and

' Haller, de Part. Corp. Hum. Fab., torn. vii.

2 Ludwig, Diss. cit.

' Oper. Mill., torn, iii, p. 214.

SECT. II.] CONSTITUTION OF THE NERVOUS SYSTEM. 385

cortical substance, the ventricles, together with the calamus
scriptorius, the plexus choroides, commissures, &c., are more
constantly present, and from this Haller concludes that these
divisions are the most essential.^ The brain is of the simplest
form in insects, in which there is little medullary matter, except
at the origin of the optic nerves;^ in some, it is bifid ; in others,
semibifid ; and, in others, only a nodule, called a brain, little
different from the nodules of the spinal cord.^ When it is of
this great degree of simplicity, it follows, that in the lowest
class of insects it is altogether wanting, and these also have no
eyes, according to Haller, nor does he think that in any
animal, eyes are unaccompanied by brain, or brain by eyes.

It is manifest from these observations, that nature proceeds
gradually from the most perfect and highly complex brain to
the simpler and the simplest ; and that at last animals exist
altogether devoid of brain ; but what variety is there in the
nerves of various animals? or whether in all animals their
structure, number of fibrils, plexuses, and ganglia are the same
as in man? or whether (as it is probable) they become more
simple ? We have not as yet collected sufiicient observations
to answer these questions. What proportion the brain bears
to other parts of the body has been attempted to be shown by
observations and experiments, but what proportion the nerves
bear, as well to the brain, as to those parts not nerves, remains
unsolved. It was a conjecture only of Boerhaave and other
distinguished men, who taught that the brain in the foetus is
larger in proportion to the rest of the body than in the adult,
and that this is the case also as respects the nerves, of which
they believed the whole foetus, at its first formation, to consist,
so that the bones, cartilages, ligaments, muscles, tendons, and
all the viscera at their origin were merely nerves. Haller
scouted this doctrine,* while many distinguished men adopted
it too much, and he observes : " Nor do the nerves constitute
the common material from which nature fabricates the other

' Oper. Min., torn, iii, p. 214.

^ Haller, de Part. Corp. Hum. Fabr., torn, viii, p. 3.

3 Ibid., p. 6.

* El. Phys.,tom. iv, p. 271. Marherr also rejected the opinion in his * Praelect. ad
Boerhaavii Instit.,' torn, iii, pp. 9 — 11, &c. ; and A. Murray, in his * Diss, de Sensibi-
litate Ossium morbosa.' Upsalae, 1780.

25

886 THE NERVOUS SYSTEM IN GENERAL, [ch. tt.

parts of the embryo^ but from all time, doubtless, the bones,
muscles, and membranes had each their own material/^

Seeing that sensation and voluntary motion in man, and
many animals, are obtained through the nerv^ous system, we
conclude from analogy, that all animals which feel and have
voluntary motion, possess a nervous system ; and so essential is
that structure, that no animal exists without it, from man
down to the smallest microscopic insect. Haller, however,
correctly shows, that this analogy does not hold good, and
observes,^ that in some animals, as polypi and zoophytes, no
nervous system has been discovered ; and since these animals
manifestly belong to the animal kingdom, their difference from
vegetables does not consist in having nerves. Spallanzani more
fully illustrates the abuse of the argument from analogy .2 He
says that if w*e examine the whole animal chain, it will appear
to us at first, passing from man to quadrupeds, that each have
their organs of digestion, circulation, various secretions; and
each also their nervous system, muscles, bones, and organs of
the senses ; and although they diverge not a little from man as
to form and structure, yet as they agree in their essential use,
the analogy may still be allowed ; but if we gradually descend
to fishes, insects, and infusory microscopic animalcules, the force
of the analogy is very much weakened or altogether lost, for
we see that in insects, the bones, the heart, arteries, and veins,
carrying red blood, are wanting ; they have, besides, no brain,
although endowed with nerves, and their organs of respiration
resemble those of vegetables. But if we descend the animal scale
still lower, we find creatures in whom this entire apparatus of
organs is wanting, and which are entirely destitute of nerves as
well as of brain. This is seen in such animals as many polypes,
whose body is nothing more than an oblong sac made up of small
granules; or such as many aquatic animalcules, whose whole
body is simply a membrane, or vesicle ; or such as many marine
zoophytes, whose whole body consists only of a sort of simple
jelly. This astonishing simplicity of structure induced Bonnet
and Needham to conclude, that these animalcules are not true
animals endowed with an immaterial sentient principle, but
merely living entities endowed with irritability only. But they

' De Part. Corp. Hum. Fabr., lib. x, sect, vi, § 1.

' Opuscules de Physique Animal, et Vegetal., tom. i, chap. xii.

»

SECT. II.] CONSTITUTION OF THE NERVOUS SYSTEM. 387

are clearly proved to be true animals by Spallanzani, who says:
" I am much more inclined to look upon them as true animals,
rather than as being solely vital and irritable, and I think my
opinion well founded, because I find in them that union of
qualities, which constitute (as I have previously stated) the cha-
racteristics of a true animal nature. I have already had occasion
to state some of those qualities in my Essay, and I include amoug
them the power of avoiding any obstacles, or individuals of their
own kind, that they may meet with ; of suddenly changing their
course and taking the opposite direction ; of passing suddenly
from movement to rest, without any apparent external shock.
I spoke of their darting towards particles in the infusions, of
the property they possess of turning incessantly upon them-
selves, of going contrary to the course of the fluid, of going to
the spots where a little moisture is left, and collecting there in
numbers, when the infusion has been dried up.^^ Erom these
and other facts advanced by the author, it is manifest that these
infusory animalcules feel, and have volition, and possess the cha-
racter of the true animal ; consequently, they are endowed with
a sentient and volitional principle, however destitute they may
be of a nervous system.

Such being the facts, it follows that a nervous system is not
present in all animals, but that many insects have not cerebra,
and that infusory animals and creatures much larger than these,
are destitute of brain and nerves. But because these creatures
feel and move voluntarily like other animals, we must not con-
clude that the nervous system in man and many other animals,
is not the immediate instrument of sensation and animal motion.
Man and other animals endowed with that system, feel and
move by means of that system, nor, their organism being such
as it is, would sensation and motion be possible without nerves.
Insects, that have no cerebra naturally, are nevertheless en-
dowed with nerves, and perform their functions by means of
nerves only, and by the vis nervosa contained in them, which
exists without a brain ; and by this vis nervosa the acephalous
foetus lives in utero, and when born gives no slight signs of life.
Polypes, zoophytes, and other infusory animalcules that have
neither brain nor nerves, feel and move without a nervous
system, because the Author of Nature appears to have endowed
the pulp of which their bodies are composed with the facidty

388 THE NERVOUS SYSTEM IN GENERAL, [ch. ii.

of sensation and motion ; just as tlie medullary pulp of the
nervous system alone, of all organs of our body_, is endowed witli
that faculty, the muscular machine being an auxiliary hereto.
It cannot be correctly objected to these remarks, that insects
have a cerebrum, and that a complete nervous system exists
even in infusory animalcules, and that it is their minuteness
alone which conceals them from our researches, however aided
by the microscope, for Haller meets these objections at once
with the statement,^ that in the larger insects at least, in tsenise,
in sea-nettles, and other zoophytes, the cerebrum could scarcely
escape observation, inasmuch as they are large, and their other
organs are obvious enough, even without the microscope ; and
since we can distinguish nodules or globules in polypes by the
microscope, and in others fibrils also, there seems no reason why
the cerebrum should not be observed as well. Bohadsch clearly
illustrates this in his description of the lernsea,^ an animal six or
eight inches long and three in breadth, which has many stomachs,
an intestinal canal, sexual organs, a heart, and a circular spinal
cord, furnished with many knots or ganglia, from which nerves
are sent ofi'to adjoining structures, but no cerebrum. It appears
to possess very small eyes, but these probably are not true organs
of vision. In this creature, in which so many organs are con-
spicuous, and the medulla spinalis itself, the cerebrum would be
visible also, if there was anything more than the ganglionated
spinal cord. In the fimbria, an animal six inches long, he
detected a tubular mouth, oesophagus, stomach, furnished Avith
muscular fibres, intestines, uterus, epididymis, but no eyes, or
lungs, or heart, no vessels or nerves : he observes, however, that
these may have escaped his observation. In the hydra, called
by others mentula maris [holothuria] , with a cylindrical body a
foot long and an inch broad, he could not detect either heart,
cerebrum, or spinal cord, nor any viscus except the oesophagus,
intestinal canal, and anus. If then a nervous system can be
discovered in much smaller animals, it would not have escaped
observation in those of a sufiicient size, if it had existed.
Therefore, although nature produces sensation and animal
motion in man and many other animals by means of a nervous
system, there are nevertheless not a few creatures to which it

' De Part. Corp. Hum. Fabr., torn, viii, p. 2.

' De quibusdam Animalibus Marinis. Dresdae, 1761.

SECT. III.] PROPERTIES OF THE VIS NERVOSA. 389

has known how to assign these animal faculties without the
aid of a nervous system : nay more ; nature has granted even
to certain irritable vegetables a sort of sensation and motion,
analogous to the motion and sensation of animals, and that
without a nervous system.

SECTION III. WHAT IS UNDERSTOOD BY THE VIS NERVOSA, AND

WHAT ARE ITS GENERAL PROPERTIES.

All the functions of the nervous system are as dependent
upon its structure and nature, as the accurate indication of time
upon the construction of the chronometer. In inquiring into
the structure of the nervous system, our senses, however well
assisted by the microscope, teach us nothing more than that the
principal portion of it, the medullary, is supplied with numerous
arterial and venous capillaries, distributed both to the cerebrum
and to the nerves. We cannot say, however, that the whole is
vascular, because, after the most successful injection of a
coloured fluid into the cortical substance of the brain, and the
medullary substance of the brain and nerves, the larger portion
remains uninfected; and this is not vascular, but inorganic in a
manner, being composed of a mass of very small globules as seen
under the microscope, not unlike the globules seen to compose the
whole organism of polypes and zoophytes, and the pulp of fruits.
Albinus long ago refuted the doctrine of Ruysch,^ that every
part of the body is composed of nothing but vessels, by showing
that in bone, cartilage, muscle, nerve, and in the medullary and
cortical portions of the brain, there was a large proportion of
matter which was not vascular. Malpighi seems to intimate the
same opinion, with reference to the cortex of the brain, and also
the medulla,^ when he says, that he found no organisation in
the cortex, except in the sanguiferous vessels with which it is
pervaded ; and if a parenchymatous substance should be at any
time assigned to the brain, in which the vessels and other
organised products might be supported, the cortex is the proper
part, inasmuch as it would seem to resemble moss mixed with
deep coloured clay. In another epistle, however, he tries to
show that it is glandular.

If any reliance is to be placed on our senses, the structure

> Adnot. Acad., lib. iii, cap. i ; et lib. i, p. 52.

' Epist. ad Fracassatum de Cerebro. In Bib. Anat. Mangeti,

890 THE NERVOUS SYSTEM IN GENERAL, [ch. ii.

of the medullary pulp of the nervous system is almost inor-
gauic j but much is still wanting, to enable us to understand
its admirable functions. We may assert, however, without
fear of contradiction, that an invisible element enters into its
composition, and that this constitutes the producing cause of
all the functions of the nervous system. Since this is as
mysterious and unknown as the vis attractiva of matter, it
seems to me that it may be termed with propriety the vis
nervosa. I leave the inquiry, as to its nature, to the very
sagacious and ingenious men already engaged in philosophical
experiments. I shall only attempt to determine some of its
general properties, before I enter upon the special functions
of the nervous system.^

1. A stimulus is necessary to the action of the vis nervosa. —
i. Although this vis nervosa is a property inherent in the me-
dullary pulp, it is not the chief and sole cause that excites the
actions of the nervous system, but is ever latent, and exists as
a predisposing cause, until another exciting cause, which we
term stimulus, is brought to bear. As the spark is latent in
the steel or flint, and is not elicited, unless there be friction
between the flint and steel, so the vis nervosa is latent, nor
excites action of the nervous system until excited by an applied
stimulus, which continuing to act, it continues to act, or if
removed, it ceases to act, or if re-applied, it acts again.

ii. This stimulus is divided into stimulus of the body and of
the mind, — This stimulus is double : either it is some fluid or
solid body applied internally or externally to the nervous
system, and termed corporeal, or mechanical stimulus ; or else
is a mental stimulus present in a portion of the nervous system,
and by means of this portion controls the rest of the nervous
system, and the rest of the body, as far as it is allowed.
Whether this mental stimulus takes place through a system of
occasional causes, or pre-established harmonies [harmonia prae-
stabilita] , or, as assumed by many, by a physical influx, matters
little to our object; it is sufficient for us that the soul can
excite the nervous system to the performance of certain actions,
and this power we call a mental stimulus.

iii. The relations of the actions of the nervous system to the

1 I have conjectured, however, that there is an analogy between the vis nervosa
and electricity, in my Inst. Physiol. $ 206.

SECT. III.] PROPERTIES OF THE VIS NERVOSA. 391

vis nervosa and stimulus, generally considered, — As effects are
proportionate to their causes, so the operations of the nervous
system are proportionate to the vis nervosa and the vis stimuli.
The operations of the nervous system_, for example, will be the
more powerful and extensive in proportion as the vis nervosa is
more active and the stimulus efficient : and contrarily in
proportion as the vis nervosa is less active and the stimulus
feebler, in that proportion will the operations of the nervous
system be more languid. A less energetic stimulus is suffi-
cient for a more active vis nervosa, just as a more powerful
stimulus will compensate for a less active vis nervosa ; so that
in both cases, the effect on the operations of the nervous system
may be equal. The vis nervosa is not, however, indifferent to the
kind of stimulus, for it is more readily excited by one than by
another, although they may appear to be equally forcible ; nay,
it sometimes responds more actively to apparently a very mild
than to a very powerful stimulus. Thus the heart and intes-
tinal canal, according to Haller,^ are thrown into more powerful
contractions by inflated air than by water, or any poison ; and,
on the other hand, a drop of water getting into the trachea
excites a violent cough, while the air is insensibly inspired and
expired through it. I shall adduce many such examples
hereafter as illustrations of idiosyncrasy.

iv. Under what circumstances the vis nervosa is increased. —
It is evident that the stimulus may be greater or less, longer
or shorter, more or less general, or quite local; and the same
is true of the vis nervosa. This, in fact, differs in degree
according to the difference of age, sex, temperament, climate,
the condition of the body as to health or disease, and other
circumstances, and in a portion of the nervous system as well
as in the whole, which it will suffice to prove by a few examples.

a. In the first place, the vis nervosa is generally greater in
childhood than adult age ; for a slight stimulus at that age will
act violently upon the nervous system, which scarcely affects
the nerves in more advanced years, a truth abundantly proved
by the testimony of celebrated men. Young animals are
the more sensitive,^ and organs which in the newly-born are
irritable, become insensible through age,^ and languid in motion

' El. Phys., torn, iv, p. 575. =» Haller, Ibid., p. 456.

3 Whytt apiid Haller, Ibid., p. 184.

392 THE NERVOUS SYSTEM IN GENERAL, [ch. ii.

and sensation. Sensation is more acute in the young man
than in the aged.^ The pupil is more contractile in the infant,
less readily acted on by light in the aged. And the same
principle illustrates the cause of senile impotence. That the
sensibility of the genital organs is diminished with age is
proved by the fact, that the seminal emissions so readily excited
in youth, cease to take place about the fiftieth year or some-
what later, even in able and strong men. Since the female
sex has a more excitable nervous system, it is established as a
general rule that the feeble, or rather the tender organisms,
feel more acutely than the robust.^ Observations also show,
that the amount of vis nervosa varies with the climate, since
those who inhabit hot climates indulge more in ease and
pleasure than the inhabitants of colder regions ; Montesquieu^
thinks we may distinguish climates by the degrees of sensibility,
just as we distinguish by degrees of latitude. Often in diseases,
the sensibility or vis nervosa of the whole nervous system, is
increased in a very remarkable manner ; whence it happens, I
think, that we cannot then bear a slight degree of cold in the
atmosphere, on account of the shiverings and unpleasant sen-
sations excited through the whole body, that in health we
should not notice. Thus, also, a moderate draught of wine
greatly increases the fever of a fever-patient, but which, if
taken by a person in health, would produce no change what-
ever in the pulse. For the same reason it happens, that in
hemicrania, gout, or any painful aifection, we are impatient, and
cannot endure any noise or light, or a variety of objects. All
nerves that have become too sensitive can no longer tolerate
even the most common impressions.* If it were not altogether
superfluous, many other instances of increased vis nervosa in
the whole nervous system might be adduced.

h. Frequently an increased degree of vis nervosa is observed
in a portion only of the nervous system, and not in the whole ;
in the animal organs alone, or only in the sensorium commune,
or in one or other of the nerves. Thus, I imagine, there is an
increased degree of vis nervosa in the delirious and maniacal,

' Haller, El. Phys., torn, iv, pp. 293, 294.
« Battle apud Haller, El. Phys., torn, iv, p. 459.

^ Esprit, de Loix. Vid. La Roche, * Analyse de Fonctions du Systeme Nerveux/
torn. i.

*' Tissot. von Nerv., 2 Band, ii Th., § 77, s, 165.

SECT. iii.J PROPERTIES OF THE VIS NERVOSA. 393

which keeps them fixed to their ideas. That condition of some
decrepid old people, in which they are more pusillanimous and
timid and ready to weep than children, seems to be referable to
this increased decree of the vis nervosa. So also may be ex-
plained the case of a man of weak mind in health, who was ren-
dered talented by a blow on the head, but when cured relapsed
into his previous simple-mindedness.^ The serene state of mind
of dying persons, which has been aptly compared with the
crackling of a dying taper,^ seems dependent, for the moment
at least, on increased vis nervosa. When the vis nervosa is
increased in the general sensorium, it seems also to have this
effect, — that external impressions made on the sensitive nerves,
and transmitted to the sensorium, are too suddenly and violently
reflected, and pass over into the motor nerves, and excite move-
ment and convulsions in spite of the will, as happens in the
frights of infants, and also of some adults, who are terrified by
any slight crash or noise. Further, that the vis nervosa may
be locally increased in one nerve or another, is proved by innu-
merable examples of contused, lacerated, wounded, and in-
flamed parts, a slight touch of which excites much suffering,
although in the natural condition it would scarcely have been
felt, and this while other sound parts of the body possess their
natural sensibility. Thus the amount of vis nervosa is greatly
increased in the gouty foot, but the other limbs are in their
natural condition. Inflammation is the most frequent cause
of a topical increase of the vis nervosa, as Haller observes, who
says^ that the increase of the sentient nature in nerves is won-
derful, as observed in inflamed parts, in certain acute diseases,
in inflammation of the brain, or in rabies canina; that the
younger Albinus experienced the greatest annoyance from sounds
so slight, as not to be audible to other persons ; and that a cer-
tain man could see by night so long as his eye was inflamed, but
lost the faculty along with the inflammation. Nor were these
very remarkable, for parts of the body in which sensation in the
natural state is so imperfect that it may scarcely be said to exist,
experience from disease such an increase of the vis nervosa in the

» Haller, El. Phys., torn, iv, pp. 293, 294.

2 Kemrae von der Heiterkeit des Geistes bey einigen Sterbenden. Halle, 1774,
Seit. 89.

^ Loco citato.

394 THE NERVOUS SYSTEM IN GENERAL. [ch. ii.

very few nerves distributed to them, that they become extremely
painful: of this class are tendons, ligaments, and the bones, which
in the natural state have no sensation, but when diseased, become
so sensitive that a touch gives pain. Thus in a case observed
by Martini,^ a denuded tendon had no feeling, but being ren-
dered black by an ointment applied to it, it became, at the
same time, so sensitive, that a touch could not be borne, and
not without great pain could the black and dead fibre be torn
from the healthy. Since, then, mortification in this tendon
rendered its nerves so very sensitive, the same result may be
expected in the ligaments of the joints, when a gouty matter
is deposited in them. Richter is of this opinion.^ A man
having many schirrous tumours beneath the skin, one was
removed from the dorsum of the hand by Klinkosch,^ on account
of its hindering the movements of the fingers. The patient
bore the removal of the tumour tolerably well, but not the
denudation of the tendon, the irritation of which caused such
a trembling of the body generally, that he would for no
consideration suffer a repetition of the experiment. In this
case it appears, that the tendon had acquired greater sensibility
from disease of the superjacent skin. Plenk also asserts,* that
a divided tendon at first causes no bad symptoms, but when,
after a while, it becomes inflamed, it is then painful. Adolph
Murray confirms the remark,^ observing, that if healthy liga-
ments be pricked, wounded, or burnt, they feel no pain ; but
if the structure of the ligament be affected, either by fungus
or pus, or any other acrid humour, then incisions into them are
not only painful, but often cause so much suffering that it ex-
cites convulsions. And thus also bones, when not diseased, have
no sensation, although nerves are manifestly distributed here
and there ; and this he ingeniously explains by the hypothesis,
that the nerves are constricted by the accumulation of earthy
matter in the foramina, through which they enter the bone ;

' Versuche und Erfahrungen iiber die Empfindlichkeit der Sehnen. Copenhagen,
1770.

» Chirurg. Biblioth., Ite Band, Ite Stuck.

3 Observ. de Sensibilitate tendinis et raro Cutis Aibrbo. It is in his * Collectio
Diss. Select. Med. Pragensium.'

* Chirurg. Lehrsatze.

^ Diss, de Sensibilitate Ossium morbosa. Upsalae, 1780.

SECT. III.] PROPERTIES OF THE VIS NERVOSA. 395

but when tlie bones are softened by some morbific cause, the
constriction of the foramina is relaxed, and the nerves no longer
strangulated again become sensitive. That bones morbidly
softened are rendered sensitive, is proved by the observations
of Deidier and Petit. He also found that the slightest touch
of a carious bone excited intense pain.^ Murray rightly ob-
serves, that the following questions are worthy the diligent
investigation of physiologists : — how does it happen that nerves
entering the substance of bones, are compressed and strangu-
lated in the narrow foramina for many years, and thus ren-
dered unfit to excite sensation, yet when the bone is softened
and the constriction of the nerves diminished, they again become
fit for sensation, nay, acquire the most exquisite sensibility ?
If the nerves be small channels for a nervous fluid, they are
compressed so long that the channels ought to coalesce, and the
nerves be impermeable ever after to the nervous fluid. Then this
author seems to ask, why is it that in disease of the bones we
often find so much more sensibility than could be expected from
so few and such minute nerves ? The increased sensibility, or
vis nervosa, seems to compensate for this paucity of the nerves.
V. When the vis nervosa is diminished. — The vis nervosa
is diminished in proportion as we observe the vital powers
which are dependent on the vis nervosa, to be diminished and
weakened; and which becomes so weak in death, that the natural
stimuli, as for example, the influence of the inspired air, and of
the blood in the heart, can no longer excite it, and a mortal
repose of all the vital and animal movements results. In this
ordinary termination of life, the vis nervosa is undoubtedly at
a minimum, but it is not quite lost, for a few sparks can still
be excited, if a strong stimulus be applied to the nerves.
Vesalius was taught this fact by sorrowful experience, for when
dissecting a body shortly after death, he excited the heart to
renewed action. Brunner^ succeeded in doing the same thing
in the bodies of men and various animals, by forcing air into
the heart, through the thoracic duct or veins. In many expe-
riments on frogs, I observed, that when the heart was still and

* Brambilla, Surgeon in Ordinary to the Emperor Joseph II, and First Surgeon to the
Guards, &c., also demonstrated the sensibility of diseased bones before the author at
Vienna.

* Parerg. Anat. Genevae, 1681. Miraculum anatomicum in cordibus resusci-
tatis, &c.

396 THE NERVOUS SYSTEM IN GENERAL, [ch. ii.

could no longer be excited by a stimulus, that the muscles of
the thigh continued to be slightly contracted, whenever the
sciatic nerve was punctured or compressed. We hence conclude,
that a certain portion of the vis nervosa remains for a time in
the nerves after death, which, although insufficient to maintain
life, is sufficient to develop movements in the heart and some
muscles, if excited by a powerful stimulus. For they contract,
although so feebly, that weak jerking rather than contractions
are only produced, and these cease after awhile, however strongly
the nerves or muscles may be stimulated. When after death
no muscle responds to a stimulus, are we to conclude that all
vis nervosa has left the nerves, or is it that it cannot display
itself on account of the muscles being rendered unfit for action?
We cannot determine these questions. The vis nervosa is also
diminished by opium, according to the observations of Whytt.
Haller and Sprogel^ found that opium destroyed the vis irrita-
bills of the stomach and intestinal canal, and since (as will be
hereafter shown) irritability presupposes a vis nervosa, the vis
nervosa is also diminished by it. Smith2 observed, that opium
or nitre applied to the nerves destroyed the irritability of the
muscles to which the nerves were distributed. Monro also ob-
ser\ned, that narcotics diminished the contractility of the heart.^
Many celebrated men, and amongst them Tralles, were, on the
other hand, of opinion, that opium had not a cooling but a
heating property, increasing the motion of the humours, and
they attempted to prove the doctrine by experiments. Wirtenson
advanced a curious and ingenious argument for the purpose
of reconciling these conflicting statements : it was certain, he
said, as proved by his own experiments, that opium diminished
the power of the heart, but since it also had the remarkable
property of relaxing the capillaries or terminations of the arte-
ries, thus by a diminution of resistance, the circulation might
be increased, although at the same time the force of the heart
were somewhat diminished. Opium does not increase the
motion of the humours in the Turks habituated to it, nor heats
them, but refrigerates them, because their capillaries, being
already relaxed by the climate and by the continual use of
opium, are not susceptible of further relaxation ; the resistance

' Haller, Op. Min., torn, i, p. 485.

' Diss, de Motu Musculari. Edinburg., 1767.

' Act. Gotting., vol. ii, pp. 147, 154.

SECT. III.] PROPERTIES OF THE VIS NERVOSA. 397

being therefore undiminished, a slower motion of the humours
and an agreeable coolness from the diminished action of the
heart only ensues.^ The celebrated Fontana infers, from his
experiments, that opium does not diminish the amount of that
power by which the nerves move the muscles, but that it is the
spirit of wine which, whether used as a solvent of opium, or alone,
renders them insensible to irritation, and destroys that property
of the nerves which controls the muscles. ^ The latest opinion
of Haller as to these experiments is, that they partly require
confirmation, and partly admit of another explanation ; and he
ends his opinion with these words : " Lastly, from the remark-
able effect which opium produces on the stomach and intestine,
there is ground for suspecting that the vis insita is diminished
by opium as well as the vis nervosa.''^ But it has already been
abundantly proved by distinguished men (and it will be shortly
rendered more evident), that the vis insita of Haller, or irrita-
bility, is dependent upon the vis nervosaj and cannot exist
without it; and, consequently, as opium diminishes the vis
nervosa, it is thus only that it diminishes irritability, or the
vis insita.

vi. The vis nervosa is divisible, and exists in the nerves in-
dependently of the brain, — Vis nervosa is as divisible as the ner-
vous system, so that it remains in each portion of a bisected
nerve, as if it were still entire and connected with the brain.
Nor does the vis nervosa of the nerves require continual supplies
from the brain, since nerves possess their own vis nervosa,
which never had a connection with the brain. The experiments
that prove this have long been perfectly well known ; namely,
that if a nerve be cut or tied, although by these means its
connection with the brain be destroyed, it is still as able, if
irritated, to cause the muscles to contract as if its connection
with the brain were entire. Haller clearly states this fact in
many places.* He observes : " a nerve compressed or tied, and
then irritated below the ligature, excites those muscles to con-
vulsive contraction, to which it is distributed, just as if it was

• Dissert. Demonstrans Opium vires Fibrarum cordis Debilitare, et Motum tameii
sanguinis augere. Monasterii, 1775.

2 Vid. Halleri Oper. Min., torn, i, p. 487.

3 De Part. Corp. Hum. Fabr. et Usu, tom. ii, pp. 391, 392.

* El. Phys., tom. iv, p. 337.

398 THE NERVOUS SYSTEM IN GENERAL, [ch. ii.

perfectlj free/^ And elsewhere : " if the nerve of a muscle be
compressed, or tied, or divided, and then irritated, provided
it be fresh and moist, the irritation will produce in the muscle
to which the nerve is distributed the same movements as it
would have produced, if the continuity of the nerve with the
brain had remained unbroken. This proposition having been
proved with regard to the voluntary nerves, is here shown to
be applicable to the organic nerves.'^^ In the same work
(p. 237), he observes : " it is not necessary to the excitation of
muscular action by irritation of the nerves, that the nerve be in
connection with either the brain or spinal cord ; for irritation of
a nerve entirely separated from the spinal cord and brain, ex-
cites the same muscular contractions as irritation of a nerve in
unbroken connection wdth them.^' And in a sentence before
quoted,^ he remarks : " Thus, when after the destruction of
that part of the spinal cord from which it proceeds, a nerve is
irritated, it still, as before, throws the limb into contractions,
to which it is distributed. The same thing takes place in the
medulla spinalis after division of the medulla oblongata. In
short, if the head or whole brain be removed, and the heart
taken away, and the animal be apparently dead, on irritating in-
dividual nerves, or the spinal cord, the muscles are convulsed.^'
This vis nervosa, which remains in the nerves when separated
from the brain, is not exhausted by one or two muscular con-
tractions they excite when irritated, but is equal to the produc-
tion of numerously repeated movements, as I observed in a frog,
the spinal cord of which I divided in the back» It survived this
wound several days, and during the whole of that period, by
irritating that portion of the spinal cord which was below the
section, I excited innumerable convulsions in the lower extremi-
ties, nor did these die sooner than the whole frog. I am com-
pelled to defer a more detailed and accurate account of these and
similar experiments to another opportunity, as this is not the
proper place. That the vis nervosa can remain a long time in the
nerves, independently of the brain, seems to be proved by the
state of paralytic limbs, the nerves of which are deprived of all
connection with the brain on account of some preternatural com-
pression, and yet for a long period the paralysed muscles are

• Memoires sur la Nature Sensible et Irritable, torn, i, p. 245, exper. 225.
= Elem. Phys., torn, iv, pp. 337, 338.

SECT. III.] PROPERTIES OF THE VIS NERVOSA. 399

convulsed by the stimulus of the electric spark. ^ The vis nervosa
of the spinal cord, and of the nerves given off by it, remained in a
case after atheroma of the medulla oblongata, pons varolii, and
entire cerebellum had destroyed the connection between the
spinal cord and a dropsical brain.^ Moreover, the vis nervosa
not only continues in the spinal cord and nerves long separated
from their connection with the brain, but exists in nerves that
never had any connection with the brain whatever. This is
proved by the histories of acephalous foetuses, which lived
during the whole period of intra-uterine life, were nourished,
increased in growth, and when bom evinced no obscure signs
of vitality, without having a brain, and by the sole vis of the
nerves and spinal cord, if the latter was not also defective.
Animals which have nerves but no cerebrum also demonstrate
the same fact.

From these facts it is obvious, that the vis nervosa remaining
in the nerves after the severance of their connection with the
brain, must be considered as the cause whereby the heart was
able to continue its movements, in the experiments instituted
by Haller and other distinguished men, after the brain and
cerebellum were destroyed, the head cut off, and even all the
nerves of the heart divided. For the stimulus of the blood, alter-
nately flowing into the cavities of the heart, irritated its nerves
still endowed with vis nervosa, although separated from the
brain, and thus excited it to alternate contractions. But
another interpretation has been given to these facts; and espe-
cially by Haller, namely, that it is manifest, that if the heart's
action continues after decapitation, or destruction of the whole
cerebrum and cerebellum, the cardiac movements are not in
connection with the nerves, but with an irritability innate in
the heart, and not dependent on the nerves. But the fallacy
in this conclusion is most manifest, since it can only be fairly
inferred that the heart can continue its action without the brain
and spinal cord, but not without its own nerves, which, although
entirely separated from the brain, are still united to the heart,
and still as endowed with the vis nervosa, and as impatient of a

' Caldani excited movements of paralysed muscles by the electric spark. Consult
Haller's Bib. Anat.

2 De Haen. Rat. Med. Contin., torn, iii, section i, cas. ix, the dissection of which
I performed before my lamented teacher.

400 THE NERVOUS SYSTEM IN GENERAL. [ch. ii.

stimulus, as wlien in connection with the brain. If any other
muscle, the nerve of which is divided, contracts when the nerve
is irritated, why not also should the heart alternately contract,
though its nerves be divided, when alternately stimulated by the
inflowing venous blood ? These same nerves are the cause why
the heart, or any other muscle, when separated from the body,
or even when cut into pieces, continues to contract at each
irritation; for with each portion there are nerves also cut away,
since they cannot be separated from the substance of the
muscle, beiQg lost in it as invisible filaments. These minute
invisible nerves are also endowed with their own vis nervosa,
are irritated when the muscle is irritated, and feel the stimulus,
and cause the muscle or fragment of a muscle to contract.
This continues longer in the heart and intestines, according to
the experiments of Haller, than in other muscles, and only
ends when the animal heat being dissipated, the cold coagulates
the fat, and seems also to diminish the flexibility of the fibres,
to lessen the fluidity of the blood remaining in the vessels of
the muscle, and to fix the vis nervosa itself. It is now placed
beyond doubt by many distinguished men, that the irritability
of muscles is dependent on the nerves, and cannot exist without
them ;^ although it is certain that some have incon-ectly con-
founded irritability with sensibility. Irritability belongs solely
to muscle, and sensibility to nerve; but irritability is the eff'ect
of the muscle as a compound instrument, into the composition
of which enter muscular fibres enveloped in their proper

' Whytt, 'Essays. Phys.;* also, 'Von den Nerven und Hypochondrischen K>ank.'
(Leipzig, 1766), Seit. 4; Unzer, 'Erste Griinde einer Physiologie,' Seit. 435 — 437,
und §§ 382 — 387 ; Rehfeld, ' Diss, an Vis Irritabilis Fibrarum Muscularum Innata ipsis
inhaereat, an aliunde accedat' (Gryphiae, 1770). Winterl, * Inflammationis theoria
Nova' (Viennae, 1767), cap. iii; Crantz in 'Trabucchy Diss, de Mechanis. et Usu
Respirationis ' (Viennae, 1768); Trzebiczky, 'Diss, de firitabilitate et Sensibilitate'
(Pragae, 1770); Marherr, 'Praelect. in Boerliaavii Instit. Med.,' torn, ii, p. 131;
Thaer, 'Diss, de Actione Systematis Nervosi in Febribus' (Gott., 1774); Isenflamm,
'Praktische Anmerkungen iiber die Nerven' (Erlang., 1774), § 16; also 'Praktische
Anmerkungen uber die Muskeln' (Erlang., 1778), Seit, 73. Ern. Platner, 'De
Principio Vitali' (1777), also speaks of it in 'Anton von Haen's Heilungsmethode,'
3ten Band, 1781 ; iibersetzt von Ern. Platner, Prof, zu Leipzig, ira 1 Aufsatze iiber
einige Scbwierigkeiten des Hallerischen Systems; Prochaska, ' De Carne Musculari'
(Viennae, 1778); La Roscb, 'Analyse des Fonctions du Sys. Nerv.' (Geneve, 1778),
torn, i ; Cremadel's ' Nova Elem. Physiol.' (Romae, 1779) ; and many others who are
quoted in Haller's ' Elem. Phys.,' torn, iv, p. 456.

SECT. III.] PROPERTIES OF THE VIS NERVOSA. 401

sheaths, arteries and veins, together with their fluid contents,
and nerves. Not only can no part of this machine be wanting,
but it is also necessary to its due action that there be flexibility
of the fibres, fluidity of the fluids contained in the vessels, and
vis nervosa remaining in its nerves, which may perceive the
stimulus, and excite contractions of the muscle. The cele-
brated Tissot recognised this truth ;^ for although he main-
tained irritability to be a property innate in muscles, and
independent of the nerves, yet he observes, that it is probable
no muscle is perfectly organised without nerve. Consequently,
if irritability be the efiPect of a well-organised muscle, irritability
cannot exist without nerve in the muscle. The illustrious
Haller seems also to have felt the force of truth, for he altered
much of par. ii, section v, book iv, in the new edition of his
' Elementa Physiol.^ :^ and although he heads it with '* cordis
motus non a nervis/' he nevertheless says, that it must be
granted, when his own and the opposing experiments are well
weighed, that " it is possible that some property of the nerves
is necessary to the due action of the heart, and to maintain the
power of the fibres. Nevertheless, another motive power is more
influential in the heart, namely, its irritability, which cannot be
excited when the nerves are entirely wanting.^' And in many
other places he acknowledges, that the motion of the heart
depends on the nerves, which, however, he elsewhere declares is
independent of the nerves.^ So long as a nerve is continuous
with the brain, if it be irritated, it produces sensation, and excites

' Abhandl. uber die Nerven, &c., Ite Band, 2 Th., Seit. 176, § 267.

2 De Part. Corp. Hum. Fabrica et Usu, torn, ii, p. 392.

^ Ibid., p. 439, Haller further says : " Another conjecture is, that the heart is more
irritable, because the sentient nerves of the heart being in close relation with the
inner membrane of the heart, are stimulated by the contact of the blood ; and that
thence a more active movement arises than from irritation of the external portion
of another muscle. The external surface of the intestines is, in like manner, almost
insensible to stimuli, the internal most sensitive, and when irritated, continually ex-
cites extensive movements. Is it that the auricles are more excitable than the heart,
and more apt for motion, because being so delicate the nerves are almost naked, and
consequently exposed to the immediate stimulus of the blood? If any one will
advance any other cause for the greater aptness of the heart for motion on being
irritated, I will willingly listen," &c.

At page 158 of vol. iv of this same work, he continues: "Lastly, another cause
of the more rapid and frequent contraction of the heart is latent in the stimulus.
"Whether the nerves be vehemently excited by any cause whatsoever, or whether the
vis sanguinis bv which the heart is put in motion, shall have been increased. Conse-

26

402 THE NERVOUS SYSTEM IN GENERAL, [ch. ii.

motion in tlie muscle under its control ; no sooner, however, is it
tied or cut, than it loses the power of producing sensation when
irritated, but retains the power of exciting the muscles to move-
ment. No one will, I think, infer from this, that by that
division any portion of the vis nervosa escapes when the power
of exciting sensation is taken away : certainly the power to
produce both motion and sensation remains in the divided
nerve, but it cannot excite sensation, because on account of the
division or ligature, it cannot communicate its external im-
pressions to the brain, in which organ the perception of sen-
sations takes place. It is certain that the divided nerve retains
the power of producing motion, but it is necessary to this, that
there be an uninterrupted connection between the muscle and
the irritated point of the nerve ; if this be broken by division
or ligature, no movement is excited in the muscle, however
much the nerve may be irritated above the ligature or section ;
and the same holds good as to the production of sensation.

vii. A peculiar affection of the vis nervosa, or idiosyncrasy,
— That state, termed idiosyncrasy, is evidently a peculiar affec-
tion of the nervous system, which may indeed be referred
to an increase or diminution of the vis nervosa, yet not in
respect to all, but rather to certain peculiar stimuli. This
causes us to regard some things with the greatest love, and
with an insatiable longing, and others with the greatest
aversion ; the one is termed sympathy, the other antipathy.
That idiosyncrasies are diverse in different men is evident
from this, that some desire just what others are averse to.
There are idiosyncrasies proper to each age, temperament, and
sex ; or, more properly, to each individual ; some of these are
altered by time, the manner of life or temperament being
changed in some respects ; many are modified by habit, and
some remain companions for life ; some again are excited by
pregnancy, and others by diseases, and disappear when these
are removed. Consequently, it would appear that idiosyncra-
sies may be divided into idiosyncrasies of the healthy, of the
pregnant, and of the sick. As to other points, if we be igno-

quently, the pulse is accelerated by affections of the mind, anger, terror, shame, and
various passions. Van Helmont was not ignorant of the quicker pulse, which is said
1 0 accompany every violent pain, as in the instance of a thorn sticking in the finger,"

&c. And in 'Elem. Physiol.,' tom. iv, p. 356, he adds: " In many (acephalous
foetuses) there was only so much of the spinal cord as was sufficient to maintain the

motions of the heart," &c.

SECT. III.] PROPERTIES OF THE VIS NERVOSA. 403

rant of the nature of the vis nervosa in general, much more may
this peculiar vis nervosa be unknown to us, the visible eflPects
of which can only be observed. If any person would collect
these from his personal observation and from medical writings,
and arrange them well, he would certainly accomplish a useful
work, from which we might hope to obtain much light for
understanding the functions of the nervous system, and much
for the cm^e of its diseases. And Haller spoke truly of idio-
syncrasy, when he said : " As yet this field has certainly not
been sufficiently cultivated, and there is the prospect of an
abundant harvest from it.^^ ^ As in this dissertation I propose
only to give an introduction to the functions of the nervous
system, rather than to work out a complete treatise, I shall
only enumerate a few examples of idiosyncrasy, hoping from
others a full systematic account.

It happens to some men, in other respects perfectly healthy,
that they cannot see, taste, or even hear certain things, but they
are affected unpleasantly, and sometimes to fainting. Some
cannot be present at a venesection, and see the blood flow, with-
out fainting away. I know a female who, when young, could
never see the beet-root that is usually placed on the table, without
swooning and fainting; she was at last by habit enabled to look at
it, but could never eat it. The exhalations of a cat, although
concealed, excite in some men disquietude, perspiration, and
fainting ; an example of this kind is narrated by Kaaw;^ and also
the history of a man who was always affected with a bleeding
at the nose, from the odour of cheese. Fainting, in some, is
induced by the fragrance of roses ; and the pale rose of a
pleasant odour, the red, unpleasant. "* Fainting has also been
excited by the odour of apples.^ Strawberries have produced
remarkable symptoms.^ Musk and civet can excite in some
persons violent hysterical attacks, which in others are induced
by the fetid gums. We may meet every day with illustrations
of idiosyncrasy of taste, for we see some persons esteem articles
of diet as delicacies which others abhor : I myself, when young,
had such an aversion for spinach, beet-root, and cod-fish, that

• Elena. Phys., torn, iv, p. 575.

2 Impet. Faciens dictum Hippocrati, § 408, p. 358.
^ Eph. Nat. Cur., Dec. ii, An. v, observ. 8.

* Ibid,, An. I, observ., 72.
Ibid., An. v, observ., 214.

404. THE NERV^OUS SYSTEM IN GENERAL. [ch. ii.

by taking the smallest particle of them, I could have excited
nausea and vomiting; becoming habituated to them all, that
disposition gradually disappeared. Tissot observed in one of
his friends, that he could not bear the smallest quantity of
sugar, and would presently vomit it, even if taken unknow-
ingly.^ Music, so pleasant to us, is very disagreeable to most
dogs, as is shown by their disquietude and bowlings. I knew
a female, on whose skin a plaster of any kind excited redness,
swelling, and pustules. Many persons cannot sit with their back
to the horses in a carriage without experiencing vertigo, nausea,
vomiting, and swooning. Tissot rightly maintains, that the anti-
pathy between certain animals, as for example, between the hare
and the dog, the cat and the mouse, depends on idiosyncrasy of
the nerves ; ^ and he shows that the sympathies and antipathies
between men are due to the same cause, as when a person at
the first glance finds something in another person which pleases
or displeases him, and impels him to love or hate that person.

Pregnancy frequently induces idiosyncrasy of the nerves of the
pregnant, so that they are affected with a dislike for various foods
and drinks, or have the greatest desire for other things, even
the most absurd. Many recorded examples of this extraordinary
appetite, which is termed pica, or malacia, are current. Schenk
relates the history of a pregnant female, in whom the sight of
the bare arm of a baker excited such an inexphcable desire to
bite and devour it, that she compelled her husband to offer
money to the baker to allow her only a bite or two from his arm.
He also mentions another female, who had such an urgent
desire to eat the flesh of her husland that she killed him, and
pickled the flesh, that it might serve her for several banquets.
But it is also true that this detestable appetite for human flesh
has affected men and unimpregnated females, as well as the
pregnant, and these have also been impelled to commit murder,
when not restrained by reason or humanity. This happened
with Elizabeth of Milan, who allured boys to her by caresses,
killed them, and ate their pickled flesh every day. A Scotch
girl, the daughter of an anthropophagous robber, had the same
wicked desires as her father, and although long separated from
him, and educated apart, she still, from an innate depraved dis-
position remained prone to the same crime.^ We have a recent

' Von Nerven, 2 Band, 2 Th., § 58. ^ Lqc^ cjt., ^$ 58, 59.

^ See Gaubius in Orat. I, de Regimine Mentis, quod Medicorum est.

SECT. III.] PROPERTIES OF THE VIS NERVOSA. 405

example in the case of a cannibal of Berg [Westphalia], who
being a man in other respects of a depraved disposition, and
incited by an appetite for human flesh, did not hesitate to slay
certain innocent persons, namely, a girl, and a traveller.^

Idiosyncrasies have been frequently observed to arise from
disease ; thus, a person aflPected with fever arising from
internal putrescence, dislikes flesh, fish, eggs, and broths made
from them, but has a great desire for acids ; as the disease de-
clines, the appetite returns for the things that were previously
rejected. Persons, who in health esteem tobacco as a great
luxury, when sick, neglect and dislike it, but with returning
health, regain their desire for it. Pale girls, commonly aff'ected
with acidity, have a taste for chalk or lime, or for charcoal and
ashes, or for vinegar and salt. Hydrophobic patients are
horrified even at the sight of water. To this class of examples,
belong those cases in which remedies having been applied in
vain, suddenly an appetite is excited for some particular thing,
which, being taken, the patients are happily cured.

The influence of habit on the vis nervosa^ and especially on
idiosyncrasy, deserves to be noticed here. By means of this
the nerves become easily tolerant of those things, by which
they were at first violently aff'ected. Thus, those who are
habituated to wine and the smoke of tobacco, can imbibe a
large quantity with impunity, while in those unaccustomed to
their use, they excite vertigo, drunkenness, and other unpleasant
symptoms. Thus, also, a seaman habituated to the sea is not
annoyed with the nausea and vomiting which the motion of
the ship will excite. These and many other instances show,
that the degree of sensibility of the nerves is diminished by
habit, not indeed with regard to any stimuli, but only in re-
spect of those which are frequently applied, the nerves remaining
equally sensitive to other stimuli. Thus, also, an idiosyncrasy
may be diminished, or entirely overcome by habit alone ; just
as on the other hand, by habit alone, the nervous system becomes
accustomed to certain things, and acquires a true idiosyncrasy,
so that we cannot easily do without those things, as, for example,
in the case of a man accustomed to the use of tobacco. It is
from hence, that the proverb has originated — " habit is second
nature.^'

See this history in the inaugural dissertation of Jacobi, defended at Jena in 1781.

CHAPTER III.

THE FUNCTIONS OF THE NERVES. -

Inasmuch as I have already divided the nervous system into
three principal portions, namely,, the animal organs, sensorium
commune, and the nerves properly so called, I shall also divide
its functions into three classes, namely, into animal operations,
operations of the sensorium, and operations of the nerves. The
functions of the nerves are first to be considered; then the
operations of the common sensory, and lastly, the animal
operations.

SECTION I. ON THE ACTION OF THE NERVES IN PRODUCING

SENSATION AND MOTION.

Since the nerves represent cords commencing in the cerebrum,
medulla oblongata, and medulla spinalis, and thence extended
throughout the whole body, two extremities are noted in each
nerve; of these, the one is internal and continuous with the
cerebrum, or medulla oblongata, or medulla spinalis, and termed
the origin or beginning of the nerve ; the other is external where
the nerves terminate in various parts of the body, and termed,
therefore, the end of the nerve. It is besides certain, that the
nerves have the property of most readily receiving impressions,
however great or of whatever kind they may be, and of trans-
mitting them when received with great rapidity along their
whole length. Consequently, if an impression be made at the
termination of a nerve, which is termed an external impression,
it is very rapidly transmitted along the whole length of the nerve
quite to its origin ; and vice versa, if the impression be made
at the commencement of the nerve, which is termed an internal
impression, it is transmitted with the same rapidity to the
termination of the nerve. But if the impression be made
midway on the trunk of the nerve, it is rapidly transmitted a
the same moment to both its origin and termination. This

SECT. I.] ACTION OF THE NERVES ON IMPRESSIONS. 407

aptitude of the nerves to receive impressions, and when received
of transmitting them either way with great rapidity, appears to
be that called the vis nervosa of the nerves, which is also cor-
rectly designated, the sensibility or mobility of the nerves, and
which is also well designated by Unzer, " corporeal sensation
without concomitant perception.^^

This property of the nerves does not depend solely on their
medullary pulp, (which possibly is capable of some slight vibra-
tion, or oscillation, although the nerves do not appear at all
tense,) but it appears, as I have already observed in § 3 of
the preceding Chapter, to be rather some other principle added
to the medullary pulp, the conjunction of the two constituting
the whole vis nervosa j and possibly the diligence of the very
sagacious observers of nature may discover whether that prin-
ciple be electricity, or phlogiston, or some species of air, or the
matter of light, or a something compounded of these. That other
principle, whatever it may be, seems to come to the nerves with
the arterial blood, by means of the numerous blood-vessels which
accompany the nerves of the whole body throughout their whole
course ; or to be attracted from the air through inorganic pores;
or in both these ways, and not to be sent into the nerves
from the brain, as its only source, although the brain itself
appears to acquire a suitable portion of the same principle
through its own vessels. For, as I have before shown, the
nerves when separated from the brain have equally vis nervosa
as the nerves in connection with the brain, and in proof
hereof may be mentioned the nerves of acephalous foetuses
and of brainless animals, which are endowed with the vis
nervosa, although they could not possibly derive it from a brain.
Nevertheless, a certain cohesion of the medullary pulp of the
nerves is necessary to the vis nervosa, because if we so injure
the pulp of a nerve by strong compression, that the connection
of its globules is destroyed, and their relations broken up, the
vis nervosa ceases in the portion of the nerve thus compressed,
neither can impressions be propagated through it, nor can that
portion of the nerve produce motion or sensation, if pricked or
irritated.

Although a nerve be necessary to sensation and motion, it does
not excite motion or feel alone, but feels by means of the brain,
which, when an impression made on a nerve is brought to it,

408 FUNCTIONS OF THE NERVES. [ch. hi-

communicates the impression to the mind ; and the nerve pro-
duces motion by means of a muscle, when an impression made
on the nerve descends to the muscle/ and excites it to move-
ment. Consequently, a nerve separated from the brain, and no
longer able to communicate impressions to it, can no longer
produce sensation, just as a nerve separated by division from a
muscle can no longer excite motion in the muscle, however
much it may be irritated. Consequently, a nerve has a similar
office in exciting sensation and motion, namely, to receive the
impression of a stimulus, and to transmit it with the greatest
rapidity along its whole length, which, when it arrives at the
brain, produces the perception of a sensation, but when it
arrives at a muscle, excites its contraction.

SECTION II. THE ACTION OF THE NERVES ON THE VESSELS AND

THEIR FLUIDS.

Another function of the nerves consists in a certain power
over the blood-vessels, and specially the capillaries, in virtue
of which, when the nerves are stimulated, they excite in that
part to which they are distributed a much more copious
accumulation of blood than would have taken place in the
normal condition of the circulation. This phenomenon is
termed congestion of the humours, afflux, derivation, abnormal
direction, descent of the humours. Stahl termed it the tide of
the microcosmic sea, or the ebb and flow of the blood.

The causes that determine a more copious derivation of the
humours into any part of the body, are usually considered to be
twofold ; the one, a mere mechanical cause, consists in a dimi-
nished resistance of the vessels of the part, so that the humours
contained in the vessels being forced on by the power of the
heart and the vessels themselves, flow to the point of least
resistance, according to the laws regulating other fluids, and
cause congestion of the humours ; for this reason, when a vein
or artery is divided, the blood rushes from the adjoining vessels,
even against its natural direction and gravity; for this reason,
also, congestion takes place, when vessels are relaxed by emol-
lient cataplasms and pediluvia.^ Thus also the blood is cou-

' Haller, De Part. Corp. Hum. Fabr., torn, iv, pp. 93, 289.

SECT. II.] ACTION OF THE NERVES ON THE VESSELS. 409

gested under a cupping-glass when the usual atmospheric pres-
sure is removed from the part ; a local derivation of the humours
takes place also when a compression of the vessels occurs in any
part, and the blood is repelled into other parts ; as occurs, for
example, when the stomach is filled, by which the abdominal
vessels are compressed and the lungs forced into less room,
and, consequently, a greater quantity of blood goes to the head,
rendering the face redder. The other cause is a stimulus to
the nerves ; which when applied to the nerves excites a more
copious flow of humours. Innumerable phenomena of daily
occurrence show this. Thus a stimulus applied to the nerves is
the cause why the cheeks, ears, and nose, become intensely red,
and a sense of heat is felt when exposed to a cold wind in winter.
No one is ignorant how much the stimulus of sinapisms and
blisters cause derivation of the humours to the stimulated part;
an acrid smoke or fine powder getting into the eyes excites a
copious flow of tears, and the vessels of the conjunctiva, pre-
viously invisible, become distended with blood. The smoke of
tobacco, or any other acrid aroma, retained in the mouth,
excites a copious flow of saliva ; purgatives and emetics bring
off* much gastric and intestinal mucus ; titillation of the nipple
of the mamma causes it to become turgid and erect ; the touch,
or the stimulus of the semen or urine, or a gonorrhoea, cause
the penis to be distended and erected by exciting a more copious
flow of blood into the corpora cavernosa. These phenomena
take place if the nerves be stimulated locally ; but the same
thing happens when the nerves are excited not directly, but
indirectly, through the brain. We know, that thus the face is
suffused with the blush of modesty ; grief causes a copious flow
of tears, congestion of the vessels of the conjunctiva, and
redness and swelling of the whole face. The sight of agree-
able food provokes a flow of saliva ; it is not unusual for some
persons to vomit, or be purged by only seeing a medicine ; a
lascivious idea erects the penis, &c.

Although it is placed beyond a doubt, that stimulated
nerves cause congestion and derivation of the humours to the
part stimulated, the mode in which the nerves accomplish this is
as yet unknown. Distinguished writers have advanced various
conjectures, by which they have attempted to explain this in-
fluence of the nerves on the vessels. Some have supposed that

410 FUNCTIONS OF THE NERVES. [ch. in.

there are nervous loops and nooses at the termination of the
arteries and roots of veins, similar to those which are seen to sur-
round the larger arteries in many places ; and they opined that
these loops could be tightened or relaxed, and so be able to
admit blood to the part or retain it. Haller, together with some
of his disciples, followed Willis in adopting this opinion ; but
when he learnt, from experiments, that the nerves do not con-
tract when stimulated, he rejected the doctrine. Some located
muscular sphincters at the terminations of the arteries and
roots of the veins, which constricting the vessels, and causing
the blood to accumulate above the constriction, so inundated
the lateral vessels : Boerhaave in particular propounded this
opinion in his theory of obstruction,^ and also founded his
theory of inflammation upon it. But many and weighty ob-
jections have been raised against this production of accu-
mulation and inflammation by obstruction and constriction
only; for obstruction of a vessel does not cause such an
accumulation of fluid, anterior to the obstruction, because it
easily finds an exit through the lateral vessels so obvious in every
part of the body ; and the comparison of a river swelling from an
obstruction, and inundating the adjoining parts, does not apply
to our vessels ; for if one, or even many of them, be obstructed,
there still remain innumerable lateral vessels, through which
the fluids find a free outlet. For this reason, Haller found that
the trunk of an artery, when tied, became swollen indeed for a
moment, between the ligature and the heart, and manifested
T)ne or two pulsations ; but so far is it from the fact, that
the impetus of the fluids is directed against the ligature, that
rather the canal is contracted, and it impels the blood into
the communicating arteries, until that which was tied is quite
empty. The same thing is shown by the umbilical arteries,
which also become empty, and impervious. WinterP fully
sets forth these and other arguments of distinguished men,
and proves that the fluids do not rush towards an obstruction,
but rather prefer to pass away by the lateral and unobstructed
vessels ; consequently, no congestion and no inflammation can
arise from an obstruction only, but the stimulus of the nerves
is the cause, which immediately excites the fluids to accumulate
more copiously in the vessels subjected to them. Moreover,
' Aphoris., 113. ^ Nova Theoria Inflammationis, p. 19.

SECT. 11.] ACTION OF THE NERVES ON THE VESSELS. 411

that distinguished man propounds a peculiar and singular con-
jecture, which appears to me, however, unfounded, to the effect
that since a stimulus has quite a different result on the mus-
cular arteries, than on the heart and other muscles — inasmuch
as the arteries appear to be dilated by a stimulus, whereas we
see that the heart and other muscles to be contracted — he
thinks that the blood is attracted, and flows from all sides into
the arteries dilated by a stimulus. An opinion of other eminent
men, as to the cause of the derivation of the fluids to a stimu-
lated part is, that the stimulus renders the arterial action
more frequent and powerful, consequently that the arteries carry
a greater quantity of the fluids onwards than the veins can return,
and thus they explain why the fluids should accumulate more
copiously in a stimulated part.^ But even this doctrine does

* I may be permitted to make some observations here on the irritability and mus-
cular contraction of arteries. The experiments of Haller appeared to render the irri-
tability of arteries doubtful, as he never found them irritable ; and to show that the
systole of the pulsating arteries in the natural state arises solely from their elasticity,
by which they are restored to their former condition after being distended by the
blood projected from the heart, and enabled to transmit the blood thus received
inwards into the veins, so that along with the eminent men who have repeated the
experiments, I expressed my assent to their validity in * Controversis Quaestionibus
Physiologicis,' p. 30. The experiments of Verschuir on the irritability of arteries,
were not then known to me ; they are contained in his Dissertation ' De Arteriarum
et Venarum vi irritabili ejusque in vasis excessu ; et inde oriunda Sanguinis direc-
tione abnormi,' printed at Grbningen in 1766, and fully demonstrate that some-
times arteries and veins manifestly contract on the application of a powerful
stimulus, as scraping with a scalpel, oil of vitriol, spirit of sal ammoniac, &c. ; but
generally the contractions were very indistinct, and not unfrequently neither re-
sponded to these acrid stimulants, nor, as in the experiments of Haller, could
irritability be detected. It is also shown from all these experiments of Verschuir,
when properly collated, that although arteries were found to respond to these
acrid stimulants in one or more places, in another part of the same animal it
was the least possible. Further, it is to be observed, that those contractions which
were excited continued for some time before they ceased, and the artery was re-
stored to its former condition ; consequently the contraction and relaxation of the
artery did not follow each other so quickly as the systole and diastole of the artery
in its natural condition, nor as quickly as the heart, when irritated, contracts and
then immediately relaxes. Lastly, it also appears from the experiments of this dis-
tinguished physiologist, that a portion of an artery, which an acrid poison had
caused to contract, was hard and rigid, and no longer pulsated ; while, at the same
time, other portions of the same artery, untouched by the acrid stimulus, continued
to repeat their pulsations. But are the results of these experiments opposed to the
doctrine, that the elasticity of the arteries is the cause of their systole ? By no
means ; for the elasticity of the arteries is ever demonstrable in any animal, whether

412 FUNCTIONS OF THE NERVES. [ch. iii.

not appear to have the real stamp of truth, which I leave,
however, to be decided on by other perspicacious men, to
whose attention I would also commend this conjecture, namely,
whether when the vis nervosa is increased by a stimulus, it
does not render the force of attraction of the fluids circulating
through the vessels greater, so that by this means the fluids are
attracted from every side to the centre of stimulation, as occurs,
for example, when sealing-wax is gently rubbed on a piece of
cloth, and made electrical, and attracts sand and particles of
various kinds? Speculations of this kind are not vain and
useless, because if the true reason be known why the nerves
when stimulated cause accumulation of the fluids in the tissues
to which they are distributed, much light will be thrown on
the nature of the vis nervosa itself, for one truth leads to another.

living or dead, and is so great that it appears to be a power quite sufficient to restore
the artery to its former condition after being dilated by the blood sent into it from
the heart, and to pass that blood onwards to the veins : it is by this elasticity only,
that the systole of the arteries so immediately and quickly follows the systole of the
heart, as happens in the regular and natural pulse ; while, on the contrary, the irri-
tability of arteries is small, requiring the strongest stimulus, and not always respond-
ing to this, so that it obviously appears inadequate to the repeated natural systole
of the arteries. According to the experiments of Haller (De Part. Corp. Hum. Fabr.
et Funct., tom. iv, pp. 93, 289), it is only the elasticity of the arteries, which, after
the death of an animal, impels the blood from every point through a wound, since
all irritability had disappeared. As the irritability of arteries, according to the ex-
periments of Verschuir, is hardly excited even by very acrid stimuli, it will scarcely
be developed by the unstimulating blood sent from the heart into the artery ; but it
seems to presuppose great disturbance of the nervous system, by which it is excited.
This takes place differently in different parts, and to it, perhaps, ought to be ascribed
those abnormal pulsations, diflferent in different parts, and even complete pulse-
lessness ; examples of which, given by authors worthy of credit, are cited by Verschuir
in the Dissertation just noticed, and by Gruber in his Dissertation * De Excessu Vis
Vitalis,' published in Klinkosh's collection of disputations at the University of
Prague. Consequently, it appears to me, that the natural systole of the arteries
ought to be attributed to their elasticity only ; but as to the cause of the different
pulses in different parts, observed in the same individual at the same time, and also
as to the want of pulsation in pulselessness, it is clearly demonstrated by the experi-
ments of Verschuir to be the irritability of the arteries. Whence it therefore follows,
that arteries in their natural condition react solely by their elasticity, and are not
irritable ; but that they become irritable and contract, in a preternatural condition,
when the vis nervosa of the nerves distributed to the arteries is preternaturally in-
creased ; or when a very powerful stimulus, as in the experiments of Verschuir, is
applied to them ; and we have additional confirmation of this, when we remember
that some parts of our bodies, which are without sensation in the natural state, be-
come extremely sensitive in disease.

SECT. 111.] CONTRACTION OF THE MUSCLES. 413

SECTION III. BY THIS DERIVATION OF THE FLUIDS TO THE

STIMULATED PART, THE MUSCLES ARE MADE TO CONTRACT,
AND MANY OTHER PHENOMENA PRODUCED.

The fasciculi of the muscles are made up of fibres and
carneous filaments, and bound together by sheaths, and are so
traversed by blood-vessels, that these are everywhere inter-
mingled with the fibres and filaments, and decussate with them
more or less transversely; and since the fibres and carneous
filaments are closely compressed together by their sheaths, the
least congestion and distension of the vessels distributed amongst
them cannot take place without the filaments and the fibres
which they constitute being thrown into many serpentine in-
flexions, and thus their length be diminished. Since, therefore,
irritation of the nerves causes congestion of humours in the
vessels, it is easy to infer that in this same manner nerves, when
irritated, excite the muscles to which they are distributed to con-
traction, that is to say, by the greater accumulation of the
humour alone, caused in the vessels of the contracting muscle.
When the cause, originating in the nerves, which attracts fluids
more freely to the muscle, ceases to act, the distended vessels
and deflected fibres react by their elasticity on the accumulated
fluids, and propel them into the larger blood-vessels not en-
tangled amongst fibrils and muscular filaments ; this process is
facilitated by the raising of the weight, which resists the con-
traction of the muscle that raises it, by the action of the over-
stretched muscles antagonistic to it ; and thus the contracted
muscle is again relaxed. It is now four years since I sub-
mitted this theory of muscular action to the criticism of the
learned public, in my Tract, ^De Carne Musculari.^ It is
founded on the intimate anatomy of the muscular tissues, is
well adapted to the phenomena, and I am not aware that any
one has opposed the theory, or advanced any doubts regarding
it ; nor in meditating upon it myself have I been able to dis-
cover any arguments against it, except that irritability exists
more extensively than muscular structure. But it appears
to me that this argument, when rightly considered, is not
an objection to my theoiy ; for if we observe that polypes
and other zoophytes are irritable, in whose structure the

414 FUNCTIONS OF THE NERVES. [ch. hi.

microscope enables us to detect only a granular mass, but
no muscle, no bones, no vessels, no nerves ; if, more-
over, there are vegetables, and portions of vegetables, which
display no doubtful irritability, and yet cannot be suspected of
containing muscles and nerves, it does not, therefore, follow,
that the irritability of muscles is not produced by the mechan-
ism described above ; it does follow, however, that that irrita-
bility, which in the greater and more perfect animals ought to
be adapted to the development of greater strength, is neces-
sarily dependent on the mechanism described by me ; while,
again, irritability in plants and polypes is not so powerful, and
can be produced by the Author of Nature by another and dif-
ferent mechanism than that of muscles. If this appear incre-
dible to any one, let him reflect that the function of generation
is more widely extended than irritability, yet, nevertheless, that
Nature accomplishes it, not in one way always, but by many
and by the most varied methods. Some animals are viviparous,
others oviparous ; and of these latter some have the ova fecun-
dated by the male after extrusion from the female, and some
before extrusion ; some incubate their ova, some abandon them
to be incubated by others ; some deposit fecundated ova,
without the coitus of the sexes ; some propagate by shoots ; the
polypus tintinabuliformis is reproduced by dividing its body
into two ; ^ the poh^pus plumosus propagates both by shoots and
by ova, which are always fecundated without coitus. 2 Why,
then, might not nature be able to produce irritability by dif-
ferent mechanisms — in muscles by the method described by
me — and in polypes, zoophytes, and plants, devoid of muscular
fibre, in some other way as yet unknown ? I am persuaded
that these things being weighed, my theory of muscular con-
traction is very near the truth; and I should be much delighted
if any attempts of mine should avail anything in elucidating
such a difficult subject, since I am not ignorant of the very
great anxiety of very learned men to understand the cause of
muscular contraction ; who to this end have not only spared
no labour, but have also endeavoured to stimulate other in-
quirers by great and most honorable rewards to perfect this

• Spallanzani Opus. Physique, Tom. i, tab. i, fig. vii. (This figure represents a
vorticella. — Ed.)
'^ lleaumur.

SECT. III.] CONTRACTION OF THE MUSCLES. 415

department of physiology : I need only mention the prizes
offered by the Royal Academy of Prussia,^ and William Croon
of London.^

Verschuir, in the dissertation already quoted, has attempted
to explain the flow of the menses hy this same derivation of the
blood, excited every month through the nerves, since this pheno-
menon cannot be accounted for either by the theory of a general
plethora, which Van Swieten has ah'eady fully refuted in his
' Comments on Boerhaave^s Aphorisms,' or by the notion of a
partial uterine plethora. Marherr in particular, following
Haller, has attempted to show, that the cause of the flow of the
menses is a special plethora of the uterus. He asserts, for
instance, that the arteries of the uterus are more capacious and
less contractile than the veins, consequently the arteries receive
more blood than the veins can return ; that the veins have no
valves, and consequently, as the veins cannot so well support
the pressure of the blood, its return from the uterus is rendered
more difficult ; and thus, from these causes, the blood accumu-
lates for a period in the uterine arteries and venous capillaries,
until by that time a sufficient quantity being present, it bursts
forth. But these distinguished writers do not appear to have
considered how much the weight and size of the uterus must be
increased every month before the flow of the menses, if it con-
tains the whole quantity of blood that is thus discharged. If
we estimate its weight at 4, 5, 6, 7, 10, 12 ounces, and this be
accumulated in the uterine arteries just before menstruation, the
uterus ought at that period to appear manifestly increased in
weight and size, a fact which has not been as yet observed or
recorded by anatomists. It is thus manifest, that the menstrual
blood is not contained in the uterine vessels previously to
menstruation, but is derived to the vessels and cavity of the
uterus at the time of menstruation, and this by means of the
nerves, which seem to be irritated by some stimulus as yet

• Vide M. Le Cat's ' Dissertation, qui a remporte le prix propose par I'Academie
Royale de Prusse, sur le principe de TAction des Muscles/ &c. Berlin, 1753.

2 Lectures are delivered every year at the College of Physicians of London, on
the nature of the muscles and the functions of the nerves, a handsome sum heing
bequeathed to the Lecturer. See Thomas Lawrence, * De Natura Musculorum
Praelectiones tres in Theatre CoUegii Medicorum Londinensium habitae anno 1759.'
Recusje Venetiis, 1766.

416 FUNCTIONS OF THE NERVES. [ch. hi.

unknown, recurring periodically, and thus produce the derivation
of blood to the uterus. Probably it is some latent peculiarity
of the vis nervosa, which recurs periodically, and causes a deriva-
tion of blood to the uterus, just as we observe intermittent fevers
to return periodically.

Not only is dilatation of the minute radiated vessels of the
iris produced by congestion, but also elongation and deflection
from a serpentine to a straight line, in consequence of which
the iris is dilated and the pupil contracted, when the retina is
irritated by a strong light, and this again acts on the ciliar,y
nerves by consentience.^ The cause ceasing, which through the
nerves induced congestion, the congested fluids appear to be
driven into the larger vessels by the elastic and tense capillaries,
and thus the minute radiated vessels of the iris are again short-
ened, and arranged in serpentine folds, and so the iris is con-
tracted and the pupil dilated.

By a similar but greater accumulation of blood in the cor-
pora cavernosa of the penis and clitoris, excited by the nerves,
these parts become turgid, hard, and erect, when their nerves
are excited, either locally by a mechanical stimulus, or by
lascivious ideas.^

Thus also the papillae of the mammae swell, become hard,
and those which are retracted into their fossae protrude, when
rubbed with the tip of the finger, or taken within the lips of
the infant, because their nerves being vellicated, excite a greater
flow of fluids into the vessels (for a corpus cavernosum is not
found in them), and produce the whole phenomenon.^

That appearance of the human skin termed cutis anserinaj
arises also from a greater derivation of the fluids caused by the
cutaneous nerves, for the spongy bulbs of the hairs become
turgid by the blood attracted more copiously to them, and pro-
duce those small eminences on the skin, from which the term
cutis anserina is derived, and by which also the hairs proceeding
from them are rendered erect. When that greater derivation

» Haller, *Elem, Phys.,' torn, v, lib. xvi, sect, ii, § xii; Caldani, 'Instit. Physiol.,'
Nro. 320 ; and my tract, • De Carne Muscular!,' may be consulted, p. 10.

2 Caldani, loc. cit., Nro. 494 ; Winterl, ' Inflamm. Theor. Nov.,' p. 143.

' Kolpin's Dissertation, * De Structura Mammarum,' may be consulted, translated
into German (Berlin, 1767), p. 16, where the translator in a note supposes a con-
gestion of humours into the irritated part, by oscillation of the vessels increased
through the nerves.

SECT. IV.] OPPOSITE PROPERTY IN THE NERVES. 417

to the bulbs of the hairs ceases, the small prominences subside
and disappear, and in their place there are little depressions, in
consequence of which the hairs cease to be erect.

Other phenomena, occurring in the natural state, besides those
mentioned in the preceding paragraphs are intelligible by this
congestion arising in the irritated part. And in diseases there
are frequently opportunities for observing the operation of that
nervous influence on the vessels, in virtue of which fluids flow
more copiously and immediately to the irritated part. Inflamma-
tion itself is nothing else than a powerful attraction and deriva-
tion of blood from a stimulus, by which the vessels become filled,
swell, are rendered tense, red, painful, &c.j for eminent writers^
have already demonstrated the incorrectness of the doctrine of
Boerhaave, that obstruction is the only cause of inflammation,
and all recognise the cause to be a stimulus which attracts the
fluids more powerfully to the stimulated part, and produces
inflammation. If this stimulus be suflSciently powerful, it
draws the nerves of the heart into sympathetic action, and by
increasing the movements of the latter produces fever, the con-
comitant of inflammation. Eminent men have already taught,
that the motion of the blood cannot be so much accelerated
through free vessels by the obstruction alone of other vessels, as
to excite fever. Thus also haemorrhoids continually arise from
the stimulus of hard and acrid faeces in the rectum and other
similar causes, since the vessels gradually give way, and dilate
into varices, from the frequent derivation of blood to that part.
And those deposits, termed metastases by physicians, are pro-
bably owing in a great degree to a stimulation of the nerves.

SECTION IV. DOES AN OPPOSITE PROPERTY EXIST IN THE

NERVES, SO THAT THEY CAN REPEL THE BLOOD FROM THE VES-
SELS UNDER THEIR INFLUENCE INTO OTHER PARTS?

The face of a man struck with sudden terror is pale, and
some men become pale when in a paroxysm of rage, which pale-
ness is without doubt owing to a repulsion of the blood from
the cutaneous blood-vessels, to those in the interior of the body.
Inasmuch as the nervous system is afiPected in terror or rage,

' Galen, Senac, Gorter, Haller, in Winterl's * Inflamraationis Theoria Nova,
(Viennae, 1767) ; and Caldani in his ' Institutiones Pathologiae,' cap. ix.

27

418 FUNCTIONS OF THE NERVES. [ce. iii.

the question arises whether the cutaueous nerves then affected
completely repel the blood from the cutaneous vessels, by con-
tracting them, to the inner vessels of the body? or whether,
the heart disturbed at the time and not contracting, ceases for
a moment to impel the blood to the surface of the body, the
cutaneous vessels acting at the same time as in fainting, and by
virtue of their own elasticity repelling the blood to the internal
organs ? Often if one kidney be affected with calculus, or in-
flammation, a true ischuria comes on, for the other kidney,
although healthy, ceases to secrete urine. Physicians are aware
that this takes place from sympathy of the nerves of the two
kidneys. Do the renal nerves in this case drive away and repel
the blood that comes to the kidneys to be subservient to the
secretion of urine ? or do they not rather totally prevent the
secretion from the blood by causing spasm of the secreting ves-
sels? Truly, although there are numerous facts which teach
us that a stimulus may cause the fluids to be drawn to a
locality, there is hardly one to show that the nerves have the
opposite property of repelling the fluids.

SECTION V. HAVE THE NERVES ANY INFLUENCE IN SECRETION ?

In considering the causes which operate in producing such
varied secretions from the same blood, Boerhaave does not
detail how great a share the nerves may have in that function
of the animal economy.^ The illustrious Haller, in his notes to
the lectures of Boerhaave,^ conjectures that the nerves operate
in the secretion of the fluids, since they surround the vessels
of the viscera like sphincters, and thus either delay or pro-
mote secretion. It has already been stated why tliis eminent
man withdrew the doctrine as to the sphincters and loops of
the nerves, but he shows that the secretions and excretions
have a close connection with the nerves, when he treats on
the greater or less irritability of the excretory ducts.^ The
celebrated Tissot also devotes an entire section of his work on
the functions and diseases of the nerves, to the secretions, for
the purpose of demonstrating how much these latter are de-
pendent on nervous influence.

» Instit. Med., Nro. 253. » Note (14) vi.

' De Part. Corp. Hum. Fabr. et Ubu, lib. vii, sect, iii, § xii.

SECT, v.] INFLUENCE OF NERVES IN SECRETION. 419

In truths since it has been shown how great is the influence
of the nerves on the vessels, in virtue of which stimuli can
excite a more copious flow of fluids to a part, we infer that the
same thing occurs in the secreting viscera, which consist
almost entirely of vessels. So soon, therefore, as by nervous
action the fluids are more copiously attracted to secreting
viscera, the secretions are necessarily increased. Moreover,
since the nerves have the property of causing spasms, or con-
traction of the capillaries, it is manifest that the secretions
may be diminished, or entirely interrupted by the influence of
the nerves, the secreting vessels being entirely closed by con-
striction. Illustrations, confirmatory of this doctrine, have
been already brought forward.

But it may further be asked, is the influence of the nerves
on the fluids so great, either at the time of secretion, or when
secreted, that it can modify, or alter them, or entirely change their
nature ? Thaer^ seems to have held an opinion somewhat to this
eff'ect, when he observes, that in fevers the blood becomes some-
times putrid and dissolved, sometimes acrid, again imperfectly
coagulable, or in some other way altogether changed from the
healthy condition preceding the fever. Musgrave^ attempts
to prove, from many facts, that the fluids are vitiated by
irritation of the nerves. In the first place, he brings forward
the experiments of Haller, who observed the contents of
the stomachs of rabbits to become putrid and thoroughly
tainted, in a short time, after tying the eighth pair of nerves ;
and that a very ofi*ensive suppuration was also brought on in
the foot by tying the nerve. Next, he shows that a vomiting
of fetid bilious matter has been excited by an afi'ection of the
head, and by the irritation of calculi passing along the ureters.
Further, diarrhoea is often excited by mental emotion, and this,
indeed, because that afi'ection of the nerves renders the secre-
tions more acrid and loose. The milk of a nurse, aff'ected
with anger, immediately acquires an unpleasant taste, and
becomes injurious to the child. The bite of an enraged animal
is difficult to cure, and is often followed by bad consequences.
He thinks he can explain why, when blood is drawn, it is
often inflammatory in the first cups, and less so in the later,

' De Usu System. Nervosi in Febribus, § xxxviii.
* Betrachlung iiber die Nerven, 3ten Hauptst.

420 FUNCTIONS OF THE NERVES. [cii. in.

on the liypothesis that the febrile irritation being diminished
after the first cupfuls are drawn^ the blood that remains in the
body is very similar to healthy blood. Clearer illustrations
are given by the celebrated Gaubius, and ^hich prove that all
the fluids of the body may be rapidly altered and vitiated
through the nerves. He observes/ " Ye wonder, my hearers,
and justly, at the great number of evils, which anger only
sheds over the body, as from Pandora's box. Nor is it
difficult to discover the origin of so great an evil, for in
addition to the fact, well established, that the motive forces
diffused through all the organs of the body are very powerfully
excited by that affection of the mind, and consequently that
the whole organism and the internal viscera, as well as the
vessels and their contained fluids, are agitated by most violent
movements, it is shown, beyond doubt, by an almost incredible
number of observations, that the natural properties of the
juices may be so altered, that with astonishing rapidity, the
bland becomes acrid, and the salubrious, hurtful, — nay, truly
virulent. Do you doubt this ? I give you the example of a
hysterical woman, who being seized, when in a passion, with
her disease, vomits vitiated bile of every colour and acridity;
of a nurse, whose breasts, when angry, supply poison instead
of food to the infant, causing death with horrid convulsions.
Tame domestic animals, when provoked, not only contract rabies
themselves, but transfuse it with the foaming poison of their
saliva into the man bitten by them. Two dunghill cocks fight
ferociously with each other, as is their habit ; a man interferes
to separate them; he is bit by one of them, and dies of
hydrophobia. You will, perhaps, allege in reply, that there is
a difference between man and brutes ; I will therefore give you
examples of our own species. A soldier quarrels with a woman,
who bites him in the hand; he is seized with rigor and dies. An
Italian youth, excited by rage, and unable to revenge himself,
bites his own hand, and is seized with a deadly fear of water,
as if bitten by a rabid dog. I am aware, and I do not hesitate
to confess it, that I am ignorant of the mode in which such
pestilent corruptions of the fluids are so suddenly excited ; but
this I think to have been attained by me, that you can under-
stand that the whole foundations of life are shaken by this
* Sermo alter de Regimine Mentis quod Medicorura est. Edit. Argent., 1776, p. 96.

SEC. VI.] INFLUENCE OF NERVES ON ANIMAL HEAT. 421

passion, and consequently that there is no function of the
human economy, which can easily resist so great an evil."
It seems, indeed, possible, that the nerves, when irritated by
anger, may, in virtue of their influence on the secreting
viscera, render the secretions irregular, disordered, and impure,
although we cannot determine in what that impurity may
consist, which is added to the secretions by the nerves, when
irritated by anger ; and, consequently, the saliva secreted and
excreted under such circumstances, and inserted in a wound
inflicted by an enraged animal, may possibly prevent its cica-
trization, and subsequently induce horrid evils. Thus, also,
the milk of an angry nurse being disordered and rendered im-
pure, may become hurtful to the infant. It appears more diffi-
cult to explain what share the nerves have in inducing a morbid
coagulation of the blood, or a putrid deliquescence, acrimony,
putridity, and impurity of the fluids in a cancerous or gan-
grenous part, &c. ; these things posterity may inquire into.

SECTION VI. DO THE NERVES EXERT ANY INFLUENCE IN THE

PRODUCTION OF ANIMAL HEAT?

What opinions various authors have expressed concerning the
source and maintenance of animal heat are well known; I think,
therefore, I need not detail them. Among them all, that was best
received which maintained that animal heat arises from the
attrition of the particles of blood with each other, and with the
walls of the vessels. After Haller had weighed all the various
views, he adopted the theory of Boerhaave, according to which
animal heat is acquired by friction, observing : '' Hitherto it
seems to me by far the most probable, that the blood acquires
heat from motion.^' ^ In the meanwhile, he appears not to
have disagreed altogether with the opinion of those who main-
tained that the nerves have some share in the production of
animal heat ; for he observes, in another place : " I refer heat,
which arises from friction, to stimulus.^^^ The objections to the
doctrine, that friction is the sole cause of animal heat, raised
by De Haen,^ seem to have particularly influenced recent

' De Part. Corp. Hum. Fabr. et Usu, torn, iv, p. 253.

^ Ibidtm, p. 159.

3 Rat. Med., torn. iv. p. 248.

422 FUNCTIONS OF THE NERVES. [ch. hi.

eminent writers, who have sought for the source of animal
heat in the nerves^ and not in the friction of the particles of
the blood with each other, or with the sides of the vessels.
Amongst these were Caverhill^ and Roederer.^ Wrisberg^
followed the latter, and seems to have wished to corroborate
his doctrine by his own arguments and observations. In
comparing animals with vegetables, he saw that it was the
nervous system that was wanting in the one and present in
the other ; and since animal heat was enjoyed by animals, and
not by vegetables, it seemed to him that there existed some
connection, between a nervous system and animal heat.
Further, he thought this was confirmed by the fact, that the
passions, which excite the nervous system, increase animal
heat, but that those which depress the nervous system induce
cold. In further corroboration he observes, that if the back be
turned towards the fire, and the spinal marrow warmed, warmth
is rapidly transmitted along the nerves arising from it to all
parts of the body ; while, on the contrary, if the front of the
body be towards the fire, the body is not warmed so quickly.
Thaer also thought that this theory of the dependence of the
animal heat upon the operation of the nerves, was not deficient
in probability.* Musgrave also maintained, that animal heat
arises neither from the intestine motion of the fermenting
blood, nor from the friction of the blood against the sides of
the vessels, but from irritation of the nerves, whether from an
external agent applied to the nerves, as in inflammation, or an
internal irritant, as anger.^ La Roche was of the same opinion,
and attempted to reconcile his views with those of Haller, for
he conjectured, with Newton, that the nervous fluid is aetherial,
and that its oscillatory motion in the nerves is the proximate
cause of animal heat, the circulatory motion of the blood in
the vessels being only secondary, and by continually stimulating
the nerves, exciting the oscillation of the nervous fluid in them;

1 In Haller. de Part. Corp. Hum. Fabr. et Usu, torn, iv, p. 248.

2 In Programmate de Animalium Galore. Ad Diss. CI. Grimm, de Visu. Got-
tingse, 1758.

3 In Program, de Respiratione prima, Nervo phrenico, et Calore animali.
Gottingae, 1763. It has also been printed in Sandifort's ♦Thesaurus Diss. Med.,'
tom. ii.

* De Actione Systematis Nervosi in Febribus. Gottingae, 1774, p. 83.
' Op. citato.

SECT. VII.] NECESSITY OF NERVES TO NUTRITION. 423

which oscillatory motion is the proximate cause of heat.^
Cremadells^ may be also mentioned, who maintained that
animal heat is directly generated, kept up, and increased by
the vital principle, by which principle he explains all those
phenomena of the animal economy, which by others are attri-
buted to the nervous system. Schaffer ^ is another writer, who
rejecting the doctrine that the cause of animal heat consists in
the fermentation of the blood, or in its friction against the
sides of the vessels, refers it to a certain vital principle, which
is in the nerves.

Although the doctrine, which teaches that the nerves have
a share in the production of animal heat, is not destitute of
probability, yet the arguments hitherto advanced do not fully
establish it. Perhaps the cause of animal heat is more complex,
and cannot be attributed to the nerves only. Undoubtedly
there remain many things to be known before we can determine
what is the true cause. Especially we ought to wnit and see
what the industry of distinguished men may discover"^ respecting
inflammable bodies, fire, light, heat in general, and animal heat
in especial; taught by these, posterity may be enabled to
decide more accurately respecting the cause of animal heat.

SECTION VII. ARE THE NERVES NECESSARY TO NUTRITION ?

By the term nutrition, all physiologists understand the con-
servation of the body, which is accomplished by the action of
certain powers inherent in our body, and which have the power
of converting food and drink iuto a fluid, analogous to the
constituents of our body, termed the nutritive juice, and thereby

' Analyse de Fonct. du Syst. Nerv., torn, ii, chap, xviii, xix. Geneve, 1778.

» Nova Elem. Physiol. Romae, 1779.

^ Erster Versuch aus der theoretischen Arzneikunde iiber Bewegung und Mischung
der Safte. Nurnberg, 1782.

* Crawford, ' Experiments and Observations on Animal Heat, and the Inflammation
of Combustible Bodies.' London, 1779. This little work is reviewed in the Got-
tingen Magazine, part v, of the past year. The celebrated Forster also quotes it in
a very beautiful article inserted in the same periodical. (See Getting. Magazin, Iten
Jahrgangs, 2tes Stiick : *' A theory proposed to explain the cause which occasions
the leaves of plants to purify the foul air in sunlight, but to vitiate the air in the
shade.") The celebrated Baldinger promises (in the new Magazine) that the illus-
trious Landriani is about to give his experiments on light and animal heat.

424 FUNCTIONS OF THE NERVES. [ch. hi.

to maintain its continued existence by restoring^ the solid
and fluid particles worn away and dissipated by the movements
going on. It is necessary to the proper performance of this
function, that there be not only a due supply of food of a proper
quality, but also that those various viscera be healthy, which
carry on digestion, and by the combined function of which, the
food is converted into chyle, and rendered fit to be mixed with
the blood. Yet when this process is completed, nutrition is
not accomplished, but only the nutritive materials supplied to
the blood, from which the wasted portion of our body may
be restored; and the reparation of the lost material takes
place by some admirable arrangement, and by a power as yet
unknown, which knows how to restore to each portion of the
body its lost particles, to apply them, and cause them to
adhere.

Many physiologists, both ancient and modern, have main-
tained that nutrition is carried on through the nerves. Thus
Sylvius, Willis, Glisson, and others, considered that there were
two fluids in the nerves, one thick and albuminous, subservient
to nutrition, the other very thin and spirituous, intimately
connected with the former, and subservient to sensation and
movement. The school of Boerhaave allowed one nervous fluid
only, and that most refined and active ; and held, not only that
sensation and motion were performed by this, but nutrition also
accomplished, when that fluid experienced the final elaboration
by which it was rendered similar to our organism. Haller
denied this nutritive property of the nervous fluid, because he
thought that our body must be nourished with a less spiritual
and more viscid fluid than the nervous fluid. ^ Marherr followed
Haller, and maintained the same doctrine.^ Tissot also adopted
it,* although in another place he attributes with Boerhaave a

• This doctrine of attrition, and the destruction of the solid particles thence
arising, has been maintained by many distinguished persons, but too exclusively,
T think, as has been correctly shown by Kemme in his Essay entitled, ' Zweifel und
Errinnerungen wider die Lehre der Aerzte von der Ernahrung der festen Theile.'
Halle, 1778. This wearing away and loss of substance manifestly does not occur in
the nerves and brain, since the abrasion of so sensitive a substance could not occur
without pain, or, at least, without an unpleasant sensation.

2 Elem. Phys,, tom. iv, p. 405.

3 Prajlect. ad Boerh. Inst., torn. ii.

< Yon Nerven, Iten Bandes, 2ter Theil, § 271.

sECT.vii.] NECESSITY OF NERVES TO NUTRITION. 425

nutritive property to the nervous fluid, observing:^ " If the nerves
were not tubuli pervious to the nervous fluid, they could not be
nourished ; for the vessels surrounding the nerves on all sides
give nutrition to their cellular investment only, but the medullary
tubuli are nourished by the nervous fluid/' Tissot, moreover,
specifies three modes in which the nerves co-operate in nutrition.
In the first place, they pour animal spirits into the stomach,
intestine, lacteal vessels, &c., carry on digestion conjointly with
the gastric juice, impress an animal character on the food, and
act as a stimulus to the stomach itself. Secondly, they cause
the animal spirits to concur in nutrition by exciting muscular
action, and promoting digestion : thirdly, they promote the
secretion of gastric juice, saliva, &c.^ Tralles has lately again pro-
mulgated the doctrine denied by Haller and others, of a nutrient
property in the nervous fluid, observing that if a nerve be tied,
compressed, or destroyed, not only are motion and sensation
in the muscle destroyed, but also nutrition, and atrophy comes
on ; whence he thinks, the conclusion is undoubted, that some
fluid passes from the brain along the nerves to the muscles, by
which not only the muscles but the nerves also are nourished.^
But all theories founded on the hypothesis of a nervous fluid
are untenable, if the hypothesis itself be demonstrated to
be untrue.

For the better understanding what share the nerves have
in nutrition, it is advisable with Tissot to divide the nutritive
process into the two processes of assimilation, and the ap-
plication of the nutrient materials. No one can deny that
the nerves concur, at least remotely, in the assimilation and
transformation of food into nutrient material ; promoting, for
example, the secretion of saliva, of the gastric, intestinal,
and pancreatic juice, and of bile; by producing action of the
muscles subservient to mastication and deglutition ; by exciting
the movements of the stomach and intestines, nay, even those
of the heart, of respiration, and of the whole body, inasmuch
as all these actions concur in the elaboration of the nutrient
fluid. But the question arises, have the nerves also a share
in restoring the lost particles, and therefore in forming and

' I])id. ill Iten Bande, Itcn Theile, § 153.

^ Iteii Bandes, 2ter Theil, j 269.

^ See Kemme's Zwcifel uud Eniiinerun}?en.

4.26 FUNCTIONS OF THE NERVES. [ch. hi.

repairing our bodies? Wonderful, indeed, is that property
whereby the adaptation of nutrient material to each portion of
the body is effected. This is done with such skill and wisdom,
that suitable and analogous particles are applied to every
part, and thus neither the composition nor character of their
constituent particles, nor the form or structure of the nourished
parts themselves, are disturbed by the continuous apposition of
new molecules. Particles which are adapted to the composition
of muscles or cartilage, are not deposited in bones, otherwise
bones would gradually lose their proper character, and become
cartilaginous or muscular. For these reasons, Blumenbach
correctly maintains,^ that generation, nutrition, and reproduc-
tion are effects or modifications of one and the same force,
which forms in the first, maintains in the second, and restores
in the third. ^

' Von dem Bildungstriebe, ^ 7. Gottingen, 1781.

2 This expression, that the foetus is formed by generation, and not evolved from a
germ created from the beginning of the world, should not appear to the indulgent
reader altogether new ; for Casper F. Wolff has long ago much weakened the system
of evolutions set up by Bonnet and Haller, and established in its place the doctrine
of epigenesis of the ancients. Haller, it is true, continued to maintain his views in
his * Element. Physiol.,' tom. viii ; but after having carefully weighed his arguments,
I do not think them sufficient to estabUsh the doctrine of evolution, and confute that
of epigenesis. Hybrid animals, malformations of the parent transmitted to the off-
spring, the reproduction of whole structures, especially of certain animals, as well as
the generation of polypes and certain vegetables by cuttings, all confute the doctrine
of evolution, and prove that those germs in which, from all time, entire animals or
parts of them are marked out, do not exist; but that there must be some vis
structrix, which constructs the bodies of animals, however complicated, from suit-
able materials that it has ready at hand. I have treated of this more fully in my
dissertation on the system of generation, inserted in the Second Fasciculus of my
* Adnotationes Acaderaicae' for 1781. In the same year in which my dissertation
appeared, that elegant tract by Blumenbach, Professor at Gottingen, was published,
in which this vis structrix, or nisus formativus, as he terms it, is proved to exist,
and the doctrine of evolution by germs is rejected. This essay gives the greater
support to the doctrine of epigenesis, because the distinguished author himself
brought forward much in favour of the hypothesis of evolution in his work ' De Generis
Humani Varietate Nativa,' (Gotting., 1776 ;) but now, having had an opportunity of
observing the phenomena of reproduction in polypes, and feeling the weight of the
arguments in favour of epigenesis, has adopted it in place of the system of evolution.
He maintains that in every animal and vegetable organism, there is intimately
connected with it, during its whole life, a certain innate and ever-acting instinct,
which he terms the nisus formativus, in virtue of which animals and vegetables at-
tain their proper and fixed form ; when this is attained, the same force maintains it ;

SECT. VII.] NECESSITY OF NERVES TO NUTRITION. 427

For that wondrous force, which forms a foetus similar to the
parents, out of the semen of the male projected into the uterus,
and that part which the female contributes, whether it be an
ovum or semen — that force, I say, is not exhausted in the forma-
tion of a puny foetus,^ but continues active in it, and thus
carries forward the human body through all its phases of growth
and age, to the perfect state, fittingly replaces from the nutrient
material, the particles worn away and dissipated by the con-
tinual movements and operations of life, nay, regenerates in a
great measure portions of skin lost by violence, consolidates
wounds, forms the callus of bones, &c. To this are owing
those so-called efforts of nature, by which she attempts to
preserve health and remove disease. In some animals, as
lizards, for example, this vis structrix is so efficient, that it repro-
duces in them tails, extremities, and jaws, together with their
bones, muscles, vessels, and nerves.^ Eminent philosophers
readily perceived, that these and many other phenomena observed
in the animal organism, and also in the vegetable, can be
referred neither to the wisdom of a rational soul, nor to any
mechanical and physical laws as yet known ; and, consequently,
they have very properly termed that wonderful cause innate in
the animal and vegetable organism, the vital principle, inas-
much as to that, as a proximate cause, both animal and vegetable
owes its life ; which is also distinct from the thinking principle,
for it far excels this in wisdom, and is not subject to it, and
has higher faculties, than it has hitherto been agreed that
bodies possess. The vital principle is not some simple force,
but seems to be compounded of various unknown forces co-
operating together ; amongst which unknown forces so co-ope-

and when injured, repairs it as much as may be. Very lately, also, Metzger, Professor
at Kbnigsberg, in the first volume of his work entitled ' Vermischte Medicinische
Schriften,' (Konigsberg, 1782,) weakens the force of the arguments adduced by
Haller in favour of evolution ; and in the supplement to the second volume, declares
his assent to the views of Blumenbach. He differs, however, in thinking that the
nisus formativus cannot be considered as distinct from the vis plastica of the ancients
and the vis essentialis of Wolff, since it so much resembles them ; so that the vis
essentialis is primary, and analogous to the vis vitalis of physiologists, which con-
stitutes life, both in animals and vegetables: secretion, nutrition, generation, and
reproduction, are portions, or rather branches, of this.

' See Fasciculus ii of my ' Acad. Adnot.,' p. 31.

^ See my * Comment, de System. Generat.*

428 FUNCTIONS OF THE NERVES. [ch. iti.

rating for the formation of the vital principle in man and many
animals, the vis nervosa seems to claim an important position,
since in many operations ascribed to the vital principle, the
function of the nerves is predominant. The nerves appear
also necessary to the application of nutrient material, and the
reproduction of cut off parts, because if the nerves of a part be
injured, its nutrition is impaired, and because the animals
which are tenacious of life and of irritability, also possess a
remarkable property of reproducing separated parts.

Since vegetjibles and some animals generate, are nourished,
and reproduce cut-off parts, and, consequently, possess a vital
principle, although they appear to be destitute of a nervous
system, it follows that the vital principle may exist independently
of the vis nervosa in plants and certain animals not endowed with
nerves ; but it does not hence follow, that the vital principle can
exist without the vis nervosa in man and animals endowed with
a nervous system. For nature seems to have bound all parts
of our body together by such an agreement and combination,
that one part assists another, and one cannot easily exist without
another ; and especially the vis nervosa seems to be necessary
to the constituting of the vital principle in our own body and
in the bodies of animals endowed with a nervous system,
although it appears that the principle may exist without the
vis nervosa in plants and animals that have no nervous system.
There are certain animals and vegetables which reproduce their
kind without distinction of sex, but is the congress of both
sexes, therefore, not necessary to generation in man and other
animals and vegetables?

CHAPTER IV.

THE FUNCTIONS OF THE SENSORIUM COMMUNE.

SECTION I. WHAT IS THE SENSORIUM COMMUNE, WHAT ITS

FUNCTIONS, AND WHAT ITS SEAT?

The external impressions which are made on the sensorial
nerves are very quickly transmitted along the whole length of
the nerves, as far as their origin j and having arrived there, they
are reflected by a certain law, and pass on to certain and
corresponding motor nerves, through which, being again very
quickly transmitted to muscles, they excite certain and definite
motions. This part, in which, as in a centre, the sensorial
nerves, as well as the motor nerves, meet and communicate,
and in which the impressions made on the sensorial nerves are
reflected on the motor nerves, is designated by a term, now
adopted by most physiologists, the sensorium commune.

Distinguished men have not agreed as to the seat of the
sensorium commune. Bontekoe, Lancisi, De La Peyronie
have placed the sensorium commune in the corpus callosum ;
Willis derived the perception of sensation and the source of
movements from the corpora striata ; Des Cartes attributed the
function of the sensorium commune to the pineal gland ;
Vieussens to the centrum ovale j Boerhaave decided that aggre-
gate of points to be the sensorium commune, in which all the
sensory nerves terminate, and from which all the motor nerves
arise, and accordingly placed it in the medulla fornicata, sur-
rounding the cavity of the ventricles.^ In a later work, ' De
Morbis Nervorum,^ Boerhaave places the sensorium commune
in the boundary line of the medullary and cortical substance,
which opinion Tissot thought to be extremely probable, regarding
it as confirmed by the observations of Wepfer.^ Mayer seems
to place the sensorium commune in the medulla oblongata;^
that distinguished man, J. D. Metzger, appears to be also of

' Praelect. Acad, in proprias Inst, cum Notis Halleri, torn, iv, § 574.

'■' Abhandl. iiber Neiven und Nervenkrankh. Iten Bandes, 2ter Tlieil, § 236.

3 Abhandlung vom Gehirn, Ruckenmark, &c., Seite 34 — 38.

430 FUNCTIONS OF THE SENSORIUM COMMUNE, [ch.iv.

the same opinion;^ the celebrated Camper said, that if the
sensorium commune has a seat at all, it ought to be in the
pineal gland, and in the nates and testes, and that, therefore,
the opinion of Des Cartes was not so very absurd.^ It certainly
does not appear that the whole of the cerebrum and cerebellum
enters into the constitution of the sensorium commune, which
portions of the nervous system seem rather to be the instru-
ments that the soul directly uses for performing its own actions,
termed animal ; but the sensorium commune, properly so called,
seems not improbably to extend through the medulla oblongata,
the crura of the cerebrum and cerebellum, also part of the
thalami optici, and the whole of the medulla spinalis; in a
word it is co-extensive with the origin of the nerves. That
the sensorium commune^ extends to the medulla spinalis is
manifest from the motions exhibited by decapitated animals,
which cannot take place without the consentience and interven-
tion of the nerves arising from the medulla spinalis ; for the
decapitated frog, if pricked, not only withdraws the punctured
part, but also creeps and leaps, which cannot be done without
the consensus of the sensorial and motor nerves, the seat of
which consensus must necessarily be in the medulla spinalis
— the remaining portion of the sensorium commune.

The reflexion of sensorial into motor impressions, which
takes place in the sensorium commune, is not performed ac-
cording to mere physical laws, where the angle of reflexion is
equal to the angle of incidence, and where the reaction is equal
to the action ; but that reflexion follows according to certain
laws, writ, as it were, by nature on the medullary pulp of the
sensorium, which laws we are able to know from their eff'ects
only, and in nowise to find out by our reason. The general
law, however, by which the sensorium commune reflects sen-
sorial into motor impressions, is the preservation of the individual;
so that certain motor impressions follow certain external impres-
sions calculated to injure our body, and give rise to movements
having this object, namely, that the annoying cause be averted

' Advers. Med., p. 15 ; Vermisch. Schrift., Iten Bandes, Seite 56.

' Kleine Schriften, (Leipzig, 1782,) Iter Band; Nachricht von der Zergliederung
eines jungen Elephanten., § 21.

^ Marherr contends that the medulla spinalis ought also to be referred to the
sensorium commune in * Praelect. ad Inst. Med. Boerhaavii,' tom. ii, p. 404.

SECT. I.] SEAT OF THE SENSORIUM COMMUNE. 431

and removed from our body ; and vice versa, internal or motor
impressions follow external or sensorial impressions beneficial
to us, giving rise to motions tending to the end that the
agreeable condition shall be still maintained. Very many
instances which might be adduced, undoubtedly prove this
general law of the reflexions of the sensorium commune, of
which it may be sufficient to mention a few. Irritation being
made on the internal membrane of the nostrils excites sneezing,
because the impression made on the olfactory nerves by the
irritation is conducted along them to the sensorium commune,
there by a definite law is reflected upon motor nerves going to
muscles employed in respiration, and through these produces a
strong expiration through the nostrils, whereby the air passing
with force, the cause of the irritation is removed and ejected.
In like manner it happens that when irritation is caused in the
trachea by the descent of a particle of food, or a drop of fluid,
the irritation excited is conducted to the sensorium commune,
and there reflected on the nerves devoted to the movement of
respiration, so that a violent cough is excited, a most suitable
means for expelling the cause of irritation, which does not
cease until the irritant be ejected. If a friend brings his
finger near to our eye, although we may be persuaded that
no injury is about to be done to us, nevertheless the impres-
sion carried along the optic nerve to the sensorium commune
is there so reflected upon the nerves devoted to the motion
of the eyelids, that the eyelids are involuntarily closed, and
prevent the offensive contact of the finger with the eye. These
and innumerable other examples which might be brought
forward, manifestly show how much the reflexion of sensorial
impressions into motorial, effected through the sensorium com-
mune, has reference to maintaining the conservation of the body.
Wherefore, Tissot justly enumerates the action of the sen-
sorium commune amongst those powers, the sum and co-
ordination of which constitute the nature of our living body.^

Since the principal function of the sensorium commune thus
consists in the reflexion of sensorial impressions into motor,
it is to be noted, that this reflexion may take place, either

' Von Nerven, 2ten Bandes, 2ter Theil, § 55, in the first note; and ibidem, § 6
No. 6 ; Thaer's dissertation already referred to, ' De Actione Systematis Nervosi in
Febribus,' and especially §§ viii, ix, &c,, should also be read.

432 FUNCTIONS OF THE SENSORIUM COMMUNE, [ch.iv.

with consciousness or without consciousness. The movements
of the heart, stomach, and intestines, are certainly in nowise de-
pendent on the consciousness of the soul, for whilst no muscular
movement can be excited, unless a stimulus applied to the sen-
sorial nerves passes by a peculiar reflexion to the motor nerves,
and excites contraction of the muscle, it is at the same time
certain that the reflexion of the impressions suitable for exciting
those movements, if it takes place in the sensorium commune,
is effected without consciousness. But it is a question whether
these impressions, in order that they may be reflected, do really
travel so far as the sensorium commune, or, without taking this
long circuit, are reflected nearer in the ganglia, from whence
these parts derive many nerves ? This matter is further to be
considered afterwards. But that reflexions of sensorial im-
pressions into motor are effected in the sensorium commune
itself while the mind is altogether unconscious, is shown by cer-
tain acts remaining in apoplectics deprived entirely of conscious-
ness ; for they have a strong pulse, breathe strongly, and also
raise the hand, and very often unconsciously apply it to the
affected part. The sensorium commune also acts independently
of consciousness in producing the convulsive movements of epi-
leptics, and also those which are sometimes observed in persons
buried in profound sleep, namely, the retractions of pricked or
irritated limbs, to say nothing of the motion of the heart and
the respiratory acts. To this category also belong all those
motions which remain some time in the body of a decapitated
man, or other animal, and are excited when the trunk, and par-
ticularly the medulla spinalis, are irritated, which motions cer-
tainly take place without consciousness, and are regulated by
the remaining portion of the sensorium commune existing in
the medulla spinalis. All these actions flow from the organism,
and by physical laws peculiar to the sensorium commune ; and
are, therefore, spontaneous and automatic. The actions taking
place in the animal body, with accompanying consciousness, are
either such as are independent of volition, or such as the mind
can restrain and prohibit at pleasure ; the former being governed
by the sensorium commune alone, independently of the mind,
are as much automatic as those of which the soul is unconscious.
Of this character are sneezing from an irritant applied to the
nostrils, cough from an irritant fallen into the trachea, vomiting

SECT. II.] CONSENSUS OF THE NERVES. 433

from a titillation of the fauces^ or after taking an emetic ; the
tremors and convulsions in St. Vitus^s dance, and in a paroxysm
of intermittent fever, &c. Those actions, however, which the
soul directs or limits by its own power, even although the
sensorium commune has its share in producing them, are never-
theless called animal, and not automatic, and concerning them
we treat in the next chapter.

SECTION II. DOES EVERY CONSENSUS OF THE NERVES TAKE

PLACE THROUGH THE SENSORIUM COMMUNE ONLY?

Since the nerves depend so much on each other in performing
their functions, so that one is required to regulate the action of
another, and one to come to the help of another as it were,
it is manifest how necessary it is that there should be a consensus
of the nerves, and how necessary is that part of the nervous
system in which this consensus takes place ; for if this part be
destroyed, presently all those actions to the production of which
the consensus of many nerves is required necessarily cease. I
will not waste time in narrating examples of consensus of the
nerves, for the latter is abundantly treated of in physiology and
pathology, and examples of it are ex professo related by those
highly distinguished men Whytt^ and Tissot.^ I will, however,
direct consideration to one question, namely, whether the nerves
communicate with each other in the sensorium commune only,
or whether there be other localities besides the sensorium com-
mune, in which the consensus of at least some nerves takes
place? Willis taught, that the consensus took place not only
through the brain, but through the connections and com-
municating branches of the nerves, which we perceive to be
pretty numerous in their course ; Vieussens ascribed the con-
sensus of the nerves to both their ganglia and anastomoses,
and Boerhaave, Bergen, Vater, Buchner, &c., were also of a
similar opinion, as well as the celebrated Meckel in his essays,
' De Nervo Quinti Paris,' and ' de Nervis Faciei.' Gasser
followed him -^ and lastly, Camper also explained the consensus
of the nerves by their communicating branches. Eminent

1 On Diseases of the Nerves. See all his practical works in German.

» Von Nerven, 2ten Bandes 2ter Theil, lOtes Kapit.

^ In the dissertation of George Egger, ' De Consensu Nervorum.' Viennae, 1766,

38

434 FUNCTIONS OF THE SENSORIUM COMMUNE, [ch.iv.

men were also of a contrary opinion ; that is to say, that the
nerves do not communicate with each other through their
anastomoses, but in the brain only. Amongst these were
Perault, Astruc, Kau Boerhaave, Haller, Whytt, Van Swieten,
Monro, Marherr, Thaer, La Roche, and Martin j^ add to these
Tissot,^ who specially lays stress on the following arguments of
Whytt: firstly, that all the nerve-fibrils from their commence-
ment to their termination are entirely separate from each
other, so that they have no communication, and are connected
with each other by their investing membrane only. Secondly,
that there is sympathy between parts, the nerves of which
have no anastomoses with each other. Thirdly, that there
ought to be many sympathies of parts, the nerves of which
are seen to be closely interwoven and connected with eacli
other, and yet no such sympathies are manifested. Fourthly, he
adds also to these arguments of Whytt, another, namely, that
if the trunk of a nerve be divided, the consensus of its
branches is destroyed. That eminent man, therefore, attempts
by these arguments to establish the doctrine, that consensus
of the nerves takes place in the sensorium commune only, and
in no degree in the nerves. Yet nevertheless, in the next
page^ he observes, that it may be assumed as a demonstrated
truth, that consensus is most frequently noted in the nerves
between which the communicating branches are numerous;
still he does not believe that consensus takes place through
these communicating branches, but that they contribute some-
thing to it, of the nature of which we are as yet ignorant.

It is difficult to decide on a point regarding which so many
persons have disagreed, and which is as yet involved in so much
obscurity. The first glance at the anastomoses or communi-
cations of the nerves leads us to think, that they are consti-
tuted to maintain some consensus and interchange of their
functions, and no other probable reason can be assigned for so
many anastomoses of the nerves and of their funiculi.* With
regard to the arguments which eminent men have advanced in
favour of a contrary doctrine, they establish nothing as far as I

1 Instit. Neurolog., sect, i, p. 87.

^ Loc. cit.

3 2ten Bandes 2ter Theil, § 6, Nro. 4.

* These may be seen delineated in my treatise * De Structura Nervorum.'

SEC. III.] CONSENSUS OF NERVES IN THE GANGLIA. 435

perceive, for the first argument of Whytt is founded on this,
that every nerve-fibril is a canal continued from its commence-
ment to its termination without any connection with another ;
but since this supposition is nothing more than an improbable
conjecture, to which anatomy is opposed, for the pulp of the
nerves is found to be rather granular than tubular, we cannot
allow it to have any demonstrative force. The second argument,
which alleges that there are nerves which are consentient
in their functions, but have no anastomoses in their whole
course, proves, indeed, that these nerves communicate only in
the sensorium commune^ but does not prove that the anastomoses
of other nerves do not contribute to their necessary inter-
communication. As to the third argument, that there should
be many sympathies displayed by those nerves which have
many anastomoses, and yet are these not displayed, we would
answer in the words of Tissot himself,^ that we are not as yet
informed as to all the sympathies and consensus of nerves,
and therefore there may be many which have hitherto escaped
the diligence of observers. From which, therefore, I think we
may conclude, that although the principal and greatest consensus
of the nerves takes place in the sensorium commune, it is not
possible to deny some share in connecting and combining the
functions of the nerves to their anastomosing and communicating
branches.

SECTION III. DOES CONSENSUS OF THE NERVES ALSO TAKE PLACE

IN THE GANGLIA?

The functions of the ganglia of the nerves have also been
hitherto involved in much obscurity; so that, after the labours
of such great men to determine their nature and use, scarcely a
spark of the light necessary to elucidate that mystery of nature has
appeared. The celebrated Tissot^ has so learnedly and elegantly
treated of this matter, as well as of the consensus of the nerves,
that I think it altogether superfluous to consider the structure
and functions of the ganglia in complete detail. Having
weighed all the opinions that have been advanced regarding the
functions of the ganglia, he esteems that which Johnston has
propounded as the most probable, namely, that the ganglia ren-

• Instit. Neurolog., § 6, No. 5.

' Iten Bandes 2ter Theils, Eilfter Artikel.

436 FUNCTIONS OF THE SENSORIUM COMMUNE, [ch.iv.

der the nerves -whicli arise from tliem independent of the will,
and therefore that the heart and intestinal canal are not subject
to volition, since they receive their nerves from the ganglia of
the intercostal [great sympathetic] nerve. Tissot thinks, that
the doubts advanced by Haller, and more fully entered into by
Haase, are not at all unanswerable, and are indeed of that cha-
racter, that they may be easily made to comport with the doc-
trine of Johnston. Pfeffinger has also studiously investigated
this theory as to the uses of the ganglia, and approved of it in
an elegant dissertation, ^De Structura Nervorum,^ published
in 1782.

It is not an improbable conjecture, therefore, that the
ganglia found around the nerves act as a sort of gentle ligature
or compress, so that the connection between the two extremities
of a nerve is so far interrupted, as to prevent the impressions
made on the one extremity of the nerve being communicated
through the ganglion to the other extremity ; yet the com-
munication of all impressions is apparently not altogether
interrupted; for if they be powerful, they appear to pass
through the ganglia, and to be transmitted forward along the
length of the nerves, but with broken and diminished force.
From this it appears to be possible to understand, why the
mind has no immediate control over the movements of the
heart, stomach, and intestines, namely, because the impressions
made by the will on the origins of the nerves do not appear to
pass through the ganglia of the intercostal, or great sympathetic
nerve, to the parts mentioned, which derive their nerves princi-
pally from the intercostal. For this reason it also appears, that
although, when the medulla spinalis is irritated, all the muscles
are spasmodically contracted, yet the movements of the heart,
stomach, and intestines, are scarcely, if at all, accelerated, since
the impression of the stimulus applied to the medulla spinalis
cannot be transmitted to the intercostal [great sympathetic]
nerve through its ganglia. But eminent men testify, that they
have seen the motion of the heart increased, and the heart when
at rest excited into action by irritation of the medulla spinalis, as
also certainly that from too great emotion, — anger, for example,
— the hearths action is immediately accelerated ; whence it neces-
sarily follows, that the impressions of a stimulus from the brain
and spinal cord may pass through the ganglia of the intercostal

SEC.iii.] CONSENSUS OF NERVES IN THE GANGLIA. 437

nerve j but that it is necessary that these impressions be more
powerfuh Hence we have an explanation, why the heart is so
obtuse as regards sensation, and the stomach and intestine not
acute, namely, because impressions made on the nerves of those
parts do not penetrate the ganglia of the intercostal nerve to
reach the brain, where the perception of sensations takes place.
As regards the impressions, however obtuse they may be, that do
reach the brain from the heart, stomach, and intestines, is it
not rather that they reach the brain through the branches of
the eighth pair distributed to those viscera, than that they pass
through the intercostal [great sympathetic] ganglia? The
conjecture is difficult. Further, the structure of the ganglia, as
described by eminent inquirers, is not opposed to this doctrine
of the functions of the ganglia, but if anything rather appears
to confirm it. Meckel, Haase, and Zinn maintain, that the
ganglia are made up of the nerves entering into them, which
divide into very minute filaments, so that they are variously
subdivided, and make a sort of net-work. Condensed cellular
tissue is intermingled with this net-work of nervous filaments,
and the whole is enveloped in a somewhat tense external mem-
brane; whence may arise a somewhat gentle compression of the
nerves entering the ganglion, which is sufficient to stifle, or
rather intercept the less powerful impressions propagated along
the nerves, and manifestly to obtund the more powerful. The
whole of this doctrine, as to the uses of the ganglia, can how-
ever be brought forward only as a conjecture not manifestly
improbable, but meriting the investigation of the learned, and
possibly containing a spark of truth, from which some acute
genius may be able to produce greater light for us. He who
shall unravel the uses of the ganglia will also give a reason
why the fifth pair of cerebral nerves pass through the semi-
lunar [Gasserian] ganglia, with the exception of a fasciculus
which joins the third division without touching the ganglion;*
and why only the posterior roots of the spinal nerves enter the
ganglia, whilst the anterior roots pass by without any com-
munication with them.^

Further, it may be asked, whether the external impressions
made on the terminations of the nerves and passed onwards to

' See my treatise ' De Structura Nervorum,' tab. ii, figs, v, \i.
' Ibidem, tab. iii, figs, i, ii.

438 FUNCTIONS OF THE SENSORIUM COMMUNE, [ch. iv.

the ganglia are extinguished in the ganglia themselves? or
whether being reflected there by a fixed law, they return
again along the nerves to the parts to be moved ? The cele-
brated Unzer/ and the eminent Winterl taught, that ex-
ternal impressions are reflected in the ganglia, as they are
reflected in the sensorium commune, and that the ganglia are
special sensoria, — a doctrine which does not appear altogether
destitute of probability. For, if we consider that the minute and
invisible nerves disseminated over the internal membrane of the
heart and auricles, perceive the stimulus of the inflowing venous
blood/ and although they cannot transmit the impression of
that stimulus to the sensorium commune through the ganglia of
the intercostal [great sympathetic] nerve, yet communicate it
to the motor nerves distributed through the substance of the
heart [ventricles] and auricles, it follows that there is neces-
sarily a consensus between the sensory nerves distributed on
the inner membrane of the heart and the motor nerves dis-
seminated through the substance of the heart [ventricles] and
auricles, which must take place either in the ganglia of the
intercostal nerve or below them, in the communicating branches
or plexuses of nerves. It seems probable, therefore, that
besides the sensorium commune, which we conjecture to be in
the medulla oblongata, medulla spinalis, pons varolii, and crura
of the cerebrum and cerebellum, there are special sensorna in
the ganglia and plexuses of the nerves in which external im-
pressions ascending along the nerves are reflected, that need
not ascend all the way to the sensorium commune, to be reflected,
thence.

' Erste Griinde einer Physiologic, &c.
2 Haller, De Part. Corp. Hum. Fabr.

CHAPTER V.

THE ANIMAL FUNCTIONS.

SECTION I. A SHORT ENUMERATION OF THEM.

In that portion of the nervous system which we have termed
the sensorium commune^ such a mechanism lies concealed, that
external sensory impressions of the nerves are reflected in it
upon the motor nerves in a singular manner, and by unerring
and peculiar laws, so that they produce distinct and definite
movements of the muscles. It has already been stated, that
many motions truly automatic take place in man by means of
this vis nervosa of the sensorium commune only; nevertheless,
although many animals which are destitute of brain, and the
higher endowments of animals are regulated and live only
through this vis of the sensorium commune, and therefore may
be termed true automata, in man and many allied animals the
nervous system is increased by the addition of a brain; and
moreover, with a certain principle which we call the soul, an ens
of incorporeal origin, and which we are taught by faith to have
been granted to man alone, to constitute him an immortal crea-
ture by the special favour of God. So long as the soul is joined
with the body, it manifestly produces no operation which depends
solely and exclusively upon itself, but all take place by means
of the nervous system as the instrument; so that in all the animal
functions, the nervous system has a share as the instrument,
and the mind a share as the acting and determining principle.

Animal actions under the name of internal senses, or under
the name of faculty of thought, or of reason, or of intellect,
come continually under the observation of physicians. I by
no means propose to treat of these so accurately and profoundly
as has been done by metaphysicians and psychologists, but
only to touch on those points with which it behoves physicians
to be fully acquainted. The principal divisions into which the
animal functions may be conveniently divided, are perception,
understanding, and will, to which may be added imagination and
recollection, or memory,

440 THE ANIMAL FUNCTIONS. [ch. v.

The mind perceives the external impressions made on the
nerves, and communicated to the sensorium commune, by
acquiring certain notions and images of them termed ideas.^
These differ according as they are brought from the various
organs of the senses to the sensorium commune, for vision excites
one kind of ideas in the mind, hearing another kind, taste,
smell, and touch other kinds. Ideas also differ in their degree of
vividness, for the more vivid ideas presuppose a more impres-
sible nervous system, that many impressions are not commu-
nicated at the same time to the sensorium, (for the mind clearly
perceives one idea after another,) or an impression more powerful,
repeated, continuing longer, or new and unusual.

Whilst engaged in the examination of ideas, the mind judges
whether there be discrepancy or agreement amongst them,
whether they be new or often-repeated ideas — whether they
threaten anything injurious to our body, or promise anything
beneficial. When engaged in this judgment, the mind must
remember the idea first perceived, when it compares it with
another for the purpose of seeing their agreement or discrepancy,
and consequently the faculty of judging presupposes memory.
If many compound ideas be compared one with another, a
compound judgment is made, and this is termed reasoning.

The mind wills, when it endeavours to retain or remove that
which by the ideas is understood to be good or evil.

It imagines, when the ideas of things formerly present but
now absent are excited, voluntarily or involuntarily, either
from some internal disposition of the brain, or from some
similar or associated idea excited in the mind. Those ideas

• I do not here treat of the hypotheses as to the formation of ideas in perception
and imagination, whether they be impressions traced on the brain, which Haller
defends in his ' Elem. Phys.,' torn, v, p. 541, &c. ; or whether they are a certain
motion and minute vibrations or oscillations, which, being different, are suitable to
the excitation of different ideas, as Bonnet ingeniously supposes. (See his ' Analy-
tischer Versuch uber die Seelenkrafte.') Reimarus (see Gbttingen Magazine for the
past year, part vi,) strongly disapproves of the doctrine, that there are material
tracings of the ideas impressed on the brain, since the memory being lost in disease
could never be restored, as it often is, if, indeed, the tracings of the ideas, once
obliterated, cannot be restored when the disease terminates, with the same facility
as the fibres of the brain can be re-excited into similar oscillations on the oppor-
tunity being afforded; and because, as the traces are always present, there could
be no reason why the representation of ideas should cease during profound sleep.
In this matter those more acute than I will decide.

SECT. I.] ENUMERATION. 441

which arise from imagination are less vivid than those from
perception ; but by continual meditation and fixing of the
attention upon them, they become gradually more and more
vivid, until at last they may become equal to those ideas which
arise from perception; so that the mind cannot distinguish them,
and confounds things present with things absent, when it is
said to wander.

When an idea arising from perception or imagination, is
accompanied with the consciousness that it is not new, but has
been perceived by us formerly, the circumstances also occurring
in which it was formerly perceived, the mind is said to remember
or recollect.

We are conscious, when the animal actions are in actual
operation (as takes place during waking); and consciousness is
abolished in the same proportion that the animal functions
cease to be exercised, as for example, in sleep, apoplexy, or
fainting. Thus consciousness seems properly to belong to the
actual exercise of the faculty of thought.

The mind does not enjoy an equal degree of freedom in all
these mental operations. It does not perceive voluntarily but
compulsorily, since it is not able, for example, not to see if the
object be placed properly before it. Nor does the mind per-
ceive the harmony or discordance of ideas more voluntarily.
The mind has the greatest freedom in willing, for it can desire
a pleasing object, or neglect, or refuse it ; nevertheless, if what
is pleasing or displeasing becomes an object of any great pleasure
or pain, the mind loses much of its freedom in willing, nay, is
compelled to desire or dislike, and passions arise of which we
are not the masters but the obsequious slaves, since we may
often see and approve the better, and yet unwillingly follow the
worse. For this reason they are rightly termed passions of the
mind, since in them the mind scarcely acts, but is impelled to
action by the body. I avoid adducing here special instances of
the passions, and examining them with reference to their
causes and effects, since I think that this has already been
fully done by others, nor can I add anything new or par-
ticular; I will only treat on some questions relating to the
animal functions, respecting which distinguished men have
entertained opposing opinions.

442 THE ANIMAL FUNCTIONS. [ch. v,

SECTION II. IS THE FACULTY OF THOUGHT THE SPECIAL PRO-
PERTY OF THE MIND, OR IS IT NECESSARY TO THOUGHT THAT
THE MIND USE THE BRAIN AS AN INSTRUMENT?

Many pliilosophers and physicians have asserted, that the
mind alone thinks, and the body takes no part in that opera-
tion ; on the other hand, some have maintained that thought
itself is a faculty belonging to matter, and denied that the soul
is immaterial ; others, thinking that both were far wide of the
truth, have imagined they could set the matter at rest by
stating that certain operations of the thinking faculty are partly
owing to the body, as memory, for example, but that others
are performed by the mind alone, and independently of
the body.

If we consult daily observation, we learn that the faculty of
thought is subject to various viscissitudes, and corresponds
closely with the condition of the brain. The foetus hid in the
uterus of its mother, neither sees, nor hears, nor tastes, nor
smells, nor scarcely feels the fluids that surround it. Thus
destitute of ideas, it neither judges nor imagines, nor remem-
bers. On emerging into light, the fcetus, indeed, begins to
perceive objects through the organs of the external senses, but
it cannot as yet correctly judge between ideas, and quickly
forgets its perceptions, for the semi-fluid brain seems unfit to
retain them, and consequently, we remember nothing of that
period. The same mind in the youth, with a firmer and more
condensed brain, retains ideas readily and with remarkable
facility, and is endowed with somewhat of the power of judg-
ment as to serious matters, although but feebly. In manhood,
the solids generally, and therewith the brain, being consolidated,
it commits new ideas to memory, and retains them with less
facility, but enjoys by so much the more a riper judgment. In
old age, new ideas are retained with still greater difficulty, but
the old being indurated, as it were, like the brain, pertinaciously
adhere to it ; yet some aged persons lose even these, and
return to the state almost of plants, oblivious of the world,
their friends, and themselves.^ The mental endowments diff"er

^ Haller, in his notes to the * Prselect. Instit. Med.' of Boerhaave, and in his
' Elem. Phys.,' torn, v, p. 538.

SECT. II.] THE BRAIN THE ORGAN OF MIND. 443

not only according to age, but also in persons of every age,
according to the varying constitution of the brain proper to
each individual ; for just as an equally vigorous stomach, lungs,
and other viscera is not seen in all men, so the brain does not
acquire the same strength and perfection in all men; and hence
we should expect a diversity in the faculty of thought, of which
the brain is the instrument, in different men ; and this, in fact,
we daily find to be the case. For some persons endowed with
a more fortunate condition of the brain, are quick in perception,
sound in judgment, prompt in willing, happy in retaining and
recalling ideas ; others with little talent, as the phrase is, owing
to a less fortunate condition of the brain, are dull in perception,
weak in judgment, slow to action, unfortunate and imperfect in
the exercise of memory. Some, again, perceive quickly, and
remember most felicitously, but judge foolishly; whilst others
who are endowed with an excellent judgment, have by so much
the more imperfect a memory. Some, in consequence of a
congenital defect of the brain, are stupid and fatuous through-
out their whole life ; ^' many of whom,^^ says Haller,^ '^ have a
face scarcely human, large mouth, dribbling saliva, numerous
strumous swellings, harsh voice, and a mind unfit for all the
duties of life. Another equally numerous class spend their
whole life in bed, incapable of any corporeal movement : they
pass a long life in a condition not much superior to brute
animals, and having rather less intelligence for the functions
of life ; and, indeed, their senses are so dull, that lately one of
them perished from a collection of fseces, which distended the
rectum to the diameter of a foot and a half, and of which he
felt nothing.^^ This effect of a vitiated state of the brain in
depraving the intellect is so well known that it cannot be
doubted that if the state of the brain of Newton and Alexander
had been changed in infancy by slight concussion or compres-
sion, the one might have been a stupid man, and the other a
wise king. Who, in short, does not daily observe the faculty
of thought to be disturbed, impaired, and even extinguished by
disease, and all consciousness for a time abolished? If his
kinsfolk be placed before a man delirious in fever, he often
does not recognise them, for either the perception is affected,

' Elem. Phys., torn, v, p. 570.

444 THE ANIMAL FUNCTIONS. [ch. v.

or tlie understanding, or the memory, which does not retain the
old idea of the kinsfolk to be compared with the new perception.
The organ of the understanding seems to have been especially
affected in the patient of Wepfer, ^ who mistook a piece of paper
for a handkerchief, and the handle of the spoon for the bowl. The
organ of memory is not unfrequently so disordered by disease
that individuals lose the recollection of their past life, and forget
acquired knowledge; of this, the illustrious Linnaeus lately
afforded an example. Not unfrequently, all the organs of the
animal functions are so affected that none of them can be
exercised, and for the time at least consciousness is entirely
abolished, as is seen not only in persons affected with apo-
plexy, earns, fainting, and epilepsy (during the paroxysm), but
also in profound sleep in which all the animal functions enjoy
a full holiday, since the brain requires rest for itself after
having been wearied with the exercise of thought throughout
the day. Nay, frequent use has no slight effect in changing
and perfecting the animal functions. By use alone the per-
ception becomes more acute, for the musician perceives the
least discord, and is annoyed by that which a person, not a
musician, never notices ; use renders the memory more tena-
cious, the judgment more acute, the will more prompt; all
which may also be observed in musicians, who acquire so much
readiness and facility by practice, that they perceive the notes,
judge what time and tone they denote, will, and apply the
fingers in fulfilment of the volition, almost at the same moment.
From all these things it evidently follows, that thought
cannot depend solely and entirely upon the mind, nor is the
whole essence of the soul exempted from thought ; otherwise
we must conclude that a soul of an inferior nature is given to
dull persons, and of a superior to the intelligent ; that it can
increase with age, be perfected by exercise, become sick, and be
deprived of one faculty or another, — as memory, for example,
and consequently, that the substance is material, and may be
increased or diminished. But these changes and defects may
be attributed to the brain, when in a state more or less im-
perfect, as being the instrument of the soul, and necessary to
thought, so long as the soul is connected with the body; if it

' Hist., 98.

SECT. III.] THE BRAIN A COMPOUND ORGAN. 445

be injured, thought is injured; if destroyed, thought is de-
stroyed, and consciousness abolished.

Eminent men of all ages have acknowledged this dependence of
the faculty of thought upon the body: of these I need onlymention
Hippocrates \ Galen, ^ Des Cartes,^ Abraham Kau Boerhaave,'^
and Gaubius^. The force of truth also made Tralles subscribe to
this opinion^, for although he carried the doctrine that the
mind is independent of the body too far, yet he observes : " It
is indeed certain that experience teaches us that so long as the
soul is connected with the body, a well-constituted brain is
absolutely necessary for it to think, imagine, reproduce ideas,
and judge concerning them.^' Ernest Platner, also, in his
elegant essay, ' De Vi Corporis in Memoria,^'^ observes : " Since
such are the facts, it is manifest from the observations already
made as to the mode of perception, that every one of our senses
is put in action by the common agency of the body and mind,
so that no sensation or thought can be produced by the mind
without the body, nor by the body without the mind." And
this doctrine, that the soul, so long as it is connected with the
body, can neither think, nor have self-consciousness without a
properly-constituted brain, derogates certainly in no degree
from the immateriality and immortality of the soul, which God,
by special favour, can endow with an eternal consciousness of
itself and of things external to it, although the body it had in-
habited be destroyed, — a doctrine we are taught to believe by
religion, which also in every age has been desired by mankind^
and which great philosophers have approved by their assent^.

' In the Epistle of Democritus, • De Natura Hominis,' which is extant among the
works of Hippocrates.

2 Cap. ix, Libri quod anirai mores corporis temperamenta sequantur.

3 Diss, de Meth., n. vi, p. m. 38.

* Impetum faciens dictum. Hippocrati, cap. i, he says : " The Supreme Ruler
has associated the mind with the body by such a law, that without a suitable state
of body the mind is evidently inactive, and becomes so disconsolate and unlike itself,
that you in vain search for mind in the mind itself."

^ De Regimine Mentis quod Medic, est, Sermo i.

^ De Animse existentis Immaterialitate et Immortalitate, p. 31.

' In Baldinger, Syloge Selector. Opusculor. Argum. Medico-Pract., vol. iii, p. 86.

8 This closing sentence is omitted in the edition published in the Opera Minora ;
the reference to the doctrines of Christianity at the commencement of Section I,
is also omitted. — Ed.

446 THE ANIMAL FUNCTIONS. [ch. v.

SECTION III. DO EACH OF THE DIVISIONS OF THE INTELLECT

OCCUPY A SEPARATE PORTION OF THE BRAIN?

It is our consciousness and a certain peculiar feeling which
convinces every one that he thinks with his brain. But since
the brain, as well as the cerebellum, is composed of many
parts, variously figured, it is probable, that nature, which
never works in vain, has destined those parts to various uses,
so that the various faculties of mind seem to require different
portions of the cerebrum and cerebellum for their production.
Since, however, the sensorium commune reflects the sensorial
impressions into motor by definite laws peculiar to itself,
and independently of consciousness, and since we have laid
down that the sensorium commune comprises the medulla ob-
longata, medulla spinalis, and the origin of all the nerves, it
follows that the cerebrum and cerebellum, together with their
connections, the sensorium commune excepted, constitute the
organs of the faculty of thought ; and as in some animals
these organs are entirely wanting, it is fair to conjecture that
the faculty of thought is also wanting, and that they exist
solely in virtue of the vis nervosa of the sensorium commune and
of the nerves with which they are endowed. Hitherto it has
not been possible to determine what portion of the cerebrum
or cerebellum are specially subservient to this or that faculty
of the mind. The conjectures by which eminent men^ have
attempted to determine these are extremely improbable, and
that department of physiology is as obscure now as ever it was ;
and we think with Haller that no light can be thrown upon it
in any other way than by a careful dissection of the brains of
fatuous persons, apoplectics, and such as have other disorders
of the understanding. There are indeed, many observations
extant bearing upon this point, but few have been rightly made,
and with many there is interwoven a preposterous judgment on
what has been observed. As hitherto there has been so much
reason to lament the dearth of judiciously-made observations,
I hope more ingenious men may be incited to note, as occasion

* The sentiments of the Arabians may be seen in § iii of chap, i; and in § vi, the
opinion of WilUs, Lancisi, De la Peyronie, and Mayer.

SECT. IV.] THE PROPER ANIMAL MOVEMENTS. 447

offers, what has been observed during life in cases of this kind,
and having duly examined, after death, the cerebrum and
cerebellum, together with the remainder of the nervous system,
to make the facts public, with or without a suitable judg-
ment on the case. The distinguished Metzger has promised^
to watch diligently for such observations, and has raised our
hopes, since much may be expected from his genius and
dexterity.

It is, therefore, by no means improbable, that each division
of the intellect has its allotted organ in the brain, so that there
is one for the perceptions, another for the understanding, pro-
bably others also for the will, and imagination, and memory,
which act wonderfully in concert and mutually excite each other
to action. The organ of the imagination, however, amongst
the rest, will be far apart, I should think, from the organ of
perceptions, since the organ of perceptions being asleep and
at rest, the organ of the imaginations may be in action, a con-
dition which produces dreams. There is this peculiarity in
dreams, however, that the ideas represented are often very
absurd, and are continually combined and judged of erroneously,
and we are not convinced of their falsity and emptiness, until
all these phantasms are discovered to be false and corrected
by the waking up of the organ of the perceptions.

SECTION IV. WHAT MOVEMENTS ARE PROPERLY TERMED ANIMAL?

There are only two kinds of muscular action in the human
body, according to the cause which excites it ; the one kind
is termed voluntary or animal, because according as the mind
commands and wills, it may be excited, increased, diminished,
and arrested; the other involuntary, of which the mind is
either unconscious, or if conscious, the motion is performed
without its consent, and is excited only by a mechanical cor-
poreal stimulus applied to the nervous system, for which reason
it is also termed spontaneous and automatic. Nerves are
necessary to produce both kinds of movement.^ The nerves
do not act, however, without a stimulus, which is either pro-
duced by the mind willing, or, if unconscious and unwilling, by

' Vermischte Medicinische Schriften, Iten Bandes, Seite 58.
* See Chap. II, § in, (6).

448 > THE ANIMAL FUNCTIONS. [ch. v.

some body applied to the nerves. Whence, therefore, it is
manifest, that those movements ought alone to be termed
animal which depend upon the untrammelled control of the
soul, and which it produces or restrains by its own free will;
on the other hand, those which in no degree depend on the
will, but are performed when the mind is unconscious or un-
willing, cannot be termed animal, but are purely mechanical
and automatic.

Observation teaches, that there are some muscles in the
human body over which the mind has no control whatever,
and the movements of which are purely automatic during the
whole of Ufe; these are the heart [the ventricles], the auricles,
oesophagus, stomach, and intestinal canal; with these may be
mentioned the motion of the iris. There are other muscles
which are ordinarily subject to the control of the will, and
for this reason are termed voluntary, such as the muscles of
the limbs, trunk, head, face, eyes, tongue, genitals, and the
sphincter of the anus and urinary bladder. It sometimes
happens, however, that all these muscles renounce the authority
of the miud, and while it is either unconscious or unwilling, are
violently agitated by some preternatural mechanical stimulus,
as is seen in hysterical, epileptic, or infantile convulsions, or
in those affected with St. Vitus^s dance; and these movements,
although performed by muscles designated voluntary, can only
be termed automatic. In the foetus in utero and in the newly-
born these muscles are not moved voluntarily, but for the most
part automatically, for at that age the cerebrum is not as yet
capable of thought, until the organs of the faculty of thought
being gradually evolved, the mind learns to think, and to use
the muscles subjected to its control. The raising of the hand
and the application of it to the head in apoplexy belong also
to the class of automatic movements, also the turning of the
body in sleep, and partly even somnambulism itself, which,
however, it would seem is partly also to be ascribed to obscure
sensations and vohtions which the mind instantly forgets. In
the third place, there are muscles which continually act in-
dependently of the will, being excited thereto by a mechanical
stimulus only, but over which the mind possesses voluntary
command, and can at will accelerate, or retard, or entirely stop
their movements for a time; the action of these is termed

SECT. IV.] NATURE OF THE SOUL. 449

mixed. Of this kind are the muscles of respiration, which
almost constantly act automatically, but over which, however,
the mind has such control, that it can accelerate, retard, or even
stop the respiratory movements for a time. But if a mechanical
stimulus be too powerful, then the muscles of respiration are
excited into action in spite of the will; for example, if a
crumb slips into the trachea, a violent cough ensues altogether
uncontrollable by the will; thus also the mind cannot prevent
sneezing when the pituitary membrane of the nostrils is stimu-
lated by an acrid stimulus.

In establishing that no action and no movement can be
termed animal, of which the mind is not conscious, and which
does not depend upon its free will, I shall possibly seem to have
restricted the influence of the soul over the body too much, since
there are very distinguished men, especially of the Stahlian School,
who have taught that not only every movement is directly re-
gulated by the soul, but also other functions of the animal body ;
adopting this fundamental principle, that consciousness is not
necessary to each function of the mind. But it is certain that
as yet we know nothing more of the human soul than that it
thinks,^ and that it cannot do this, so long as it is connected
with the body, without the assistance of the brain. It is not
proved, as assumed by the Stahlians, that the soul is the im-
mediate cause of other animal functions which do not involve
thought. But although we were to concede the assumption,
deductions follow from it which must be pronounced absurd,
and which admit of no defence, as has been fully shown by
Haller,^ and Platner,^ who, although an eminent supporter of
the Stahlian doctrine, says that it is true that muscles continue
to act, the nerves of which have been tied, or divided, and that
some Stahlians have gone too far, since they wished to attribute
these movements also to the soul, which to this end they
maintain to be diflPused through the body, and spoke of the
remaining portions of the soul as if it were divisible, and as if
they continued the movement that originated from the divided

' See "Van Swieten's Commentary, torn, i, $ 1.
^ Elem. Physiol.

^ See De Haen's Heilungsmethode, 3ter Band. In the first division, on some
difficulties in the system of Haller.

29

450 NATURE OF THE SOUL. [ch. v.

nerves. Moreover, that he was of opinion that Stahl either
held the soul to be material, or confounded the rational soul
with the anima sensitiva or vegetativa of the ancients, which
alone we can affirm to be diflfused through the whole body.

Si quid novisti rectius istis
Candidas imperii ; si non, his utere mecum.

END OF 'FUNCTIONS OF THE NERVOUS SYSTEM.

INDEX

UNZER'S PRINCIPLES OF PHYSIOLOGY.

[N.B. — The figures in this Index refer to the numbers of .the paragraphs.]

Abstraction, definition of, 77 ; many ma-
terial ideas cease, or become weaker in,
77, 140
Action, muscular, animal when excited
by nerves, 163; from external im-
pressions and their direct nerve-ac-
tions, 452-465 ; from internal non-
conceptional impressions, 507 ; may
be a sentient action or a nerve action,
or both, 514 ; nature of investigated,
161, 380; effected solely through
nerves, 388
Action, reflex, see Reflexion, and Im-
pressions, external and internal.
Actions, animal, see Animal actions.
Actions, sentient, defined, 6 ; are direct
and indirect, 97-110; the conceptive
force co-operates in, 111; how pro-
duced, 112; a conceptional impression
necessary to, 123 ; when produced
directly by external sensations, 129;
when produced by conceptions, 130 ;
chai'acter of those excited by cerebral
impressions, 133 ; when produced by
external sensations, how prevented,
134 ; when caused by spontaneous
conceptions, hindrances to, 136, 138 ;
when produced by external sensations,
how enfeebled, or prevented, 139 ;
occur in the oesophagus and intestinal
canal, 170; occur in the stomach,
174 ; in the liver, 175 ; in the kidneys,
176; in the urinary bladder, ib.\ in
the organs of the external senses, 177 ;
in the sexual organs, 178 ; when not
direct results of the external sensa-
tions, 181 ; when at the same time
nerve-actions, 183, 363 ; how influ-
enced by the consciousness of an im-
pression,184,ii; from other conceptions,
often confounded with those from ex-
ternal sensations, 185 ; of agreeable
and disagreeable external sensations,
195 ; of gratification, 197 ; of pain,
198 ; developed even in the non-mus-
cular membranes, 208 ; of external

Actions {continued)

sensations in the heart, stomach, &c.,
204-218; the incidental [zufallig],
219-224; the subordinate, 225; the
co-ordinate, 227 ; of imaginations, see
Imaginations ; of the memoiy, 238 ;
of the foreseeings, see Foreseeings ; of
the sensational desires and aversions,
255 ; of the sensational propensities
and emotions, 260 ; of the instincts,
281-292; of the passions, 306-329;
of the intellectual conceptions, 330;
may all be produced without brain, or
mind, or conceptions, 367 ; transfor-
mation of, into nerve-actions, or vice
versa, 367, 368 ; often result from
direct nerve-actions of external im-
pressions on the muscles, 448 ; substi-
tution of, for nerve-actions, 580-593
Affections, 91
Affectentriebe, the instinctive passions,

296-304
Afferent and efferent fibrils in the same
nerve, doctrine of, 127 note, 486-
488
Age, old, its phenomena, 701
Ahndungen, 73. See Forebodings.
Albinus, his doctrine of the anatomical
distinctness of the nerve-fibrils anti-
cipating Miiller, 39 note; MSS. of, in
possession of Sir W. Hamilton, ib.
Anger, always a passion, 301 ; a de-
pressing one, 322 ; its sentient actions
how composed, ib. ; its union with
revenge, 324 ; the special changes its
sentient actions produce, 325 ; means
of controlling, 326 ; its sentient ac-
tions may be induced by the vis
nervosa only, 572
Animal, a purely sensational, see Sensa-
tional animal.
Animal, a reasoning, see Reasoning ani-
mal.
Animal, a sentient, see Sentient animal.
Animal, an insentient, see Insentient
animal.

453

INDEX TO UNZER'S

Animal, an, characteristic distinction of,
600 ; distinction indefinite, GOl ; its
life divided into four periods, 644

Animal actions defined, 6 ; how excited, 32

Animal death, 6. See Death.

Animal forces, their natural subordina-
tion, 666 ; certain, not naturally sub-
ordinate to any other, 667, 670 ; those
subordinate to others, 668, 669 ; their
natural connecting points, 672 ; their
centres, 673; no general centre of,
674 ; primary, defined, 6 ; only two
known, 356; communicated, defined,
6 ; pure, see Nerve forces.

Animal function, the action of an animal
force, 666

Animal life, defined, 6 ; its most essen-
tial elements, 15, i; sensational, 640;
spiritual, 641 ; complete, 643 ; its four
periods, 641-658; the system of its
forces, 659; the heart and brain es-
sential to, 675 ; conditions of its
duration, 693 ; cessation of, 694 ; may
continue after proper animal death, 717

Animal machines, defined, 6, 9 ; the,
general, 15, ii ; in no species defective,
ib.; constitute a special system, 671 ;
are centres of the animal forces, 673

Animal movements, primary, defined, 6 ;
when purely animal, 193 ; from non-
conceptional impressions, 356

Animal nature defined, 6 ; gives animal
bodies peculiar forces, 7 ; philosophy
of its great divisions, 8 ; treated of in
general, 600-728 ; the general princi-
ples on which its whole physiology
must be based, 618 ; its origin, 628-637

Animals, distinguished into sentient and
insentient, 603 ; all, do not require to
have a soul, 622

Animal sentient forces, see Forces.

Anticipation, or expectation, 92-95 ; of
the understanding, 96

Anxiety, a distressing passion, 313

Apparitions, imperfect external sensa-
tions, 148

Arbitrary, as applied to conceptions, 27

Arteries, their contraction and dilation
explained, 460

Artistic machines, differ from natural or
organic, 5

Attention, definition of, 51, v, 77; can
excite and maintain many sentient
actions, 140

Aversions, how developed, 81 ; if active,
three things to be distinguished in,
81-87 ; sensational and intellectual,
89; may be wholly sensational, or
more spontaneous, ib. ; when a Wind
abhorrence, or antipathy, 90; intel-
lectual, 96

Beseelte, rendered sentient, 349 note.

Bewegungsgriinde, the motives, 96. See
Motives.

Bezauberung, the wonderful in instincts,
263, 270

Bladder, the gall, little susceptible of ex-
ternal sensations, 213 ; the efl'ect of
anger and revenge on, 325 ; its irrita-
bility somewhat doubtful, 476

Bladder, the urinary, effect of vivid ex-
ternal sensations on, 176 ; the effect of
sensational conceptions and foresee-
ings on, ib.; its functions may be
nerve-actions of external impressions,
478 ; how situate as to nerve-actions
from non-conceptional internal im-
pressions, 537

Blood-vessels, how external sensations
act upon, 205

Body, definition of a, 1 ; physical nature
of a purely physical, 2 ; its mechanical
nature, 4 ; reciprocal connection of,
with the soul, 345-352

Brain, the seat of the soul and of con-
sciousness, 10, 25 ; if imperfect, the
mind imperfect, 25 ; the laboratory of
the vital spirits, 11; gives origin to
all the nerves, 12 ; has a double move-
ment, 24 ; the whole not immediately
necessary to thought, 25 ; its medul-
lary matter possesses an animal-sen-
tient force peculiar to itself, ib. ; every
act of mind in connection with its
force, 29 ; the whole not put into
action by each conception, 124; com-
pression of, the results and cause,
128 ; certain fibrilli of the medulla
receive external impressions, 132 ; the
mechanical machines in connection
with the, 156-159; its cortical sub-
stance can be influenced indirectly by
sentient actions, 159 ; may not be re-
quired for all animal movements, 366 ;
its medullary and cortical substance
have some share in the vis nervosa,
373-4; when necessary to the con-
tinued production of nerve-actions,
416; when requisite to nerve-actions,
511; always imperfect at first, 649;
the effect of daily waste and repair on
its functions, 662 ; as a centre of the
animal forces, 673; whether one point
of it the seat of mind, doubtful, 719

Capillary vessels, effect of external im-
pressions on, 207, 462 ; their animal
forces, 682

Care, a distressing passion, 313

Cerebral forces, see Forces.

Cerebral impressions, 121-141

PRINCIPLES OF PHYSIOLOGY.

453

Conceptions, how caused, 25 ; impressions
or representations of, 26 ; definition of
natural, or organic and arbitrary voli-
tions, 27 ; dependent on material ideas,
ib.\ preceded by sensations, 65; of
the understanding, 7^ ; of the me-
mory, 71 ; their relation to attention,
abstraction, meditation, and reflection,
77 ; either please or displease, 80 ;
their relation to material ideas, 97-
151 ; necessary to true sentient ac-
tions, 123, see Actions sentient ; their
course independent of others, 125;
sensational and intellectual, 347 ; in-
ternal impressions of, 359 note.
Conceptive force [Empfindhchkeit], 65
Congestion, theory of, 207, 462
Connatural, as applied to agreeable ex-
ternal sensations, 191, 196, 440
Connection, reciprocal, defined, 345
Consciousness, 80
Contractility, so called [Reiz], 3
Contranatural, as applied to disagreeable

external sensations, 191, 196, 200
Convulsions, their nature, 204

Death, definition of, 703 ; the spiritual
of a reasoning animal, 704; sensa-
tional, 705 ; complete, 706 ; natural,
707 ; animal, 708 ; from what com-
plete, may result, 711 716; animal
life may continue after proper, 717

Desires, how developed in the mind, 81 ;
three things to be distinguished in,
84-87 ; may be sensational or intel-
lectual, wholly sensational, or more
spontaneous, 89 ; sensational, nature
of, 90 ; intellectual nature of, 96

Despair, a distressing passion, 313; its
sentient actions may be induced by
the vis nervosa only, 571

Diaphragm, the, is sensitive, and sub-
ject to the will, 171 ; its sentient ac-
tions from external sensations, 208 ;
is capable of direct nerve-actions, 464 ;
may be excited by non-conceptional
internal impressions, 523; its natural
action in respiration, 525 ; a centre of
animal forces, 673, 688

Dichtungskraft, the poetic faculty, 248

Distress, how excited and developed,
309; its mental actions and various
forms, ib.

Dreams, the rules applicable to, 67-69 ;
70, 236 ; sensational foreseeings often
produced in, 75, 247

Emotions, the, nature of, 91 ; their effect
on the penis, 178 ; strong sensational
stimuli conjoined in, 258 ; effects of
the pleasing or distressing, how regu-
lated, 259

Empfindung, commonly used in a three-
fold sense, 34 note.
Empfindlichkeit, see Sensibility.
Erdichtungen, fictions, 70
Ersetzung, see Substitution.
Excitants of the feelings, see Peelings.
Exhilaration, the instinct for, 287, ii
Expectations, see Anticipations.
External impressions, see Impressions.
External sensations, see Sensations.

Faculty, the higher perceptive, 76; the
poetic, 228

Fear, a distressing passion, 313, in what
resembles and differs from terror, 320 ;
may be induced by the vis nervosa
only, 571

Feelings, incitements of the, 83 ; are
sensational or intellectual, 88 ; add a
special sentient action to those of con-
ceptions, 250 ; excite the origin of
those nerves by which vital move-
ments are regulated, 251

Flesh, the, 90 ; warring against the spi-
rit, 337

Food, the instinct for, its sensational
stimulus, 281 ; its effects as a foresee-
ing, 282

Forces of physical bodies, the general, 3 ;
their aggregate, 4

Forces, animal, see Animal forces.

Forces, animal-sentient, or cerebral, na-
ture of, 6 note, 82 and note; their
actions, 97-110 ; their relations to the
vis nervosa, 541-597 ; their reciprocal
connection, 590-597

Forces, nerve, defined, 6 ; depend on the
vital spirits, 21 ; what retard the ac-
tion of, 22 ; what strengthen and en-
liven, 23

Forces, primary vital, nature of the, 675 ;
the two reciprocally subordinate, 676

Forebodings, the nature of, 73

Foreseeings, nature of, 73, 23^; relations
of, to desires and aversions, 81 ; rela-
tions of, to instincts and passions, 90-
94 ; in what differ from true expecta-
tions, 249; accompanying the depres-
sing passions, 315-328

Free will, 96. See Will.

Gall-bladder, see Bladder.

Ganglia, are possessed by the motor
nerves, 14 ; do not possess true cere-
bral tissue, 35 note-, 624, iv; their
probable use, 48, iv; their functions
maybe changed through habit, 49, iv;
probably deflect external impressions,
48, iv, 399 ; to the motor nerves per-
form the office of brain, 399

GefiJhl, the external feeling of the
nerves, 402

454

INDEX TO UNZER'S

Generation, definition of, 628 ; fissipa-

rous, oviparous, and viviparous, 629
Glands, the, their nature and function, 172
Gratification, nature of, 80, 187, 195 ;

its actions, when very vivid, allied to

pain, 199
Grief, a distressing passion, 313 ; what

favour, 317

Habit, distinct from expertness, 137

Haller, the dead force of, 3 ; probably
the Gottingen reviewer of Unzer's
work, 35 note-, his objection to the
hypothesis of afferent and efferent
fibrils in the same nerve, 127 note',
seems to think, the voluntary move-
ments alone produced by the soul,
162 note\ has shown that respiration
is a sentient action, 285 ; his terms of
muscular and nervous irfltability, 354 ;
his doctrine of vis insita refuted, 379,
388

Hamilton, Sir W., his abstract of the
doctrines of Albinus, 39 note.

Heart, the, its action animal, 167; Hal-
ler's theory of its motion confuted,
386 ; the effect of sensations on, 211,
250 ; its action in grief and fear, 314 ;
its action in anger and revenge, anxiety
and terror, 323; its stroke probably an
indirect nerve-action, 517 ; a centre of
animal forces, 673 ; its proper motor
force, 678

Hunger, the sensational instinct of, how
excited, 265 ; stimulates the machines
which receive food to discharge their
functions, 281

Incitements of the feelings, see Feelings.

Ideas, material, the nature of, 25 ; neces-
sary to thought, ib. ; their relations to
thought, 26 ; in what probably consist,
28 ; higher, abstract, or general, 66 ;
of imaginations, 67 ; of anticipations,
94 ; act either directly or indirectly,
115; their actions on the nervous
system, 117, 122, 142-151 ; their ac-
tions in the brain, 118, 159; the pri-
mary excite those of a second kind,
119; their action in the mechanical
machines, 160-180

Idiosyncrasy, 52

Imaginations, nature of the sensational,
66; their relation to external sensa-
tions, 68, 230-233 ; relations to in-
sanity, 69, 70; their action on the
mechanical machines, 228-238

Impression, a sense-like, defined, 31, and
note

Impressional, sinnlich, 31, 66

Impressibility, SinnlicMeit, 32

Impressions, cerebral, 121, 133

Impressions, conceptional, 121 note;
359 ; characters of, 31 ; their course ■
along the nerves, ib. ; respondence 1
to, a property of nerves, or " nerve- i
feeling," 31 note; of pleasure and
pain, the bases of the desires, 82

Impressions, external, — why so termed;
32 ; a definite change in the nerve,
ib. ; how developed, 32-36 ; to be felt,
must be propagated upwards to the
brain, 36, 37 ; all determined by the
mind, 38 ; conditions requisite to their
developing external sensations, 45;
the cause of all conceptions, 65, 66 ;
their course in animals, with a sen-
tient brain, 366 ; by their reflexion,
sentient acts may be performed without
brain, 367 ; their vis nervosa in general,
409, 443 ; every muscle, like the nerves,
has its own special, 451 ; their action
on the muscles and heart, 452-517

Impressions, internal, — their nature, 121 ;
propagated, without being commingled,
125 ; non-conceptional can produce the
same movements as the conceptive
force, 360 ; the reflexion of external
into, 366, 399; how non-concep-
tional originate; 371; their relation
to external and internal sensations,
402 ; course of the non-conceptional,
486, 487 ; when the brain and cere-
bral forces necessary to the nerve-
actions of the non-conceptional, 494 ;
non-conceptional subject to the same
law of deflection as those from con-
ceptions, 504 ; reflex action of, on the
heart, 515; action of non-conceptional
on the capillaries, diaphragm, viscera,
&c., 522-537; each of the two kinds
may reciprocally excite the other, 398 ;
excite whole series of acts, ib.

Inflammation, theory of, 207, 462

Insanity, the rules apphcable to, 67-69,
70, 236 ; sensational foreseeings and
forebodings often produced in, 75, 247

Insentient animal, an, its nature, 604;
how moved, 606; all their animal
movements dependent on the vis ner-
vosa, 608 ; excite all sentient move-
ments by the vis nervosa alone, 611

Instincts,sensational, their different kinds,
90 ; their actions in the economy, 93 ;
how developed, 94 ; how cease, or are
prevented, 95 ; doctrines applicable to,
256-259; arrangement of, 262; in
what differ from all other desires,
aversions, and passions, 263-265 ;
depend on no innate wisdom, 266;
the order of their phenomena, 268;
their stimuli, 270 : general and special,
natural aindunnatural,29b ; the felt im-
pression in, reflected by the brain, 564.

PRINCIPLES OF PHYSIOLOGY.

455

Intellect, see Understanding.
Intestinal canal, how the nerves act on
the, 170; often really sensitive, ib.

Joy, the nature of, 306 ; how far bene-
ficial or contranatural, 307

Judgment, the, may err respecting ex-
ternal sensations, 38 ; to what class of
conceptions it belongs, 76

Kidneys, the, have but few nerves, 176 ;
susceptible only of extraordinary ex-
ternal impressions, 215 ; their secern-
ing function, a nerve-action, 477 ; how
situate as to nerve-actions from non-
conceptional internal impressions, 526

Kitzel, titillation, or gratification, 80,
187, 195-197

Krijger, his law as to the movements fol-
lowing external sensations, 218

Laughter, the instinct of, 284

Life, the love of, the fundamental in-
stinct in all animals, 280

Liver, the, its sensibility not great, 175 ;
is little susceptible of external sensa-
tions, 213; the effects of anger on,
325 ; how far capable of nerve -actions,
476, 535

Loathing, 282

Longing, its sentient and special actions,
327

Love, the enchantment of, 289 ; phy-
sical, 302 ; of offspring, 303; the passion
of, 306 ; the instinctive emotions of,
308

Lungs, the, little susceptible to ordinary
external impressions, 214; congestion
of, in the distressing passions, 310;
how situate as to nerve-actions, 475,
534

Machines, animal, see Animal machines.

Machines, mechanical, — meaning of the
term, 4, 155-159 ; divided into artistic
and organic, 5 ; how put in motion,
153, 505, 506 ; actions of the material
ideas in, 160-180 ; actions of external
sensations in, 181-227; actions of
imaginations on, 228-238 ; actions of
the sensational foreseeings on, 250-
254 ; actions of sensational desires and
aversions in, 255-261 ; actions of sen-
sational instincts in, 262-304 ; actions
of the passions on, 305-329 ; actions
of the understanding in, ib. ; actions of
intellectual pleasure and pain in, 334-
335 ; actions of the will in, 335-344 ;
direct actions produced by the vis
nervosa in, 444-481

Material ideas, see Ideas.

Meditation, the act of, 77

Membranes, the, are sensitive, 171 ; effect
of external impressions on the non
muscular, 208 ; the serous, how situate
as to external sensations, 208 ; nerve-
actions in the muscular, mucous, and
fibro-serous, 464, 527

Memory, an act of the, 71 ; the material
ideas induced by sensational, 72 ; to
what class of conceptions it belongs,
238

Merkmahlen, elements, 53

Merkmale, sub-impressions, 68, 73, &c.

Mind, an act of the, 6 note; 25, 34-36;
effect of injury of the medulla of the
brain on the, 25 ; material ideas are
not the ideas of the, 25 ; determines
the point of impression in external
sensations, 30 ; can produce voluntarily
many kinds of conceptions, 64 ; its
inner sense, 80; actions excited by
the, 97-111; not necessary to direct
nerve-actions in muscles, 449

Monstrosities, origin of, 636

Motives, the nature of, 88, 89 ; the im-
pressions they add to passive concep-
tions, 96 ; as stimuli, 250 ; excite the
origin of certain nerves, 251

Movements, the respiratory, generally
neither mechanical nor volitional, 285.
See Respiration.

Movements, voluntary, distinguished into
sensational and intellectual, 283 note ;
the instinct to perform the sensa-
tional, 283 ; instincts for particular
kinds of sensational, 284

Movements, the free-will, with what
often confounded, 335 ; how produced
and hindered, 336, 342 ; why take
place in a given series, 341 ; their im-
portant influence in the economy,
343; power of the soul not to be
limited to, 351

MiiLLER, J., anticipation of his neurolo-
gical views by Albinus, 39 note.

Muscles, as mechanical machines, 161 ;
the nature of the action of the nerves
on, 162; their vis insita, 379-388;
have each their own special external
impressions, 451; reflexion of unfelt
external impressions in, 514

Natural, as applied to mechanical ma-
chines, 5 ; conceptions, 27 ; instinct,
90 ; subordination of animal functions,
666

Nerve-actions, definition of, 6 ; which
may be at the same time sentient
actions, 183, 184, 233, 364, 368, 441 ;
from the external impression, 358 ; from
the internal impression, 359, 360 ; may

456

INDEX TO UNZER'S

Nerve-actions {continued)

occur without cerebral force, or brain,
362 ; change of sentient actions into,
367; advantages to reasoning animals
from, 370 ; machines must be supplied
with nerves, to be capable of, 390, 391 ;
of the heart, 392 ; of the oesophagus,
stomach, &c., 393 ; of the glandular
tissues, 394 ; of the sexual organs, 395^
of the instincts, 396 ; of unfelTln-
ternal impressions, 397 ; of reflected
impressions, 398 ; of the brain's vis
nervosa, 409 ; from several external
impressions at the same time, do not
confuse each other, 412; different kinds
of impressions difficult to be discrimi-
nated from their, 413 ; from a reflected
external impression occur in the proper
machine, 415, ii; from reflected im-
pression often misunderstood, 415, iii;
how far the brain necessary to, 416,
494, 511 ; direct and indirect, 419, 425 ;
how enfeebled or prevented, 427-430;
their relation to external sensations,
433, 438 ; how resemble the sentient,
435-437 ; why they excite our wonder,
438 ; are connatural or contra-natural,
440 ; muscular fibre peculiarly adapted
to direct, 445 ; in muscles, 449-453,
513; in the heart, 455, 517, 518; in
the membranes, 464 ; in the capillaries,
463 ; of the stomach, 469, 470 ; of the
viscera, 475-479; of the senses, 480;
of the sexual organs, 481 ; of non-con-
ceptional internal impressions, 483,
494, 506, 507, 524-544 ; produced by a
primary internal impression, 490, 496,
498 ; of imaginations or foreseeings,
549 ; of the sensational desires and
aversions, 530 ; of the blind instincts
and emotions, 551 ; of the sensational
instincts, 552, 561 ; of the instinctive
passions, 562 ; of the passions, 563-
567 ; three principal kinds of, in the
mechanical machines, 580; threefold
division of those of primary non-con-
ceptional internal impressions, 581;
substitution of, for sentient actions and
vice versa, 541, 589 ; from a sensational
conception, 591 ; in the foetus, 634

Nerve feeling, its nature, 31 ; from with-
out inwards, 32 ; internal, 121

Nerve forces, see Forces.

Nervous fluid, see Vital spirits.

Nerves, all arise from the brain, 12 ; their
course, 13 ; their external terminations,
14 ; division of, into motor and sensitive,
14; contain the vital spirits, 15 ; dif-
ferent efl"ects of impressions on different
parts of, 31; how animal actions ex-
cited in their medulla, 32 ; of motion

Nerves (continued)

and sensation, no difference of in
receiving and transmitting impressions,
33 ; sensational force of, 34 ; external
impressions on, 35-39, 55 ; impressions
on the cerebral origin of, 121 ; action of
material ideas in, 122, 142-151, 405;
impressions of the conceptions on, 124,
125 ; probably have aflferent and efferent
fibrils, 126-127 ; hidden movements
in them inferred, 145, 404, 405 ; erec-
tion of their terminations, 147-150;
vivid impressions probably deflected at
their bifurcations, 151; effect of a
cerebral impression at their loops, 160;
their action on the muscles, 162-164,
510 ; various ways in which may in-
fluence the secretions and circulation,
167-180 ; the action of external sensa-
tions through them, 181-227; actions
of imaginations through them, 228-
238 ; actions of the sensational foresee-
ings through them, 239-249 ; actions of
sensational pleasure and pain through
them, 250-254 ; actions of the sensa-
tional desires and aversions through
them, 255-261 ; actions of the sensa-
tional instincts through them, 262-304 ;
actions of the passions through them,
305-329 ; actions of intellectual plea-
sure and pain through them, 333-334 ;
actions of the will through them, 335-
336 ; the principal seat of the primary
vis nervosa, 372 ; vis nervosa must be
a general property of, 375 ; impressions
on the sensory, 376, 377; external
feeling of, 402 ; internal feehng of, 405-
407; secondary points in them, probable
for the reflexion of impressions, 428 ;
nerve-actions explained from the doc-
trine of afferent and eflferent fibrils in,
486-488 ; their ordinary stimuli caus-
ing internal impressions, 489 ; the pe-
culiar kind of irritation of their medulla
to produce a certain kind of internal
impression, unknown, 492 ; changes in,
from non-conceptional internal impres-
sions, 504 ; eflfect of opium on, 558 ;
their growth, and development in new
growths, 647 ; their daily wear and
repair, 662

(Esophagus the, action of the nerves on,

170: direct nerve-actions of, 466-468;

nerve-actions from non-conceptional

internal impressions, 531
Offspring, the instinct for, 262, iv
Organic life, what, 5
Organic machines, in what diflfer from

artistic, 5 ; when termed animal, 6

PRINCIPLES OF PHYSIOLOGY.

457

Organism the, how far the general forces
of physical bodies belong to, 3 ; to
what extent the laws of mechanics
applicable to, 5; a sensible and in-
sensible, 52 ; an irritable and inirritable,
432 ; as a living animal, 600

Organs, of the external senses, 55 ; as
mechanical machines, subject to same
laws, 177 ; effect of external sensations
on, 216 ; seat of the same nerve-actions
as the muscular system, 539

Organs, the sexual,are extremely sensitive,
178; their functions may be induced
by the vis nervosa alone, 481 ; nerve-
actions from non-conceptional internal
impressions on, 340 ; all animals born
with, 654 ; as centres of animal forces,
673

Pain, in what consists, 80; sensational
and intellectual, 88 ; action of, on the
organism, 136-200; its actions on the
mechanical machines, 204 ; its action
on the vital movements, 250, 333

Passions, the, 91 ; each of, how com-
pounded, 93 ; what doctrines apply
to, 256 ; instinctive, 302 ; incidental
action of the primary, 305 ; actions of
the joyous, 306-308 ; actions of the
painful and distressing, 309-328 ; the
instinctive as nerve-actions, 562 ; their
sentient actions as nerve-actions, 563-
573

Penis, effect of foreseeings and desires on
the, 178; Haller's opinion on the
swelling of its corpora spongiosa, 178

Perceptions, sensational, 76

Physiognomy, 166

Physiologically free, as applied to con-
ceptions, 27, 89

Pleasure, impression of, distinct from
that of pain, 80 ; sensational and in-
tellectual, 89 ; its action on the organ-
ism, 191 ; its action on the vital move-
ments, 250, 333; calm, more favorable
to health and life than when in excess,
252, 253

Pleasure and pain, nature of their im-
pressions, 124

Preservation, pain the sentinel of, 184 ;
impressions necessary to, in insentient
animals given by nature, 609 ; move-
ments, necessary to, effected by the vis
nervosa, 610

Procreation, see Generation.

Propagation of the species, instinct of,
262, iii, 289 ; its excitement and satis-
faction, 263 ; analysed, 273 ; its sensa-
tional stimulus, 289 ; its sentient as
nerve-actions, 560 ; as a period in the
life of an animal, 652-657

Propensities, actions of the sensational,
260, 261

Pulse, the arterial, how far may be a nerve-
action, 519, 520 ; influenced by all non-
conceptional impressions exciting mus-
cular action, 521

Reasoning animal, a, 605

Reasons, 88

Reciprocal connection, defined, 345 ; of
the animal-sentient forces with the vis
nervosa, 590-597

Reflection, the act of, 77

Reflex action, of an external impression
on the heart, 515 ; of the brain in the
instincts, 564

Reflexion, of an external impression in a
sentient brain, or ganglion, 365, 415,
ii ; see also Nerve-actions and impres-
sions, external and internal

Regret, its nature and sentient actions,
312

Reiz, so called contractility, 3

Repose, the instinct for, its nature and
natural stimulus, 287; its nerve-actions,
558

Respiration, the instinct of, 285; how
far a nerve-action in thenewly-bom,285,
286, 526 ; may take place independently
of brain or mind, 475

Revenge, the desire of, an instinctive
passion, 301 ; a depressing passion, 322 ;
the heart's action in, 323; its union
with anger, 324 ; the special changes
by its sentient actions, 325 ; means of
controlling it, 326 ; may be induced
by the vis nervosa only, 572

Reverie, [dichtet,] 237

Schmerz, suffering, 80, 187, 195

Secretion, animal, but sometimes a sen-
tient action, 172; may be a direct nerve-
action, 471-473

SeelenwirJcungen, mental, sentient, or sen-
sational acts, 6, 99, iii

Self-defence, the instinct of, 262, ii, 288

Self-love, sensational, 280

Self-preservation, the instinct of, 262, ii,
263

Sense-like impression, a, 31

Senselikeness, 32 ; its varying degree in
the conceptions, 112

Sensation, the term used in a threefold
sense, 34 note\ precedes all other
conceptions, 65 ; a certain use of the
term proposed, 402

Sensation, as used by Buffon, 402

Sensational, 31 note', force, or sensi-
bility, 34 ; memory, 72 ; foreseeings
and expectations, see Foreseeings and
Expectations; pleasure and suffering.

458

INDEX TO UNZER'S

Sensational (continued)

see Pleasure and Pain ; stimuli, 88 ;
instincts, see Instincts ; desires and
aversions, see Desires and Aversions.
Sensational animal, a, 605 ; of what vital
actions capable, 614 ; perform nerve-
actions as sentient actions, 624
Sensations, external, nature of, 34-36 ;
what requisite to their development,
45 ; what interrupts or hinders them,
46-51 ; the material ideas of, 53, 54 ;
their organs, 54 ; special, 55 ; their
relation to the material ideas of ima-
ginations, 67 ; of pleasure and suffer-
ing, 80 ; material, how excited, 132 ;
imperfect, 148, 378; actions of, on
the mechanical machines, 181-227;
the majority of their sentient actions
at the same time nerve-actions, 183 ;
agreeable and disagreeable, 189, 190 ;
of imaginations and instincts, 229-
276 ; external feeling of the nerves to
be distinguished from, 402-404 ; their
nerve-actions, 436-452
Senses, the, their number and seat, 55-

64 ; their nerve-actions, 480
Sensible, meaning of the term, as used

by the French, 31 note.
SensibiUty, 34, 65 ; may co-exist with

irritability, 432
Sensual gratification, or titillation, 80,

88 ; propensity, or inclination, 90
Sentient actions, see Actions, sentient.
Sentient animal, a, the idea of, 349 ; how

moved, 612, 613
Sentient faculty, what, 10
Shame,its nature and sentient actions, 328
Shivering, how ought probably to be

classed, 147
Sinnlich, in what sense used by Unzer,

31 note, 66 note.
Sleep, as an impediment to external sen-
sations, 49, v; the instinct for, see
Repose.
Somnambulism, the rules, 67-69 ; appli-
cable to, 70, 236 ; foreseeings in, 247 ;
the movements during it explained,
454
Sorrow, its nature and actions, 310; in-
jurious to health and life, 311
Soul, the seat of the, 10, 25 ; acts of the,
27; its union with the body, 29; its
reciprocal connexion with the body,
345-352 ; error of the ancients con-
cerning the, 404 ; not indispensable to
animal acts, 594 ; its disseverance
from the body, 717-726
Spasms, their nature, 204
Spleen, its nerve-actions, 479
Spinal cord, reflexion of impressions in,
35 note.

Spontaneous, as applied to conceptions,
27

Stomach, the, has many and considerable
nerves, 174; is susceptible of impres-
sions from conceptions, ib. ; the exter-
nal sensations excited in and about,
212 ; its direct nerve-actions, 466,
468, 531; a centre of animal forces,
673, 688

Substitution of nerve- actions for sen-
tient, and vice versa, 541-589

Suck, the instinct to give, 290 ; the in-
stinct to, ib.

Suffering, impression of, 80 ; a sentinel
of our preservation, 184 ; a natural
medicine, 196

Sympathy, 90 ; of sentient actions in the
muscles, 165

Temperament of an animal body, defined,
52 ; mainly determines the sensational
faculty, 329; how and when deter-
mined, 651

Terror, its nature and actions, 318 ; in
what resembles and differs from fear,
320

Thierische-seelen KrUfte, rendered by
" cerebral forces," or, " animal-sentient
forces,' 6 note, 82 and note.

Thierischer Kbrjjer, the equivalent of
animal organism, 6 note.

Thierischer Krdfte, the vis nervosa, 6
note.

Thierischer Maschinen, what used for,
9 note.

Thirst, the sensational stimulus of, 282

Thought, on what dependent, 25 ; effect
of, on abstract subjects, 333

Titillation, 80; excites vivid contrac-
tions in muscles, 204 ; as a nerve-
action, 434
Triebfedem des GemUths. See Feelings.

Understanding, conceptions of the, 76 ;
their sentient actions, 331, 332, 380;
the direct cannot be induced as nerve-
actions, 574 ; the motives and desires
of the, cannot be induced by the vis
nervosa, 576

Viscera, action of the nerves in the, very
complex, 1 73 ; their nerve-actions,
474-479

Vis nervosa, its synonyms, 6 and note; the
functions the body is rendered capa-
ble of, by the, 354 ; of the external im-
pression, its nerve-actions, 358 ; of the
internal impression, its most prominent
examples, 359 ; properties of both
kinds of, 361 ; does not necessarily
require the cerebral force, 362 ; seat
of the primai-y, 372-374 ; of nerves.

PRINCIPLES OF PHYSIOLOGY.

459

Vis nervosa (continued)

excited by non-conceptional internal
impressions, 381, ii ; no animal motor
force independent of, 389 ; machines
not endowed with nerves not adapted
to, 390 ; of the heart, 392 ; of the
oesophagus, stomach, &c., 393 ; of the
glandular tissues, 394 ; of the sexual
organs, 395 ; in the movements of the
limbs, 396; either kind of, may be
excited without the conceptive force,
398 ; of external imprjessions, 409-
413 ; of non-conceptional internal im-
pressions, 482-540; all the sentient
actions of imaginations and fore-see-
ings, sensational conceptions, desires,
and aversions, instincts, and emo-
tions, imitated by, 545-553 ; effect of
opium on, 558 ; how far the passions
may be imitated by, 562-573 ; intel-
lectual conceptions and motives can-
not be induced by, 575, 576; how
far the influence of the will can
be induced by, 577 ; as possessed
by sentient and insentient animals,
604-617; causes movements, neces-
sary to the preservation of animals,
610 ; of a reasoning animal, 618, 626 ;
a large class of animals endowed alone
with, 621-624 ; of a purely sensational
animal, 626; abolition of, 709, 710

Vital spirits, the, how secreted, 11, 362,
416; their existence probable, 15, i;

Vital spirits (continued)

course of the impressions propagated
by, 17, 18; how weakened, 20; func-
tions of the sentient forces dependent
upon, 21 ; the movements of the nerves
probably only movements of, 145;
effect of an irregular influence of, 314.

Vorstellung, generally translated by "con-
ception," 5 note, 25 note.

Forstellungskraft, conceptive force, sen-
tient force, or mind, 6

War-instinct, the, its nature, 301, 326;
its sentient actions may be nerve-ac-
tions, 559

Whytt, his renewal of an erroneous pro-
position of the ancients, 404

Will, the free, 96 ; sentient actions of its
desires and aversions, 335 ; conflict
between the sensational faculty and,
337 ; satisfaction of, prevented, 338 ;
the flesh has always a part in, 339 ;
how far its incidental influence may be
exercised by the vis nervosa, 577 ; how
far its desires and aversions may be
induced by vis nervosa, 378 ; move-
ments of, see Movements.

Wille and WillMhr, how used, 283 note.

Willkiihrlich, how rendered, 283 note,
335 note.

Yawning, its nature, 287, ii.

INDEX

PROCHASKA ON TPIE NERVOUS SYSTEM.

[N.B. — The figures in this Index refer to the pages.]

Albinus shows the cortex of the brain
not altogether vascular, 377, 389

Anatomy of the nervous system — its
bibliography, 383 note.

Animal functions, see Functions.

Animalcules shown by Spallanzani to
be true animals, 386 ; how feel and
move, 387

Arabs, the, located the animal functions
in the ventricles, 369

Aristotle, his opinion as to the use of
the brain and heart, 365

Arteries, irritability and muscular con-
traction of, 411

AsTRuc, quoted, 377

Anger, its effect on the secretions, 419-
421

Bartholin, 373

Bauhin Caspar, the first to deny the
doctrines of Galen, 370

Benevenius, his doctrine as to the ani-
mal functions, 369

Blood-vessels, action of the nerves on
the, 408-412

Blumenbach, his hypothesis of a nisus
formativus, 426

Boerhaave, doctrines of his school on
the brain, 377 ; his opinion on the
animal spirits, 377 ; where places the
sensorium commune, 429

BoHADSCH, his description of the lernaea,
388

Bones, morbid, sensibility of, 394 ;
Murray on, 394 ; Brambilla on
395 note.

Bonnet, 386

Brain, its use, according to Aristotle,
365 ; the opinions of Hippocrates,
Plato, Galen, and others, as to its
functions, 365-369 ; its systole and
diastole, 367, 369 ; intellect, according
to Galen, does not depend on its
convolutions, 368 ; case of injury of,
by Galen, 367 ; the use of its cir-
cumvolutions, according to Columbus,

Brain (continued)

369 ; its cortical substance secretes the
animal spirits, 374; Malpighi and
Willis support this opinion, 375 j
man has the largest, except certain
apes, 384; structure and composition
of, in animals, ib. ; the proportion it
bears to other parts of the body, 385 ;
its medullary matter not wholly vas-
cular, 389 ; is the organ of the mind,
442 ; is probably a compound organ,
446, 447

Caldani opposed the doctrine of animal
spirits, 379

Camper, his opinion on the consensus
of the nerves, 433

Capillaries, action of the nerves on
the, 408-412

Cerebellum, use of the vermiform process
of the, according to Galen, 368 ; the
seat of involuntary motions, according
to Willis, 375; description of the,
381

Cerebrum, why softer than the nerves,
and double, according to Galen, 367;
its use, according to Willis, 375 ; de-
scription of the, 381 ; what portion of,
subservient to this or that faculty, un-
known, 446

Circulation, influence of the nerves on, in
the capillaries, 408 ; excited by a sti-
mulus to the nerves, 409 ; can it be
repelled by the nerves? 417

Columbus, his opinion on the use of the
circumvolutions of the brain, 369

Conarium, see Pineal Gland.

Congestion caused by the action of
nerves, 409 ; theories of, 410 ; various
phenomena caused by, 416

Consensus of the nerves, inquiry into,
433 ; where it takes place, ib. ; when
in the ganglia, 435

Consciousness, to what it belongs, 441

Corpora striata, functions of their ascend-
ing and descending fibres, 375

ON THE NERVOUS SYSTEM.

461

Corpus callosum, seat of the understand-
ing, 375 ; the centre of sensation and
motion according to Lancisi, &c.,
377,429

Cremadells, his theory of animal heat,
423

Cutis anserina explained, 416

CRAWFOKD,his theory of animalheat, 423

De Haen on animal heat, 421
Des Cartes, his opinion on the animal
spirits, 370 ; placed the sensorium
commune in the pineal gland, 429
Diemerbroeck, 373

Erasistratus, his opinion as to the

functions of the brain, 366
Erectile tissue, influence of nerves on, 416

Fallopius, denies the systole and dias-
tole of the brain, 369

False resemblances of truths, injurious
influence of, on science, 364

Fernelius, a follower of Plato, 366 ;
his doctrine as to the origin of the
sensory and motor nerves, 369

FiORATi, his edition of Tissot on the
Nerves, 379

Foetus, the, formed by generation, not
evolution, 426 ; acephalous, in utero
lives by vis nervosa, 387, 399

FoNTANA, his experiments on opium, 397

Fornix, the, its use, according to Galen,
368

Functions, the animal, distributed
amongst the ventricles of the brain by
the Arabs, 369; enumeration of,
439-441

Galen recognised three faculties of the
mind and three spirits, 365, 366 ;
refutes Aristotle's doctrine on the
brain, 366 ; his opinion as to the use
of the cerebrum, cerebellum, &c., 367-
369 ; doctrines held by his followers,
369 ; the use assigned by him to the
ventricles shown to be erroneous,
372, 373

GangUa, known to Galen and others,
378; functions of, first taught by
ViEussENs, &c., ib. ; opinions as to
their probable use, 378, 436 ; con-
sidered to be little cerebra, 378 ; con-
sensus of the nerves takes place in,
435 ; act as ligatures on the nerves,
436 ; are special sensoria for reflexion
of impressions, 438

Gasser quoted, 377

Gaubius, his account of the effects of
anger on the secretions, 420

Habit, its influence on the vis nervosa, 405

Haller, his opinion as to the infundi-
bulum, 373, and pituitary gland, 374 ;
his error as to irritability in muscle,
390 ; supports the doctrine of animal
spirits, 379 ; the inconsistency of his
doctrines on the motion of the heart,
401 ; his opinion on animal heat, 421;
denied the nutritive property of the
nervous fluid, 424

Harvey, nature of opposition to his
views, 371

Heart, the seat of the soul, according to
Aristotle, 365 ; movements depend-
ent on the vis nervosa, 399 ; the doc-
trine of its irritability controverted,
407 ; reflexion of impressions on the,
438

Heat, animal, its production, 421-3

Herophilus, his doctrine as to the
functions of the brain, 366

Hippocrates, his opinion as to the
functions of the brain, 365

Haase on the ganglia, 378

Hoffman opposes the doctrine as to the
use of the ventricles in preparing the
animal spirits, 370

Humours, cause of a more copious de-
rivation to any one part, 408

Ideas, their nature, 440

Idiosyncrasy, its nature, and various ex-
amples of, 402-5; dependent on a
change in the vis nervosa, 402 ; of
pregnant women, 404 ; a cause of Pica,
404-5 ; influence of habit on, 405

Impressions, mode of their transmission
along nerves, 406 ; reflexion of senso-
rial into motor, in the sensorium com-
mune, 430; reflexion of, in the
gangha, 438

Inflammation, its nature explained, 417

Infundibulum, its use according to
Lower, Willis, &c., 373 ; found hol-
low by Murray, ib.

Insects perform their functions by nerves
only, 387

Intellect, probably each division of, has
its organ in the brain, 447

Intercostal nerve, how far impressions
from the brain and spinal cord reach
the, 436

Iris, the, how dilated, 416

Irritability of muscles dependent on their
nerves, 401

Klinkosch, case by him, 394
KoLPiN, his theory of congestion, 416

La Roche, theory of animal heat, 422

462

INDEX TO PROCHASKA

Lancisi, where sensation and motion

centered, by, 577
Lectures, Croonian, 415
LiNNiEus, case of, referred to, 444

Malpighi, his opinion on the anatomy,
&c., of the brain, 374, 375, 389

Mammae, erection of the papillae of the,
explained, 416

Martini on the susceptibility of ten-
dons, 394

Mayow, his opinion on the animal
spirits, 377

Meckel quoted, 377-8

Memory, the nature of, 441

Menses, the influence of the nerves on
the flow of, 415 ; not dependent on
congestion, ib. ; caused by vis nervosa,
416

Metzger quoted, 379; his promised
inquiries into the functions of the
brain, 447

Meyer, where the mental faculties
located, by, 377

Mind, three distinct faculties of the,
recognised by Plato, 365 ; whether it
alone thinks, 442; faculties of, located
in the brain, 374 ; influenced by vary-
ing states of the brain, 442

Movements, what properly termed ani-
mal, 448-9 ; automatic, ib.

Murray, his anatomy of the infundi-
bulum, 373 ; on the morbid sensi-
bility of bones, 394

Muscles, their irritability dependent on
the nerves, 400 ; theory of their con-
traction, 413; the automatic, 448

Muscular action, the two kinds of, 448 ;
theory of, 413

Musgrave, theories of, as to secretion,
419 ; as to animal heat, 422

Nates, see Tubercula Quadrigemina.

Needham, quoted, 386

Nerves, the, Galen's doubts as to their
function in transmitting the animal
spirits, 368 ; unity and use of the
loops of, according to Willis and
others, 376, 377; their origin, &c.,
described, 382 ; their medulla not
wholly vascular, 389; vis nervosa
exists in, independently of the brain,
397 — 402 ; their action in sensation
and motion, 406; on what their pro-
perty of receiving and transmitting
impressions depends, 407 ; their oflSce
as respects the brain and muscles, 407,
408 ; their action on the vessels and
their fluids, 408—412; have they the
property of repelling fluids ? 417 ; their

Nerves (continued)
influence in secretion, 418 — 421 ; do
they exert any influence in the produc-
tion of animal heat ? 421 — 423 ; how
far necessary to nutrition, 423 — 428 ;
consensus of, probably not wholly in
the sensorium commune, 435

Nervous system, what parts it includes,
381 ; bibliography of its anatomy, 383
note; the author's threefold division
of, 383 ; comparative anatomy of, 384 ;
in some animals, does not exist, 386 ;
not always necessary to sensation and
animal motion, 388

Newton on the nervous fluid, 422

NucK quoted, 377

Nutrition, how effected, 423—428 ; ac-
tion of the nisus formativus in, 426

Opium, experiments by Whytt with,

396
Otto Horstius, 373

Parencephalis, a term of Galen, 367

Passions, the, 441

Penis, its erection explained, 416

Perception, its nature, 440 ; is a com-
pelled act, 441

PiccoLHOMiNEus quotcd, 370

Pineal gland, its use according to Galen
and Willis, 368, 376

Pituitary gland, its use according to
LowER,WiLLis, Haller,&c., 373,374

Plato, recognised three distinct faculties
of the mind, 365 ; his opinion on the
brain, 375

Platner, his opinion on the union of
body and mind, 445, 449

Polypes, how feel and move without a
nervous system, 387 ; their irritability
produced by other mechanism than
that of muscles, 414

Preservation, the, of the individual, the
general law of reflexion of impres-
sions, 430

Recollection, its nature, 441

Reflexion,of impressions, in the sensorium
commune, described, 430 ; general law
of, ib. ; illustration of, 431 ; indepen-
dent of mind or consciousness, 432 ;
in the ganglia, 438

RiOLANUs, the son, defends the doc-
trines of Galen, 371

RuYscH, tries to prove cortex of the brain
not glandular, 377

Schneider, proves that the ventricles
of the brain are not cloacae, 372 ; his
work, ' De Catarrhis.' quoted, 372

ON THE NERVOUS SYSTEM.

463

Secretion, influence of the nerves in, 418 ;
Musgrave's doctrines on, 419

Sensorium commune, its functions and
seat, 429—432 ; centre of motor and
sensorial nerves, 429 ; its law of
action, consensus of nerves in, 433 —
435 ; its function is the reflexion of
external sensory impressions of the
nerves upon the motor, 429, 430, 431.

Soul, the rational, seat of, according to
Aristotle, 365 ; the rational and
corporeal, according to Willis, 376 ;
its union with the body, 439 ; all we
know of the, 449

Spallanzani, his remarks on animal-
cules, 386

Spirits, three acknowledged by Galen
and others, 366 ; the animal, their
origin and seat, according to Galen,
367, 368 ; Des Cartes' opinion on
the secretion of, 370 ; dislodged from
the ventricles of the brain, 370, 371 ;
said by Malpighi, &c., to be secreted
by the cortical substance of the brain,
374; their existence denied, 378

Stahlians, opponents of the animal
spirits, 379 ; their error as to the soul,
449

Tarin quoted, 378

Tendons, morbid sensibility of, 394

Testes, see Tubercula Quadrigemina.

Thought, cannot depend solely on the
mind, 442; organs of the faculty of,
446 ; its acknowledged depijdence
upon the body, 445

TissoT, supports the doctrine of animal
spirits, 379; his views as to the ne-
cessity of nerves to nutrition, 424 ;
lays stress on "Whytt's arguments on
the consensus of the nerves, 434 ;
his opinion on the functions of the
ganglia, 378, 435

Tralles quoted, 396 ; his opinion on
the union of soul and body, 445

Tubercula quadrigemina, their use ac-
cording to Galen and Willis, 368,
376

Understanding, one of the animal func-
tions, 439

Unzer, J. A, value of his doctrines as to
vis nervosa, 380 ; on the reflexion of
impressions in the ganglia, 438

Ventricles of the brain, the use of the
anterior or superior, according to

Ventricles of the brain {continued)
Galen, 367; the animal functions
distributed amongst the, by the Arabs,
369 ; the animal spirits dislodged from
the, 370, 371 ; shown not to be cloacae,
372—374

Verschuir, his experiments on arteries,
412; his theory of the flow of the
menses, 415

Vesalius, a follower of Plato, 366;
indifi'erent as to the course of the
animal spirits, 369

ViEussENs, where the seat of imagina-
tion placed by, 377 ; first taught the
function of the ganglia, 378 ; where
placed the sensorium commune, 429;
his opinion on the consensus of the
nerves, 433

Vis nervosa, in what sense the term is
used, 380 ; the cause of the functions
of the nervous system, 380; a stimulus
necessary to its action, 389 ; is not
indifferent to the kind of stimulus,
391 ; how increased, 391 — 395 ; in-
creased locally, 392 ; when diminished,
395 — 397; action of opium on, 396;
is divisible and exists in the nerves
independently of the brain, 397 — 402 ;
is the cause of the heart's movements,
399; its action modified in idiosyn-
crasies, 402; is a substitute for the
mind, 446

Vital principle, compounded of various
forces, 427 ; may exist independently
of vis nervosa in plants and certain
animals, 428

Whytt, his arguments on the consensus
of the nerves, 377, 435 ; his experi-
ments on the nerves, 396 ; his doc-
trines on consensus of the nerves, 435

Will, definition of the, 440

Willis, his opinion on the functions
of the brain, 373, 375 ; and on the
animal spirits, 375 ; his opinion on
the consensus of the nerves, 433

WiNSLow, his doctrine that the ganglia
are little brains, 378

WiNTERL, his conjecture on the nature
of the action of nerves on the vessels,
410

WiRTENSON, his dissertation on opium,
396

ZiNN quoted, 378

Zoophytes, how feel and move without a
nervous system, 387.

THE END.

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