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DR. CARPENTER'S PHYSIOLOGICAL WORKS.

A MANUAL, OK ELEMENTS OF PHYSIOLOGY,

INCLUDING PHYSIOLOGICAL ANATOMY,

FOR THE USE OF THE MEDICAL STUDENT.

With one Hundred and Eighty Illustrations. In one octavo volume of 566 pages. Elegantly
printed to match his " Principles of Human Physiology."

A POPULAR TREATISE ON VEGETABLE PHYSIOLOGY.

With numerous Illustrations on Wood. In one neat duodecimo volume.

(Preparing.)

PRINCIPLES OF GENERAL AND COMPARATIVE

PHYSIOLOGY,

INTENDED AS AN INTRODUCTION TO THE STUDY OF HUMAN PHYSIOLOGY, AND
AS A GUIDE TO THE PHILOSOPHICAL PURSUIT OF NATURAL HISTORY.

With numerous Illustrations on Wood. From the Third London Edition.

(Preparing.)

PRINCIPLES OF ANIMAL PHYSIOLOGY.

With ahout Three Hundred beautiful Illustrations on Wood.

LEA AND BLANCHARD.

PRINCIPLES

OF

HUMAN PHYSIOLOGY,

WITH THEIR CHIEF APPLICATIONS TO PATHOLOGY, HYGIENE, AND

FORENSIC MEDICINE.

BY

WILLIAM B. CARPENTER, M.D., F.R.S.,

FULLERIAN PROFESSOR OF PHYSIOLOGY IN THE ROYAL INSTITUTION OF GREAT BRITAIN, CORRESPONDING
MEMBER OF THE AMERICAN PHILOSOPHICAL SOCIETY, AND OF THE

NATIONAL INSTITUTE OF THE UNITED STATES ;

LECTURER ON PHYSIOLOGY AT THE LONDON HOSPITAL MEDICAL SCHOOL,

ETC. ETC.

American, front tlje last SLonSon Htittfon.

WITH NOTES AND ADDITIONS,

BY

MEREDITH CLYMER, M.D.,

CONSULTING PHYSICIAN TO THE PHILADELPHIA HOSPITAL J

LATE PROFESSOR OF THE PRINCIPLES AND PRACTICE OF MEDICINE, AND CLINICAL MEDICINE, IN THE

FRANKLIN MEDICAL COLLEGE, PHILADELPHIA J FELLOW OF THE

COLLEGE OF PHYSICIANS, ETC. ETC. ETC.

WITH

THREE HUNDRED AND SEVENTEEN WOOD- CUT AND OTHER ILLUSTRATIONS.

PHILADELPHIA:
LEA AND BLANCHARD.

1847.

Entered according to Act of Congress, in the year 1845, by

LEA AND BLANCHARD,
in the Office of the Clerk of the District Court for the Eastern District of Pennsylvania.

PHILADELPHIA :
T. K. AND P. G. COLLINS, PRINTERS.

TO

WILLIAM PULTENEY ALISON,

M.D., F.R.S.E., &c. &c.

PROFESSOR OF THE PRACTICE OF MEDICINE OF THE UNIVERSITY OF EDINBURGH.

MY DEAR SIR,

I take the liberty of inscribing the following Work to you, as an ex-
pression of my grateful remembrance of the value of your instructions,
of my respect for those intellectual faculties which render you pre-emi-
nent amongst the Medical Philosophers of our time, and of my admira-
tion for those moral excellencies which call forth the warm regard of all
who are acquainted with your character.

In many parts of this Treatise, you will find that doctrines, which you
have long upheld in opposition to almost the whole Physiological world,
are defended with such resources as I could command; and that, in
many instances, such convincing evidence of their truth has been afforded
by recent observations, that further opposition to them would now seem
vain. And if I have presumed to differ from you on some points, it has
been in the spirit of that independence which you have uniformly encou-
raged in your pupils; yet with a distrust of my own judgment, w:herever
it came into collision with yours.

That you may long be spared to be the ornament of your University,
and the honour of your City, is the earnest wish of,

Dear Sir,

Your obliged Pupil,

WILLIAM B. CARPENTER.

1*

EDITOR'S PREFACE.

THE character of the present Work is too well known and established
to need any commendation. Within a period of four years, it has passed
through three editions both in this country and Great Britain. It will
be seen, upon referring to the Author's Preface, that the present edition
has been essentially modified and improved ; and, besides attentive re-
vision, has undergone material alteration in the arrangement.

Many of the Notes of the American Editor to former editions have
been incorporated by the Author in the text of the present ; others remain ;
whilst such additions have been made, as the progress of the science
required.

By the liberality of the Publishers, the Editor has been enabled to add
numerous additional illustrations; which, accompanied by copious refer-
ences, will, he trusts, be found to enhance the value of this edition, and
to peculiarly adapt it to the Student of Physiology. There are one
hundred and fifteen more wood-cuts in this than in the third English
edition, and one hundred and one more than in the last American.

The new matter added by the American Editor is in smaller type, and
is distinguished thus [ — M. C.] The new cuts are included between
brackets [ ]. M. C.

230; Spruce Street, Philadelphia,
September, 1847.

PREFACE

TO

THE THIRD LONDON EDITION.

THE Author gladly avails himself of the opportunity afforded him by
the call for a Third Edition of the following work, to express his grateful
acknowledgments for the kind reception it has experienced, both in this
country and in the United States. The rapid sale of two large impres-
sions on each side of the Atlantic, has been the most satisfactory proof that
he had not been in error when he supposed that an opening existed for
an additional Treatise on Physiology, notwithstanding the large number
of those already before the public ; and that he has not been altogether
unsuccessful in supplying the deficiency.

The present Edition has not only undergone a very careful revision ;
but has in many parts received large additions, and has been in many
others entirely remodelled. By an increase in the size of the page, and in
the proportion of small type, the quantity of matter has been augmented
by an amount equivalent to the addition of fully a hundred pages. A
considerable number of new wood engravings, of first rate execution,
have also been introduced. Many of these are from original drawings
by Mr. Leonard.

Among the principal additions will be found a Chapter on the Varie-
ties of the Human Race ; intended to convey to those, who have not
time or opportunity to peruse Dr. Prichard's elaborate treatises, a general
view of his arguments and conclusions. The account of the Primary
Tissues, also, which was formerly included in the Chapter on Nutrition,
has been extended in a degree commensurate with the Author's estimate
of its importance, and has been made to form a distinct Chapter nearer
the commencement of the work. Other additions and changes, which
constitute, when taken collectively, no inconsiderable proportion of the
entire Treatise, are scattered through the volume. The materials of
these have been drawn from the numerous contributions to Physiological
Science, which have been made within the last two years, and from

PREFACE.

among which the Author has endeavoured to select the most import-
ant and the most stable ; — not rashly introducing changes inconsistent
with usually-received views ; — nor, on the other hand, showing an un-
Avillingness to reject the statements of those who have taken much pains
to arrive at accurate conclusions. He trusts that he may be found to
have generally exercised a sound discretion, both as to what he has
admitted, and what he has rejected; and that his work will appear to
exhibit on the whole, a faithful reflection of the present aspect of Phy-
siological Science. He cannot venture to expect, however, that he has
succeeded in every instance, so that each of his readers will be in con-
stant agreement with him ; since it is impossible that they should all
survey the subject from the same point of view.

Many, however, of the additions and alterations scattered through the
work, are the result of the Author's own investigations. He has par-
ticularly directed his attention to the settlement of points, which ap-
peared to him to be left doubtful by others ; and hence will sometimes be
found to have expressed his views with a degree of confidence, which
the evidence adduced by them may scarcely appear to warrant.

The Author feels called upon to express his particular obligations to
the valuable Reports on the Progress of Anatomy and Physiology, con-
tributed by Mr. Paget, to the British and Foreign Medical Review; and
also to those contained in the Half- Yearly Abstract, edited by Dr. Rank-
ing. He has made a point, however, of consulting the original sources
of information referred to in these Reports, in every instance in which
he could gain access to them. He has derived much assistance, also,
from Dr. Day;s Reports on the Progress of Chemistry, published in the
second of the works just named ; as well as from the translation of
Simon's Animal Chemistry, edited by the same gentleman.

He would be doing injustice to his own feelings, if he did not specially
refer to the admirable "Anatomical and Pathological Observations" of
Messrs. Goodsir, as one of the most valuable contributions to Physiolo-
gical Science which has been made since the date of his former Edition.

The subjoined Extracts from the First Edition will explain the plan
and scope of his Treatise to those who may now examine it for the first
time.

Stoke Ncwington,

October, 1846.

FROM THE

P E E F A C E

TO

THE FIRST EDITION

THE composition of such a Treatise as the following was a part of the
original plan of the Author when he first came before the Public as a
writer on Physiology. Being desirous, however, of making his first essay
in the path which had been previously the most incompletely explored,
he deemed it better to await the verdict upon this before proceeding
further ; and he was not without hope, that some Writer, more fully com-
petent to the task, might in the meantime take up the subject of Human
Physiology in such a way as to leave nothing for the Student to desire.
This, however, has not been accomplished. The previously existing
Treatises upon it, which have been every year becoming more antiquated,
have not been replaced by any works, that can be considered as at the
same time sufficiently elevated in their character, to represent the present
condition of Physiological Science, — sufficiently compendious in their
bulk for the limited time at the disposal of most Students, — and suffi-
ciently practical in their tendency to lead their readers to the useful
applications of the facts and principles they place before them. This is
not the opinion of the Author alone, but that of numerous experienced
Teachers throughout the country ; and he has been led to regard the
present as a good time for carrying his purpose into execution.

The plan and objects of his Treatise may be gathered from the pre-
ceding statement of the reasons which have occasioned its production.
In this, as in his previous work, it has been his object to place the
Reader in the possession of the highest principles, that can be regarded
as firmly established, in each department of the Science; and to explain
and illustrate these, by the introduction of as many important facts as
could be included within moderate limits. In every instance, he has
endeavoured to make his statements clear and precise without being
formal or dogmatical; and definite enough to admit of practical applica-

Xll PREFACE.

tion without appearing to be unimprovable by further inquiry. Physiology
is essentially a science of progress; and it must happen that much of
what is now regarded as established truth, will need great modification
to be brought into accordance with the results of new inquiries. It is
very desirable, therefore, that the Student should not be made to think
so confidently of his acquirements, as to be indisposed to receive new
information, even though it should tend to diminish their value.

The present Treatise is to be regarded as complete in itself, and as
quite independent of the Author's " Principles of General and Compara-
tive Physiology." That it may be so he has inserted an introductory
chapter on the "Place of Man in the Scale of Being," and numerous
references to the Comparative Physiology of the lower Animals. Still
he does not hesitate to express the opinion that, the greater the amount
of the Student's previous general knowledge of the Science, the better
will he be prepared to enter upon any department of it, especially that
peculiarly complex and difficult branch, the Physiology of Man. On
every topic, it has been the author's aim to present the latest and most
satisfactory information within his reach ; and he believes that the Volume
contains much that will be new to the Physiologist, whose reading has
not been tolerably extensive. Its materials have been but little derived
from other Systematic Treatises on the subject ; and it will not be found
to bear, as a whole, any considerable resemblance to those already before
the public. The author has rather endeavoured to bring together the
valuable facts and principles, scattered through the best of the numerous
Monographs, that have been recently published on special divisions of
Physiology and Medicine ; and to reduce these disjecta membra to that
systematic form, wThich they can only be rightly made to assume, when
brought into relation with each other, and shown to be subservient to
principles of still higher generality. In regard to this, as to his former
Treatise, the Author believes that he may claim a somewhat higher
character than that of the mere Compiler ; and that even the well-read
Physiologist will find in it many facts and deductions, which have not
been previously brought before him in the same form.

In apportioning the amount of space to be devoted to each division of
the subject, the Author has had in view its practical relations, much
more than its merely scientific interest; and he has on this account
bestowed a much larger share on the organs of Animal life than some
may think just when compared with the narrow limits within which other
important topics are discussed. But he has endeavoured to keep always
in view, that he is writing for the guidance of the Student who is to be-
come a Practitioner, rather than for him who makes the pursuit of Science
his professed object; and that much that is of the highest interest to the

PREFACE. Xlll

latter is comparatively valueless to the former. Hence many topics of
great scientific interest are entirely passed over; and it is hoped that
such omissions will not be accounted as faults in the estimation of those,
who dread lest the attention of the Student should be too much drawn off'
by the seducing novelties of Science, from his less attractive, but more
important objects.

For a large part of his illustrations, the Author is indebted to the
valuable and beautiful Icones Physiologies of Prof. Wagner. He has
indicated the sources of all which are not original.

In conclusion, the Author would repeat what he has already had oc-
casion to state;- — that in a work involving many details, it is not to be
expected that no error should have crept in; but that he has endeavoured
to secure correctness, by relying only upon such authorities as appeared
to him competent, and by comparing their statements with such general
principles as he considers well established. For the truth of those
principles, he holds himself responsible ; for the correctness of the details,
he must appeal to those from whom they are derived, and to whom he
has generally referred. He hopes that he will not be found unwilling to
modify either, when they have been proved to be erroneous ; nor indis-
posed to profit by criticism, when administered in a friendly spirit.

Bristol, Feb. I, 1842-

TABLE OF CONTENTS.

INTRODUCTION.

PAGE

NATURE AND OBJECTS OF PHYSIOLOGICAL SCIENCE -

CHAPTER I.

ON THE PLACE OF MAN IN THE SCALE OF BEING.

1. Distinction between Animals and Plants 39

2. General sub-divisions of the Animal Kingdom - - 41

3. General characters of Radiata • 42

4. General characters of Mollusca - 45

5. General characters of Articulata - 48

6. General characters of Vertebrata 50

7. General characters of Fishes 54

8. General characters of Reptiles - 55

9. General characters of Birds 58

10. General characters of Mammalia 62

11. Chief sub-divisions of Mammalia 65

12. Characteristics of Man - 67

CHAPTER II.

OF THE MUTUAL RELATIONS OF THE DIFFERENT BRANCHES OF THE HUMAN

FAMILY.

1. General Considerations - - 76

2. On the Discrimination of Species 77

3. On the possible Extent of Variation within the limits of Species 79

4. On the Extremes of Variation among the Races of Men 81

5. On the value of Physiological and Psychological peculiarities as specific distinc-

tions - - ... 82

6. On the Comparative Peculiarities of the different Races of Mankind

7. Of the Principal Branches of the Human Family 91

CHAPTER III.

OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

1. On Organized Structures in General

2. On the Original Components of the Animal Fabric ' • 102

3. Of the Elementary Parts of Organized Tissues; — Cells, Membrane, and Fibre - 108

4. Of the Simple Fibrous Tissues ..... - 120

XVI CONTENTS,

PAGE

5. Of simple Cells, floating in the Animal Fluids - 124

6. Of Cells developed upon Free Surfaces • 137

7. Of the Compound Membrano-Fibrous Tissues • 147

8. Of Simple Isolated Cells, forming Solid Tissues by their aggregation - 150

9. Of Tissues consolidated by Earthy deposit. — Bones and Teeth - 161

10. Of Simple Tubular Tissues. — Capillary Blood-vessels - 188

11. Of Compound Tubular Tissues. — Muscle and Nerve - 192

CHAPTER IV.

GENERAL VIEW OF THE FUNCTIONS.

1. Of Vital Actions, and their mutual dependence 216

2. Functions of Vegetative Life - 224

3. Functions of Animal Life 232

CHAPTER V.

FUNCTIONS OF THE NERVOUS SYSTEM.

1. General Summary 236

2. Comparative Anatomy and Physiology of the Nervous System in Invertebrata 247

3. Nervous System of Vertebrata - 265

4. Functions of the Spinal Cord and its Nerves. — Reflex Action - 285

Respiratory Movements - 292

Deglutition and Defecation 297

Movements of the Genital Organs - 305

Protecting Agency of the Spinal Cord - - 305

Movements of Locomotion 307

Influence on Muscular Tension - 307

Pathological Phenomena - 308

Nerves of the Spinal System - -310

5. Of the Sensory Ganglia and their Functions. — Consensual Movements - 326

Emotional Actions - - - - - 335

Nerves connected with the Sensory Ganglia - - 339

Consensual Movements of the Eye 344

6. Functions of the Cerebellum - • 349

7. Functions of the Cerebrum - • • 357

8. General Recapitulation, and Pathological Applications - • 376

CHAPTER VI.

i

OF SENSATION, AND THE ORGANS OF THE SENSES.

1. Of Sensation in General 385

2. Sense of Touch - - - 395

3. Sense of Taste . 399

4. Sense of Smell - - 404

5. Sense of Vision ...... 407

6. Sense of Hearing ....... 422

CHAPTER VII.

•

OF MUSCULAR CONTRACTILITY.
1. Of Contractility in General ....... 433

CONTENTS. XVii

PAGE

2. Of Muscular Irritability - - - 439

3. Of Muscular Tonicity - 449

4. Energy and Rapidity of Muscular Contraction • 452

CHAPTER VIII.

OF THE VOICE AND SPEECH.

1. The Larynx, and its Actions - - 455

2. Of Articulate Sounds - - - 464

CHAPTER IX.

INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS. 470

CHAPTER X.

OF FOOD AND THE DIGESTIVE PROCESS.

1. Sources of the Demand for Aliment. — Hunger and Thirst 477

2. Nature and Destination of the Food of Animals 483

3. Of the Passage of Food along the Alimentary Canal - 492

Mastication and Deglutition - 494

Action of the Stomach - 496

Action of the Intestinal Tube - 501

Act of Defecation - 502

4. Nature of Chymification and Chylification 503

CHAPTER XI.

OF ABSORPTION AND SANGUIFICATION.

1. Absorption from the Digestive Cavity - 509

2. Absorption from the Body in general - 512

3. Of the Elaboration of the Nutrient Materials 517

4. Composition and Properties of the Chyle and Lymph - 523

5. Physical and Vital Properties of the Blood 527

6. Pathological Changes in the Blood 535

CHAPTER XII.

OF THE CIRCULATION OF BLOOD.

1. Of the Circulation in General - 540

2. Action of the Heart 546

3. Movement of the Blood in the Arteries and Capillaries 556

4. Of the Venous Circulation 566

5. Peculiarities of the Circulation in different Parts 568

CHAPTER XIII.

OF RESPIRATION.

1 . Nature of the Function ; and Provisions for its Performance -

2. Effects of Respiration on the Air •

2*

XV111 CONTENTS.

PAGE

3. Effects of Respiration on the Blood 586

Exhalation and Absorption by the Lungs 589

4. Effects of Suspension of the Respiratory Process 591

CHAPTER XIV.

OF NUTRITION.

1. General Considerations. — Selective Power of Individual Parts - 593

2. Varying Activity of the Nutritive Processes - 596

Reparative Operations 599

3. Abnormal Forms of the Nutritive Process 604

4. Varying Duration of Different Parts of the Organism 609

5. Of Death, or Cessation of Nutrition 612

CHAPTER XV.

OF SECRETION.

1. Of Secretion in General 614

2. The Liver.— Secretion of Bile 618

3. The Kidneys. — Secretion of Urine 632

4. Mammary Gland. — Secretion of Milk 647

5. Salivary Glands and Pancreas - 655

6. Lachrymal Gland 657
V. The Testis. — Spermatic Fluid 657
8. Cutaneous and Mucous Follicles 661

CHAPTER XVI.

GENERAL REVIEW OF THE NUTRITIVE PROCESSES. ANIMAL HEAT.

1. Review of the Nutritive Processes, with Practical Applications 671

2. Animal Heat 676

CHAPTER XVII.

OF REPRODUCTION.

1. General Character of the Function 687

2. Action of the Male 689

3. Action of the Female - 692

4. Development of the. Embryo - 713

APPENDIX.

1. ON PHRENOLOGY - 731

II. ON ARTIFICIAL SOMNAMBULISM AND MESMERISM 733

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EXPLANATION OF PLATES.

PLATE I.

The first 16 Figures in this Plate are from Dr. Barry's Embryological Researches in the
Philosophical Transactions for 1837, 1839 and 1840.

FIG.

1. A very early stage of the formation of the Ovum; the vesicles, the largest of which

measures only l-1125th of an inch, are seen in the midst of dark granules or
globules (§ 906).

2. A stage somewhat more advanced ; the vesicles are surrounded by envelopes of smaller

vesicles, amongst which the granules are still seen (§ 906).

3. A still later stage ; a central vesicle a, is seen, with a spot, b, upon its walls, and sur-

rounded with numerous granules ; this has now evidently become the Germinal
Vesicle (§ 906).

4. Ovisacs from Human Ovum, l-200th of an inch and upwards, in diameter; the largest

exhibits the Germinal Vesicle, a, very distinctly (§ 906).

5. Ovisac from Cat, showing its contents when near maturity; a, ovisac; b, its contained

granules ; c, zona pellucida ; d, granules of the yolk ; e, germinal vesicle ; /, germinal
spot; magnified 440 diameters (§ 905).

6. Ovum of Rabbit at the periphery of the Graafian follicle, with part of the membrana

granulosa removed; g, g, membrana granulosa; ov, ovulum; r, retinacula (§§ 906,
912).

7. Ovum with its tunica granulosa and retinacula, removed from the Graafian follicle ; a,

germinal vesicle ; b, germinal spot ; c, zona pellucida ; d, globules of the yolk ; r, r.
retinacula; t, g, tunica granulosa (§ 906).

8. Graafian follicle discharging its Ovum, ov, to which the tunica granulosa, tg, and retina-

cula, r, r, remain attached (§ 912).

9. Ovarium Ovum in preparation for fecundation : a, germinal spot beginning to resolve it-

self into cells at its margin ; b, germinal vesicle ; c, elliptical cells in the place of
the yolk; d, zona pellucida. 100 Diameters (§§ 915, 916.)

10. Ovum nearly ready for fecundation: a, germinal spot more fully developed into cells, of

which concentric layers occupy the germinal vesicle b ; c, elliptical discs or cells ;
«?, zona pellucida; e, outer layer of cells of yolk (§§ 130, 915, 916).

11. Fecundated Ovum of nine hours; the germinal vesicle, having returned to the centre of

the ovum, is concealed by the large elliptical discs, which fill the cavity of the
zona pellucida (§ 916).

12. Plan of one of these discs or cells: its nucleus, a, has developed itself into concentric

rings of cells: and in the most fully developed of these, the nucleus, b, is seen to
be commencing the same kind of evolution. In the centre of the original nucleus,
a pellucid spot, the nucleolus of Schwann and Schleiden, is observed (§§ 130, 916).

XX EXPLANATION OF PLATES.

TIG.

13. Ovum from the Uterus, measuring about l-68th of an inch in diameter: a, pair of cells
now occupying the greater part of the germinal vesicle b ; c, zona pellucida ; d,
chorion, a new envelope, separated from the last by the fluid it has absorbed
(§§ 130, 917).

34. Ovum, of which the essential part, a, the pair of cells occupying the germinal vesicle,
has advanced further than in the last case; the other contents of the germinal
vesicle have undergone liquefaction. The chorion is here incipient; and the re-
mains of the cells of which it is composed are seen at cho (§§ 130, 918).

15. More advanced ovum; the cavity of the germinal vesicle filled with cells, a, that have

originated in the two represented in the last figure; these cells have nuclei, 6,
which are undergoing a corresponding process of evolution into secondary cells ; c
and d as in Fig. 13 (§§ 130, 935).

16. Ovum in a state rather more advanced; a, central cell of the germinal mass, now come

to the surface, and showing the nucleus 6 with a pellucid centre, from which most
of the embryonic structures are developed ; c, cavity in the germinal mass, caused
by the approach of its peripheral cells to the enclosing membrane, d (§§ 935, 936).
17: Formation of the Membrana Decidua; a, a, a, interfollicular substance of the mucous
membrane of the uterus ; 6, cavities of the follicles ; c, uterine vessels prolonged
into the decidua and forming loops. After Baer (§ 919).

18. Human Spermatozoa; a, seminal granules. After Wagner (§ 902).

19. Cyst of evolution. After Wagner (§ 902).

20. Capsular bundle of Spermatozoa, just previous to their separation. After Wagner

(§ 902).

21. Globules from the Chyle; a, ordinary globules; b, a globule (cytoblast ?) surrounding

itself with an envelope (a forming cell?); c. minute molecules of chyle; d, a
colourless corpuscle from the blood. After Wagner (§§ 692, 693).

22. Particles of Blood undergoing multiplication : a, b, c, d, e, successive stages. After Barry

(§ 148).

23. Extremity of one of the tufts of foetal vessels forming the Placenta; this includes (like

a branchial tuft) an artery and vein. After Reid (§ 922).

24. Plan of the structure of the Placenta, according to Dr. J. Reid's view of it ; a, a, portion

of substance of uterus ; b, b, b, b, section of uterine sinuses, some of them opening
on the inner surface into the cavity of the placenta; c, curling artery of uterus ; d, d,
ramifications of fcetal vessels, some of them sending down prolonged tufts which
dip into the uterine sinuses (§ 923).

PLATE II.

25. Uterine Ovum of Rabbit, showing the Area Pellucida, with the annular nucleus of the

embryonic cell (Fig. 14, b) now elongated. In the clear space enclosed by this is a
well-marked dark groove, occupying the position in which the nervous centres are
subsequently to be developed. The cephalic extremity of this is already rounded
and the caudal extremity pointed. After BischofT (§ 937).

26. More advanced ovum, showing the incipient formation of the Vertebral column ; and

the dilatation of the primitive groove at its anterior extremity. After Bischoff
(§ 937).

PLATE H.

EXPLANATION OF PLATES. XXI

FIG.

27. More advanced embryo, seen on its ventral side, and showing the first development of
the Circulating apparatus. Around the Vascular Area is shown the terminal sinus,
a, a, a. The blood returns from this by two superior branches, b, b, and two infe-
rior, c, c, of the omphalo-meseraic veins, to the heart, d; which is, at this period, a
tube curved on itself, and presenting the first indication of a division into cavities.
The two aortic trunks appear, in the abdominal region, as the inferior vertebral
arteries, e, c; from which are given off the omphalo-meseraic arteries, /,/, which
form a network that distributes the blood over the vascular area. In the cephalic
region are seen the anterior cerebral vesicles, with the two ocular vesicles, g. After
Bischoff(§ 938).

LIST OF WOOD-EIGBAYIEGS.

FIG. PAGE

1. Structure of the Star-fish, after Tiedemann 43

2. External aspect of Aplysia, after Rang, 46

3. .Structure of Aplysia, after Cuvier 47

4. Section of Cockchafer, after Strauss-Durckheim - 50

5. Comparative view of base of Skull of Man, and of Orang-Outan, after Owen - 68

6. Comparative view of the Skeletons of Man aud the Orang, after Owen

7. Views of Prognathous Skull, after Prichard

8. Views of Pyramidal Skull, after Prichard

9. View of Oval Skull, after Prichard

10. Fibrous structure of Exudation-membrane, after Gerber 107

11. Fibrous membrane from the Egg-shell - 107

12. Simple Isolated Cells, containing reproductive Molecules 110

13. Cells of Zygnema, showing spiral arrangement of nuclear particles, after Hassall 110

14. Cells of Pelargonium, showing stellate prolongations of nuclei - 111

15. tfematococcus binalis, in various stages of development, after Hassall - 111

16. Coccochloris cystifera, in various stages of development, after Hassall - 111

17. Heematococcus sanguineus, in various stages of development, after Hassall 112

18. Nostoc macrosporum, in two states, after Hassall

19. Section of branchial Cartilage of young Tadpole, after Schwann 114

20. Endogenous cell-growth in cells of a meliceritous tumor, after Goodsir - 115

21. Colorless cells with active molecules and fibres of fibrine, after Addison 118

22. Arrangement of Fibres in Areolar Tissue 120

23. White Fibrous Tissue, from Ligament - 122

24. Yellow Fibrous tissue, from Ligamentum nuchse of Calf 122

25. Elements of Areolar Tissue, after Todd and Bowman - 122

26. Development of Areolar Tissue, after Schwann 122

27. Red Corpuscles of Human Blood, after Donne - 124

28. Red Corpuscles of Frog's Blood, after Wagner - 125

29. Production of Red Corpuscles in Chick, after Wagner - 129

30. Small Venous Trunk, from web of Frog's foot, after Wagner - 132

31. Vertical Section of Epidermis, after Wilson 137

32. Choroid Epithelium, with pigment cells, after Todd and Bowman 139

33. Cells of Pigmentum Nigrum - 139

34. Section of the nail and its matrix, after Todd and Bowman 140

35. Hairs of Sable and Musk-Deer - 141

36. Hair and hair follicles seen in section, after Todd and Bowman 141

37. Structure of Human Hair, after Wilson - 142

38. Pavement-Epithe hum-cells 144

39. Ciliated Epithelium 144

40. Examples of Cilia, after Todd and Bowman. - - 145

41. Secreting Follicles from the Liver of Crab 146

42. Capillary Network of Skin, after Berres

43. Capillary Network of Intestinal Villi, after Berres 148

44. Capillary Network of Mucous Membrane, after Berres -

45. Diagram of the Structure of Mucous Membrane, after Todd 149

46. Extremity of Intestinal Villi, after Goodsir 151

47. Secreting Cells of Human Liver, after Bowman 152

48. Shape of Fat Vesicles in close pressure, after Todd and Bowman

49. Cells of Adipose Tissue 153

50. Blood Vessels of Fat, after Todd and Bowman - 153

XXIV LIST OF WOOD-ENGRAVINGS.

i

PIG. PACE

51. Fat Vesicles from an emaciated subject, after Todd and Bowman 154

52. Section of Branchial Cartilage of Tadpole, after Schwann - 155

53. Section of Fibro-Cartilage - - 155

54. Ampullary Loops of Vessels of Cartilage, after Toynbee 1 57

55. Nutrient Vessels of Cartilage, after Toynbee ..... 157

56. Nutrient vessels of the Cornea, after Toynbee - 158

57. Vertical section of Sclerotica and Cornea, after Todd and Bowman - - 158

58. Tubes of the Cornea of an Ox, injected, after Todd and Bowman 159

59. Calcified Areolar Structure from shell of Echinus ... 161

60. Cellular Membrane from Shell of Pinna 161

61. Section of Bone - - 162

62. Transverse section of a long Bone, after Todd and Bowman - 163

63. Transverse section of a Tibia, after Tomes - - 163

64. Lacunse of Osseous Substance - - 163

65. Haversian canals in a long Bone, after Todd and Bowman 164

66. Section of Cartilage at Seat of Ossification, after Wilson 168

67. Vertical section of Cartilage, after Todd and Bowman 168

68. Scapula of a Fcetus, showing the process of ossification, after Tomes - 170

69. Longitudinal section of an Incisor and Molar Tooth 174

70. Vertical section of an adult Bicuspid ----- 174

71. Vertical Section of an imperfectly developed Incisor - 174

72. Hexagonal terminations of Fibres of Enamel, after Retzius - 174

73. Fibres of Enamel viewed sideways, after Retzius 175

74. Vertical section of Bicuspid highly magnified - - 175

75. Most interior portion of Main Tubes of Dental Bone - 175

76. Ramifications of the Main Tubes of Dental Bone 175

77. Transverse section of Crown of Bicuspid, highly magnified - 176

78. Position of the Main Tubes near the Root of Bicuspid 176

79. Sections of a Human Incisor, highly magnified, after Todd and Bowman 1 76

80. Transverse sections of Tubules of Dentine, after Todd and Bowman - 177

81. Oblique Section of Dentine, after Owen 177

82. Vessels of Dental Papilla, after Berres ISO

83. Diagram of development of Dentine, after Owen 180

84. Inner surface of cap of dentine, after Owen - 181

85. Formation of Enamel, after Owen 182

86. Formation of the Cementum, after Owen 182

87. First stage of Formation of Teeth, after Goodsir 183

88. Diagram illustrating subsequent stages of formation of Teeth, after Goodsir - 183

89. Do. do. do. after Goodsir - 184

90. Capillary network in Frog's foot, after Wagner - - 189

91. Capillary vessels from pia mater, after Henle - 190

92. Formation of capillaries in germinal membrane, after Wagner 191

93. Fasciculus of fibres of Voluntary Muscle, after Baly - 193

94. Portion of Human Muscular Fibre, separating into disks, after Bowman 193

95. Cleavage of Striped Elementary Fibres 194

96. Muscular Fibre broken across, showing Myolemma, after Bowman - 194

97. Transverse Section of Muscular Fibres of Teal, after Bowman 196

98. Fragment of Muscular Fibre from Heart of Ox, after Bowman 197

99. Structure of ultimate fibrillas of striated Muscular Fibre 197

100. Muscular fibre of Dytiscus, contracted in the centre, after Bowman - 198

101. Muscular fibre of Skate, in different stages of contraction, after Bowman 199

102. Attachment of Tendon to Muscular Fibre in Skate, after Bowman - 200

103. Non-striated Muscular Fibre, after Bowman - 200

104. Do. showing nodosities, after Wilson - 200

105. Muscular Fibres from Fo3tus, after Bowman - 202

106. Do. treated with tartaric acid, after Wilson 202

107. Capillary network of Muscles, after Berres - 204

108. Terminating loops of Nerves in Muscles, after Burdach 204

109. Structure of Sympathetic Ganglion, after Valentin - 205

110. Diagram of Tubular Fibre of a Spinal Nerve, after Todd and Bowman 206

111. Structure of Nerve-tubes, after Wagner 207

112. Primitive fibres and ganglionic globules of human brain, after Purkinje 208

113. Nerve-vesicles from the Gasserian ganglion, after Todd and Bowman 209
314. Caudate nerve-vesicles from the cerebellum and cord, after Todd and Bowman 210

LIST OF WOOD-ENGRAVINGS. XXV

FIB. PAGE

115. View of piece of Otic ganglion of sheep, after Valentin 210

116. Two views of the vesicular and fibrous matter of the cerebellum, after Todd

and Bowman ... 211

117. Vesicular and fibrous matter in the Gasserian ganglion, after Todd and Bowman 211

118. Primitive Fibres and ganglionic globules, after Wagner - - 211

119. Distribution of tactile nerves in skin, after Gerber ... 212

120. Terminal loops of nerve in the pulp of a tooth, after Valentin 213

121. Capillary network of nervous centres, after Berres - 214

122. Capillary loops in skin of finger, after Berres • 214

123. Stages of the development of nerve, after Schwann - 215
12 1. Nervous system of Solen, after Blanchard - 251

125. Nervous system of Aplysia, after Cuvier 254

126. Nervous system of larva of Sphinx ligustri, after Newport - 25G

127. Portion of ganglionic tract of Polydesmus, after Newport 257

128. Parts of Nervous System of Articulata, after Newport 259

129. Stomato-gastric system of Gryllotalpa vulgaris, after Brandt - 261

130. A View of the Great Sympathetic Nerve - 267

131. Roots of a dorsal Spinal Nerve, after Todd and Bowman 268

132. Nervous centres in Frog, after Leuret - - 270

133. Transverse sections of Spinal Cord at different points, after Solly 271

134. Structure of the Spinal Cord, after Stilling 272

135. Connection of nerve-roots with the Spinal Cord, after Stilling - 272

136. A posterior superior view of the Pons Varolii, Cerebellum, &c. 275

137. An anterior view of the Medulla Oblongata, after Todd and Bowman 275

138. A posterior view of the Medulla Oblongata, after Todd and Bowman 275

139. Transverse section of the Medulla Oblongata, after Stilling - 276

140. Course of the Motor tract, after Sir C. Bell 277

141. Course of the Sensory tract, after Sir C. Bell - 278

142. Analytical diagram of the Encephalon, after Mayo - 279

143. Brains of Fox-shark, Cod, and Pike, after Leuret 281

144. Human Embryo of 6th week, showing rudiments of Brain, after Wagner 282

145. Brain of Turtle, after Solly - 283

146. Brain of Buzzard, after Leuret 283

147. Brain of Human Embryo at 12th week, after Tiedemann 284

148. Brain of Squirrel laid open, after Solly 284

149. Upper and under surface of Brain of Rabbit, after Leuret 285

150. Diagram of the distribution of the Fifth Pair - 311

151. A view of the distribution of the Trifacial nerves 312

152. A view of the Third, Fourth, and Sixth Pairs of nerves 313

153. Diagram of the distribution of the Seventh Pair 314

154. Diagram of the distribution of the Eighth Pair 315

155. A view of the distribution of the Glosso-Pharyngeal, Pneumogastric and Spinal

Accessory Nerves, or Eighth Pair - 316

156. A view of the course and distribution of the Hypoglossal, or Ninth Pair - 324

157. Base of the Cerebrum and Cerebellum with their nerves 327

158. A view of the Optic nerve and the origins of seven other pairs 340

159. Plan of the optic tracts and nerves, after Todd and Bowman - 342

160. Course of Fibres in the Chiasma, after Todd and Bowman - 342

161. Origin and distribution of the Portio Mollis of the Seventh Pair, or Auditory

Nerve 343

162. Capillary network at margin of lips, after Berres 396

163. Dorsal surface of the Tongue, from Scemmerring 399

164. Simple papilla? near the base of the tongue, after Todd and Bowman - 400

165. Vertical section of one of the circumvallate papilla?, after Todcl and Bowman 400

166. Compound and simple papillae of Foramen Caecum, after Todd and Bowman 400

167. Capillary network of fungiform papilla of tongue, after Berres 401

168. Fungiform papilla with its simple papilla? and vessels, after Todd and Bowman 401

169. Forms of the conical or filiform papilla?, after Todd and Bowman - 9 - 401
1 «n (A. Section of filiform and fungiform papilla? ) m -, , , T>

'• I B. Structure of filiform papilla \ after Todd and Bowman

171. Nerves of the papilla? of the tongue, after Todd and Bowman 403

172. Distribution of Olfactory nerve on Septum Nasi 405

173. Longitudinal section of globe of the eye ... 408

174. Horizontal section of the eyeball - - 409

3

.

XXVI LIST OF WOOD-ENGRAVINGS.

FIG. PAGE

175. Outer surface of retina of Frog, after Treviramis 412

176. Capillary network of retina, after Berres - 412

177. A portion of the retina of an Infant, magnified - 412

178. Vertical section of the Human retina and Hyaloid membrane, after Todd and

Bowman - - - 413

179. Membrane of Jacob, after Jacob 413
ISO. General section of the Ear, after Scarpa 423

181. Diagram of the Inner wall of Tympanum, after Todd and Bowman - 424

182. Axis of Cochlea and Lamina Spiralis - 425

183. Cochlea of a new born Infant, after Arnold - 425

184. Section of the Cochlea, after Breschet - - 426

185. Papillee of Auditory nerve on spiral lamina of cochlea of young mouse 426

186. Auditory nerve taken out of the cochlea 426

187. Magnified view of the Lamina Spiralis 427

188. Plexiform arrangement of cochlear nerves, after Todd and Bowman - 427

189. Soft parts of the Vestibule 428

190. Ampulla of the External Semicircular Membranous Canal - 428

191. Labyrinth laid open, after Breschet - . 433

192. Labyrinth of the Left Side 434

193. Left Ear in its natural state - - 435

194. Anterior view of the External Ear, Meatus Auditorius, &c. - 435

195. External and Sectional views of the Larynx, after Willis 456

196. Bird's-eye view of Larynx from above, after Willis - 457

197. Diagram of the direction of the muscular forces of the Larynx, after Willis - 458

198. Artificial Glottis, after Willis - - 461

199. View of the Organs of Digestion in their whole length 493

200. Muscles of the Tongue, Palate, Larynx and Pharynx - - 495

201. Front view of the Stomach distended - 499

202. Interior of the Stomach - 499

203. Interior of the Stomach and Duodenum 500

204. Commencement of Lacteal in Villus. after Krause 510

205. Vessels of Intestinal Villus of Hare, after Dollinger - 511

206. Do. Do. of Man, after Krause . - 511

207. Diagram of Lymphatic Gland, after Goodsir - 517

208. Portion of intra-glandular Lymphatic, after Goodsir - 517

209. Section showing the anatomy of the Thymus gland, after Cooper 521

210. Microscopic appearance of Inflammatory Blood, after Addison 534

211. Web of Frog's foot, slightly magnified, after Wagner - 541

212. The anatomy of the Heart - 551

213. Hsemadynamometer of Poisseuille 555

214. Gill-tuft of Doris, after Alder and Hancock - 573

215. Lung of Triton, slightly magnified, after Wagner 574

216. Portion of the same more highly magnified, alter Wagner 574

217. Capillary Circulation in lung of living Triton, after Wagner - 575

218. The Larynx, Trachea and Bronchia - 576

219. Bronchia and Blood-vessels of the Lungs • 577

220. Development of Lungs, after Rathke - 578

221. Arrangement of Capillaries in Human Lung - 579
'222. Mammary Gland of Ornitliorrhyncus, after Miiller - 616

223. Exterior of lobule of liver of Squilla, after Miiller . 619

224. Interior of do. do. do. 619

225. Inferior Surface of the Liver - - (>'-'i >

226. Tlircc Coats of the Gall Bladder 620

227. (lull hhidiliT distended, with vessels injected - 621

228. Nucleated Cells of Parenchyma of Liver 621

229. Lobules of Liver, with branches of Hepatic vein, after Kiernan 622

230. llori/nnial section of lobules, showing arrangement of their blood-vessels, after

%-rnan - - 622

231. Horizontal section of lobules, showing arrangement of their bile-ducts, after

Kiernan - - - - 622

232. Nucleated Cells forming Parenchyma of Liver, after Bowman 624

233. Origin of Liver in Chick, after Miiller - 624

234. Lobules in a state of Anirniia, after Kiernan - 625

235. Do. in first stage of hepatic-venous congestion, after Kiernan - 625

LIST OF WOOD-ENGRAVINGS. XXV11

FIG. PAGE

236. Lobules in second stage of hepatic-venous congestion, after Kiernan 625

237. Do. in a state of portal-venous congestion, after Kiernan - 625

238. Hepatic cells loaded with Fat, after Bowman 627

239. Right Kidney, with Renal Capsule - 632

240. Section of Kidney after Wilson 632

241. Half a Kidney, divided vertically 633

242. Kidney divided vertically, with Arteries injected - 633

243. Section of Kidney, after Wagner - 634

244. Portion of Tubulus Uriniferus, after Wagner - 634

245. Section of a Pyramid of Malpighi 635

246. Magnified view of small portion of the Kidney, after Wagner 636

247. Structure of Malpighian Body, after Bowman - - 637

248. Diagram of Circulation in the Kidney, after Bowman - 637

249. Corpora Wolffiana, after Muller ' 637

250. Mammary Gland - - 647

251. Vertical section of Mammary Gland - 647

252. Distribution of Milk-ducts in Mammary Gland, after Sir A. Cooper - 648

253. Termination of portion of milk-duct in a cluster of follicles, after Sir A. Cooper 648

254. Mammary follicles, with contained cells, after Lebert - 648

255. Lobule of Parotid Gland, after Wagner - - - 656

256. Capillary Network of Glandular follicles, after Berres - 656

257. Rudimentary Pancreas of Cod, after Muller ... . 656

258. The Testicle injected with Mercury - - ... 658

259. Minute structure of the Testis - .... 658

260. Human Testis, injected with Mercury, after Lauth - - 659

261. Diagram of the structure of the same - - - 659

262. Sudoriferous Gland, after Wagner - 661

263. Layer of Sweat-glands of the Axilla, after Todd and Bowman 662

264. Sweat-gland and its blood-vessels, after Todd and Bowman - - 662

265. Cuticular portion of a Sweat-duct of the Heel, after Todd and Bowman 662

266. Three views of Sebaceous glands and hair-follicles, after Todd and Bowman - 664

267. Cutaneous glands of external Meatus Auditorius, after Wagner - - 665

268. Cutaneous follicles of the Axilla, after Homer - - - 665

269. Gastric glands in Human Stomach, after Wagner ... 666

270. Horizontal section of a Stomach-cell and tubes, after Todd and Bowman - 666

271. Vertical sections of mucous membrane of Stomach, after Todd and Bowman - 667

272. Entrances to secreting follicles, after Boyd - - 667

273. Stomach-cells and Epithelium, after Todd and Bowman - - 667

274. Villi and follicles of Lieberkuhn on surface of Ileum - 668

275. One of the Glandulse solitaries of Peyer, after Boehm ... 668

276. Mucous coat of Small Intestine, as altered in Fever, after Boehm - 668

277. Glands of Peyer on Small Intestine - .... 669

278. Conglomerate gland of Brunner, after Boehm - - 669

279. Patch of agminated Peyerian glands, after Boehm - - 670

280. Extremity of Placental Villus, after Goodsir - - - 705

281. External membrane and cells of Placental villus, after Goodsir - - 705

282. Diagram of the arrangement of the Placental Decidua, after Goodsir - - 706

283. Plan of early Uterine Ovum, after Wagner - . 715

284. Diagram of Ovum, showing formation of digestive cavity and of amnion, after

Wagner - - 715

285. Do. do. still more advanced, the allantois beginning to appear, after

Wagner - - 717

286. Diagram of Ovum in the second month, showing incipient formation of Pla-

centa, after Wagner - . 717

287. Section of Uterus, showing ovum, membranes, &c., at the time of formation of

Placenta, after Wagner - 718

288. Diagram illustrating the Foetal Circulation .... 731

289. Curve representing the relative Viability of Human Male and Female at dif-

ferent ages, after Quetelet - ..... 727
290 Do. do. do. Heights and Weights of the Human Male

and Female at different ages, after Quetelet .... 728

ALSO,
Two Lithographic Plates, with 27 figures.

INTRODUCTION.

THE object of the science of Physiology is to bring together, in a sys-
tematic form, the phenomena which normally present themselves during the
existence of living beings; and to classify and compare these, in such a man-
ner as to deduce from them the general laws or principles, according to which
they take place.

The term Law having been frequently applied to physical and physiological
phenomena, in a manner very different from that which sound philosophy
sanctions, it is desirable to explain the acceptation (believed by the author to
be the only legitimate one) in which it is here employed. The so-called
Laws of Nature are nothing else than general expressions of the conditions,
under which certain assemblages of phenomena occur ; so far as those con-
ditions are known to us. Thus the law of Gravitation, in General Physics
(the most universal in its action of any with which we are acquainted), is
nothing else than a simple expression of the fact, that, under all circum-
stances, two masses of matter will attract each other with forces directly pro-
portional to their respective bulks, and inversely as their distances. So, again,
the law of Cell-growth, which seems to hold the same rank in Physiology
with that of Gravitation in Physics, embodies these two general facts, — that
all organised beings originate in cells, — and that the various functions of life
are carried on, even in the adult condition, by the continued growth and de-
velopment of cells.

In no case can natural phenomena be correctly said to be governed by
laws ; since the laws themselves are nothing else than manifestations of the
Will of the governing Power. But they may be properly said to take place
according to certain laws ; these laws being framed by Man as expressions
or descriptions of the slight glimpses he possesses, of the plan according to
which the Creator sees fit to operate in the natural world. Thus understood,
the use of the term Law can be in no way supposed to imply, that the Deity
stands in any other relation to the phenomena of the Universe than as their
direct and constantly-operating Cause.

In order to determine the true laws, or most general principles, of Phy-
siological Science, a very extensive comparison is requisite. Principles, which
might seem of paramount importance in regard to one group of living beings,
are often found, on a more general review, to be quite subordinate. For
example, the predominance of the Nervous System in the higher classes of
Animals, and its evidently close connection with many of the functions of
life, has led several Physiologists to the opinion, that its influence is essential
to the performance of the functions of Nutrition, Secretion, &c. ; but, on
turning our attention to the Vegetable kingdom, in which nothing analogous
to a nervous system can be proved to exist, we find these functions going on
with even greater activity than in animals. It is clear, therefore, they may
be performed without it ; and, on a closer examination of the phenomena
4

38 INTRODUCTION.

presented by Animals, it is seen that these may be explained better, on the
principle that the nervous system has a powerful influence on such actions,
than on the idea that it affords a condition essential to them. Recent inquiries
have shown that the agents immediately concerned in these operations are of
the same nature in both kingdoms ; the separation of the nutrient materials
from the circulating fluids, or the elimination of substances which are to be
withdrawn from it, being performed in the animal, as in the plant, by cells, in
the manner to be explained hereafter. — This is only one out of many in-
stances, which it would be easy to adduce, in proof of the necessity of bring-
ing together all the phenomena of the same kind, in •whatever class of living
beings they may be presented, before we attempt to erect any general princi-
ples in Physiology.

The object of the present treatise, however, is not to follow out such an
investigation ; but to show the detailed application of the principles of which
Physiological science may now be said to consist, to the phenomena exhibited
by the Human being during the continuance of health or normal life. These
phenomena, when they occur in a disturbed or irregular manner, constitute
disease or abnormal life ; and become the subjects of the science of Pathology.
It is impossible to draw a precise line of demarcation, between the states of
health and disease ; since many variations may occur, which do not pass the
limits of what must be called in some individuals the normal state, but which
must be regarded as decidedly abnormal actions in others. The sciences of
Physiology and Pathology, therefore, are very closely related to each other;
and neither can be pursued with the highest prospect of success, except in
connection with the other.

Equally close is the relation between Hygiene, — or the art of preserving
the body in health, which is founded on the science of Physiology, — and
Therapeutics, which is the art of curing disease, founded upon the science of
Pathology. In proportion as the science of Physiology is perfected, will the
simplicity and certainty of its practical applications increase ; and although
we may not anticipate a return of patriarchal longevity, yet the experience of
the last century has amply shown, that every general increase of attention to
its simple and universally-acknowledged truths is attended with a prolonga-
tion of life, and contributes to that not less important object, its emancipation
from disease. In like manner, with every advance in Pathological science,
will the art of Therapeutics lose its merely empirical character, and become
more and more rational ; that is, the rules laid down for the treatment of
disease will be less and less founded upon the results of a limited experience
as to the efficacy of particular remedies in removing certain abnormal phe-
nomena ; and will have reference more and more to the nature of the morbid
action, which is indicated by the symptoms. Thus, when the urine presents
a particular sediment, our inquiries are directed, not so much to the condition
of the kidney itself, as to the constitutional state which causes an undue
amount of the substance in question to be carried off by the urinary excre-
tion, or which prevents it from being (as usual) dissolved in the fluid.

In proportion as our treatment of disease thus loses its empirical character,
and is founded on scientific principles, must it increase in perfection and suc-
cess ; and in like proportion will the Medical Profession acquire that dignity
to which the nobility of its objects entitles it, and that general estimation
which will result from the enliglitened pursuit of them.

39

CHAPTER I.

ON THE PLACE OF MAN IN THE SCALE OF BEING.

1 . Distinction between Animals and Plants.

1. IN entering upon the general survey of the Animal Kingdom, which it
is desirable to take before we consider in detail any particular member of it,
the question naturally arises, — how is the Animal distinguished from the
Vegetable ? There is no difficulty in replying to this, if we keep in view
merely the higher tribes of each division ; no one, for example, would be in
any danger of confounding a Whale with a Palm, or an Elephant with an
Oak. It is when we descend to the opposite extremity of the scale, that we
encounter the greatest difficulty ; from the circumstance that the distinguish-
ing characters of each kingdom disappear, one after another, until we are
reduced to those which seem common to both. So completely is this the
case, that there are many tribes which cannot, in the present state of our
knowledge, be referred with certainty to either one division or the other. We
are accustomed to think of Animals as beings, which -not only grow and
reproduce themselves, but which also possess the power of spontaneously
moving from place to place, and which are conscious of impressions made
upon them : and we usually regard Plants as beings which are entirely des-
titute of sensibility and of the power of spontaneous motion, — going through
all their processes of growth, reproduction and decay, alike unconscious of
pleasure and of pain, and devoid of all power of voluntarily changing their
condition. Such a definition is probably the most correct that we can employ ;
but great difficulties lie in the way of its application. There are many tribes
which possess a general structure more allied to that of beings known to be
Animals, than to that of any Plants ; and which yet present no decided indi-
cations, either of sensibility or of voluntary power. Such is the Sponge,
the fabric of which closely corresponds with that of many Alcyonian Polypes,
whose animality is undoubted ; whilst there are no known Vegetables to
which it presents any near resemblance : and yet neither observation nor
experiment has ever succeeded in proving that the Sponge feels or spontane-
ously moves. On the other hand, many Vegetables perform evident move-
ments, which, at first sight, appear to be spontaneous, as if they indicated
sensibility on the part of the being that executes them. Such movements,
however, can in some instances (as in that of the Sensitive-Plant, or of the
Venus's Fly-trap), be referred to a sort of mechanism, the action of which
does not involve sensibility, and which may be compared with the many
movements (such as that of the heart) that are constantly taking place in the
bodies of the highest animals, without their consciousness ; and in other cases
(as in the Oscillatorise) they are so rhythmical, as to impress the observer
with the idea that they are rather the result of some physical, than of any
mental, influence. In this respect they correspond with the motions of the
constantly-vibrating cilia; which cover the surface of the mucous membranes
of Animals ; and which have been recently detected in the reproductive par-
ticles of certain among the lower tribes of aquatic Plants.

40 ON THE PLACE OF MAN IN THE SCALE OF BEING.

2. However difficult it may be for us, owing to our imperfect knowledge,
to draw the line in individual cases, it cannot be doubted that a boundary does
exist ; and, in general, a very simple mark will suffice to establish the dis-
tinction. This mark is the presence or absence of a Stomach, or internal
cavity for the reception of food. The possession of a stomach cannot be re-
garded, however, as in itself an essential distinction between the two kingdoms
(as some have represented it) ; for its presence is merely a result, so to speak,
of the nature of the food of Animals, and of the mode in which it is obtained.
Vegetables are dependent for their support, upon those materials only, which
they obtain from the surrounding elements ; carbonic acid, water and ammonia,
duly supplied to them, with a small quantity of certain mineral ingredients,
affording all the conditions they require for the production of the most mas-
sive fabrics, and the greatest variety of secretions. But these same elements,
if supplied to Animals, could not be converted by them into the materials of
organized structures; for they can only employ them as food, after they have
been united into certain peculiar organic compounds ; and Animals are con-
sequently dependent, either directly or indirectly, upon the Vegetable kingdom
for their means of support. Now they cannot incorporate any alimentary
substance into their own tissues, until it has been reduced to the fluid form;
hence they need the means of effecting this reduction, which are supplied by
the stomach. Again, they cannot be always in immediate relation with their
food ; they have to go in search of it, and need a store-room in which it may
be deposited during the intervals ; this purpose also is supplied by the stomach.
It is evident, moreover, that the powers of voluntary locomotion and sensa-
tion, which Animals enjoy, are connected with the peculiar nature of the food
they require; for if they were fixed in the ground, like Plants, they would
not be able to obtain that which they require for their support. It is true that
there are some, which seem almost rooted to one spot; but these have the
power of bringing their food within their reach, though they cannot go in
search of it. Such is the case with many Polypes, which use their outspread
tentacula for this purpose ; and with the lower Mollusca, which can create
currents by means of ciliary action.

3. A distinction might probably be erected, between the Animal and Vege-
table kingdoms, upon the mode in which the first development of the germ
takes place. The seed of the Plant, at the time of fertilisation, principally
consists of a store of nourishment prepared by the parent for the supply of
the germ, which is introduced into the midst of it. The same may be said of
the egg of the Animal. In both instances, the first development of the germ
is into a membranous expansion, which absorbs the alimentary materials with
which it is in contact; and it prepares these by assimilation, for the nourish-
ment of the embryonic structure, the most important parts of which — the
only permanent parts in the higher classes of Animals and in Phanerogamic
Plants — are in its centre. Now in Plants, this membranous expansion (the
single or double cotyledon) absorbs by its older surface, which is applied to
the albumen of the seed, and takes it more or less completely into its own
substance. In Animals, this expansion is developed in such a manner, that
it surrounds the albumen, inclosing it in a sac, of which the inner surface
only is concerned in absorption. This sac is, then, the temporary stomach
of the embryonic structure ; it becomes the permanent stomach of tho liadi-
ata ; but -in the higher classes, only a portion of it is retained in the fabric of
the adult, — the remainder being cast oil', like the cotyledon of Plants, as soon
as it has performed its function. Thus, then, the first nisus of Animal de-
velopment is towards the formation of a stomach, for the internal reception
and digestion of food; whilst the first processes of Vegetable evolution tend
to the production of a leaf-like membrane, which, like the permanent frond of

GENERAL SUBDIVISIONS OF THE ANIMAL KINGDOM. 41

the lower classes of Plants, absorbs nourishment by its expanded surface
only.

4. Some Physiologists have asserted that the nature of the respiratory pro-
cess affords a ground of distinction between Animals and Plants ; — oxygen
being absorbed, and carbonic acid evolved, by the former, — and a converse
change being effected in the surrounding air by the latter. It is not correct,
however, to designate this converse change as a consequence of the respiratory
process ; for in Plants, as in Animals, there is a continual absorption of oxygen
and evolution of carbonic acid, which constitute the true function of respira-
tion; but the effects of this change are masked (as it were), in Plants, by
those of the fixation of carbon from the atmosphere, which only takes place
under the influence of sun-light, and which is much more analogous to the
digestion of Animals. The most valid distinction, in doubtful cases, seems
likely to be founded on the chemical constitution of the tissues themselves.
In the plant, the whole of the organized structure, when freed from the pro-
ducts of secretion which are deposited in it, (many of these containing the
same proportion of nitrogen as exists in animal flesh,) is found to have the
same composition with starch ; being formed of oxygen, hydrogen, and car-
bon only. In the animal, on the other hand, the organised tissues all contain
azote as part of their proper substance ; non-azotised compounds, such as
fatty matter, being merely deposited in these, as products of secretion. Hence
if the chemical composition of the organised tissues themselves can be cor-
rectly determined, the Vegetable or Animal nature of a doubtful body may be
ascertained. By this test, the long-disputed question of the nature of the
true Corallines has been set at rest ; their tissue, when freed from the lime de-
posited in it, being found to have the composition of that of Plants : and upon
evidence of the same kind, (the presence of starch in their interior,) a large
number of tribes, which have been described by Ehrenberg as Animalcules,
are now generally referred to the Vegetable kingdom.

2. General Subdivisions of the Minimal Kingdom.

5. The animal kingdom was formerly divided into two primary groups, — the
Vertebrated and the Invert ebrat ed; the former comprising those which are dis-
tinguished by the possession of a jointed spinal column, consisting of a num-
ber of internal bones, termed vertebrae ; and the latter including all those ani-
mals which are destitute of this support. It was pointed out by Cuvier,
however, that among the Invertebrata there are three types of organization,
as distinct from each other as any of them are from the Vertebrata ; and he
accordingly distributed the whole under four primary, divisions or sub-king-
doms: of these, the VERTEBRATA rank highest; next, the ARTICULATA and
the MOLLUSCA, which may be said to form two parallel series, both of them
inferior in degree of organization to the Vertebrata, but superior to the lowest
group ; and lastly, the RADIATA, which include those animals that border most
closely, both in external aspect, and in general character, upon the Vegetable
kingdom. The members of these groups are readily separated from each
other by the structure of their skeletons, or organs of support and protection ;
as well as by many other characters. In the Vertebrata, the skeleton consists
of a number of internal jointed bones, which are clothed by the muscles that
are attached to them and move them ; these bones are traversed by blood-
vessels, a.nd are to be regarded as in all respects analogous to the other living
tissues of the body. In the Articulata, the soft parts are supported by a hard
external envelope, which is of corresponding form on the two sides of the
median line, and which is divided into several pieces, jointed or articulated

together by a membrane, in such a manner as still to allow of free motion ;

4*

42 ON THE PLACE OF MAN IN THE SCALE OF BEING.

and the muscles, which are numerous and complex, are attached to the inte-
rior of these. In the Mollusca, the whole body is quite soft; and many spe-
cies exist, in which it has no external protection; in a large proportion of the
group, however, the surface has the power of producing shelly matter, so as
to form a protective habitation, within which the animal can withdraw its
body, but which does not exhibit any very definite type of form. In the
Radiata, all the parts are arranged in a circular manner, the mouth being in
the centre; some of them are protected by firmly-jointed external skeletons,
like those of the Articulata ; whilst others deposit calcareous matter in the cen-
tre of their soft fleshy structures, as if sketching out the internal skeleton of
the Vertebrata. The skeletons of most of the Inverteb.rata differ, however,
from those of Vertebrate animals, in this important character, — that they are
not permeated by vessels, and are formed only by superficial deposition.
Hence they are termed extra-vascular : and it is an obvious result of an ar-
rangement of this kind, that parts once formed are never changed, except by
the ordinary processes of decay, and that they can only be extended by addi-
tion to their exterior ; whilst in Vertebrata, the bones are subject to alterations
of any kind, whether of removal or addition, throughout their entire substance.
It is not correct to regard them, however, as mere exudations, or as being des-
titute of vitality ; since they consist, in all instances, of a regularly-organized
tissue, in which the mineral matter, where such exists, is deposited ; and in
several cases they are traversed by tubes, which seem to convey a fluid de-
stined for their nutrition, if not actual blood. Fabrics of this kind are on the
same footing with the dentine and enamel of the teeth of Vertebrata (§§ 209,
210); to which they sometimes bear a very strong resemblance. — A more
detailed account of the general structure of these sub-kingdoms will now be
given, beginning with the lowest.

3. General characters of Radiata.

6. The RADIATA possess many points of affinity with the Vegetable king-
dom ; and of these, the circular arrangement of their parts is one of the most
evident. Many species of Sea-Anemone, for instance, present an appearance
so much resembling that of various composite blossoms, as to have been com-
monly termed Animal-flowers, — a designation to which they further seem
entitled, from the small amount of sensibility they manifest, and the evident
influence of light upon their opening and closing. But it is in the tendency to
the production of compound fabrics, — each containing a number of individu-
als, which have the power of existing independently, but which are to a cer-
tain degree connected with one another, — that we recognise the greatest affinity
in structure, between this group and the Vegetable kingdom. Every tree is
made up of a large number of buds, which are composed of leaves arranged
round a common axis ; each bud has the power of preserving its own life,
and of reproducing the original structure, when removed from the parent stem,
if placed in circumstances favourable to its growth ; and yet all are connected
in the growing tree, by a system of vessels, which forms a communication
between them. This is precisely the nature of the structures formed by the
animals of that class, which may be regarded as the most characteristic of the
Radiate group. Every mass of Coral is the skeleton of a compound animal,
consisting of a number of polypes, connected together by a soft flesh, in which
vessels are channelled out ; these polypes are capable of existing separately,
since each one, when removed from the rest, can in time produce a massive
compound fabric, like that of its parent ; but they all contribute to the main-
tenance of the composite structure, so long as they are in connection with it.
In some instances the skeleton is stony, and is formed by the deposition of

GENERAL CHARACTERS OF RADIATA.

43

calcareous matter — either in the centre of each fleshy column, so as to form a
solid stem, — or on its exterior, so as to form a tube. In other cases it is horny ;
and then it may be a flexible axis, or a delicate tube. Both the stony and
horny Corals frequently possess the form of plants or trees: and as their
skeletons are often found with no obvious traces of the animals to which they
belonged, they have been accounted Vegetable growths. There is not the
least doubt, however, as to the Animal origin of the greater part of these plant-
like structures.

7. The affinity between the lowest Radiata and Plants, in regard to the
vital phenomena they exhibit, is still more close than that manifested by their
structure. Although, in the higher, groups, movements may be constantly
witnessed, which evidently indicate consciousness and voluntary power, this
is far from being the case in the lower. There are many tribes, whose recep-
tion of food, growth, and reproduction, are not known to be accompanied by
any phenomena which distinctly indicate their animal character. The most
violent lacerations produce no signs of sensibility ; and the movements occa-
sionally exhibited by them have not so much of a spontaneous aspect as
those which are performed by many plants. This is the case, for example,
with the Sponge tribe; and also with a number of microscopic species. So

Fig. 1.

Asterias auraniiaca, with the upper side of the hard envelope removed ; a, central stomach; b, coeca
upon its upper surface, probably answering to the liver ; c, c, coecal prolongations of stomach into rays;
c', c', the same empty ; d, the same opened ; e, under surface, showing vesicles of feet ;/", vesicles con-
tracted: showing skeleton between them.

44 ON THE PLACE OF MAN IN THE SCALE OF BEING.

doubtful is the nature of these beings, that their Animal or Vegetable charac-
ter )s rather to be decided by their affinity with species known to belong to
one or the other kingdom, and by the chemical composition of their tissues,
than in any other way. «.

8. It is very different, however, in regard to the higher Radiata. Even
among the Zoophytes (as the plant-like animals just alluded to are com-
monly termed), there are some species which are unattached during the
whole period of their lives, and which have a power of voluntarily moving
from place to place, such as is never possessed by plants. And in the high-
est class, the Echinodermata, including the Star-fish, Sea Urchin, &c., we
meet with a considerable degree of complexity of structure, and a correspond-
ing variety of actions. Still, except in those species which connect this group
with others, the same character of radial or circular symmetry is maintained
throughout ; and in no animal is it more remarkable than in the common Star-
fish. It is exhibited alike in its internal conformation and in its external
aspect. The mouth, placed in the centre of the disk, leads to a stomach
which occupies the greatest part of the cavity of the body; and this sends
prolongations into the arms, which are exactly alike in form, and whicli oc-
cupy a precisely similar position in every one. Each arm is furnished, on its
under side, with a curious apparatus for locomotion, consisting of a series of
short elastic tubes, which are prolonged through apertures in the hard enve-
lope, from a series of vesicles placed along the floor (as it may be termed) of
the ray. The system of vessels for absorbing nutriment and conveying it
through the system, is also disposed upon the same plan; and the same may
be said of the nervous system, and of the only organs of special sensation
which this animal appears to possess — the rudimentary eyes, of which one is
found at the extremity of each ray.

9. Amongst other results of the repetition of similar organs, so remarkable
in the Radiated group, is this, — that one or more of them may be removed with-
out permanent injury to the whole structure, and may even develope them-
selves into an entire fabric. Thus in the Star-fish, instances are known of the
loss of one, two, three, and even four rays, which have been gradually repro-
duced ; the whole process appearing to be attended with little inconvenience
to the animal. In some species of isolated Polypifera, such as the common
Sea-Anemone, and Hydra (Fresh-water Polype), this power of reproduction
is much greater. The Hydra may be cut into a large number of pieces (it is
said as many as 40) of which every one shall be capable of developing itself
in time into a perfect polype. The Sea-Anemone, when divided either trans-
versely or vertically, still lives ; and each half produces the other, so as to re-
form the perfect animal. This is another character which shows the affinity
of the Radiata to the Vegetable kingdom ; and there is yet another, derived
from their mode of reproduction. In many Polypifera, we observe a propa-
gation by buds, in all respects conformable to that which plants effect, and
quite different from the regular multiplication by distinct germs. This gem-
miparous reproduction, as it is called, takes place, not only in the compound
Polypifera, whose plant-like structures are extended by it, but also in some
isolated species, such as the Hydra ; from the body of which one or more young
polypes bud forth at the same time ; and these buds may themselves put forth
another generation, previously to their separation from their parent. This
kind of reproduction is not seen anywhere else in the whole Animal kingdom,
except in a few of the lowest Mollusca and Articulata, which border most
closely on the Radiata.

10. In the lowest animals of this group, such as the simplest forms of Po-
lypes, we find the whole body to consist of nothing else than a stomach, fur-

GENERAL CHARACTERS OF MOLLUSCA. 45

nished with tentacula for drawing food to its orifice.* The nutrient materials
are imbibed by the walls of the stomach, and are transmitted by them to the
tentacula, without any regular circulation ; and the exposure of the whole of
the soft surface of the body to the surrounding liquid, affords all the aeration
which is requisite. In the Medusae, or Jelly-fish, we often find the stomach
extending itself into a ramified system of tubes, which convey its contents to
the thin border of the umbrella-shaped disk, for more effectual aeration ; but
there is still no separate circulating system, except in a few instances. In the
class of Echinodermata, however, which includes the highest forms of Ra-
diated animals (such as the Asterias or Star-fish, Echinus or Sea-Urchin, and
Holothuria or Sea-Cucumber), we find the digestive cavity restricted within
much narrower limits ; and there is here a distinct system of vessels, adapted
to absorb the nutrient fluid from the digestive cavity, and to convey it to the
remoter parts of the system for their nutrition, as well as to effect its aeration,
by exposing it to the influence of the air contained in the surrounding liquid,
in organs especially adapted for that purpose.

4. General characters of Mollusca.

11. The range of Animal forms comprehended in the Sub-Kingdom MOL-
LUSCA is so great, that it would be difficult to include them in any positive
definition which should be applicable to all. They present few traces of the
circular disposition of organs around the mouth, which is characteristic of the
Radiated classes ; and we seldom meet with any marked approach to the
elongation of the body, — still seldomer with any indication of that division
into segments, — which are the chief peculiarities of the Articulata. It is by
the absence of these, and of any trace of the Vertebrated structure, that the
Mollusca are most readily defined. The variety of form which they present,
is less surprising, when it is considered that the bulk of their bodies is almost
entirely made up by organs of nutrition ; the organs of sensation and locomo-
tion, which they possess, being chiefly subservient to the supply of these.
We find, in the lowest tribes of this group, living beings which are fixed to
one spot during all but the earliest period of their lives ; and which scarcely
possess within themselves so much power of movement, as that enjoyed by
the individual Polypes in a compound polypidom ; and yet these exhibit a
complex and powerful digestive apparatus, a regular circulation of blood, and
an active respiration. We never find, throughout the whole Animal kingdom,
that the apparatus of organic life is arranged on any definite plan of its own ;
its confirmation being adapted to the type which predominates in the struc-
ture of each group, and which is principally manifested in the disposition of
the locomotive organs. Thus, the stomach of the Star-fish is circular, and
sends a prolongation into each ray ; whilst the digestive cavity of the Articu-
lata is prolonged into a tube. In the Mollusca, there is no such definite
type, the apparatus of nutrition having the predominance over that of loco-
motion ; and the form of the body is, therefore, extremely variable. The re-
lative places, even of the most important organs (such as the gills), are found
to undergo complete changes, as we pass from one tribe to another ; although
their general structure is but little altered.

12. The lower Mollusca may be characterised as consisting merely of a

* It is usual to speak of the orifice of the stomach, in the Polypes, as the mouth ; and to
regard the tentacula as prolonged lips. It appears to the author much more reasonable, how-
ever, to consider this aperture as the cardiac orifice of the stomach ; and to regard the tenta-
cula in the light of pharyngeal constrictors, their office being to grasp the food and convey it
to the stomach. This view is borne out by the conformation of the superaddcd parts in the
Ciliobrachiate Polypes and Ascidian Molluscs.

46 ON THE PLACE OF MAN IN THE SCALE OF BEING.

bag of viscera ; they have not even any prominence for the mouth, nor any
organs of special sense, such as would distinguish a head ; and they are
entirely destitute of symmetry, — the radiated arrangements of parts seen in
Zoophytes being absent, as well as the bi-lateral correspondence which is
characteristic of the higher sub-kingdoms. In the more elevated Mollusca,
however, which possess not merely sensitive tentacula, but eyes and even or-
gans of smell and hearing, we find these disposed in a symmetrical manner ;
so that the head, which is the part concerned peculiarly in animal life, does
present a bi-lateral equality of parts, even when the remainder of the body
wants it. Further, in the more active among the higher classes, we find this
bi-lateral symmetry showing itself in the exterior of the whole body ; evi-
dently bearing a pretty close relation to its degree of locomotive power. It
is most evident and complete in the Cephalopoda (Cuttle-fish tribe); many
of which are adapted to lead the life of Fishes, and resemble them in the
general form of the body, as also in the structure of many of the individual
organs. It is also manifested in many of the shell-less Gasteropoda, such as
the Slug, or the Aplysia (Sea-Hare) ; as will be seen by the accompanying
representation of a species of the latter. But this symmetry does not extend

Fig. 2.

Aplysia depilans ; a, branchiae or gills.

to the arrangement of the internal organs ; and appears to be only designed to
adapt the body for more convenient locomotion.

13. As a group, however, the Mollusca are to be characterised rather by
the absence, than by the possession, of any definite form ; arid there is a
corresponding absence of any regular organs of support, by which such a
form could be maintained. The name they have received designates them
as soft animals ; and this they are pre-eminently, as every one knows, who
has taken a Slug between his fingers. The shell, where it exists, is to be
regarded rather in the light of an appendage, designed for the mere protec-
tion of the body, and deriving its shape from the latter, than as a skeleton,
giving attachment to muscles, and regulating the form of the whole structure.
It is in no instance a fixed point for the muscles of locomotion ; and it is only,
indeed, where the body is uncovered by a shell, or where a locomotive organ
may be projected beyond it, that any active movements can be executed.
This locomotive organ, — ihefoot, as it is commonly termed — is nothing else
than a fleshy mass, formed by the increased development of the muscular
portion of one part of the general envelope of the body, termed the mantle,
in which the visceral mass is loosely included. The mantle is not essen-
tially different from the skin of other animals ; but it is usually thicker, pos-
sessing a considerable amount of muscular fibre interwoven with it, and its

GENERAL CHARACTERS OF MOLLTJSCA.

47

surface having frequently a glandular character. This general muscular
envelope is the only locomotive organ possessed by a large portion of the
Mollusca ; but its contractile properties are usually greatest at some particular
spot, where it is thickened into a sort of disk, by the alternate contraction
and extension of which the animal can slowly propel itself; this is well seen,
by causing a Snail or Slug to crawl over a piece of glass, so that the under
surface of the disk may be seen whilst it is in operation. The general cha-
racter of their locomotion, however, is well expressed by the term sluggish;
and there are scarcely any among the typical Mollusca, whose activity is such
as to demand for them any higher appellation.

14. The general development of their organs of Nutrition, however, is

Fig. 3.

TV

V

Aplysia cut open, showing the viscera ; a, the upper part of oesophagus ; 6, penis ; e, c, salivary glands ;
d, superior or cephalic ganglion ; e, e, inferior or subcesophageal ganglia; /, termination of oesophagus ;
g, g, first stomach ; h, third stomach ; i, second stomach ; k, intestine ; I, I, I, liver ; m, posterior ganglion ;
n, aorta; o, hepatic artery; p, ventricle of heart; q, auricle; r, s, branchiee ; i,testis; u, lower part of
intestine ; f, ovary ; w, anus.

48 ON THE PLACE OF MAN IN THE SCALE OF BEING.

much higher than is met with among the Articulata ; and, in proportion to
that of the organs of Locomotion, it is much greater than will be elsewhere
observed throughout the Animal kingdom. The justice of this statement will
be made evident by a slight examination of the preceding figure, in which
the interior structure of the Jlplysia, showing the general character of that
of the group, is displayed. The only distinct set of muscles, possessed by
this animal, is that connected with the mouth ; which it is able to push for-
wards or to draw back, and which possesses considerable powers of mastica-
tion, and is furnished with large salivary glands. The nervous centres (of
which more will be said hereafter) are seen to be principally disposed around
the ffisophagus. The whole digestive apparatus is observed to be very com-
plex and highly developed ; the liver alone occupying a considerable part of
the cavity. The heart has distinct muscular walls, and is divided into a
separate auricle and ventricle ; and a large respiratory organ is developed for
the aeration of the blood. The position of the gills, which are external to
the cavity, but which are concealed in part by a fold of the mantle, and in
part by the rudimentary shell, is seen at a, Fig. 2. The generative apparatus,
also, is highly developed. Yet with all this complex organization, the loco-
motive power of the animal is not much greater than that of the Slug; no
other means being provided for the purpose than the contractility of the gene-
ral envelope, which is greatest in the thickened portion on the under side of
the body.

15. The blood of the Mollusca is white, and the number of corpuscles in
it is small. Their temperature is low, being seldom more than one or two
degrees above that of the surrounding medium; but many of them are capa-
ble of being subjected to extreme variations of heat and cold, without their
vitality being thereby destroyed. Their respiration is for the most part aquatic ;
and is performed by means of gills, over which a current of water is con-
stantly being propelled, by the vibration of the cilia that cover their surface.
Many of them are dependent on the same current for their supplies of food ;
part of the water so introduced being taken into the stomach ; and a part
flowing over the respiratory surface. The higher tribes, however, go in
search of their food, and have instruments of mastication for reducing it; but
in these, as in the former, the anal orifice of the intestine opens into the
passage through which the current that has passed over the respiratory organs
finds egress ; so that the faecal matter from the former, Snd the fluid that has
served the purpose of the latter, are discharged together. Although very
voracious when supplies of food come in their way, most of the Mollusca are
capable of fasting for long intervals, where none offer themselves, — a fact
which is readily explained by that general inertness of their vital processes,
which has been stated to be characteristic of the group.

5. General characters of Articulata.

16. The members of the sub-kingdom, ARTICULATA, are distinguished, for
the most part, by characters which are exactly opposed to those just enume-
rated. Their characteristic form is easily defined ; and in no instance is there
any wide departure from it. The body is more or less elongated, and presents
throughout a most exact bi-lateral symmetry. It is completely inclosed in an
integument of greater density than the rest of the structure, which is divided
into distinct rings or segments ; these, being held together by a flexible mem-
brane, allow considerable freedom of motion, whilst they firmly protect the
soft parts, and afford attachment to numerous muscles. It is in the Centipede,
and other such animals, that this division into segments is most distinctly and
regularly marked. In the lower Articulata, such as the Leech and the Earth-

GENERAL CHARACTERS OF ARTICULATA. 49

worm, the integument is altogether so soft, that the intervals of the articulations
are not very distinct from the rings themselves ; and in the highest Crusta-
cea and Arachnida, the segments are so closely united together, as to be in
some instances scarcely recognizable. In the former, the movements of the
body are entirely effected by its own flexion ; whilst in the latter, they are
committed to members developed for that special purpose. These members
also have an articulated external skeleton. The bulk of the body in the Ar-
ticulata is made up of the muscles, by which the several segments and their
various appendages are put in motion ; these muscles have their fixed points
on the interior of the hard envelope, just as they are attached in Vertebrated
animals to the exterior of the bones ; and they form a system of great com-
plexity.

17. The development of the organs of nutrition in Articulata, would seem
to be altogether subservient to that of the Locomotive apparatus, — their func-
tion being chiefly to supply the nerves and muscles with the aliment necessary
to maintain their vigour. The power of the muscles is so great in proportion
to the size of the animals, that in energy and rapidity of movement, some of
the Articulated tribes surpass all other beings. Their movements are directed
by organs of sensation, which, although not developed on so high a plan as
those of some Mollusca, are evidently very acute in their powers. There are
very few instances of Articulated animals being in any way restrained as to
freedom of locomotion ; and these are found in a single group, the Cirrhopoda
or Barnacle tribe, which connects this sub-kingdom with the last. In general,
they roam freely abroad in search of food, and are supplied with prehensile
organs for capturing their prey, and with a complex masticating apparatus for
reducing it. Their actions are evidently directed almost solely by instinctive
propensities, which are adapted to meet every ordinary contingency, being of
similar character in each individual of the same species, and presenting but
little appearance of ever being modified by intelligence. Hence these animals
seem like machines, contrived to execute a certain set of operations ; many of
them producing immediate results, which even Man, by the highest efforts of
his reason, has found it difficult to attain.

18. All the Articulata, save a few of the very lowest species, possess a
distinct head at one end of the body, furnished with organs of special sensa-
tion, and with lateral jaws for the prehension and reduction of food ; and their
movements, being principally guided by the special senses, take place in this
direction. The bi-lateral symmetry of the body is not confined to its exte-
rior ; for it prevails most completely in the whole muscular apparatus ; and
even the organs of nutrition present more distinct traces of it than are to be
seen elsewhere. The compact heart of the Mollusca, for instance, is here
replaced by a long tube, the dorsal vessel, placed on the median line ; and the
respiratory organs, which are usually diffused through the whole system, are
uniform on the two sides. Even the intestinal canal partakes of this symme-
try ; in some species it runs straight from end to end of the body ; and even
where it is otherwise disposed, its appendages are nearly equal on the two
sides. The respiration of this group is for the most part aerial ; and the ap-
paratus for the purpose consists of a series of chambers or tubes, which are
dispersed or extended through the whole body, and which are expanded at
certain points, in insects possessing considerable powers of flight, into large
air-sacs. By this means, the air, the blood, and the tissue to be nourished,
are all brought into contact at the same points ; and a much less vigorous cir-
culation is required than would otherwise be needed ; whilst, at the same
time, the specific gravity of the body is diminished, and flight thereby rendered
more easy. The whole apparatus of nutrition is comprised within a compa-
ratively small part of the body ; and the bulk of the organs which compose

5

50

ON THE PLACE OF MAN IN THE SCALE OF BEING.

it, is never at all comparable with that which we ordinarily find in the Mol-
lusca. Thus, the liver, which in the Oyster forms a large part of the whole
substance, is often scarcely recognizable as such in the Insect; and the intes-
tinal tube seldom makes many convolutions in its course from one extremity
to the other. The blood is usually white, as in the other Invertebrated classes :
but it contains a larger number of corpuscles than are seen in that of most of
the Mollusca. The temperature varies to a certain degree with that of the
atmosphere; but many Insects have the power of generating a large amount of
independent heat, which is strictly proportionable to the quantity of oxygen
converted by them into carbonic acid in the respiratory process. All the ac-
tions of the Articulata are performed with great energy ; and, at the time of
the most rapid increase of the body, the demand for food is so great, that a
short suspension of the supply of aliment is fatal. Many of them are capa-
ble, however, of being submitted to the influence of very extreme temperatures,
with little permanent injury.

19. The adjoining figure, which displays the muscular apparatus of the
interior of the body of a Cock-chafer, will give an idea of its complexity and
variety, and of the large portion of the trunk which is occupied by it ; and
will also show the division of the skeleton into segments, the number of
which in Insects is limited to thirteen. These are nearly equal and similar
to each other in the Larva ; but, in the perfect Insect, the three behind the
head are united into the thorax, to which the legs and wings are attached ;
and the remainder form the abdomen, which has little concern in locomotion.

Fig. 4.

it

Section of the trunk of Melolontha vulgaris, (after Strauss-Durckheim,) showing the complexity of the
Muscular system. The first segment of the thorax (2) is chiefly occupied by the muscles of the head,
and by those of the first pair of legs. The second and third segments (3 and 4) contain the very large
muscles of tin; wings, and those of the other two pairs of legs. The chief muscles of the abdomen are
the long dorsal and abdominal recti, which move the several segments one upon the other.

6. General characters of Veriebrata.

20. In none of the three preceding divisions of the Animal kingdom, does
the Nervous System attain such a degree of development, as to give it that
predominance in the whole fabric which it evidently possesses in VERTE-
BRATA. In the Radiata and Mollusca, its functions are obviously restricted to
the maintenance of the nutritive operations ; and to the guidance of the ani-
mal, by moans of its sensory endowments, in the choice of food, as well as
(in some instances) in the search for an individual of the opposite sex : in the

GENERAL CHARACTERS OF VERTEBRATA. 51

Articulata, its purpose appears similar, but is carried into effect in a different
manner, the locomotive organs being the parts chiefly supplied by it. In the
Vertebrata, on the other hand, the development of all the other organs appears
to be subordinate to that of the Nervous System ; their object being solely to
give to it the means of the exercise of its powers. This statement is not, of
course, as applicable to the lower Vertebrata, as it is to the higher ; but it is
intended to express the general character of the group. The predominance
of the nervous system is manifested, not only in the increased size of its cen-
tres, but also in the special provision which we here find, for the protection
of these from injury. In the Invertebrated classes, wherever the nervous sys-
tem is inclosed in any protective envelope, that envelope serves equally for
the protection of the whole body. This is the case, for example, in regard
to the spiny integument of the Star-fish, the shell of the Mollusca, and the
firm jointed rings of the Insect. The only exceptions occur in a few tribes,
in which the nervous system is much concentrated ; and in which the general
organization approaches that of the Vertebrata.* In Vertebrated animals, we
find that the skeleton essentially consists of a series of parts, which are de-
stined to inclose the nervous centres, and to give attachment on their exterior
to the muscles by which the body is moved ; hence it may be termed the
neuro-skeleton ; in contradistinction to the denno-skeleton, which envelopes
the whole body in many Invertebrata, being formed on the basis of their in-
tegument. The tissues, bone and cartilage, of which the former is composed,
are more closely connected with the vascular system, than are the hard parts
of Invertebrata ; and are consequently more capable of undergoing interstitial
change.

21. In considering the essential character of the skeleton of Vertebrata, we
should look at its simplest forms, — those in which it has the least number of
superadded parts. We find these in the Serpent tribe, among Reptiles, and
in the Eel and its allies among Fish. If we examine their skeletons, we per-
ceive that the Spinal Column, with the Cranium at its anterior extremity,
constitutes the essential part of the vertebrated frame-work ; and that the de-
velopment of members is secondary to this. The Spinal Column usually
consists of a number of distinct bones, the Vertebrae ; each of which is per-
forated by a large aperture, in such a manner that, when the whole is united,
a continuous tube is formed for the lodgment of the spinal cord. The Cra-
nium, which it bears at its upper end, is in reality formed of the same elements
as the vertebrae, instead of differing from them completely in structure, as we
might be led to suppose by examination of its most developed forms only.
The object of this enlargement is to inclose the brain, or mass of cephalic
ganglia, which attains a greatly-increased size in the Vertebrata; and also to
afford support and protection to the organs of special sense, which are far
more highly developed among them than they a're in the lower classes. The
true nature of the cranium is best seen in those animals, in which the brain
bears but a small proportion to the spinal cord, such as the lower Reptiles
and Fishes ; and an examination of its structure in these satisfactorily proves
the reality of this view, which is further borne out by the history of its de-
velopment, and of that of its contained parts, in the higher Vertebrata.

22. The Vertebral column at its opposite extremity, is usually contracted
instead of being dilated, — forming a tail, or a rudiment of one, from which
the nervous centres are entirely withdrawn ; the development of the tail is

Thus, in the highest Crustacea, there is an internal projection from the shell, on each
side of the median line, •which forms a sort of arch inclosing the ventral cord ; and in the
naked Cephalopoda, the nervous centres are supported, and in part protected, by cartilagi-
nous plates, which are evidently the rudiments of the internal skeleton of the Vertebrata.

52 ON THE PLACE OF MAN IN THE SCALE OF BEING.

commonly seen to be in an inverse proportion 1o that of the cranium. To
this column, the ribs and extremities are merely appendages, which we find
more or less developed in the various tribes, and often entirely absent ; whilst
the vertebral column is never wanting, although reduced in some species to a
very rudimentary state. It is interesting to compare its various conditions,
with those which have been noticed in the external skeleton of the Articulata.
In the lowest animals of the group, locomotion is principally or even entirely
performed by flexion of the body itself; and here, as in the worm tribe, we
find the skeleton extremely flexible, the whole being comparatively soft, and
its divisions indistinct. This is the case, for example, in the Lamprey and
other Cyclostome fishes : in which there is no distinct division into vertebrae,
the spinal column scarcely possessing even the density of cartilage. In pro-
portion, however, as distinct members are developed, and the power of loco-
motion is committed to them, we find the firmness of the spinal column in-
creasing, and its flexibility diminishing ; and in Birds, — in which, as in In-
sects, the movements of the body through the air are effected by muscles that
must have very firm points of support, — the vertebral column is much conso-
lidated by the union of its different parts, so as to form a solid frame-work.
As a general rule, then, the mobility of the extremities, and the firmness of
the vertebral column, vary in a like proportion. The number of these ex-
tremities in Vertebrata never exceedsybz«'/ and two of them are not un fre-
quently absent. The power of locomotion is not developed to nearly the
same proportional extent, as in the Articulata ; the swiftest bird, for example,
not passing through nearly so many times its own length in the same period,
as a large proportion of the Insect tribes : but it is far greater than that, which
is characteristic of the Mollusca ; and there is no species that is fixed to one
spot, without the power of changing its place. On the other hand, the high-
est Mollusca approach them very nearly in the development of organs of spe-
cial sense, of which Vertebrata almost invariably possess all four kinds — sight,
hearing, smell, and taste.

23. The perfection of the Articulate structure has been shown to consist
in the development of those powers which enable the animal to perform
actions denoting the highest instinctive faculties. That of the Vertebrata
evidently tends to remove the animal from the dominion of undiscerning,
uncontrollable, instinct; and to place all its operations under the dominion of
an intelligent will. We no longer witness in these operations that uniformity,
which has been mentioned as so remarkable a characteristic of instinctive
actions. There is evidently, among the higher Vertebrata especially, a power
of choice and of determination, guided by a perception of the nature of the
object to be attained, and of the means to be employed, constituting the
simplest form of the reasoning faculty ; and the amount of this bears so close
a relation with the development of the cerebrum, that it is scarcely possible to
regard the two as unconnected. In Man, whose cerebrum is far larger in pro-
portion to his size, as well as more complex in its structure, than that of any other
animal, the reasoning faculties attain the highest perfection that we know to
be anywhere manifested by them in connection with a material instrument ;
the instinctive propensities are placed under their subjection; and all his acts,
excepting those immediately required for the maintenance of his organic func-
tions, are put under their control. It is to Man, therefore, that what was just
now stated, of the predominance of the nervous system in Vertebrata, parti-
cularly applies ; but the same may be noticed, though in a less striking degree,
throughout the group. Not only is the influence of the nervous system to be
traced, in the sensible movements which they perform ; but also in various
modifications of the organic functions, which take place under the influence
of particular states of mind, and the occurrence of which there is no reason

GENERAL CHARACTERS OF VERTEBRATA. 53

to suspect in the lower tribes of animals. These are even much more strik-
ing in Man, than in the lower Vertebrata; indeed the comparative slightness
of the influence of the mind upon the body, is one of the causes which ren-
der the lower Mammalia more able than Man is to recover from the effects
of severe injuries. The Mollusca seem to grow like plants ; their massive
organs increasing by their own separate vitality, and being but little depend-
ent upon each other. Even the act of respiration, which is in most animals
performed by a series of distinct muscular contractions, is there principally
effected through the medium of the cilia which clothe the respiratory surface.
But in the Vertebrata, the nervous system possesses a distinct and independ-
ent rank ; its offices are those which more particularly constitute the active
life of the animal ; the organic functions have for their chief object, the main-
tenance of the nervous and muscular apparatus in the condition requisite for
their activity ; and in consequence, all these different kinds of apparatus are
so interwoven together, that their mutual dependence is very close.

24. The foregoing remarks will be found to have an important bearing on
the details subsequently to be given respecting the functions of the Nervous
system in Man ; and it is desirable to set out with clear ideas on this subject,
since there is no department of Physiology, regarding which more error is
prevalent. There is no valid reason for believing that the Organic functions
in Animals, any more than the corresponding changes in Plants, are depend-
ent on the nervous system for their performance ; but common observation
shows, that they are much influenced by it in the higher animals ; and from
such a comparison as that which has been just now briefly made, it would
appear that, the higher the general development of the nervous system, the
closer is their relation with it.

25. This general character of the Vertebrata harmonises well with what
may be observed, on a cursory glance at the structure of their bodies, as to
the proportion between the organs of Nutritive and those of Animal life. The
former, contained in the cavities of the trunk, are highly developed ; but, as in
the Mollusca, they are for the most part unsymmetrically disposed. Of the
latter, the nervous system and organs of the senses occupy the head; whilst
the muscles of locomotion are principally connected with the extremities:
both are symmetrical, as in the Articulata ; but, whilst that part of the nerv-
ous centres, which is the instrument of reason, is very largely developed, the
portion which is specially destined to locomotion, together with the muscular
system itself, bears much the same proportion to the whole bulk of the body,
as it does in the Articulated series. Hence we observe that the Vertebrata
unite the unsymmetrical apparatus of nutrition, characteristic of the Mollusca,
with the symmetrical system of nerves and muscles of locomotion, which is
the prominent characteristic of the Articulata ; both, however, being rendered
subordinate to the great purpose to be attained in their fabric, — the develop-
ment of an organ, through which intelligence peculiarly manifests itself. — For
the operations of this, a degree of general perfection is required, which is
not met with elsewhere. The higher Vertebrata have a power of constantly
keeping the temperature of the body up to a point, which it can only attain
occasionally, and under peculiar circumstances, in the Articulata, and which
it never reaches in the Mollusca. This involves an energetic performance of
the functions of respiration and circulation ; and these again require consider-
able activity of digestion. All the Vertebrata have red blood, which is pro-
pelled through the system by a distinct muscular heart ; and the number of
red corpuscles, which any given amount of the fluid contains, bears a nearly
constant proportion to the ordinary temperature of the animal. They are
further distinguished from Articulata by a character which seems of little im-
portance, but which is very constant in each group. Whilst the mouth of the

5*

54 ON THE PLACE OF MAN IN THE SCALE OF BEING.

latter is furnished with two or three pairs of jaws which open sideways, that
of the former has never more than one pair of jaws, which are placed one
above or before the other; and these jaws are usually armed with teeth, which
are very analogous in their structure to bone.

7. General characters of Fishes.

26. The Vertebrata are subdivided into classes, principally according to
their mode of performing the functions of respiration and reproduction. Thus,
FISHES are at once separated from all other groups, by the circumstances of
their being adapted, like the aquatic Invertebrata, to aerate their blood by
gills ; and being hence enabled to inhabit water during their whole lives,
without the necessity of coming to the surface to breathe. The low amount
of their respiration prevents their bodies from ever attaining a temperature
much above that of the surrounding medium ; hence they are spoken of as
cold-blooded. Further, they are oviparous ; an ovum or egg being deposited
by the parent, from which, in due time, the young makes its way ; or if, as
sometimes happens, the ovum is retained within the body of the parent until
it is hatched, the young animal, though produced alive, is not subsequently
dependent upon its parent for support. In many respects, the organization
of Fishes is not much advanced beyond that of the higher Mollusca. Their
respiratory apparatus has the same character; and the organs by which the
blood is depurated of its superfluous azote, rather correspond with the tem-
porary Corpora Wolffiana of higher animals, than with their true Kidneys
(CHAP- XV. 3). The vertebral column itself is often very imperfectly deve-
loped ; in a large proportion of the group, the skeleton is cartilaginous only ;
and in the lowest species, it does not even manifest a trace of division into
vertebrae. Living habitually in an element, which is nearly of the same speci-
h'c gravity with their own bodies, Fishes have no weight to support, and have
only to propel themselves through the water. Accordingly we find their
structure adapted rather for great freedom of motion, than for firmness and
solidity ; and as progressive motion is chiefly effected by the lateral action of
the spine, the vertebrae are so united, as to move very readily upon one ano-
ther. Instead of being articulated together by surfaces nearly flat, as in
Mammalia, or by ball-and-socket joints, as in Serpents, they have both their
surfaces concave : and these glide over a bag of fluid (the representative of the
intervertebral substance in the higher animals), which is interposed between
each pair. The tail is flattened vertically ; so as, by its lateral stroke, to pro-
pel the Fish through the water. By this character, true Fishes are distin-
guished from those aquatic Mammalia, which are adapted to inhabit their
element, and which commonly receive the same designation ; for the latter,
being air-breathing Animals, are obliged to come frequently to the surface to
respire ; and their tail is flattened horizontally, to enable them to do this with
facility. The lateral surface of the body of Fish is further extended above, by
the projection of the dorsal fin, which is supported on the spinous processes of
ihe vertebrae ; and below, by the abdominal fin, which also is placed on the
median line ; these will, of course, increase the power of the lateral stroke of
the body, and can only be moved with the spine. The pectoral and ventral
fins, on the other hand, — the former of which answer to the superior extre-
mities, and the latter to the inferior extremities, of Man, — serve, by their in-
dependent movements, rather as steering than as propelling organs ; and they
also assist in raising and depressing the animal through the water. The
scales with which the bodies of all Fishes are covered, are frequently of a
bony hardness, and sometimes form a firmly-jointed casing, in which the
trunk is completely inclosed ; this is especially the case, when the internal

GENERAL CHARACTERS OF REPTILES. 55

skeleton is imperfectly developed ; so that here we have an approach to the
character of the Invertebrata.

27. The swimming-bladder, as it is commonly termed, of the Fish, is not
an organ sui generis ; but is ascertained, by comparison with the pulmonary
sacs of the lower Reptiles, to be a rudimentary lung. It does not, however,
give any assistance in the aeration of the blood, except in a few instances;
but seems to be in general subservient to the elevation and depression of the
body in its element. The heart of the Fish is extremely simple in its con-
struction, containing two cavities only ; and the course of the circulation is
equally simple. The blood which returns from the body in a venous condi-
tion, is received into the single auricle or recipient cavity ; and from this it
passes into the ventricle or propellent cavity. The latter forces it into a large
trunk, which subdivides into branches that are distributed to the branchial
arches on each side ; and in these it undergoes aeration. { Being collected
from the gills by returning vessels, the blood, now become arterial in its cha-
racter, is transmitted to the large systemic trunk, the aorta, by which it is dis-
tributed through the system, — returning again to the heart, when it has passed
through the organs and tissues of the body. Hence it is evident that the
whole of the blood passes through the gills, before it goes a second time to the
system ; by which the imperfection of the aerating process itself is in some
degree compensated. There is a special provision, too, for renewing by
muscular power the stratum of water in contact with the gills ; continual cur-
rents being sent over them from the pharynx, with which their cavity com-
municates. It is worth noticing, that whilst, in the Osseous Fishes, there is
a single large external-gill opening on either side, with a valve-like opercu-
lum or gill-cover, there are, in the Cartilaginous Fishes, several slits on each
side of the neck, one corresponding with each branchial arch. Similar aper-
tures in the neck maybe seen in the embryo of Man and of other Mammalia,
as well as of Birds and Reptiles, at the time that the circulation is in the con-
dition of that of the Fish, — the heart possessing only two cavities, and the
blood being first propelled through a series of branchial arches.

8. General characters of Reptiles.

28. The class of REPTILES is oviparous and cold-blooded, like that of
Fishes ; but the animals belonging to it are formed to breathe air, and to
inhabit the surface of the earth, — the few which are adapted to make the
water their dwelling, being obliged to come to the surface to breathe. Al-
though they breathe air, however, their respiration is not usually so energetic
as that of Fishes, and their general activity is much less. The mechanism
for the inflation of their lungs is very imperfect. Being destitute of a dia-
phragm, they are obliged to force air into the chest, by a process resembling
deglutition or swallowing; so that, strange as it may seem, a Reptile may be
suffocated by holding its mouth open. The heart possesses three cavities,
one of which receives the blood from the lungs, and another from the general
system ; the arterial and the venous blood, contained in these two auricles
respectively, are transmitted to the third or propelling cavity, the ventricle,
where they are mixed ; and the half-arterialised fluid is then transmitted to
the system at large, a part being sent to the lungs. Thus only a portion of
the blood expelled from the heart is exposed to the influence of the air ; and
that which is transmitted to the body is very imperfectly arterialised. In
some of the higher Reptiles, as the Crocodile, the ventricle is double, as in
the superior Vertebrata; and the course of the circulation is so arranged, that
pure arterial blood shall go to the head, where it is most required, whilst a
mixed fluid is sent to the rest of the body. This plan exactly corresponds

56 ON THE PLACE OF MAN IN THE SCALE OF BEING.

with the one, which is adopted in the circulation of the Human foetus, from
the time of the formation of the four cavities in its heart, and of the perma-
nent system of vessels, up to the period of birth. The imperfect arterialisa-
tion of the blood in Reptiles, causes a great degree of general inertness in
their functions. Their motions are principally confined to crawling and
swimming ; their general habits are sluggish, and their sensations are obtuse ;
and their nutritive functions are very slowly performed. Hence they can
exist for a long time, with a very feeble exercise of these functions, under
circumstances that would be fatal to animals, in which they are performed
with greater activity. In cold and temperate climes, they pass the whole
winter in a state of torpidity ; and at other seasons, they may be kept during
a long time from their due supplies of food and air, without appearing to suf-
fer much inconvenience.

29. In regard to the structure of their skeleton, and the external form of
the body, there is a considerable variation among the several orders of Reptiles.
Thus, Tortoises, Lizards, and Serpents, differ from each other so widely,
that a common observer would separate them completely ; and yet they not
only agree in all the foregoing characters, but pass into one another by links
of transition so gradual, that it is even difficult to classify them. They differ,
however, more in the configuration of the accessory parts, than in the struc-
ture of the essential portion of the skeleton, — the spinal column. This is
characterised by the ball-and-socket articulation of the vertebras, each vertebra
having one surface convex and the other concave, — a structure which is more
strongly marked in Serpents, Avhose movements are performed chiefly by the
flexion of the spinal column itself, than it is in the other tribes. The chief
characteristic of the Tortoise tribe, is the shell or case in which the body is
contained. The upper arch of this shell, termed the carapace, is formed by
a bony expansion from the edges of the ribs, which is covered by a set of
horny plates, that are to be regarded (like smaller scales) as epidermic appen-
dages. The under portion, termed the plastron, is composed of the sternum,
which is in like manner extended laterally. In the Land-tortoises, this usu-
ally forms a complete floor ; but in the aquatic species, a part is commonly
absent, the interval being filled up by cartilage and membrane. The skeleton
of the Lizards is formed more upon the general plan of that of Mammalia,
but may be readily distinguished from it. The sternum is usually prolonged
over the front of the abdomen, and the ribs are continued through a much
larger part of the spinal column ; of these abdominal ribs, the white lines
across the recti muscles in the higher Vertebrata, are evidently the rudiments.
In the higher Lizards, the power of locomotion is almost entirely delegated
to the extremities ; but in the less typical species, the body and tail are much
prolonged, so as to present a serpentiform aspect ; and first one pair of feet,
and then the other, disappear, until the form is altogether that of the Serpent.
Even in Serpents, however, rudiments of extremities are frequently to be
found ; but their mode of progression is very different, and these rudiments
are of no assistance to them. The most remarkable feature in the Serpent's
skeleton, besides the absence of legs, and the large number of ribs and verte-
brae, is the deficiency of a sternum; through the absence of this, the extremi-
ties of the ribs are free, and they become in fact the fixed points, on which
the animal crawls, when advancing slowly forwards, in a manner which bears
a strong resemblance to the progression of the Centipede.

30. Although the configuration of the cranium varies much in the different
orders of Reptiles, yet there is a remarkable agreement in certain general cha-
racters, and in the general degree of development. It consists of a much
larger number of parts, than are to be found in the cranium of adult Birds or
Mammalia ; each principal bone being subdivided, as it were, into smaller ones.

GENERAL CHARACTERS OF REPTILES. 57

This condition exactly corresponds with that, which may be observed during
the process of ossification in higher Vertebrata ; for each of the larger bones
of the cranium is formed from several centres of ossification ; so that, if the
cranium of a fetus or young infant be macerated, it will fall into a number of
pieces nearly corresponding with those of the Reptile's skull. The different
orders of Reptiles have a close agreement in various other points ; especially
in the degree of development of their several organs of nutrition. Thus, in
all of them, the lungs, though commonly of large size, are so little subdivided,
as really to expose but a small extent of surface. The glandular structures,
too, are formed upon a much more simple type, than is characteristic of the
warm-blooded Vertebrata. They all agree, moreover, in having the body
covered with stales ; which, though generally small, are sometimes large flat-
tened plates.

31. Between Fishes and true Reptiles, there is a group that remarkably
combines the characters of both ; being composed of animals which come
forth from the egg in the condition of Fishes, but Avhich afterwards attain a
form and structure closely corresponding with that of true Reptiles. This
group, consisting of the Frog and its allies, is sometimes associated as an or-
der (Batrachia} of the class of Reptiles ; though it should probably take rank
as a distinct class, the AMPHIBIA. The Tadpole or larva of the Frog is in
every essential respect a Fish. Its respiration and circulation, its digestion
and nutrition, its locomotion and sensation, are entirely accordant with those
of Fishes. The body is destitute of members for progression, but is propelled
through the water by the lateral undulations of the spinal column, which is
articulated in the same manner as that of Fishes. At a certain period, a me-
tamorphosis commences in which almost every organ in the body undergoes
an essential change. Lungs are developed, which take the place (in regard
to their function) of the gills ; and the latter are atrophied. The auricle of
the heart is divided into two ; and the circulation is performed on the plan of
that of the true Reptile. Two pairs of members are usually formed, to which,
when they are fully developed, the power of progression is committed, — the
tail disappearing; in some species, however, the tail remains, and the extre-
mities are small. The digestive system undergoes a remarkable alteration ;
the intestinal canal, which was previously of enormous length in proportion
to the body, being now considerably shortened, in accordance with the differ-
ent kind of food on which the animal has to subsist. The mode of articu-
lation of the spinal column also, undergoes a change, which brings it to the
type of that of Reptiles. The most obvious point of difference in external
characters, between the higher Amphibia and true Reptiles, is the absence of
scales or plates on the skin of the former. In this manner, the common Sala-
mander or Water-Newt may be recognised as belonging to the Batrachia
though its form would otherwise lead us to place it among the Lizards; and
the Coecilia, which has the form of the Serpent, is in like manner known to
be really allied to the Frog. An acquaintance with the history of these ani-
mals confirms such an arrangement, by showing that the Salamander and the
CoBcilia undergo a metamorphosis ; breathing by gills, and having the general
structure of Fishes, in the early part of their lives.

32. Besides those animals, however, which attain the condition of perfect
Reptiles, this group contains several, whose development is arrested, as it
were, in an intermediate or transition state ; their adult form presenting a re-
markable mixture of the characters of the two classes, which they thus con-
nect. This is the case in the Proteus, Siren, and other less known species,
which retain their gills through the whole of their lives, whilst their lungs are
at the same time developed ; so that, as they can respire in either air or wa-
ter, they are the only true amphibious animals. In their general organization,

58 ON THE PLACE OF MAN IN THE SCALE OF BEING.

they correspond with the Tadpole of the Frog at an advanced period of its
metamorphosis ; and it is a most interesting fact (which has been established
by the experiments of Dr. W. F. Edwards) that, if Tadpoles be kept in such
a manner, as to be amply supplied with food, and exposed to a constantly-
renewed current of water, but be secluded from light and from the direct in-
fluence of the solar heat, they will continue to grow as Tadpoles ; their me-
tamorphosis being checked. The metamorphosis of the Batrachia closely
corresponds with that of Insects ; the young animal, in each case, at the time
of its emersion from the egg, having a resemblance, in all essential particulars,
to a class below that to which it is ultimately to belong. This kind of meta-
morphosis is by no means confined to them, however ; for the gradual exten-
sion of our knowledge of the early history of the different tribes of animals,
is constantly bringing to light new facts of the same kind. The Polypes and
lower Mollusca, for instance, come forth from the egg, and swim about for
some time, in a condition which can scarcely be termed animal; for there is
not even a mouth leading to a digestive cavity ; nor are there any other or-
gans of locomotion than the cilia, the action of which is involuntary. And,
in tracing the development of the Human embryo, we shall find that it under-
goes a series of progressive changes equally remarkable; — the principal differ-
ence being, that these changes are not so arranged in harmony with each
other, as to cause the embryo to present, at any one time, the combination of
characters which belong to the Fish, Reptile, &c., or to enable it to sustain an
independent existence.

9. General characters of Birds.

33. From Reptiles to BIRDS, the transition would seem rather abrupt ; since
the latter class is, in almost every respect, the opposite of the former. Never-
theless, it would seem to have been effected by the now-extinct Pterodac-
tylus, which combined, in a most remarkable degree, the characters of the
two groups. Birds are, like Fishes and Reptiles, oviparous Vertebrata ; but
they differ essentially from both, in being warm-blooded, and in affording as-
sistance by their own heat in the development of the ovum. Birds correspond
with Mammalia, in possessing a heart with four cavities, and a complete dou-
ble circulation ; by which the whole of the blood that has circulated through
the body, is exposed to the influence of the air before being again transmitted
to the system. This high amount of oxygenation of the blood is accompa-
nied by great activity and energy of all the organic functions, acuteness of the
senses, and rapid and powerful locomotion ; as well as by the evolution of a
degree of heat, superior to that which we ordinarily meet with among the
Mammalia. The temperature of Birds ranges from about 104° to 112°. The
lowest is in the aquatic species, whose general activity is much less than that
of the tribes which spend most of their time in the air; the highest is among
those distinguished for the rapidity and energy of their flight, such as the
Swallow.

34. Birds have been denominated, and not inappropriately, the Insects of
the Vertebrated series; as in the animals of that class, we find the whole
structure peculiarly adapted to motion, not in water, nor upon solid ground,
but in the elastic and yielding air. It is impossible to conceive any more
beautiful series of adaptations of structure to conditions of existence, than
that which is exhibited in the conformation of the Bird, with reference to its
intended mode of life. In order to adapt the Vertebrated animal to its aerial
residence, its body must be rendered of as low specific gravity as possible.
It is further necessary that the surface should be capable of being greatly ex-
tended; and this by some kind of appendage that should be extremely light,

GENERAL CHARACTERS OF BIRDS. 59

and at the same time possessed of considerable resistance. The degree of
muscular power required for support and propulsion in the air, involves the
necessity of a very high amount of respiration (§ 275), for which it has been
seen that an express provision exists in Insects; and as the general activity
of the vital processes depends greatly upon the high temperature, which this
energetic respiration keeps up, a provision is required for keeping in this heat,
and not allowing it to be carried away by the atmosphere, through which the
Bird is rapidly flying.

35. The first and third of these objects, — the lightening of the body, and
the extension of the respiratory surface, — are beautifully fulfilled in a mode,
which will be found to correspond with the plan adopted for the same purpose
in Insects. The air which enters the body, is not restricted to a single pair
of air-sacs or lungs placed near the throat; but is transmitted from the true
lungs, to a series of large air-cells, disposed in the abdomen and in various
other parts of the body. Even the interior of the bones is made subservient
to the same purpose; being hollow, and lined with a delicate membrane, over
which the blood-vessels are minutely distributed. In this manner, the respi-
ratory surface is greatly extended; whilst, by the large quantity of air intro-
duced into the mass, its specific gravity is diminished. The subservience of
the cavities in the bones to the respiratory function, is curiously shown by
the fact, which has been ascertained both accidentally and by a designed ex-
periment, that, if the trachea of a Bird be tied, and an aperture be made in
one of the long bones, it will respire through this.

36. The other two objects, — the extension of the surface, and the retention
of the heat within the body, — are also accomplished in combination, by a most
beautiful and refined contrivance, the covering of feathers. Like hair or
scales, feathers are to be regarded as appendages to thecutis; the stem is
formed from it by an apparatus, which may be likened to a hair-bulb on a
very large scale ; but there are some additional parts for the production of the
laminae, which form the vane of the feather, and which are joined to the stem
during its development. These laminae, when perfectly formed, are connected
by minute barbs at their edges, which hook into one another, and thus give
the necessary means of resistance to the air. The substance of which feathers
consists, is a very bad conductor of heat ; and when they are lying one over
the other, small quantities of air are included, which still further obstruct its
transmission by their non-conducting power. Thus the two chief objects are
fulfilled ; — power of resistance and slow-conducting properties being obtained,
in combination with lightness and elasticity. At the two extremes of the
class, however, we meet with remarkable modifications in the typical structure
of feathers. In the Penguin, those which cover the surface of the wings
have a strong resemblance to scales ; and the wings are not employed to raise
this Bird in the air, but only to propel it through water (as fins would do) by
their action on the liquid. On the other hand, in the Ostrich tribe, the laminae
of the feathers are separated from each other, so as no longer to form a con-
tinuous surface ; the feathers more resembling branching hairs. Here the
wings are almost or completely absent; the birds of this tribe being constantly
upon the ground, propelling themselves by running, and approaching the
Mammalia in many points of their conformation.

37. The bony frame-work of Birds presents many remarkable adaptations
to the same purposes. In the first place it is to be remarked, that the faculty
of locomotion is here entirely delegated to the extremities; and that the skele-
ton of the trunk must be consolidated, in proportion to the power with which
they are to be endowed, in order to afford their muscles a firm attachment
(§ 22). Just as the segments of the external skeleton of the Articulata,
therefore, are consolidated in Insects, do we find that the vertebral column

60 ON THE PLACE OF MAN IN THE SCALE OF BEING.

and its appendages are firmly knit together, in the upper part of the trunk of
Birds. The vertebra are closely united to each other; and the ribs are con-
nected with the sternum by bony prolongations of the latter, instead of by
cartilages. This union is so arranged, that the state of expansion is natural
to the thorax, whilst that of contraction is forced. The diaphragm is absent
among birds, as among Reptiles ; except in a few species, which most nearly
approach the Mammalia. But its deficiency is compensated by this contriv-
ance, which keeps the lungs and air-sacs always full, — except when the Bird
by a muscular effort, expels the air from them, in order that they may be re-
filled by a fresh supply. By this means, also, the specific gravity of the body is
more constantly kept down, than it could have been, if the lungs had been
subjected to the constantly-alternating contractions and expansions, which they
perform in Mammalia. It is worthy of remark, that the air which enters the
bones and the air-sacs, passes through the lungs, both on its entrance and
return ; so as to yield to their capillaries all the oxygen which they can take
from it, and of which the blood that it has elsewhere met with has not de-
prived it. It is only in the lungs, that it meets with purely venous blood ; for
they alone receive the branches of the pulmonary artery; the vessels which
are distributed upon the respiratory surface of the air-sacs and bones, being
a part of the systematic circulating apparatus. Hence we may regard this
curious provision, as being partly designed for the aeration of the blood in its
course through the system (this, it will be remembered, being the sole mode
in which the function is performed in Insects), and partly for supplying the
lungs with air, as from a reservoir, during the violent actions of flight.

38. The articulation of the anterior extremity with the trunk exhibits a
peculiar provision for strength and power, which we find in no other Verte-
brata. The two clavicles are united together on the central line, forming the
furcula or merry-thought ; and the use of this is to keep the shoulders apart,
notwithstanding the opposing force exerted by the pectoral muscles in the
action of flight. It is generally firm, and its angle open, in proportion to the
power of the wings. Besides this bone, there is another connecting the
sternum with the scapula on each side ; this is the coracoid bone, which in
Man and most other Mammalia is scarcely developed, being merely a short pro-
cess which does not reach the sternum. The sternum of Birds usually ex-
hibits a very remarkale development on the median line ; an elevated keel or
ridge being seen on it, which serves for the attachment of the powerful mus-
cles that depress the wings. In the great development of the sternum, Birds
have some analogy with the Turtle tribe : which they also resemble in the
deficiency of teeth, and in the development of a horny covering to the jaws:
but in these, the lateral elements of the sternum are the parts most developed;
whilst in Birds it is the central portion which exhibits the peculiarity. From
the depth of the keel of the sternum, a judgment may be formed of the thick-
ness of the pectoral muscles, and thence of the powers of flight ; in the Os-
trich tribe, where the wings are not sufficiently developed to raise the bird
off the ground, the sternum is quite flat, as in the Mammalia. The want of
flexibility in the trunk is counterbalanced by the length and flexibility of the
neck ; the number of cervical vertebrae is very considerable, varying from 12
to 23, — the highest number being present in the Swan tribe. They are so
articulated that the head can be turned completely round, or moved in any
direction. The anterior extremities of Birds being solely adapted to sustain
them in flight, the posterior are necessarily modified for their support on the
ground. They are usually placed rather far back ; but the spine has a posi-
tion more inclined than horizontal, so that the weight may not be altogether
thrown forwards. The trunk is supported on the thighs by powerful muscles;
and there is another series, which passes from the lower part of the spine

GENERAL CHARACTERS OF BIRDS. 61

continuously to the toes, turning over the knee and heel, in such a manner
that the flexion of these joints shall tighten the tendons ; by this contrivance,
the simple weight of the body flexes the toes ; and Birds are thus enabled to
maintain their position, by grasping their perch, during sleep, without any
active muscular effort.

39. Not only do Birds resemble Insects in their general structure and
mode of life, but also in the peculiar development of the instinctive powers.
Under the direction of these, the place for their nests appears to be selected ;
their materials collected ; the nest themselves built, and the young reared in
them ; the migrations are performed ; and many curious stratagems are em-
ployed to obtain food. It is sufficient to indicate these in general terms ;
since it is well known that the habits of Birds have peculiarities restricted to
each species ; and that in all the individuals of each species ; they are as
precisely alike as their circumstances will admit. Nevertheless, there are ob-
served in Birds a degree and kind of adaptation to varying conditions, which
Insects do not possess, and which display an amount of intelligence far su-
perior to what is found in that class (§ 17). This is evinced also in their edu-
cubility ; for no animal can be taught to perform actions which are not
natural to it, unless it possesses in a considerable degree the powers of memory
and association, at least, if not some of the higher mental faculties, such as
the power of perceiving and comparing the relations of ideas. Moreover,
in the domesticability of many tribes of Birds, we see this educability com-
bined with a degree of that higher form of attachment to Man, which is so
strikingly exhibited by certain species of Mammalia. The development of
the senses of Birds varies in different tribes, according to the mode in which
they are adapted to obtain their prey. The sight is almost always extremely
acute, and is their chief means of seeking food ; and where this would be of
comparatively little service, as in the nocturnal rapacious birds, it is compen-
sated by a much higher development of the faculty of hearing, than is com-
mon amongst other tribes. The senses of smell, taste, and touch, do not
seem to be usually very acute in Birds ; but there are particular tribes, in
which each of these is more developed than in the rest.

40. As might be expected from the analogy of Birds with Insects, the de-
velopment of their organs of nutrition (excepting that of the respiratory organs)
is much less striking J,han is that of the locomotive apparatus. The whole
cavity of the trunk, especially in Birds distinguished for their powers of
flight, is small in comparison with that of the body ; but what is wanting in
the size of the organs, is made up in their energy of function. Hence the
demand for food is more active in them than in any other class of animals.
It is interesting to observe, that there is more bi-lateral symmetry in the
arrangement of the viscera, than we usually find in the class above. This is
evidently connected with their active locomotive powers ; as it is obviously
necessary, that the two sides of the body should be balanced with perfect
equality, and that their energy should be exactly correspondent. The lungs
and air-sacs are precisely similar in size and situation on the two sides ; con-
sequently the heart is placed on the median line ; and the mode of origin,
from the aorta, of the trunks supplying the head and upper extremities, is
alike on the two sides. The liver, also, is less asymmetrical than we usually
find it in the Mammalia.

41. It has been remarked, that the assistance afforded by the parent, in
the development of the young, is greater in Birds than in the lower Verte-
brata ; but is less than in Mammalia* Whilst Reptiles and Fishes show little
or no concern for their eggs after they have deposited them, Birds sedulously
tend them, affording them not only protection but warmth, by means of their
powerful heat-producing apparatus. The yolk-bag of the Bird's egg is so

6

62 ON THE PLACE OF MAN IN THE SCALE OF BEING.

suspended in the midst of the white albumen, that, when the egg is laid upon
its side, it will always rise to the highest part of it; and the relative weight
of the several parts is further adjusted in such a manner, that the cicatricula
or germ-spot shall always be at the point nearest the shell, so as to come into
the closest proximity with the source of heat, and also to be in the most im-
mediate relation with the surrounding air. There are some Birds, inhabiting
the equatorial region, which do not always incubate their eggs, trusting to the
solar heat for their maturation. It is said that the Ostriches of the intertro-
pical deserts are content with covering their eggs with a thin layer of sand,
so as to admit the action of the sun by day, and to keep them warm at night ;
but that those living under a less constantly elevated temperature, sit upon
their eggs — if not constantly, at any rate when the solar heat is not sufficient.
This statement has been disputed ; but its truth seems to be confirmed by a
curious observation made by Mr. Knight, that a Fly-catcher, which built for
several years in one of his hot-houses, sat upon its eggs when the temperature
was below 72°, but left them when it rose above that standard. Certain Birds
inhabiting New Holland, deposit their eggs in a sort of hot-bed, composed of
decaying vegetable matter; a number associating together for the construction
of this artificial incubating apparatus, although they live separately at other
times. The degree of assistance afforded by the parent Birds to their young,
after their emersion from the shell, varies much in different tribes ; in general
it may be remarked, however, that it is most prolonged in those which ulti-
mately attain the highest development, and especially in those whose intelli-
gence becomes the greatest. Thus the Chicken and the Duckling, when just
hatched, are able to shift for themselves ; but among the Raptorial and Inses-
sorial Birds, which rank far higher in the scale, the young is for a long time de-
pendent upon the parent for food ; and in the Parrot tribe, which unquestion-
ably surpasses all others in intelligence, the parent not only supplies its young
with food which it has obtained for them, but partly nourishes them by a
milky secretion from the interior of the craw ; impregnating with this the
aliment which it swallows, and which it afterwards disgorges for its offspring.

10. General characters of Mammalia.

42. The MAMMALIA are universally regarded as the highest group in the
Animal kingdom ; not only from being that to which Man belongs (so far, at
least, as his bodily structure is concerned), but also as possessing the most
complex organization, adapted to perform the greatest number and variety of
actions, and to execute these with the greatest intelligence. The contrast is
here extremely strong between the reasoning and the instinctive powers ;
even when we put Man out of view. When we compare, for example, the
sagacity of a Dog, Monkey, or Elephant, and the great variety of circum-
stances in which they will display an intelligent adaptation of means to ends,
with the limited operations of Insects, over which the judgment and will seem
to have no control, we cannot help being struck with the difference. The
former are educable in the highest degree next to Man; the latter could not
be made to change their habits, in any essential degree, by the most prolonged
course of discipline. Man is actuated, like the lower animals, by instinctive
propensities, which have an immediate bearing on his corporeal wants ; whilst
they have, like him, the power of adapting their actions to gain certain ends,
of which they are conscious. A Dog or an Elephant may show more real
wisdom, in controlling for a time its instinctive propensities, from the desire
to accomplish some particular object, than is displayed by many Men, who
give free scope to the exercise of their sensual passions, although warned by
their reason of the injurious consequences of such indulgence.

GENERAL CHARACTERS OF MAMMALIA. 63

43. This high development of the intelligence in Mammalia, is evidently
connected with the greatly-prolonged connection between the parent and the
offspring, which we find to be a characteristic of this class. Mammalia are,
like Birds, warm-blooded Vertebrata, possessing a complete double circula-
tion ; and some of them are adapted to lead the life of Birds, passing a large
part of their time in darting through the air on wings, in pursuit of Insect
prey. But they differ from Birds in this essential particular, that they are
not oviparous, but viviparous; producing their young alive, — that is, in a
condition in which they can perform spontaneous movements, and can appro-
priate nourishment supplied to them from without. But they are not distin-
guished from all other animals by this character alone ; for there are some
species among Reptiles, Fishes, and even Insects, which produce their young
alive, — the egg being retained within the oviduct and hatched there. The
real distinction lies partly in that, which the name of the class imports, — the
subsequent nourishment of the young by suckling ; and partly in the mode
in which the embryo is nourished before its birth. In Mammels, the yolk-
bag is very small in proportion to its size in Birds ; and the contents of the
ovum, instead of furnishing (as in that class) the materials necessary for the
development of the young animal, up to the time when it can ingest food for
itself, only serve for the earliest set of changes in which this process con-
sists. In the latter stages of the evolution of the embryo, it is supplied with
nutriment directly imbibed from its parent. This is at first accomplished
by means of a series of root-like tufts, which are prolonged from the surface
of the ovum, and insinuate themselves among the maternal vessels, without,
however, uniting with them. These tufts absorb, from the maternal fluid,
the ingredients necessary for the support of the embryo ; and also convey
back to the parent its effete particles, which are received back into her blood,
and are then cast out of her system, by the process of secretion, respiration,
&c.

44. The Mammalia may be divided into two sub-classes ; in one of which
the structure just described is the greatest advance ever made, in the appa-
ratus by which the fcetus is nourished ; whilst in the other a more concen-
trated form is subsequently assumed by it. The ovum of the latter is delayed
for a longer period, in a cavity formed by the union of the two oviducts,
termed the uterus; which can be scarcely said to be developed in the Marsu-
pialia and Monotremata, the two orders constituting the first sub-class. The
vascular tufts proceeding from the chorion become especially developed at one
point, and the vessels of the uterus are extremely enlarged in a corresponding
situation ; the tufts dip down, as it were, into a chamber formed by an exten-
sion of the inner lining of these vessels, and serve the combined purpose of
the roots of plants and of the branchiae of aquatic animals, — absorbing from
the maternal blood the materials required for the nourishment of the embryo,
and aerating the blood of the fcetus, by exposing it to the influence of that of
the parent. The peculiar organ thus formed is termed the placenta ; and the
two sub-classes of the Mammalia have thence received the appellations of
placental and non-placental. The animals belonging to the latter present
many points of affinity to Birds, in the structure of their internal organs.
That of the brain is very nearly allied in these two groups ; and their amount
of intelligence seems, as far as can be determined, to bear a close correspond-
ence. The Ornithorhyncus in particular, has so many marks of alliance to
oviparous animals, and its osteology, as well as in its horny bill and in less
important particulars, that Naturalists have much debated whether it could
really be termed a Mammiferous animal. No positive evidence has yet been
obtained that its young are born alive ; but on the other hand, there is a strong
reason to believe that they come into the world uninclosed in the ovum, al-

64 ON THE PLACE OF MAN IN THE SCALE OF BEING.

though in a very imperfect condition. Moreover, it has been satisfactorily
ascertained that the young are nourished, for some time after their birth, by
a mammary secretion, which the organization of their mouth at that period
enables them to obtain from the parent. In the Marsupialia, there is a
remarkable compensation for the abrupt termination of the period of uterine
gestation, — the young being received into a pouch or marsupium, within which
the nipple is situated ; this is extremely prolonged, and the mouth of the foetus
(for so the being must still be regarded) is adapted to receive and hold on by
it; so that the little creature, which looks at first more like an earth-worm
than a Mammiferous animal, is thus suspended within the protective pouch,
until its development is so far advanced, that it can shift for itself in the same
degree as other new-born animals can do.

45. The period of gestation in the higher sub-class of Mammalia, is usually
prolonged, until the foetus is able, on its entrance into the world, to execute
regular movements ; some of these being merely indicative of its desire for
food, and others evidently designed for the acquirement of it. In many species,
the young animal seems to be from the first in the full possession of its senses,
and has considerable power of active locomotion; in general, however, it is
very dependent upon its parent ; only being able to obtain food when this is
placed within its immediate grasp. Such is the case with the Human infant,
which is closely dependent upon its parent, during a larger proportion of its
existence, than is the young of any other animal. Here again, therefore, we
perceive the application of the general law, that, the higher the grade of
development a being is ultimately to assume, the more does it require to be
assisted during the early stages of its progress. In the case of Man, the pro-
longation of this period has a most important and evident influence upon the
social condition of the race; being, in fact, one of the chief means, by which
the solitary are bound together in families.

46. The class Mammalia, taken as a whole, is not characterized so much
by the possession of any one particular faculty, — like that which has been
seen in Birds, — as by the perfect combination of the different powers, which
renders the animals belonging to it susceptible of a much greater variety of
actions, than any others can perform. There are none that can compete with
Birds in acuteness of sight ; but there are few that do not possess the senses
of smell, taste, and touch in a more elevated degree. There are none which
can rival Birds in rapidity of locomotion ; but there are few which cannot per-
form several kinds of progression. Several of their movements require a
considerable amount of flexibility in the spine ; hence the vertebral column,
and the bony framework of the trunk, are never so much consolidated as they
are in Birds. On the other hand, the neck is much less movable ; it never
consists of more than seven vertebra, and these are always present ; so that
they are sometimes of great length, as in the Giraffe, and sometimes ex-
tremely short, as in the Whale, which seems to have no neck at all. In the
greatest number of Mammalia, the body is supported upon all the four extre-
mities, as in Reptiles ; being adapted for progression along the surface of the
earth. There are some species, however, in which the typical structure has
undergone a metamorphosis, by which it is made to resemble that of a Bird ;
whilst in others it is modified, so as to conform to the character of the Fish.
In the Bats, the power of motion is almost entirely delegated to the wings,
which are composed of skin, stretched over a bony framework formed of the
widely-extended hand ; and the sternum has a projecting keel for the attach-
ment of the pectoral muscles, as in Birds. And in the Whale tribe, the power
of locomotion is almost completely taken from the extremities, and given
back to the trunk, as in Fishes ; for the posterior extremities are entirely ab-
sent, and the anterior serve only for guidance: there is this important differ-

CHIEF SUB-DIVISIONS OF MAMMALIA. 65

ence, however, that the tail, which is flattened vertically in Fishes, is flattened
horizontally in the Cetacea, which require the power of frequently coming to
the surface to breathe.

47. The inferior energy of muscular movement in the Mammalia, is ac-
companied by an inferior amount of respiration ; the type of the respiratory
apparatus, however, is higher than in Birds, a large extent of surface beino-
comprised within a smaller space. The lungs are confined to the cavity of
the thorax ; and there is a provision for the regular renewal of the air received
into them, by the action of the diaphragm, which here completely separates
that cavity from the abdomen. The diminished amount of respiration, again,
involves the production of a lower degree of animal heat ; so that the tempe-
rature of this class seldom rises above 104°. There is, therefore, less need
of means for effectually confining the caloric, — especially, too, as their greater
average size causes their radiating surface to be much less, in proportion to
their bulk, than is that of Birds ; and accordingly, we find them provided
only with a covering of hair or fur, which is much less warm than that of
feathers, and which is thin and scanty in Mammals inhabiting tropical climates.
The chief exception to the last rule is in the case of the Sloths and of some
Monkeys, which inhabit situations exposed to the most powerful rays of the
sun, and which are covered with a long but thin and coarse hair ; the purpose
of this is evidently the protection of their skin from the external heat. The
inferior energy of the respiration and circulation, involves a diminished activity
of the other functions of nutrition, as compared with those of Birds ; and the
demand for food appears to be somewhat less constant. Their various organs,
however, are developed upon a higher plan ; as we have already observed in
regard to those of respiration.

11. Chief Sub-divisions of Mammalia.

48. In sub-dividing the truly Viviparous division of the class, so as to sepa-
rate Man from the tribes with which he is associated in it, we may be advan-
tageously guided, in the first place, by the conformation of the extremities ;
since upon the perfection of the organs of touch, will depend much of the
address of an animal in executing the actions to which it is prompted by its
intelligence. The degree of this perfection is estimated by the number and
mobility of the fingers, and by the degree in which their extremities are en-
veloped by the nail, claw, or hoof, that terminates them. When the fingers
are partly absent, or are consolidated together, and a hoof envelopes all that
portion which touches the ground, it is obvious that the sensibility must be
blunted, whilst, at the same time, the member becomes incapacitated for pre-
hension. The opposite extreme is where (as in Man) a thin nail covers only
one side of the extremity of the finger, leaving the other possessed of all its
delicacy ; — where several such fingers exist, of which one can be opposed to
the rest, so as to render prehension more perfect, and to perform a great va-
riety of actions : — and where the plane of the whole hand can be turned in
any position, by the nature of its attachment to the fore-arm. Between these
there are many intermediate gradations. By these characters, the viviparous
Mammalia may be divided into the Unguiculated, which have separate fin-
gers, terminated by distinct nails or claws ; and the Ungulated, in which the
ringers are more or less consolidated, and inclosed at their extremity in a hard
hoof. Hoofed animals are necessarily Herbivorous, inasmuch as the con-
tormation of their feet precludes the possibility of their seizing a living prey ;
and they have flat-crowned grinding teeth for triturating their food. The
summits of these teeth are usually not covered by a smooth coat of enamel,
but present a series of elevations and depressions ; these are occasioned by

6*

66 ON THE PLACE OF MAN IN THE SCALE OF BEING.

the peculiar structure of the teeth, which consist of alternating plates of ena-
mel, ivory or dentine, and cementum or crusta petrosa, — substances of three
different degrees of hardness ; and, as the softer portions will of course wear
down first, the harder remain as projecting ridges. In order to give effect to
these, there is usually a considerable power of lateral motion possessed by
the lower jaw ; so that a regular grinding action may be performed, which is
favourable to the complete reduction of the tough vegetable substances that
serve as their food.

49. Animals with Unguiculated fingers are capable of more variety in the cha-
racter of their food. In some it is almost exclusively vegetable, as in the Roden-
tia ; and here the power of prehension possessed by the extremities is small,
the fore-arm not being so constructed as to be capable of the motions of pro-
nation and supination. In this order, the mouth is remarkably adapted for
grinding down hard vegetable substances ; the molar teeth being furnished with
transverse ridges of enamel; and the jaws having a powerful movement back-
wards and forwards.* In other orders, again, there is an almost exclusive adap-
tation to animal food. The toes are furnished with long and sharp claws ;
and the fore-feet may be placed in a variety of positions, by the rotation of
the two bones composing the lower part of the leg. The grinding teeth are
very narrow, and are formed with sharp points and edges, so as to be adapted
for dividing animal flesh ; these are firmly set in short strong jaws, which are
fitted together like the blades of a pair of scissors, having no action but a
vertical one ; and the constant friction of the edges of the molar teeth against
each other, keeps them sharp.t In the Carnivorous group, too, we find the
greatest development of the canine teeth, which are commonly absent or but
slightly developed among herbivorous quadrupeds ; these are instruments of
great power, serving both for the first attack of their prey, and for subse-
quently tearing it in pieces. It is evident that the whole structure of the body
must undergo modification, in conformity with the nature of the food. The
simple stomach and intestinal canal of the Carnivorous animal, adapted only
to the digestion of aliment consisting of materials similar to those of its own
body, would be totally useless to an animal prevented by its general organi-
zation from obtaining any other than vegetable food ; and, on the other hand,
the teeth and hoofs of the Herbivorous quadruped would be of little assist-
ance to an animal, whose instincts and general conformation adapted it for the
pursuit of animal prey. It will be presently seen that, in regard to his or-
ganization, Man holds an intermediate place between the purely Herbivorous
and the purely Carnivorous tribes ; being capable of subsisting exclusively
upon either kind of diet, but being obviously intended by Nature to employ
both in combination.

50. The classification of the Mammalia by Linnaeus, although not strictly
natural, affords us the readiest means of separating Man, zoologically, from all
other animals. He arranged under his order Primates, all the unguiculated
Mammalia which have four incisor teeth and two canines in each jaw; and
thus Man, with the Monkeys and the Bats, was distinguished from the re-

' The action of trituration is chiefly performed by the external pteregoid muscles. When
these are in operation together, they draw the whole of the lower jaw forwards, so as to
make the lower teeth project beyond the upper; and the jaw being dnuvn back again by
the digastric nmsrlcs, a rapid alternate movement maybe thus effected, such as is seen in the
Rodcntia. When only the muscle of one side acts, the condyle of that side is thrown for-
wards; and by the alternating operation of the two, aided by other muscles, that rotatory
motion is given which we see especially in Ruminating Quadrupeds.

| In Carnivorous animals, the muscles which elevate the lower jaw attain a very high
degree of development. This is very remarkably seen in the internal pteregoid, which in
Alan is of subordinate size and importance, but which is a very powerful muscle in the Lion,
Tiger, &c.

CHARACTERISTICS OF MAN. 67

maiiuler of those Quadrupeds which have separate fingers with distinct nails
or claws. This group is now sub-divided into three orders, corresponding
with the Linnoean genera, Homo, Simla, and Vespertilio. The last of these
orders, named Cheiroptera, consists of the Bat tribe, which is easily separated
from all others by the peculiar conformation of the anterior extremities, from
which its name is derived. The second, termed Quadrumana, comprehends
the Apes, Monkeys, and Baboons, which exhibit a regular series ; the highest
approaching Maa in general conformation ; and the lowest having much more
of the general organization of the inferior carnivorous quadrupeds. They are
distinguished from other viviparous Mammalia, by possessing an opposable
thumb on all four extremities (whence they are termed four-handed), — a cha-
racter which is only found elsewhere in the Opossums. Although some of
the higher members of this group are capable of maintaining the erect posi-
tion without difficulty for some time, even whilst walking, it is certainly not
that which is natural to them. The posterior extremity, — being formed on
the plan of a hand, for prehension rather than for direct support, — is destitute
of the heel, which is characteristic of Man ; and although Apes can climb
trees with facility, they cannot plant the foot firmly on the ground, so as to
resist attempts to overthrow them ; since the foot rests rather upon the outer
side than upon its sole, and the narrowness of the pelvis is unfavourable to an
equilibrium. There are many points of striking resemblance to Man, how-
ever, in the details of the conformation of the Quadrumana, especially among
the most elevated species ; the order being distinguished by the same charac-
ters from most others. The structure of their alimentary canal differs ex-
tremely little from his. The eyes are directed forwards, when the trunk is
erect; and the orbit is completely separated from the temporal fossae, by a
bony partition. The mammas are situated on the thorax ; and the penis is
pendent. The coitus, however, is reverse, as in the lower Mammalia. The
form of the brain in the higher species corresponds with that of Man in this
remarkable character, — that it is divided into three lobes, of which the poste-
rior is prolonged backwards so as to cover the cerebellum ; this is not the case
in the highest of the other Mammalia.

12. Characteristics of Man.

51. We shall now review, somewhat in detail, the distinctive characters
that separate Man from those animals which present the nearest approach to
him in general structure and aspect. These may be advantageously classified
according to their obvious purposes ; and the first series we shall notice con-
sists of those by which Man is peculiarly adapted to the erect attitude. On
examining his cranium we remark that the condyles, by which it is articulated
with the spinal column, are so placed that a perpendicular dropped from the
centre of gravity of the head would nearly fall between them, so as to be
within the base on which it rests. The foramen magnum is not placed in the
centre of the base of the skull, but just behind it; in order to compensate for
the greater specific gravity of the posterior part of the head, which is entirely
filled with solid matter, whilst the anterior part contains many cavities. There
is, indeed, a little over-compensation, which gives a slight preponderance to
the front of the head; so that it drops forwards and downwards when all the
muscles are relaxed. But the muscles which are attached to the back of the
head are far larger and more numerous than those in front of the condyles ;
so that they are evidently intended to counteract this disposition; and we
find, accordingly, that we can keep up the head for the whole day, with so
slight and involuntary an effort that no fatigue is produced by it. Moreover,
the surfaces of the condyles have a horizontal direction when the head is

68

ON THE PLACE OF MAN IN THE SCALE OF BEING.

upright ; and thus the weight of the skull is laid vertically by them upon the
top of the vertebral column. If these arrangements be compared with the
position and direction of the occipital condyles in other Mammalia, it will
be found that these are placed in the latter much nearer to the back of the
head, and that their plane is more oblique. Thus, whilst the foramen mag-
num is situated, in Man, just behind the centre of the base of the skull, it is
found in the Chimpanzee and Orang Outan to occupy the middle of the
posterior third ; and, as we descend through the scale of Mammalia, we ob-
serve that it gradually approaches the back of the skull, and at last comes
nearly into the line of its longest diameter, as we see in the Horse. The
obliquity of the condyles differs in a similar degree. In all Mammalia except
Man their plane is oblique; so that, even if the head were equally balanced
upon them, the force of gravity would tend to carry it forwards and down-
wards. In Man, the angle which they make with the horizontal is very
small ; in the Orang Outan it is as much as 37°; and in the Horse their
plane is vertical, making the angle 90°. If, therefore, the natural posture of
Man were horizontal, he would in this respect be circumstanced like the
Horse; for the plane of his condyles, which is nearly horizontal in the erect
position, would then be vertical : and the head, instead of being nearly
balanced in the erect position, would hang at the end of the neck, so that its
whole weight would have to be supported by some external and constantly-
acting power. But for this there is neither in the skeleton, nor in the muscu-
lar system of Man, any adequate provision. In other Mammalia the head is
maintained in such a position by a strong and thick ligament (the ligamentum
micha?), which passes from the spines of the cervical and dorsal vertebra? to
the most prominent part of the occiput; but of this there is scarcely any

Fig. 5.

View of the base of skull of Man, compared with that of the Orang Outan.

trace in Man. In the horizontal position, therefore, he would have the heavi-
est head, with the least power of supporting it.

52. The position of the face immediately beneath the brain, so that its
1'ront is nearly in the same plane as the forehead, is peculiarly characteristic
of Man ; for the crania of the Chimpanzee and Orang, which approach
nearest to that of Man, arc entirely posterior to, and not above, the face. It
should be remarked that in the young Ape there is a much greater resem-
blance to Man in this respect than there is in the adult. For at the time of
the second dentition the muzzle of the Ape undergoes a great elongation, so

CHARACTERISTICS OF MAN. 69

that it projects much more beyond the forehead; this is seen in Fig. 5. The
whole cast of the features is altered at the same time, so that it approaches
much more to that of the lower Quadrumana than would be supposed from
observation of the young animal only.* This increased projection of the
muzzle is an evidence of want of perfect adaptation to the erect posture :
whilst the absence of it in Man shows that no other position is natural to him.
Supposing that, with a head formed as at present, he were to move on all
fours, so that his face would be brought into a plane parallel with the ground,
— as painful an effort would be required to examine with the eyes an object
placed in front of the body, as is now necessary to keep the eyes fixed on
the zenith ; the nose would be unable to perceive any other odours than those
which proceeded from the earth or from the body itself; and the mouth could
not touch the ground without bringing the forehead and chin also into contact
with it. The oblique position of the condyles in the Quadrumana enables
them, without much difficulty, to adapt the inclination of their heads to the
horizontal or to the erect position of the body; but the natural position, in
the highest among them, is unquestionably one in which the spinal column is
inclined, the body being partially thrown forwards, so as to rest upon the
anterior extremities ; and in this position the face is directed forwards without
any effort, owing to the mode in which the head is articulated with the spine.
53. The vertebral column in Man, though not absolutely straight, has its
curves so arranged, that, when the body is in an erect posture, a vertical line
from its summit would fall exactly on the centre of its base. It increases
considerably in size in the lumbar region, so as to be altogether somewhat
pyramidal in form. The lumbar portion, in the Chimpanzee and Orang, is
not of the same proportional strength ; and contains but four vertebras instead
of five. The processes for the attachment of the muscles of the back to this
part, are peculiarly large and strong in Man ; and this arrangement is obviously
adapted to overcome the tendency, which the weight of the viscera in front
of the column would have, to draw it forwards and downwards. On the
other hand, the spinous processes of the cervical and dorsal vertebrae, which
are in other Mammalia large and strong, for the attachment of the ligamentum
nuchse to support the head, have in Man but little prominence, his head being
nearly balanced on the top of the column. The base of the human vertebral
column is placed on a sacrum of greater proportional breadth, than that of
any other animal; this sacrum is fixed between two widely expanded ilia;
and the whole pelvis is thus peculiarly broad. In this manner, the femoral
articulations are thrown very far apart, so as to give a wide basis of support;
and by the oblique direction of the whole pelvis, the weight of the body is
transmitted almost vertically, from the top of the sacrum to the upper part of
the thigh bones. The pelvis of every other species of the class is very dif-
ferently constructed ; as will be seen in the adjoining Figure (6), in which the
skeleton of the Orang is placed in proximity with that of Man. It is much
longer and narrower, having a far smaller space between the iliac bones and
the lowest ribs ; the sacrum is lengthened and reduced in width ; the ala3 of
the ilia are much less expanded ; and the whole pelvis is brought nearly into
a line with the vertebral column. The position of the human femur, in which
it is most securely fixed in its deep acetabulum, is that which it has when
supporting the body in the erect attitude. In the Chimpanzee and Orang, its
analogous position is at an oblique angle to the long axis of the pelvis, with
the body supported obliquely in front of it; in many Mammalia, as in the

None but young specimens of the Chimpanzee and Orang Outan have ever been
brought alive to this country ; and they have never survived the period of their second
dentition.

70 ON THE PLACE OF MAN IN THE SCALE OF BEING.

Elephant, it forms nearly a right angle ; and in several others, as the Horse,
Ox, &c., it forms an acute angle with the axis of the pelvis and spinal column.

54. The lower extremities of Man are remarkable for their length ; which
is proportionally greater than that which we find in any other Mammalia,
except the Kangaroo tribe. It is evident that there could be no greater ob-
stacle to his prorgession in the horizontal posture, than this length of what
would then be his hind legs. Either Man would be obliged to rest on his
knees, with his thighs so bent towards the trunk, that the attempt to advance
them would be inconvenient, his legs and feet being entirely useless ; or he
must elevate his trunk upon the extremities of his toes, throwing his head
downwards, and exerting himself violently at every attempt to bring forward
the thighs by a rotatory motion at the hip-joint. In either case, the only use-
ful joint would be that at the hip; and the legs would be scarcely superior to
wooden or other rigid supports. The chief difference in their proportional
length, between Man and the semi-erect Apes, is seen in the thigh ; and from
the comparative shortness of his arms, his hands only reach the middle of the
thighs; whilst in the Chimpanzee they hang on a level with the knees, and
in the Orang they descend to the ancles. The human femur is distinguished
by its form and position as well as by its length. The obliquity and length
of its neck still further increase the breadth of the hips; Avhilst they cause
the lower extremities of these bones to be somewhat obliquely directed towards
each other, so that the knees are brought more into the line of the axis of the
body. This position is obviously of great use in walking, when the whole
weight has to be alternately supported on each limb; for if the knees had
been further apart, the whole body must have been swung from side to side
at each step, so as to bring the centre of gravity over the top of each tibia ;
and, as a matter of fact, it is noticed that the walk of women, in whom the
pelvis is broader and the knees more separated, is less steady than that of
men.

55. There is a very marked contrast between the knee-joint of Man, and
that even of the highest Apes. In the former, the opposed extremities of the
femur and the tibia are expanded, so as to present a very broad articulating
surface; and the internal condyle of the femur is lengthened, so that the two
are in the same horizontal plane, in the usual oblique position of the femur.
In this manner, the whole weight of the body, in its erect posture, falls verti-
cally on the top of the tibia, when the joint is in the firmest position in which
it can be placed: and a comparison of the knee-joint of the Orang with that
of Man, will make it at once evident, that the former is not intended to serve
as more than a partial support. The weight of the body is transmitted through
the tibia, to the upper convex surface of the astragalus, and thence to the other
bones of the foot. The Human foot is, in proportion to the size of the whole
body, larger, broader, and stronger, than that of any other Mammal save the
Kangaroo. The sole of the foot is concave, so that the weight of the body
falls on the summit of an arch, of which the os calcis and the metatarsal bones
form the two points of support. This arched form of the foot, and the na-
tural contact of the os calcis with the ground, are peculiar to Man alone. All
the Apes have the os calcis small, straight, and more or less raised from the
ground ; which they touch when standing erect, with the outer side only of the
foot: whilst in animals more remote from Man, the os calcis is brought still
more into the line of the tibia; and the foot being more elongated and nar-
rowed, only the extremities of the toes come in contact with the ground.
Hence Man is the only species of Mammal, which can stand upon one leg. —
If we look at the structure of the upper extremity of Man, we observe simi-
lar proofs that it is not intended as an organ of support; being destitute of all
these adaptations ; and having a conformation obviously designed for other

CHARACTERISTICS OF MAN.

71

Fig. 6.

Comparative view of the Skeleton of Man and that of the Orang Outan.

72 ON THE PLACE OF MAN IN THE SCALE OF BEING.

purposes, which could not be possibly answered, if it were not completely
relieved from the necessity of bearing the weight of the body. This peculiar
conformation will be subsequently considered.

56. The other parts of the Human body concerned in locomotion are
exactly adapted to the peculiar construction of the skeleton. The tibia is
kept erect upon the foot by the very powerful muscles which are attached to
the heel and form the calf of the leg, — a prominence observed in no other
animal in nearly the same degree. The flexor longus pollicis pedis, which is
attached in the Chimpanzee and Orang to the three middle toes, proceeds in
man exclusively to the great toe, on which the weight of the body is often
supported. The extensors of the leg upon the thigh are much more power-
ful than the flexors, an arrangement seen in no other animal. The glutaei, by
which the pelvis is kept erect upon the thigh, are of far greater size than is
elsewhere seen. The superior power of the muscles tending to draw the
head and spine backwards, has been already referred to. In the general form
of the trunk, there is a considerable difference between Man and most other
Mammalia. His chest is large, but is flattened in front, and expanded late-
rally, so that its transverse diameter is greater than its antero-posterior ; — a
peculiarity in which only the most Man-like monkeys partake. His sternum
is short and broad ; and there is a considerable distance between the lower
ribs and the ilia, in consequence of the small number of ribs, and the length
of the lumbar portion of the vertebral column. The viscera in this space,
which in the horizontal position would be but insufficiently held up by the
abdominal muscles, are, in the erect attitude, securely supported by the ex-
panded pelvis. — From all these facts, it is an indisputable conclusion, that the
erect attitude and biped progression are natural to Man ; and we must regard
as in great degree fabulous, all those histories of supposed wild men, who, it
has been said, were found in woods, dumb, hairy, and crawling on all-fours.
The most elaborate investigation* of the structure of the anthropoid Apes,
and the fullest acquaintance with their habits, concur in proving, that their
movements are not easy or agile, unless they employ all their limbs for the
support of their bodies.

57. The name Bimana is the most appropriate that could be found, for an
order constituted by the Human species only ; since Man alone is two-handed.
" That," says Cuvier, " which constitutes the hand, properly so called, is the
faculty of opposing the thumb to the other ringers, so as to seize the most
minute objects, — a faculty which is carried to its highest degree of perfec-
tion in Man, in whom the whole anterior extremity is free, and can be em-
ployed in prehension." Some naturalists refuse the term hand to the extremi-
ties of the monkey tribe, preferring to call them graspers ; for it is certainly
true, that, although usually possessing an opposable thumb, they are destitute
of the power of performing many of those actions which we regard as most
characteristic of the hand. Such actions are chiefly dependent on the size
and power of the thumb ; which is much more developed in Man than it is
even in the highest Apes. The thumb of the Human hand can be brought
into exact opposition to the extremities of all the fingers, whether singly or
in combination; whilst in those Quadrumana which most nearly approach
Man, the thumb is so short and weak, and the fingers so long and slender,
that their tips can scarcely be brought into opposition, and can never be op-
posed in near contact with each other, with any degree of force. Hence,
although admirably adapted for clinging round bodies of a certain size, such
as the small branches of trees, &c., the extremities of the Quadrumana can

* Soo especially Mr. Owen's paper on the Chimpanzee and the Orang Outan in the Zoolo-
gical Transactions, vol. i.

CHARACTERISTICS OF MAN. 73

neither seize very minute objects with such precision, nor support large ones
with such firmness, as are essential to the dexterous performance of a variety
of operations for which the hand of Man is admirably adapted. Hence
the possession of " four hands" is not, as might be supposed, a character
which raises the animals that exhibit it above two-handed Man ; for none of
these four hands are adapted to the same variety of actions of prehension of
which his are capable ; and all of them are in some degree required for sup-
port. In this respect their character approaches much nearer to that of the
extremities of the lower Mammalia ; and there are several among them in
which, the opposable power of the thumb being deficient, there is no very
marked distinction between the so-called hand, and the foot of some Carni-
vora. There is much truth, then, in Sir C. Bell's remark, that " We ought
to define the hand as belonging exclusively to Man." There is in him, what
we observe in none of the Mammalia that approach him in other respects,
a complete distinction in the functional character of the anterior and posterior
extremities ; the former being adapted for prehension alone, and the latter for
support alone. Thus each function is performed with a much higher degree
of perfection than it can be where two such opposite purposes have to be
united. The arm of the Ape has as wide a range of motion as in Man, so
far as its articulations are concerned ; but it is only when the animal is in the
erect attitude, that its arm can have free play. Thus the structure of the
whole frame must conform to that of the hand, and must act with reference
to it. But it cannot be said with truth (as some have maintained) that Man
owes his superiority to his hand alone ; for without the directing mind, the
hand would be comparatively valueless. His elevated position is due to his
mind and its instruments conjointly; for if destitute of either, mankind would
be speedily extinguished altogether, or reduced to a very subordinate grade of
existence.

58. Thus, then, although the order Bimana cannot be separated from the
order Quadrumana by any single obvious structural distinction, like that which
characterises the Cetacea or the Cheiroptera, it is really as far removed by
the minuter, but not less important, modifications which have been detailed.
A few other distinctive characters will now be noticed. With one exception
(the fossil genus Anoplotherium, which is allied to the Tapir tribe), Man is
distinguished from all other animals, by the equality in the length of all his
teeth, and by the equally close approximation of them all in each jaw. Even
the anthropoid Apes have the canine teeth longer than the others, and an in-
terval in the line of teeth in each side of the jaw, to receive the canine teeth
of the opposite jaw. This is more evident in the adult than in the young
animal. The vertical position of the Human teeth, on which one of the most
characteristic features of the Human face — the prominent chin — depends, is
also quite peculiar; and is intimately connected both with his erect attitude,
and with the perfection of the hands, by which the food is divided and con-
veyed to the mouth. He has no occasion for that protrusion of the muzzle
and lips, which, in animals that seize their food with the mouth only, is re-
quired to prevent the face from coming into general contact with it. — The
absence of any weapons of offence, and of direct means of defence, are
remarkable characteristics of Man, and distinguish him from other animals.
On those to whom Nature has deaied weapons of attack, she has bestowed
the means either of passive defence, of concealment, or of flight. Yet Man,
by his superior reason, has not only been enabled to resist the attacks of other
animals, but even to bring them under subjection to himself. His intellect
can scarcely suggest the mechanism, which his hands cannot frame ; and he
has devised and constructed arms more powerful than those which any other
creature wields, and defences so secure as to defy the assaults of all but his
7

74 ON THE PLACE OF MAN IN THE SCALE OF BEING.

fellow-men. — We find, on comparing the brain of Man with that of the lower
Mammalia, that, as might have been anticipated, its proportional dimensions
are much greater, and its structure more complex. The former part of this
statement is easily verified by an examination of the cranium alone, comparing
the size of its cavity with that of the face. The amount of the facial angle,'
taken after the manner of Camper, affords a tolerably correct indication of the
relative sizes of these parts. In Man, the facial angle is, in the average of
Europeans, 80°; in Negroes, it is about 70°. In the adult Chimpanzee (which
approaches in this respect nearest to Man), the facial angle is only 35°; and
in the Orang, it is no more than 30°. In other animals it is still less, except
when it is increased by the prominence of large frontal sinuses, or by the
comparative shortness of the jaws. In regard to the structure of the brain, we
shall here only remark generally, that the Encephalon of Man far exceeds that
of the highest Quadrumana, in the size of the cerebral hemispheres, in the
complexity and development of its internal parts, and in the depth and num-
ber of its convolutions.

59. Man cannot be regarded as distinguished from other Mammalia, how-
ever, either by acuteness of sensibility, or by muscular power. His swiftness
in running, and agility in leaping, are inferior to that of other animals of his
size, — the full-grown Orang for example. The smallness of his face, com-
pared with that of the cranium, shows that the portion of the nervous system
distributed to the organs of sense, is less developed in him than it is in most
other animals ; and the small proportional size of the ganglionic centres, with
which these organs are immediately connected, is another indication of the
same fact. Accordingly, he is surpassed by many in acuteness of sensibility
to light, sound, &c. ; but he stands pre-eminent in the power of comparing
sensations, and of drawing conclusions from them. Moreover, although none
of his senses are very acute in his natural state, they are all moderately so,
which is not the case in other animals ; and they are capable (as is also his
swiftness of foot) of being much improved by practice, especially when cir-
cumstances strongly call for their exercise. This power of adaptation to va-
rieties in external conditions, which makes him to a great extent independent
of them, is manifested in other features of his structure and economy. He
is capable of sustaining the lowest, as well as the highest, extremes of tempe-
rature and of atmospheric pressure. In the former of these particulars, he is
strikingly contrasted with the anthropoid Apes, such as the Chimpanzee, which
is restricted to a few of the hottest parts of Africa, and the Orang-Outan,
which is only found in Borneo and Sumatra: these cannot be kept alive in
temperate climates, without the assistance of artificial heat ; and even when
this is afforded, they speedily become diseased and die. His diet is naturally
of a mixed kind ; but he can support himself in health and strength, on either
animal or vegetable food exclusively. It is by the demands which his pecu-
liar condition makes upon the exercise of his ingenuity, that his mental
powers are first called into active operation ; but, when once aroused, their
development has no assignable limit. The slow growth of Man, and the
length of time during which he remains in a state of dependence upon his
parents, have been already mentioned as peculiarities, by which he is distin-
guished from all other animals. He is unable to seek his own food, during
at least the three first years of his life ; and he does not attain to his full
stature, until he is more than twenty years of age. In proportion to his size,
too, the whole sum of his life is greater than that of other Mammalia. The
greatest age of the Iloise, for example, which is an animal of much superior
bulk, is between thirty and forty years. That of the Orang, which, when full
grown, surpasses Man in stature, is about the same, so far as it can be ascer-
tained. The age to which the life of Man is frequently prolonged, is well

GENERAL CONSIDERATIONS. 75

known to be above a hundred years ; and instances of such longevity are to be
found in all nations.

60. Still, however widely Man may be distinguished from other animals,
by these and other peculiarities of his structure and economy, he is yet more
distinguished by those mental endowments, and the habitudes of life and
action thence resulting, which must be regarded as the essential characteris-
tics of humanity. In the highest among brutes, the mere instinctive propen-
sities (as already defined, §§ 17, 23), are the frequent springs of action ; and
although the intelligent will is called into exercise to a certain extent, the
character never rises beyond that of the child. In fact, the correspondence
between the psychical endowments of the Chimpanzee, and those of the
Human infant before it begins to speak, is very close. In Man, however, the
instinctive propensities only manifest themselves strongly, whilst the intellect
is undeveloped ; and nearly all the actions of adult life are performed under
the direction of the intelligent will. From the intelligence of Man results his
mental improvability ; and his improved condition impresses itself upon his
organization. This capability of improvement in the bodily as well as the
mental constitution of Man, is the cause of the comforts now enjoyed by
civilised races, and of the means which they possess of still further elevation.
In the processes by which these are attained, we observe a remarkable differ-
ence between the character of Man, and that of other animals. The arts of
which these last are capable, are limited, and peculiar to each species ; and
there seems to be no general power of adapting these to any great variety of
purposes, or of profiting by the experience of others. Where a particular
adaptation of means to ends, of actions to circumstances, is made by an indi-
vidual (as is frequently the case, when some amount of intelligence or ration-
ality exists), the rest do not seem to profit by it ; so that there is no proof
that any species or race among the lower animals ever makes a voluntary
advance towards an improvement or alteration in its condition. That modifi-
cations in structure and instincts may be induced by circumstances, in some
of the most improvable species, such as the Dog, has been shown by abun-
dant evidence ; and these modifications, if connected with the original habits
and instincts of the species, maybe hereditarily transmitted. There is ample
proof that the same is the case, in regard both to the corporeal structure and
the psychical endowments of Man. Under the influence of education, phy-
sical and mental, continued through successive generations, the capabilities of
his whole nature, and especially those of his brain, are called out; so that the
general character of the race is greatly improved. On the other hand, under
the influence of a degraded condition, there is an equally certain retrogression;
so that, to bring up the New Holland Savage, or the African Bushman, to the
level of the European, would probably require centuries of civilisation. One
of the most important aids to the use and development of the human mind, is
the power of producing articulate sounds, or language ; of which, as far as
we know, Man is the only animal in possession. There is no doubt, that
many other species have certain powers of communication between individu-
als ; but these are probably very limited, and of a kind very different from a
verbal language.

61. Although, as we have stated, there is nothing in Man's present condi-
tion, which removes him from the pale of the Animal kingdom, and although
his reasoning powers differ rather in degree than in kind from those of the
inferior animals, he seems distinguished by one innate tendency ; to which
we have no reason to suppose that anything analogous elsewhere exists ; and
which we might term an instinct, were it not that this designation is generally
applied to propensities of a much lower character. The tendency here
referred to, is that which seems universal in Man, to believe in some unseen

76 MUTUAL RELATIONS OF THE HUMAN FAMILY.

Existence. This may take various forms, but is never entirely absent from
any race or nation, although (like other innate tendencies) it may be defective
in individuals. Attempts have been made by some travellers to prove, that
particular nations are destitute of it ; but such assertions have been based
only upon a limited acquaintance with their habits of thought, and with their
outward observances. For there are probably none, that do not possess the
idea of some invisible Power external to themselves ; whose favour they seek,
and whose anger they deprecate, by sacrifice and other religious observances.
It requires a higher mental cultivation than is always to be met with, to con-
ceive of this Power, as having a Spiritual existence ; but wherever the idea
of spirituality can be defined, it seems connected with it. The vulgar readi-
ness to believe in demons, ghosts, &c., is only an irregular or depraved
manifestation of the same tendency. Closely connected with it, is the desire
to share in this spiritual existence ; which has been implanted by the Creator
in the mind of Man ; and which, developed as it is by the mental cultivation
that is almost necessary for the formation of the idea, has been regarded by
philosophers in all ages, as one of the chief natural arguments for the im-
mortality of the soul. By this Immortal Soul, the existence of which is thus
guessed by Man, but of whose presence within him he derives the strongest
assurance from Revelation, Man is connected with beings of a higher order,
amongst whom Intelligence exists, unrestrained in its exercise by the imper-
fections of that corporeal mechanism, through which it here operates ; and to
this state, — a state of more intimate communion of mind with mind, and of
creatures with their Creator, — he is encouraged to aspire, as the reward of
his improvement of the talents here committed to his charge.

CHAPTER II.

OF THE MUTUAL RELATIONS OF THE DIFFERENT BRANCHES OF THE HUMAN

FAMILY.

1. General Considerations.

62. AMONGST the various tribes of Men, which people the surface of the
globe, and which are separated from all other animals by the foregoing cha-
racters, there are differences of a very striking and important nature. They
are distinguishable from each other, not merely by their language, dress,
manners and customs, religious belief, and other acquired peculiarities, but in
the physical conformation of their bodies ; and the difference lies, not merely
in the colour of the skin, the nature of the hair, the form of the soft parts
(such as the nose, lips, &c.,) but in the shape of the skull, and of other parts
of the bony skeleton, which might be supposed to be less liable to variation.
It is a question of great scientific interest, as well as one that considerably
affects the mode in which we treat the races that differ from our own, — whe-
ther they arc all of one species, that is, descended from the same or from
similar parentage, — or whether they are to be regarded as distinct species,
the first parents of the several races having had the same differences among
themselves, as those now exhibited by their descendants.

63. It has been a favourite idea, among those who wished to excuse the
horrors of slavery, or the extirpation of savage tribes, that the races thus

ON THE DISCRIMINATION OF SPECIES. 77

treated might be considered as inferior species, incapable of being raised by
any treatment to our own elevation; and as thus falling legitimately under the
domination of the superior races, just as the lower animals have been placed
by the Creator in subservience to Man. This doctrine, which has had its
origin in the desire to justify as expedient what could not be defended as
morally right, finds no support from scientific inquiries conducted in an en-
larged spirit. In order to arrive at a just conclusion on the subject, it is ne-
cessary to take a very extensive survey of the evidence furnished by a number
of different lines of inquiry. Thus, in the first place, it is right to investigate
what are the discriminating structural marks, by which species are distin-
guished among the lower tribes of animals. — Secondly, it should be ascer-
tained to what extent variation may proceed among races, which are histori-
cally known to have a common parentage ; and what are the circumstances
which most favour such variations. — Thirdly, the extreme variations, which
present themselves among the different races of men, should be compared
with those which occur among tribes of animals known to be of the same
parentage; and it should be questioned, at the same time, whether the cir-
cumstances which favour the production of varieties in the latter case, are in
operation in the former. — Fourthly, where it is impossible to trace back dis-
tinct races to their origin, it is to be inquired how far agreement in physiolo-
gical and psychological peculiarities may be regarded as indicating specific
identity, even where a considerable difference exists in bodily conformation ;
and this test, if it can be determined on, has to be applied to Man. Fifthly,
it must be attempted, by a detailed examination of the varieties of the human
race themselves, to ascertain whether their differences in conformation are
constant; or whether there are not occasional manifestations, in each race, of
a tendency to assume the characters of others ; so as to prevent a definite line
being drawn between the several tribes, which together make up the (sup-
posed) distinct species.*

2. On the Discrimination of Species.

64. Theirs/ of the foregoing questions is a fertile source of perplexity to
the Naturalist ; owing to the tendency that exists in certain races of Plants
and Animals, to exhibit variations of form much greater than those which
are relied upon in other instances as characterizing distinct species. In our
ignorance as to the history of the origin of the greater part of the dissimilar
forms or races of organized beings, with which the globe is peopled, we are
accustomed to regard two races of Plants or animals as of the same species, —
that is, as having had the same or similar progenitors, — when they are not
distinguished from one another by any peculiarities, but such as the one may
be supposed to have gained, or the other to have lost, by the influence of
external circumstances during a long period of time. On the other hand, two
races are regarded as constituting distinct species, — that is,*are believed to
have descended from dissimilar parents, — when a constant well-marked dif-
ference exists between them, such as exhibits no tendency to variation in the
individuals of either race (being equally characteristic of every one), and is
not affected by the lapse of time or by change in external conditions.

65. Thus, if we compare together the different breeds of Dogs, we find

This investigation has been most elaborately, and in the Author's opinion most suc-
cessfully, worked out by Dr. Prichard, in his profound and philosophical Treatise on the
Physical History of Man. The sketch of the argument given above does little more than
exhibit the conclusions at which he has arrived ; and for the grounds on which these are
based, reference .must be made to that work, or to the abridgment of it published by Dr.
Prichard, under the title of the Natural Histoiy of Man.

78 MUTUAL RELATIONS OF THE III MAN FAMILY.

that, although they are distinguished by very marked peculiarities, yet that
these peculiarities are by no means consiant. There is historical evidence of
the great change, which may take place in their conformation and habits,
under the influence of a change in their external circumstances ; in the case,
for example, of the blood-hounds, introduced into the West Indies by the
Spaniards, which have now degenerated into a wild race of very different
form, and have lost all the distinctive characters of the breed. And there is
not that close agreement in the distinctive characters of the several breeds,
among the individuals respectively composing them, which is requisite for the
establishment of a definite specific distinction ; the characters being shaded
off, as it were in individuals, so as to cause a near approximation between the
less decided forms of the different races. — On the other hand, in spite of the
varieties of conformation exhibited by the several races of Dog, (which even
affect the number of vertebrae in the tail, as well as the shape and proportions
of the bones, we never see any which present so strong a resemblance to the
Fox, as to be at all in danger of being mistaken for that animal ; and they
may always be distinguished by this obvious character, — that the pupil of the
eye of the Dog is always round, whilst that of the Fox is oval when con-
tracted. This difference may appear a very trifling one, in comparison with
the important variations presented in the structure of the different breeds of
Dogs ; but it is constant ; and it may therefore be assumed to have existed
in the progenitors of each race, as it exists at present in all their descendants.

66. There are many instances of an opposite character, in which the tend-
ency to variation is extremely small; and in which the Naturalist feels jus-
tified in assuming a specific difference, from variations in size or colour,
which in themselves are very trifling, but which are important in classifica-
tion, because they are constant. Thus, among the several species of the
genus Felis (or Cat tribe), there is scarcely any perceptible osteological varia-
tion, except in point of size ; so that even Cuvier was unable to find out a
positive means of distinguishing the skull of the Lion from that of the Tiger;
and the skeleton of a Wild Cat is a reduced copy of that of the largest Felines.
There are certain species, which are distinguished by no other external indi-
cations, than the markings upon their skins ; — characters, which are in other
cases subject to extreme uncertainty ; but which are here so constant, as to
present scarcely the slightest variation amongst the individuals of each race.
Thus, if a certain patch or stripe be repeated from generation to generation, in
a wild feline race, the Naturalist is inclined to regard this as a sufficient proof
of the specific difference of that race from another which is differently marked.
The Domestic Cat is the only one of the group, which is liable to any con-
siderable variation ; and in this species, as every one knows, the markings
characteristic of the several breeds or races are not thus constantly repeated,
and therefore cannot be indicative of original difference. Now it is precisely
in this species ,that we should look for such variations ; since it is the only
one which can be domesticated; and the capability of domestication implies
a power in the original constitution of the animal, to adapt itself to a change
of circumstances, and thus to exhibit various departures from its original type.

67. This striking contrast, between variable and invariable groups of ani-
mals nearly allied to each other, is found through the whole kingdom ; every
division of it appearing to contain some species, which do not change their
forms or other characteristics under any circumstances, but which cease to
exist if a change takes place in their conditions, incompatible with the regular
performance of their functions; whilst it also includes others, in whose phy-
sical and psychical constitutions there is such a susceptibility of modification,
that new forms and new instincts may arise, adapted to a great variety of
external conditions, and thus new and very different races may be originated.

EXTENT OF VARIATION IN RACES OF THE SAME SPECIES. 79

Thus, the Feline races, with a few exceptions, are fitted to maintain life only
in tropical climates, and very speedily die in colder countries (unless kept
warm by artificial means), in consequence of their deficiency of heat-pro-
ducing power, and the want of a close downy fur adapted to retain the caloric
generated in their bodies. On the other hand, the Dog is enabled to accom-
pany Man, in the coldest as well as the hottest regions of the globe ; his
power of generating heat being capable of variation, in accordance with the
external temperature ; and his entire organization undergoing modifications,
which adapt it to the change in the conditions of its existence. It appears,
then, that it is quite impossible to fix upon any difference of structural pecu-
liarities, as indications of the distinctness of species ; until it has been ascer-
tained by observation, whether they are constant and invariable, — the races
neither exhibiting any tendency to change in successive generations, — nor
showing any disposition to mutual approximation, by the occasional modifi-
cation of the distinctive characters in the individuals composing them.

3. On the possible Extent of Variation within the Limits of Species.

68. We now come to the second point of our inquiry, — namely, the
amount of variation which may take place in races, historically known to
have had a common parentage. There is considerable difficulty in obtaining
the most complete evidence upon this subject ; owing to the want of accurate
observation in the more remote historical periods, when it is probable that
most of the varieties or breeds of our domesticated animals were first origi-
nated. Still there is an adequate amount of proof, that these races may
undergo very considerable modifications, in the course of a few generations ;
and that new races or breeds, distinguished by marked peculiarities, may
originate even at the present time. Our most satisfactory information is de-
rived from the changes, which have taken place in the races of domesticated
animals, introduced into the West Indies and South America, by the Span-
iards, three centuries since. Many of these races have multiplied exceed-
ingly, on a soil and under a climate congenial to their nature; and several of
them have run wild in the vast forests of America, and have lost all the most
obvious appearances of domestication. The wild tribes are found to differ
physically from the domesticated breeds, from which they are known to have
originated ; and there is good reason to regard this change, as a partial restora-
tion of the primitive characteristics of the wild stocks, from which the tamed
animals originally descended. Thus we find that the Hog, where it has re-
turned to its wild state, nearly resembles the Wild Boar, which has never
been in a state of domestication. The colour loses the variety found in the
domestic breeds ; the Wild Hogs of the American forests being uniformly
black. The thin covering of hair and scattered bristles is replaced by a thick
fur, often somewhat crisp ; beneath which is found, in those which inhabit
the colder regions, a species of wool. The head, too, becomes much larger
in these wild races, as in the original Boar; and the differences in the conform-
ation of the cranium, between these and the domesticated breeds, are fully
equal to anything that is seen in the human race. — The variations which pre-
sent themselves in other races of domesticated animals introduced into South
America at the same period, — such as the horse, ass, ox, sheep, goat, dog,
cat, and gallinaceous birds, — are not less striking. — Still more remarkable
variations are seen in certain domesticated breeds, which must without doubt
have sprung from the same stock with the ordinary ones, although their origin
cannot be traced historically ; thus, in some localities we find swine with
solid hoofs ; in others, the hoof is cleft into five parts ; and in others, again,
the toes are developed to a monstrous length.

SO MUTUAL RELATIONS OF THE HUMAN FAMILY.

69. Although the numerous examples furnished by the Vegetable Kingdom
may seem to have but a remote bearing on the question, it would still be
wrong to pass them by without notice ; since the general principles already
noticed are recognized by Botanists, as serving for the discrimination or iden-
tification of species of Plants ; to which they apply equally with Animals.
We have abundant evidence, in the case of our cultivated fruits and flowers,
of the origination of new and well-marked varieties from stocks originally the
same; the differences between these races being such, as Avould undoubtedly
have led to their being ranked as distinct species, if their common parentage
were not known. Thus, of the numerous widely-different varieties of Apple,
Pear, Strawberry, Plum, &c., many have been produced in our own time ;
and there is no doubt, that all the forms of each fruit are descended from
wild stocks, extremely unlike any one of them. So the Cowslip, Primrose,
Oxslip, and Polyanthus, which were formerly regarded as constituting at least
two distinct species, have been shown to be all producible from the seeds of
one parent. And a single plant of the Orchideous tribe has borne flowers and
pseudo-bulbs, which were formerly considered as characteristic of three dis-
tinct genera.

70. Of the origination of entirely new races of animals, distinguished by
physical peculiarities, and disposed to become permanent under circumstances
favourable to their perpetuation, we have frequent examples at the present
time. It is not uncommon to meet with individuals among our domesticated
animals, which differ from others of their kind, in some marked feature of
their conformation. If this be of a nature which impairs the value of the
animal, care is taken that it shall not propagate its race ; but, on the other
hand, if it afford a prospect of utility, the skill of the breeder is employed to
perpetuate it. One of the most remarkable examples of this kind, is to be
found in the origin of the Jlncon or Otter breed of Sheep, now common in
New England. In the year 1791, one of the ewes on the farm of Seth
Wright, in the State of Massachusetts, produced a male lamb, remarkable for
the singular length of its body, the shortness of its limbs, and the crookedness
of its fore-legs. This physical conformation, incapacitating the animal from
leaping fences, appeared to the farmers around so desirable, that they wished
it continued. Wright consequently determined on breeding from this ram ;
but the first year he obtained only two with the same peculiarities. In the
following years, he obtained greater numbers ; and when they became capable
of breeding with one another, the new race became permanent, — the offspring
invariably having the Anton conformation, when both the parents belonged
to that breed. In the Human race, it is not uncommon to find particular
families distinguished by the possession of six fingers on each hand, and six
toes on each foot. If such were to intermarry exclusively with one another,
there can be no reasonable doubt that the children would invariably exhibit
the same peculiarity ; and the six-fingered race, which now tends, whenever
it is originated, to merge in the more general form, would then become per-
manent. When it is remembered that the influence of a scanty population, in
the early ages of the world, would have been precisely the same as that which
is now exercised by the breeders of animals, we can understand why the va-
rieties, which then arose, should have had a much greater tendency to become
permanent, than most of those which now present themselves. At the present
time, any peculiarity which may occasionally arise, speedily merges by inter-
.nixture with the mass, and returns to the common standard; but when popu-
lation was scanty, any peculiarities existing in one family would be perpetuated,
hy the intermixture of its members, rendered necessary by their isolation from
others ; and thus a new race would originate.

71. For the cause of these occasional variations from the common type,

ON THE VALUE OF SPECIFIC DISTINCTIONS. 81

we must look in part to the original constitution of the species, and in part
to the influence of external conditions. As already mentioned, there is a
marked difference among various species of animals (even those nearly allied,
such as the Domestic Cat and the Tiger), in regard to their respective capa-
cities for variation. And among the peculiarities of conformation which oc-
casionally present themselves in the Human and other most variable species,
there are several, which cannot be in any way attributed to the modifying
influence of external conditions; — such, for example, as the development of
additional fingers or toes, the alteration in the number of the vertebra in the
tail, the unusual consolidation or separation of the toes, &c. But it cannot
be doubted, when the known history of the domesticated races is fairly con-
sidered, that a change of external circumstances is capable of exerting a very
decided influence upon the physical form, upon the habits and instincts, and
upon various functions of life. The variations thus induced, extend to con-
siderable modifications in the external aspect, such as the colour, the texture,
and the thickness of the external covering ; to the structure of limbs, and the
proportional size of parts ; to the relative development of the organs of the
senses and of the psychical powers, involving changes in the form of the cra-
nium; and to acquired propensities, which, within certain limits (depending, it
would appear, on their connection with the natural habits of the species), may
become hereditary.

4. On the Extremes of Variation among the Races of Men.

72. We have now to inquire, in the third place, how far the same influ-
ences might be expected to operate in the Human race ; and whether the ex-
treme varieties, which we encounter among Mankind, are really greater than
those, which we meet with m the races of domesticated animals, known to
have had a common ancestry. It must be admitted by every one, that both
of the conditions just noticed as favouring the origination of peculiarities, ope-
rate to their fullest extent in Man. There is no other species of animals, in
which an equal tendency to variation exists. The different individuals of the
same breed of Dogs, for example, resemble each other far more closely in
physical and mental characters, than the individual men of one nation ; and
there is no species of animals, which possesses an equal power of maintain-
ing life in the remote extremes of climate, atmospheric pressure, &c., which
are encountered at different parts of the earth's surface, and at different ele-
vations above it. Again, we should expect to find these varieties in external
circumstances, together with the change of habits induced by civilization
(which is far greater than any change effected by domestication in the condi-
tion of the lower animals), producing still more important alterations in the
physical form and constitution of the Human body, than those effected in
brutes by a minor degree of alteration. And it may be reasonably antici-
pated, that, as just now explained, there would be a greater tendency to the
perpetuation of these varieties, in other words, to the origination of distinct
races, during the earlier ages of the history of the race, than at the present
time, when, in fact, by the increasing admixture of races which have long
been isolated, there is a tendency to \hefusion of all these varieties, and to a
return to a common type. Now, when the extreme varieties which are pre-
sented by the different races of Man are carefully compared together, it is
found that their differences are all of the same kind as those, which present
themselves among the breeds of domesticated animals; and do not by any
means exceed them (perhaps not even equalling them in degree. This will
be shown in detail hereafter.

73. It appears, then, that the analogical argument derived from the pheno-

82 MUTUAL RELATIONS OF THE HUMAN FAMILY.

rnena presented by the domesticated species among the lower animals, is de-
cidedly in favour of the specific unity of the Human race; the differences
which have sprung up, in course of time, amongst the inhabitants of different
parts of the world, being such as we have a fair right to attribute — according to
the recognized principles of Zoology — to the modifying influence of external
conditions, acting upon a constitution peculiarly disposed to yield to it.

5. On the Value of Physiological and Psychological Peculiarities, as

Specific Distinctions.

74. We have now to inquire, in the fourth place, what other arguments in
favour of this position may be drawn from agreement or difference in Physi-
ological and Psychological peculiarities. A comparison of the physiological
history of two races, is often found to afford a better criterion of their specific
difference or identity, than the comparison of their structural characters.
Now, in every important point of physiological history, there is a wonderful
agreement amongst the different races of Men ; the variations not being greater
than are those with which we meet among the different individuals of any
one race. Thus, we not only find the average duration of life to be every-
where the same, (making allowance for circumstances which are likely to in-
duce disease), but the various epochs of life have a close correspondence, —
such as the times of the first and second dentition, the period of puberty, the
duration of pregnancy, the intervals of the catamenia, and the time of their
final cessation. And the different races of Man are all subject to the same
diseases, both sporadic, contagious, and epidemic ; whilst there are no two
really-distinct species among the lower animals, which have more than a very
slight conformity in this respect.

75. The most important physiological test of specific unity or diversity, is
derived from the phenomena attending the Reproductive process. It is well
known that, in Plants, the stigma of the flower of one species may be fertil-
ized with the pollen of an allied species ; and that, from the seeds produced,
plants of an intermediate character may be raised. These hybrid plants,
however, will not perpetuate the new race ; for, although they may ripen their
seed for one or two generations, they will not continue to reproduce them-
selves beyond the third or fourth. But, if the intervention of one of the pa-
rent species be employed, — its stigma being fertilized by the pollen of the
hybrid, or vice versa, — a mixed race may be kept up for some time longer ;
but it will then have a manifest tendency to return to the 'form of the parent
whose intervention has been employed. Where, on the other hand, the pa-
rents themselves were only varieties, the hybrid forms but another variety,
and its powers of reproduction are rather increased than diminished ; so that
it may continue to propogate its own race, or may be used for the production
of other varieties, almost ad infinitum. In this way, many beautiful new
varieties of garden flowers have been obtained ; especially among such species
as have a natural tendency to change their aspect. Amongst Animals, the
limits of hybridity are much more narrow, since the hybrid is totally unable
to continue its race with one of its own kind ;* and although it may be fertile
with one of its parent species, the progeny will of course approach in cha-
racter to the pure breed, and the race will ultimately merge into it. On the
other hand, in Animals, as among Plants, the mixed offsprings originating from
different races within the limits of the same species, generally exceed in vi-

* One or two instances have been stated to occur, in which a Mule has produced offspring
from union with a similar animal; but this is certainly the extreme limit, since no one has
ever maintained that the race can be continued farther than the second generation, without
admixture with one of the parent species.

DISTINCTIVE PECULIARITIES OF THE RACES OF MAN. 83

gour, and in the tendency to multiply, the parent races from which they are
produced, so as to gain ground upon the older varieties, and gradually to su-
persede them. In this manner, by the crossing of the breeds of our domes-
ticated animals, many new and superior varieties have been produced. The
general principle is, then, that beings of distinct species, or descendants from
stocks originally different, cannot produce a mixed race, which shall possess
the capability of perpetuating itself; whilst the union of varieties has a tend-
ency to produce a" race superior in energy and fertility to its parents.

76. The application of this principle (if it be admitted as such) to the Hu-
man races, leaves no doubt with respect to their specific unity ; for, as is well
known, not only do all the races of Men breed freely with each other, but the
mixed race is generally superior in physical development, and in tendency to
rapid multiplication, to either of Use parent stocks ; so that there is much rea-
son to believe that, in many countries, the mixed race between the Aborigines
and European colonizers will ultimately become the dominant power in the
community. This is especially the case in India and South America.

77. Not less conclusive is the result of the test, furnished by agreement
or difference in psychological characters. Among the lower animals, we find
every species characterised by the possession of instincts and propensities
peculiar to itself; and these instincts often differ remarkably in species, which
present the closest structural alliance. On the other hand, in the several
varieties of domesticated animals, notwithstanding their strongly-marked di-
versities of physical structure, we may recognize instincts which are fun-
damentally the same, although they have been modified by the continued
influence of Man, and by the new circumstances in which the animals are
placed. Now from an impartial survey of the psychological characters of the
different races of Men, so far as our present knowledge extends, the follow-
ing conclusion may be drawn. " We contemplate, among all the diversified
tribes, who are endowed wijh reason and speech, the same internal feelings,
appetencies, and aversions; the same inward convictions, the same sentiments
of subjection to invisible powers, and (more or less fully developed) of ac-
countableness or responsibility to unseen avengers of wrong and agents of
retributive justice, from whose tribunal men cannot even by death escape.
We find everywhere the same susceptibility, though not always in the same
degree of forwardness or ripeness of improvement, of admitting the cultiva-
tion of those universal endowments, of opening the eyes of the mind to the
more clear and luminous views which Christianity unfolds, of becoming
moulded to the institutions of religion and of civilised life : in a word, the
same inward and mental nature is to be recognized in all the races of men.*

6

6. On the Comparative Peculiarities of the Different Races of Mankind.

78. We have now to inquire, fifthly and lastly, whether it is possible, after
a detailed and careful examination of the ensemble of the characters of the
different races of Men, to make any division of them into distinct groups,
capable of being defined by such constant and well-marked features, as shall
entitle them to be regarded in the light of distinct species. The general re-
sults, only, of this inquiry, can here be given ; and this in a very summary
manner. They will be almost entirely drawn from the profound and labo-
rious investigations of Dr. Prichard.

79. The characters which are most relied on for the discrimination of the
several races of Mankind, are the colour of the skin, the nature of the hair,
and the conformation of the skull and other parts of the skeleton. The Co-

* Prichard's Natural History of Man, p. 546.

84 MUTUAL RELATIONS OF THE HUMAN FAMILY.

lour of the skin exists in the epidermis only ; and it depends upon the ad-
mixture of certain peculiar cells, termed pigment-cells, with the ordinary
epidermic cells. These pigment-cells, as will be shown hereafter (§ 163), are
distinguished by their power of generating or secreting colouring-matter of
various hues ; and all the varied shades of colour, presented by the different
races of men, are due to the relative amount of these cells, and to the parti-
cular tint of the pigment which they form. It would be easy, by selecting
well-marked specimens of each race, to make it appear that colour affords
sufficient distinctive marks for their separation: thus, for example, the fair
and ruddy Saxon, the jet-black Negro, the olive Mongolian, and the copper-
coloured North American, would seem positively separated frdm each other
by this character, propagated, as it seems to be, with little or no perceptible
change, from generation to generation. But although such might appear to
be the clear and obvious result of a comparison of this kind, yet a more pro-
found and comprehensive survey tends to break down the barrier that would
be thus established. For, on tracing this character through the entire family
of Man, we find the isolated specimens just noticed to be connected by such
a series of links, and the transition from one to the other to be so very gradual
that it is impossible to say where the line is to be drawn. There is nothing
here, then, which at all approaches to the fixed and definite marks, which have
been noticed as serving — though equally trivial in themselves — to establish
specific distinctions among other tribes of animals.

80. But further, there is abundant evidence that these distinctions are far
from being constantly maintained, even in any one race. For among all the
principal subdivisions, alblnoism, or the absence of pigment-cells, occasion-
ally presents itself; so that the fair skin of the European may present itself
in the offspring of the Negro or of the Red Man. On the other hand, in-
stances are by no means rare, of the unusual development of pigment-cells
in individuals of the fair-skinned races ; so that parts of the body are of a
dark red or brown hue, or are even quite black. Such modifications may
seem of little importance to the argument; since they are confined to indi-
viduals, and may be put aside as accidental. But there is ample evidence,
that analogous changes may take place in the course of time, which tend to
produce a great variety of shades of colour, in the descendants of any one
stock. Thus, in the great Indo-Atlantic family, which may be unquestion-
ably regarded as having had a common origin, we find races with fair com-
plexion, yellow hair, and blue eyes, — others presenting the xanthous or olive
hue, — and others decidedly black. A similar diversity may be seen among
the American races, which are equally referrible to one common stock ; and
it exists to nearly the same extent among the African nations, which are simi-
larly related to each other. It may be freely admitted that, among European
colonists settled in hot climates, such changes do not present themselves within
a few generations ; but in many well-known instances of earlier colonization
they are very clearly manifested. Thus the wide dispersion of the Jewish
nation, and their remarkable isolation (maintained by their religious observ-
ances) from the people among whom they live, render them peculiarly appro-
priate subjects for such observations; and we accordingly find, that the bru-
nette complexion and dark hair, which are usually regarded as characteristic
of the race, are frequently superseded, in the Jews of Northern Europe, by
red or brown hair and fair complexion ; whilst the Jews who settled in India
some centuries ago, have become as dark as the Hindoos around them.

81. The relation of the complexions of the different races of Men to the
climates they respectively inhabit, is clearly established by an extended com-
parative survey of both. From such a survey the conclusion is inevitable,
that the intertropical region of the earth is the principal seat of the black races

DISTINCTIVE PECULIARITIES OF THE RACES OF MAN. 85

of Men ; whilst the region remote from the tropics is that of the white races;
and that the climates approaching the tropics are generally inhabited by na-
tions, which are of an intermediate complexion. To this observation it may
be added, that high mountains, and countries of great elevation, are generally
inhabited by people of a lighter colour, than are those of which the level is
low, such as swampy or sandy plains upon the sea-coast. These distinc-
tions are particularly well seen in Africa, where the tropics almost exactly
mark out the limits of the black complexion of the inhabitants ; and where
the deepest hue is to be seen among the Negroes of the Guinea Coast, whose
residence unites both the conditions just mentioned.

82. The nature of the Hair is, perhaps, one of the most permanent charac-
teristics of different races. In regard to its colour, the same statements apply,
as those just made with respect to the colour of the skin; the variety of hue
being given by pigment-cells, which may be more or less developed under
different circumstances. But it has been thought that its texture afforded a

o

more valid ground of distinction; and it is commonly said that the substance
which grows on the head of the African races, and of some other dark-colour-
ed tribes (chiefly inhabiting tropical climates), is wool, and not hair. This,
however, is altogether a mistake : for microscopic examination clearly de-
monstrates, that the hair of the Negro has exactly the same structure with
that of the European; and that it does not bear any resemblance to wool, save
in its crispness and tendency to curl. Moreover, even this character is far
from being a constant one ; for, whilst Europeans are not unfrequently to be
met with, whose hair is as crisp as that of the Negro, there is a great variety
amongst the Negro races themselves, which present every gradation from a
completely crisp (or what is termed woolly) hair, to merely curled or even
flowing locks. A similar observation holds good in regard to the natives of
the islands of the great Southern Ocean, where some individuals possess crisp
hair, whilst others, of the same race, have it merely curled. It is evident, then,
that no characters can be drawn from the colour or texture of the hair in Man,
sufficiently fixed and definite to serve for the distinction of races: and this
view is borne out by the evident influence of climate, in producing changes
in the hairy covering of almost every race of domestic animals ; — the change
often manifesting itself in the very individuals that are transported from one
country to another, and showing itself yet more distinctly in succeeding gene-
rations.

83. It has been supposed, that varieties in the configuration of the Skeleton
would afford characters for the separation of the Human races, more fixed
and definite than these derived from differences in the form, colour, and tex-
ture of the soft parts which clothe it. And attention has been particularly
directed to the skull and the pelvis, as affording such characters. It has been
generally laid down as a fundamental principle, that all those notions which
are found to resemble each other in the shape of their heads, must needs be
more nearly related to each other, than they are to tribes of Men who differ
from them in this particular. But if this principle be rigorously carried out,
it will tend to bring together races, which inhabit parts of the globe very re-
mote from each other, and which have no other mark of affinity whatever :
whilst, on the other hand, it will often tend to separate races, which every
other character would lead us to bring together. It is to be remembered,
moreover, that the varieties in the conformation of the skeleton, presented by
the breeds of domesticated animals, are at least equal to those which are ma-
nifested in the conformation and colour of their soft parts; and we might rea-
sonably expect, therefore, to meet with similar variations among the Human
races. It is probable, however, that climate has not so much influence in
producing such changes in the configuration of the body, as is exerted by the

8

86

MUTUAL RELATIONS OF THE HUMAN FAMILY.

peculiar habits and mode of life of the different races ; and Dr. Prichard has
pointed out a very remarkable relation of this kind, in regard to the three
• principal types of form presented by the skull.

84. Among the rudest tribes of Men, hunters and savage inhabitants of fo-
. rests, dependent for their supply of food on the accidental produce of the soil
or on the chase, — among whom are the most degraded of the African nations,
and the Australian savages, — a form of head is prevalent, which is most aptly
distinguished by the term prognathous, indicating a prolongation or forward-
Fig. 7.

Profile and basal views of the prognathous skull of a Negro.

extension of the jaws. This character is most strongly marked in the Ne-
groes of the Gold Coast, whose skulls are usually so formed, as to give the
idea of lateral compression. The temporal muscles have a great extent, rising
high on the parietal bones ; the cheek-bones project forward, and not out-
ward ; the upper jaw is lengthened and projects forwards, giving a similar
projection to the alveolar ridge and to the teeth; and the lower jaw has
somewhat of the same oblique projection, so that the upper and lower incisor
teeth are set at an obtuse angle to each other, instead of being nearly in pa-
rallel planes, as in the European. From the shape of the upper jaw alone,
would result a marked diminution in the facial angle, measured according to
the method of Camper; but this diminution is far from being sufficient to ap-
proximate the Ethiopian races to the higher Apes, as some have supposed it
to be. For, whilst the average facial angle of the European may be stated at
80°, and that of the Negro at 70°, that of the adult Chimpanzee is only 35°,
and that of the adult Orang only 30°.* Independently of the diminution of
the facial angle, resulting from the projection of the upper jaw, it is quite cer-
tain that, in the typical prognathous skull, there is a want of elevation of the
forehead ; but it does not appear that there is a corresponding diminution in
the capacity of the cranial cavity, the retreating form of the forehead being
partly due to the general elongation of the skull in the antero-posterior direc-
tion. Nor is it true, as stated by some, that the position of the foramen mag-
num in the Negro is decidedly behind that, which it holds in the European,
— in this respect approaching that of the Apes (§ 51) : since, if due allowance

* The different statements made by some writers, who have estimated the facial angle of
the higher Apes at from 60° to 04°, are due to the measurements having been made upon
young skulls; the projection of the jaws, in these animals, undergoing an extraordinary in-
crease at the time of the second dentition.

DISTINCTIVE PECULIARITIES OF THE RACES OF MAN.

87

be made for the projection of the upper jaw, this aperture is found to have
the same position in the prognathous skull as in the oval one, namely, ex-
actly behind the transverse line bisecting the antero-posterior diameter of the
base of the cranium. The prognathous skull is further remarkable for the
large development of the parts connected with the organs of sense, especially
those of smell and hearing. The aperture of the nostrils is very wide ; and
the internal space allowed for the expansion of the Schneiderian membrane,
and for the distribution of the olfactory nerve, is much larger than in most
European heads. The posterior openings of the nasal cavity are not less re-
markable for their width than the anterior. The external auditory meatus is
also peculiarly wide and spacious ; and the orbital cavities have been thought
to be of more than ordinary capacity, — but this last is by no means a constant
character.

85. A second shape of the head, very different from the preceding, belongs

Fig 8.

Front and basal views of the pyamidal skull of an Esquimaux.

principally to the nomadic races, who wander witli their herds and flocks
over vast plains ; and to the tribes who creep along the shores of the Icy Sea,
and live partly by fishing, and in part on the flesh of their reindeer. This
form, designated by Dr. Prichard as the pyramidal, is typically exhibited by
various nations of Northern and Central Asia ; and is seen in an exaggerated
degree, in the Esquimaux. Its most striking character is the lateral or out-
ward projection of the zygoma, which is due to the form of the malar bones.
These do not project forwards and downwards under the eyes, as in the pro-
gnathous skull ; but take a direction laterally or outwards, forming, with the
zygomatic process of the temporal bone, a large rounded sweep or segment
of a circle. From this, in connection with the narrowness of the forehead,
it results, that lines drawn from the zygomatic arches, touching the temples on
either side, instead of being parallel (as in Europeans), meet over the forehead,
so as to form with the basis a triangular figure. The upper part of the face
being remarkably flat, the nose also being flat, and the nasal bones, as well as
the space between the eyebrows, being nearly on the same plane with the
cheek-bones, the triangular space bounded by these lines may be compared to
one of the faces of a pyramid. The orbits are large and deep; and the pecu-
liar conformation of the bones which surround it, gives to the aperture of the
lids an appearance of obliquity, — the inner angle seeming to be directed
downwards. The whole face, instead of presenting an oval form, as in most
Europeans and Africans, is of a lozenge-shape. The greater relative develop-

88

MUTUAL RELATIONS OE THE HUMAN FAMILY.

Fis. 9.

Oval skull of a European.

ment of the zygomatic bones, and of the bones of the face altogether, when
compared with the capacity of the cranium, indicates in the pyramidal skull
a more ample extension of the organs subservient to sensation; the same
effect being thus produced by lateral expansion, as by the forward extension
of the facial bones in the prognathous skulls.

86. The most civilized races, — those which live by agriculture and the arts
of cultivated life, — all the most intellectually-improved nations of Europe and
Asia, have a shape of the head, which differs from both the preceding forms,

and which may be termed oval or
elliptical. This at once approves it-
self as a more symmetrical form; no
part having an excessive prominence;
whilst on the other hand, there is no-
where an appearance of undue flat-
tening or compression. The head is
altogether of a rounder shape than in
other varieties ; and the forehead is
more expanded ; while the maxillary
bones and the zygomatic arches are
so formed, as to give the face an oval
shape, nearly on a plane with the
forehead and cheek-bones, and not
projecting towards the lower part.
Owing to the more perpendicular di-
rection of the alveolar processes, the
front teeth are fixed in planes, which
are nearly or quite parallel to each other. The principal features in
this form of cranium are thus of a negative character ; the chief positive dis-
tinction is the large development of the cranial cavity, and especially the full-
ness and elevation of the forehead, in proportion to the size of the face ; —
indicating the predominance of the intellectual powers over those merely
instinctive propensities, which are more directly connected with sensations.
Among European nations, the Greeks have probably displayed the greatest
symmetry and perfection in the form of the head; but various departures
may be traced, towards the preceding forms, when we compare the crania of
different races, and even of individuals, belonging to the same stock, — some
approaching the pyramidal form of the Northern Asiatics, whilst others ap-
proximate to the prognathous type of the Negro.

87. The influence of habits of life, continued from generation to generation,
upon the form of the head, is remarkably evinced by the transition from one
type to another, which may be observed in nations that have undergone a
change in their manners, and customs, and have made an advance in civiliza-
lion. Thus, to mention but one instance, the Turks at present inhabiting the
Ottoman and Persian empires, are undoubtedly descended from the same stock
with the nomadic races, which are still spread through Central Asia. The
former, however, having conquered the countries which they now inhabit,
eight centuries since, have gradually settled down to the fixed and regular ha-
bits of the Indo-European race, and have made corresponding advances in
civilization ; whilst the latter have continued their wandering mode of life,
and can scarcely be said to have made any decided advance during the same
interval. Now, the lon»--since civilized Turks have undergone a complete
transformation into the likeness of Europeans ; whilst their nomadic relatives
retain the pyramidal configuration of the skull in a very marked degree. Some
have attributed this change in the physical structure of the Turkish race, to
the introduction of Circassian slaves into the harems of the Turks ; but this

DISTINCTIVE PECULIARITIES OF THE RACES OF MAN. 89

could only affect the opulent and powerful amongst the race ; and the great
mass of the Turkish population have always intermarried among themselves.
The difference of religion and manners must have kept them separate from
those Greeks whom they subdued in the new Ottoman countries ; and in Per-
sia, the Tajiks, or real Persians, still remain quite distinct from their Turkish
rulers, belonging to a different sect among the Mussulmans, and commonly
living apart from them. In like manner, even the Negro head and face may
become assimilated to the European, by long subjection to similar influences;
thus, in some of our older West Indian Colonies, it is not uncommon to meet
with Negroes, — the descendants of those first introduced there, — who exhibit
a very European physiognomy; and it has even been asserted that a Negro
belonging to the Dutch portion of Guiana, may be distinguished from another
belonging to the British settlements, by the similarity of his features and ex-
pression to those which peculiarly characterize his masters. The effect could
not be here produced by the intermixture of bloods, since this would be made
apparent by alteration of colour.

88. Next to the characters derived from the form of the head, those which
are founded upon the form of the pelvis seem entitled to rank. These have
been particularly examined by Professors Vrolik and Weber. The former
concluded from his examinations of this part of the skeleton, that the pelvis
of the Negress, and still more that of the female Hottentot, approximates to
that of the 8imia3 in its general configuration ; especially in its length and
narrowness, — the iliac bones having a more vertical position, so that the ante-
rior spines approach one another much more closely than they do in the Euro-
pean ; and the sacrum also being longer and narrower. On the other hand,
Prof. Weber concludes, from a more comprehensive survey, that no particular
figure is a permanent characteristic of any one race. He groups the principal
varieties which he has met with, according to the form of the upper opening,
— whether oval, round, four-sided, or wedge-shaped. The first of these is
most frequent in the European races ; the second, among the American races ;
the third, most common among the Mongolian nations, corresponds remarka-
bly with the form of their heads ; whilst the last chiefly occurs among the
races of Africa, and is in like manner conformable with the oblong com-
pressed form usually presented by their cranium. But though there are par-
ticular shapes which are most prevalent in each race, yet there are numerous
individual deviations ; of such a nature, that every variety of form presents
itself occasionally in any given race.

89. Other variations have been observed by anatomists, in the relative length
of the bones, and in the shape of the limbs, between the different races of
Man ; but these also seem to have reference to the degree of civilization, and
to the regularity of the supply of wholesome nutriment. It is generally to
be observed, that the races least improved by civilization, like the uncultivated
breeds of animals, have slender, lean, and elongated limbs ; this may be es-
pecially remarked in the natives of Australia. In nearly all the less civilized
races of Men, the limbs are more crooked and badly formed than the average
of those of Europeans; and this is particularly the case in the Negro, the
bones of whose legs bow outwards, and whose feet are remarkably flat. It
has been generally believed, that the length of the forearm in the Negro is so
much greater than in the European, as to constitute a real character of ap-
proximation to the Apes. The difference, however, is in reality extremely
slight ; and is not at all comparable with that which exists between the most
uncultivated races of Men and the highest Apes (§ 54). And in regard to all
the peculiarities here alluded to, it is to be observed, that they can only be
discovered by the comparison of large numbers of one race with correspond-
ing numbers of another ; for individuals are found in every tribe, possessing

8*

90 MUTUAL RELATIONS OF THE HUMAN FAMILY.

the characters which distinguish the majority of the other race. Any such
peculiarities, therefore, are totally useless as the foundation of specific charac-
ters; being simply variations from the ordinary type, resulting from causes
which might affect the entire race, as well as individuals.

90. The connection between the general form of the body, on the one hand,
and the degree of civilization (involving the regular supply of nutriment) on
the other, is made apparent, not merely by the improvement which we per-
ceive in the form, development, and vigour of the frame, as we advance from
the lowest to the most cultivated of the Human races ; but also by the degra-
dation which is occasionally to be met with in particular groups of the higher
tribes, Avhich have been subjected for several generations to the influence of
depressing causes. Of this class of facts, the following is a very interesting
example : — " On the plantation of Ulster, and afterwards on the successes of
the British against the rebels of 1641 and 1689, great multitudes of the na-
tive Irish were driven from Armagh and the south of Down, into the moun-
tainous tract extending from the barony of Flews eastward to the sea: — on
the other side of the kingdom, the same race were expelled into Leitrim, Sligo
and Mayo. Here they have been almost ever since, exposed to the worst
effects of hunger and ignorance, the two great brutalizers of the human race.
The descendants of these exiles are still readily distinguishable from their
kindred in Meath, and in other districts where they are not in a state of phy-
sical degradation ; being remarkable for open projecting mouths, with prominent
teeth and exposed gums ; their advancing cheek-bones and depressed noses
bearing barbarism on their very front. In Sligo and northern Mayo, the con-
sequences of two centuries of degradation and hardship exhibit themselves in
the whole physical condition of the people ; affecting not only the features,
but the frame, and giving such an example of human deterioration from known
causes, as almost compensates, by its value to future ages, for the suffering
and debasement which past generations have endured in perfecting its appall-
ing lesson. Five feet two inches upon an average, pot-bellied, bow-legged,
abortively-featured, their clothing a wisp of rags, — these spectres of a people,
that were once well-grown, able-bodied, and comely, stalk abroad into the day-
light of civilization, the annual apparitions of Irish ugliness and Irish want.
In other parts of the island, where the population has never undergone the
influence of the same causes of physical degradation, it is well known that
the same race furnishes the most perfect specimens of human beauty and
vigour, both mental and bodily."*

91. From the foregoing survey of the phenomena, bearing upon the ques-
tion of the specific unity or diversity of the Human races, the following
conclusions may be drawn : —

I. That the physical constitution of Man is peculiarly disposed, like that
of the domesticated animals, to undergo variations; some of which can be
traced to the influence of external causes; whilst others are not so explicable,
and must be termed spontaneous.

II. That the extreme variations which present themselves, between the
races apparently the most removed from one another, are not greater in degree
than those which exist between the different breeds of domesticated animals,
which are known to have descended from a common stock ; and that they
are of the same kind with the variations which present themselves in any
one race of Mankind, — the difference of degree being clearly attributable, in
the majority of cases, to the respective conditions under which each race
exists.

III. That none of the variations, which have been pointed out as existing

* Sec Dublin University Magazine, No. XLVIII.

PRINCIPAL BRANCHES OF THE HUMAN FAMILY. 91

between the different races of mankind, have the least claim to be regarded
as valid specific distinctions ; being entirely destitute of that fixity, which is
requisite to entitle them to such a rank; and exhibiting, in certain groups of
each race, a tendency to pass into the characters of some other.

IV. That, in the absence of any valid specific distinctions, we are required,
by the universally-received principles of zoological science, to regard all the
races of Mankind as belonging to the same species, or (in other words) as
having had either an identical or similar parentage; and that this conclusion
is supported by the positive evidence, afforded by the agreement of all the
races in the physiological and psychological characters, that most distinguish
them from other species, and especially by the ready propagation of mixed
breeds or hybrid races.

7. Principal Branches of the Human Family.

92. The above conclusions are found to be in entire accordance with those
derived from an examination of the relative affinities of the different races of
Men at present existing ; as far as these are deducible from the analogies of their
language, from their correspondence in peculiar habits and observances, and from
traditional or other evidence in regard to their original sources. For it appears,
from such investigations, that very great difference in colour, texture of the hair,
form of the skull, and other important physical characters, exist among nations,
which may be referred with great confidence to a common source ; whilst on
the other hand, we find traits of physical resemblance, in tribes which exist
under corresponding circumstances in remote parts of the world, and which
seem to have nothing else in common. It has been attempted by Blumenbach
and Cuvier to arrange the different races of Men under five principal varie-
ties; the Caucasian, Mongolian, Ethiopian, Malay, and American. But, for
the reason just given, it is impossible to establish any constant distinguishing
characters, which shall serve to mark these clearly out ; and it moreover ap-
pears that several additional groups must be created, for the reception of tribes,
that differ as much from the preceding as these do from each other. In the
following brief enumeration, the views of Dr. Prichard will be adopted.

93. The Caucasian variety of Blumenbach and Cuvier was so named from the
idea, that the Caucasian range of mountains might be regarded as the centre
or focus of the races belonging to it; and that the Caucasian people present
the typical conformation of the variety in the most perfect degree. Neither
of these ideas are correct, however; and some other designation might very
properly be substituted for that which conveys them. In this variety are pre-
sented all the characters of highest physical perfection of the race, such as
were, perhaps, most pre-eminently combined among the Ancient Greeks; as
well as those of intellectual and moral elevation. No uniformity exists, how-
ever, as to colour; for this character presents every intermediate gradation,
from the fair and florid hue of the Northern Europeans, to the jet black of
many tribes in North Africa and Hindustan. The hair is generally long and
flexible ; but departures from the ordinary type present themselves in this
respect, also, both among individuals and among whole tribes. Although
there is general agreement in these characters among the nations of South-
western Asia, Northern Africa, and nearly the whole of Europe, yet we are
required by the evidence of ancient history, as well as by the characters de-
rived from language, to separate these nations into two groups ; which appeared
to have been distinct from each other at the earliest period of which we have
any traces ; and which we must regard, therefore, as alike entitled to rank as
primary branches of the human family. These are the Syro-Arabian, and the
Indo-European groups of nations.

92 MUTUAL RELATIONS OF THE HUMAN FAMILY.

94. The Syro-Arabian nations, distinguished from all others by their very
peculiar idiom, originally inhabited the region of Asia intermediate between
the countries of the Indo-European and of the Egyptian races ; having as its
centre the region watered by the great rivers of Mesopotamia. Several of the
nations originally constituting this group have become extinct, or nearly so ;
and the Arabs, which originally formed but one subdivision of it, have now
become the dominant race, not only throughout the ancient domain of the
Syro-Arabian nations, but also in Northern Africa. In the opinion of Baron
Larrey, who had ample opportunities for observation, the skulls of the Arabian
race furnish, at present, the most complete type of the human head ; and he
considered the remainder of the physical frame as equally distinguished by
its superiority to that of other races of men. The different tribes of Arabs
present very great diversities of colour, which are generally found to coincide
with variations in climate. Thus the Shegya Arabs, and others living on the
low countries bordering on the Nile, are of a dark-brown or even black hue ;
but even when quite jetty, they are distinguished from the Negro races by
the brightness of their complexions, by the length and straightness of their
hair, and by the regularity of their features. The same may be said of the
wandering Arabs of Northern Africa ; but the influence of climate and cir-
cumstances is still more strongly marked in some of the tribes long settled in
that region, whose descent may be traced to a distinct branch of the Syro-
Arabian stock, namely, the Berber, to which belong the Kabyles of Algiers
and Tunis, the Tuaryks of Sahara, antl the Guanches or ancient population
of the Canary Isles. Amongst these tribes, whose affinity is indisputably
traceable through their very remarkable language, every gradation may be
seen, from the intense blackness of the Negro skin, to the more swarthy hue
of the inhabitants of the South of Europe. It is remarkable that some of the
Tuaryk inhabitants of particular Oases in the great desert, who are almost as
insulated from communication with other races as are the inhabitants of
islands in a wide ocean, have hair and features that approach those of the
Negroes ; although they speak the Berber language with such purity, as to
forbid the idea of the introduction of these characters by an intermixture of
races. The Jews, who are the only remnants now existing of the once pow-
erful Phoenician tribe, and who are now dispersed through nearly every coun-
try on the face of the earth, present a similar diversity; having gradually
assimilated in physical characters to the nations among which they have so
long resided (§ 80).

95. The affinity of the Indo-European nations, now spread from the
mouth of the Ganges to the British Islands and the Northern extremity of
Scandinavia, is in like manner proved by the cognate character of their lan-
guages ; in spite of the differences in colour and other traits, which present
themselves among the inhabitants of that vast tract. The type of physical
configuration, however, is the same ; and the differences of colour are such,
as may readily be traced to external agencies. Thus among the Hindoo
races we find that the distinction of castes (perpetuating the same mode of life
in particular families from generation to generation), the marked differences
of climate (as between the mountainous regions of Kashmir and Kafiristan,
and the plains bordering the great rivers of India), and other circumstances,
are accompanied, as in the case of the Arabian race, with diversities in phy-
sical conformation, which are now established as belonging to different sections
of the people. In many instances, the origin of these varieties can be clearly
traced by historical evidence, as well as by affinities of language and con-
formation ; and it cannot be questioned, that Hindoos as black as Negroes,
others of a copper-colour, others little darker than the inhabitants of Southern
Europe, and others of fair complexion with blue eyes and auburn or even red

PRINCIPAL BRANCHES OF THE HUMAN FAMILY. 93

hair, have all had a common parentage; some having become darker, and
others lighter than their ancestors, generally in accordance with changes in
their residence and habits. This group seems to have been early divisible
into two primary branches ; the northern or Median; and the southern or
Indian. Between the original languages of these races, a marked resem-
blance can be traced ; and the traditions of both races point to contiguous
regions as their original seat, — the earliest records of the Persians indicating
that they migrated westwards from a spot in the ancient Bactria, not far from
Balkh, to the westward of the Indus ; whilst the traditions of the Brahmans
refer the origin of the Hindoos to the north-western part of the country lying
between the Himalaya and the Vindhya mountains, whence they afterwards
moved eastwards and southwards into the Peninsula. Both these races ap-
pear to have migrated in a north-westerly direction, at a period long preceding
our earliest knowledge of European history ; for the European languages pre-
sent indications of affinity to the ancient languages of both Medians and
Indians. The classical languages of Greece and Italy appear more referrible
to the Sanskrit or ancient Indian, than to the Zend or ancient Median ; whilst,
on the other hand, the Germanic languages would seem to have originated
rather in the latter. Of all the extant European dialects, the Lettish and
Lithuanian approach most nearly to the ancient type.

a. It may be well to notice here, the nature of the evidence on which statements of this
kind are grounded. The extensive and profound inquiries which have been in progress
for many years, have enabled Philologists to distinguish, usually with little difficulty, between
the intermixture of languages, which may arise from the intercourse of any two nations that
happen to be connected by local proximity, commercial intercourse, &c. ; and that funda-
mental correspondence, which indicates anginal affinity. The latter is to be sought rather
in the analogies of grammatical structure, and in the laws of combination, or the mechanism
of speech, than in the vocabulary; and it sometimes happens that a relationship may thus
be traced between languages, which have scarcely a single word in common. The most
satisfactory evidence, however, is derived from resemblance in those parts of the vocabu-
lary, which serve to represent the ideas of a people in the most simple state of existence; —
such as terms expressive of family relations; names for the most striking objects of the visi-
ble universe; terms distinguishing different parts of the body; nouns of number, up to 5, 10,
or 20 ; verbs descriptive of the most common sensations and bodily acts, such as seeing,
hearing, eating, drinking, and sleeping. As no nation was ever found destitute of similar
expressions; and as we know by the observation of facts, in addition to abstract probability,
that tribes however rude, do not exchange their own stock of primitive words for those of a
foreign idiom ; it may be inferred that dialects, which correspond in those parts of their
vocabulary, were originally one speech, or the language of one people.

b. It has been fully demonstrated, that both these indications of affinity or family relation-
ship exist between the languages of the several races, from which the great mass of the popu-
lation of Europe is derived; and, further, that this affinity not only unites them with each
other, but connects them all with the common Eastern stock.

96. The second primary division of the human family, according to the
usual arrangement, is that commonly termed Mongolian. The real Mon-
goles, however, constitute but a single and not very considerable member of
the group of nations associated under this designation; which is, therefore,
by no means an appropriate one. The original seat of these races appears
to have been the great central elevated plain of Asia, in which all the great
rivers of that continent have their sources, whatever may be their subsequent
direction. Taken as a whole, this division of the human family is charac-
terized by the pyramidal form of the skull, and by a xanthous or olive com-
plexion; but these characters are only exhibited, in a prominent degree, in
the more typical members of the group, and may become so greatly modified
as to cease altogether to be recognizable. This has been remarkably the case
with regard to the Turkish people, now so extensively distributed. All the
most learned writers on Asiatic history are agreed in opinion, that the Turkish

94 MUTUAL RELATIONS OF THE HUMAN FAMILY.

races are of one common stock ; although at present they vary in physical
characters, to such a degree that, in some, the original type has been alto-
gether changed. Those which still inhabit the ancient abodes of the race,
and preserve their pastoral nomadic life, present the physiognomy and gene-
ral characteristics which appear to have belonged to the original Turkomans;
and these are decidedly referrible to the so-called Mongolian type. Before
the Mohammedan era, however, the Western Turks or Osmanlis had adopted
more settled habits, and had made considerable progress in civilization ; and
their adoption of the religion of Islam incited them to still wider extension,
and developed that spirit of conquest, which, during the middle ages, dis-
played itself with such remarkable vigour. The branches of the race, which.
from their long settlement in Europe, have made the greatest progress in
civilization, now exhibit in all essential particulars the physical characters of
the European model; and these are particularly apparent in the conformation
of the skull. — In like manner we find that the Ugorian division, which mi-
grated towards the northwest at a very early period, planted a colony in
Europe, which still tenants the Northern Baltic countries, forming the races
of Fins and Lappes. In the time of Tacitus, the Fins were as savage as the
Lappes ; but the former, during the succeeding ages, became so far civilized,
as to exchange a nomadic life for one of agricultural pursuits, and have gra-
dually assimilated with the surrounding people; whilst the Lappes, like the
Siberian tribes of the same race, have ever since continued to be barbarous
nomades, and have undergone no elevation in physical characters. The same
division gave origin to the Magyars or Hungarians ; a warlike and energetic
people, unlike their kindred in the North; in whom a long abode in the centre
of Europe has, in like manner, developed the more elevated characters, phy-
sical and mental, of the European nations. The nations inhabiting the south-
eastern portion of Asia, also, appear -to have had their origin in the Mongolian
or Central Asiatic stock; although their features and form of skull by no
means exhibit its characteristic marks, but present such departures from it as
are elsewhere observable in races that are making advances in civilization.
Even the great peninsula of Hindostan appears to have been peopled, long
previously to the settlement of the present Hindoo race, by tribes of the
Central Asiatic stock, so distinguished by its migratory propensities ; and
remains of these aborigines are still found in the hilly parts of Northern
India, in the Dekhan, and in Ceylon, constituting numerous tribes, which are
now for the most part isolated from each other, and which exhibit very dif-
ferent degrees of civilization.

97. According to the usual mode of dividing the Human family, the Ethi-
opian or Negro stock is made to include all the nations of Africa, to the
southward of the Atlas range. But there is good reason for separating the
Hottentots and Bushmen as a distinct race; and for restricting the designation
of Negroes to the nations inhabiting the region southward of the Great Desert,
as far as the Hottentot country, — the inhabitants of the oases of the desert
itself being mostly, as already pointed out, of Syro-Arabian origin, although
assimilating closely to the Negro race in physical characters. The nations
thus*ln geographical proximity with each other, are found to have sufficient
affinities of language, to justify the belief in their common origin; and they
all present, in a more or less evident degree, the physical peculiarities of the
Negro race. But these are far from constituting a sufficient ground for regard-
ing the African nations as a distinct race, separated from all other families of
men by a broad and definite line of demarcation. Our idea of the Negro
character is principally founded upon that division of the people which in-
habits the low countries of the Western part of Central Africa, and in which
the Negro peculiarities are most strongly marked. There are very few nations

PRINCIPAL BRANCHES OF THE HUMAN FAMILY. 95

which present in a high degree all the characters that are commonly regarded
as typical of the Negro; these being generally distributed among different
nations in various ways ; and being combined, in each instance, with more
or fewer of the characters belonging to the European or Asiatic. Thus the
race of Jolofs near the Senegal, and the Guber in the interior of Sudan, have
woolly hair and deep black complexions, but fine forms and regular features
of a European cast; and nearly the same may be said of the darkest of the
Kafirs of Southern Africa. The Bechuna Kafirs present a still nearer ap-
proach to the European type; the complexion being of a light brown, the
hair often not woolly but merely curled, or even in long flowing ringlets, and
the figure and features having much of the European character. The nations
of the northeast of Africa, also, present similar departures from the typical
characters of the Negro.

98. There is no group which presents a more constant correspondence
between external conditions and physical conformation, than that composed
of the African nations. As we find the complexion becoming gradually
darker, in passing from northern to southern Europe, thence to North Africa,
thence to the borders of the Great Desert, and thence to the intertropical re-
gion where alone the dullest black is to be met with, — so do we find, on
passing southwards from this, that the hue becomes gradually lighter in pro-
portion as we proceed further from the equator, until we meet with races
of comparatively fair complexions among the nations of Southern Africa.
Even in the intertropical region, high elevations of the surface have the same
effect, as we have seen them produce elsewhere, in lightening the complexion.
Thus, the high parts of Senegambia, where the temperature is moderate and
even cool at times, are inhabited by Fulahs of a light copper colour; whilst
the nations inhabiting the lower regions around them, are of true Negro black-
ness; and nearly on the same parallel, but at the opposite side of Africa, are
the high planes of Enarea and Kaffa, where the inhabitants are said to be
fairer than the natives of Southern Europe. Again, those races which have
the Negro character in an exaggerated degree, and which may be said to ap-
proach to deformity in persons, — the ugliest blacks, with depressed forehead,
flat noses, and crooked legs, — are in most instances inhabitants of low coun-
tries, often of swampy tracts near the sea-coast, where many of them have
scarcely any other means of subsistence than shell-fish and the accidental gifts
of the sea. Such tribes are uniformly in the lowest stage of society, being
either ferocious savages, or stupid, sensual, and indolent. Such are most of
the tribes along the Slave Coast. On the other hand, wherever we hear of
a Negro state, the inhabitants of which have attained any considerable degree
of improvement in their social condition, we constantly find that their phy-
sical characters deviate considerably from the strongly-marked or exaggerated
type of the Negro. Such are the Ashanti, the Sulima, and the Dahomans of
Western Africa; also the Guber of Central Sudan, among which a consider-
able degree of civilization has long existed, which are perhaps the finest race
of genuine Negroes on the whole continent, and which present in their lan-
guage distinct traces of original relationship to the Syro-Arabian nations, not
to be accounted for by any subsequent intermixture of races.

99. The highest civilization, and the greatest improvement in physical
characters, are to be found in those nations, which have adopted the Moham-
medan religion; this was introduced, three or four centuries since, into the
eastern portion of Central Africa; and it appears that the same people, which
were then existing in the savage condition still exhibited by the pagan nations
further south, have now adopted many of the arts and institutions of civilized
society, subjecting themselves to governments, practising agriculture, and
dwelling in towns of considerable extent, many of which contain 10,000, and

96 MUTUAL RELATIONS OF THE HUMAN FAMILY.

some even 30,000 inhabitants ; a circumstance which implies a consider-
able advancement in industry, and in the resources of subsistence. This last
fact affords most striking evidence of the improvability of the Negro races ;
and, taken in connexion with the many instances that have presented them-
selves, of the advance of individuals, under favourable circumstances, to at
least the average degree of mental development among the European nations,
it affords clear proof that the line of demarcation, which has been supposed
to separate them intellectually and morally from the races that have attained
the greatest elevation, has no more real existence than that, which has been
supposed to be justified by a difference in physical characters, and of which
the fallacy has been demonstrated.

100. The Bushmen or Bojesmen of South Africa are generally regarded
as presenting the most degraded and miserable condition, of which the human
race is capable: and they have been supposed to present resemblances in
physical characters to the higher Quadrumana. Yet there is distinct evidence,
that this degraded race is but a branch or subdivision of the once extensive
nation of Hottentots ; and that its present condition is in great part due to the
hardships, to which it has been subjected in consequence of European colo-
nization. This race differs from all other South African nations, both in lan-
guage and in physical conformation. The language cannot be shown to possess
affinities with those of any other stock; but in bodily structure there is a re-
markable admixture of the characters of the Mongolian with those of the Ne-
gro. Thus the face presents the very wide and high cheek-bones, with the
oblique eyes and flat nose, of the Northern Asiatics; at the same time that, in
the somewhat prominent muzzle and thick lips, it resembles the countenance
of the Negro. The complexion is of a tawny buff or fawn colour, like that
of the Negroes 'diluted with the olive of the Mongoles. The hair is woolly
like that of the Negroes, but it grows in small tufts, scattered over the surface
of the scalp, instead of covering it uniformly, resembling in its comparative
scantiness that of the Northern Asiatics. It is most interesting to observe this
remarkable resemblance in physical characters, between the Hottentots and
the Mongolian races ; in connexion with the similarity that exists between the
circumstances under which they respectively live. No two countries can be
more similar, than the vast steppes of Central Asia, and the karroos of South-
ern Africa. And the inhabitants of each were nomadic races, Avandering
through deserts remarkable for the wide expansion of their surface, their scanty
herbage, and the dryness of their atmosphere, and fee'ding upon the milk and
flesh of their horses and cattle. Of the original pastoral Hottentots, however,
very few now remain. They have been gradually driven, by the encroach-
ments of European colonists and by internal wars with each other, to seek
refuge among the inaccessible rocks and deserts of the interior; and they have
thus been converted from a mild unenterprising race of shepherds, into wander-
ing hordes of fierce, suspicious, and vindictive savages, treated as wild beasts
by their fellow-men, until they become really assimilated to wild beasts in their
habits and dispositions. This transformation has taken place under the ob-
servation of eye-witnesses, in the Koranas. a tribe of Hottentots well known
to have been previously the most advanced in all the improvements which
belong to pastoral life. Having been plundered by their neighbours and driven
out into the wilderness to subsist upon fruits, they have adopted the habits of
the Bushmen, and have become assimilated in every essential particular to
that miserable tribe.

101. The American nations, taken collectively, form a group which ap-
pears to have existed as a separate family of nations from a very early period
in the world's history. They do not form, however, so distinct a variety, in
regard to physical characters, as some anatomists have endeavoured to prove ;

PRINCIPAL BRANCHES OF THE HUMAN FAMILY. 97

for, although certain peculiarities have been stated to exist in the skulls of the
aboriginal Americans, yet it is found, on a more extensive examination, that
these peculiarities are very limited in their extent, — the several nations spread
over this vast continent differing from each other in physical peculiarities, as
much as they do from those of the Old World, so that no typical form can be
made out among them. In regard to complexion, again, it may be remarked,
that although the native Americans have been commonly characterized as
" red men," they are by no means invariably of a red or coppery hue, some
being as fair as many European nations, others being yellow or brown, and
others nearly, if not quite, as black as the Negroes of Africa ; whilst, on the
other hand, there are tribes equally red, and perhaps more deserving that epi-
thet in Africa and Polynesia. — In spite of all this diversity of conformation,
it is believed that the structure of their languages affords a decided and
clearly-marked evidence of relationship between them. The words, and even
the roots, may differ entirely in the different groups of American nations ;
but there is a remarkable similarity in grammatical construction amongst them
all, which is of a kind not only to demonstrate their mutual affinity, but to
separate them completely from all known languages of the old continent.
Notwithstanding also their diversities in mode of life, there are peculiarities
of mental character, as well as a number of ideas and customs derived from
tradition, which seem to be common to them all, and which for the most part
indicate a former elevation in the scale of civilization, that has left its traces
among them even in their present degraded condition, and that still distin-
guishes them from the sensual, volatile, and almost animalized savages, that
are to be met with in many parts of the Old Continent. — The Esquimaux
constitute an exception to all general accounts of the physical characters of
the American nations ; for in the configuration of their skulls, in their com-
plexion, and in their general physiognomy, they conform to the Mongolian
type, even presenting it in an exaggerated degree. Their wide extension
along the whole northern coast of America, and the near proximity of this
coast to Kamschatka, certainly lend weight to the idea, that they derive their
origin from the Northern Asiatic stock ; but, on the other hand, they have a
marked affinity, in regard to language, to the other American nations. The
Athapascan Indians, various tribes of which inhabit the country south of the
Esquimaux country, seem intermediate in physical characters, as they are in
geographical position, between the Esquimaux and the ordinary Americans.
They have a tradition which seems to indicate, that they are derived from the
North-Eastern Asiatics, with whom they have many points of accordance in
dress and manners.

102. It now remains for us to notice the Oceanic races, which inhabit the
vast series of islands scattered through the great ocean, that stretches from
Madagascar to Easter Island. There is no part of the world, which affords a
greater variety of local conditions than this, or which more evidently exhibits
the effects of physical agencies on the organization of the human body.
Moreover, it affords a case for the recognition of affinities by means of lan-
guage, that possesses unusual stability ; since the insulated position of the
various tribes, that people the remote spots of this extensive tract, prevents
them from exercising that influence upon each others' forms of speech, which
is to be observed in the case of nations united by local proximity or by fre-
quent intercourse. Tried by this test, it is found that the different groups of
people, inhabiting the greater part of these insular tracts, are more nearly con-
nected together, although so widely scattered, and so diverse in physical
characters, than most of the families of men, occupying continuous tracts of
land on the great continents of the globe. The inhabitants of Oceanica seem
divisible into three groups, which are probably to be regarded as having con-
9

98 MUTUAL RELATIONS OF THE HUMAN FAMILY.

stituted distinct races from a very early period ; these are the Malayo-Poly-
nesian race, the Pelagian Negroes (commonly termed Papuas), and the Alforas
or Alfourous.

103. The Malabo-Polynesian group is by far the most extensive of the
three, and comprehends the inhabitants of the greater part of the Indian and
Polynesian Archipelagoes, with the peninsula of Malacca (which is the cen-
tre of the Malays proper), and the inhabitants of Madagascar. These are all
closely united by affinities of language. The proper Malays bear a strong
general resemblance to the Mongolian races, and this resemblance is shared,
in a greater or less degree, by most of the inhabitants of the Indian Archi-
pelago. They are of a darker complexion, as might be expected from their
proximity to the equator ; but in this complexion, yellow is still a large in-
gredient. The Polynesian branch of the group presents a much wider
diversity ; and if it were not for the community of language, it might be
thought to consist of several races, as distinct from each other as from the
Malayan branch. Thus the Tahitians and Marquesans are tall and well-
made ; their figures combine grace and vigour: their skulls are usually re-
markably symmetrical ; and their physiognomy presents much of the Euro-
pean cast, with a very slight admixture of the features of the Negro. The
complexion, especially in the females of the higher classes, who are sheltered
from the wind and sun, is of a clear olive or brunette, such as is common
among the natives of Central and Southern Europe; and the hair, though
generally black, is sometimes brown or auburn, or even red or flaxen. Among
other tribes, as the New Zealanders, and the Tonga, and Friendly Islanders,
there are greater diversities of conformation and hue ; some being finely pro-
portioned and vigorous, others comparatively small and feeble ; some being
of a copper-brown colour, others nearly black, others olive, and others almost
white. In fact, if we once admit a strongly-marked difference in complexion,
features, hair, and general configuration, as establishing a claim to original
distinctness of origin, we must admit the application of this hypothesis to
almost every group of islands in the Pacific ; — an idea of which the essential
community of language seems to afford a sufficient refutation. Among the
inhabitants of Madagascar, too, all of which speak dialects of the same lan-
guage, some bear a strong resemblance to the Malayan type, whilst others
present approaches to that of the Negro.

104. The Pelagian- Negro races must be regarded as a group altogether
distinct from the preceding ; having a marked diversity of language ; and
presenting more decidedly than any of the Malayo-Polynesians, the characters
of the Negro type. They form the predominating population of New Bri-
tain, New Ireland, the Louisiade and Solomon Isles, of several of the New
Hebrides, and of New Caledonia; and they seem to extend westwards into
the mountainous interior of the Malayan Peninsula, and into the Andaman
Islands, in the Bay of Bengal. The Tasmanians, or aborigines of Van Die-
man's Land, which are now almost completely exterminated, undoubtedly
belonged to this group. Very little is known of them, except through the
reports of the people of Malayo-Polynesian race inhabiting the same islands ;
but it appears that, generally speaking, they have a very inferior physical de-
velopment, and lead a savage and degraded life. There is considerable diversity
of physical characters among them ; some approximating closely in hair, com-
plexion, and features, to the Guinea-Coast Negroes ; whilst others are of
yellower tint, straight hair, and better general development. The Papuans,
who inhabit the northern coast of New-Guinea, and some adjacent islands,
and who are remarkable for their large bushy masses of half-woolly hair, have
been supposed to constitute a distinct race ; but there is little doubt that they
are of hybrid descent, between the Malays and the Pelagian Negroes.

ON ORGANIZED STRUCTURES IN GENERAL. 99

105. Still less is known of the Alfouroiis, or Jllforian race, which are
considered by some to be the earliest inhabitants of the greater part of the
Malayan Archipelago, and to have been supplanted by the more powerful peo-
ple of the two preceding races, who have either extirpated them altogether,
or have driven them from the coasts into the mountainous and desert parts of
the interior. They are yet to be found in the central parts of the Moluccas
and Philippines; and they seem to occupy most of the interior and southern
portion of New Guinea, where they are termed Endamenes. They are of
very dark complexion ; but their hair, though black and thick, is lank. They
have a peculiar repulsive physiognomy ; the nose is flattened, so as to give
the nostrils an almost transverse position; the cheek-bones project; the eyes
are large, the teeth prominent, the lips thick, and the mouth wide. The limbs
are long, slender and misshapen. From the close resemblance in physical
characters, between the Endamenes of New Guinea, and the aborigines of
New Holland, and from the proximity between the adjacent coasts of these
two large islands, it may be surmised that the latter belong to the Alforian
race; but too little is known of the language of either, to give this inference
a suflicient stability. In the degradation of their condition and manner of life
the savages of New Holland fully equal the Bushmen of South Africa ; and
it is scarcely possible to imagine human beings, existing in a condition more
nearly resembling that of brutes. But there is reason to believe, that the
tribes in closest contact with European settlers are more miserable and savage
than those of the interior ; and even with respect to these, increasing acquaint-
ance with their language, and a consequent improved insight into their modes
of thought, tend to raise the very low estimate which had been formed and
long maintained, in regard to their extreme mental degradation. The latest
and most authentic statements enable us to recognize among them the same
principles of a moral and intellectual nature, which, in more cultivated tribes,
constitute the highest endowments of humanity, and thus to show that they
are not separated, by any impassable barrier, from the most civilized and cul-
tivated nations of the globe.

CHAPTER III.

OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

1. On Organized Structures in General.

106. THE Human body, in common with the bodies of all the higher Ani-
mals, is composed of an immense number of parts, whose structure and
whose actions are alike dissimilar ; but which are yet so arranged, as to make
up a fabric distinguished by its perfect adaptation to a great variety of pur-
poses, whilst their actions, though in a great degree independent of each other,
concur in effecting one common object, — the maintenance of the integrity of
the entire organism. In the lowest and simplest forms of living being, such
as we meet with among the humblest Cellular Plants, we find a single cell
making up the whole fabric. This cell grows from its germ, absorbs and as-
similates nutriment, converts a part of this into the substance of its own cell-
wall, secretes another portion into its cavity, and produces from a third the
reproductive germs that are to continue the race ; and having reached its own

100 OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

term of life, and completed the preparation of these germs, it bursts and sets
them free, — every one of these being capable, in its turn, of going through
the same set of operations. In the highest forms of Vegetable life, we find
but a multiplication of similar cells ; amongst which these operations are dis-
tributed, as it were, by a division of labour; so that, by the concurrent labours
of all, a more complete and permanent effect may be produced. If we ana-
lyze the structure of a forest tree, for example, we find that all the soft and
growing parts are composed of similar cells ; whose office it is, to absorb and
prepare the nutriment, which is afterwards to be applied to the extension of
the solid internal skeleton of the trunk and branches. This latter part is not
concerned in the functions of vegetation, in any other way than as supporting
and connecting the different groups of cells, which form the operative -part of
the fabric; and it is composed of two forms of tissue, — woody-fibre, and vas-
cular tissue, — each of which may be regarded as originating in the metamor-
phosis of cells (§ 120).

107. At the extremities of the roots of all the more perfect Plants, we find
a set of soft cells, making up those succulent bodies which are known as the
spongioles ; these are specially destined to perform the Absorption of nutri-
tious fluid. This fluid, being conveyed by the vessels of the stem and branches
to the leaves, is there subjected to the action of the cells which make up the
parenchyma of those organs. The crude watery ascending sap is thus con-
verted, by a variety of chemical and vital operations, into the thick glutin-
ous latex; which, like the blood of animals, contains the materials for the
production of new tissue, and also the elements of the various secretions.
This process of conversion includes the Exhalation of superfluous liquid ;
and also that interchange of gaseous ingredients between the sap and the air,
which may be termed Aeration ; but it involves, beside these obvious chemi-
cal alterations, a new molecular arrangement of the particles of the sap, by
which a variety of new products are generated, — some of them possessing
such a tendency to pass into the form of solid organized tissue, as to present
a sort of sketch of this, by a process of coagulation, when withdrawn from
the living vessels. To this peculiar converting process, which is such an
important step towards the production of perfect living tissue from the crude
aliments, the term Assimilation is applied. As the elaborated sap or latex
descends in its proper vessels through the stem, it yields up to the growing
parts the nutrient materials they respectively require. These growing parts
may be either the ordinary tissues, of which the chief part of the fabric is
composed, and which are destined to a comparative permanency of duration ;
and in the growth and extension of these, the process of Nutrition is com-
monly regarded as consisting. On the other hand, certain groups of cells
have for their office the separation of peculiar products from the sap, such as
oil (fixed or essential), starch, resin, &c. ; which they store up against the
time when they may be demanded ; and these are said to perform the act of
Secretion. In both cases, however, the act is essentially the same ; for the
process of Secretion, like that of Nutrition, consists in the growth of a cellular
tissue, and the difference consists only in the destination of the contents of the
cells ; which, in the one case, are adapted merely to give firmness and solidity
to their walls ; whilst, in the other, they are set apart for some other purpose,
to be given up again when required.

108. It is very important to remark, in regard to all the cells thus actively
concerned in the Vegetative functions, by which the development and exten-
sion of the permanent fabric is provided for, that they have but a very transi-
tory life as individuals. The Absorbent cells at the extremities of the rootlets
are continually being renewed ; some of the old ones dying and decaying
away, whilst others are converted into the solid texture of the root, and thus

ON ORGANIZED STRUCTURES IN GENERAL. 101

contribute to its progressive elongation. Of the transitory duration of the
Assimilating cells, we have an obvious proof in the "fall of the leaf;" which
takes place at intervals (alike in evergreen and deciduous species), to be fol-
lowed by the production of a new set of cells, having similar functions. And
the Secreting cells have usually a like transitory duration ; being destined to
give up their contents by the rupture or liquefaction of their walls, whenever
called upon to do so, by the demand set up in the growing parts of their
neighbourhood, for the peculiar products they have set apart.

109. Not only are the proper organic functions of all Plants thus dependent
upon the agency of cells ; but their Reproduction is likewise. In the lowest
tribes of the Cryptogamia, where each cell is an independent individual, every
one has the power of preparing within itself the reproductive germs, from
which new generations may arise. In the higher tribes, on the other hand,
the general principle of the division of labour, which separates the absorbing,
assimilating and secreting cells, involves also the setting apart of a distinct set
of cells for the preparation of the reproductive germs ; these cells are known
in the Cryptogamia as spores, and in the Phanerogamia as pollen-grains. In
the higher Plants we find a complex apparatus superadded ; for the purpose
of aiding the early development of these germs, by supplying them with nu-
triment previously elaborated by the parent; yet still this operation is of a
purely accessory kind, and the essential part of the process remains the same.

110. Now we shall find that, although the fabric of Animals appears to be
formed on a plan entirely different from that of Plants, and although the ob-
jects to be attained are so dissimilar, there is a much greater accordance
amongst their elementary parts, than might have been anticipated. The starting-
point of both is the same ; for the embryo of the Animal, up to a certain grade
of its development, consists, like that of the Plant, of nothing else than an aggre-
gation of cells (Plate I., Fig. 15). And amongst the lowest tribes of animals, as
well as among certain of the highest tribes that retain many embryonic peculi-
arities, even in the adult condition, (such as the curious Jlmphioxus or Lancelot,)
we find a great proportion of the complete fabric to be possessed of a similar
constitution. In most of the higher animals, however, Ave find that a large
proportion of the fabric consists of tissues in which no distinct trace of a cel-
lular origin is apparent ; and it has been only since improved powers of ob-
servation have been brought to bear upon their analysis, and more especially
since they have been examined, not only in their complete state, but in the
course of their development, that they have been reduced to the same category
with the tissues of Plants and of the lower Animals. Other tissues, which
are peculiar to Animals, cannot be referred to the same origin ; but these will
be found to have a grade of organization even lower than that of simple iso-
lated cells, and to be referrible to the solidification of the plastic or organizable
fluid prepared by the assimilating cells, and set free by their rupture. We
shall find, however, that (as in Plants) all the tissues most actively concerned
in the Vital operations, retain their original cellular form ; and we shall be
able to refer to distinct groups of cells in the bodies of Animals, not merely
the functions of Absorption, Assimilation, Respiration, Secretion, and Repro-
duction, which are common to them with Plants, but also those of Muscular
Contraction, and Nervous Action, which they alone perform. Before proceed-
ing to this investigation, however, it will be desirable to examine into the na-
ture of the original components at the expense of which the Animal fabric
is built up. Our knowledge of these is principally derived from the researches
which have been made into their character in Man and the higher Animals;
but there can be little doubt that they are common, with trifling modifications,
perhaps, to the entire kingdom.

9*

102 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

2. On the Original Components of the Animal Fabric.

111. Putting aside, for the present, the inorganic or mineral matters which
enter into the composition of the Animal body, and which are left in the form
of an ash, when the organic compounds are decomposed and dissipated by
heat, we shall confine our attention to the peculiar characters of the latter.
As already stated (§ 4), the organized tissues of Plants are found, when en-
tirely freed from the contents of their cells, to have a very uniform composi-
tion; being entirely made up of Carbon united with the elements of Water in
a very simple proportion, — that of 8 of the former to 7 of each of the latter;
and this simplicity in their chemical character partly accounts for their com-
parative durability. There are various compounds found in the cells of Plants,
and elaborated by them for the purpose of affording food to Animals, which
do not undergo organization, so long as they are contained in the Vegetable
fabric; but these very products, when transferred to the bodies of Animals,
form the components of their solid tissues. These substances are distinguished
by the presence of Azote or Nitrogen, in considerable amount; and also by the
large number of atoms of the four components, which are united in each of
them, — giving them a much more complex composition, and a much greater
tendency to decay, this being brought about by the disposition of the compo-
nents to enter into new compounds of a simpler and more permanent nature.
A considerable variety of such substances exists in the different parts of the
Human body ; but the nature and composition of these may be better studied,
when their structure and actions are being described; and at present we shall
confine ourselves to the fundamental or original components, of which all the
others may be regarded as modifications.

112. When we examine the Egg of an Oviparous animal, we find that,
putting aside the fatty matter of the yolk (which is destined, not to be con-
verted into tissue, but to be stored up in cells), the sole organic constituent is
that which is known to Chemists as Mbumen. By the wonderful processes
of chemical and vital transformation, which take place during the period of
incubation, and which are effected by the germ-cell and its descendants, this
Albumen is metamorphosed into nerve, muscle, tendon, ligament, membrane,
areolar tissue, horny substance, feathers, the organic basis of bone, &c. The
same metamorphosis is continually taking place in the adult animal; for every
substance of similar composition, that is employed as food, is reduced to the
form of Albumen in the digestive process; so that this becomes the essential
constituent of whatever fluid is absorbed for the nutrition of the tissues. It
is true that Gelatine, taken in as food, may be absorbed and carried into the
current of the circulation ; but there is little doubt, that it is incapable of
being applied to the reconstruction of any but the gelatinous tissues ; and in
these it exists in the very lowest form of organization, if organization it can
be called. Moreover, as it is clear, from what has been just stated, that the
gelatinous tissues may be formed at the expense of Albumen, we are justified
in regarding the latter substance as the common pabulum for all. Hence Albu-
men seems to hold very much the same position in the Animal economy, witli
Gum in the Vegetable.

113. The properties of Albumen may be studied in the White of Egg, or
in the Serum of Blood ; from both of which situations it may be obtained in
a pure state by very simple means. In the Animal Fluids it exists in a so-
luble state; and even when it has been dried (at a temperature of 126°), it
is readily dissolved again in water, forming a glairy, colourless, and nearly
tasteless fluid. In this condition it is always combined with a small quan-
tity of free soda; to the separation of which (whether by the agency of heat
or acids), its coagulation is thought by many Chemists to be due. On this

COMPONENTS OF THE ANIMAL FABRIC. ALBUMEN. 103

view, pure Albumen is not soluble in water; its solution being only accom-
plished by union with an alkali. — When dissolved in water, it coagulates
at 158° ; a very dilute solution, however, does not become turbid until it is
boiled. When the coagulation of Albumen takes place rapidly, a coherent
mass is formed, which shows no trace whatever of organization ; but, when
the process is more gradual, minute granules present themselves, which do
not, however, exhibit any tendency towards a higher form of structure. It is
thrown down from its solution, in a coagulated state, by Alcohol, Creosote,
and by most Acids (particularly nitric) with the exception of the acetic.
These precipitates are definite compounds of the Acids with the Albumen,
which here acts the part of a base. On the other hand, coagulated Albumen
dissolves in caustic Alkalies, and neutralizes them ; so that it must here act
as an acid. A solution of Albumen in water is precipitated by acetate of lead,
and by many other metallic solutions: and insoluble compounds are formed,
of which one — the albuminate of the chloride of mercury — is of much interest,
as being that which is produced by the mixture of a solution of albumen with
one of corrosive sublimate. Albumen, both in its soluble and insoluble state,
always contains a small amount of Sulphur, which blackens metallic silver ;
and also a minute quantity of Phosphorus. Soluble albumen dissolves Phos-
phate of Lime ; and about two per cent, of this salt may be separated from it
in its coagulated state.

114. So long as Albumen remains in the state regarded by Chemists as
characteristic of it, no tendency to become organized can be discerned in it ;
but subsequently to its introduction into the living Animal body, it undergoes
a transformation into a compound, termed Fibrine, which is distinguished from
it by new and peculiar properties. It appears from the analyses of Mulder
and Scherer, that there is no essential difference in the ultimate composition
of these two substances ; the relative proportions of the constituents of each
being, according to them, as follow: —

MULDER. SCHERER.

Albumen. Fibrine. Albumen. Fibrine.

Carbon .... 54-84 54-56 53-850 53-671

Hydrogen . . . 7-09 6'90 6-983 6-87S

Nitrogen . . . 15-83 15-72 15-673 15-763

Oxygen . . . 21-23 22-13 )

Phosphorus ... -33 -S3 S 23-494 23-688

Sulphur ... -68 -36 )

100-00 100-00 100-000 100-000

The wide difference in their properties must be referred, on this view, solely
to a change in the molecular arrangement of their ultimate particles. Accord-
ing to Dumas, however, there is a marked difference in composition, between
Fibrine and the various forms of Albumen; — the former having less Carbon,
and more Nitrogen, than the latter. The following are the results of his
analyses : —

ALBUMEX. FIBRINE.

From serum. From eggs.

Carbon .... 53-32 53'37 52-78

Hydrogen .... 7-29 7-10 6-96

Nitrogen .... 15-70 15-77 16-78
Oxygen ^

Sulphur . 23-69 23-76 23'48
Phosphorus . . ;

100-00 100-00 100-00

104 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

It is not, perhaps, of any great moment whether this difference has a real
existence or not; for the conversion of Albumen into Fibrine is unquestion-
ably a process much more of vital than of chemical transformation. We
shall presently see, that Fibrine may be regarded as Albumen, in which the
process of Organization has begun ; its molecules being ready to assume the
peculiar arrangement that is so designated : this arrangement takes place
most completely, when the fibrinous mass is in contact with a living tissue,
and is therefore to a certain degree under its influence. Fibrine, like Albu-
men, may exist in a sohible or in a coagulated state ; its soluble form only
occurs, however, in certain living animal fluids, — the Chyle, Lymph, and
Blood; — and it seems to be the intermediate condition between the soluble al-
bumen, and the solid organized substances which are formed from it. When
withdrawn from the blood-vessels, the Blood soon coagulates, as do also the
Chyle and Lymph, when they contain sufficient fibrine ; and this coagulation
is entirely due to a change in the condition of the Fibrine, the particles of
which have a tendency to aggregation in a definite manner. The Fibrine may
be obtained in a separate form, by stirring fresh-drawn blood with a stick, to
which it adheres in threads ; these contain some fatty matter, which is to be
washed out with alcohol. In this condition it possesses the softness and elas-
ticity which characterize the flesh of animals; and contains about three-fourths
of its weight of water. It may be deprived of this water in dry air, and then
becomes a hard and brittle substance ; but, like flesh, it imbibes water again
when moistened, and recovers its original softness and elasticity. When
burned, it always leaves, like albumen, a portion of phosphate of lime. Fi-
brine is insoluble in alcohol and ether, and also, under ordinary circumstances,
in water; but when long boiled in water, especially underpressure, its nature
is altered, and it becomes soluble. This change, which may be effected also
in coagulated Albumen, is attributed by Mulder to the oxidation of the Pro-
teine, which is its principal constituent (§ 116, «). When Fibrine is treated
with strong acetic acid, it imbibes the acid, and swells up into a transparent
colourless jelly, which is soluble in hot water; this solution is precipitated by
the addition of another acid.

115. Fibrine, like Albumen, unites with acids as a base, forming definite
compounds ; and with bases as an acid. Its correspondence with Albumen
is further indicated by the fact (first stated by M. Denis), that it may be en-
tirely dissolved in a solution of nitrate of potash; and that this solution is
coagulated by heat, and greatly resembles a solution of Albumen. This is
only true, however, of the ordinary Fibrine of venous blood; for that which
is obtained from arterial blood or from the buffy coat, or which has been ex-
posed for some time to the air, is not thus soluble. This is an important and
interesting circumstance. The difference appears to depend upon the larger
quantity of oxygen contained in the latter; for a solution of Venous Fibrine in
nitre, contained in a deep cylindrical jar, allows a precipitate in fine flocks to fall
gradually, provided the air have access to the surface, but not if it be prevented
from coming in contact with the fluid ; this precipitate is insoluble in the solution
of nitre, and possesses the properties of arterial fibrine. Hence it may be
inferred, that the Fibrine of Venous blood most nearly resembles Albumen ;
whilst that of Arterial blood, and of the Buffy coat, contains more oxygen,
and is more highly animalized. — When decomposition commences in a coagu-
lum of Fibrine withdrawn from the body (and even in the greatly-debilitated
living body, in which the Fibrine appears to be imperfectly formed), a granu-
lar mode of aggregation is evident in the particles of the mass, — thus showing
its affinity to Albumen, when its peculiar vital characters have departed, or
are possessed by it in an inferior degree.

116. The close chemical relation existing between Albumen and Fibrine

PROTEINE, AND ITS TRANSFORMATIONS. 105

is further shown by the fact, that from both of them (as well as from various
substances used as food, which are furnished by the Vegetable kingdom, § 111)
an identical substance may be obtained by a simple process. If boiled al-
bumen be dissolved in a weak solution of caustic alkali, and the liquid be
neutralized by an acid, a precipitate falls down in grayish-white flocks ; this,
being collected and washed, is gelatinous, of a grayish colour, and semi-trans-
parent; and, when dried, it is yellowish, hard, easily pulverized, tasteless, in-
soluble in water arid alcohol, and decomposed by heat without fusing. This
substance has been termed Proteine, from an idea that it is the fundamental
proximate principle of which Albumen, Fibrine, &c., are modifications. It
contains the same proportions of Carbon, Hydrogen, Nitrogen and Oxygen, with
Albumen and Fibrine ; but it has been commonly regarded as destitute of their
Sulphur and Phosphorus; the most recent investigations of Liebig, however,
render it doubtful whether this is the case. According to Mulder (its dis-
coverer), its composition may be represented by the formula 40 C, 31 H, 5 N,
12 O ; whilst by Liebig it is represented by the formula 48 C, 36 H, 6 N, 14 O.
Either of these correctly represents the relative proportions of the elements,
as deduced from analysis ; but the formula of Mulder is asserted by him to
represent more accurately the combining equivalent of the entire substance,
as deduced from the compounds it forms with others.

a. According to Mulder, Proteine unites with Oxygen in definite proportions, so as to form
a binoxide and a tritoxide. These are both produced when Fibrine is boiled in water for
some time; the latter being then found in solution, whilst the former remains insoluble.
The tritoxide may also be formed by boiling Albumen for some time in water, when it is in
like manner taken up in solution ; but the insoluble residue is still albumen. It is further
attainable by decomposing the chlorite of proteine with ammonia. In its properties it some-
what resembles Gelatine, and has been mistaken for that substance. There is reason to
think that this compound really exists as such in the blood; a small quantity of it being
formed every time that the blood passes through the lungs, and given out again when it
returns to the system ; and a much larger quantity being generated during the inflammatory
process, so that it may be easily obtained from the buffy coat by boiling. It is also said to
be contained in pus. The binoxide is quite insoluble in water, but dissolves in dilute acids.
It may be obtained by dissolving Hair in potash, adding a little acid to throw down the
proteine, and then adding a large excess of acid, which precipitates the binoxide. Accord-
ing to Mulder, this compound also is produced in small quantity at every respiration; and it
enters into the normal composition of several of the animal tissues. — These views, however,
must still be received with some hesitation. They are liable to the fundamental objection,
advanced against them by Liebig; that the binoxide and tritoxide, like proteine itself, contain
the sulphur of albumen and fibrine. Still, the production of new and peculiar compounds,
by the processes indicated, is an important fact which cannot be overthrown ; whatever
may prove to be the case in regard to the ultimate composition of these substances.

b. One of the most characteristic and important properties of Proteine, is the facility with
which it undergoes decomposition, when acted on by other chemical substances, especially
by alkalies. If a proteine-compound be brought into contact with an alkali, ammonia is im-
mediately disengaged ; indeed the alkaline solution can hardly be made weak enough to
prevent the disengagement of ammonia. This is a property, which must be continually
acting in the living body ; since the blood has a decidedly alkaline reaction. If either albu-
men, or any other proteine compound, be boiled with potash, it is completely decomposed;
not, however, being resolved at once into its ultimate constituents, or altogether into simple
combinations of them; but in great part into three other organic compounds, — Leucin, Protid,
and Erythroprotid. Leucin is a crystalline substance, which forms colourless scales, destitute
of taste and odour ; it is soluble in water and alcohol, and sublimes unchanged. It consists
of 12 Carbon, 12 Hydrogen, 1 Nitrogen, and 4 Oxygen. There is not at present any evi-
dence, that it is produced in the living body; but considerable interest attaches to it from the
fact, that it may be procured from Gelatine, as well as from Proteine ; a near relationship
between these two substances being thus indicated. The other two compounds, Protid and
Erythroprotid, are uncrystalline substances ; the former of a straw-yellow, the latter of a red-
dish-brown colour ; they belong to the class of bodies which were formerly included under
the vague general term of extractive matter; and they bear a strong resemblance to Gelatine,
not only in their solubility in water, but also in their chemical composition, as is shown by
the following comparison of their formulae : —

106 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

C. H. IT. O.

Protid 13 914

Erythroproticl ....... 13 15

Gelatine 13 10 2 5

Besides these substances and Ammonia, Formic and Carbonic Acids are produced by the
decomposition of Proteine with potash ; the acids unite with the potash, whilst the ammonia
is set free.

117. It is very important, however, to bear in mind, that however close
may be the chemical approximation between Albumen and Fibrine, there is a
wide difference between them, as regards their relations to living organized
structures : and this difference is one of which chemistry takes no cogni-
zance. To use a rather homely illustration, the relation between Albumen,
Fibrine, and Organized Tissue is somewhat of the same nature as that which
exists between the raw cotton, the spun yarn, and the woven fabric. Albu-
men shows no tendency to coagulate, except under the influence of purely
chemical agents, and its coagulum is entirely destitute of structure, being a
mere homogeneous aggregation of particles. On the other hand, Fibrine
exhibits a constant tendency to pass into the form of a solid tissue ; and it
seerns only restrained from doing so by certain influences, whose nature is
not understood, to which it is subjecte'd whilst contained in the vessels of the
living body. The conversion of Albumen into Fibrine, therefore, is the first
great step in the process of Nutrition, by which the materials supplied by the
food are made to form part of the living tissues of the body ; and it is the one
to which the term Assimilation may be most appropriately applied. As
already mentioned, Albumen is always the starting-point ; since the fibrinous
elements of organized tissues are reduced, by the solvent power of the gas-
tric fluid, to the same form with the unorganized coagulum of the albumen of
the egg. The first appearance of Fibrine is in the Chyle, or fluid of the
Lacteals ; and when this is examined in the neighbourhood of the part where
it has been absorbed, the traces of Fibrine which it presents are very slight.
As the Chyle flows along the lacteals, however, the proportion of Fibrine in-
creases ; and it reaches its maximum at the point where the Chyle is de-
livered into the current of the circulating Blood. The proportion of Fibrine
in the Blood, as indicated by the firmness of the coagulum which it forms, is
much greater than that contained in the Chyle, notwithstanding that there is
a constant withdrawal of this element for the purpose of nutrition. And in
certain disordered states of the system, in which the formative powers of the
Blood are so exalted, as to produce a tendency to the formation of tissue in
abnormal situations, the proportion of Fibrine is found to be increased to
twice, thrice, or even four times its usual amount. And even where there is
no such general increase, a local increase is made evident in the large pro-
portion of fibrine, which exists in the exudations poured forth for the repara-
tion of injuries; these exudations, when possessed of a high formative pro-
perty (that is, a readiness to produce an organized tissue), are said to be
composed of plastic, or coagulable lymph; but this is nothing more than the
Liquor Sanguinis, or fluid portion of the Blood, holding in solution an unu-
sual quantity of Fibrine. It is evident, from these facts, that some peculiar
agency must exist within the vessels, by which the elaboration of the Fibrine
from the Albumen is effected ; and we shall hereafter endeavour to bring
together certain facts, which seem to indicate its nature.

J18. The tissue that is produced by the apposition of the particles of
Fibrine, when left to themselves, and solely influenced by their own mutual
attraction, is of a very simple character, being composed of fibres interlaced
with each other in various directions. This arrangement can be seen in the
ordinary Crassamentum, or clot of healthy Blood, by examining thin slices

FIBRILLATION OF COAGULATED FIBRINE.

107

Fis. 10.

under the microscope ; especially after the clot has been hardened by boiling.
A number of fibres, more or less distinct, may be seen to cross one another;
forming by their interlacement a tolerably regular network, in the meshes of
which the red corpuscles are entangled. This fact was known to Haller ;
but it has been generally overlooked by subsequent Physiologists, until atten-
tion was drawn to it by the inquiries of Messrs. Addison, Gulliver, and
others. It is in the Bufly Coat, however, that the fibrous arrangement is best
seen; on account, "as it would appear, of the stronger attraction which the
particles of fibrine have for one another, when its vitality has been raised by
the increased elaboration to which it has been subjected. That there are va-
rieties of plasticity in the substance, which, on account of its power of spon-
taneously coagulating, we must still call fibrine, appears from this fact among
others, — that, in tuberculous subjects,
the quantity of fibrine in the blood is
higher than usual (Andral and Gavarret),
although its plasticity is certainly below
par. It is as easy to understand, that
its plasticity may be increased, as that it
may be diminished ; and this either in
the general mass of the blood, or in a
local deposit. In fact, the adhesions
which are formed by the consolidation
of coagulable lymph, — or in other words,
of the fluid portion of the blood, whose
plasticity has been heightened by the
vital actions that take place within the
capillaries of the part on which it has

-r Fibrous structure of inflammatory exudation

been effused, — often acquire very eon- from peritoneum.
siderable firmness, before any vessels

have penetrated them ; and this firmness must depend upon that mutual
attraction of the particles for one another, which in aplastic deposits is alto-
gether wanting, and which in cacoplastic deposits is deficient. — A very inte-
resting example of a structure entirely composed of matted fibres, and evi-
dently originating in the simple consolidation of Fibrine, is found in the
membrane adherent to the interior of the Egg-shell (Membrana putaminis) ;
and also in that which forms the basis of the Egg-
shell itself. Between the two, there is no essen-
tial difference ; as may be seen by examining " an
egg without shell," as it is commonly termed, (or
rather one in which the shell-membrane has been
unconsolidated by the deposition of calcareous
matter) ; or by treating the egg-shell with dilute
acid, so as to remove the particles of carbonate of
lime, which are deposited in the interstices of the
network. The place of the shell is then found to
be occupied by a membrane of considerable firm-
ness, closely resembling that which lines the shell
and surrounds the albumen of the egg, but thicker
and more spongy. After maceration for a few

-]„,,.„ -,i r L Fibrous membrane from the

days, either of these membranes may be separated Egg-shell.
into a number of lamina, each of which (if suffi-
ciently thin) will show a beautiful arrangement of reticulated fibres. It is
impossible to refuse to such a structure the designation of an organized tis-
sue, although it contains no vessels, and must be formed by the simple con-
solidation of Fibrine, poured out from the lining membrane of the oviduct of

Fig. 11.

108 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

the bird. It is probably in the same manner, that the Chorion of the Mam-
miferous animal originates ; since this is a new envelope, formed around the
ovum, during its passage along the Fallopian tube. In the latter, for an ulte-
rior purpose, vessels are afterwards developed, by extension from the con-
tained ovum; and by the nutrition they supply, its size is increased, and
changes take place in its texture. But in the Egg-membrane of the Bird,
there is no need of vessels ; because no subsequent change in its texture is
required, and its duration is sufficient for the purpose it has to answer.

119. The completeness of the transformation of Fibrine into simple Fi-
brous Tissue, appears to depend upon two circumstances in particular ; — the
perfect elaboration of the Fibrine itself; and the vitality of the surface upon
which the concretion takes place. When the Fibrine is highly elaborated, it
will coagulate in the form of a definite network of minute fibrillae, even upon
a dead surface, as a slip of glass ; this is the case, for instance, with the Fi-
brine of the bufTy coat of the Blood, or with that of the Liquor Sanguinis
(coagulable lymph) poured out for the reparation of an injured part. But in
the ordinary Fibrine of the blood, the fibrillation is less distinct when the con-
cretion takes place upon a dead surface. When it occurs in contact with a
living surface, however, the coagulation takes place more gradually ; and it
seems as if the particles, having more time to arrange themselves, become ag-
gregated into more definite forms, so that a more regular tissue is produced —
just as crystals are most perfectly formed when the crystalline action takes
place slowly. It was formerly imagined that the Muscular tissue is the only
one produced at the expense of the Fibrine of the blood ; the other tissues
being formed from its Albumen. This, however, is unquestionably erroneous.
There is no proof whatever that Albumen, as long as it remains in that con-
dition, ever becomes organized ; whilst, on the other hand, there is abundant
evidence, that the plasticity of any fluid deposit — that is, its capability of be-
ing metamorphosed into organized tissue — is in direct relation with the quan-
tity of Fibrine which it contains. Thus the Liquor Sanguinis, or Coagulable
Lymph, thrown out for the reparation of injuries, contains a large amount of
Fibrine ; and this substance is converted, not at first into muscular fibre, but
(whatever may be the tissue to be ultimately produced in its place) into a
fibrous network, which fills up the breach and holds together the surrounding
structure. This may be regarded as a simple form of areolar tissue ; Avhich
gradually becomes more perfectly organized by the extension of vessels and
nerves into its substance ; and in which other forms of tissue may subse-
quently make their appearance. This process will be more particularly de-
scribed hereafter ; it is at present noticed here as an illustration of the general
fact, that Jib rine is to be regarded as the plastic element of the nutritive fluids.

3. Of the Elementary Parts of Organized Tissues; — Cells, Membrane,

and Fibre.

120. The cells, which have been spoken of as making up the chief part of
the Vegetable Organism, are minute closed sacs; whose walls are composed
in the first instance of a delicate membrane, frequently strengthened, at a
period long subsequent to their first formation, by some internal deposit. The
form of these cells is extremly variable ; and depends chiefly upon the degree
and direction of the pressure, to which they may have been subjected at the
period of their origin, and subsequently to it. Sometimes they are spheroidal ;
sometimes cubical or prismatic ; sometimes cylindrical ; and sometimes very
much prolonged. These cells may undergo various transformations. — One of
the most common, is the conversion of several into a continuous tube or Duct.
This is principally seen in the vessels, through which the sap ascends the stem ;

DEVELOPMENT AND METAMORPHOSES OF CELLS. 109

these appear to have been formed by the breaking-down of the transverse
partitions, between a regular series of cylindrical cells laid end to end ; and
the remains of such partitions may frequently be seen in them. The ducts
which convey the ascending sap, do not inosculate with each other ; their
purpose being merely to carry it direct to the leaves ; but the vessels, through
which the descending or elaborated sap flows, are of very different character;
for their purpose is to distribute the nutritious fluid through the tissues ;
and they anastomose very freely, just as do the capillaries of Animals. The
network which they form, however, can be as clearly traced to an origin in cells,
whose cavities were originally distinct, as can the bundles of straight non-
communicating ducts. — Another important transformation of the original cells,
is that by which the Woody Fibres, which compose nearly all the fibrous
textures of Vegetables, are produced. These fibres are still cells, but their form is
very much elongated ; they have a fusiform or spindle shape, being tubes drawn
to a point at each end ; at first they are quite pervious, like ordinary cells ;
but in the older wood, their cavity is filled up by interior deposit.

121. Such deposits may take place in cells of the ordinary form ; and they
present many variations in their character, which give corresponding peculi-
arities to the cells which contain them. In many instances, they consist merely of
concentric layers, one within the other, each layer completely lining the one
which preceded it; and the cavity of the cells being thus gradually but uni-
formly contracted in every dimension. In other cases, certain points of the
original external cell-membrane are left uncovered by the secondary deposits ;
and thus, the same vacuities being left in the successive layers, passages are
formed, which stretch out from the central cavity to certain spots of the peri-
phery of the cell. Cells of this character are found in certain parts of plants,
which are required to possess unusual firmness, without losing the power of
transmitting fluid, the former endowment being conferred by the secondary
deposits; whilst the latter is retained by the peculiar system of passages just
described, — the thin or uncovered parts of the wall of one cell being in contact
with corresponding spots on the walls of adjacent cells, as we see in the tissue
of the stones of fruit, the central gritty matter of the pear, &c. — Lastly, the
new deposit may present the form of a more or less regular spiral fibre, winding
within the cell from end to end ; and this may present itself alike in cells of
the ordinary shapes, or in fusiform cells (constituting the proper spiral ves-
sels], or in cells that have coalesced into continuous tubes or ducts. The
spiral may break up into rings or irregular pieces ; and these may be united
again by additional deposits of a still more irregular character, so as completely
to obscure theiroriginal spiral form. This spiral fibre is very completely gene-
rated, in some instances, when the cell-wall itself has not acquired any greater
tenacity than that of mucus, very easily dissolved ; which (as we shall presently
see) is a stage in the production of cells in general. Such spiral fibres spring
out from the external coats of many seeds, when they are moistened with
fluids.

122. So far as is yet known, all Cells originate in germs, that have been pre-
pared by some previously-existing cell ; and these germs may either be de-
veloped within the parent-cell, or may be set free by its rupture, and may be
developed quite independently. The latter case, being the simplest, will be
first considered ; we have numerous examples of it among the lower Cellular
Plants. In the first place, the germ, from which the cell originates, is a mi-
nute granule, only to be seen with a good microscope, and apparently quite
homogeneous. It has the power of drawing to itself the nutrient elements
around, and of combining these into the proximate principles, that may serve
as the materials for its development. By the incorporation of these with its
own substance, it gradually increases in size, and a distinction becomes ap-

10

110

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Fis;. 12.

Simple isolated cells con-
taining productive mole-
cules.

parent, between its transparent exterior and its coloured interior. Thus we
have the first indications of the cell-wall, and the cavity. As the enlarge-
ment proceeds, the distinction becomes more obvious ; the cell-wall is seen to
be of extreme tenuity, perfectly transparent, and apparently homogeneous in
its texture ; whilst the contents of the cavity are distinguished by their colour,
which (in the species here alluded to) is commonly either green or bright red.
At first they, too, seem to be homogeneous ; but a finely-granular appearance
is then preceptible amongst them ; and a change gradually takes place, which

seems to consist in the aggregation of the minuter
molecules into granules of more distinguishable size and
form. These granules, which are the germs of new
cells, seem to be at first attached to the inner wall of the
parent-cell ; afterwards they separate from it, and move
about in its cavity ; and at a later period, the parent-
cell bursts and sets them free. Now this is the ter-
mination of the life of the parent-cell ; but the com-
mencement of the life of a new generation : since every
one of these germs may develope itself into a cell, after
precisely the foregoing manner ; and will then, in turn,
propagate its kind by a similar process.

123. The development of new cells within the pa-
rent, — or what may be termed the endogenous mode

of cell-growth, — takes place in many instances on a plan which differs in no
respect from the preceding, except that the parent-cell does not rupture. The
granules it contains derive their nutriment from the surrounding fluid, which
is included within the cell ; by their progressive increase in size, they gradu-
ally fill up the whole cavity of the parent-cell ; and by a further increase, they
distend its wall, which becomes thinner and thinner, and at last ceases to be
visible around the newly-formed cluster.

124. In other instances, however, we find that the development of new
cells proceeds, not from granules scattered through the whole
interior of the cell, but from a determinate spot or nucleus,
which is seen upon its wall. This nucleus is frequently formed
very early, by the aggregation of molecules around the original
granule or cell-germ, even previously to the first appearance of
the distinct cell-membrane ; and by Schleiden, who first ob-
served this process, it was thought that the body thus produced
was essential to the development of the new cell, whence he
gave it the name of cytoblast. It appears, however, from more
extended inquiries, that this is not the case ; and that the nu-
cleus is rather concerned with the subsequent operations which
the cell performs, than with its original development. Fre-
quently the nucleus does not make its appearance, until the cell
itself has been completely formed. It is chiefly in the higher
tribes of Plants, that we find these nucleated cells; the nucleus
in the cells of the lower Cryptogamia being usually more or
less expanded or diffused (as it were), through the entire cavity.
The destination of the several forms of cells which make up
the complex structure of the higher plants, is very different;
and their office seems in great measure to depend upon the
peculiar powers of the nucleus. In some instances, this body
seems to be the centre which attracts new deposits ; even the
spiral filament being probably formed by its agency. We
»io, showing spiral have, in some of the lowest Cellular Plants, a curious fore-sha-
arriingementoftiic jowing Of ^ie Spirai vessels of the most perfect ; the green
nuclear particles.

Fis. 13.

* : <
•

Cells of

DEVELOPMENT AND MULTIPLICATION OF CELLS.

Ill

Fig. 14.

particles (or diffused nucleus ?) of the cells, in the genus Zygnema, presenting
a regular spiral arrangement at one period of their growth (Fig. 13). And
in other instances, as in the cells of the petal of
the common Geranium (Pelargonium), we find
the nucleus sending out curious stellate or radi-
ating prolongations (Fig. 14.) These facts are
of much interest, as illustrating some of the more
obscure changes which are believed to take place
in animal tissues.

125. But the nucleus may also be the source
from which the new cells arise, that are devel-
oped within the cavity of the parent. Several vari-
eties in the mode in which this process takes place,
are presented to our observation in the simplest of
the Cellular Plants, belonging to the group of the
Fresh-water Algae ; the growth of which may be
studied with peculiar facility. In some of these
the cell is destitute of a nucleus, but is filled with

a very finely-divided granular matter, the en- Cells from the petal

. J •> ,, ,, ' ,. showing stellate prolongations 01 the

dochrome; and the process oi cell-multiplication nuciei
is effected by the subdivision of this matter into •

two distinct masses, around each of which a pellucid cell-membrane subse-
quently makes its appearance, thus forming two new cells within the parent.
By a repetition of the same process, each of these new cells may again pro-
duce two new ones ; and thus the multiplication may be rapidly effected.

Fiz. 16.

Hematococcus binalis, in various stages of devel.
opment; a, a, simple rounded cells; b, elongated
cell, the endochrome preparing to divide ; c, c, cells
in which the division has taken place ; d, large pa-
rent cell, in which the process has been repeated
a second time, so as to form a cluster of four se-
condary cells, such as is often seen in Cartilage.

Coceochloris cystifera, showing various stages of
development: — a, simple globular cells, surround-
ed by a well-defined mucous envelope ; b, elon-
gated cell about to divide; c, cell doubled by (di-
vision, both the new cells still enclosed in original
mucous envelope ; rf, further stage of the same
process, one of the secondary cells having agai:i
divided, whilst the other has not yet undergone
this change, but is about to do so ; e, group of
cells formed by the same process, and still re-
tained within the original mucous envelope.

This form of cell-development is best seen in some of the simplest Alga\
which consist of isolated cells, and in which the individuals composing the
successive generations are quite independent of one another ; and we have a
good illustration of it in the Hematococcus binalis, whose various stages ol
cell-multiplication are shown in Fig. 15. In many other instances, the cells
of successive generations, without losing their individuality, are held together

112

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

by a consistent mucous envelope ; so that we may find two, three, four, or a
larger number, clustered together within a well-defined investment, which has
tenacity enough to prevent them from separating. Of this we have a good
example in Coccochloris cyslifera (Fig. 16) ; and a yet more remarkable one
in Hematococcus sanguineus (Fig. 17). The cells forming such masses of
vegetation may be likened to those of Cartilage, which are similarly enveloped
by an intercellular substance, and which present the same binary method of
multiplication (§ 129). In the Confervas we find the cells, which are succes-
sively produced in this manner, remaining in connection with each other, so
as to form articulated filaments. The terminal cell of each filament is con-
tinually undergoing subdivision in the manner just described, and thus the
filament is elongated ; whilst other cells produce regular reproductive granules,
which are set free by an opening that forms in the cell-wall, and which devel-
ope themselves into new individuals without any further aid from the parent
structure, in the manner already described. The difference between these
two modes of propagation seems to have reference to the age and degree of
development of the cell ; the binary division being characteristic of cells which
are in a growing state, and being destined to extend the original structure ;
whilst the formation and emission of a number of reproductive granules is the
function of the mature cell, and is destined to give origin to new individuals.
These processes are* analogous in the higher plants, the first to the develop-
ment of leaf-buds, the second to the production of seeds. In the Nostoc we
find the moniliform filaments, which are composed of a linear series of cells,
invested by dense gelatinous sheaths of definite extent, looking almost like

Fig. 17.

Hemntorcicc-i/s sanguineits in various stages of development , — a, a single cell, enclosed in its mucous
envelope ; b, c, clusters formed by division of parent-cell ; il, more numerous cluster, ils component cells
in various stages of division ; e, large mass of young cells, formed by continuance of the same process,
and enclosed within common gelatinous envelope.

large parent-cells (Fig. 18, n) ; and the extension of the filaments may so dis-
tend their sheaths as to give them the appearance of capacious globular cells
(Fig. 18, A). There is reason to believe that the long convoluted filaments
then separate into a cluster of shorter ones, each having its own share of the
mucous envelope.

126. The history of the Animal cell, in its simplest form, is precisely that
of the Vegetable cell of the lowest kind. It lives for itself and by itself, and

DEVELOPMENT AND MULTIPLICATION OF CELLS.

113

Fig. 18.

A.

is dependent upon nothing but a due supply of nutriment and a proper tem-
perature for the continuance of its growth, and for the due performance of its
functions, until its term of life is expired. It originates from a reproductive
granule, previously formed by some other cell ; this granule attracts to itself,
assimilates, and organizes, the particles of the nutrient fluid in its neighbour-
hood ; and converts some of them into the substance of the cell-wall, whilst
it draws others into the cavity of the cell. In this manner the cell gradually
increases in size ; and whilst it is
itself approaching the term of its
life, it usually makes preparation
for its renewal, by the develop-
ment of reproductive granules in
its interior ; which may become
the germs of new cells, when set
free from the cavity of the parent,
by the rupture of its cell-wall. —
There is an important difference,
however, in the endowments of
the Animal and Vegetable cell.
The latter can in general obtain
its nutriment, and the materials for
its secretion, by itself combining
inorganic elements into organic
compounds. The former, how-
ever, is totally destitute of this
power ; it can produce no organic
compound, and we have yet to
learn how far its power of con-
verting one compound into an-
other may extend ; its chief en-
dowment seems to be that of at-
tracting or drawing to itself some
of the various substances, which
are contained in the nutritive fluid
in relation with it. This fluid, as
we shall hereafter see, is a mixture
of a great number of components ;
and different sets of cells appear
destined severally to appropriate
these, just as the different cells of
a parti-coloured flower have the
power of drawing to themselves
the element of their several colour-
ing matters. As far as it is yet
known, however, the composition

B.

Nostocmacrosporum:— A, a long convoluted filament,
composed of linear series of minute cells, enclosed in
general mucous envelope ; B, group of shorter fila-

of the cell-wall is everywhere the mentS) each with ils own gelatinous envelope; pro.

Same, being that Of Proteme. It bably formed by the division of the preceding.

is in the nature of the contents of

the cell (as among the cells of Plants), that the greatest diversity exists ; and
we shall find that the purposes of the different groups of cells, in the general
economy of the Animal, depend upon the nature of the products they secrete,
and upon the length of time during which these products are retained by them.
127. Of the general account just given, the development of certain cells,
which float in the Chyle, Lymph, and Blood, may be adduced as an exam-
ple ; these, which are known as the Chyle and Lymph corpuscles, and as the

10*

114

ON THE ELEMENTARY PARTS OF THE HUMAN FABlilC.

Colourless corpuscles of the Blood, have no single nucleus, but contain seve-
ral scattered particles, each of which seems to be a reproductive granule ; and
they emit these by the bursting or liquefaction of their wall, — a change which
may be effected in them at any time, by the application of chemical reagents.
The granules thus set free appear to float in the current of fluid, and to be in
their turn developed into cells at the expense of the materials it affords. The
exudations of the plastic or organizable matter of the blood, which are thrown
out upon inflamed or wounded surfaces, appear to contain some of these gra-
nules ; for similar cells are speedily developed in these exudations, giving rise,
in their turn, to new generations, when their own term of life is ended.

128. In general, however, we find the cells of Animal tissues furnished with
a nucleus ; and this may be formed, as in Plants, either at an early stage of
the development of the cell, by the aggregation of minute molecules around
the original granular germ (which germ seems to be the nucleolus of some
authors) ; or after the cell has attained its full size. The nucleus, where it
exists, appears to be the chief instrument in the functions of the cell; the
cell-membrane probably having little else, than the mechanical office of
bounding or limiting the contents of the cell. In some cells the function is
restricted to the attraction of certain constituents, by which the cavity of the
cell is filled. These constituents may be of a nature to give solidity and
permanence to the texture; thus, the cells of the Epidermis are strengthened
by a deposit of horny matter, those of Shell by the deposit of carbonate of
lime; those of Bones and Teeth by a mixture of mineral and earthy matter,
&c. Or they may be of a fluid nature, readily passing into decomposition,
and destined to be retained only for a short time; being given up again by
the rupture or liquefaction of the cell-wall, as in the case with the cells of
Glandular structures in general. Now such cells do not usually reproduce
themselves, but successive crops of them are generated as fast as required
from other sources; and the function of their nuclei appears to be limited to
their chemical agency upon the materials which they select. It would seem,

in fact, as if the direction of thenisus
or power of the cell to this object,
prevented the exercise of its repro-
ductive powers ; and where we find
these last most strongly manifested,
it is usually observable that the cell
performs little or no other duty.

129. In the endogenous develop-
ment of Animal cells, the nucleus
seems always to perform an important
part, where it has a distinct existence.
In many cases, the multiplication can
be clearly perceived to take place, by
the division of the nucleus into two
or more portions ; each part giving
origin to a new cell. This seems to
be the case, for example, in the ordi-
nary production of Cartilage-cells; for
on examining sections of cartilage that
is undergoing rapid extension, we find
groups of cells, in all respects corre-
sponding with those of the simple
cellular plants, which can be seen to
increase in the same way. Thus in
Fig. 19, which represents a section of one of the branchial cartilages of the

Fig. 19.

Section of branchial Cartilage of young Tadpole ;
o, b, c, intercellular substance ; rl, single nucleus; e,
nucleus dividing into two ; //', e't two nuclei in one
cell, formed by division of single nucleus;/", second-
ary cell, forming around nucleus g-/ h, two nuclei
within single secondary cell ; i, three secondary
cells, within one primary cell.

DEVELOPMENT AND METAMORPHOSES OF CELLS.

115

Fig. 20.

Tadpole, we observe, within the large parent-cells that are held toge.ther by
intercellular substance, a, b, c, secondary cells in various stages of develop-
ment: at </, the nucleus is single ; at e it is dividing into two ; in the adjoining
cell, the division into two nuclei, d' and e', is complete ; at h, two such nuclei
are inclosed within a common cell-membrane; at i, we see three new cells
(one of them elongated, and itself probably about to subdivide) within the
parent ; and in each of the two groups at the top and bottom of the figure,
we have four small cells, now separated by partitions of intercellular sub-
stance, but having manifestly originated from one parent cell. (See also Fig.
43.)

130. In other cases, the granular nucleus subdivides into a greater number
of parts, so as to give origin to a cluster of young cells, which may completely
fill the parent-cell; various stages of

this process are seen in Fig. 20.
This process seems to be adopted,
where rapid multiplication is need-
ed, and where the new or secondary
cells are not destined to possess any
great duration. The same nuclei
or "germinal centres," continually
drawing new materials from the
blood, may thus develope many suc-
cessive crops of new cells, when an
opening in the wall of the parent-
cell permits them to be discharged
as fast as they are formed ; and this
we shall find to be the way in which
the cells of the secreting structures
are developed within the glandular
follicles. According to Dr. Barry, it
is not uncommon for several annuli
of young cells to be generated from
the periphery of the nucleus, and to
attain a certain degree of develop-
ment within the parent cell, the first-
formed being the largest, as shown
in Plate I., Fig. 10, a, b ; some of
these, moreover, having distinct nu-
clei of their own, from which a third
generation is being developed on the
same plan (Fig. 12, b); and yet for all these to disappear by liquefaction,
leaving the cavity of the parent-cell unoccupied, except by a pair of cells ori-
ginating in the central part of the nucleus (Fig. 13). If this account be cor-
rect, it is probable that these temporary cells perform the office of preparing
the contents of the parent-cell for the nutrition of the offspring which is to
succeed it ; and each of these twin cells, in its turn, going through the same
series of changes (Fig. 14), gives origin to a new pair; the continuance of
which process generates a cluster. This is the mode, according to Dr. Barry,
in which the first cells of the embryo are developed into the "mulberry mass"
(Fig. 15), by whose subsequent development and metamorphoses, the tissues
and organs of the foetus are progressively evolved.

131. Notwithstanding the numerous varieties that exist, in the particular
modes in which the cells are developed, it seems to be well established as a
simple general principle, that all cells take their origin in germs prepared by
a previously-existing cell ; and that these germs may be developed, either

Endogenous cell-growth in cells of a meliceritous
tumour; a, cells presenting nuclei in various stages
of development into a new generation; fc, parent-
cell filled with a new generation of young cells,
which have originated from the granules of the nu-
cleus.

116 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

within the parent-cell, or when set free by its rupture. The difference ob-
servable in the several cases that have been enumerated, and in others that
might be mentioned, seems to have reference chiefly to the degree of prepara-
tion that is effected in the nutriment with which the young cells are supplied ;
— some drawing it directly from the blood ; whilst others receive it through
the medium of the parent-cell, which probably exerts a certain degree of pre-
paring influence upon it ; — and others, again, requiring a further preparation
to be effected, by the elaborating or assimilating influence of a group of tem-
porary cells, expressly developed for this purpose.

132. We shall find, as we proceed, that all the tissues most actively con-
cerned in the maintenance of the Vital functions of the Human body, — both
those of a Vegetative nature, and those which are peculiarly Animal, are
composed of Cells which have undergone no considerable metamorphosis,
and of which one generation is produced after another with a rapidity that is
proportioned to the activity of the function. But there are other structures
of an accessory character, in which a departure from the original type is to
be traced, sometimes so complete, as to prevent their real nature from being
understood, except by a very careful scrutiny into their history. This depart-
ure is the result of various kinds of metamorphosis of the cells and of their
nuclei ; of which the following are the principal. The cells, originally sphe-
roidal, oval, or polygonal, may become elongated to such a degree, as to as-
sume the spindle or fusiform shape ; thus resembling woody fibres. They
may at the same time lose their nuclei ; and their cavities may be occupied
by internal deposits, so that they may be mistaken for solid fibres. Such
fusiform cells are often found in exudation-membranes. — Again, the cells may
shoot out prolongations, either in a radiating manner, so that they assume a
stellate form ; or in no definite direction, so that their shape becomes altogether
irregular. Such forms are seen amongst the pigment-cells of the Batrachia
and Fishes, and among the vesicles of the gray matter of the nervous system.
Further, the original boundaries of the cells may be altogether lost, by their
coalescence with each other. This is the case with many membranes that
seem to have originated in a layer of flat cells ; the situation of which is rather
to be traced by their nuclei, than by their former boundaries, which have alto-
gether disappeared. It is often the case, too, with the horny cells, of which
the nails, hoof, &c., are made up ; and still more with the cells of shell, bone,
tooth, &c., which have been consolidated by the deposition of a calcifying
deposit. — Lastly, the character of the original cell may be completely altered
by a solution in the continuity of its wall, in one or more spots, so that its
cavity is laid open, and coalesces with some other. In this manner, by the
disappearance of the partitions between cells laid in apposition, end to
end, may be formed a tube ; and this tube may coalesce with others, in like
manner, so as to form a capillary network for the circulation of the blood.
Or the tube may form a simple straight fibre ; and the nuclei of its component
cells may give origin to a new deposit, either in an amorphous condition, as
in the fibrous portion of nervous tissue, or in the form of an aggregation of
new cells, as in the most perfect kind of muscular fibre. In these cases, also,
the original composition of the tubes may be frequently traced by the nuclei
that remain in their interior. In the follicles of glands, the solution of con-
tinuity takes place at one point only, which establishes a communication be-
tween the cavity of the parent-cell, and some canal by which its contents may
be discharged ; and the nucleus situated at the blind or closed extremity of the
follicle, may then continue to form successive generations of secondary cells,
which are discharged by this outlet.

133. The metamorphoses of the nucleus are not less important, though
not as numerous. In some instances we find it sending out radiating prolonga-

FIBROUS TISSUES. BASEMENT MEMBRANE. 117

lions, so that it assumes a stellate form, like that of the cells of the Geranium-
petal ; this seems to be the case in regard to the nuclei of the Bone-cells. —
In other instances it appears to resolve itself into a fasciculus of fibres ; and
this is stated by Henle to be the origin of the yellow fibrous tissue. — Further,
it may separate into a number of distinct fibres, each composed (like those of
the Nostoc, Fig. 18,) of a linear aggregation of granules; it seems to be in
this manner, that the tubuli of the Dental structure are formed. — Lastly, it
may disperse itself still more completely into its component granules ; by the
reunion of which, certain peculiar vibrating filaments (the so-called Sperma-
tozoa) may be formed, possessing motor powers analogous to those of the
Oscillatoriae and other corresponding filamentous products of humble Crvpto-
gamic vegetation, but destined to perform most important offices in the func-
tion of Reproduction.

134. We have seen that, in the Vegetable structure, the component cells,
tubes, woody fibres (or elongated cells), &c., are held together by simple ad-
hesion ; a gummy intercellular substance, which answers the purpose of a
cement, being often interposed, sometimes in considerable quantity. But in
the Animal body, of which the several parts are destined to move with greater
or less freedom upon one another, the aggregations of cells that make up its
chief part, either in their original or in their metamorphic form, could not be
held together in their constantly-varying relative positions, without some in-
tervening substance of an altogether different character. It must be capable
of resisting tension with considerable firmness and elasticity ; it must admit
free movement of the several parts upon one another ; and it must still hold
them sufficiently close together to resist any injurious strain upon the deli-
cate vessels, nerves, &c., which pass from one to another, as well as to pre-
vent any permanent displacement. Now all these offices are performed in a
remarkably complete degree, by the Jlreolar Tissue (§ 138); the reason of
whose restriction to the Animal kingdom is thus evident. And as necessity
arises, in certain parts, for tissues which shall exercise a still greater power
of resistance to tension, and which shall thus communicate motion (as in the
case of Tendons), or shall bind together organs that require to be united (as
in the case of Ligaments and Fibrous Membranes), so do we find peculiar
tissues developed that shall serve these purposes in the most effectual manner.
Hence these tissues also, although not endowed with any properties that are
peculiarly animal, are nevertheless restricted to the Animal Kingdom, — as
completely as are the Muscular and Nervous Tissues, which make up the
essential parts of the apparatus of Animal Life.

135. That all the Animal tissues are in the first instance developed from
Cells, was the doctrine put forth by Schwann, who first attempted to gene-
ralize on this subject. By subsequent research, however, it has been shown
that this statement was too hasty; and that, although many tissues retain their
origin cellular type, through the whole of life, and many more are evidently
generated from Cells and are subsequently metamorphosed, there are some,
in which no other cell-agency can be traced, than that concerned in the pre-
paration of the plastic material. — This would appear to be the case, in certain
forms of the very delicate structureless lamella of membrane, now known
under the name of Basement or Primary Membrane, which is found beneath
the Epidermis or Epithelium, on all the free surfaces of the body. In many
specimens of this membrane, no vestige of cell-structure can be seen ; and it
would rather appear to resemble that, of which the walls of the cells are them-
selves constituted.* In some instances, it presents a somewhat granular ap-

* See a Paper by the Author, on the Microscopic Structure of Shells, &c., in the Annals
of Natural History, Dec. 1843. The inner layer of the Shells of Mollusca, after treatment

118

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

pearance ; and it is then supposed by Henle to consist of the coalesced nuclei
of cells, whose development has been arrested : or, in other words, such
Basement-Membrane is formed by the consolidation of a layer of the plastic
element, that includes a large number of the granules, which may serve for
the development of new cells. Other forms of the Basement-Membrane can
be distinctly seen to consist of flattened polygonal cells, closely adherent by
their edges ; every one having its own granular nucleus.* — It seems to be from
these granular germs, sometimes scattered through the membrane, and in other
instances collected into certain spots, that the cells of the superjacent Epithe-
lium or Epidermis take their origin ; and if this be the case, we must regard
the Basement-Membrane as a transitional rather than as a permanent struc-
ture,— continually disintegrating, and yielding up its contained cell-germs on
its free surface, and as constantly being renewed from the blood beneath.
For the epidermic structures appear to constitute an exception to the general
rule, that the Tissues reproduce themselves ; since they are cast off, without
leaving their germs behind them ; and the cells which replace them must be
derived from new germs, more directly supplied from the blood than is else-
where the case. In the case of the other tissues, whose disintegration takes
place inter stitially (so to speak), it would seem probable that, in the very
act of the dissolution of the parent-structure, the germs of the new structures
destined to replace it are set free ; as happens in the reproduction of the sim-
ple Cellular Plants.

136. It would seem doubtful, also, in regard to the simple Fibrous tissues,
whether they are generated by a metamorphosis of Cells, in the same manner
as the Osseous, Muscular and Nervous ; or whether they are not produced,
like the Basement-Membrane, by the consolidation of a plastic fluid, which
has been elaborated by cells. The latter view is the one which the Author
has been led to regard as most probable, from the results of his own observa-
tions, coupled with those of Messrs. Addison and Gulliver previously adverted
to. The Membrane of the Egg-shell, whose structure has been already
described (§ 118), appears to him to have essentially the same character with
the simple Fibrous tissues, which it resembles also in its tenacity (compare
Fig. 11 with Fig. 22) ; whilst its origin can scarcely be supposed to be different
from that of the fibrous network in the buffy coat of the Blood, or in the

bands formed by the coagulation of Lymph upon an
inflamed surface. The occasional vestiges of cells,
which the purely Fibrous tissues display (§ 138),
and which have been adduced in support of their
cellular origin, are not inconsistent with this view.
For in the reticulated structures just adverted to,
certain bodies are seen, which appear to be nuclei
or imperfectly-formed cells (originating probably in
germs set free by the rupture of the colourless cor-
puscles of the blood), and which closely correspond
with the nuclear corpuscles that may be brought
into view in the Fibrous tissue. Mr. Addison's
observation, too, — that the fibres formed in the
Liquor Sanguinis, and in plastic exudations, during
coagulation, often seem to radiate from the remains
of the white corpuscles that have ruptured, or from
the little aggregations of granules they contained, —
gives the explanation of several of the appearances, which have led to the

with a dilute acid, yields specimens of Basement-Membrane, in a form well adapted for
examination.

* See J. Goodsir, in " Anatomical and Pathological Observations," Chap. I.

Fig. 21.

Colourless cells, with ac-
tive molecules, and fibres, of
fibrine, from Herpes labialis.

CLASSIFICATION OF HUMAN ELEMENTARY TISSUES. 119

belief in the production of the Areolar and other fibrous tissues by Cell-trans-
formation.— An additional argument in favour of this view, may be found in
the appearances presented by the semi-fibrous Cartilages. In the Cartilages
of the ribs, for instance, a more or less distinct fibrous appearance may often
be seen in the intercellular substance, which is elsewhere quite homogene-
ous ; this appearance is sometimes so faint, that it might be considered as
an illusion, occasioned by the manipulation to which the section has been
subjected; but it is often so well defined, as to present the aspect of true
fibrous tissue. No indication of the direct operation of cells, in the develop-
ment of these fibres, has ever been witnessed ; and we can scarcely do other-
wise than regard them as produced by the regular arrangement and con-
solidation of the particles of the intercellular substance, in virtue of its own
inherent powers.

137. The following arrangement of the Human Tissues will be here adopt-
ed as expressing their respective relations to the fundamental elements which
have been now described; namely, simple Membrane, Fibres, and Cells.

a. Simple Membranous Tissues. — Of these there are scarcely any examples
in the Human body, except in the posterior layer of the cornea and the cap-
sule of the crystalline lens. The membranous element is largely found, how-
ever, in the compound Membrano-fibrous tissues.

b. Simple Fibrous Tissues. — Under this head may be classed the White
and Yellow Fibrous Tissues, and Areolar Tissue.

c. Simple Cells floating separately and freely in the fluids. Such are the
Corpuscles of the Blood, Chyle, and Lymph.

d. Simple Cells developed on the free surfaces of the body. Such are the
Epidermis and Epithelium.

e. Compound Membrano-Fibrous Tissues, composed of a layer of simple
membrane, developing Cells on its free surface, and united on the other to a
fibrous or areolar structure. — Of this kind are the Skin, the Mucous Mem-
branes, the Serous and Synovial membranes, the lining membranes of the
Blood-vessels, &c.

f. Simple Isolated Cells, forming solid tissues by their aggregation. — Un-
der this head we may rank the Fat-cells, the Vesicles of Gray Nervous matter,*
the Absorbent cells at the extremities of the Intestinal villi, and the cellular
parenchyma of the Spleen and similar bodies : the cells being held together,
in all these cases, by the blood-vessels and areolar tissue which pass in amongst
them. In Cartilage, and certain tissues allied to it in structure, the cells are
united by intercellular substance, which may be quite homogeneous, or may
have a fibrous character.

g. Sclerous or Hard Tissues, in which the cells have been consolidated by
internal deposit, and have more or less completely coalesced with each other. —
Such is the case with the substance of Hair, Nails, &c., which may be more
properly ranked under the Epidemic Tissues ; but the result is most charac-
teristically seen in Bones and Teeth.

h. Simple Tubular Tissues, formed by the coalescence of the cavities of
cells, without secondary internal deposit. — The Capillary blood-vessels, and
probably also the smallest Lymphatics and Lacteals, seem to be formed in this
manner.

i. Compound Tubular Tissues ; in which, subsequently to the coalescence
of the original cells, a new deposit has taken place within their cavities. — In
the ttobuli of the White or Medullary Nervous matter, and in those of the least

* As it is undesirable to separate from each other the descriptions of the two elementary
forms of Nervous structure, on account of their close functional connection, the gray or vesi-
cular nervous matter will be described together with the white or tubular, in the last section
of this chapter.

120

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

perfect form of Muscular Fibre, the secondary deposit has only a granular or
amorphous character ; but in the striated Muscular fibre, it is composed of
minute cells.

As it is not requisite here to say anything further of simple Elementary
Membrane, we shall at once pass on to the second group of Tissues ; one of
great extent and importance in the bodies of all the higher Animals.

4. Of the Simple Fibrous Tissues.

138. A very large proportion of the body, in the higher Animals, is com-
posed of a tissue, to which the name of "Cellular" was formerly given. This
term, however, is so much more applicable to those structures, which are
composed of a congeries of distinct Cells, and the use of it for both purposes
is likely to engender so much confusion, that it is to be wished that its appli-
cation to this purpose should be altogether discontinued. — The tissue in ques-
tion, now generally designated the Areolar, is found, when examined under
the Microscope, to consist of a network of minute fibres and bands, inter-
woven in every direction, so as to leave innumerable interstices, which com-
municate with each other. The two kinds

Fig- 22. of Fibrous tissue, which elsewhere exist se-

parately,— the white, and the yellow, — may
be detected in Areolar tissue ; as was first
pointed out by Messrs. Todd and Bowman.
The White presents itself in the form of
inelastic bands of variable size, the largest
1 -500th of an inch in breadth, somewhat
wavy in their direction, and marked longitu-
dinally by numerous streaks (Fig. 23); these
streaks are rather the indications of a longi-
tudinal creasing, than a true separation into
component fibres; for it is impossible by any
art to tear up the band into filaments of a de-
terminate size, although it manifests a decided
tendency to tear lengthways. Sometimes,
however, distinct fibres may be traced, whose diameter varies from about
l-15,000th to l-20,000th of an inch. The Yellow fibrous element exists in
the form of long, single, elastic, branched filaments, with a dark decided bor-
der, and disposed to curl when not put on the stretch (Fig. 24). These inter-
lace with the others, but appear to have no continuity of substance with them.
They are for the most part between l-5000th and 1-10,000 of an inch in
thickness ; but they are often met with both larger and smaller. The pro-
portion of this element varies greatly in different parts; being greatest in those
situations, in which the greatest elasticity is required. Sometimes we find
elastic fibres passing round the fasciculi of the white tissue, constricting them
with distinct rings, or with a continuous spiral ; such are termed by Ilcnle
nucleus-filaments, from his idea of their origin (§ 133). This remarkable
disposition of the yellow fibres is best seen in the areolar tissue, that accom-
panies the arteries at the base of the brain. — The effect of Acetic acid upon
these two elements is very different ; the while immediately swells up, and
becomes transparent; whilst the yellow remains unchanged. This agent fre-
quently brings into view certain oval corpuscles, which lie in the midst of
the bands and threads, and which sometimes appear to have delicate prolonga-
tions among them. These are usually supposed to be the persistent nuclei
of the cells, from which the tissue was developed ; but, as already pointed
out, it is doubtful whether the fibres of this tissue are ever formed by the me-

Arrangement of Fibres in Areolar Tissue-
Magnified 135 diameters.

SIMPLE FIBROUS TISSUES; AREOLAR TISSUE. 121

tamorphosis of cells, — their origin being rather, it seems more probable, in the
fluid blastema (§ 136). — The interstices of Areolar tissue are tilled during life
with a fluid, which resembles a very dilute Serum of the blood ; it consists
chiefly of water, but contains a sensible quantity of common salt and albumen,
and (when concentrated) a trace of alkali sufficient to affect test-paper. The pre-
sence of this fluid seems to result from an act of simple physical transudation;
for it has been found that, when the serum of the blood is made to percolate
through thin animal membranes, the water charged with saline matter passes
through them much more readily than the albumen, a part of which is kept
back.

139. The great use of Areolar tissue appears to be, to connect together
organs and parts of organs, which require a certain degree of motion upon
one another : and to envelope, fix, and protect, the blood-vessels, nerves, and
lymphatics with which these organs are to be supplied. It can scarcely be
said to enjoy any vital powers, and is connected solely with physical actions
(§ 134). It is extensible in all directions, and very elastic, in virtue of the
physical arrangement of its elements ; and it possesses no contractility, be-
yond that of the vessels which are distributed through it. It cannot be said
to be endowed with sensibility ; for the nerves which it contains seem to be
merely en route to other organs, and not to be distributed to its own elements.
And its asserted powers of absorption and secretion appertain rather to the
walls of the capillary blood-vessels, than to the threads and bands of which
it is composed. It is regenerated more readily than any other tissue, save
the Epithelium; being produced, it would appear, by the simple consolida-
tion of the blastema, that is poured out (in the form of organizable lymph) in
situations where there has been a breach of substance. It is also formed in
the effusions of a similar fluid, which are deposited on the surfaces, or in
the substance, of inflamed tissues. — Areolar tissue yields Gelatine by boiling ;
but this is derived from the White Fibrous element only ; the Yellow not
being affected by the process.

140. The White Fibrous tissue exists alone in Ligaments, Tendons, Fi-
brous Membranes, Aponeuroses, &c. ; where it presents the same characters
as those just described, — except that the bands are less wavy, and frequently
quite straight, so that it is inextensible. It receives very few blood-vessels,
and still fewer nerves ; indeed it would seem that, in many structures (as ten-
dons), it is totally insensible. It seems entirely destitute of any vital pro-
perty ; and its chemical nature is such, that it needs very little interstitial
change to maintain its normal composition. If dried, it has not the least tend-
ency to putrefy ; and when moist, it resists the putrefactive process more
strongly than almost any of the softer textures. The peculiar and important
property of this tissue, is its capability of resisting extension ; and we find it
in situations, where a firm resistance is to be made to traction. If the traction
be applicable in one direction only, as in Tendons and most Ligaments, we
find the bundles of fibres or bands arranged side by side ; but if it be exerted in
various directions, the fasciculi cross one another, as in Fibrous Membranes.
The reparation of this tissue is effected by the interposition of a new substance,
every way similar to the original, except that it wants its peculiar glistening
aspect, and is more bulky and transparent. — The Yellow Fibrous tissue exists
separately in the middle coat of the Arteries, the Chorda? Vocales, the Liga-
mentum Nuchse (of quadrupeds) and the Ligamenta subflava ; and it enters
largely into the composition of some other parts. It differs remarkably from
the white, in the possession of a high degree of elasticity ; so that the tissues,
which are composed of it alone, are among the most elastic of all known sub-
stances. It is, however, much more brittle than the white ; and its fibres
usually exhibit a marked tendency to curl at their broken ends. Their size

11

122

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

varies from about l-4000th, to l-24,000th of an inch; in the ligamenta sub-
flava, it is usually about l-7500th. There is less tendency to spontaneous

Fig. 23.

. 24.

White Fibrous Tissue, from Ligament.
Magnified 65 diameters.

[Fig. 25.

Yellow Fibrous Tissue, from Ligamentum
Nuchae of Calf. Magnified 65 diameters.

[Fig. 26.

The two elements of Areolar tissue, in their natural rela-
tions to one another; 1, the white fibrous element, with
cell-nuclei, 9, sparingly visible in it ; 2, the yellow fibrous
element, showing the branching or anastomosing charac-
ler of its fibrillce; 3, fibrillae of the yellow element, far
finer than the rest, but having a similar curly character,
S nucleolated cell-nuclei, often seen apparently loose. —
From the areolar tissue under the pectoral muscle, mag-
nified 320 diameters.]

Development of the Areolar tissue,
(white fibrous element:) 4, nucleated
cells, of a rounded form ; 5, 6, 7, the
same, elongated in different degrees,
and branching. At 7, the elongated ex-
tremities have joined others, and are
alri-ady assuming a distinctly fibrous
character. (After Schwann.)]

decomposition in this tissue, than in almost any other part of the fabric, — at
lenst, of its soft and moist portions; it requires but little renovation, therefore,
in the living body ; and is but very sparingly supplied with blood-vessels.

COMPOSITION AND PROPERTIES OF GELATINE. 123

141. The composition of the White .fibrous tissues is very different from
that of most others ; for they yield to boiling water the substance called
Gelatine, which does not seem capable of the same degree of organization
with the Proteine-compounds. This may be obtained by boiling portions of
Skin, Areolar tissue, Serous membrane, Tendon, Ligament, &c., in water, for
some time ; after which the decoction is allowed to cool, when it solidifies
into a jelly of greater or less thickness. Some tissues dissolve readily in this
manner, and little residual substance is left; this is especially the case with
areolar tissue, serous membranes, and (in a less degree) with skin. Others
require a long boiling for the extraction of any Gelatine ; and even then it is
obtained in but small quantity ; of this kind are the Elastic fibrous tissue,
and some forms of Cartilage. A peculiar modification of this principle
exists in most of the permanent cartilages ; and has received the name of
Chondrine. Gelatine is not found in the blood, nor in any of the healthy
fluids ; and some Chemists are of opinion, that it is rather a product of the
operation practised to separate it, than a real constituent of the living solids.
This idea seems inconsistent, however, with the fact, that the gelatinous tis-
sues will exhibit, without any preparation, the best marked of the chemical
properties which are regarded as characteristic of Gelatine, — that, namely, of
forming a peculiar insoluble compound with Tannin ; and the Tanno-Gelatine,
which may be obtained by precipitating Gelatine from a solution, and that
which results from the action of Tannin on Animal membrane, appear to be
precisely analogous in every respect, — save in the presence of structure in the
latter, which is absent in the former. Moreover, the Gelatinous tissues are
found, when submitted to ultimate analysis, to possess exactly the same com-
position with Gelatine itself. Still it seems probable, that the arrangement of
the component particles is in some degree altered by the process of boiling ;
for it is found that, the more distinct the fibrous structure of the tissue, the
less it is affected by the prolonged action of cold water, and the longer it must
be boiled, before it is resolved into Gelatine.

a. Gelatine is very sparingly soluble in cold water ; by contact with which, however, it is
caused to swell up and soften. It is readily dissolved by hot water ; and forms so strong a
jelly on cooling, that 1 part in 100 of water becomes a consistent solid. Its reaction with
Tannic acid is so distinct, that 1 part in 5000 of water is at once detected by infusion of
Galls. The following are the results of four analyses of Gelatine by Scherer and Mulder.

SCHERER. MULDER.

Carbon . . . 50'557 50-774 50-048 50-948

Hydrogen . . 6-903 7-152 6-477 6-643

Nitrogen . . 18-790 18'320 18-350 18-388

Oxygen . . 23-750 23-754 25-125 24-921

The formula deduced by Mulder from this composition, and from the combinations of
Gelatine with Tannic and Chlorous acids, is 13 C, 10 H, 2 N, 5 O. — When Gelatine is boiled
for some time, it loses its power of forming a jelly on cooling ; and it is stated by Mulder,
that this is due to its union with an additional amount of water, a true Hydrate of Gelatine
being formed by the combination of 4 Equiv. of Gelatine, with 1 Equiv. of Water. The
same product is obtained by adding Ammonia to the Chlorite of Gelatine, and removing by
Alcohol the Sal Ammoniac thus formed.

b. It is not yet known how Gelatine is produced in the Animal body. There cannot be
a doubt that it may be elaborated from Albumen ; since we find a very large amount of it
in the tissues of young animals, which are entirely formed from albuminous matter ; and
also in the tissues of herbivorous animals, which cannot receive it in their food, since Plants
yield no substance resembling Gelatine in composition. It has been suggested by Mulder,
that Gelatine may be formed by the decomposition of Proteine, which has been already
mentioned as taking place from the agency of weak alkaline solutions (§ 116 6), and which
must probably, therefore, be continually occurring in the Blood. For, if to each atom of Pro-
tid and Erythioprotid, we add one of the atoms of Ammonia which are given o±f in that

124 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

decomposition, we have compounds, of which the former differs from Gelatine only by the
presence of two additional atoms of hydrogen and the deficiency of one of oxygen, whilst
the only difference in the latter consists in the presence of one additional atom of hydrogen.
Thus the ammoniated Erythroprotid, when exposed to oxygcnation in the lungs, may have
its one superfluous atom of hydrogen carried off in the form of water, and will then have
the composition of Gelatine ; and the same result will be attained from the ammoniated
Protid, by the addition of three atoms of oxygen, which will convert it into Gelatine with
two atoms of water. According to this formula, the substances produced from the decom-
position of the proteine in blood, merely through the action of the alkali in the serum, and
the oxydizing influence of the atmosphere, are — carbonic acid, water, gelatinous tissue, and
leucin. The carbonic acid passes off through the lungs ; and the water, either by the kid-
neys, or by exhalation from the lungs or skin. The Gelatine only requires form, to become
Fibrous tissue. Leucin, however, has not yet been found in the body ; and until it shall
have been discovered, or the products of its decomposition shall have been detected, any
such attempt to explain the formation of Gelatine, must be regarded as altogether theoretical.*
c. The relation of Gelatine to the Proteine-compounds is further shown by the fact, that
Leucin may be produced from the former, as well as from the latter. When Gelatine is
boiled, either with alkalies or with dilute sulphuric acid, Leucin is formed; together with
extractive matters, and a peculiar sugar termed Glyricoll. This substance crystallizes in large
colourless prisms, which have a sweet taste, and feel gritty between the teeth ; it is soluble
in 4 2 parts of water, and is taken up in small quantity by Alcohol. This fact is one of much
interest in regard to certain Pathological relations of Gelatine.

142. The Yellow Fibrous tissue, on the contrary, undergoes scarcely any
change by long boiling ; a very small quantity of Gelatine being alone yielded
by it; and this being probably derived from the Areolar tissue, by which it is
penetrated. It is unaffected by the weaker acids, and undergoes no solution
in the gastric fluid ; and it preserves its elasticity for an almost unlimited pe-
riod. According to Scherer, the yellow fibrous tissue from the middle coat
of the Arteries consists of 48 C, 38 H, 6 N, 16 O ; which (taking Liebig's
formula for Proteine) may be regarded as 1 Proteine + 2 Water. When
burned, it leaves 1*7 per cent, of ash.

5. Of Simple Cells, floating in the Animal Fluids.

143. The red colour, which is characteristic of the Blood of Vertebrated
animals, is entirely due to the presence, in that fluid, of a very large number of
floating cells, which have the power of forming a secretion in their interior,
that is distinguished by its peculiar chemical nature, as well as by its hue.
The red Blood-corpuscles (commonly, but erroneously termed globules) are

flattened Discs, which, in Man and most

Fig. 27. of the Mammalia, have a distinctly cir-

cular outline. In the discs of Human
^ blood, when examined in its natural con-

dition, the sides are somewhat concave ;
and there is a bright spot in the centre,

Tr - ^' ^) ^^) which has been regarded by many as in-

'-^ ''^ dicating the existence of a nucleus; though

fs> TSSy^ it is really nothing else than an effect of

refraction, and may be exchanged for a
dark one by slightly altering the focus of
the Microscope. The form of the disc

Red Corpuscles of Human Blood represent- .g mu(.h ^^j , ^.^ entg .

ed at a, ;is they are seen when rather beyond J i • i •

the focus of Ihe microscope ; and at ft as they for the membrane which Composes its CX-

appear when within the focus. Magnified 400 terior or cell-well, is readily permeable by
diameters. liquids ; so as to admit a passage of li-

quid, according to the laws of Endos-
mose, either inwards or outwards, as the relative density of the contents of

* See Mulder's Chemistry, p. 326.

SIMPLE ISOLATED CELLS; RED BLOOD-CORPUSCLES.

125

the cell and of the surrounding fluids may direct. Thus, if the Red corpus-
cles be treated with water, there is a passage of that liquid into the cell ; the
disc becomes first flat, and then double-convex, so that the central spot disap-
pears ; and by a continuance of the same process, at last becomes globular,
and finally bursts, the cell-wall giving way, and allowing the diffusion of the
contents through the surrounding liquid. On the other hand, when the Red
corpuscles are treated with a thick syrup or solution of albumen, they will be
more or less completely emptied, and caused to assume a shrunken appear-
ance ; the first effect of the process being to increase the concavity, and to
render the central spot more distinct. It is probable that the Blood-corpuscles,
even whilst they are circulating in the living vessels, are liable to alterations
of this kind, from variations in the density of the fluid in which they float ;
and that such alterations may be constantly connected with certain disordered
states of the system.* We hence see the necessity, in examining the Blood
microscopically, for employing a fluid for its dilution, that shall be as nearly
as possible of the same character with ordinary liquor sanguinis.t

144. Microscopic observers have been much divided upon the question,
whether or not the Red corpuscles of the Blood of Man and other Mammalia
contain a nucleus. There seems every probability from analogy, that a nu-
cleus exists in them, as it does in the red corpuscles of all other animals ;
but it cannot be brought into view by any of the ordinary methods, which
render it distinctly visible in the oval blood-discs of Oviparous Vertebrata ;
and of late the general opinion has been, that nothing resembling their nuclei
could be present in the blood-discs of Man and Mammalia. Dr. G. O. Rees
states, however, that, by carefully examining the ruptured cell-walls, which
fall to the bottom of the water when red corpuscles have been diffused
through it, he could distinguish appearances on them, that indicated the ex-
istence of nuclei ; although they escape observation when within the corpus-
cles themselves, on account of their high refractive power. He describes
them as being circular and flattened, like the Red corpuscles themselves ; and
as about two-thirds of their diameter.

145. In all Oviparous Vertebrata, without any known exception, the red
corpuscles are oval, — the proportion between their long and short diameters,
however, being much subject to varia-
tion ; and their nuclei may always be Fig. 28.

brought into view, by treatment with
acetic acid, when not at first visible. In
the red particles of the Frog, which are
far larger than those of Man, a nucleus
can be observed to project somewhat
from the central portion of the oval,
even during their circulation ; and it
is rendered extremely distinct by the
action of acetic acid ; this renders the
remainder of the particle extremely
transparent, whilst it gives increased
opacity to the nucleus, which is then
seen to consist of a granular substance.
In the still larger blood-disc of the Proteus and Siren, this appearance is yet

See Dr. G. 0. Rees' Gulstonian Lectures, for 1845.

\ By Wagner, the filtered serum of frog's blood is recommended for this purpose. Weak
solutions of salt or sugar, and urine, answer tolerably well ; but Mr. Gulliver remarks that
all addition must be avoided, when it is intended to measure the corpuscles, or to ascertain
their true forms ; as the serum of one Mammal reacts injuriously on the blood of another.
See Philos. Magaz., Jan. and Feb. 1840.

11*

Panicles of Frog's blood; 1, 1, their flattened
face ; 2, particle turned nearly edgeways ; 3,
lymph-globule; 4, blood-corpuscles altered by di-
lute acetic acid. Magnified 500 diameters.

126 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

more distinct; the structure of the nucleus being so evident without the addi-
tion of acetic acid, that its granules can be counted.*

146. The form of the Red Corpuscles is not unfrequently seen to
change during their circulation ; but this is generally in consequence of
pressure : from the effects of which, however, they quickly recover them-
selves. In the narrow capillary vessels, they sometimes become suddenly
elongated, twisted, or bent, through a narrowing of the channel ; and this
may take place to such a degree, as to enable the disc to pass through an
aperture, which appears very minute in proportion to its diameter. When
undergoing spontaneous decomposition, the blood-discs become granulated,
and sometimes (as long ago noticed by Hewson) even mulberry-shaped ; and
particles in which these changes appear to be commencing, may be found in
the blood at all times. It has been ascertained that bile and urea exert a pecu-
liar solvent power on the blood-corpuscles ; and hence we can understand
one of the modes in which a retention of these substances in the circulating
fluid (Chap. XV., Sect. 1) proves so injurious. — The size of the blood-discs
is liable to considerable variation, even in the same individual ; some being
met with as much as one-third larger, whilst others are one-third smaller, than
the average. The diameter of the corpuscles bears no constant relation to the
size of the animal, even within the limits of the same class ; thus, although
those of the Elephant are the largest among Mammalia (as far as is hitherto
known), those of the Mouse tribe are far from being the smallest, being in
fact more than three times the diameter of those of the Musk Deer. There
is, however, a more uniform relation between the size of the animal and that
of its blood-discs, when the comparison is made within the limits of the same
order. In Man, the diameter varies from about 1 -4000th to l-2800th of an
inch; the average diameter is probably about l-3200th.

a. The following measurements of the blood-discs of various animals are chiefly given
on the authority of Mr. Gulliver. — The diameter of the corpuscles in the Quadrumana is
generally about the same with that of the Human blood-discs ; there is, however, a slight
diminution among the Lemurs, and there is more variation among them, than among the
Monkeys. Among the Cheiroptera, the diameter of the corpuscles is somewhat less than in
the preceding order, the average being about l-4300th of an inch. Passing to the Insecti-
vora, we find the blood-discs of the Mole to be still smaller, averaging only the l-4747th of
an inch; those of the Hedgehog, however, are larger, being about l-40S5th. In the corpus-
cles of the different families of the Carnivora, there is such a well-marked diversity in the
size of the corpuscles, that the fact may be used as a help to classification."}" In the Seals,

* As Professor Owen's interesting account of the blood-discs of the Siren may not be
generally accessible (Penny Cyclopfedia, Art. Siren"), the leading facts in it will be here
stated. This animal agrees with the Proteus and other species in being perennibranchiate
(§ 32); and, as in all its congeners yet examined, the blood-discs are of very large dimen-
sions. They are usually of an oval form, the long diameter being nearly twice the short;
and the nucleus projects slightly from each of the flattened surfaces. Considerable variety
in the form of the disc presents itself, some of the corpuscles being much less oval than
others; but the nuclei do not partake of these variations in nearly the same degree. The
nucleus is clearly seen to consist of a number of moderately-bright spherical granules, of
which from 20 to 30 could be seen in one plane or focus, the total number being of course
much greater. When removed from the capsule, the nuclei are colourless, nnd the compo-
nent granules have a high refracting power. Viewed in situ, they present a tinge of colour
lighter than that of the surrounding fluid, and dependent upon the thin layer of that fluid
interposed between the nucleus and the capsule. As the fluid contents of the blood-disc in
part evaporate during the process of desiccation, the capsule falls into fiilds in the interspace
between the nucleus and the outer margin; these folds generally take the direction of straight
lines, three to seven in number, radiating from the nucleus.

f Two facts of much interest in Zoology have been brought to light by Mr. Gulliver's
examination of the diameter of the blood-corpuscles of this tribe. The difference between
those of the Dog and the Wolf is not greater than that which exists among the varieties of
the Dog; whilst the discs of the Fox are much smaller. The discs of the Hyaena are far
more approximate to those of the Canidce, than they are to those of the Felida •.

COMPARATIVE SIZES OF RED CORPUSCLES OF BLOOD. 127

the diameter averages l-3280th of an inch ; in the Dog, l-3540th ; in the Bear, about
l-370Uth ; in the Weasel, l-4200th; in the Cat, l-4400th ; and in the Viverrce, l-5365th. In
two species only of the Cctacea, have the blood-discs been yet examined ; the Dolphin, in
which their diameter averages 1 -3829th of an inch ; and the great Rorqual (the largest known
Mammal), in which they are only l-3100th of an inch, or scarcely larger than those of Man.
Among the Pachydermata, the average excluding the Elephant (the diameter of whose blood-
discs is about 1 -2745th of an inch), and the Rhinoceros (in which they are about l-37G5th),
may be stated at about 1 -4200th; and there is less variation than might have been expected,
from the different size "and conformation of the several species examined. Among the Rib-
minantia, the corpuscles are for the most part smaller than in other orders ; and there is more
relation, between their diameter and the size of the animal, than is elsewhere observable.
Excluding the Camelidae (which are zoologically intermediate between the Ruminantia and
Pachydermata), we find a range of sizes extending from the l-3777th to the l-12,325th of
an inch; the former is the diameter in one of the larger Deer; the latter in the Musk Deer,
which is the smallest in the whole order. In the Camel tribe, the average of the long dia-
meter of the corpuscles is about 1 -3300th of an inch , whilst that of the short diameter is
l-6300th; and this is nowhere widely departed from: the length of the discs is, therefore,
not quite twice their breadth. Among the Rodentia, the discs are rather large, especially
considering the small size of most of the species. In the Capybara, which is the largest
animal of the order, they average 1-3 190th; and in the Mouse family (the smallest of Mam-
malia), they are as much as l-3S14th. In the Squirrels, the diameter is rather less; but in
scarcely any of the whole order is it under 1 -4000th. Among the Edentata, the Two-toed Sloth
has been found to have corpuscles of the unusually large diameter of l-2865th of an inch;
whilst in the Armadilloes they average about l-3400th. In the Marsupialia the range is
nearly the same as among the Rodentia.

b. In BIRDS, according to the observations of Mr. Gulliver, the long and short diameters
of the corpuscles usually bear to each other the proportion of 1^ or 2, to 1; and this is the
general relation among Oviparous Vertebrata, with the exception of some of the Crocodile
tribe, in which the length is sometimes three times the breadth. The size of the corpuscles
of Birds has generally more relation to that of the species, than it has in Mammalia. No
instance has yet been detected, of the occurrence of comparatively small corpuscles in the
larger species, and of large corpuscles among smaller animals, which has been seen to be
common among the former class ; the blood of the Humming-birds, however, has not yet
been examined. The largest discs are found among the Cursores; those of the Ostrich have
an average long diameter of l-1649th of an inch, and a short diameter of 1 -3000th; and
among the larger Raptores, Grallatores, and Natatores, the dimensions are but little inferior.
The least dimensions hitherto observed are among the small Passerine birds ; in which the
corpuscles have a long diameter of about 1 -2400th of an inch, and a transverse diameter of
from l-3SOOth to l-4SOOth. Circular discs may be occasionally observed in some species,
agreeing with the others in every particular but their form ; and every gradation may be no-
ticed between these and the regular oval corpuscles.

c. The large size of the blood-discs in REPTILES, especially in Batrachia, and above all,
in the Percnnibranchiate species of the latter, has been of great service to the Physiologist ;
by enabling him to ascertain many particulars regarding their structure, which could not
have been otherwise determined with certainty. Among other facilities which this occa-
sions, is that of procuring their separation from the other constituents of the blood ; for they
are too large to pass through the pores of ordinary filtering-paper, and are therefore re-
tained upon it, after the liquor sanguinis has flowed through. The blood-discs of the warm-
blooded Vertebrata cannot be thus separated. The oval corpuscles of the Frog have a long
diameter of about 1-1 108th, and a transverse diameter of about l-1800th of an inch; those
of the Salamander or Water-newt are still larger. The long diameter of the corpuscles of the
Proteus is stated by Wagner at l-337th of an inch ; that of the Siren is about l-435th, the
short diameter being about 1-SOOth of an inch; the extremes of variation, however, are very
wide. The long diameter of the nuclei is about 1-1 000th or l-1100th, and the short diame-
ter about l-2000th; hence it is about three times as long, and nearly twice as broad, as the
entire Human blood-disc, thus having six times its superficies; its thickness is about l-3800th
of an inch.

d. The number of FISHES, in which the diameters of the blood-discs have been examined,
is still inconsiderable. In the common Perch, theyaverage l-2100th by 1-2824 ; in the Carp,
they are l-2142nd of an inch by 1 -3429th; in the Gold-Fish, though of the same genus and
of much smaller size, they are as much as l-1777th by l-2824th; in the Pike, 1 -2000th by
1 -3555th; and in the Eel, 1-1 745th by 1-2 842nd.*

* A summary of Mr. Gulliver's numerous and valuable observations is contained in the
Proceedings of the Zoological Society, No. CLII.

128 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

147. In speaking of the Chemical constitution of the Red Corpuscles of
Blood, it is necessary to distinguish the substance of their walls and nuclei
from their fluid contents. These may be separated by treating them with
water ; which, as already mentioned, occasions the rupture of the cells, the
walls of which sink to the bottom, whilst their contents are diffused through
the liquid. The substance obtained from the former has been termed Globu-
line; but it does not seem to differ in any essential character from other sub-
stances, that result from the organization of the proteine-compounds. The
compound which forms the contents of the red corpuscles, however, and
which gives them their characteristic hue, is very different both in its sensi-
ble properties, and in its composition; and has received the designation of
Hsematine. When separated from albuminous matter, it is of a dark-brown
hue, and is tasteless and insoluble in water, alcohol, and ether ; but it is rea-
dily soluble in water or alcohol, that contains alkalies or acids ; whence it may
be supposed to unite with these, like albumen, as an acid or a base. In
composition, however, it differs considerably from that of the proteine-com-
pounds; its formula being 44 C, 22 H, 3 N, 6 O, with a single proportional
of iron. When burned, it yields a notable quantity of peroxide of iron ; and
one atom of this is considered to be present in combination with each equiva-
lent of the animal compound. The red colour is not due, however, as for-
merly supposed, to the presence of this peroxide ; for M. Scherer has proved,
that the metal may be entirely dissolved away by the agency of acids, and
that the animal matter, afterwards boiled in alcohol, colours the spirit intensely
red. On the other hand, the iron is most certainly united firmly with the
constituents of the Haematine, as contained in the red corpuscles ; for this sub-
stance may be digested in dilute sulphuric or muriatic acid for several days,
without the least diminution in the quantity of iron, the usual amount of which
may be obtained by combustion from the Hsematine that has been subjected
to this treatment. When diffused through water, in the manner just describ-
ed, the Haematine exhibits the same changes of colour under the influence of
oxygen, acids, saline matter, &c., as the Blood undergoes in similar circum-
stances.

148. The question of the origin of the red Blood-corpuscles is a very inte-
resting one, and cannot yet be regarded as completely determined. That they
are to be regarded as nucleated cells, — conformable in general character with the
isolated cells, which constitute the whole of the simplest Plants (§ 125), and
having each an independent life of its own, the duration of which is limited,
— there can now be no reasonable doubt. From this we should infer that they
have the power of reproducing themselves ; and the recent observations of
Dr. Barry and other Microscopists seem to confirm the statement long ago
made to that effect by Leeuwenhoek. The first change said to take place, is
the appearance of delicate radiating lines between the nucleus and the peri-
phery ; dividing the disc into several segments, usually six in number (Plate I.,
Fig. 22.) The margin is soon observed to become crenated, by indentations
at corresponding points ; and these indentations become deeper, until a com-
plete separation takes place, setting free six young cells or discs (a, 6, c, d, e),
which seem to have been formed around the margin of the nucleus of the pa-
rent cell. Between the small newly-generated disc, and the full-sized corpus-
cle, we should expect to find every intermediate size ; and this is affirmed by
these observers to be the case. — It has been lately asserted by Dr. G. O. Rees,
that, when examining a portion of Blood maintained at about its natural tem-
perature, he observed some of the corpuscles to assume an hour-glass form,
by a contraction across their middle ; and that, by the increase of this contrac-
tion, producing the complete division of the corpuscles, two unequal-sized
circular bodies were eventually produced from each ; which, when treated

ORIGIN AND MULTIPLICATION OF RED CORPUSCLES. 129

with a strong saline solution, were emptied of their contents, like ordinary
blood-discs. — It is not at all improbable, that both these methods of multi-
plication may be followed ; and it can scarcely be doubted that, by one or
both, a continual succession of Red corpuscles is kept up. That the corpus-
cles may be generated with great rapidity under peculiar circumstances, will
hereafter appear (Chap. XL, Sect. 6) ; and their amount may undergo a rapid
diminution also, without any evident abstraction of them from the circulating
fluid. This diminution seems to be traceable in some instances to a too low
specific gravity of the serum ; which will cause the Red corpuscles to rupture
by endosmose, just as when they are treated with water. — Appearances have
been seen by Wagner, Gulliver, and others, in the blood of Batrachia, which
might seem to indicate that the Colourless corpuscles (§ 151) serve as the
nuclei of cells, which, when fully developed, may become Red blood-discs ;
but in the Mammalia, it is scarcely possible to imagine that this can occur ;
since the diameter of the colourless corpuscles is very constant ; whilst that
of the Red blood-discs is so variable, that the former, though sometimes the
smaller, are in other instances far larger than the latter. If it be admitted
that the Red corpuscles have the power of reproduction, like other isolated
cells, it does not seem necessary to seek elsewhere for the source of their con-
stant renewal ; and various facts, hereafter to be stated, appear to the Author
strongly indicative of the entire functional as well as structural difference,
between the red and the colourless corpuscles of the blood of Vertebrata.

149. That the Red blood-discs, when first formed in the embryo, have an
origin common to that of all other tissues, cannot be doubted. They are pro-
duced, in the embryo of the Bird, in the portion of the germinal membrane
which afterwards becomes the area vasculosa ; this consists of delicate cells
very uniformly disposed: and whilst capillary vessels are being formed by
the union of the cavities of these, blood-discs seem to be developed from

Fig. 29.

Production of blood-corpuscles in Chick, on the fourth day of incubation ; a, particles fully formed ;
b. particles in progress of formation; c, similar particles altered by dilute acetic acid, so as to display their
nuclei.

the granules or cell-germs they contain. These changes take place about the
second or third day of incubation ; but it is not until some days afterwards,
that the discs assume their characteristic form.

a. Mr. Macleod gives the following history of the development of the blood-corpuscles
in the Chick. In blood withdrawn from the heart, on the third day, and diluted with se-
rum, or from the germinal membrane or allantois, and diluted with fluid albumen, — " a num-
ber of small granules are seen floating about the field : these enlarge and become clearer in
the centre ; this enlargement goes on very rapidly, and when they have gained to about twice
their original size, the central clear part becomes dull. 'jhis dullness slightly increases, and
in a short time it is seen to be distinctly granular; whilst the borders are observed to be
well-defined, smooth, and clearer than the central part. The enlargement of these bodies,
with the granular appearance of their centre, seems not to depend on the aggregation of
granules round a centre one, but on a property which they have in themselves of enlarging
and presenting that figure. During all this time they are quite spherical and of good con-
sistence, as they do not lose their form by considerable pressure. In the second stage, the
central portion gradually becomes less opaque, and ceases to appear granular, the external

130 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

portion at the same time separating in some degree from the central part. The blood-cor-
puscle, in this stage of development, has the appearance of a slightly flattened round cell,
formed of a somewhat delicate but elastic membrane, with a nucleus in the centre. At this
time a number of these bodies, being close together in the Held, presents a yellowish colour.
The cell is disc-like, rather concave, but the nucleus convex. In the third stage, one side of
the corpuscle gradually elongates, giving it a pear-shaped appearance ; the opposite side then
elongates itself in a similar manner, and to the same degree. The concavity between the
nucleus and border disappears, and the whole becomes slightly convex. The hue at the
same time gradually becomes redder."*

The corpuscles are generally larger in the embryo than in the adult, espe-
cially soon after the period of their first formation; it was remarked by M.
Prevost, that in the fetal goat they were at first twice the size of those of the
mother. Mr. Gulliver has observed, however, that at a later period of utero-
gestation they are sometimes smaller than the average dimension of the adult ;
but perhaps all such observations are to be received with hesitation, owing to
the fact mentioned by him, that the variety in the magnitude of the fetal cor-
puscles is much greater than in the full-grown animal.

150. In regard to the uses of the Red corpuscles of the Blood, in the Ani-
mal economy, it appears to the Author that a definite conclusion may be now
arrived at. Their existence in the circulating fluid is nearly confined to the
Vertebrated classes ; the corpuscles which are seen in the blood of the Inver-
tebrated, being mostly analogous rather to the Colourless corpuscles, presently
to be described as present in the blood of the higher animals. Among the
lower Invertebrata, indeed, the Red corpuscles seem to be altogether wanting;
and the same may be said of the embryos of the highest animals, at an early
period of their development ; as well as of the early state of parts that are
being newly formed, at any period of their lives. Hence the inference ap-
pears highly probable, that they are not essentially necessary to the produc-
tion of the organizable elements of the blood, or of the organized tissues ; in
other words, to the simple acts of growth and nutrition. The Red corpuscles
are most abundant in those classes among Vertebrata, which maintain the
highest temperature ; thus, they are somewhat more numerous, in proportion
to the whole bulk of the Blood, in Birds than in Mammalia ; and far more in
the latter, than in Reptiles and Fishes. As it is evident that they undergo
very important changes in the pulmonary and systemic capillaries, — their co-
lour being changed from purple to red in the former, and from red to purple
in the latter, — it seems highly probable that they have as their principal office,
the introduction of oxygen into the blood that circulates through the systemic
capillaries, and the removal of the carbonic acid set free there ; serving, in
fact, as the medium for bringing the tissues into relation with the air, the in-
fluence of which is necessary for the maintenance of their vital activity. In
the Invertebrata generally, whose respiration is very feeble, this end will be
sufficiently answered by the fluid plasma of the blood ; the alterations in which,
under the influence of the air, have been already noticed (§§ 115, 116 «). And
in Insects, — the only class whose respiration is at all active, we find the air
directly conveyed into the tissues ; the circulating fluid not being employed as
its carrier (§ 18). We shall hereafter find, that the influence of oxygen upon
the Nervous and Muscular systems is essential to their vital activity ; and it
seems to be by their agency in bringing these into relation, that the Red cor-
puscles possess that intimate connection with the Animal functions, which we
find them to possess. The animals whose temperature is the highest, are
also those whose senses are most acute, and whose movements are most ener-
getic : whilst, on the other hand, if there be any unusual diminution in the

* London and Edinburgh Monthly Journal, September, 1842.

COLOURLESS CORPUSCLES OF BLOOD. 131

proportion of Red corpuscles, it is invariably accompanied by muscular de-
bility and deficient nervous power.

a. By Liebig it is supposed, that the iron in the red corpuscles is the real agent in the
respiratory process : for if its original state be the protoxide, it may become the peroxide
by uniting with an additional atom of oxygen, or the protocarbonate by the addition of an.
atom of carbonic acid. The former change is supposed by him to take place in the lungs,
to which the blood comes charged with carbonic acid ; the carbonic acid is given up by the
iron, and replaced by an equivalent of oxygen taken in from the air : whilst in the syste-
mic capillaries, the converse change takes place, — the oxygen being imparted to the tissues,
and being replaced by carbonic acid which is given up by them to be conveyed out of the
system. It is stated by Liebig that there is far more than sufficient iron in the whole mass
of the blood, to convey in this manner all the oxygen and carbonic acid, which are inter-
changed between the pulmonary and systemic capillaries. The speculation is certainly an
ingenious one ; but it can scarcely be yet received as a physiological fact.

151. Besides the red particles of the Blood, there are others which possess
no colour, and which seem to have a function altogether different ; these are
known as the White or Colourless corpuscles. Their existence has long
been recognized in the blood of the lower Vertebrata, where, from being much
smaller than the red corpuscles, they could readily be distinguished. But it
is only of late, — chiefly through the researches of Gulliver, Addison,* and
others, that they have been recognized in the blood of Man and other Mam-
malia ; their size being nearly the same with that of the red corpuscles; and
the general appearance of the two (owing to "the circular form of the latter,
and the absence of a proper nucleus,) being less distinct. It is remarkable
that, notwithstanding the great variations in the size of the red corpuscles in
the different classes of Vertebrata, the dimensions of the colourless corpuscles
are extremely constant throughout ; their diameter seldom being much greater
or less than l-3000th of an inch. This has been observed even in those ani-
mals,— the Musk-deer, and the Proteus, — which present the widest departure
from the general standard in the size of their red corpuscles : so that the
colourless corpuscle is as much as four times the diameter of the red, in one
instance ; whilst it is not one-eighth of the long diameter of the red, in the
other. Hence it would seem very improbable, that the red can never be con-
verted into the white, or the white into the red. — The aspect of the two, under
the Microscope, is very different. Instead of presenting a distinct central
nucleus, like the red corpuscles of the Oviparous Vertebrata, — or being en-
tirely destitute of granular contents, as are those of Mammalia when unaffected
by reagents, the colourless corpuscles are studded with minute granules,
which may be occasionally seen in active motion within them, and which are
discharged when the corpuscles are treated with liquor potassae. They pos-
sess, moreover, a higher refracting power than the red corpuscles ; and are
further distinguished from them, by their greater firmness, and by the ab-
sence of any disposition to adhere to each other ; so that, when a drop of recent
blood is placed between two strips of glass, and these are gently moved over
one another, the white corpuscles may be at once recognized by their soli-
tariness, in the midst of the rows and irregular masses formed by the aggre-
gation of the red. This is still better seen in inflamed blood ; in which the
Red corpuscles have a peculiar tendency to adhere to one another, whilst the
White are present in unusual number.

152. The Colourless corpuscles may be readily distinguished in the cir-
culating Blood, in the capillaries of the Frog's foot ; and it is then observa-
ble, that they occupy the exterior of the current, where the motion of the fluid
is slow, whilst the red corpuscles move rapidly through the centre of the tube.

* Transactions of the Provincial Medical Association, 1842 and 1843.

132

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Fig. 30.

The Colourless corpuscles, indeed, often show a disposition to adhere to the
walls of the vessels ; which is manifestly increased on the application of an
irritant. Hence the idea naturally arises, that (to use the words of Mr. Whar-

ton Jones) " there is some reciprocal re-
lation between the colourless corpuscles,
and the parts outside the vessels, in the
process of nutrition." What that rela-
tion is, we shall now proceed to inquire.
153. In regard to the purpose of the
Colourless corpuscles in the Animal eco-
nomy, a view has been brought forward
by the Author,* which increased consi-
deration has only served to strengthen ;
and which he advances here, with some
degree of confidence that it will be found,
on attentive examination, warranted by
a large number of physiological analo-
gies, though not capable of being direct-
ly proved. That it may be rightly un-
derstood, a general sketch of certain
known operations of cells in Plants and
Animals will be first given. — It is not
difficult, on taking a comprehensive sur-
vey of the Assimilating processes, to
find a number of examples, in which
cells are developed in a temporary man-
ner ; growing, arriving at maturity, and
then disappearing, apparently without having performed any particular
function. In the albumen of the Seed, for instance, this often takes place to
a remarkable extent. In the Yolk of the Egg, there is a similar transitory
development of cells, of which several generations succeed each other, without
any permanent structure being the result ; and we have seen that, according
to Dr. Barry ,t a process of the same nature takes place within the germinal
vesicle, and in the primary embryonic cells and their descendants (§ 130).
It can scarcely be imagined by the well-judging Physiologist, that all this
cell-life comes into existence without some decided purpose ; and if we can
assign to it an object, the fulfilment of which is consistent with the facts sup-
plied by analogy elsewhere, this may be reasonably considered as having a
fair claim to be received as a physiological induction. — In all these instances,
and in many more which might be quoted, the crude alimentary materials are
being prepared to undergo conversion into permanent and regularly-organized
structures. We have seen that the very first union of the inorganic elements,
into the simplest proximate principles, is effected by the cell-life of Plants.
The change of these principles into the peculiar compounds, which form the
characteristic secretions of Plants, is another result of their cell-life. And
there seems equal ground for the belief that the change of these proximate
principles into the peculiar glutinous sap, which is found wherever a forma-
tion of new tissue is taking place, is equally dependent upon the agency of
cells. Thus, the starchy fluid, which is contained in the ovule previously to
its fecundation, is probably not in the state in which it can be immediately
rendered subservient to the nutrition of the embryo ; and the development of
successive generations of cells, which exert upon it their vitalizing influence,

A small venous trunk, a, from the Web of
the Frog's foot, magnified 350 Diam ; fc,A, cells
of the pavement-epithelium, containing nuclei.
In the space between the current of oval blood-
corpuscles, and the walls of the vessel, the rouud
transparent white corpuscles are seen.

* Report on Cells, in British and Foreign Medical Review, Jan. 1843.
| Embryological Researches. Third Series.

COLOURLESS CORPUSCLES OF BLOOD. 133

may be reasonably regarded as the means, by which the requisite change is
effected. Exactly the same may be said of the Albuminous matter contained
in the Yolk of the Egg, which is certainly not in a condition in which it can
be immediately applied to the purposes of nutrition ; and its conversion may
be regarded as commencing with the development of transitory cells within
its own substance, and as being completed by means of the cells forming the
inner layer of the germinal membrane, by which it is subsequently taken up
and introduced into the current of blood flowing through the vascular area
(§ 149). A similar purpose is probably answered by the transitory cells de-
veloped within the germinal vesicle ; and by those which appear at a similar
period, in the evolution of the descendants of the " twin cells" produced in
it. — Many similar examples have been elsewhere adduced.

o. There are probably cases, however, in which cells are very rapidly called into exist-
ence, without that preparatory elaboration of their nutrient materials, which we regard as
due to the vital operations of a preceding generation. Thus the Bovista giganteum, a large
fungus of the Puff-ball tribe, has been known to increase, in a single night, from a mere point
to the size of a huge gourd, estimated to contain 47,000,000,000 cellules. In such a case it
is difficult to suppose mat any but the most rapid mode of generating cells can have been in
operation ; and the idea that these could not have been developed by any such elaborate
process as that just alluded to, is borne out by the fact of their extremely transitory charac-
ter,— the decay of such a structure being almost as rapid as its production. The same may be
remarked of those fungous growths in the Animal body, which sprout forth most rapidly.
Hence the apparent exception assists in proving the rule.

154. We have thus a class of facts, which indicates that the conversion of
the Chemical compound into the organizable principle — the aplastic into the
plastic material — is effected, in the particular situations where it is most
wanted, by the vital agency of transitory cell-life ; that is, by the production
of cells, which are not themselves destined to form an integral part of any
permanent structure, but which, after attaining a certain maturity, reproduce
themselves and disappear : successive generations thus following one another,
until the object is accomplished, after which they altogether vanish. We
shall now consider another class of facts, which seem to indicate that a change
of this kind is being continually effected in the nutritious fluids of Animals,
during their circulation through the body : by Cells, which are either carried
about with them, or which are developed for the purpose in particular situa-
tions, as in Plants. The former is the more common occurrence ; since the
conditions of Animal life, usually involving a general movement of the body,
require also a constant general reparation of its parts, and therefore an adapt-
ation of the circulating fluid to the wants of the whole fabric.

155. It is not in the Blood alone, that floating cells are met with; for Cells,
which seem identical with the Colourless corpuscles of the blood, are found
in the Chyle and Lymph — fluids in which, as in the Blood, the elaboration
of plastic Fibrine from unorganizable Albumen is continually taking place, to
make up for the constant withdrawal of the former substance by the nutrient
processes. Hence there would seem reason for attributing this important
function to these floating cells; the number of which present in the fluids,
seems to bear a very close relation with the energy of the elaborating process.
It is a fact of great physiological interest and importance, that, whilst the
colourless corpuscles are to be met with in the nutritious fluids of all Animals
which possess a distinct circulation, the red corpuscles are nearly restricted to
the blood of Vertebrata. This observation, which was first put forth by
Wagner,* has been confirmed by the Author, who had been previously struck
with the very close analogy between tbe floating cells carried along in the

* [Elements of Physiology, translated by R. Willis.]
12

134 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

current of the circulation in some of the very transparent aquatic larvae (espe-
cially those of the Culicidae), and the lymph-corpuscles of the Frog. Now
it is evident from this fact, that, as the Blood of Vertebrata is distinguished
from their Chyle chiefly by the presence of red corpuscles in the former, and
by the absence of those bodies in the latter, the nutritious fluid of Inverte-
brated animals is rather analogous (as Wagner has remarked) to the Chyle
and Lymph, than to the Blood of Vertebrata. Or, to put the same idea in
another form, the presence of the colourless corpuscles in the nutritious fluid
appears to be the most general fact in regard to its character throughout the
whole Animal scale; whilst the presence of red corpuscles in that fluid is
limited to the Vertebrated classes and the higher Invertebrata. Hence it
would not be wrong to infer, that the function of the colourless corpuscles
must be of a general character, and intimately connected with the nutritious
properties of the circulating fluid ; whilst the function of the red corpuscles
must be of a limited character, being only required in one portion of the ani-
mal kingdom.

156. Further, it has been noticed by Mr. Gulliver, that in the very young
embryo of the Mammalia, the white globules are nearly as numerous as the
red particles: this, Mr. Gulliver has frequently observed in foetal deer of about
l£ inch long. In a still smaller foetus, the blood was pale, from the prepon-
derance of the white corpuscles. It is, therefore, a fact of much interest,
that, even in the Mammiferous embryo, at the period when growth is most
rapid, the circulating fluid has a strong analogy to that of the Invertebrata.
It then, too, bears in other respects the most striking analogy to Chyle; since
it consists of the fluid elaborated from the organizable matter supplied by the
parent, and directly introduced into the current of the circulation. The func-
tion of the placental vessels may be regarded as double : for they are at the
same time the channel, through which the alimentary materials supplied by
the parent are introduced into the circulating system of the foetus; and the
medium of aerating the fluid, which has traversed the fetal system. Hence
the placenta may be regarded as at once the digestive and the respiratory
apparatus of the foetus; and the fluid circulating through the cord, as at once
chyle and blood. It is not until the pulmonary and lacteal vessels of the
embryo have commenced their independent operation, that the distinction be-
tween the blood and the chyle of the fetus becomes evident; and we should
expect, therefore, to find that the circulating fluid, up to the time of birth,
contains a large proportion of white corpuscles, — which is actually the case.
There is a gradual decrease, however, in their proportional number, from the
earlier to the later stages of embryonic life ; in accordance with the diminish-
ing energy of the formative processes. The recent observations of Mr. New-
port upon the Blood of Insects,* present a remarkable correspondence with
the foregoing. He finds in the circulating fluid of the Larva, a number of
"oat-shaped" corpuscles or floating cells; which he regards as analogous to
the Colourless corpuscles of Vertebrata. These are most numerous at the
period immediately preceding each change of skin; at which time the blood
is extremely coagulable, and evidently possesses the greatest formative power.
The smallest number are met with soon after the change of skin; when the
nutrient matter of the blood has been exhausted in the production of new
epidermic tissue. In the Pupa state, the greatest number are found at about
the third or fourth clay subsequent to the change; when preparations appear
to be most actively going on, for the development of the new parts that are
to appear in the perfect Insect. Alter this, there is a gradual diminution; the
plastic element being progressively withdrawn by the formative processes;

* Philosophical Magazine, May 1845.

COLOURLESS CORPUSCLES OF BLOOD. 135

until, in the perfect Insect, very few remain. When the wings are being
expanded, however, and are still soft, a few oat-shaped corpuscles circulate
through their vessels; but as the wings become consolidated, these corpuscles
appear to be arrested and to break down in the circulating passages ; supply-
ing, as Mr. N. thinks, the nutrient material for the completion of these struc-
tures, which subsequently undergo no change. In the perfect Insect, a differ-
ent set of corpuscles makes its appearance ; which is rather analogous to the
red corpuscles of Vertebrata. This last fact completely harmonizes with the
views already expressed ; since the formative processes are now reduced to
their lowest condition in the Insect; whilst the respiration attains its highest
grade.

157. Even in adult animals, however, variations in formative power may
be detected; which correspond with variations in the number of the Colour-
less corpuscles. Thus it has been observed by Wagner,*' that the number of
these corpuscles is always remarkably great, in the blood of well-fed Frogs
just caught in the summer season; whilst it is very small in those which have
been long kept without food, or which are examined during the winter. In
the reparation of injuries, too, which is effected in cold-blooded animals by a
process of simple growth without inflammation, it would seem that the Co-
lourless corpuscles perform an important part; as they are observed in great
numbers, and in a nearly stationary condition, in the vessels surrounding the
spot where the new tissue is being formed; apparently having the same action
as in the first development of parts altogether new, such as the toes of the
larva of the Water-Newt.

158. A remarkable confirmation of this view of the connection between the
generation of Colourless corpuscles in the Blood, and the production of Fi-
brine, is derived fiom the phenomena of Inflammation. A decided increase
in the normal proportion of Fibrine in the Blood (from 2| to 3| parts in 1000),
may probably be looked upon as the essential indication of the existence of
the Inflammatory condition. That this production of Fibrine is due to a local
change, can scarcely be doubted ; since it is frequently observed to commence,
before any constitutional symptoms manifest themselves : and it may be re-
garded, in fact, as one cause of these symptoms. Now the microscopic ob-
servations of Mr. Addisont and Dr. Williams,! made independently of each
other, have established the important fact, that a great accumulation of Colour-
less corpuscles takes place in -the vessels of an inflamed part : this seems to
be caused at first, by a determination of those already existing in the circu-
lating fluid, towards the affected spot ; but partly by an actual increase or
generation of these bodies, which appear to have the power of very rapidly
multiplying themselves. The accumulation of Colourless corpuscles maybe
easily seen, by applying irritants to the web of a Frog's foot. Mr. Addison
has noticed it in the Human subject, in blood drawn by the prick of a needle
from an inflamed pimple, the base of a boil, the skin in scarlatina, &c. And
the Author, without any knowledge of these observations, had remarked a
very obvious difference between the proportions of Colourless corpuscles, in
blood drawn from a wound in the skin of a Frog immediately upon the in-
cision being made, and in that drawn a few minutes after ; and had been led,
like the observers just quoted, to refer this difference to a determination of
Colourless corpuscles to a part irritated. The absolute increase, sometimes
to a very considerable amount, in the quantity of Colourless corpuscles in the
blood of an inflamed subject, has been verified by Mr. Gulliver and several

* [Elements of Physiology, translated by R. Willis.]

Medical Gazette, Dec. 1840; Jan. and March, 1S41.

J Medical Gazette, July, 1841 ; and Principles of Medicine, [Am. Ed., by Dr. Clymer, pp.
214, 215.]

136 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

other observers. These facts, therefore, afford strong ground for the belief,
that the production of Fibrine in the blood is closely connected with the de-
velopment of the Colourless corpuscles ; and when we consider them in con-
nection with the facts previously urged, there scarcely appears to be a rea-
sonable doubt that the elaboration of Fibrine is a consequence of this form of
cell-life, and is, in fact, its express object.

159. This view derives further confirmation from the following recent
experiment of Mr. Addison's.* " Provide six or eight slips of glass, such as
are usually employed for mounting microscopical objects ; and as many
smaller pieces. Having drawn blood from a person with rheumatic fever,
or any other inflammatory disease, place a drop of the colourless liquor san-
guinis, before it fibrillates, on each of the large slips of glass ; cover one im-
mediately with one of the smaller slips, and the others one after another at
intervals of thirty or forty seconds: then, on examining them by the micro-
scope, the first will exhibit colourless blood-corpuscles in various conditions,
and numerous white molecules distributed through a more or less copious
fibrous network ; and the last will be a tough, coherent, and very elastic
membrane, which cannot be broken to pieces nor resolved into smaller frag-
ments, however roughly or strongly the two pieces of glass be made to rub
against each other. This is a ' glaring instance' of a compact, tough, elastic,
colourless, and fibrous tissue, forming from the colourless elements of the
blood ; and the several stages of its formation may be actually seen and
determined. Numerous corpuscles may be observed, in all these prepara-
tions, to have resolved themselves, or to have fallen down into a number of
minute molecules, which are spread out over a somewhat larger area than that
occupied by the entire corpuscles ; and although still retaining a more or less
perfectly circular outline, yet refracting the light at their edges, in a manner
very different from that in which the corpuscles themselves are seen to do.
It is from these and various other larger and more irregular masses of mole-
cules or disintegrated corpuscles, that the fibrinous filaments shoot out on all
sides, as from so many centres ; or frequently the filaments are more copious
in two opposite directions."

a. A different vievv of the cause of the production of Fibrine, however, has been enter-
tained by some eminent Physiologists ; and it does not seem right to allow the opinions of
Wagner, Henle, and Wharton Jones to pass without notice, even though they appear to the
Author to be easily set aside. By these observers, the elaboration of Fibrine has been at-
tributed to the red corpuscles, and has been regarded as one, at least, of their special func-
tions. Nearly all the arguments, however, which have led us to assign this duty to the
Colourless corpuscles, tell equally against the doctrine now under consideration. — In the first
place, the contents of the Red corpuscles have no resemblance whatever to liquid Fibrine;
but are characterized by the presence of a substance altogether different: whilst, as shown
above, the Colourless corpuscles emit, on bursting, a fibrillating matter. If, then, Fibrine be
elaborated l>y the Red corpuscles, it must be by forming part of their walls: a method alto-
gether unusual. — Again, the entire absence of Red corpuscles in the blood of the lower
Invertebrata, and in that of the larva and pupa of the Insect, the small proportion in which
they are present in the blood of any Invertebrata, and their occurrence to any large amount
in the I ilc mil ui' Vrriebrata only, seem to show that they cannot be concerned in a function
so constant and essential as the elaboration of the plastic element. The number of the Red
corpuscles, as stated above, bears a regular proportion to the amount of oxygen introduced
into the system, and thus to the heat developed, and tti the activity of the Minimal functions;
but it docs not bear the .si me relation to the activity of the I'uriiMtivc processes, which take
place most energetically in a .state of functional quieseenee. — Further, although the quantity
of Fibrine is so remarkably increased in Inflammation, the number of Red corpuscles under-
goes no decided change. Such an :iirjiiientation is even compatible with a Chlorotic state of
the blood; the peculiar characteristic of which is a great diminution in the proportion of Red
eurpuscles. By such alterations, the normal proportion between the Fibrine and the Red
corpuscles, which may be stated as A : 11, may be so much altered as to become, in Inllam-

* Transactions of the Provincial Medical Association, 1843.

EPIDERMIC CELLS.

137

Fig. 31.

mation, 4 A : n ; or, in Chlorosis, A : J B. In Fever, the characteristic alteration in the con-
dition of the blood, appears to be an increase in the amount of Red corpuscles, with a. dimi-
nution in the quantity of Fibrine ; yet if a local inflammation should establish itself during
the course of a lover, the proportion of fibrine \vill rise; and this without any change in the
amount of corpuscles. — Lastly, the effect of Loss of Blood has been shown by Andral's in-
vestigations, to be a marked diminution in the number of Red corpuscles, with no decided
reduction in the quantity of Fibrine, even when this is much above its normal standard ; and
in this condition of the blood, it has been observed by Remak that the Colourless corpuscles
are very numerous.

6. Of Cells developed upon Free Surfaces.

160. Next in independence to the cells or corpuscles floating in the animal
fluids, are those which cover the free membranous surfaces of the body, and
which form the Epidermis and Epithelium. Between these two structures
there is no essential difference, either in regard to their origin, their mode of
development, their situation, or their individual history ; but there is an im-
portant difference in the purposes which they respectively serve in the eco-
nomy. They both consist of cells, which are developed from germs furnished
by the subjacent membrane, which are nourished by its vessels, and which
are after a time cast off from its free surface to be replaced by a succeeding
generation ; but the contents of the cells vary in different situations, and give
peculiar characters to the tissue. The differences, however, are not more
striking between the Epidermis, or cellular covering of the external surface,
and the Epithelium, or cellular lining of the internal cavities, than those which
exist between the different portions of the Epithelium itself. For although
the Epidermis is distinguished by its comparatively

hard, dry, horny character, whilst the Epithelium
is soft, moist, and deficient in tenacity ; yet we shall
hereafter find that, as all the Secretions of the body
are elaborated by the agency of the cells of the
latter, there must be as many varieties of endow-
ment, in these important bodies, as there are differ-
ences in the results of their action.

161. The Epidermis, — which usually forms a
thin semi-transparent pellicle, in close apposition
with the surface of the true Skin, but occasionally
presents a great increase in thickness, — consists of
a series of flattened scale-like cells; which, when
first formed, are spherical ; but which gradually dry
up, their nucleus usually remaining visible. These
form several layers ; of which the deeper can be
seen very distinctly to possess the cellular character,
whilst the external layers are scaly ; and between
these, all stages of transformation may be traced.
The outer layers are continually being thrown off
by desquamation ; and new ones are as constantly
being formed below. They would seem to origi-
nate in germs supplied by the basement-membrane,
on whose surface they make their first appearance;
and their continued development takes place at the
expense of nutriment, which they draw through
that membrane, from the subjacent vessels. The
Epidermis is not itself traversed by vessels or
nerves; but it is pierced by the excretory ducts of
the sebaceous and sweat glands, and also by the
shafts of the hairs ; being, however, at the same

12*

Vertical section of Epidermis,
from palm of the hand ; a, outer
portion, composed of flattened
scales ; 6, inner portion, consist-
ing of nucleated cells; c, tortu-
ous perspiratory tube, cut across
by the section higher up. Mag-
nified 155 diameters.

138 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

lime continuous with the epithelial linings of these. The soft layer which
lies in immediate contact with the true skin, was formerly supposed to be a
substance of distinct nature, and was described under the name of rete muco-
sian ; it has been proved by microscopic examination, however, to consist of
the same elements with the ordinary epidermis, in an early stage of their
development; and, so far from being the exclusive seat of the colour of the
skin, as was formerly supposed, it only participates with the fully-formed
epidermis in the possession of pigment-cells (§ 163). The thickness of the
Epidermis, and consequently the number of layers of which it is composed,
vary greatly in different parts; being usually found to be greatest, where there
is most pressure or friction, — as on the palms of the hands of the labouring
man, and on the soles of the feet, particularly at the heel, and the ball of the
great toe. It would seem as if the irritation of the true skin produced an
augmented determination of blood to the part, and consequently an increased
development of epidermic cells. The Epidermis covers the whole exterior of
the body, not excepting the Cornea and the Conjunctival membrane; on the
latter, however, it has more the character of an Epithelium. This continuity
is well seen in the cast skin or slough of the Snake ; in which the covering
of the front of the eye is found to be as perfectly exuviated as that of any part
of the body.

162. The Epidermis appears solely destined for the protection of the true
Skin, from the mechanical injury and the pain occasioned by the slightest
abrasion, and from the irritating influence of exposure to air and of changes
of temperature. We perceive the value of this protection, when the Epider-
mis has been accidentally removed. It is very speedily replaced, however;
the increased determination of blood to the Skin, which is the consequence of
the irritation, being favourable to the rapid production of Epidermic cells from
its surface. The peculiar character of the tissue appears to depend upon the
property possessed by its cells, of secreting horny matter into their cavity ;
and this process seems to take place at a period subsequent to the first forma-
tion of the cells. For if a thin vertical section of the Epidermis be treated
with Acetic acid, or with a strong solution of Potass, it is found that the inner
newly-formed layers are dissolved by the re-agent, whilst the outer or scaly
ones are unaffected. Recent analysis has shown, that the dense Epidermis
from the sole of the foot, and the compact Horny matter of which Nails,
Hoofs, Horns, Hair, and Wool, are composed, have the same composition;
the formula of all of them being 48 Carbon, 39 Hydrogen, 7 Nitrogen, and
17 Oxygen. It is probable that, here as elsewhere, if we could isolate the
wall of the cell from its contents, we should find the former to consist of a
proteine-compound.

163. Mingled with the Epidermic cells, we find others which secrete Co-
louring-matter instead of Horn ; these are termed Pigment-cells. They are
not readily distinguishable in the Epidermis of the fair races of mankind,
except in certain parts, such as the areola around the nipple, and in freckles,
nacvi, &c. But they are very obvious, on account of their dark hue, in the
newer layers of the Epidermis of the Negro and other coloured races; and,
like true Epidermic cells, they dry up and become flattened scales in passing
towards the surface, thus constantly remaining dispersed through its substance,
and giving it a dark tint when it is separated and held up to the light. In all
races of men, however, we find the most remarkable development of Pigment-
cells on the inner surface of the Choroid coat of the eye : where they form
several layers, known as the Pigmcntum nignnn. When examined sepa-
rately, these are found to have a polygonal form, and to have a distinct nucleus
in their interior. The black colour is given by the accumulation, within the
cell, of a number of flat, rounded or oval granules, measuring about 1-20, 000th

PIGMENT-CELLS.

139

of an inch in diameter, and a quarter as much in thickness ; these, when
separately viewed, are observed to be transparent, not black and opaque ; and

[Fig. 32.

A. Choroid Epithelium, with the cells filled with
pigment, except at a, where the nuclei are visi-
ble. The irregularity of the pigment-cells is seen.
6. Grains of pigment.

B. Pigment-cells from the substance of the Cho-
roid. A detached nucleus is seen. Magnified
320 diameters.]

Cells from Pigmentum Ni-
grum; a, pigmentary gra-
nules concealing the nu-
cleus; b. the nucleus distinct.
Magnified 410 diameters.

they exhibit an active movement when set free from the cell, and even whilst
inclosed within it. — The Pigment-cells are not always of a simple rounded or
polygonal form; they sometimes present remarkable stellate prolongations,
such as those seen in the skin of the Frog (Fig. 88) ; and occasionally, the
cells being more nearly approximated to each other, these prolongations com-
municate, so as to form a kind of network. — The Chemical nature of the Black
pigment has not yet been distinctly ascertained ; it has been shown, however,
to have a very close relation with that of the Cuttle-fish ink, or Sepia, which
derives its colour from the pigment-cells of the ink-bag; and to include a
larger proportion of carbon than most other organic substances, — every 100
parts containing 58£ of that element.

164. It cannot be doubted that the development of the Pigment-cells of
the skin is very much influenced by exposure to light ; and in this respect
there is a remarkable correspondence between Animals and Plants, — the
coloration of the latter, as is well known, being entirely due to that agent.
Thus, it is a matter of familiar experience, that the influence of light upon
the skin of many individuals, causes it to become spotted with brown freckles ;
these freckles being aggregations of brown pigment-cells, which either owe
their development to the stimulus of light, or are enabled by its agency to
perform a decided chemical transformation, which they could not otherwise
effect. In like manner, the swarthy hue, which many Europeans acquire
beneath exposure to the sun in tropical climates, is due to a development of
dark pigment-cells, and to this we usually find the greatest disposition in in-
dividuals or races, that are already of a somewhat dark complexion. The
deep blackness of the Negro skin seems dependent upon nothing else than a
similar cause, operating through successive generations (§ 80). It is well
known that the new-born infants of the negro and other dark races, do not ex-
hibit nearly the same depth of colour in their skins, as that which they present
after the lapse of a few days, when light has had time to exert its influence
upon their surface ; and further, that in those individuals who keep them-
selves during life most secluded from its influence, we observe the lightest
hue of the epidermis. Thus among the intertropical nations, the families of
Chiefs, which are not exposed to the sun in the same degree with the com-

140

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

[Fig. 34.

mon people, almost always present a lighter hue ; and in some of the islands
of the Polynesian Archipelago, bordering on the Equator, they are not darker
than the inhabitants of Southern Europe. — An occasional development of dark
pigment-cells takes place during pregnancy, in some females of the fair races;
thus it is very common to meet with an extremely dark and broad areola
round the nipple of pregnant women ; and sometimes large patches of the
cutaneous surface, on the lower part of the body especially, become almost
as dark as the skin of a Negro. — On the other hand, individuals are occasion-
ally seen with an entire deficiency of pigment-cells, or at least of their proper
secretion ; and this not merely in the skin, but in the eye ; such are termed
Albinoes ; and they are met with alike among the fair, and among the dark
races. The absence of colour usually shows itself also in the hair ; which
is almost white.

165. The Nails, like Hoof, Horn, &c., may be regarded as nothing more
than an altered form of Epidermis. When their newest and softest portions
are examined, they are found to consist of nucleated particles, resembling
those of the newer layers of Epidermis ; in the more superficial lamina?,
however, no distinct structure can be made out; but, when treated with acetic
acid, some traces of nuclei may be detected in them. The Nail is produced
from the surface of the true skin that lies beneath it, which is folded into a

groove at its root; this surface is highly vascular.
The increase in length is effected by successive
additions at the root, causing the whole nail to
shift onwards ; but as it moves, it receives ad-
ditional layers from the subjacent skin, which
increases its thickness. The nail is continuous
with the true Epidermis at every part, except
its free projecting edge ; and in the fetus, the
continuity is maintained there also.

166. The Hair, as originally consisting of
Epidermic cells, may be properly described
here ; although, when fully formed, it departs
widely (in Man at least) from the cellular type.
It has been imagined until recently, that the
Hair, in common with the other Epidermic tis-
sues, is a mere product of secretion ; its mate-
rial, which is chiefly horny matter of the same

composition with that of the Epidermis and its appendages, being elaborated
from the surface of the pulp at its base. It is not known, however, to con-
tain a distinctly organized structure ; and to be formed by the conversion of
a cellular mass at its root. The Hair originates within a follicle, which is
formed by a little depression of the Skin, and which is lined by a continua-
tion of the Epidermis. From the bottom of this follicle, there rises up a
cluster of cells, which may be regarded as an increased development of Epi-
dermic cells ; the exterior of this cluster, which is the densest part, is known
as the butt) ; whilst the softer interior is termed the pnlp. The follicle itself
is extremely vascular ; and even the bulb is reddened by minute injection,
though no distinct vessels can be traced into it. — Although the Hairs of differ-
ent animals vary considerably in the appearances they present, we may gene-
rally distinguish in them two elementary parts ; — a cortical or investing sub-
stance, of a fibrous horny texture ; and a medullary or pith-like substance,
occupying the interior. The fullest development of both substances is to be
found in the spiny Hairs of the Hedgehog, and in the quills of the Porcu-
pine ; which are but hairs on a magnified scale. The cortical substance
forms a dense horny tube, to which the firmness of the structure seems chiefly

Section of ihe skin on the end of
the finger:— The cuticle, and nail, n,
detached fromlhe cutis and matrix, m.}

STRUCTURE OF HAIR.

141

due ; whilst the medullary substance is composed of an aggregation of very
large cells, which seem not to possess any fluid contents in the part of the
hair which is completely formed. The structure of the feather of Birds is
precisely analogous ; the cortical horny tube existing alone in the quill ; but
being filled with a cellular medulla in the stem of the feather itself. In the
hair of the Mouse and other small Rodents, we see the horny tube crossed
at intervals by partitions, which are sometimes complete, sometimes only par-
tial ; these are the walls of the single or double line of cells, of which the
medullary substance is made up. In the Sable, we sometimes meet with
hairs, in which the medulla is made up of rounded cells ; whilst the cortical
substance is composed of imbricated Epidermic scales (Fig. 35, B). In some
instances, however, there is scarcely any medulla to be traced ; whilst in
other animals, as the Musk-deer (Fig. 35, A), the entire hair seems to be made
up of it.

[Fig. 36.

B.

A, hair of Musk-Deer
consisting almost entirely
of polygonal cells; B, hair
of Sable, showing large
rounded cells in its inte-
rior, covered by imbrica-
ted scales, or flattened
cells.

Bulb of a small black hair, from the scrotum, seen
in section, a. Basement membrane of the follicle, b.
Layer of epidermic cells resting upon it, and becoming
more scaly as they approach c, a layer of imbricated
cells, forming the outer lamina, or cortex, of the hair.
These imbricated cells are seen more flattened and
compressed, the higher they are traced on the bulb.
AVithin the cortex is the proper substance of the hair,
consisting at the base, where it rests on the base-
ment membrane, of small angular cells scarcely larger
than their nuclei. At d. these cells are more bulky,
and the bulb consequently thicker; there is also pig-
ment developed in many of them more or less abun-
dantly. Above d, they assume a decidedly fibrous cha-
racter, and become condensed, e. A mass of cells in
the axis of the hair, much loaded with pigment.]

167. In the Human hair, the representation of the cortical sheath of the hair
of other animals is found in a thin transparent horny film ; which is composed
of flattened cells or scales, arranged in an imbricated manner, their edges
(Fig. 36) forming delicate lines upon the surface of the hair, which are some-
times transverse, sometimes oblique, and sometimes apparently spiral (Fig.
37, A). Within this, we find a cylinder of fibrous texture ; which forms the

142

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

principal part of the shaft of the hair ; whilst the centre is frequently more
distinctly cellular. The constituent fibres of the shaft are marked out by
delicate longitudinal stripe, which may be traced in vertical sections of the
hair (Fig. 37, B.) ; but they may be still more completely demonstrated by
crushing the hair, after it has been macerated for some time in dilute acid.
In dark hairs, pigmentary granules are frequently scattered between the fibres;
but they are usually found in greater abundance in the central cells. The
Hair of Man is commonly reputed to be tubular ; but this is seldom if ever
the case, as is shown by microscopical examination of thin transverse sec-
tions (Fig. 37, c). The mistake has arisen from a misinterpretation of the
appearance of a dark band in the interior of the hair, when viewed by trans-
mitted light ; which is really due, partly to the presence of pigmentary mat-
ter in the central portion of the shaft, and partly to the refraction of light by
the cylindrical surface. — The chemical composition of Hair, as already stated,

Eg , ji.

Eft:." ;•, ,:.. :»tni i

I !

••'

Structure of Human Hair; A, external surface of the shaft, showing- the transverse striae and jagged
boundary, caused by the imbrications of the scaly cortex ; B, longitudinal section of the shaft, showing'
the fibrous character of the medullary substance, and the arrangement of the pigmentary matter; c,
transverse sections, showing the distinction between the cortical and medullary substance, and the cen-
tral collection of pigmentary matter, sometimes found in the latter. Magnified 310 diameters.

is precisely the same with that of the horny Epidermis (§ 162). Its colour-
ing matter seems related to Haematine ; it is bleached by Chlorine ; and its
hue appears to be dependent in part upon the presence of iron, which is found
in larger proportion in dark than in light hair.

168. The real nature of the different elements of the Hair is ascertained,
by examining them at its base, where they become continuous with those of
the bulb. It is then seen, that the fibres of the shaft are identical with the
cells of the bulb ; these undergoing elongation, as they are pushed upwards
towards the mouth of the follicle, by the development of additional cells be-
neath ; and being proportionally diminished in diameter. Hence the shaft of
the hair is considerably narrower than the bulb. The central part of the hair
which more distinctly exhibits the cellular character, is derived from the pulp
or internal portion of the bulb ; whose constituent cells undergo less change.
And the imbricated layer of cells, that forms its fibrous envelope, may be said
to be a prolongation of the ordinary Epidermis over the surface of the hair;
being developed from the external portion of the bulb, where it is continuous
with the epidermic lining of the follicle. — Thus we see that the whole tissue
of the Hair is derived from Epidermic cells, developed in peculiar abundance
from the base of the follicle ; some of these cells, however, retaining their
original form ; whilst others are transformed into fibres, and others converted
(like those of ordinary Epidermis) into llattened cells. They all have the
power, however, of drawing horny matter into their cavities ; and resist the

STRUCTURE OF HAIR. EPITHELIUM. 143

solvent power of chemical re-agents, except when these are employed in un-
usual strength. — The Hair is constantly undergoing elongation, by the addi-
tion of new substance at its base ; and the part which has been once fully
formed, and which has emerged from the follicle, usually undergoes no sub-
sequent alteration. There is evidence, however, that it may be affected by
changes at its base, the effect of which is propagated along its whole extent :
thus, it is well known that cases are not unfrequent, in which, under the in-
fluence of strong mental emotion, the whole of the hair has been turned to
gray, or even to a silvery white, in the course of a single night; a change
which can scarcely be accounted for in any other way thlin by supposing that
a fluid, capable of chemically affecting the colour, is secreted at the base of
the hair, and transmitted by imbibition through the medullary substance to
the opposite extremity. Another evidence of their retention of a degree of
vitality, is found in the fact of Hairs having a tendency to become pointed,
after having been cut short off. In the hairs of some animals (particularly
the whiskers of the Seal and other Carnivora) the base is hollow, and con-
tains a true papilla, or elevation of the cutis, furnished with nerves and blood-
vessels ; this is separated by a layer of basement-membrane from the proper
tissue of the Hair. In such cases, there is bleeding from the stumps of the
hairs, when they are shaved off close to the skin. There is an approach to
this papillary structure in Man; and it may perhaps be an abnormal develop-
ment of it, which occasions the hair to bleed in the disease termed Plica Po-
lonica. The hair of individuals affected with it is further disposed to split
into fibres, often at a considerable distance from the roots, and to exude a
glutinous substance ; these two causes unite in occasioning that peculiar mat-
ting of the hair, which has given origin to the name of the disease.

169. The layer of cells covering the internal free surfaces of the body, is
known under the name of Epithelium. In some instances it appears to serve
to the subjacent membranes, like the Epidermis to the Cutis, merely as a pro-
tection; whilst in other cases, as we shall presently find, it answers purposes
of far greater importance. It has long been known that the epidermic layer
might be traced continuously from the lips to the mucous membrane of the
mouth, and thence down the o?sophagus into the stomach ; and that, in the
strong muscular stomach or gizzard of the granivorous birds, it becomes quite
a firm horny lining. But it has been only since the application of the Mi-
croscope to this investigation, that a continuous layer of cells has been traced,
not merely along the whole surface of the mucous membrane lining the ali-
mentary canal, but likewise along the free surfaces of all other Mucous Mem-
branes, with their prolongations into follicles and glands ; as well as on the
Serous and Synovial membranes, and the lining membrane of the heart, blood-
vessels, and absorbents.

170. The forms presented by the Epithelium cells are various. The two
chief, however, are the tesselated, forming the pavement-epithelium; and the
cylindrical, forming the cylinder-epithelium. — The Tesselated Epithelium
covers the serous and synovial membranes, the lining membrane of the blood-
vessels, and the ultimate follicles or tubuli of most glandular structures con-
nected with the skin or mucous membranes, as also the mucous membranes
themselves, where the cylinder-epithelium does not exist. The cells compos-
ing it are usually flattened and polygonal (Fig. 38, A.) so as to come into con-
tact with each other at their edges, like the pieces of a tesselated pavement
(Fig. 30) ; but they sometimes retain their rounded or oval form, and are se-
parated from each other by considerable interstices. (Fig. 38, B.) This last
form seems to be the commonest, where the cells are most actively renewed,
so that they have not time (so to speak) to be developed into a continuous
stratum. The number of layers is commonly small; and sometimes there is

144

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

only a single one. — The Cylinder-Epithelium is very differently constituted.
Its component cells are cylinders, which are arranged side by side ; one extre-

Fi". 38.

A.

B.

Separated Epithelium cells, a, with
nuclei, i, and nucleoli, c, from mucous
membrane of mouth.

Pavement-Epithelium of
the Mucous Membrane of the
smaller bronchial tubes; a,
nuclei with double nucleoli.

mity of each cylinder resting upon the basement-membrane, whilst the other
forms part of the free surface. The perfect cylindrical form is only shown,
however, when the surface on which the cylinders rest is flat or nearly so.
When it is convex, the lower ends or basements of the cells are of much smaller
diameter than the upper or free extremities ; and thus each has the form of a
truncated cone, rather than of a cylinder ; as is well seen on the cells covering
the villi of the intestinal canal. (Fig. 45.) On the other hand, where the cy-
linder-epithelium lies upon a concave surface, the free extremities of the cells
may be smaller than those which are attached. Sometimes each cylinder is
formed from more than one cell, as is shown by its containing two or more
nuclei ; although its cavity seems to be continuous from end to end. And
occasionally the cylinders arise by stalk-like prolongations, from a pavement-
epithelium beneath. The two forms of Epithelium pass into one another at
various points; and various transition-forms are then seen, — the tesselated
scales appearing to rise more and more from the surface, until they project as
long-stalked cells, truncated cones, or cylinders. The Cylinder-Epithelium
covers the mucous membrane of the alimentary canal, from the cardiac orifice
downwards ; it is found also in the larger ducts of the glands which open into
it, or upon the external surface — such as the ductus choledochus, the salivary
ducts, those of the prostate and Cowper's glands, the vas deferens, and urethra.
In all these situations, it comes into connection with the Tesselated Epithe-
lium, which usually lines the more delicate canals of the glands, as well as
their terminal follicles.

171. Both these principal forms of Epithelial cells are frequently observed
to be fringed at their free margins with delicate filaments, which are termed
Cllio ; [from cilium, an eyelash,] and these, although of extreme minuteness,
are organs of great importance in the animal economy, through the extraordi-
nary motor power with which they are endowed. The form of the Ciliary

filaments is usually a little flattened, and ta-
pering gradually from the base to the point.
Their size is extremely variable; the largest
that have been observed being about 1 -500th
of an inch in length, and the smallest about
1-13, 000th. When in motion, each fila-
ment appears to bend from its root to its
point, returning again to its original state,
like the stalks of corn when depressed by
the wind ; and when a number are aflected
in succession with this motion, the appear-
ance of progressive waves following one

39.

I

Vibratile or ciliated Kpillicliutn ; n. nu-
cleated cells, resting on their smaller ex-
tremities; 6, cilia.

EPITHELIUM; CILIARY MOVEMENT.

145

another is produced, as when a corn-field is agitated by frequent gusts.
When the Ciliary motion is taking place in full activir^, however, nothing
whatever can be distinguished, but the whirl of particles in the surrounding
fluid ; and it is only when the rate of movement slackens, that the shape
and size of the Cilia, and the manner in which their stroke is made, can be
clearly seen. The motion of the Cilia is not only quite independent (in all
the higher animals at least) of the will of the animal, but is also independent
even of the life of the rest of the body ; being seen after the death of the
animal ; and proceeding with perfect regularity in parts separated from the
body. The isolated epithelium cells have been seen to swim about actively
in water, by the agency of their cilia, for some hours after they have been de-
tached from the mucous surface of the nose ; and the Ciliary movement has
been seen fifteen days after death in the body of a Tortoise, in which putre-
faction was far advanced. In the gills of the River-Mussel, which are among
the best objects for the study of it, the movement endures with similar per-
tinacity.

172. The purpose of this Ciliary movement is obviously to propel fluids
over the surface on which it takes place ; and it is consequently limited in
the higher animals to the internal surfaces of the body, and always takes
place in the direction of the outlets, towards which it aids in propelling the
various products of secretion. The case is different, however, among animals
of the lower classes, especially those inhabiting the water. Thus the external
surface of the gills of Fishes, Tadpoles, &c., is furnished with cilia; the con-
tinual movement of which renews the water in contact with them, and thus
promotes the aeration of the blood. In the lower Mollusca, and in many
Zoophytes, which pass their lives rooted to one spot, the motion of the Cilia
serves not merely to produce currents for respiration, but likewise to draw
into the mouth the minute particles that serve as food. [Fig. 107, 2, 5.]
And in the free-moving Animalcules,

of various kinds, the Cilia are the [Fig. 40.

sole instruments which they possess,
not merely for producing those cur-
rents in the water, which may bring
them the requisite supply of air and
food, but also for propelling their
own bodies through the liquid ele-
ment. This is the case, too, with
many larger animals of the class
Acalepha (Jelly fish), which move
through the water, sometimes with
great activity, by the combined ac-
tion of the vast numbers of cilia, that
clothe the margins of their external
surfaces. In these latter cases, it E^mP'«of cnia; i, portionof a barof the g.iiof

•c i /~ci- sea-mussel, Mytilus eaulis, showing cilia at rest

biliary move- and in motion . 2, ciliated epithelium particles from the
frog's mouth; 3. ciliated epithelium particles from in-
ner surface of human membrana tympani ; 4, ditto,

ment were more under the control
of the will of the animal, than where

ditto, from the human bronchial mucous membrane •
5, Leucophrys patula, a polygastric infusory animal-

it is concerned only in the organic

functions. In what Way the will Cll|e; ,0 Bhow its surface covered With cilia, and the
Can influence it, however, it does mouth surrounded by them.]

not seem easy to say ; since the

ciliated epithelium-cells appear to be perfectly disconnected from the surface
on which they lie, and cannot, therefore, receive any direct influence from
their nerves. Of the cause of the movement of the Cilia themselves, no ac-
count can be given ; they are usually far too small to contain even the minutest
13

146

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

fibrillae, of muscle ; and we must regard them as being, like those fibrillae,
organs sui generis, Saving their own peculiar endowment, — which is, in the
higher animals at least, that of continuing in ceaseless vibration, during the
whole term of the life of the cells to which they are attached.

[That this movement is truly molecular and independent of muscular influence and of
both the vascular and nervous systems has been proved by experiment. For, besides continu-
ing to manifest itself in a single particle for many hours after it has been isolated from
the rest of the system, a ciliated surface continues unaffected in its movements though the
supply of blood to the subjacent tissues be completely cut off. Neither do hydrocyanic
acid, opium, strychnine, belladonna, substances which affect powerfully the nervous sys-
tem, exert any influence on ciliary motion ; this phenomenon continuing in the bodies of
animals killed by these poisons. And lastly, shocks of electricity passed through the ciliated
parts, even the removal of the brain and spinal marrow in frogs, extinguishing as it does
muscular motion, do not destroy the action of cilia. — 'M. C.]

The length of time during which the Ciliary movement continues after the
general death of the body, is much less in the warm-blooded than in the cold-
blooded animals; and in this respect it corresponds with the degree of per-
sistence of muscular irritability, and of other vital endowments.

173. A layer of Ciliated epithelium, of the Tesselated form, is found upon
the delicate pia mater which lines the cerebral cavities, not even excepting the
mfundibulum and the aqueduct of Sylvius ; and it is also found in the termi-
nal ramifications of the bronchial tubes. A Cylindrical epithelium furnished
with Cilia is found lining the nasal cavities, the frontal sinuses, the maxillary
antra, the lachrymal ducts and sac, the posterior surface of the velum pendu-
lum palati, and fauces, the Eustachian tube, the larynx, trachea, and bronchi
to their finest divisions, the upper portion of the vagina, the uterus, and the
Fallopian tubes. The function of the Cilia in all these cases appears to be
the same; that of propelling the secretions, which would otherwise accumu-
late on these membranes, towards the exterior orifices, whence they may be
carried off.

174. The Epithelium-cells, like the scales of the Epidermis, are continually
being cast off and renewed from the subjacent surface; but the rapidity of
this renewing process varies according to the particular function of the part.
Thus we shall hereafter find it to be greater on the Mucous Membranes,
which are actively engaged in the introduction of nutrient materials and in the
separation of effete matter, than it is on the Serous surfaces, which are com-
paratively inert. The epithelial cells that cover the plane surfaces, seem to
be developed from granular germs, scattered through the subjacent basement
membrane ; but it is different in regard to the cells of the glandular follicles,
which usually seem to originate in a single " germinal spot," composed of a
mass of granules, at the blind extremity of the follicles. In fact, each of these
follicles may be regarded as a parent-cell, which was closed at an earlier
period of its existence, and which, even after it has ruptured and given exit
to its contents, goes on forming a succession of new generations from its

nucleus. The accompanying figure represents
two follicles of the liver of the common Crab,
which are seen to be filled witli secreting cells ;
and it is evident, from a comparison of the sizes
of the cells at different parts, that they originate
at the blind extremity of the follicle, where there
is a germinal spot ; and that, as they recede
from that point and approach the outlet of the
follicle, they gradually increase in size and be-
come filled with their characteristic secretion ; be-
ing at the same time pushed onwards towards

Fig. 41.

Two follicles from the liver of Car-
einns mrenas (Common Crnli), with
their contained secreting cells.

SECRETING CELLS. SEROUS AND SYNOVIAL MEMBRANES. 147

the outlet, by the continual new growth of cells at the germinal spot.* — It is
by the continual growth and exuviation of the cells which line the glandular
follicles, that the various products of Secretion are separated from the blood ;
and it is in cells occupying a similar position, that the Spermatozoa or Repro-
ductive particles are developed (Plate I., Fig. 18). In each case, the growth
of the cell, and the nature of its product, depend upon its own peculiar
vital properties ; and it is a curious fact that the seminal cells, in which the
Spermatozoa are formed, are ejected from the gland in the Decapod Crusta-
ceous animals, not only before they have burst and set free the Spermatozoa,
but even long before the development of the Spermatozoa in their interior is
completed, — the process being perfected, after the cells have been deposited
in the generative passages of the female.t

7. Of the Compound Membrano-Fibrous Tissues.

175. Having now considered the Elementary components of the Tissues
of the Human body, — namely, Membranes, Fibres, and Cells, — we proceed
to notice certain structures, in which these elements are united in their sim-
plest form ; and, in the first place, those termed Serous and Synoviai Mem-
branes. AVhen examined with the Microscope, their free surface is found to
be covered with a single layer of Pavement-Epithelium, which lies on a con-
tinuous sheet of Basement-Membrane. Beneath this last is a layer of con-
densed Areolar tissue, which constitutes the chief thickness of the membrane,
confers upon it its strength and elasticity ; this gradually passes into that
laxer variety, by which the membrane is attached to the parts it lines, and
which is commonly known as the subserous tissue. The yellow fibrous
element enters largely into the composition of the membrane itself; and its
filaments interlace into a beautiful network, which confers upon it equal elas-
ticity in every direction. The membrane is traversed by blood-vessels, nerves,
and lymphatics, in varying proportions. The Serous and Synoviai mem-
branes form, as is well known, closed sacs, which contain a greater or less
proportion of fluid. The liquid effused from the Serous membranes is nearly
the same with the Serum of the blood; containing as much as 7 or 8 per cent,
of albumen and salts; and being distinctly alkaline, from the presence of
carbonate or albuminate of soda. There is no reason for regarding it in any
other light, than as a simple product of transudation. The fluid contained
in the Synoviai capsules, and in the Bursae Mucosae, may be considered as
serum with from 6 to 10 per cent, of additional albumen ; it shows an alka-
line reaction. :{; The fluid of Dropsy (at least in some forms of this disease)
contains in addition urea, and cholesterine suspended in fine plates; also
(according to Dr. Kane) stearine and elaine.

176. The general term Mucous Membrane may be applied to that great
system of membranous expansions, which forms the external tegument, or
Skin, — the lining of the internal cavities whose walls are continuous with it,
or Mucous Membrane proper, — and the prolongations of this into the secre-
ting organs, forming the tubes and follicles of the Glands. These all consist,
as Mr. Bowman has justly remarked, § "of certain elements, which the
Anatomist may detect and discriminate; some of them being essential, others
appended or superadded : and the broad characteristic distinctions between

* Goodsir, in Anatomical and Pathological Observations, Chap. v.

f Op. Cit. p. 39.

J This is probably a true secretion, formed by the agency of the epithelium-cells that cover
certain delicate highly-vascular fringe-like projections, which hang down into the synovial
capsules.

§ Cyclopaedia of Anatomy and Physiology, vol. iii. p. 485.

148

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

these structures, appreciable to ordinary sense — as well as the innumerable
gradations by which they everywhere blend insensibly with one another, —
are solely due to various degrees and kinds of modification wrought in the
form, quantity, and properties of these respective elementary parts." — The
Mucous Membrane may be said, like the Serous, to consist of three chief
parts, — the epithelium or epidermis covering its free surface, — the subjacent
basement-membrane, — and the areolar tissue, with its vessels, nerves, &c.,
which forms the thickness of the membrane, and connects it to the adjacent
parts. Of the Epithelium and Epidermis, a general description has been
given in the preceding Section. The Basement- Membrane may be fre-
quently demonstrated with very little trouble, in the tubuli of the glands,
especially the kidney ; which are but very slightly adherent, by their exter-
nal surface, to the surrounding tissue. Its existence on the Skin, and on
many parts of the proper Mucous Membrane, has not yet been fully proved ;
but there can be no reasonable doubt of its continuity in these situations. —
These two elements may be regarded as the essential constituents of Mucous
membrane ; which is thus found to be, strictly speaking, extra-vascular. Its
difference from Serous Membrane must be considered, therefore, as depend-
ing rather upon its arrangement, and upon the peculiar secretion of its epithe-
lium-cells, than upon any decided anatomical character.

177. The tissues appended to these elements, and less essential to the
character of Mucous Membrane, are Capillary Blood-vessels, Absorbents,

Fis. 43.

Distribution of Capillaries at the sur-
face of the skin of the finger.

Distribution of Capillaries in the
Villi of the Intestine.

Nerves, and Areolar tissue. The former are almost everywhere abundant;
in the Skin they seem chiefly destined to supply the nervous papilla3, and
thus minister to its acute sensibility ; whilst in the Mucous Membrane
of the Alimentary canal, they seem more concerned in the functions of Ab-
sorption and Secretion ; and in the Glandular organs, they supply the mate-
rials for the last-named process. The Absorb-
ents are most abundant, as Lymphatics, in the
Skin ; and as Lacteals, in the Mucous Mem-
brane of the first part of the Intestinal canal;
but the Lymphatics are also largely distributed
through some of the Glandular organs. The
Skin is the only part of this system, which is
largely supplied with Nerves ; except the Con-
junctival Membrane, and the Mucous Mem-
brane of the Nose: hence the sensibility of this
structure is usually low, although its import-
ance in the organic functions is so great. The
Areolar tissue of Mucous Membranes usually
makes up the greatest part of their thickness ; and is so distinct from the sub-
jacent layers, as to be readily separable from them. It differs not, however,

Distribution of Capillaries around
follicles of Mucous Membrane.

STRUCTURE AND OFFICES OF MUCOUS MEMBRANE.

149

in any important particular, from the same tissue elsewhere ; and the white
and the yellow fibrous elements may be detected in it, in varying propor-
tions, in different parts, — the latter being especially abundant in the Skin and
the Lungs, which owe to it their peculiar elasticity. Hence the Mucous
Membranes for the most part yield Gelatine, on being boiled. There is some
reason to believe, that the Skin also contains non-striated muscular fibres
scattered through it. — The regeneration of all the forms of Mucous Mem-
brane, after loss of substance by disease or injury, is very complete, and takes
place with considerable rapidity.

178. The essential character of the Mucous Membranes, in regard alike to
their offices and their arrangement, is altogether different from that of the
Serous and Synovial membranes. For, whilst the latter form shut sacs,
whose contents are destined to undergo little change, the former either cover
the external surface of the body, or line tubes and cavities in its interior,
which have free outward communications; and they thus constitute the me-
dium, through which all the changes are effected, that take place between the
living organism and the external world. Thus, in the gastro-intestinal mucous
membrane, we find a provision for reducing the food, by means of a solvent
fluid poured out from its follicles; whilst the villi, or root-like filaments,
which are closely set upon the surface of that same membrane, are specially
adapted to absorb the nutrient materials thus reduced to the liquid state. This
same membrane, at its lower part, constitutes an outlet through which are cast
out, not merely the indigestible residuum of the food, but also the excretions
from numerous minute glandule in the intestinal wall, which result from the

Fig. 45.

Diagram of the structure of an involuted Mucous Membrane, showing the continuation of its elements
in the follicles and villi; F, F, two follicles; b, basement membrane ; c, submucous tissue; e, epithelium ;
v. vascular layer ; n, nerve; v, villus, covered with epithelium; v', villus whose epithelium has been shed.

decomposition of the tissues, and which must be separated and cast forth from
them to prevent further decay. Again, the bronchio-pulmonary mucous mem-
brane serves for the introduction of oxygen from the air, and for the exhala-
tion of water and carbonic acid. The mucous membranes prolonged into the

13*

150 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

interior of the various glands, are the instruments by which their respective
products are eliminated from the blood. And lastly, the Skin is concerned
in two great classes of changes; the excretion of various matters from its
surface, and from the glandulse in its substance; and the reception of impres-
sions upon the nerves, with which it is so copiously supplied.

179. The character of the secretions formed by the Mucous Membranes,
is different in almost every part; and is dependent, as will be shown here-
after, upon the properties of the Epithelium-cells which cover them. These
cells, instead of forming a comparatively permanent stratum, like that which
covers the surface of serous membranes, are in a state of continual change
and renewal; the older layers falling off, whilst new ones are produced in
immediate contact with the subjacent membrane, — and this, not merely on its
simple plane surfaces, but on its prolongations, whether these form the cover-
ings of villi, or the lining of follicles. The purpose of the cells which form
the Epidermis, is simply to protect the sensitive surface of the true skin; and
these cells have the power of drawing a horny matter into their interior. On
the other hand, the Epithelium cells of the ultimate tubuli or vesicles of glands,
contain the substances which characterize the secretions of those glands. It
is chiefly on the bronchio-pulmonary and gastro-intestinal mucous membranes,
that we meet with the peculiar secretion termed Mucus ; which appears to be
expressly formed to shield them from the irritation they would suffer through
the contact of air, or of solids or liquids. This secretion is also found on
the lining membrane of the larger excretory ducts of most of the glands; and
it is mixed, in greater or less amount, with most of the secretions discharged
by them. It is found also upon the lining membrane of the gall-bladder,
and of the urinary bladder. When these membranes are in a state of unusual
irritation, the amount of mucus which they discharge is very considerable ;
but it ordinarily forms an extremely thin layer. The characters of Mucus,
obtained from various sources, are by no means invariable. In general, how-
ever, it may be described as a fluid of peculiar viscidity, either colourless or
slightly yellow, transparent or nearly so, incapable of mixing with water, and
sinking in it, except when buoyed up by bubbles entangled in its mass,
which is commonly the case with the bronchial and nasal mucus. This
fluid contains from 4£ to 65 per cent, of solid matter, of which a small part
consists of salts resembling those of the blood : whilst the chief organic con-
stituent is a substance termed Mil tin, to which the characteristic properties of
the secretion are due. This appears to be an albuminous compound, altered
by the action of an alkali ; for as Dr. Babington has shown, any albuminous
fluid may be made to present the peculiar viscidity of mucus, by treating it
Avith liquor potassae. That the mucin of Mucus is held in solution by an
alkali, appears from this, that it is readily precipitated by acids, which neu-
tralize the base ; and that a sort of faint coagulation may be induced even by
water, which withdraws the base from it. When Mucus is examined with
the Microscope, it is found to contain numerous epithelium-scales (or flattened
cells) ; together with round granular corpuscles, considerably larger than
those of the blood, and closely resembling the nuclei of the epithelium-cells,
which are commonly termed mucus-corpuscles. In the more opaque mucus,
discharged from membranes in a state of irritation or inflammation, these cor-
puscles are present in greatly-increased amount; and cells are often developed
around them.

8. Of Simple Isolated Cells, forming Solid Tissues by their Aggregation.

180. We now proceed to a class of Cells, which are equally independent
of each other, which begin and end their lives as cells without undergoing any

PERSISTENT CELLULAR PARENCHYMA. PLACENTAL CELLS.

151

transformation, but which form part of the substance of the fabric, instead of
lying upon its free surfaces and being continually cast oft' from them. Still
their individual history is much the same as that of the cells already noticed ;
and they differ chiefly in regard to the destination of their products. There
are many animals, in which such aggregations of cells make up a much larger
part of the fabric, than they do in Man ; and this in consequence of their re-
taining more of the embryonic type of structure in their adult condition.
Thus in the Myxinoid family of Fishes, there is no true Vertebral column :
but its place is supplied by a gelatinous tube, termed the chorda dorsalis ;
which consists of nucleated cellular tissue, and which is precisely analogous
to the structure occupying the same position in the early embryo of higher
animals. In the Short Sunfish, a corresponding form of tissue forms a thick
covering to the body, replacing the true skin. And in the Lancelot (a little
Fish which is deficient in so many of the characters of the Vertebrated di-
vision, that many naturalists have doubted its right to a place in the class), a
considerable portion of the fabric is made up of a like cellular parenchyma.

181. The first group of this class deserving a separate notice, is that which
effects the introduction of aliment into the body; — of those kinds of aliment,
at least, which are not received in solution by any more direct means. These
cells (first pointed out by Mr. J. Goodsir) form a cluster at the extremity of
each of the villi of the intestinal tube ; the origin of the lacteal being lost in
the midst of it. If examined whilst the absorbent process is going on, they
are found to be turgfid with a milky fluid, which is evidently the same with
that of the lacteals ; and to have a diameter of from l-2000th to l-1000th of
an inch (Fig. 46, A). In the intervals of the digestive process, the extremities
of the villi are comparatively flaccid : and instead of cells, they show merely

Fig. 46.

Extremity of intestinal villus; seen at A, during absorption, and showing absorbent cells and lacteal
trunks, distended with chyle ; at B, during interval of digestion, showing peripheral network of lacteals,
with granular germs of absorbent cells, as yet undeveloped, lying between them.

a collection of granular germs (Fig. 46, b). These begin to develope them-
selves, as soon as the food has been dissolved in the stomach and transmitted
to the intestine ; and their development goes on so long as they are surrounded
with nutrient matter. The cells grow, select, absorb, and prepare the nu-
tritious matter, by making it a part of themselves ; and, when their work is
accomplished, they deliver it to the lacteals by their own rupture or deliques-
cence,— at the same time, it is probable, setting free the germs, from which a
new generation maybe developed, when the next supply of chyle is prepared.
182. Although the mucous membrane of the intestinal tube is the only
channel, through which insoluble nutriment can be absorbed in the completely-
formed Mammal, and the only situation, therefore, in which we meet with
these absorbent cells, there are other situations, in which similar cells perform
analogous duties in the embryo. Thus, the Chick derives it nutriment, whilst
in the egg, from the substance of the yolk, by absorption through the blood-
vessels, spread out in the vascular layer of the germinal membrane that sur-
rounds it ; which vessels answer to the blood-vessels and lacteals of the per-

152

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Fig. 47.

manent digestive cavity, and are raised into folds or villi, as the contents of
the yolk-bag are diminished. Now the ends of the vessels are separated
from the fluid contents of the yolk-bag; by a layer of cells, which is filled
with matter of a yellow-colour; and which seems to have for its office, to
select and prepare the materials supplied by the yolk, for being received into
the absorbent vessels. In like manner, the embryo of the Mammal is nou-
rished, up to the time of its birth, through the medium of its umbilical ves-
sels ; the ramifications of which form tufts, that dip down (as it were) into
the maternal blood, and receive from it the materials destined for the nutrition
of the fetus ; besides effecting the aeration of the blood of the latter, by
exposing it to the more oxygenated blood of its mother. Now around the
capillary loop of the fetal tuft there is a layer of cells, closely resembling the
absorbent cells of the villi ; and these are inclosed in a cap of basement-mem-
brane, which completes the fetal portion of the tuft, and renders it comparable,
in all essential respects, to the intestinal villus. It is again surrounded, however,
by another layer of membrane and of cells, belonging to the maternal sys-
tem; the derivation of which will be explained hereafter (Chap. XVII).

183. The cells which make up the parenchyma of the Liver in the higher
animals, seem to be developed under conditions somewhat similar. In the
Invertebrata, the Liver is constructed upon the type of the glands in general ;
its secreting cells being developed as an epithelium upon the inner wall of the
hepatic ducts. This does not appear to be the case, however, in Man and the
Mammalia : the substance of whose liver is made up of an aggregation of
cells, which lie — so far as can be ascertained — upon the
outside of the terminal ramifications of the hepatic ducts.
That these cells are the efficient instruments in the secre-
ting process, is evident from the nature of their contents,
which consist of biliary matter with oil globules. Their
diameter is usually from 1-1 500th to 1 -200th of an inch ;
and they generally contain a very distinct nucleus. Their
connexion with the secreting process is further marked by
the fact, that, in some instances in which the bile has not
been eliminated, and death has been the result, Microscopic
examination has proved that the hepatic cells were either
very imperfectly formed or were almost entirely deficient.
Further, in cases of Fatty Liver, the cells have been found to contain an un-
usual amount of Adipose matter.

184. The Fat-cells, of which Adipose tissue
is composed, also permanently exhibit the original
type of structure in its simplest form. This tis-
sue is usually diffused over the whole body, filling
up interstices, and forming a kind of pad or
cushion for the support of moveable parts. Even
in cases of great emaciation, some Fat is always
left ; especially at the base of the heart, around
the origin of the large vessels ; in the orbit of the
eye ; in the neighbourhood of the kidney ; in the
interior of the bones ; and within the spinal ca-
nal, between the periosteum and the dura mater.
The Fat Cells are usually spherical or spheroidal ;
Fat vesicles, assuming the poly- sometimes, however, when closely pressed toge-
hedrai form from pressure against ther without the intervention of any intercellular

one another. The capillary ves- gubstance? they become polyhedral. The nucleus

sels are not represented.— From . ,f . . , ,

the omentnm; magnified about 300 1S 11Ot alwayS .tO be distinguished ;— perhaps in

Secreting Cells of
Human Liver; a, nu-
cleus; fc, nucleus ; c,
oil-particles.

[Fig. 48.

diameters.]

consequence of its having passed to the interior of

FAT CELLS; COMPOSITION AND USES OF FAT.

153

Fig. 49.

the cell ; it has been seen, however, in the fat-cells of the embryo. The dia-
meter of the greater number of fat-cells, is between l-300th and l-600th of
an inch ; but larger and smaller sizes are frequently to be met with. These
bodies frequently present themselves in an isolated condition, dispersed among
the meshes of Areolar tissue ; but when they are aggregated so as to form
masses of fat, they are first collected into little lobular clusters, each of which
lias a delicate membranous invest-
ment; and these are again united into
larger clusters, visible to the naked
eye. The aggregation of these often
forms masses of considerable size ;
the component parts being held toge-
ther by Areolar tissue, and also by the
blood-vessels which penetrate them,
and which ramify minutely among
them, forming a capillary network,
not only upon the surface of the
smallest lobules, but even (it would
appear) between their contained fat-
cells. In some forms of Adipose tis-
sue, such as the marrow of bones, it

would seem that very little areolar tissue exists, or that it is even entirely
absent; and here the capillary plexus forms the principal bond of union be-
tween the fat-cells. No lymphatics have been detected in Adipose tissue ;
and it would seem to be equally destitute of nerves, excepting such as are
passing through it on their way to other textures ; — thus accounting for the
known i'actof its being insensible, except when those trunks are injured.

[Fig. 50.

Cells of Adipose Tissue ; magnified 135 diameters.

Blood-vessels of Fat; 1, minute flattened fat-lobule, in which the vessels only are represented ; 3, the
terminal artery ; 4, the primitive vein ; 5, the fat vesicles of one border of the lobule, separately repre-
sented,—magnified 100 diameters: 2. plan of the arrangement of the capillaries on the exterior of the
vesicles,— more highly magnified.]

185. The consistency of the substance contained in the Fat-vesicles, varies
in different animals, according to the proportions of the organic elements, that
enter into its composition. These elements are known under the names of
Stearine, Margarine, and Oleine: the two former, which are solid when sepa-

154 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

[Fig- 51. rate, being dissolved in the latter, at the ordinary

temperature of the body. That the thick oil thus
formed does not escape from the fat-cells during
life, may be attributed to the moistening of their
-2 walls by the aqueous fluid circulating through the
vessels. In all fixed oils, which are fluid at com-
mon temperatures, a portion of the solid constitu-
ents of fat exists ; these may be separated by ex-
Fat vesicles from an emacia. posure to cold, which congeals them, leaving the
ted subject; i, i, the cell-mem- Oleine fluid. All these substances are regarded
brane; 2,2,2, the solid portion by chemists in the light of salts ; being compounds
collected as a star-hke mass, of ac[^s — the Stearic, Margaric, and Oleic — with

with the elaine in connection a common base? to which from its sweetish taste,
with it, but nor. filling the cell. 1 , r r~ii • i

the name of UJycerme has been given.

a. Stearine is the essential constituent of nearly all solid fats, and preponderates in propor-
tion to their consistence. It exists largely in mutton-suet ; from this it may be obtained by
the action of ether, which takes up all the oily matter. It is crystalline, like spermaceti ;
it is not at all greasy between the fingers, and melts at about 130°. It is insoluble in water,
and in cold alcohol and ether; but it dissolves in boiling alcohol or ether, crystallizing as it
cools. Stearic acid (the substance of which the slearine candles are composed) may be sepa-
rated, by causing it to combine with a stronger base, such as lime or potash, and then setting
it free from this by a stronger acid. It crystallizes in milk-white needles; is soluble in its
own weight of cold alcohol, and in all proportions at a boiling heat; and fuses at about 158°.
Its acid powers are sufficient to decompose the alkaline carbonates. — Margarine exists in
small quantity, along with Stearine, with most fats ; but it is the principal solid constituent
of Human fat, which in this respect resembles olive oil rather than the other animal fats. It
corresponds with Stearine in many of its properties ; but it is much more soluble in alcohol
and ether; and it melts at 116°. Margaric acid closely resembles stearic acid in most of its
properties; but it is more soluble in cold alcohol; and has a lower melting-point, viz., 140°,
or thereabouts. It may be procured from stearic acid, by subjecting the latter to a dry dis-
tillation.— Oleine exists in small quantity in the various solid fats ; but it constitutes the great
mass of the liquid fixed oils. The tendency of these to solidification by cold, depends upon
the proportion of Stearine or margarine they may contain ; for oleine itself remains fluid
at the zero of Fahrenheit's thermometer. It is soluble in cold ether, from which it can only
be separated by the evaporation of the latter. Oleic acid much resembles oleine in physical
characters, being colourless, lighter than water, and not prone to solidify ; but it has a dis-
tinct acid reaction, and a sharp taste, and is miscible with cold alcohol in all proportions. —
Glycerine, the base of all the fatty acids, may be obtained from any fatty matter, by saponi-
fying it with an alkaline base, by which this compound is set free. It cannot be obtained
in a solid form, but may be brought to the consistence of a thick syrup. It dissolves in
water and alcohol; but is insoluble in ether. It has a sweetish taste, whence its name is
derived ; and it is remarkable far its solvent powers, which are scarcely inferior to those of
water. — The following table shows the atomic composition of the fatty acids, and of their
base.

Stearic Acid .... 68 Carbon, 66 Hydrogen, 5 Oxygen.

Margaric Acid ... 68 Carbon, 66 Hydrogen, 6 Oxygen.

Oleic Acid .... 44 Carbon, 39 Hydrogen, 4 Oxygen.

Glycerine 6 Carbon, 8 Hydrogen, 6 Oxygen.

The following results of the ultimate analysis of different kind of Fat, show the close
correspondence in their composition ; and at the same time make apparent the very large
proportion of carbon which they all contain.

Hog's Lard. Mutton Fat. Human Fat.

Carbon 79-098 78-996 79-000

Hydrogen .... 11-146 11-700 11-4 1C.

Oxygen .... 9-756 9'304 9-584

100-000 100-000 100-000

186. Besides the support, combined with facility of movement, which Fat
affords to the moving parts of the body, it answers the important purpose of
assisting in the retention of the animal temperature, by its non-conducting
power; and the still more important object, of serving as a kind «f reservoir
of combustible matter against the time of need. Herbivorous animals, whose

STRUCTURE AND COMPOSITION OF CARTILAGE.

155

52.

food is scanty during the winter, usually exhibit a strong tendency to such an
accumulation, during the latter part of the summer, when their food is most
rich and abundant ; and the store thus laid up is consumed during the winter.
This is particularly evident in the hybernating Mammalia, which take little or
no food during their seclusion. Fat appears to be deposited, only where there
is an excess, in the alimentary matter introduced into the body, of non-azo-
tized compounds which may be converted into it. But the ingestion of a large
quantity of these in the food, is by no means sufficient for the production of
Fat ; for they may not be absorbed into the vessels ; and, if absorbed, there
may be a want of power to generate Adipose tissue, — so that they would ac-
cumulate injuriously in the blood, if not drawn off by the Liver. Hence
some persons never become fat, however large the quantity of oily matter
ingested ; and it is in such persons, that the pendency to disorder of the Liver
from over-work is most readily manifested ; hence they are obliged to abstain
from the use of fat-producing articles of food.

187. In Cartilage, also, the simple cellular structure is very obviously re-
tained, and frequently exists alone ; although in some forms of this tissue, it
is united with the fibrous, or partly
replaced by it. In all, however, the
early stage of formation appears to
be the same. The structure origi-
nates in cells, analogous to those of
which the rest of the fabric is com-
posed ; but between these cells, a
larger quantity than usual of hyaline
or intercellular substance is depo-
sited; and the amount of this sub-
stance continues increasing, simul-
taneously with the bulk of the cells.
The original cells are pushed far-
ther and farther from one another ;
but new cells arise between them
from germs which are contained in
the hyaline substance. The first
cells frequently produce two or more
young cells from their nuclei ; and
thus it is very common to meet with

groups of such cells or corpuscles, consisting of two, three, or four. — The
varieties in the permanent Cartilages principally depend upon the degree of
organization, which subsequently
takes place in the intercellular sub-
stance. If a mass of Fibres, analo-
gous to those of the fibrous mem-
branes (§ 138), should originate in
it, the Cartilage presents a more or
less fibrous aspect; in some instan-
ces the Fibrous structure is deve-
loped so much, at the expense of
the Cells, that the latter disappear
altogether, and the whole structure
becomes fibrous. Sometimes the
fibres which are developed, are
rather analogous to those of the
Elastic tissue (§ 140) ; these are dis-

posed around the cells, forming a Fibro.Cartiiage , showing disposiuon of

kind of network, in the areolae of cartilage cellB> in areote of fibrous tissue.

Section of the Branchial cartilage of Tadpole ; af
group of four cells, separating from each other; 6,
pair of cells in apposition: c. c, nuclei of cartilage
cells ; rf, cavity containing three cells.

Fig. 53.

156 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

which they lie; and this kind of cartilage may be termed the elastic or
reticular. The primitive cellular organization is for the most part retained
in the ordinary articular cartilages,* the cartilaginous septum narium, the car-
tilages of the alae and point of the nose, the semilunar cartilage of the eye-
lids, the cartilages of the larynx (with the exception of the epiglottis), the
cartilage of the trachea and its branches, the cartilages of the ribs (in Man)
and the ensiform cartilage of the sternum ; and it is seen also in the tempo-
rary cartilages, or those which are destined to undergo ossification. The
fibrous structure is seen in all those Cartilages, which unite the bones by
synchondrosis ; this is the case in the vertebral column and pelvis, the
cartilages of which are destitute of corpuscles, except in and near their cen-
tres. In the lower Vertebrata, however, and in the early condition of the
higher, the fibrous structure is confined to the exterior, and the whole interior
is occupied by the ordinary cartilaginous corpuscles. The reticular structure
is best seen in the epiglottis and in the concha aims : in the former of these,
scarcely any trace of cartilage-cells remains ; in the latter, the fibrous net-
work disappears by degrees towards the extremity of the concha, and the
structure gradually passes into the cellular form.t

a. The substance that gives to the Cellular Cartilages their peculiar character, has received
the designation of Chondrine. It bears much resemblance to ordinary Gelatine, but requires
longer boiling in water for its solution; the solution fixes on cooling, like that of gelatine;
and when it becomes dry by evaporation, it has the appearance of solid glue. Choudrine
is not precipitated, however, by tannic acid; on the other hand, it gives precipitates with
acetic acid, alum, acetate of lead, and proto-sulphate of iron, which do not disturb a solution
of Gelatine. That the Chondrine obtained by boiling Cartilage is an actual component of
that tissue, and is not a product of the operation, appears from the agreement between its
elementary composition and that of cartilage, when analyzed by combustion. According to
Mulder, the proportions of the elements, as deduced from the definite compound which
Chondrine forms with Chlorine, are 32 C, 26 H, 4N, 14 0, with l-10th of an equivalent of
Sulphur. Chondrine agrees much more nearly with the proteine-compounds, in its element-
ary composition, than does Gelatine ; and may be considered as a sort of intermediate stage
between the two. Chondrine is not obtainable from any of the Fibro-cartilagcs ; these
yield gelatine, on boiling, exactly similar to that of the tendons. The Elastic cartilages,
after being boiled for several days, yield a small quantity of an extract, which does not form
a jelly, but which has the other chemical properties of Chondrine. The cartilage of Bone,
before ossification, yields only Chondrine ; after ossification, however, it affords only Gelatine ;
and it is curious that, even when bony deposits take place in the permanent cartilages, the
ossified portion contains ordinary Gelatine in the place of Chondrine. Many of the carti-
lages naturally contain a large proportion of mineral matter ; in the costal cartilages, frac-
tures in which are generally repaired by osseous substance, from 3 to 7 per cent, of ash is
left by calcination. This contains a large proportion of the carbonate and sulphate of soda,
together with carbonate of lime and a small proportion of phosphate ; as age advances, the
phosphate of lime predominates, and the soluble compounds diminish.

188. Cartilage (at least in its simplest form) is nourished, without coming
into direct relation with the Blood through the medium of blood-vessels; the
cellular Cartilages not being penetrated by vessels in the healthy state; al-
though in certain diseased conditions they become distinctly vascular. They
are, however, surrounded by Blood-vessels ; which form large ampullae or
varicose dilatations at their edges or on their surfaces (Fig. 54): and from
these the Cartilages derive their nourishment by imbibition ; in exactly the
same manner as the frond of a Sea-weed (the structure of which is alike cel-
lular) draws into itself the requisite fluid from the surrounding medium. In
the thicker masses of cartilaginous tissue, however, such as the cartilages of

* The articular cartilages, at the points win-re tendons arc implanted into them, have all
the characters of fibre-cartilage; the fibres nf the temlun beiuu; spread through, the intercel-
lular substance of the cartilage, for some distance, and gradually coalescing with it.

"j" See Mr. Toynbee's Memoir on the Non-Vascular Tissues, Phil. Trans. 1841.

STRUCTURE AND COMPOSITION OF CARTILAGE.

157

Fig. 54.

the ribs, we find canals excavated at wide distances from each other ; which
are lined by a continuation of the perichondrium or investing membrane of
the cartilage, and which thus allow
its vessels to come into nearer prox-
imity with parts, that would be other-
wise too far removed from them.
The vessels, however, nowhere pass
from the walls of these canals into
the substance of the cartilage. Si-
milar vascular canals are found in the
temporary cartilages, near the points
where the ossifying process is taking
place ; this is well seen in the long
bones, towards their extremities. At
an early period of foetal life, there is
no distinction between the cartilage that is ultimately to become the Osseous
Epiphysis, and that which is to remain as Articular Cartilage ; both are alike
cellular ; and the vessels that supply them with nutrient materials penetrate
no further than their surfaces. At a subsequent period, however, when the
ossification of the epiphysal cartilage is about to commence, vessels are
prolonged into it ; and a distinct line of demarcation is seen betwixt the vas-
cular portion, which is to be converted into Bone, and the non-vascular part,
which is to remain as Cartilage. At this period, the Articular Cartilage is

Fig. 55.

Vessels between the Articular Cartilage and attached
Synovial Membrane. (After Toynbee.)

Vessels situated between the attached synovial membrane, and the articular cartilage, at the point
where the ligamentum teres is inserted in the head of the os femoris of the human subject, between the
third and fourth months of fetal life ; a, the surface of the articular cartilage ; 6, the vessels between the
articular cartilage and the synovial membrane ; c, the surface to which the ligamentum teres was at-
tached ; d, the vein ; e, the artery.

nourished by a plexus of vessels spread over its free surface, beneath its sy-
novial membrane; as well as by the vessels, with which it comes in contact
at its attached extremity. Towards the period of birth, however, the sub-sy-
novial vessels gradually recede from the surface of the articular cartilage ; and
at adult age they have entirely left it, though they still form a band which
surrounds its margin. The Fibrous cartilages are somewhat vascular ; but
the vessels do not extend to the cellular portions, where such exist.

189. No vessels can be traced (according to Mr. Toynbee) into the sub-
stance of the true Cornea ; which, contrary to the statement of Miiller, is a
cellular rather than a fibrous cartilage. The cells are not so numerous as are
those of the articular cartilages; and they are surrounded by a plexus of bright
14

158

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Fig. 56. fibres, laxly connected together, so as to re-

semble areolar tissue. Two sets of vessels, a
superficial and a deep-seated, surround the mar-
gin of the cornea. The arteries of the former
are prolonged for a short distance upon the
Conjunctival membrane, which forms the outer
lamina of the cornea ; but they terminate in
veins at from 5 to 5 a line from its margin.
The deep-seated vessels belong to the Cornea
proper ; but they do not enter it, the arteries
terminating in veins just where the tissue of
the Sclerotic becomes continuous with that of
the Cornea. In diseased conditions of the
Cornea (as of the articular cartilages), both sets
of vessels extend themselves through it ; the
superficial not unfrequently form a dark band
of considerable breadth round its margin ;
whilst the deep-seated are prolonged into its
entire substance. Notwithstanding the absence
of vessels in the healthy condition of this struc-
ture, incised wounds commonly heal very rea-
dily, as is well seen after the operation of. ex-
traction of Cataract ; but the foregoing details
make evident the importance of not carrying

the incision further round than is necessary ; since the corneal tissue should
not be cut off from the supply of nourishment, afforded by the vessels in its
immediate proximity.

[This structure has been recently studied by Messrs. Todd and Bowman, and is described
by them with great accuracy. We subjoin their description. " The cornea, though a beau-
tifully transparent substance, and appearing at first sight as homogeneous as glass, is never-
theless full of elaborate structure. It is in fact composed of five coats or layers, clearly
distinguishable from one another. These are, from before backwards, the conjunctival layer
of epithelium, the anterior elastic lamina, the cornea proper, the posterior elastic lamina, and the
epithelium of the aqueous humour, or posterior epithelium. The cornea, when uninflamed, con-
tains no blood-vessels; those of the surrounding parts running back in loops, as they arrive
at its border.

On the cornea proper, or lamellated cornea, the thickness and strength of the cornea mainly
depend. It is a peculiar modification of the white fibrous tissue, continuous with that of the
sclerotic. At their line of junction (fig. 57), the fibres, which in the sclerotic have been

Fig. 57.

ft

Nutrient Vessels of the cornea. A,
superficial vessels belonging to the
Conjunctival membrane, and continu-
ed over the margin of the Cornea; B,
vessels of the Sclerotic, returning at
the margin of the Cornea.

Vertical section of the Sclerotic and Cornea, showing the continuity of their tissue between the dotted
lines:— a. Cornea, b. Sclerotic. In the cornea the tubular spaces are seen cut through, and in the
sclerotic the irregular areolfo. Cell-nuclei, as at c. are seen scattered throughout, rendered more plain
by acetic acid. Magnified 320 diameters.

CORNEA, AND CRYSTALLINE LENS. 159

densely interlaced in various directions, and mingled with elastic fibrous tissue, flatten out
into a membranous form, so as to follow in the main the curvatures of the surfaces of the
cornea, and to constitute a series of more than sixty lamellae, intimately united to one ano-
ther by very numerous processes of similar structure, passing from one to the other, and
making it impossible to trace any one lamella over even a small portion of the cornea. The
resulting areolaj, which in the sclerotic are irregular, and on all sides open, are converted in
the cornea into tubular spaces, which have a very singular arrangement, hitherto undescribed.
They lie in superposed planes, the contiguous ones of the same plane being for the most part
parallel, but crossing those of the neighbouring planes at an angle, and seldom communica-
ting with them (fig. 58). The arrangement and size of these tubes can be shown by

Fig. 58.

Tubes of the Cornea Proper, as shown in the eye of the Ox by mercurial injection. Slightly magnified.

driving mercury, or coloured size, or air, into a small puncture made in the cornea. They
may also be shown under a high power by moistening a thin section of a dried cornea, and
opening it out by needles. The tissue forming the parietes of these tubes is membranous
rather than fibrous, though with the best glasses a fibrous striation may be frequently seen,
both in the laminae separating the different series of tubes, and in that dividing those of the
same layer from each other. By acetic acid, also, the structure swells, and displays corpus-
cles resembling those apparent in the white fibrous tissue. Such is the lamellar structure of
the cornea, which makes it so much easier to thrust an instrument horizontally than verti-
cally into its substance. The tubes or elongated spaces of which we have spoken, are not
distended with any fluid, but are merely moistened in the same way as the areolas of ordi-
nary areolar tissue. A perfectly fresh and transparent cornea is rendered opaque by pres-
sure, but it regains its brilliance on the removal of the compressing force. Some have sup-
posed this to result from the expulsion of fluid from between its laminae ; but that the opa-
city is owing simply to a derangement of the elementary parts of its structure is plain from
the fact, that the same phenomena are exhibited by a section, however thin, immersed in
water, and deranged by stretching.]

190. In connection with the cornea, it is natural to allude to the Crystal-
line lens and Vitreous humour, which have a structure essentially the same.
The structure of the Crystalline lens has long been known to be fibrous ; and
Sir D. Brewster has shown, by the aid of polarized light, the very beautiful
manner in which the fibres are arranged.* They are united into laminae, by
means of numerous teeth or sinuosities at their edges, which lock into one
another. That these fibres originate in cells, has been clearly ascertained ;
but the nature of the metamorphosis has been differently stated by two emi-
nent observers, Schwann and Barry. By the former, the fibres are considered
to be prolonged cells : whilst the latter regards them as rather formed upon
the plan of the tubes of muscular fibre (§ 235), several cells coalescing into
one ; in this he is supported by Mr. Toynbee, who states that he has fre-
quently seen the fibres, towards the margin of the lens, made up of such cells.
After it is fully formed, however, it is not permeated by blood-vessels ; these
being confined to the capsule. During the early part of fetal life, and in in-
flammatory conditions of this membrane, both the anterior and posterior por-
tions of the capsule are distinctly vascular; but at a later period, according to

* Philosophical Transactions, 1833.

160 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Mr. Toynbee, the posterior half only of the capsule has vessels distributed
over it surface ; and these are derived from the Arteria centralis retinae.
From optical experiments which have been suggested to him by this circum-
stance, he infers that "objects (radiating lines for instance), situated on the
anterior surface of the crystalline lens, produce an indistinctness in the image
which is formed upon the retina ; whereas, when these lines exist upon the
posterior surface of the lens, the image is clear." The substance of the Lens
contains about 42 per cent, of animal matter, with 58 parts of water. Nearly
the whole of the former may be dissolved in cold water by trituration ; the
solution is coagulated by heat, and forms a granular but not coherent mass;
alcohol and acids produce the same effect. Hence it appears that the Lens
chiefly consists of albumen in its soluble form ; and this may be supposed
to be contained in the cavities of the cells, as it is in those of the vitreous
humour. From the latest analyses, it appears that the substance of the lens
corresponds most with that modification of albumen, which forms the Glo-
buline of the blood (§ 147). — In the Vitreous humour, we have an example
of a very loose form of cellular tissue ; strongly resembling that which con-
stitutes the entire structure of Acalephse (Jelly-fish). That the cells com-
posing it have no open communication with each other, is evident from the
fact that, when the general enveloping membrane is punctured in several
places, it is long before the contained fluid entirely drains away. This
fluid is analogous to that of the Aqueous humour ; being little else than Wa-
ter, holding a small quantity of Albumen and Saline water in solution. From
Mr. Toynbee's inquiries it would appear, that the vessels which pass through
the Vitreous humour do not send branches into its substance ; but that it is
nourished by the vessels, which are minutely distributed upon its general en-
velope. The Ciliary processes of the Choroid membrane are almost entirely
composed of large, plexiform vessels, closely resembling those of synovial
membrane (Fig. 54), which allow a great quantity of blood to circulate through
them ; and these have probably an important share in the nutrition of the Vi-
treous body.

191. Cartilage is perfectly insensible ; and neither nerves nor lymphatics
can be traced into its substance. Its functions are purely mechanical ; the
consolidation of its texture by internal deposit renders it little disposed to
change by spontaneous decay ; and it is protected by its toughness and elas-
ticity from those injuries, to which softer or more brittle tissues are liable.
These very circumstances, however, interfere with the activity of its nutrition.
Cells which are choked up with interior deposit do not readily transmit fluid :
it is doubtful whether any interstitial change can take place in the interior of
a permanent Cartilage (except when it has become vascular by disease, or
undergoes ossification), through the whole of life; and there seems ground to
believe that, when it has been injured by disease or accident, the loss of sub-
stance is not repaired by real cartilaginous tissue. In the process of ulcera-
tion of Cartilage (as observed by Mr. J. Goodsir), it appears that the formation
of depressions on the surface is due, not so much to any change originating
in the substance of the cartilage, as to the eroding action of the cells of the
false membrane, which is the product of inflammatory action upon its surface;
and it is in lliis false membrane that the new vessels are formed, which dip
down into nipple-like prolongations of the membrane, entering corresponding
hollows excavated in the cartilage. — On the other hand, the softer tissues of
the Eye are capable of complete regeneration. Every oculist is aware that
a great loss of Vitreous humour may take place without permanent injury;
and it has been found that even the Crystalline lens may be completely rege-
nerated, after it has been entirely removed by extraction.

CALCIFICATION OF FIBRES AND CELLS.

161

Fig. 59.

Calcified Areolar Structure, of which the Skele-
1on of the Echinodermata is composed ; from the
Spine of an Echinus. Magnified 150 diameters.

Fig. 60.

9. Tissues consolidated by Earthy deposit. — Bones and Teeth.

192. Both the Fibres and Cells of the Animal tissue, there is reason to be-
lieve, may be consolidated by mineral deposits ; these being chemically united
with the Gelatine of the Fibres ; or secreted, either alone, or in combination
with gelatine, into the cavities of the
Cells, by their own inherent powers.
— We have an example of the form-
ation of a skeleton by the consoli-
dation of fibres, in the shell and
other hard parts of the Echinoder-
mata ; the intimate structure of which,
as shown by the Microscope, strong-
ly reminds us of Areolar tissue that
might have undergone the calcifying
process. Again, we have an exam-
ple of the formation of a skeleton
by the deposit of mineral matter in
the cavities of cells, in the shells of
Mollusca; in many of which (espe-
cially among the Bivalves) the cellu-
lar character is permanently shown,
— a consistent membrane being left,

after the Carbonate of Lime that consolidated the cell has been dissolved
away by an acid. An arrange-
ment precisely similar, as regards
the animal constituent, is found
in the Enamel of Teeth (§ 215) ;
the only difference being in the
consolidating material, which is
chiefly the Phosphate of Lime,
a mineral far harder than the
Carbonate. It is not always,
however, that the original cells
preserve their character so dis-
tinctly; for it is very commonly
found, that they have coalesced
with each other, in such a man-
ner as not to be distinguishable
in the fully-formed tissue. We
also frequently observe, in the
skeletons of Vertebrata, that the

whole substance is not consolidated, but that cavities and channels are left in
it ; which seem destined to perform some office connected with the interstitial
changes, that continue to take place in the tissues subsequently to their first
formation. It has been already pointed out (§ 5), that the internal bony ske-
letons of Vertebrated animals are destined to undergo a degree of interstitial
change (in order to adapt them to the progressive growths of the parts that
cover them), which is not required in the external envelopes of Invertebrated
animals ; these being capable of sufficient enlargement by addition to their
edges merely ; or else being periodically thrown off, and renewed upon a
larger scale. It is obvious that, if the whole substance be consolidated by
calcareous deposit, there can be no permeation of nutritive fluid through it ;
but, on the other hand, if it be traversed by tubuli, commencing from the near-
est vascular surface ; or if a series of minute chambers, connected by still

14*

Cellular membrane, left after the removal of the Cal-
careous matter from the shell of Pinna. Magnified 165
diameters.

162

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

more minute passages, be excavated in its substance, it is evident that, even
though blood cannot circulate through it, a nutritive fluid drawn from the
blood, may be carried into its minutest parts. This is the kind of structure
which we find in Bone, and in the principal substance of Teeth. The mode
in which it is generated, will become the subject of inquiry hereafter.

193. When examined with the naked eye, it is seen that Bone possesses
in some degree a laminated texture : in the long bones, the external and in-

Fig. 61.

Portion of Transverse Section of Human Clavicle, showing the orifices of the Haversian canals, and
the concentric arrangement of the laminse of bony matter, and of the lacunae, around them. Magnified
t-5 diameters.

ternal laminae are arranged concentrically round the medullary canal ; and in
the flat bones, they are parallel to the surface. Towards the extremities of
the long bones, and between the external plates of the flat bones, are a num-
ber of cancelli, or small hollows bounded by very thin plates of bone ; these
communicate with the medullary canal where it exists ; having, like it, an
extremely vascular lining membrane; and their cavities being filled with a
peculiar adipose matter. The hard substance of the bone also is traversed by
canals, on which the name of Haversian has been bestowed, after their disco-
verer ; these canals run for the most part in the direction of the laminae ; but
they have many transverse communications, both with each other and with
the medullary cavity, so that they form a complete network, which is lined
by a continuation of the membrane of the latter. Their diameter varies from
l-200th to l-2000th of an inch; the average being probably about 1-500.
The smaller ones contain only a single capillary vessel ; but several such ves-
sels seem to exist in the larger ones, together with adipose matter. When a
thin transverse section of a long bone is made, and is highly magnified, it is
seen that the bony matter of the greater part of its thickness is arranged in
concentric circles round the orifices of the canals ; these circles are marked
by a series of stellated points ; and when the latter are magnified still more
highly, it is seen that they are cavities or lacunae of a peculiar form, which
seems characteristic of Bone. They are usually oval or lenticular in form ;
and are so placed, that one of their largest surfaces is turned from, and the

STRUCTURE OF BONE. 163

other towards, the Haversian canal. Their long diameter is commonly from
[Fig. 62. [Fig. 63.

Transverse section of the compact tissue
of along Bone; showing 1, the periosteal
layer ; 2, the medullary layer, and the inter-
mediate Haversian systems of lamellae, each
perforated by an Haversian canal. Mag-
nified about 15 diameters.]

Transverse section of the compact tissue of a Tibia
from an aged subject, treated with acid ; showing the
appearance of lamellae surrounding the Haversian ca-
nals. Portions of several systems of lamella are seen.
The appearance of the lacunae, when their pores are
filled with fluid, is also seen, as well as the radiation
from the canals which then remain. From Mr. Tomes.]

l-2400th to l-1600th of an inch ; their short diameter is about one-third, and
their thickness about one-sixth, of their length.

a. It has been lately shown by Mr. J. Quekett, that there are differences in the form and
size of the lacunae, in the several classes of animals, sufficiently characteristic to allow of the
assignment of minute fragments of bone, with the aid of the microscope, to their proper class.
The lacuna? of Reptiles are distinguishable by their large size, and long oval form; and those
of Fish, by their angular form and the fewness of the radiating canaliculi. The osseous
lacuna? of the Bird maybe distinguished from those of the Mammal, partly by their smaller
size, but chiefly by the remarkable tortuosity of their canaliculi, which wind backwards and
forwards in such a manner, as frequently to destroy the concentric lamellar appearance. It
is interesting to remark further, that the sizes of the lacuna; in the four classes of the Verte-
brated animals, bear a close relation to the sizes of their blood-corpuscles. Here, as else-
where, the dimensions of the ultimate parts of the tissue are tolerably constant in each group
of animals, and show little variation in accordance with the size of the species ; thus there
is little or no perceptible difference in the size of the elements of the osseous tissue of the
enormous extinct Iguanodon, and of the smallest Lizard now inhabiting the earth.

Fig. 64.

194. From all parts of these cavities,
but especially from their two largest
surfaces, proceed a large number of
minute tubuli, which traverse the sub-
stance of the bone, and communicate
irregularly with one another. Their
direction, however, possesses a certain
degree of determinateness ; for those
passing off from the inner surface con-
verge towards the Haversian canal ;
whilst those passing off from the outer
surface diverge in the contrary direc-
tion, so as to meet and inosculate with
those proceeding inwards from the

cavities of the next annulus. In this manner, a communication is kept up
between the Haversian canal, and the most external of its concentric lamellae

Lacunae of Osseous Substance; magnified
500 diameters : a, central cavity ; b, its ramifica-
tions.

164

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

3

of bone. It is not to be imagined, however, that blood can be conveyed by

these tubuli, their size being far too small ; for
[Fig. 05. their diameter, at their largest part, is estimated at

from 1-1 4,000th to l-20,000th of an inch, whilst
that of the smaller branches is from l-40,000th to
1-60, 000th of an inch ; so that the blood-corpus-
cles could not possibly enter them. But it may be
surmised that they draw fluid from the nearest
blood-vessels, and thus keep up a sort of circulation
through the osseous substance, which may con-
tribute to its growth, and may keep it in a state fit
for repairing itself, when injured by disease or vio-
lence. The lacunae, however, do not seem to be
unoccupied in the living bone ; for each contains
(according to Mr. J. Goodsir) a minute granular
substance, which seems to be identical with the
nucleus of the original bone-cell, and which pro-
bably serves as a " nutritive centre," — attracting to
itself, through its own system of canaliculi, the
nutritive materials supplied by the blood-vessels of
the nearest surface, and diffusing these through the
surrounding substance.*

canals, seen on a 195, Although a large quantity of blood is sent
longiiudmai section of the com- to Bone? the vessels do not penetrate its minute
pact tissue of the shaft of one of being confined to the Medullary cavity,

the longbones: 1, arterial canal; . . "= _ . . _ /. . . •'

2, venous canal ; 3, dilatation of and to the Haversian Canals, and Cancelli, which
another venous canal.] are prolongations of it. The substance oi the Bone,

therefore, is really as non-vascular as that of Carti-
lage ; the only difference being, that it is channelled out by more numerous
inflexions of the external surface, and that the vessels are thus brought into
nearer proximity with its several parts. The delicate osseous lamellae, which
form the walls of the cancelli, and of the large cells excavated in some of the
cranial bones, have a structure precisely analogous to that of the cylindrical
laminae surrounding the Haversian canals of the long bones ; and derive their
nourishment from the vascular membrane covering their surface, through the
medium of a similar set of lacunas and canaliculi. They do not themselves
contain Haversian canals or cancelli ; because no part of their substance is far
removed from a vascular membrane. The cylindrical rods, that make up the
hollow shaft of a long bone, are connected together by solid osseous sub-
stance, which is composed of lamellae running parallel to the external surface
of the bone; and these derive their nutriment either from the periosteum, or
from the membrane lining the great central medullary cavity ; according as
they are nearest to one or to the other. — The membranous lining of the canals
of Bone appears to be supplied with lymphatics, and also with nerves ; but
with both in a very limited amount. The periosteum seems to be scarcely
(if at all) sensible in the state of health, although painfully so when inflamed ;
and the same may be said of the membrane lining the Haversian canals and
cancelli. The membrane lining the central medullary cavity, however, is more

' The lacunae and canaliculi of Bone were formerly supposed, on account of the black
appearance they exhibit under the Microscope, to be filled with opaque matter; but this ap-
pearance is common to all cavities excavated in a highly-refracting substance (being shown
by a bubble of air in water), and ceases when a very thin section of Bone is examined, es-
pecially if it have been placed in Canada Balsam. In the Bones of Mummies, they are found
to be filled with a waxen material ; and in those which have lain in bogs, they are rendered
peculiarly distinct by the infiltration of some of the surrounding black matter: so that their
power of imbibing liquids is clearly proved.

STRUCTURE AND COMPOSITION OF BONE. 165

sensitive; since unequivocal signs of pain are manifested by an animal, when,
a bone having been sawn across, a probe is passed up the cavity, or an acrid
fluid is injected into it.

196. The ultimate substance of Bone, lying between the lacuna? and cana-
liculi, appears to be usully granular ; the granules are stated by Mr. Tomes*
to be often distinctly visible without any artificial preparation, in the sub-
stance of the delicate spicula of the cancelli, when they are viewed with a
high power ; and to be made very evident by prolonged boiling in a Papin's
digester. They vary in diameter from l-6000th to 1-14, 000th of an inch ;
their shape is oval or oblong, often angular; and they cohere firmly together,
possibly by the medium of some different material. Their own substance,
however, appears to be perfectly homogeneous ; but it is made up of several
components, as appears from the following statements regarding the chemical
composition of Bone.

a. When the Calcareous matter of Bone has been dissolved away by the action of an acid,
the Animal substance which remains is almost entirely dissolved by a short boiling in water;
yielding to it a large quantity of Gelatine. This, indeed, may be obtained by long boiling
under pressure, from previously-unaltered Bone; and the calcareous matter is then left almost
pure. The Lime of bones is, for the most part, in the stale of Phosphate, especially among
the higher animals; it is curious, however, that in callus and exostosis, there is a much larger
proportion of Carbonate of lime, than in the sound bone; in which respect these formations
correspond with the bones of the lower animals ; but in caries, the quantity of the carbonate
is much smaller than usual. The composition of the Phosphate of Lime in Bones is peculiar ;
8 equiv. of the base being united with 3 of the acid. According to Prof. Graham, it is to be
regarded as a compound of two tribasic phosphates ; namely, 2 Ca, 0, H O, P O5-j-2 (3 Ca 0,
P O5) ; with the addition of an equiv. of water, which is driven off by calcination. The fol-
lowing are the results of some of the most recent and careful analyses of Human Bone, by
Marchand and Lehmann : those of the former were made on the compact substance of the
femur of a man aged 30 ; and those of the latter on the long bones of the arm and leg of a
man of 40 years of age.

Organic matter. MAHCHAND. LEHMANIT.

Cartilage insoluble in hydrochloric acid . . . 27'23 }
Cartilage soluble in hydrochloric acid . . . 5-02 > 32-56

Vessels . 1-01 )

Inorganic matter.

Phosphate of lime 52'26 > ,.

Fluoride of calcium . . . . . . 1-00 £

Carbonate of lime 10-21

Phosphate of magnesia ..... 1-05

£oda -92

Chloride of sodium 0-25

Oxide of iron and manganese, and loss . . 1'05

100-00 100-00

b. According to Dr. Stark,f the relative proportions of cartilaginous and earthy matter, in
the bones of different animals, in the bones of the same animals at different ages, and in the
different bones of the same body, never depart widely from the preceding standard; the
amount of earthy matter being always found to be just double that of the cartilaginous basis,
when the bones have been carefully freed from oily matter, and completely dried, previously
to the analysis. The hardness of bone, he maintains, does not at all depend upon the pre-
sence of an unusually large proportion of earthy matter; nor does their increased flexibility
and transparency indicate a deficiency of the mineral ingredients ; for the transparent readily-
cut bones of fish contain the same amount of earthy matter, in proportion to their gelatinous
basis, as do the dense ivory-like leg-bones of the deer or sheep. The same holds good of
the bones even of the so-called Cartilaginous Fish. The difference seems to depend upon
the molecular arrangement of the ultimate particles ; and especially, it seems likely, upon
the relative amount of water which the bones contain.

Todd and Bowman's Physiological Anatomy, p. 108, and Cyclopaedia of Anatomy, art.
Osseous Tissue.

f Edinburgh Med. and Surg. Journal, April 1845.

166

OF THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Femur.

29-54
1-82

57-42

Scapula. Rib.

Os innomi-

natum. Vertebra. Sternum.

c. Probably the most exact and comprehensive analyses yet made of Bone, are those of
Von Bibra;* whose laborious investigations may be said to have almost exhausted the sub-
ject. The following table shows the relative proportions of the principal ingredients in some
of the principal bones of a woman aged 25 years.

Occipital

bone.

Organic matter.
Cartilage
Fat .

Inorganic matter.
Phosphate of lime }
with a little fluo- >
ride of calcium. )
Carbonate of lime

29-87
1-40

57-66

32-90
1-73

33-06
2-37

54-75 52-91

38-26
1-77

49-72

43-44
2-31

44-28

46-57
2-00

42-63

Phosphate of magnesia
Soluble salts

8-92 8-75 8-58 8-66 8-08 8-00

1-70 1-69 1-53 1-40 1-57 1-44

0-60 0-63 0-51 0-60 0-60 0-53

?• 19
1-11
0-50

100-00 100-00 100-00 100-00 100-00 100-00

The analyses of the long bones of the arm and leg correspond closely with that of the
femur; but we observe that the proportions of ingredients in the more spongy bones are
widely different. It is difficult, however, to say how far this variation is due to a difference
in the proportions of gelatine and earthy matter, in the actual osseous substance ; or how far
it may be accounted for by the presence of an increased proportion of membrane, forming
the lining of the cancelli. — The same uncertainty must attend the explanation of the differ-
ences that present themselves at different ages; as shown in the folio wing table, which gives
the comparative analyses of the long bones (generally the femur) at different ages.

Man Woman
25 years. 62 years.

Organic matter.

Cartilage

Fat .

Inorganic matter.

Phosphate of lime }
with a little fluo- >
ride of calcium. }

Carbonate of lime

Phosphate of magnesia

Soluble salts

Fcetus
6 mouths.

40-38
a trace

Foetus
7 months.

34-18
0-63

Child
2 months.

33-86
0-S2

Child
5 years.

31-28
0-92

53-46

3-06
2-10

1-00

57-G3

5-86
1-10
0-60

57-54

6-02
1-03
0-73

59-96

5-91
1-24
0-69

29-70
1-33

59-63

7-33
1-32
0-69

28-03
2-15

63-17

4-46
1-29

0-90

100-00 100-00 100-00 100-00 100-00 100-00

From this it will be seen that there is a gradual diminution in the proportion of animal
matter, through life ; and a corresponding increase in the proportion of the earthy components.
But this is not nearly so great as is usually supposed ; and the greater solidity of the bones
of old persons is doubtless owing chiefly to the fact, that their cavities are progressively con-
tracted, by the addition of new bony matter (§ 201).

d. The following comparative analysis of the bones of different animals, are selected from
the very extensive series given by Von Bibra; which contains 143 of Mammalia (independ-
ently of Man), 151 of Birds, 31 of Reptiles, and 23 of Fishes. They were mostly made
upon the long bones ; except in the case of Fishes, in which they were made upon the Ver-
tebrae.

Organic matter.
Cartilage
Fat ...

Inorganic matter.
Phosphate of lime with

a little fluoride of cal-

ciuin.

Carbonate of lime
Phosphate of magnesia
Soluble salts

Sheep. Horse. Wolf. Thrush. Frog. Cod. Salmon.

29-68
0-70

27-99
3-11

27-44
1-45

28-02
1-54

30-19
5-31

31-90
2-34

21-80
3S-S2

!>•

J

55-94 54-37 57-87 62-65 59-48 57-65 36-84

12-18
1-00
0-50

12-00
1-83
0-70

11-09
1-13

1-02

6-05
0-90
0-84

2-25
0-99
1-78

4-81
2-30
1-00

1-01
0-70
0-S3

100-00 100-00 100-00 100-00 100-00 100-00 100-00

* Chemische Untersuchungen iibcr die Knochen und Ziihne des Menschen, und der Wir.
belthiere.

COMPOSITION AND DEVELOPMENT OF BONE. 167

It will be observed that, in all cases, the proportion between the cartilaginous basis and
the earthy matter is very nearly the same ; being almost exactly as 1 to 2, even where the
composition of the bone is most altered, by the presence of an unusual quantity of fatty mat-
ter. Hence there is strong reason to believe, that a definite chemical compound is formed
by the union of the Gelatine and Earthy salts ; and this corresponds well with the fact
already noticed, in regard to the homogeneousness of the ultimate particles of bone.

197. The first Development of Bone may take place in the substance,
either of Membrane, or of Cartilage.* The tabular bones forming the roof
of the cranium afford a good example of the first, or intramembranous form
of Ossification : for their place is but in part pre-occupied by cartilage ; only
a membrane being elsewhere interposed between the dura mater and the in-
teguments. This membrane is chiefly composed of fibrous fasciculi, corre-
sponding with those of the white fibrous tissues ; but amongst these are seen
numerous cells, some about the size of blood-discs, but others two or three
times larger, containing granular matter ; and a soft amorphous or faintly-
granular matter is also found interposed amidst the fibres and cells. In cer-
tain parts, the fibres predominate ; and in others, the cells. The process of ossi-
fication here seems at first to consist in the consolidation of the fibres by earthy
matter ; for the first bony deposit consists of an irregular reticulation, very loose
and open towards its edges, and there frequently presenting itself in the form
of distinct spicula, which are continuous with fasciculi of fibres in the sur-
rounding membrane. The limits of the calcifying deposit may be traced by
the opaque and granular character of the parts affected by it, and it gradually
extends itself, involving more and more of the surrounding membrane, until the
foundation is laid for the entire bone. Everywhere the part most recently
formed consists of a very open reticulation of fibro-calcareous spicula ; whilst
the older part is rendered harder and more compact, by the increase in the
number of these spicula, and perhaps also by the calcification of the interve-
ning cells. As the process advances, and the plate of bone thickens, a series
of grooves or furrows, radiating from the ossifying centre, are found upon its
surface ; and these by a further increase in thick ness, occasioned by a deposit
of ossific matter all around them, are gradually converted into closed canals
(the Haversian), which contain blood-vessels, supported by processes of the
investing membrane. Further deposits subsequently take place in the interior
of these canals ; which thus gratlually produce a diminution of their calibre,
and a consolidation of the bone ; and in this manner its two surfaces acquire
their peculiar density, whilst the intervening layer or diploe retains a charac-
ter more resembling that of the original osseous reticulation. — The mode in
which the peculiar lacunae and canaliculi are formed, in the concentric layers
around the Haversian canals, probably corresponds with that in which they
are generated in the intracartilaginous form of ossification, to which we shall
next proceed.

198. In a very large proportion of the skeleton, the appearance of the Bones
is preceded by that of Cartilages ; which present the same form, and which
seem destined to afford a certain degree of support, to the surrounding soft
parts, until the production of Bone has taken place. As already mentioned
(§ 187), the temporary cartilages differ in no essential particular from the/>er-
manent. They present the same irregular scattering of cells through a homo-
geneous intercellular substance, and there is the same absence of any vascu-

* In recent times, the development of Bone from Cartilage has received almost exclusive
attention ; but the older opinion, that Bone is often developed in Membrane, has been lately
brought again into notice by Dr. Sharpey (Introduction to Fifth Edition of Quain's Anatomy),
who has demonstrated its truth by Microscopic research. The statements in the text, upon
this part of the subject, are derived from Dr. Sharpey's observations, which the author has
since confirmed.

168

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

larity in the Cartilaginous tissue itself. In all considerable masses, how-
ever, we find a coarse network of canals, lined by an extension of the peri-
chondrium or investing membrane ; and these canals, which may be regarded
as so many involutions of the external surface, allow the vessels to come into
nearer relation with the interior parts of the Cartilaginous structure, than
they would otherwise do. They are especially developed at certain points,

Fig. 66.

Section of Cartilage at the seat of
ossification ; the clusters of cells are
arranged in columns ; the intercellular
spaces between the columns being
l-3250th of an inch in breadth. At the
lower end of the figure, osseous fibres
are seen occupying the intercellular
spaces, at first bounding the clusters
laterally, then splitting them longitudi-
nally and encirclingeach separate cell.
The greater opacity of this portion is
due to a threefold cause; the increase of
osseous fibres, the opacity of the con-
tents of the cells, and the multiplica-
tion of oil-globules.

[Fig. 67.

Vertical section of Cartilage near the surface of ossifi-
cation; 1, ordinary appearance of the temporary cartilage;
1', portion of the same more highly magnified; 2, the cells
beginning to assume the linear direction; 2', portion more
magnified; opposite 3, the ossification is extending in the
intercellular spaces, and the rows of cells are seen resting
in the cavities so formed, the nuclei being more separated
than above; 3', portion of the same more highly magnified.
From a new-born rabbit which had been preserved in
spirit.]

which are to be the centres of the ossifying process ; and it is always observ-
able, that the vascularity is greatest at the zone, in which the conversion of
cartilage into bone is actually taking place. During the extension of the vas-
cular canals into the Cartilaginous matrix, certain changes are taking place

OSSIFICATION OF CARTILAGE. 169

in the substance of the latter, which are preparatory to its conversion into
Bone. Instead of single isolated cells, or groups of two, three, or four, such
as we have seen to be characteristic of ordinary Cartilage (Fig. 52), we find,
as we approach the centre or line of ossification, clusters made up of a larger
number arranged in a linear manner; which seem to be formed by a continu-
ance of the same multiplying process as that formerly described (Fig. 66).
And when we pass still nearer, we see that these clusters are composed of a
yet greater number of cells, which are arranged in long rows, whose direc-
tion corresponds to the longitudinal axis of the bone ; these clusters are still
separated by intercellular substance ; and it is in this, that the ossific matter
is first deposited. If we separate the cartilaginous and the osseous substance
at this stage of the process, we find that the ends of the rows of cartilage-
cells are received into deep narrow cups of bone, formed by the calcification
of the intercellular substance between them. Thus the Bone first formed in
the cartilaginous matrix, is seen to consist of a series of lamellae of a some-
what cylindrical form ; inclosing oblong areolse, or short tubular cavities,
within which the piles of cartilage-cells yet lie : and it thus corresponds
closely with the reticular structure, which first makes its appearance in the
intra-membranous form of the process. — So far it would appear that the blood-
vessels are not directly concerned in the operation; for although they advance
to the near neighbourhood of the first ossific deposit, they do not make their
way into its substance, or even into the intervening areolte.

199. This state of things, however, speedily gives place to another. On
examining the subjacent portion, in which the ossification has advanced further,
it is found that the original closed cavities have coalesced to a certain extent
(probably by the absorption of their walls), both laterally and longitudinally;
and that they now receive numerous blood-vessels, prolonged into them from
the previously-ossified portion. The groups of cartilage-cells, which origi-
nally occupied the cavities, are no longer seen ; and their place is filled with
a blastema, composed of cells, containing a granular matter, and closely re-
sembling those seen in the intra-membranous ossification, with a few fibres
scattered amongst them. It is by a change in this blastema, that the walls of
the cavities are gradually consolidated; new deposits of ossific matter being
formed in their interior, which occasion the gradual contraction of the cavities,
and give an increasing density to the bone. The cancellated structure, which
remains for a time in the interior of the long bones, and which continues to
occupy their extremities, represents the early condition of the ossifying sub-
stance, with very little change ; whilst the cavities, which have formed more
regular communications with each other, and which have been gradually con-
tracted by the subsequent deposit of concentric lamella?, one within another,
form the original Haversian canals. Thus we see that they all form one
system in their origin ; as they may be considered to do, notwithstanding
the difference of their form, in the complete bone.

200. The original osseous lamella?, formed by the consolidation of the car-
tilaginous substance, are entirely composed of granular matter ; and exhibit
none of the lacunae and canaliculi, which are commonly regarded as charac-
teristic of Bone. These excavations present themselves, however, in all the
subsequent deposits ; and into the origin of these, we have now to inquire.
According to the views of some Microscopists, the cells of the blastema fill
themselves with ossific. matter, except at the points occupied by the nuclei ;
at the same time, they become flattened against the walls of the canals, and
their nuclei send out radiating prolongations ; so that, when the calcification
of the cell has been completed, a stellate cavity is left in the hard deposit,
which is occupied by the granular matter of the nucleus. The centre of this
cavity forms the lacuna, in which the original granular matter may frequently

1 5

170

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

be found remaining, and presenting an appearance as if developed into a cluster
of minute cells ; whilst its prolongations form the ranaliculi, from which the
nuclear matter seems afterwards to disappear altogether. This view is sup-
ported by several considerations; amongst others, by the fact of the existence
of such stellate nuclei in many Vegetable cells (Fig. 14); and by the corre-
sponding appearances witnessed by Professor Owen in the formation of the
Cementum of Teeth, a structure identical with bone, and produced by the
calcification of the capsule (§ 216). — Others, again, regard the lacunae and
their radiating prolongations as themselves constituting cells ; and examples
are not wanting of similar forms in bodies known to have this character, as
the pigment-cells of the skin of Batrachia (Fig. 90, c). — Dr. Sharpey, on the
other hand, states as the result of his observations, that the concentric layers
within the Haversian canals are formed by a process analogous to the intra-
membranous ossification ; namely, by the calcification of successive layers of
fibres, generated in the blastema, and possibly derived from the granular cells.
These fibres, being arranged in a reticular manner, may here and there include
an entire cell or cell-nucleus, the presence of which may determine the posi-
tion of a lacuna; whilst the canalicula may result from the apposition of the
minute apertures, existing between the other reticulations of the decussating
fibres. This view seems to derive confirmation from the appearances pre-
sented by very thin shreds of the gelatinous matrix, left after the removal of
the calcareous matter by acid ; for these, according to Dr. S., are plainly com-
posed of transparent fibres, resembling those of the white fibrous tissues, in-
tersecting one another at acute angles, and forming a network, in the meshes
of which are minute perforations, that are nothing else than transverse sections
of the canaliculi.

20J. In the formation of a long bone, we usually find one centre of ossifi-
cation in the shaft, and one in each of the epiphyses; in the flat bones, there
is one in the middle of the surface, and one in each of the principal processes.

The ossification usually proceeds to a considerable
extent, however, in the main centre, before it com-
mences in the extremities or processes; and these
remain distinct from the principal mass of the bone,
long after this has acquired solidity. During the
spread of the ossifying process, the cartilaginous
matrix continues to grow, like cartilage in other
parts; but after the bony deposit has pervaded its
entire substance, in the manner just described, a
change takes place in the method adopted. The
osseous laminae, that subdivide the whole texture,
are removed by absorption from the interior of the
shaft, so as to leave the great central medullary
cavity; whilst, on the other hand, they receive pro-
gressive additions in the external portion, which is
thus gradually consolidated into the dense bone,
that forms the hollow cylinder of the shaft. This
consolidation is effected by the deposit of a series
of concentric laminae, one within another, on the
lining of the Haversian canals. — The bone con-
tinues to increase in diameter, by the formation of
new layers upon its exterior ; anil Dr. Sharpey has
pointed out that these layers are formed, not (as usually stated) in a cartila-
ginous matrix, but in the substance of a membrane, consisting of fibres and
granular cells, and exactly resembling that in which the flat bones of the roof
of the skull are developed. The Haversian canals, too, of these new layers

[Fig. 68.

Scapula of a Fcetus at the
seventh month ; showing the pro-
gress of ossification. Natural
size. The light parts are epiphy-
ses as yet cartilaginous.— From
the Museum of King's ColU-ge,
London.]

DEVELOPMENT AND GROWTH OF BONE. 171

are formed in the same manner as those of the tabular bones of the skull ; the
osseous matter being not only laid on in strata parallel to the surface, but also
being deposited around processes of the vascular membranous tissue, which
extend obliquely from the surface into the substance of the shaft; the canals,
in which these membranous processes lie, becoming narrowed by the depo-
sition of concentric osseous laminae, and at last remaining as the Haversian
canals. Whilst this new deposition is taking place on the exterior of the
shaft, absorption of the inner and older layers goes on : so that the central
cavity is proportionally enlarged. — The increase of the bone in length ap-
pears due to the growth of the cartilage between the shaft and the epiphyses,
so long as this remains unconsolidated by ossific deposit ; and this state con-
tinues, until the bone has acquired nearly its full dimensions. What further
increase it gains, seems chiefly if not entirely due to the progressive ossifica-
tion of the articular cartilage covering the extremities ; which progressively
diminishes in thickness during the whole of life, and which in old age some-
times appears to have been almost completely converted into bone.

202. It thus appears doubtful, whether there be anything like a proper
interstitial growth in bone ; that is, whether the part, through which the
ossific process has made its way, is capable of any further extension than by
addition to its surface. By the. admirable system of prolongations, however,
by which the vascular membrane is conveyed into its intimate substance, we
rind this method of superficial deposit adapted to the consolidation of parts, at
first sketched out (as it were) by a slight osseous reticulation ; whilst by the
facility with which the bony matter is absorbed in the internal part of the shaft,
whilst it is being deposited upon its exterior, the same effect is produced, as
if the whole cylinder could enlarge uniformly by a proper interstitial growth,
in the manner of the softer tissues. — Much of our information regarding the
mode in which new bony matter is deposited, is derived from observations
made upon the bones of animals that have been fed with madder ; for this
colouring-matter, having a strong affinity for bone-earth, tinges all those parts
which are in close relation with the vascular surfaces. In very young ani-
mals, a single day serves to colour the entire substance of the bones ; for
there is in them no osseous matter far removed from a vascular surface.
At a later period, however, the colouring matter is deposited less rapidly ; and
is found to be confined to the innermost of the concentric laminae of bone,
surrounding each Haversian canal, showing that this is the last formed.
When madder is given to a growing animal, the external portion of the bone
is first reddened ; showing that the new deposit takes place exclusively in
that situation. And if, when time has been allowed for this part to become
tinged, the administration of the madder be discontinued, and the animal be
killed some weeks afterwards, the red stratum is surrounded by a colourless
one of subsequent formation ; whilst the colourless layer internal to the red
one, and formed previously to it, is thinned by absorption from within. By
alternately administering and withholding the madder, a succession of coloured
and colourless cylinders may thus be formed in the shaft of a long bone ;
which present themselves as concentric rings in its transverse section.

203. The nature of the Ossifying process receives some additional light
from the abnormal forms in which it occasionally presents itself in Cartilages
that are usually permanent ; as well as in various softer tissues, such as the
coats of the arteries, fibrous and serous membranes, muscular substance, &c.
In these cases, the ossific deposit may often be seen to take place, in the first
instance, in the form of distinct granules, which gradually coalesce ; or in the
form of spicular fibres, to which additions are progressively made; until a
solid mass is produced. This adventitious bone, however, almost invariably
differs from true or normal bone, in the want of a regular Haversian system

172 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

with concentric laminae, and in the absence of the characteristic lacunae and
canaliculi. Irregular cavities, however, are scattered through them ; which
may in some degree answer the same purpose. The osseous plates not un-
frequently found in the dura mater, are stated by Mr. Tomes to possess a
structure more closely allied to that of true bone ; which may be connected
with the fact that, in some of the lower Mammalia, certain parts of this mem-
brane (the falx and tentorium) are normally ossified.

204. The Regeneration of Bone, after loss of its substance by disease or
injury, is extremely complete ; in fact, there is no other structure of so com-
plex a nature, which is capable of being so thoroughly repaired. Much dis-
cussion has taken place with respect to the degree in which the different
membranous structures, that surround bone and penetrate its substance, con-
tribute to its regeneration ; but the fact seems to be, that any or all these
membranes may contribute to the formation of new bone, in proportion to
their vascularity, — the new structure, however, being most readily produced
in continuity with the old. Thus, when a portion of the shaft of the bone
is entirely removed, but the periosteum is left, the space is filled up with
bony matter in the course of a few weeks ; though, if the periosteum also be
removed, the formation of new osseous matter will be confined to a small
addition in a conical form to the two extremities, a large interspace being left
between them. The production of new bony tissue, in this experiment, as
in cases where the periosteum has been detached by disease and remains alive
while the shaft dies, is in continuity with minute spicula of original bone,
which still adhere to the membrane ; and it is well known that, in comminuted
fractures, every portion of the shattered bone, that remains connected with
the vascular membranes, whether these be internal or external, becomes the
centre of a new formation ; the loss of substance being filled up the more ra-
pidly? in proportion to the number of such centres.

205. The most extensive reparation is seen, when the shaft of a long bone
is destroyed by disease. If violent inflammation occur in its tissue, the death
of the fabric is frequently the consequence ; apparently through the blocking-
up of the canals with the products of inflammatory action, and the consequent
cessation of the supply of nutriment. It is not often that the whole thickness
of the bone becomes necrosed at once ; more commonly this result is confined
to its outer or to its inner layers. When this is the case, the new formation
takes place from the part that remains sound ; the external layers, which
receive their vascular supply from the periosteum, and from the Haversian.
canals continued inwards from it, throwing out new matter on their interior,
which is gradually converted into bone ; whilst the internal layers, if they
should be the parts remaining uninjured, do the same on their exterior, de-
riving their materials from the medullary membrane, and from its prolonga-
tions into their Haversian canals. But it sometimes happens that the whole
shaft suffers necrosis; and as the medullary membrane and the entire Haver-
sian system have lost their vitality, reparation can then only take place from
the splinters of bone which may remain attached to the periosteum, and from
the living bone at the two extremities. This is consequently a very slow-
process ; more especially as the epiphyses, having been originally formed as
distinct parts from the shaft, do not seem able to contribute much to the re-
generation of the latter.

206. When the shaft of a long bone has been fractured through, and the
extremities have been brought evenly together, it is found that the new matter
first ossified is that which occupies the central portion of the deposit, and
which thus connects the medullary cavities of the broken ends, forming a kind
of plug that enters each. This was termed by Dupuytren, by whom it was
first distinctly described, the provisional callus, and it is usually formed in

REPARATION OF BONE. 173

the course of five or six weeks, or less, in young persons. At that period,
however, the contiguous surfaces of the bone itself are not cemented by bony
union ; and the formation of the permanent callus occupies some months ;
during which the provisional callus is gradually absorbed, and the continuity
of the medullary canal is thus restored, in the manner in which it was first
established. Mr. Gulliver has remarked that, when the broken portions of
bone form an angle, there is quite a Distinct centre of ossification in the new
matter ; from which that portion of it is ossified, that lies between the sides
of the angle; thus forming what has been termed an accidental callus, and
giving support to the two portions of the shaft, in a situation which is exactly
that of the greatest mechanical advantage. Though for some time quite uncon-
nected with the old bone, it soon becomes united to the regular callus. This
instance proves, that continuity with previously-formed bone is not absolutely
requisite for the production of new osseous structure ; although the process
is decidedly favoured thereby.

207. The reparation of Bone, after disease or injury, seems to take place
upon a plan essentially the same as that of its first formation. A plastic or
organizable exudation is first poured out from the neighbouring blood-vessels ;
and thus forms a sort of bed or matrix, in which the subsequent processes
take place. The next stage, in young animals, is the formation of a true car-
tilaginous substance, exactly resembling their temporary cartilages; and this
is gradually converted into bone, in the manner in which those cartilages are
consolidated in the first instance. In older animals, however, the new struc-
ture appears to be rather of a membranous character; and the ossifying pro-
cess would therefore correspond rather with that by which the normal in-
crease of their bones is effected. Mr. Tomes states* that he has examined
various cases of fracture of the neck or shaft of the femur, in which union
had not been effected, in consequence of the patient's advanced age; and that
he found in these no intervening cartilage, and but a scanty amount of con-
densed areolar tissue. In this latter, traces of an attempt at repair may be
generally found, in the presence of osseous matter in granules or granular
masses; but in these there is no arrangement of tubes or bone-cells of definite
character; indeed, such osseous masses are generally small, and are deficient
in density, owing to the want of union between the individual granules.

208. The Teeth are nearly allied to Bone in structure ; and in some of the
lower Vertebrata, there is an actual continuity between the bone of the jaw,
and the teeth projecting from it, notwithstanding that the latter form part of
the dermal skeleton, whilst the former belongs to the neural or internal. In
Man and the higher animals, however, there is an obvious difference in their
structure ; as in their mode of development. These subjects have lately re-
ceived much attention; and the practical importance of an acquaintance with
them, renders it desirable that they should be here treated somewhat fully. —
The Teeth of Man, and of most of the higher animals, are composed of three
very different substances ; Dentine (known as ivory in the tusk of the Ele-
phant), Enamel and Cementum or Crusta Petrosa. These are disposed in
various methods, according to the purpose which the Tooth is to serve: in
Man, the whole of the crown of the tooth is covered with Enamel ; its root or
fang is covered with Cementum; whilst the substance or body of the tooth is
composed of Dentine. In the molar Teeth of many Herbivorous animals,
however, the Enamel and Cementum form vertical plates, which alternate
with plates of Dentine, and present their edges at the grinding surface of the
tooth ; and the unequal wear of these substances, — the Enamel being the
hardest, and the Cementum the softest, — occasions this surface to be always
kept rough.

* CyclopeetUa of Anatomy and Physiology, vol. iii , p. 857.

15*

174

ON THE ELEMENTARY PARTS Of THE HUMAN FABUIC.
[Fig- 69- [Fig. 70.

A view of an Incisor and of a Molar Tooth,
given by a longitudinal section, and showing
that the enamel is striated, and that the strias
are all turned to the centre; the internal
structure is also seen ; 1, the enamel ; 2, the
ivory ; 3, the cavitas pulpi.]

209. The Enamel is composed
an inch in diameter, arranged side

[Fig. 71.

A vertical section of an adult Bicuspid, cut from
•without inwards— magnified 4 times; 1, 1, the cor-
tical substance which surrounds the root up to the
commencement of the enamel; 2, 2, the ivory of
the tooth, in which are seen the greater parallel
curvatures, as well as the position of the main
tubes; 3, apex of the tooth, where the tubes are al-
most perpendicular ; 4, 4, the enamel ; 5, the cavity
of the pulp, in which are seen, by means of the
glass, the openingsof the tubes of the dental bone.]

of solid prisms or fibres, about l-5600th of
by side, and closely adherent to each other ;

[Fig. 72.

A vertical section of an imperfectly developed Incisor,
taken from the follicle in wliicli it was enclosed; this
section is meant to show the position of the enamel
fibres, and also that a part of the appearances which are
seen in this substance under a less magnifying power,
originate in parallel curvatures of the fibres; 1,1, the
enamel ; 2, 2, the dental bone, or ivory; 3, 3, the minute
indentations and points on the surface of the ivory, on
which the enamel fibres rest ; 4, 4, brown parallel fibres;
5, parallel flexions of the fibres of the dental bone in these
stripes ]

A portion of the surface of the Enamel
on which the hexagonal terminations
of the fibres are shown — highly magni-
fied; 1, 2, 3, are more strongly marked
dark crooked crevices, — running be-
tween the rows of the hexagonal
fibres.]

STRUCTURE OF TEETH; ENAMEL, DENTINE.

175

their length corresponds with the thickness of the layer which they form;
and the two surfaces of this layer present the ends of the prisms, which are
usually more or less regularly hexagonal. The course of these prisms is
generally wavy ; but their curves are for the most part parallel to each other.
In the perfect state, the Enamel contains but an extremely minute quantity of
animal matter ; but if a young tooth be examined, it is found that, after the

[Fig, 73.

'JR. 74.

The Fibres of the Enamel viewed sideways
under a magnifying power of 350 times; 1,1,
the enamel fibres ; 2, 2, the transverse stripes
upon them.]

A small portion of fig. 70 covered with turpentine
varnish, viewed under a magnifying power of 350
times; 1,2,3, are the tubes containing a powdery,
lumpy substance. They are regular, and closely un-
dulating; but the branches do not appear, because
they are penetrated by the varnish.]

calcareous matter of the tooth has been dissolved away by an acid, there re-
mains a set of distinct prismatic cells, which formed (as it were) the moulds
in which the mineral substance was deposited.* The Enamel is the least
constant of the dental tissues ; being more frequently absent than present in
the teeth of Fishes ; being deficient in the whole order of Serpents; and form-
ing no part of the teeth of the Edentate and Cetacean Mammals.

210. The Dentine^ consists of a firm substance, in which mineral matter
largely predominates, though to a less degree than in the enamel. It is tra-

[Fig. 75.

[Fig. 76.

A view of the most interior portion of the main
tubes of the dental bone in an incisor of a child
two years old, close to their commencement in the
cavitas pulpi, in order to show their first division.]

A view of the external portion of the tubes of
the same tooth, exhibiting their more minute ra-
mifications, which, for the most part, turn towards
the crown.]

\nversed by a vast number of very fine cylindrical branching wavy tubuli ; which

The Author has discovered a structure precisely resembling this, in the shells of many
Mollusca. See Annals of Natural History, December, 1843.

t A structure exactly resembling Dentine has been found by the Author in the shell of
the Crab, especially at the tips of the claws; and a less regular structure of the same kind
in the shells of many Mollusca. (Loc. cit.)

176

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

commence at the pulp-cavity (on whose wall their openings may be seen),
and radiate towards the surface. In their course outwards, the tubuli occa-
sionally divide dichotomously ; and they frequently give oft' minute branches,
which again send off smaller ones. In some animals, these tubuli may be
traced at their extremities into cells exactly resembling the lacuna? of bone ;
and here the Ivory must be considered as presenting a form of transition into

[Fig. 78.

A view of a small portion of a transverse section of
the crown of the Tooth seen in fig. 70, viewed under a
magnifying power of 350 times ; 1, 2, 3, are the round
openings of the tubes, with parietes of a peculiar sub-
stance ; 4, 5, 6, are the tubes cut more obljfluely, in
consequence of their more external position ]

A view of the position of the same main
tubes, in a transverse section near the root
of a bicuspid, magnified 5 diameters. The
dark patches in this figure mark the places
in •which the bone was especially white and
less transparent than in the clear interme-
diate tracts.]

[Fig. 79.

Sections of a human incisor, showing:—

A. Junction of dentine and enamel near the neck of the tooth, a. Tubes of the dentine, dividing and
ending on b b, the cupped surface on which the enamel rods vertically rest. c. Free surface of the ena-
mel. The enamel rods are crossed by transverse lines and also by oblique dark lines.

B. Bifurcation of the tubuli of the dentine, soon after their commencement on d the surface of the pulp-
cavity.

c. Branching of the tubuli of the fang, and their termination in the small irregular lacuna? of the " gra-
nular layer."

In these longitudinal views of the tubuli, their cavities only, and not their walls, are visible.
Magnified 300 diameters.]

STRUCTURE OF TEETH; ENAMEL, DENTINE.

177

the substance next to be described. The tubuli, in their radiating course, de-
scribe two, three, or more curvatures, appreciable by a low magnifying power;
these are termed by Prof. Owen, the "primary curvatures." With a higher
power, the tubes are seen to be bent, throughout the whole of their flexuous
course, into minute and equal oblique undulations, of which 100 may be
counted within the space of l-10th of an inch ; these are the "secondary cur-
vatures" of Prof. Owen. Both the primary and the secondary curvatures of
one tube are usually parallel with those of the contiguous tubes ; and from
the radiating course of the tubuli, the rows of curvatures have the appearance
of lines running parallel with the external contour of the tooth. — The dia-
meter of the tubuli in their largest part averages about 1-10, 000th of an inch ;
their smallest branches are immeasurably fine. It is impossible that they
can receive blood; but it may be surmised that, like the canaliculi of bone,
they absorb matter from the vascular lining of the pulp-cavity, which aids in
the nutrition of the tooth. Although, when once fully formed, the Tooth un-
dergoes little or no change, there is evidence that it possesses a certain power
of repairing the effects of disease ; — a new layer of hard matter being some-
times thrown out on a surface, which has been laid bare by Caries. It has
been found, too, that the Dentine is sometimes tinged by colouring matters
contained in the blood. This is most evident, when a young animal is fed
upon madder, during the period of the formation of the tooth ; but even in an
adult, some tinge will result from a prolonged use of this substance; and it
has been noticed that the teeth of persons, who have long suffered from Jaun-

[Fig. 80.

Fig. 81.

Transverse sections of tubules of dentine,
showing their cavities, their walls, and the
intertubular tissue.

a. Ordinary distance apart.

b. More crowded.
e. Another view.

Human molar.— Magnified 400 diameters.]

Oblique section of Dentine of human
tooth, highly magnified, showing the calci-
gerous tubuli, and the outlines of the original
cells.

dice, sometimes acquire a tinge of bile. Attention has been particularly di-
rected by Prof. Owen, to appearances which he regards as indicating the

178 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

boundaries of the original cells of the dentinal pulp (§ 213) that have not been
obliterated by the process of calcification.* These are particularly evident
in the teeth of the Dugong, and of the extinct Mylodon; but they occasionally
present themselves in the Dentine of Man (Fig. 81). — In certain Mammals
and Reptiles, and in a large number of Fishes, the Dentine is traversed by
canals, which are prolonged into it from the central pulp-cavity, and which
are lined (like the pulp-cavity itself) by a highly-vascular membrane ; and it
is then distinguished as Vascular Dentine. These canals are obviously ana-
logous to the medullary or Haversian canals of bone ; and the tubuli usually
radiate from them, rather than from the central cavity. In some instances,
there is no central cavity whatever ; but the whole tooth is traversed by an
irregular network of these medullary canals, which become continuous with
the Haversian canals of the subjacent bone. — A substance still more resem-
bling bone, but formed from the dentinal pulp, is found in the interior of the
teeth of certain Reptiles and Mammalia, and occasionally in the teeth of
Man, especially at the later periods of life. This substance possesses not
only vascular or medullary canals, but also the stellate lacunae and radiating
canaliculi of true bone. It sometimes occupies the whole of the cavity of the
pulp, and is formed by the ossification of its cellular parenchyma ; but in
other cases, it forms merely a thin shell upon the interior of the ordinary
Dentine.

211. The Cementum or Crusta Petrosa corresponds in all essential parti-
culars with Bone ; possessing its characteristic lacuna? ; and being also tra-
versed by vascular medullary canals, wherever itoc4curs of sufficient thickness,
— as in the exterior of the tooth of the extinct Megatherium, and in the thick
plates interposed within the islands of Enamel in the teeth of Ruminants, Ro-
dents, &c. The varieties of microscopic structure presented by the Cemen-
tum in different classes of animals, correspond with the modifications of the
osseous tissue, which exist in the skeletons of those animals respectively.
The Cementum was formerly supposed to be restricted to the compound
teeth of Herbivorous animals ; and its presence in the simple teeth of Man
and the Carnivora can be shown only by the application of the Microscope.
In the latter it forms a layer, which invests the fang, and which decreases in
thickness as it approaches the crown of the tooth; at the time of the first
emersion of the tooth, it covers the crown with a very thin lamina ; but this
is speedily worn away by use ; on the other hand, its thickness around the
apex of the fang often undergoes a subsequent increase, especially when chro-
nic inflammation and thickening take place in the membranous contents of the
socket.

212. The following are the results of the most recent Chemical Analyses
of the component structures of Human Teeth : — t

Incisors of Mult Man.

Dentine. Enamel. Cementum.

Organic matter . . . 28-70 3-59 29-27

Earthy matter . . 71-30 96-41 70-73

100-00 100-00 100-00

The proportion of these two components varies considerably in different species; thus the
i r-auic basis of the Elephant's tusk forms as much as 43 per cent, of the whole. It would
M-em even to vaiy considerably in different individuals of the same species: thus in the
n.nlar teeth of one man,Bibra found the organir matter to constitute as little as 21 per cent.,

* See Prof. Owen's Odontography, Introduction.

t Op. Cit.; and Bibra's "Chemische Untersuchungen iibcr die Knochcn und Ziihne."

COMPOSITION AND DEVELOPMENT OF TEETH.

179

whilst in another it was 28. — The following analyses afford a more particular view of the
components of each substance: —

Molars of Mult Man.

Phosphate of Lime, with traces of fluate of lime
Carbonate of Lime .....
Phosphate of Magnesia .....

Other Salts .-

Chondrine .......

Fat

Dentine.

Enamel

. 66-72

89-82

3-30

437

IDS

1-34

0-83

OSS

. 27-61

339

0-40

020

10000

100-00

Incisors of Ox.

Dentine.

Phosphate of Lime, with trace of finale
of lime ......

Carbonate of Lime
Phosphate of Magnesia

Salts

Chondrine

Fat

59-57
7-00
099
0-91

30-71
0-82

IIIIHIO

Enamel.

81-86
9-33
1-20
0-93
6-66
0-02

100-00

Cement.

58-73

7-22

0-99

0-82
31-31

093

100-00

213. The Dentine and its modifications, the Enamel, and the Cementum,
originate in three distinct structures ; which may be termed respectively, the
dentinal-pulp, the enamel-pulp, and the capsule or cemental-pulp ; the whole
forming the " matrix" from which the entire tooth is evolved. — The Dentinal
pulp is always the first-developed part of the matrix ; and it makes its appear-
ance in the form of a papilla, budding out from the free surface of a fold or
groove of the mucous membrane of the mouth. This may be converted into
dentine, without ever becoming inclosed within a capsule; as we see in the
Shark, whose dentition never advances beyond this papillary stage. The
dentinal pulp consists of a mass of nucleated cells, imbedded in a semi-fluid
granular blastema, and the whole inclosed in a dense structureless pellucid
membrane. This substance is copiously supplied with blood-vessels, origin-
ating in a trunk that enters the base of each papilla; the branches ramify and
diverge in their progress through the pulp ; and at last they form a capillary
network, which terminates in loops near the apex of the pulp (Fig. 82).
These vessels are accompanied by nerves; which also have looped termina-
tions.— The following is the substance of the account given by Prof. Owen,
of the conversion of the dentinal pulp into dentine; based upon his observa-
tion of this process as it occurs in the foetal Shark. The primary cells, which
are smallest at the base of the pulp, and have large simple sub-granular nuclei,
soon fall into linear series, directed towards the periphery of the pulp ; and
those which are nearest to the periphery become closely aggregated, increase
in size, and present a series of important changes in their interior (Fig. 83, a).
A pellucid point appears in the centre of the nucleus ; and the latter increases
in size, and becomes more opaque around it. A division of the nucleus in
the course of its long axis is next observed (b] ; and in the larger and more
elongated cells, still nearer the periphery of the pulp, a further subdivision of
the nuclei is observed, in a transverse as well as a longitudinal direction (c, c),
the subdivisions becoming elongated, with their long axes vertical, or nearly
so, to the surface of the pulp. The subdivided and elongated nuclei become
attached by their extremities to the corresponding nuclei of the cells in ad-
vance; and the attached extremities become confluent (</); so that lines or

180

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Fig. 82. Fig. S3.

f

Vessels of Dental Papilla.

files of nuclear matter are formed, which
present an unbroken continuity from
one primary cell to another. While
these changes are proceeding, the cal-
careous salts furnished by the blood
begin to be accumulated in the interior
of the cells, and to be aggregated in a
semi-transparent state around the cen-
tral granular part of the elongated nu-
clei, which now present the character
of rows of minute secondary cells ; and
the salts occupy, in a still clearer and
more compact state, the cavity of the
primary cell not occupied by the trans-
formed nuclei. The rows of minute
secondary cells (which appear scarcely
to advance beyond the condition of
simple granules) remain uncalcified in
the midst of the solid calcareous sub-
stance ; and thus constitute the tubuli
of the dentine, in which a granular or
bead-like aspect may generally be traced.

214. Around the tubes, in a transverse section, is a small circular space
(Fig. 84, 6,) manifestly distinct from the intertubular substance; and this is
regarded by Professor Owen as the indication of a membrane surrounding
the elongated and coalesced secondary cells. The traces of the original
boundary of the primary or parent-cells (Fig. 84, «, a), are generally lost;
but, as already remarked (§210) they are sometimes preserved with suffi-
cient distinctness to be quite recognizable. The " primary curvatures" ob-
servable in the tubuli are due to the arrangement of the original linear series

Diagram of development of Dentine ; a, end
of a linear series of primary deminal cells ; 6,
cells with nuclei dividing ; e, subdivision and
elongation of nuclear mailer; d, elongated
nuclei uniting to form the area; of dentinal
lubes; e, e, calcified cap of dentine, formed by
the mtus-susception of the clear hardening
salts into the walls and cavities of the cells
and intercellular blastema f, e, and by their
partial exclusion from the monilifonn nuclear
tracts/1 f ; g, union of two peripheral nucle-
olar or secondary cells with one nearer the
centre of the pulp.

DEVELOPMENT OF DENTINE.

181

Inner surface of portion of calcified dentinal pulp,
forming cap of dentine ; a, inter vals and walls of pri-
mary dentinal cells ; 6, walls of dentinal tubes ; c, nu-
clear matter, establishing arese of dentinal tubes.
For clearer demonstration, the number of tubes in
tlie area of each cell is made less than in nature.

of parent cells; whilst the " se- Fig. 84.

condary curvatures" are accounted for
by the fact, that the elongated nuclei
usually unite with each other at ob-
tuse angles, and not in perfectly straight
lines, (Fig. 83, d.) — Thus we are to
regard the Dentine as composed of the
original cells of the pulp, which have
become consolidated by the calcifying
process, in every part save that which
is occupied by the rows of granules
or incipient cells, developed from the
metamorphosed nuclei. The calca-
reous matter appears to be chemically
united, as in Bone, with an animal
base ; the cavity of each cell being
pervaded by both ; so that, when the
whole of the calcareous matter is re-
moved by dilute acid, a cartilaginous-
looking mass remains, which preserves
the form of the tooth. The calcifying process takes place first on the exterior
of the pulp, and gradually extends inwards ; and the capillary blood-vessels alto-
gether retreat from the calcifying portion, and form their terminal loops upon
the surface of the part which still remains unconsolidated. As the calcifica-
tion extends inwards, the pulp, of course, progressively decreases ; fewer
nuclei are formed in the cells ; and these do not acquire so large a size. Here
and there it is seen, that the inner extremities of two of the granular tracts,
in the part last calcified, converge, and connect themselves with a single tract
in the layer nearer the centre of the pulp, (Fig. 83, g) ; in which we see the
origin of the bifurcation of the tubuli. This bifurcation becomes more fre-
quent, as the calcifying process approximates towards the centre and base of
the pulp ; and it is thus that the main tubes are formed. In some of the cells,
at and near the central and basal part of the pulp, the nucleus undergoes no
division ; but it merely elongates, and sometimes becomes angular or radiated,
— thus showing a form of transition to the stellate nucleus of the bone-cells.
As already stated, we occasionally find modifications of the dentine in this
situation, which closely resemble true bone in structure.

215. The Enamel-pulp is not formed -until after the dental papilla has
become inclosed in a capsule, by the process to be presently described (§ 217,
c). It differs from the dentinal pulp, at its first formation, in the more fluid
state of its blastema ; and in containing fewer and more minute cells. The
enamel-pulp is derived from the free inner surface of the capsule ; of which
we may regard its cells as the epithelium. The cells are largest and most
numerous in that portion of the pulp which most nearly approaches the den-
tal papilla ; and many of them show a nuclear spot (Fig. 85, A, A). In the
portion of the enamel-pulp most distant from the capsule, the cells, at first
spherical, become impacted against one another, and are pressed into hexago-
nal or polygonal forms (i, i) ; the fluid blastema being now almost excluded from
between them. In the part in closest contiguity with the surface of the den-
tinal pulp, the cells increase in length, either by the elongation of each indi-
vidual cell, or by the coalescence of several (j) ; the nuclei (k) disappear -T and
the cells, now forming long prisms (/), absorb into themselves calcareous salts,
which henceforth completely fill them, in a clear and crystalline form. These
salts would not seem to be united^ as in bone and dentine, with any organic
matters; the small quantity of this existing in Enamel, being probably em-

182 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Fig. 85. Fig. 86.

K

Formation of the Cementum ; m, primary cells ; j>, their
granular nuclei ; n, more minutely granular blastema; o, the
primary cell enlarged, and receiving the hardening salts ; n' >
calcified blastema; p',p', stellate nuclei of fully-formed ce-
mental cells.

ployed wholly in forming the walls of the pris-
matic cells. The disappearance of the nucleus,
previously to the calcification of the cell, is
evidently the reason of the absence of any
permanent space or tube in its interior unoccu-
pied by mineral matter. The islands of Ena-
mel, which are found in the midst of the dentine,
in the compound teeth of Herbivorous animals,
are formed from extensions of the same ena-
mel-pulp, with that which gives origin to the
general envelope of the tooth (§ 217, c).

216. The "Cemental pulp," or matrix of
the Crusta Petrosa, is in fact nothing else than
the capsule itself; in which, at an early period,
nucleated cells are found, distributed in the
midst of a granular blastema, which is copi-
ously supplied by vessels. The process of
calcification begins in the portion nearest the
dentine ; And consists, as elsewhere, in the
absorption of calcareous matter into the cavi-
ties of the cells, in the more close aggregation
of the cells with each other, and in the changes which take place coincidently
in their nuclei. These, which are at first large granular spots of a rounded
form, send out radiating prolongations, which extend quite to the borders of
the cell; and as the calcareous salts which penetrate the cell, are not depo-
sited in the space occupied by the nuclei, the stellate cavities, or lacunae and
diverging canaliculi, are left, which are so analogous to those of bone, as to
serve to identify the two tissues. In the cementum, as in Bone and Dentine,
the consolidating substance appears to consist of mineral and organic matter
in a state of chemical union. The boundaries of the original cells usually
disappear in this, as in similar cases ; so that nothing remains in the fully-
formed cementum, to mark its cellular origin, save the stellate lacunae which
represent the positions of the formerly-existing nuclei.

Formation of Enamel ; h, primary
cells suspended in fluid blastemag-;
t , the same more fully developed and
become angular; j, the same be-
coming prismatic ; k, the nucleus
disappearing; I, the modified pris-
matic cells, filled with calcareous
salts, forming the spicula and fibres
of enamel.

DEVELOPMENT OF THE TEETH.

183

Fig. 87.

217. As it is of much practical importance to understand the origin of the
several kinds of Human Teeth, and the times of their appearance, some de-
tails upon these subjects will be given ; those which relate to the mode of de-
velopment being principally derived from the researches of Mr. J. Goodsir.*

a. At the sixth week of Festal life, a deep narrow groove may be perceived, in the upper
jaw of the Human embryo, between the lip and the rudimentary palate; this is speedily
divided into two by a ridge, which afterwards becomes the external alveolar process; and
it is in the inner groove, that the germs of the teeth subsequently appear. Hence this may
be termed the primitive dental groove. At about the seventh week, an ovoidal papilla,
consisting of a granular substance, makes its appearance on the floor of the groove, near
its posterior termination ; this papilla is the germ of the Anterior superior Milk Molar
tooth. About the eighth week, a similar papilla, which is the germ of the Canine tooth,
arises in front of this; and during the ninth week the germs of the Incisors make their ap-
pearance under the same form. During the tenth week, processes from the sides of the
dental groove, particularly the external one, approach each other, and finally meet before
and behind the papilla of the anterior Molar ; so as to inclose it in a follicle, through the
mouth of which it may be seen. By a similar process, the
other teeth are gradually inclosed in corresponding follicles.
The germ of the Posterior milk Molar also appears during
the tenth week,.as a small papilla. By the thirteenth week,
the follicle of the Posterior Molar is completed ; and the
several papilla? undergo a gradual change of form. Instead
of remaining, as hitherto, simple, rounded, blunt masses of
granular matter, each of them assumes a particular shape ;
the Incisors acquire in some degree the form of the future
teeth; the Canines become simple cones; and the Molars
become cones flattened transversely, somewhat similar to
carnivorous molars. During this period, the papillae grow
faster than the follicles ; so that the former protrude from
the mouth of the latter. At this time, the mouths of the
follicles undergo a change, consisting in the development of
their edges, so as to form Opercula; which correspond in
some measure with the shape of the crowns of the future
teeth. There are two of these opercula in the Incisive follicles, three for the Canines, and

a

Upper jaw of human embryo
at Gth week ; showing b, the primi-
tive Dental Groove, behind a, the
Lip.

1 Diagrams illustrative of the formation of a Temporary, and its corresponding Permanent Tooth, from

a Mucous Membrane.

four or five for the Molars. At the fourteenth week, the inner lip of the dental groove has
increased so much, as to meet and apply itself in a valvular manner to the outer lip or

* Edin. Med. and Surg. Journal, vol. li.

184

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

ridge, which has been also increasing. The follicles at this time grow faster than the pa-
pilla', so that the latter recede into the former. The primitive dental groove then contains
ten papillae, inclosed in as many follicles; and thus all necessary provision is made for the
production of the first set of teeth. (This series of changes is represented in Fig. 88, a — g.)
The groove is now situated, however, on a higher level than at first ; and it has undergone
such a change by the closure of its edges, as to entitle it to the distinctive appellation of
secondary dental groove. It is in this secondary groove that those structures originate, which
are destined for the development of the Second or Permanent set of Teeth, — of those at
least which replace the Milk Teeth. This is accomplished in the following manner.

b. At about the fourteenth or fifteenth week, a little crescentic depression may be observed,
immediately behind the inner Opercula of each of the Milk-tooth follicles. This depres-
sion gradually becomes deeper, and constitutes what maybe termed a cavity of reserve :
adapted to furnish delicate mucous membrane, for the future formation of the sacs and pulps
of the ten anterior Permanent teeth. These cavities of reserve are gradually separated
from the secondary dental groove, by the adhesion of their edges; and they thus become
minute compressed sacs, situated between the surface of the gum and the milk-sacs. They
gradually recede, however, from the surface of the gum, so as to be posterior instead of in-
ferior to the milk sacs; and at last they imbed themselves in the submucous cellular tissue,
•which lias all along constituted the external layer of the milk-sac. The implantation of the
Permanent tooth-sacs in the walls of the Temporary follicles, gives toth£ former the appear-
ance of being produced by a gemmiparous process from the latter. This series of changes
is represented in Fig. 88, g — n.

c. We now return to the Milk-teeth, the papillae of which, from the time that their follicles
close, become gradually moulded into their peculiarly Human shape. The Molar pulps be-
gin to be perforated by three canals, which, proceeding from the surface towards the centre,
gradually divide their primary bases into three secondary bases ; and these become deve-
loped into the fangs of the future teeth. Whilst this is going on, the sacs grow more rapidly
than the papillse, so that there is an intervening space, which is filled with a gelatinous gra-
nular substance — the enamel blastema ; this closely applies itself to the surface of the pa-
pilla, but does not adhere to it. The branch of the dental artery which proceeds to each
sac, ramifies minutely in its'pruper membrane, but does not send the smallest twig into the
granular substance. At this period, the tubercles and apices of the papillee or pulps become
converted into real dentine or tooth-substance, in the manner already stated (§ 213) ; and the
granular matter is absorbed as fast as this appears ; so that, when the process of conversion
has reached the base of the pulp, the interior of the dental sac is left in the villousand vas-
cular condition of a true Mucous membrane, having upon it a very thin Inyerof the granular
substance, or enamel-pulp, which may be considered as a sort of Epithelium ; and it is by
the deposition of calcareous matter in the long prismatic cells of this, that the enamel is

Fig. 89.

00

J

Diagrams illustrative of the formation of the three Permanent Molar teeth, from the non-adherent

portion of the Dental Groove.

formed. The opercula, which close the mouth of the dental sac, attain a much greater de-
velopment in the Molar teeth of Herbivorous animals; where they dip down into the midst
of the dentinal pulp, and give origin to insulated spots both of enamel and cementum. It
lias been remarked by Mr. Lintott, that the lines along which the opercula meet, on the

DEVELOPMENT OF THE TEETH. 185

crown of the Human molar teeth, — that is to say. the groove which separates their tubercles,
— is by far the most frequent seat of incipient decay ; probably from its tissue having been
at the first less perfectly formed than that of the remainder.

d. Whilst these changes are going on, other important preparations are being made for the
Permanent set. The general adhesion of the edges of the Primitive Dental Groove, (§ a)
docs not invade the portion which is situated behind the Posterior Milk follicle; this retains
its original appearance for a fortnight or three weeks longer, and affords a nidus for the de-
velopment of the papilla and follicle of the Anterior Permanent Molar tooth, which is de-
veloped in all respects on the same plan with the Milk teeth. After its follicle has closed,
the edges of the dental groove meet over its mouth ; but as the walls of the groove do not
adhere, a considerable cavity is left between the sac of the tooth and the surface of the
gum. The cavity is a reserve of delicate mucous membrane, to afford materials for the
formation of the Second Permanent Molar, and of the Third Permanent Molar, or Wisdom-
tooth. The process just described is represented in Fig. 89, a — c. It will be convenient
here to continue the account of the development of these teeth, although it takes place at a
much later period. Towards the end of foetal life, the increase of the bulk of the Milk-tooth
sacs takes place so much more rapidly than the growth of the jaw, that the sac of the An-
terior Permanent Molar is forced backwards and upwards, into the maxillary tuberosity ;
and thus it not only draws the surface of the gum in the same direction, but lengthens out
the great cavity of reserve (Fig. 99, rf). During the few months which succeed birth, how-
ever, the jaw is greatly lengthened ; and when the infant is eight or nine months old, the
Anterior Permanent Molar resumes its former position in the posterior part of the dental
arch; and the great cavity of reserve returns to its original size and situation (e). This
cavity, however, soon begins to bulge out at its posterior side, and projects itself, as a sac, into
the maxillary tuberosity (/) ; a papilla or pulp appears in its fundus ; and a process of con-
traction separates it from the remainder of the cavity of reserve. Thus the formation of
the Second Permanent Molar from the first, takes place on precisely the same plan with the
formation of the Permanent Bicuspids from the Temporary Molars. The new sac at first
occupies the maxillary tuberosity (*r) ; but the lengthening of the jaw gradually allows it to
fall downwards and forwards, into the same line, and on a level, with the rest (/a). Before
it leaves the tuberosity altogether, the posterior extremity of the remainder of the cavity of
reserve sends backwards and upwards its last offset — the sac and pulp of the Wisdom-tooth
(i) ; this speedily occupies the tuberosity after the second molar has left it (j") ; and ulti-
mately, when the jaw lengthens for the last time, at the age of nineteen or twenty, it takes
its place at the posterior extremity of the range of the adult teeth (£). Thus, the Wisdom-
teeth are the second products of the posterior or great cavities of reserve ; and the final effects
of development in the secondary dental groove. In the Elephant, in which there is a con-
tinual new production of molar teeth at the back of the jaw, it is probable that from each
sac a cavity of reserve is formed, which produces the succeeding tooth ; and thus the only
essential difference between its dentition and that of Man, consists in the degree of continu-
ance of this gemmiparous process; which ceases in Man, after being twice performed, but
is repeated in the Elephant until nearly the close of its life.

e. We have thus sketched the history of the Development of the Teeth, up to the time
when they prepare to make their way through the gum. The first stage of this development
may be termed the papillary ; and the second the follicular. The latter terminates when the
papilla? are completely hidden by the closure of the mouths of the follicles, and of the groove
itself. The succeeding stage, which has long been known as the saccular, is the one during
which the whole formation of the Tooth-substance, and of the Enamel, takes place. It is
during this period, also, that the ossification of the jaw is being effected ; and that the bony
sockets are formed for the teeth, by the consolidation of the anterior and posterior ridges
bounding the alveolar groove (in which the dental groove was originally imbedded), and of
the interfollicular septa, which are produced by the meeting of transverse projections from
these ridges. — The history of development in the Lower Jaw is very nearly the same; the
chief difference being in the origin and situation of the primitive dental groove.

/. We have now only to consider the fourth or eruptive stage, — that in which the Teeth
make their way through the gum. This process chiefly results from the lengthening of the
fang, by the addition of new bony matter ; and the crown of the tooth is thus made to press
against the closed mouth of the sac (Fig. 98, m). This at last gives way, so that the sac as-
sumes its previous condition of an open follicle. When the edge of the tooth has once made
its way through the gum, it advances more rapidly than can well be accounted for by the
usual rate of lengthening of its fang ; and this appears to be due to the separation of the
bottom of the sac from the fundus of the alveolus ; so that the whole tooth-apparatus is car-
ried nearer to the surface, leaving a space at the bottom of the alveolar cavity, in which the
further lengthening of the root can take place (n). The open portion of the sac remains as
the narrow portion of the gum, which forms a vascular border and groove round the neck
of the perfected tooth (o). The deeper portion of the sac adheres to the fang of the tooth,

16*

186 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

and is converted by ossification into the Cementum or Crusta Petrosa (§ 210). What is
commonly denominated the Periosteum of the Tooth, really belongs as much to the Alveolus.
It is connected with the tooth by the submucous cellular tissue, which originally intervened
between the tooth-sac and the walls of the osseous cavity. It appears from Mr. Nasmyth's
researches, that the inner layer of the portion of the capsule which covered the crown of
the tooth, remains adherent to it; forming a thin coating of Crusta Petrosa (most of which
is, however, soon worn off) over the Enamel. — During the period that the Milk-teeth have
been advancing, along with their sockets, to their perfect state and ultimate position, the Per-
manent sacs have been receding in an opposite direction, and have with their bony crypts
been enlarging; and at last they occupy a position almost exactly below the former (wando).
They still retain a communication with the gum, however; the channel by which they de-
scended not having completely closed up, and the neck of the sac being elongated into a
cord which passes through this. The channels may afterwards serve as the itinera ckntium,
and the cords as gubernacula ; but it is uncertain whether they really afford any assistance in
directing the future rise of the tooth to the surface ; the successive stages of which are repre-
sented in Fig. 98, p — t. The sacs of the permanent teeth derive their first vessels from the
gums ; ultimately they receive their proper dental vessels from the Milk-sacs ; and, as they
separate from the latter into their own cells, the newly-formed vessels, conjoining into com-
mon trunks, also retire into permanent dental canals, and gradually become the most direct
channels for the blood transmitted through the jaw.

g. The following interesting generalizations respecting the development of the teeth, result
from Mr. Goodsir's researches. 1. The Jfi^-teeth are formed on both sides of either jaw
in three divisions,' — a Molar, a Canine, and an Incisive ; in each of which, dentition pro-
ceeds in an independent manner. 2. The dentition of the whole arch proceeds from
behind forwards ; the Molar division commencing before the Canine, and the Canine
before the Incisive. 3. The dentition of each of the divisions proceeds in a contrary direc-
tion, the Anterior Molar appearing before the Posterior, the Central Incisor before the La-
teral. 4. Two of the subordinate phenomena of nutrition also obey this inverse law ; —
the follicles closing by commencing at the median line and proceeding backwards ; and the
dental groove disappearing in the same direction. 5. Dentition commences in the Upper
Jaw, and continues in advance during the most important period of its progress. The
development of the Superior Incisors, however, is retarded by a peculiar cause; so that the
Inferior Incisors have the priority in the time of their completion and appearance. 6. The
germs of the Permanent teeth, with the exception of that of the Anterior Molar, appear in a
direction from the median line backwards. 7. The Milk-teeth originate, or are developed,
from mucous membrane. 8. The Permanent teeth, also originating from mucous membrane,
are of independent origin, and have no connection with the milk-teeth. 9. A tooth-pulp
and its sac must be referred to the same class of organs, as the combined Papilla and Folli-
cle from which a hair or feather is developed.

h. The following is the usual order and period of appearance, of the several pairs of Milk-
teeth. The Four Central Incisors first present themselves, usually about the seventh month
after birth ; but frequently much earlier or later : those of the Lower Jaw appear first.
The Lateral Incisors next show themselves, those of the Lower Jaw coming through before
those of the upper ; they usually make their appearance between the seventh and tenth months.
After a short interval, the Anterior Molars present themselves, — generally soon after the
commencement of the Second Year ; and these are followed by the Canines, which usually
protrude themselves between the fourteenth and twentieth months. The Posterior Molars are
the last, and the most uncertain in regard to their time of appearance; this varying from
the eighteenth to the tJtirty-sixth month. In regard to all except the front teeth, there is no
settled rule as to the priority of appearance of those in the Upper or Under Jaw : some-
times one precedes, and sometimes the other; but in general it may be stated, that, when-
ever one makes its appearance, the other cannot be far off. The same holds good in re-
gard to the two sides, in which development does not always proceed exactly paripassu. —
The period of Dentition is one of considerable risk to the Infant's life. The pressure upon
the nerves of the gum, which necessarily precedes the opening of the sac and the eruption
of the tooth, is a fruitful source of irritation; producing disorder of the whole system, espe-
cially of the Digestive organs, and not unfrequently giving origin to fatal Convulsive affec-
tions. These last have been particularly studied by Dr. M. Hall, who recommends the free
use of the gum-lancet, as a most important means of prevention and cure. Even where
Dentition proeeeds quite naturally and is not itself a cause of diseased action, it induces an
irritable state of the whole constitution, which aggravates the elferfs of other morbific causes.
It is, therefore, of the greatest consequence that the infant should be withdrawn during this
period, from all injurious influences; and that no irregularity of diet, or deficiency of fresh
air and exercise, should operate to its disadvantage.

i. After the lapse of a few years, the further elongation of the jaw permits the appear-
ance of the First True Molar; which, as already remarked, is really a Milk-tooth, so far as
its formation is concerned. This commonly presents itself about the middle or end of the

DEVELOPMENT OF THE TEETH. 187

Seventh Year ; sometimes preceding, and sometimes following, the exchange of the Central
Incisors, which takes place about the same time. When the Permanent Teeth have so
much enlarged, that they can no longer be contained within their own alveoli, they press
upon the anterior parietes of those cavities, and CEuise their absorption; so that each tooth
is allowed to come forwards, in some degree, into the lower part of the socket of the cor-
responding Temporary tooth. The root of the temporary tooth now begins to be absorbed,
generally at the part nearest its successor ; and this absorption proceeds as the new tooth
advances, until the root of the Milk-tooth is completely removed: when its crown falls off,
leaving room for the permanent tooth to supply its place (Fig. 88, p — f). This absorption
is usually regarded as due to the pressure of the Permanent tooth, but this does not appear
to be the case; for it is mentioned by Mr. Bell, that it is not an uncommon occurrence for
the root of the temporary tooth to be wholly absorbed, and for the crown to fall out spon-
taneously, long before the succeeding tooth has approached the vacant space. The same
has been remarked by Mr. Bell, of the cavity in the jaw which is formed for the reception
of the sac of the Permanent tooth, at the time that it buds off from that of the milk-tooth ;
the excavation being often seen to commence before the new sac is formed. Hence, although
the two processes, growth, and absorption, are usually contemporaneous in each instance,
they are by no means dependent on each other. Still it would seem that the existence, if
not the pressure of the new Tooth is necessary to determine the absorption of the old ; for
cases are' not unfrequent, in which the Temporary teeth retain their situation in the mouth,
with considerable firmness, until adult age, — the corresponding permanent ones not having
been formed.

k. In the successive replacement of the Milk-teeth by the Permanent set, a very regular
order is usually followed. The Middle Incisors are first shed and renewed, and then the
Lateral Incisors. The Anterior Milk Molars next follow ; and these are replaced by the An-
terior Bicuspid teeth. About a year afterwards, the Posterior Milk Molars are shed, and are
replaced in like manner by Bicuspid teeth. The Canines are the last of the Milk-teeth to
be exchanged ; the development of the new ones not taking place until the 12th year. In
the succeeding year, the Second pair of the True Molars appears ; the third pair, or denies
sapienti(Z, are seldom developed until three or four years subsequently, and often much
longer. It has been recently proposed* (and, from the evidence adduced in its favour, the
proposition would seem entitled to considerable attention) to adopt the successive stages in
the Second Dentition, as standards for estimating the physical capabilities of Children, es-
pecially in regard to those two periods which the Factory Laws render it of the greatest
importance to determine, namely, the ages of nine and thirteen years. Previously to the for-
mer, a child is not permitted to work at all ; and up to the latter, it may be only employed
during 9 hours a day. The necessities or the cupidity of Parents are continually inducing
them to misrepresent the ages of their children; and it has been found desirable, therefore,
to seek for some test, by which the capability of the Child may be determined, without a
knowledge of its age. A standard of Height has been adopted by the Legislature for this
purpose ; but upon grounds which, Physiologically considered, are very erroneous ; since, as is
well known, the tallest children are frequently the weakliest. According to Mr. Saunders,
the degree of advance of the Second Dentition may be regarded as a much more correct
standard of the degree of general development of the organic frame, and of its physical
powers ; and it appears from his inquiries, that it may be relied on as a guide to the real
age, in a large proportion of cases ; whilst no serious or injurious mistake can ever arise
from its use. It may happen that local or constitutional causes may have slightly retarded
the development of the Teeth ; in which case the age of the individual would rather be
under-estimated, and no harm could ensue : on the other hand, instances of premature de-
velopment of the Teeth very rarely, if ever, occur : so that there is no danger of imputing
to a Child a capability for exertion which he does not possess, as the test of height is con-
tinually doing. Moreover, if such an advance in Dentition should occur, it might probably
be regarded as indicative of a corresponding advance in the development of the whole or-
ganism ; so that the real capability would be such as the teeth represent it.

/. The following is Mr. Saunders' statement of the Ages at which the Permanent teeth
respectively appear. The first True Molars usually make their appearance towards the end
of the 7th year. Occasionally one of them protrudes from the gum at 6, or more frequently
at 63 years of age ; but the evolution of the whole of them may be regarded as an almost
infallible sign of the Child's being 7 years old. In other instances, however, where the tooth
on one side of the mouth is freely developed, it is fair to reckon the two as having emerged
from their capsule ; since the development of the other must be considered as retarded. This
rule only holds good, however, in regard to teeth in the same row ; for the development of
the teeth in either jaw must not be inferred from that of the corresponding teeth in the other.

" The Teeth a Test of Age, considered with reference to the Factory Children." By
Edwin Saunders.

188 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

With this understanding, the results of the application of the following table will probably
be very near the truth.

Central Incisors developed at .... 8 years.

Lateral Incisors . . . . . . 9 —

First Bicuspid . . . . . .10 —

Second Bicuspid . . . . . .11 —

Canines 12 to 12J

Second Molars 12^ to 14

The following are the results of the application of this test, in a large number of cases
examined by Mr. Saunders. Of 708 children of nine years old, 530 would have been pro-
nounced by it to be near the completion of their ninth year ; having the central, and either
three or four lateral, incisors fully developed. Out of the remaining 178, it would have in-
dicated that 126 were 8^ years old, as they presented one or two of the Lateral Incisors;
and the 52 others would have been pronounced 8 years old, all having three or four of the
Central Incisors. So that the extreme deviation is only 12 months ; and this in the incon-
siderable proportion (when compared with the results obtained by other means) of 52 in 708,
or 7| per cent. Again, out of 338 children of 13 years of age, 294 might have been pro-
nounced with confidence to be of that age, having the Canines, Bicuspid, and Second Molars,
either entirely developed, or with only the deficiency of one or two of either class. Of the
44 others, 36 would have been considered as in their 13th year, having one of the Posterior
Molars developed ; and 8 as near the completion of the 12th, having two of the Canines,
and one or two of the Second Bicuspid. In all these instances, the error is on the favourable
side, — that is, on the side on which it is calculated to prevent injury to the objects of the
inquiry ; in no instance did this test cause a Child to be estimated as older or more fit for
labour than it really was.

m. The value of this test, as compared with that of Height, is manifested by a striking ex-
ample adduced by Mr. Saunders. The height of one lad, J. J., aged 8 years and 4 months,
was 4 feet and £ of an inch ; that of another boy, aged 8 years and 7 months, was only 3
feet 7£ inches. According to the standard of height adopted by the Factory Commissioners
(namely, 3 feet 10 inches), the taller lad would have been judged fit for labour, whilst the
shorter would have been rejected. The Dentition of the latter, however, was further ad-
vanced than that of the former; for be had two of the Lateral Incisors, whilst the former
had only the Central ; and the determination of their relative physical powers, which would
have been thus formed, would have been in complete accordance with the truth. The elder
boy, though shorter than the other by 5^ inches, possessed a much greater degree both of
corporeal and mental energy, and his pulse was strong and regular ; whilst that of the
younger lad, who was evidently growing too fast, was small and frequent. — An instance
even more striking has come under the Author's own observation.

10. Simple Tubular Tissues.

218. We have seen that all the Animal Tissues, whose structure has been
yet considered, derive the materials of their growth and renovation from the
nutrient fluid ; which is brought into a more or less close relation with their
elementary parts, by means of Capillary blood-vessels. These seem to have
a claim to be regarded as among the elementary parts of the fabric; since they
are formed quite independently of the larger trunks, and have little in common
with them in their function. All those changes which take place between
the blood and the surrounding parts, whether ministering to the functions of
Nutrition, Secretion, or Respiration, occur during its movement through the
Capillary vessels: and the function of the larger trunks is merely to bring to
them a constant supply of fresh blood, regulated according to the demand
created by the actions to which it is subservient; and to remove the fluid
which has circulated through them. When we examine into the structure of
the Circulating apparatus in Plants and in the lower Animals, we rind that
the canals, which convey the nutritive fluid, are of two kinds ; — either simple
excavations in the solid tissues or unfilled vacuities ; — or tubes with definite
membranous walls. The former are known, in Plants, under the name of
inter-cellular passages ; and, among the lower tribes in particular, they have
a large share in the conveyance of the nutritious fluid from one part of the

STRUCTURE OF CAPILLARY BLOOD-VESSELS.

189

structure to the other. Similar passages exist to a great extent among the In-
vertebrata ; the venous circulation in particular being mainly carried on by
them. We have an example of them, even in Man, in the Sinuses through
which the venous blood is returned from the Brain ; these sinuses being simple
passages formed by the folds of the Dura Mater. Tn the higher Plants, however,
the circulation of fluid is for the most part carried on through Ducts, having
distinct membranous parietes ; and these ducts may be either straight and
simple tubes, as are those of the interior of the stem through which the sap
ascends ; or they may form a network by their mutual anastomosis, such as
that by which the sap descends through the bark and newer wood. Both of
these forms of ducts appear to be formed by the coalescence of cells ; the
straight cylindrical ducts being formed from cells, arranged in a simple linear
manner; and the network of vessels for the descent of the elaborated sap,
being produced by the junction, at various points, of cells of less regular form,
which stretch out to meet each other.

219. In all the higher Animals, — in their adult condition at least, — the
Capillary circulation is entirely carried on through tubes having distinct mem-
branous parietes. These tubes commonly form a minutely-anastomosing net-
work ; into which the blood is brought by the ramifications of the arteries on
one side, and from which it is returned by the radicles of the veins on the other.
The walls of the tubes are composed of a delicate membrane, in which an
appearance of transverse striation (as if produced by minute annular fibres)
can sometimes be discerned. The diameter of the Capillaries varies in dif-
ferent animals, in accordance with that of their blood-corpuscles; thus the

Fig. 90.

Capillary circulation in a portion of the web of a Frog's foot, magnified 110 diameters ; 1, trunk of

vein ; 2, 2, its branches j 3, 3, pigment cells.

Capillaries of the Frog are of course much larger than those of Man. The
diameter of the latter appears, from the measurements of Weber, Muller, and
others, to vary from about the 1 -3700th to the l-2500th of an inch ,• but as
they can only be examined after death, it is probable that these statements are

190

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

not altogether exact, particularly as tubes of the smallest of the above sizes
would not admit ordinary blood-corpuscles. The dimensions of the individual
vessels, indeed, are by no means constant ; as may be seen by watching the
Circulation in any transparent part, for some little time. Putting aside the
general changes, in diameter, which result from circumstances affecting all the
capillaries of a part, it may be observed that a single capillary will sometimes
enlarge or contract by itself without any obvious cause. Thus, the stream
of blood will sometimes be seen to run into passages, which were not before
perceived ; and it has hence been supposed that they were new excavations,
formed by the retreating or removal of the solid tissue through which it passes.
But a more attentive examination shows, that such passages are real capilla-
ries, which did not, at the time of the first observation, admit the stream of
blood-corpuscles, in consequence of the contraction of their calibre, or of some
other local impediment ; and that they are brought into view by the simple
increase in their diameter. The compression of one of the small arteries
will generally occasion an oscillation of the corpuscles of blood in the small-
est capillaries, which will be followed by the disappearance of some of them ;
but when the obstruction is removed, the blood soon regains its former velocity
and force, and flows exactly into the same passages as before.

220. The opinion was long entertained, that there are vessels adapted to sup-
ply the white or colourless tissues ; carrying from the arteries the Liquor
Sanguinis, or fluid portion of the blood ; and leaving the Corpuscles behind,
through inability to receive them. But such a supposition is altogether
groundless. Some of the white tissues, as Cartilage, are altogether destitute
of vessels ; and in others, the supply of blood is so scanty, as not to commu-
nicate to them any decided hue. It is evident from what has been already
stated, that the idea that Nutrition can only be carried on by means of Capil-
lary vessels, is entirely gratuitous. There is no essential difference, in fact,
between the nutrition of the non-vascular tissues, and that of the islets in the
midst of the network of capillary vessels, which traverses the most vascular.

Fig. 91.

Capillary vessels from the pia mater; a. calibre of the tube, partly occupied by oval nuclei, alter-
nately arranged lengthways, and epithelial in their character; 6, 6, 6, nuclei projecting on the exterior
of the tube ; c, c, walls, and d, calibre, of a large branch ; /,/, oval nuclei, arranged transversely. Mag-
nified 410 diameters.

FORMATION OF CAPILLARY BLOOD-VESSELS. 101

•

In both cases, the nutrient materials conveyed by the blood are absorbed by
the cells or other elementary parts of the tissue immediately adjoining the
vessels, and are imparted by them to others which are further removed ; and
the only variation which exists, is in the amount of the portion of tissue that
has to be thus traversed. There is great variety in this respect, as we
have seen, among the vascular tissues ; and we are only required to extend
our ideas, from the largest of the islets which we find in these, to the still
more isolated structures, of which the non-vascular tissues are composed.
The distribution of Capillaries through the vascular tissues, and the character
of the reticulation which they form, vary so greatly in the different parts of
the fabric, that it is possible to state with tolerable certainty the nature of the
part from which any specimen has been detached, — whether a portion of
skin, mucous membrane, serous membrane, muscle, nerve, fat, areolar tissue,
gland, &c. But the arrangement of vessels peculiar to each evidently has
reference only to the convenience of the distribution of blood among the
elementary parts of the tissue, and varies with their form. It is not possible
to imagine that it has any other relation than this to their function ; since, as
already shown, the function of each separate element of the organ, of which
that of the entire organ is the aggregate, is due to its own inherent vital
powers, — the supply of blood being only required as furnishing the material,
on which these are to be exercised.

221. It has been rendered highly probable, by the observations of Schwann
and other Physiologists, that the Capillaries of Animals originate in cells, like
the straight and anastomosing Ducts of Plants. Bodies having the appear-
ance of cell-nuclei may frequently be seen in the walls of the capillaries of
embryos and of tadpoles ; and these are too wide apart to warrant the idea, that
they are the nuclei of epithelial cells, such as those which line the larger
vessels. Similar nuclei may be brought into view in the capillaries of adult
animals, by treating them with acetic acid ; and they are particularly well
seen in the Pia Mater, which consists almost entirely of a congeries of blood-
vessels (Fig. 91). The accompanying figure shows the contrast between the
long oval nuclei b, b, imbedded at intervals in the walls of the true capillaries,
and rather projecting on their exterior; and the nuclei of the epithelium-cells,

f, /', lining the interior of a larger branch, which last are more numerous and
of less regular form, and are sometimes placed transversely to the direction of
the tube.

222. The first formation of the Capillary blood-vessels in the vascular
area in the Bird's egg, is described by Schwann as being

affected entirely by the coalescence of cells, which send -pitr go

off prolongations in various directions, in the manner of
stellate pigment-cells, such as those seen at c, c, Fig. 90.
By the junction of these prolongations, a network of tubes
is formed, which is at first very irregular in its character ;
the greatest diameter of the tubes being in the situation
of the centres or bodies of the original cells ; whilst be-
tween these, at the points where their prolongations coa-
lesced, they are much contracted. The calibre of the ves-
sels, however, gradually becomes equalized (Fig. 92); and
the network becomes connected with the larger trunks, and
bears a part in the general circulation. — Appearances indica- ,-,. .

f> . . . 1 l

live ot a similar process, have been seen in the tail ot very blood-vessels in the

young Tadpoles; so that it may probably be regarded as the vascular layer of the

general method, by which new capillaries are formed in germinal membrane of

the natural process of growth. Observations upon the a FOM>* at the 36th hour

history of the operations, which are performed for the ofl"cul

192 ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

repair of injuries, lead to precisely the same conclusions. The first appear-
ance of the vascular network in the newly-forming tissue, is in the form of
transparent arborescent streaks ; which push out extensions on all sides ; these
encounter one another, and form a complete series of capillary reticulations,
some of which come into connection with the vessels of the surrounding parts.
According to the observations of Mr. Travers,* isolated corpuscles enter these
newly-formed capillaries, and perform an oscillating movement in them for
some hours, before any series of them passes into it ; so that we cannot re-
gard the new channel as burrowed out by a string or file of red corpuscles,
pushed forth from the nearest capillary by vis a tergo, as some have main-
tained.

11. Compound Tubular Tissues.

223. There now remain to be described two elements of the Animal fabric,
to which there is scarcely anything that bears the least analogy in the struc-
ture of Plants ; — namely, the Muscular and Nervous tissues. We have seen
that, putting aside the Simple Fibrous tissues, whose function is purely me-
chanical, the Animal fabric, so far as we have yet passed its elements under
review, is constructed upon the very same type with that of Plants ; all the
parts actively concerned in the processes of nutrition, secretion, reproduction,
&c., retaining their original cellular character ; the vessels that serve for the
conveyance of fluid, having their origin in cells, whose cavities have coalesced ;
whilst the more solid portions of the frame-work are made up of united cells,
whose cavities are occupied by internal deposit. — Now the purpose of the
Muscular and Nervous system is entirely different. The former is the one,
by which all the sensible movements of the body are immediately effected ;
and it is only amongst a small number of Plants, that any such movements
are exhibited. The latter serves as the instrument by which sensations are
received ; and by which the instincts, emotions, or volitions, excited by these
sensations, act upon the muscles : — a class of functions which we have no
reason whatever to regard as performed by Plants. In fact, as already pointed
out (§ 1 — 4), the distinction between the two kingdoms is more properly
founded upon the presence of these functions and of their instruments in the
Animal, and upon their absence in the Plant, than upon any other structural
character.

224. Now it might have not been unreasonable to expect, that tissues alto-
gether so dissimilar in their properties, and in the purposes to which they are
destined, should have a structure departing widely from the type of the simple
Cell. Yet it does not appear that this is the case. That portion of the Nerv-
ous matter, by which its most active functional changes are effected, retains
its original cellular character without alteration ; and the so-called fibres,
which constitute the Nerve-trunks, and which convey the influence of these
changes, are in reality tubes, formed as it would seem by the coalescence of
a linear series of cells, and chiefly distinguished by the peculiar nature of
their internal deposit. In like manner, we shall find that the ultimate Mus-
cular Fibre is also a tube, formed out of the same elements, and distinguished
by the nature of its contents ; which, in the most perfect form of the tissue,
are composed of linear series of extremely minute secondary cells.

225. Muscular tissue exists under two forms ; one in which the ultimate
fibres are marked by transverse striae ; and the other in which they are plain
orunstriped. The former is chiefly employed in performing the various move-
ments, which are effected through the agency of the Nervous system, and which

* Physiology of Inflammation and the Healing Process.

STRIATED MUSCULAR FIBRE.

193

Fig. 93.

are connected with the peculiarly Animal powers of the being. The latter is
with difficulty called into action through the nervous system, but is much
more readily excited by stimuli applied to itself; and this is employed to per-
form various movements, which are more immediately concerned in the Vege-
tative or organic functions.*

226. When we examine an ordinary Muscle (from one of the extremities,
for example) with the naked eye, we observe that it presents a fibrous ap-
pearance ; and that the fibres are arranged with great regularity, in the direc-
tion in which the muscle is to act. Upon further examination it is found,
that these fibres are arranged in fasciculi or bundles of larger or smaller size,
connected by means of areolar tissue ; and when the Microscope is applied to
the smallest fibre which can be seen with the naked eye, it' is seen itself to
consist of a fasciculus, composed of a number of cylindrical fibres lying in a
parallel direction, and closely bound to-
gether. These primitive fibres present
two sets of markings or striae ; one set
longitudinal, — the other transverse or
annular. By more closely examining
these fibres, when separated from each
other, it is frequently seen that each may
be resolved into Jibrillx, by the splitting
of its contents in a longitudinal direction,
as shown in Fig. 93. These fibrillae have
a peculiar beaded appearance, which will
be presently noticed more particularly. —
It not unfrequently happens, however, that
when a fibre is drawn apart, its contents
separate in the direction of the transverse striae ; forming a series of discs, as
shown in Figs. 94 and 95. This cleavage is just as natural as the former,
though less frequent; and it leads us to a view of the composition of Muscu-
lar Fibre, somewhat different from the one commonly adopted. To use the

Fig. 94.

Fasciculus of Fibres of Voluntary Muscle;
the fibres separated at one end, into brush-
like bundles of fibrillse.

Portion of Human Muscular fibre, separating into discs, by cleavage in direction of transverse stria.

words of Mr. Bowmanj it would be as proper to say, "that the fibre is a pile
of discs, as that it is a bundle ofjibrillse; but in fact it is neither the one nor
the other, but a mass in whose structure there is an intimation of the existence
of both, and a tendency to cleave in the two directions. If there were a gene-
ral disintegration along all the lines in both directions, there would result a

By some, the two classes have been spoken of as those of Voluntary and Involuntary
muscles; but this distinction is not correct; since every muscle ordinarily termed voluntary,
may be called into action involuntarily.

t See Bowman on the Minute Structure and Movements of Voluntary Muscle: in Phil.
Trans. 1840.

17

194

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

series of particles, which may be termed primitive particles or sarcous ele-
ments, the union of which constitutes the mass of the fibre. These elementary

[Fig. 95.

Fragments of Striped Elementary Fibres, showing a cleavage in opposite directions; magnified 300
diameters; 1, longitudinal cleavage; the longitudinal and transverse lines are both seen ; some longitu-
dinal lines are darker and wider than the rest, and are not continuous from end to end ; this results from
partial separation of the fibriHEe ; 6, fibrilloe, separated from one another by violence at the broken end
of the fibre, and marked by transverse lines equal in width to those on the fibre ; 7, 5 represent two ap-
pearances commonly presented by the separated single fibrilla, (more highly magnified ;) at 7 the borders
and transverse lines are all perfectly rectilinear, and the included spaces perfectly rectangular; at 8 the
borders are scalloped, the spaces bead-like ; when most distinct and definite, the fibrilla presents the
former of these appearances ; 2, transverse cleavage ; the longitudinal lines are scarcely visible ; 3, in-
complete fracture following the opposite surfaces of a disc, which stretches across the interval and re-
tains the two fragments in connection ; the edge and surface of this disc are seen to be minutely granular,
the granules corresponding in size to the thickness of the disc, and to the distance between the faint
longitudinal lines; 4, another disc nearly detached; 5, detached disc more highly magnified, showing the
sarcous elements.]

particles are arranged and united together in the two directions. All the re-
sulting discs, as well as fibrillae, are equal to one another in size ; and con-
tain an equal number of particles. The same particles compose both. To
detach an entire fibrilla, is to abstract a particle of every disc; and vice versa."
227. The elements of Muscular Fibre are bound together, in the perfect
condition of the fibre, by a very delicate tubular sheath. This cannot always
be readily brought into view; but it is occasionally seen with great distinct-
ness : thus, when the two ends of a fibre are drawn apart, its contents will

sometimes separate without the rupture
of the sheath, which then becomes evi-
dent ; and this, during the act of con-
traction, may sometimes be observed
to rise up in wrinkles upon the surface
of the fibre, as seen in Fig. 100. This
sheath is quite distinct from the areolar
tissue, which binds the fibres into fasci-
culi; and it has been termed, for the
Its existence may be demonstrated

Fig. 96.

Fibre of Human Muscle broken across; the
fragments connected by the untorn Myolemma.

in

sake of distinction, the Myolemma.
any Muscular fibre, by subjecting it to the action of lluids, which occasion a
swelling of its contents ; this is especially the effect of acids and alkalies, and
may be well produced by the citric and tartaric acids, and by potash. For a
time, the Myolemma yields to the distention which takes place from within;
but at last it bursts at particular points, and a sort of hernia of its contents
takes place, making the existence of a perfect envelope in all other parts quite

STRIATED MUSCULAR FIBRE. 195

evident. This membrane is itself perfectly transparent, and has nothing to do
with the production of either the longitudinal or the transverse striae. There is
no reason to believe that it is perforated either by nerves or by capillary ves-
sels ; in fact it seems to be an effectual barrier between the real elements of
Muscular structure, and the surrounding parts. That it has no share in the
contraction of the fibre, is evident from the fact just mentioned, respecting the
condition which it occasionally presents when the fibre is much shortened.

228. Muscular Fibres are commonly described as cylindrical ; but there is
reason to believe that they are rather of a polygonal form, their sides being
flattened against those of adjoining fibres (Fig. 97). In some instances the
angles are sharp and decided ; in others they are rounded off, so as to leave
spaces between the contiguous fibres for the passage of vessels. In Insects,
the fibres often present the form of flattened bands. The average diameter of
the fibres in Man maybe stated at about l-400th of an inch; being somewhat
greater than this in the Male, and less in the Female. Their size varies con-
siderably, however, in different classes of animals; and even in the same ani-
mal, and the same muscle. The following table gives illustrations of these
varieties; the extremes are those met with by Mr. Bowman himself; but
other observers speak of dimensions more widely separated.

Fractions of an inch.

MAMMALIA

BIRDS . .
REPTILES .

FISH . .

INSECTS

It is interesting to remark, upon this table, that the Muscular Fibre of Rep-
tiles and Fishes is upon the whole much larger than that of other Vertebrata,
and that its dimensions present the greatest extremes of variation ; whilst in
Birds, it is much smaller than in all other Vertebrata, and its dimensions are
also less variable. Further, the size of the fibres bears no proportion to that
of the animal; for we observe that in the Chaffinch they are larger than in
the Owl, in the Cat larger than in the Horse, and in the Frog often larger
than in the Boa. Moreover in Insects, the diameter of the fibres is even
greater than it is in Mammalia. — The average distance of the transverse striae,
in the muscular fibre of different animals, is very nearly uniform ; as will be
seen from the following table. Between the extremes, however, there is con-
siderable variation ; and this will be presently shown to depend upon the con-
dition of the muscle, at the time of examination. The distance is not only
often different in the same muscle and the same fasciculus, but even in the
same fibre in different parts of its length. The figures indicate the number of
striae in l-1000th of an inch. The extremes in the same specimen, however,
are in no instance so widely apart, as the table indicates for the Class ; the

f u ( Male . .
Human I Female
I Cat

• • 557

• • HT*

to
to
to

384-

Horse

I

Mole

i

to

~SuS

Mouse

61 b

Owl

i „

40 0

to

I

Chaffinch

1000

1

Heron

800
1

to

'tuu

!Fro£

1

to

4 JO

x i \JQ,
Lizard . .

' 1000

1

aoo

Boa

I

(To 0

to

1

! Skate ........

to

J»0

Cod

Triir

to

J

65

SStaghorn Beetle
Blue-bottle Flv .

_JL

to

250
I _

196

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

greatest proportion between the maximum arid minimum being, except in In-
sects, as 2 to 1.

Human

Other Mammalia

Birds

Reptiles

Fish

Insects

Maximum.

Minimum.

. 35-0

6-0

. 15-0

6-7

. 140

7-0

. 20-0

6-7

. 18-0

7-5

16-0

4-5

Mean.

9-4
10-9
10-4
U-7
11-1

9-5

229. It has been maintained by some, that each Muscular Fibre is a hol-
low bundle of fibrillae ; but the appearance presented by transverse sections
proves that this is not the case, the whole area of the tube being occupied by
nbrillre, without any trace of central cavity. The extremities of the cutfibrillae,
however, cannot always be distinguished in Mammalia, in consequence, as it
would seem, of their close and intimate lateral union ; but they are very evi-

Fig. 97.

Transverse section of Muscular fibres from pectoral muscle of Teal ; showing the irregular form of the
fibres, and the aggregation of circular particles, with which they are completely filled.

dent in Birds, Reptiles, and Fishes (Fig. 97). The addition of an acid in-
creases the distinctness of the fibrilla?, by widening the interstices between
them.

230. When the fibrillse are separately examined, they are found to present
an alternation of dark and light spaces, corresponding with the transverse
stria; of the fibre, and the lighter intervals between them. It is this alterna-
tion, which gives to the fibrillas the beaded appearance they present, when
their outline is not perfectly seen. When good specimens, however, are
carefully examined under a sufficient magnifying and good defining power, it
is seen that the border of the fibrillac is straight or nearly so ; so that the
beaded appearance is an optical illusion. Moreover, each of the light spaces
is seen to be crossed by a delicate but distinct line, separating it into two
equal parts ; and upon attentive examination it is seen, that a transparent
border, equal in breadth to either of these parts, is seen at the sides, as well
as between the ends, of the dark spaces. Thus each dark space is completely
surrounded by this pellucid border ; and it can scarcely be doubted that the
whole constitutes a complete though minute cell, and that the entire librilla

STRIATED MUSCULAR FIBRE.

197

Fig. 98.

Fragment of Muscular fibre
from macerated heart of Ox,
showing formation of striae by
the aggregation of fibrilte.

Fig. 99.

is made up of a linear aggregation of such cells.* When the fibril is in a
state of relaxation, as seen at or, the diameter of the cells is greatest in the

longitudinal direction ; but when it
is contracted, the fibril increases in
diameter as it diminishes in length ;
so that the transverse diameter of
each cell equals or even exceeds the
longitudinal diameter, as seen at b.
The difference between the two
states is frequently much more strik-
ing than is represented in the figure.
— Thus the act of Muscular contrac-
tion seems to consist in a change of

form in the cells of the ultimate fibrillae, consequent upon an
attraction between the walls of their two extremities, or per-
haps between their nuclei ; and it is interesting to observe
how very closely it thus corresponds with the contraction of
certain Vegetable tissues, of which the component cells change
their form when irritated, and thus produce a movement (§ 1).
The essential difference, therefore, between the striated mus-
cular tissue of Animals, and the contractile tissues of Plants,
consists in the subjection of the former to nervous influence.
— The diameter of the ultimate fibrillae, and the length of the
component cells, will of course vary according to the contract-
ed or relaxed condition of the fibre ; but they otherwise seem
to be tolerably uniform in different animals. The average
diameter may be stated at about 1-10, 000th of an inch; but
it has been observed as high as l-5000th, and as low as 1-
20,000th, even when not put upon the stretch. The length of
the component cells corresponds, of course, to the distance of
the striae on the entire fibre ; and this also has been just shown
to average about 1-1 0,000th of an inch.

231. The general opinion as to the disposition of the fibres during the con-
traction of Muscle, has been, until lately, that of Prevost and Dumas, who
stated that they were thrown into a sinuous or zig-zag flexure. Recent ob-
servations, however, have fully demonstrated the incorrectness of this view ;
the improbability of which might have been suspected from the consideration,

* This account of the ultimate structure of Muscular Fibre was first published simulta-
neously (March, 1S4G), by the Author of this Treatise, in his Manual of Physiology, and by
Dr. Sharpey, in his new edition of Dr. Quain's Anatomy. Both of these statements, which
were completely independent of each other, were founded upon the examination of the very
beautiful preparations of Muscular Fibre, made by Mr. Lealand the Optician ; who appears
to have been the first to direct attention to the transverse line dividing the bright space, and
to the bright border edging the dark spot. A similar delineation had previously been pub-
lished, however, by Dr. Goodfellow (Physiological Journal, No. IV.) ; but his interpretation
of the appearances was altogether different; for he considered the dark spaces as the " sar-
cous elements" of Mr. Bowman, and regarded them as separately inclosed within partitions
formed by internal prolongations of the general investing Myolemma. By Mr. Erasmus
Wilson, again, the appearances were described as leading to the belief that two kinds of
cells exist in each fibrilla, a dark and a light ; a pair of b'ght cells, separated by the delicate
transverse line just spoken of, being interposed between each pair of dark ones [System of
Anatomy, 3d Am. Edit., p. 183]. The bright edging to the dark spots was overlooked by
him. The view taken by Dr. Sharpey and the Author has the entire concurrence of several
of the most eminent Microscopists in London and elsewhere ; and it is confirmed by the
remarkable similarity between the aspect of the Muscular fibrilla, and that of a minute Con-
i'erva, seen under the same magnifying power, — the cellular constitution of the latter being
indubitable.

17*

Structure of the
ultimate fibrillse of
striated muscular
fibre :— a, a fibril
in a state of ordi-
nary relaxation ;
b, a fibril in a state
of partial contrac-
tion.

198

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

that fibres in this state of flexure could scarcely be imagined to be exerting
any force of traction. Prof. Owen has noticed that, in the contracted state of
the very transparent muscles of some Entozoa, each separate fibre, which
may be seen with great distinctness, presents a knot or swelling in the middle,
besides being generally thickened; but that it is simply shortened, without
falling out of the straight line. Dr. A. Thomson remarked the same thing in
the Frog; single fibres, whilst continuing in contraction, being simply short-
ened, without falling into zig-zag lines : and he was led to suspect, from this
and other circumstances, that the zig-zag arrangement was not produced, until
the act of contraction had ceased. The recent inquiries of Mr. Bowman
have proved most satisfactorily, that, in the state of contraction, there is an
approximation of the transverse striae, and a general shortening of the fibre ;
and that its diameter is a,, the same time increased ; but that it is never thrown
out of the straight line, except when it has ceased to contract, and its two
extremities are still held in proximity by the contraction of other fibres. The
whole process may be distinctly seen under the Microscope, in a single fibre
isolated from the rest : it is, of course, desirable to select the specimen from
those animals, in which the contractility of the Muscle is retained for the
longest period after death, — which is particularly the case in Reptiles .among
Vertebrata, and in most Invertebrata (Mr. Bowman particularly recommends
the Crab and Lobster) ; but the change has been fully proved to differ in no
essential degree, in the warm-blooded Vertebrata. The contraction usually
commences at the extremities of the fibre; but it frequently occurs also at one
or more intermediate points. The first appearance is a spot more opaque
than the rest, caused by the approximation of a few of the dark points of
.some of the fibrillae : this spot usually extends in a short time through the
Avhole diameter of the fibre; and the shading, caused by the approximation
of the transverse striae, increases in intensity. The striae are found to be
two, three, or even four times as numerous, in the contracted, as in the un-
contracted part; and are also proportionally narrower and more delicate.
The line of demarcation between the contracted and uncontracted portions is
well defined; but, as the process goes on, fresh stria3 are absorbed (as it
were) from the latter into the former. The contracted part augments in thick-
ness ; but not in a degree commensurate with its diminished length ; so that
its solid parts lie in smaller compass than before, — the fluid which previously
intervened between them, being pressed out in bullae under the myolemma
(Fig. 100). The force with which the elements of the fibre thus tend to ap-
proximate is evidently considerable ; for if the two extremities be held apart,

Fig. 100.

.Muscular fibre of Dytiscus, contracted in the centre; the striae approximated; the breadth of the fibre
increased ; and the sarcolemma raised in bulls; on its surface.

the fibre is not unfrequently ruptured. This corresponds with the appear-
ances found in the muscles of persons who have died from tetanus ; for in
the ruptured fibres of those muscles, which have been the subjects of the
spasmodic action, the striae have been observed to approximate so closely,
as to be scarcely distinguishable. When the contraction is not very decided,
the dark and elevated spot appears to play like a wave along the fibre, before
it involves the whole diameter in any part (Fig. 101, 2) ; and even when con-

STRIATED MUSCULAR FIBRE.

199

Fig. 101.

$;
^iliifii-...

-j

siderable traction is being exercised, there is continual interchange in the ele-
ments by which it is effected, — the discs at one end of the contracted part
receding from each other, whilst at the other end new discs are being re-
ceived into it.

232. The foregoing description is chiefly
derived from the appearances presented by
muscular fibre, when spontaneously passing
into that state of contraction, which is termed
the rigor mortis ; but there can be no rea-
sonable doubt, that the phenomena of con-
traction, excited by the agency of the nerves,
are precisely similar. Mr. Bowman has re-
marked, that stimuli of various kinds, direct-
ly applied to them, produce corresponding
effects, although, in the case of galvanism,
the change is too rapid for its steps to be
followed ; and that, from the appearances
presented by muscles which have been af-
fected with tetanic spasms, the contraction
produced by nervous agency may be inferred
to correspond in character. — It now remains,
therefore, to inquire what is the cause of the
zig-zag arrangement, which is often seen in
the fibres. This may be easily produced, by
approximating the ends of a fasciculus, after
the irritability of its fibres has ceased ; and
it would not seem unlikely, that the passage
of vessels or nerves should determine the
points at which the flexures take place.
Hence it appears, that the sinuous or zig-zag
arrangement is that into which fibres are
naturally thrown, if, on elongation following

contraction, they are not at once stretched by antagonist muscles.* Many
facts support the opinion, which has long been held by several Physiologists,
that, when an entire muscle is contracting, all its fasciculi are not in con-
traction at once ; but that there is a continual interchange in the parts,
by which the tension is effected ; some relaxing, whilst others are short-
ening. When the ear is applied to a muscle in vigorous action, an exceed-
ingly rapid faint silvery vibration is heard; which seems to be attributable to
this constant movement in its substance. Now, on examining a muscle, of
which some fasciculi present the zig-zag arrangement, others will be seen (if
the two extremities have not been purposely approximated) to be quite straight,
and in a state of contraction ; and it thence appears, that the former appear-
ance is presented by bundles of fibres, which have either not yet entered into
contraction, or which have relaxed after undergoing it; but of which the ex-
tremities are still approximated, by the agency of other contracting fibres. —
The result of various experiments made for the purpose, leads to the conclu-
sion, that the total bulk of a muscle in contraction is not less than when it is
in a relaxed state ; or that the difference, if any exist, is extremely trifling.

233. Every Muscular Fibre, of the striated kind at least, is attached at its
extremities to white fibrous tissue ; through the medium of which it exerts its
contractile power on the bone or other substance, which it is destined to move.

Muscular fibre of Skate,'in a state of
rest (1), and in three different stages of
contraction (2, 3, 4). ,

* Mr. Bowman's conclusions have recently been confirmed by Prof. E. Weber. (Archives
d'Anatomie Generale, Jan. 1846.)

200

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

The whole fasciculus of fibrillae usually seems to end abruptly in a perfect
disk ; and the myolemma terminates there. The tendinous fibres are attached
to the whole surface of the disk; and probably become continuous with the

Fig. 102.

Attachment of Tendon to Muscular Fibre, in Skate.

myolemma. Thus the whole muscle is penetrated by minute fasciculi of tendi-
nous fibres ; and these collect at its extremities into a Tendon. Sometimes the
muscular fibres are attached obliquely to the Hendon, which forms a broad
band that does not subdivide ; this is seen in the legs of Insects and Crusta-
cea, in which the muscular fibres have apenniform arrangement; being inserted
into the tendon, 'on either side, like the laminae of a feather into its stem.

234. The Muscular Fibre of Organic Life is very different from the pre-
ceding. It consists of a series of tubes, which do not present transverse

Fig. 103.

Non-slriated Muscular Fibre; at
b, in its natural state ; at a, show-
ing the nuclei after the action of
acetic acid.

[Fig. 104.]

4. A muscular fibre
of Organic Life with
two of its nuclei ;
taken from the uri-
nary bladder, and
magnified (inn diam-
eters ; 5, muscular
fibre of organic life
from the stomach,
magnified the same.]

strife, and in which the longitudinal strife are very faint ; these tubes are
usually much flattened, and cannot be shown to contain distinct fibrillae.

NON-STRIATED MUSCULAR FIBRE. 201

Their size is usually much less than that of the fibres of Animal life ; but,
owing to the extreme variation in the flattening whicli they undergo, it is dif-
ficult to make a precise estimate of their dimensions. Those of the aliment-
ary canal are stated by Dr. Baly to measure from about the l-2500th to the
l-5600th of an inch; in the foot of the common Mussel, the Author has
found them 1o be as much as the 1-1 920th of an inch ; whilst in the respira-
tory sac of a Phallusia (an Ascidian Mollusk), their diameter is no more than
l-8400th. They sometimes present markings, which indicate a granular ar-
rangement in their interior ; and these markings have occasionally a degree
of regularity, which approaches that of the stria? on the striped Muscular fibres.
They frequently present nodosities at intervals, which are the nuclei of their
original component cells ; and, where these nuclei are not otherwise visible,
they may be brought into sight by acetic acid (Fig. 103, a). The plain or
non-striated fibres, like those of the other muscles, are usually arranged in a
parallel manner, into bands or fasciculi ; but these fasciculi are generally in-
terwoven into a net-work, not having any fixed points of attachment, but con-
tracting against each other. It is of this kind of structure, that the muscular
substance of the walls of the oesophagus, stomach, intestinal tube, bladder,
and uterus, is composed ; it occurs also in the bronchial tubes, in the ureters,
and most of the larger gland-ducts, and in the iris. In the Heart, are found
various forms of Muscular fibre ; some being distinctly striated, others quite
plain ; and others of intermediate character. The average size of the fibres
is less than that of the fibre, of which the voluntary muscles are composed ;
and the fasciculi, instead of being straight and parallel, are considerably in-
terlaced. This intermediate character accords well, as we shall hereafter see,
with the actions of the organ ; which correspond in their energy and rapidity,
with the contractions of voluntary muscles ; whilst they agree with those of
the non-striated kind, in being but little influenced by the nervous system.
The middle coat of the Arteries contains a contractile tissue, very similar to
that of unstriped muscle; and fibres of a similar nature are interwoven Avith
other fibrous tissues in the Skin, and especially in the Dartos, — giving rise in
the former to the state termed culis anserina, under the influence of cold or
of depressing emotions ; and in the latter to the wrinkling of the scrotum.
There are certain points, at which the one system of fibres comes into close
connection with the other. This is the case, for example, in the oesophagus;
the upper part of which contains striated fibres, and is thrown into contrac-
tion by nerves ; whilst the muscular wall of the lower part seems entirely
composed of non-striated fibres, and acts for the most part independently of
the nerves. The point of transition varies in different animals (§ 386) ; and
seems not to be constant among individuals of the human species.

235. The Myolemma of the Muscular Fibre appears to be the part first
formed ; being distinctly visible long before any traces of fibrillae can be ob-
served in it. This tube seems to take its origin, like the ducts of Plants, in
cells laid end to end, the cavities of which coalesce, by the disappearance of
the partitions, at a subsequent period ; and the nuclei of these original cells
may be distinctly seen, for some time after the appearance of the strire, which
indicate the formation of the fibrillas in their interior. In an early stage of
the development of the fibres, indeed, these bodies project considerably from
their sides : in this respect, as well as in others, there is a close correspond-
ence between the temporary character of the Muscular fibre of Animal life,
and the permanent condition of that of Organic life. In the fully formed
muscle of Animal life, they are not perceptible, except when a peculiar me-
thod has been adopted for bringing them into view. This method consists in
treating the fibre with weak acids, which render the nuclei more opaque,
whilst the surrounding structure becomes more transparent. They are usually

202

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

numerous in proportion to the size of the fibre. There is every probability
that these nuclei continue to act, like the " germinal spots" of the glandular

Fig. 105.

A

Fig. 106.

Muscular fibres from fetal pectoralis ;
A, from Calf at two months ; B, from hu-
man fetus of nine months.

Mass of ultimate fibres from
the pectoralis major of the hu-
man fetus, at nine months.
These fibres have been im-
mersed in a solution of tartaric
acid ; and their " numerous cor-
puscles, turned in various direc-
tions, some presenting nucle-
oli," are shown.

follicles or parent-cells, as centres of nutrition ; from which the minute
secondary cells, that compose the fibrillae, are developed as they are re-
quired. The diameter of the Muscular fibre of the foetus is not above one-
third of that which it possesses in the adult ; and as the size of their ultimate
particles is the same in both cases, their number must be greatly multiplied
during the growth of the structure. But we shall find reason to believe, that
a decay is continually taking place in the component cells, with a rapidity
proportional to the functional activity of the Muscle, and their generation,
which occurs as constantly when the nutrient operations proceed in their
regular course, is probably accomplished by a development from these cen-
tres, at the expense of the blood, with which the muscle is copiously supplied.

236. From the preceding history it appears, that there is no difference, at
an early stage of development between the striated and non-striated forms of
Muscular fibre. Both are simple tubes, containing a granular matter, in which
no definite arrangement can be traced, and presenting enlargements occasioned
by the presence of the nuclei. But whilst the striated fibre goes on in its
development, until the fibrillse, with their alternation of light and dark spaces,
are fully produced, the non-striated fibre retains throughout life its original
embryonic character.

237. Notwithstanding the energy of growth in Muscular Fibre, and the
constant interstitial change which seems to take place in its contents, it is
doubtful if it is ever regenerated, when there has been actual loss of substance.
Wounds of muscles are united by Areolar tissue, which gradually becomes
condensed; but its fibres never acquire any degree of contractility.

238. The Chemical Composition of Muscular Fibre seems to be very uni-
form, from whatever source it is obtained. It is impossible, however, to de-
termine it with precision ; on account of the difficulty of completely isolating
the substance of the fibres from the areolar tissue, vessels, and nerves, that
are blended with them. The proper muscular substance differs from the
simple fibrous tissues, in not being resolvable into gelatine by the prolonged
action of boiling water; and in being soluble in acetic acid, from which it is

it

CHEMICAL COMPOSITION OF MUSCLE. 203

precipitated by ferrocyanide of potassium, showing that it belongs to the pro-
teine-conipounds. The following analyses of Muscle by Berzelius corre-
sponds very exactly with those since made by Braconnot, Schultz, Marchand,
and other Chemists :

Fibrine (from the proper muscular substance) .... 15-80

Gelatine (from areolar tissues) . . . . . 1'90

Albumen and ha'inatine ........ 2'20

Phosphate of lime, with albumen ...... '08

Alcoholic extract, with salts (lactates?) 1-80

Watery extract, with salts ........ 1'05

Water, and loss 77-17

100-00

Thus something less than 23 percent, of solid matter exists in ordinary meat ;
and in 100 parts of this solid mattter, there are about 7 k parts of fixed salts.

[Kreatine (from xjsaj, flesh), originally discovered by Chevreul, in 1835, has been proved
by the recent investigations of Liebig to be a constant ingredient of the muscles of all the
higher classes of animals. Schlossberger found it in the flesh of the alligator. Its crystals
are colorless, perfectly transparent, and of great lustre. They form groups, the character
of which is exactly similar to that of sugar of lead. Its formula is C8 N3 Hn O6. It dissolves
easily in boiling water, and a solution saturated at 212° forms on cooling a mass of small bril-
liant crystals, and is nearly insoluble in cold alcohol. It is neither acid nor basic. From the
action of strong mineral acids, a new body of totally different chemical qualities, a true or-
ganic alkali is formed, which Liebig has called Kreatinine. It is easily obtained from the
hydrochlorate or the sulphate. Kreatinine is more soluble both in cold and hot water than
kreatine; it dissolves in boiling alcohol, and crystallizes on cooling. In its chemical cha-
racter it is analogous to ammonia. — Its formula is C8 N3 H7 O2. — Researches on the Chemistry
of Food, byj. Liebig.— London, 1847.— M. C.]

a. The exact correspondence in ultimate composition, between dried Muscle, and dried
Blood, according to the analyses of Playfair and Bockmanh, is not a little remarkable. The
following are their results.

PlATFAIH. BOCKXAZTN.

Muscle. Blood. Muscle. Blood.

Carbon . . . 51-83 51-95 51-89 51-90

Hydrogen . . . 7-57 7-17 7-59 7-33

Nitrogen . . . 15-01 15-07 15-05 1508

Oxygen . . . 21-36 21-39 21-24 21-21

Ashes . . . 4-23 4-42 4-23 4-42

It may be questioned, from these results, whether the amount of Hsematine in Muscle is not
greater than that which is represented by the previous analysis ; since a tissue composed of
Fibrine and Albumen alone, could not possess the same ultimate composition with one, in
which Hsrnatine is present in large proportion.

b. Some very interesting researches have lately been made by Helmholtz,f on the changes
induced in the tissue by Muscular action. Powerful contractions were induced by electricity
in the amputated leg of a Frog ; and were kept up as long as the irritability was retained.
The flesh of the two limbs was then analyzed; and it was found that, in every instance the
water-extractive was diminished in the electrized muscle, to the extent of from 20 to 24 per
cent.; whilst the alcoholic extract was increased to about the same amount. — Similar results
were obtained from experiments on warm-blooded animals; the amount of change, how-
ever, being less, on account of the shorter duration of th«r muscular irritability.

239. Muscular tissue, properly so called, is as extra-vascular as cartilage
or dentine; for its fibres are not penetrated by vessels ; and the nutriment
required for the growth of its contained matter must be drawn by absorption
through the myolemma. But the substance of Muscle, as a whole, is ex-

* [The recent researches of Liebig make it exceedingly probable that lactic acid is a con-
stituent of muscle. Its purpose hi the animal organism will be alluded to hereafter. — M. C.]
| Miiller's Archiv., 1845.

204

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

Fis;. 107.

Capillary net-work of Muscle.

tremely vascular, the capillary vessels being distributed in parallel lines, united

by transverse branches, in the minute inter-
spaces between the fibres (Fig. 107); so that it
is probable that there is no fibre, which is not in
close relation with a capillary. The number
of blood-vessels in a given space will of course
be greater, where the fibres and the capilla-
ries are both small, as in Mammals and Birds,
than where they are of larger diameter, as in
Reptiles and Fishes ; and the former condition
will obviously be the one most favourable to
the performance of active changes between the
blood and the muscle. These changes consist,
it would appear, not merely in the nutrition of

the tissue; but in' the supply of oxygen, which is a necessary condition of
the excitement of its activity. We shall hereafter see, indeed, that every
muscular contraction probably involves the disintegration of a certain amount
of its substance, through the union of oxygen, supplied by arterial blood,
with its elements ; and that the great demand for nutrition, which is occa-
sioned by muscular activity, is for the purpose of repairing this loss. The
muscles of warm-blooded animals speedily lose their irritability, after the
supply of arterial blood has been suspended, either through the cessation of
the general circulation, or by deficient aeration of the fluid. But the muscles
of cold-blooded animals, which are very inferior in the energy and rapidity
of their action, preserve their properties for a much longer period, after the
deprivation of their supply of arterial blood ; in accordance with the general
principle, that, the lower the usual amount of vital energy, the longer is its
persistence, after the withdrawal of the conditions on which it is dependent.
The very indisposition to a change of composition, on which the less ready
action depends, produces a longer retention of the power of acting.

240. The Muscles of Animal life are, of all the tissues except the skin,
those most copiously supplied with Nerves. These, like the blood-vessels,
lie on the outside of the Myolemma of the several fibres ; and their influence
must consequently be excited through it. The general arrangement of these
nerves is shown in Fig. 108. Their ultimate fibres or tubes cannot be said

Fig. 108.

Form of the terminating loops of the nerves in the muscles.

to terminate anywhere in the Muscular substance; for after issuing from the
trunks, they form a series of loops, which return either to the same trunk, or

NERVOUS SYSTEM; ITS GENERAL STRUCTURE.

205

to an adjacent one. The occasional appearance of a termination to a nervous
fibril is caused by its dipping down between the muscular fibres, to pas^ to-
wards another stratum. The nerves are almost exclusively of the motor
kind; but a few sensory are blended with them. We see this most clearly
in cases in which the motor and sensory trunks supplying the muscles are
distinct; as in the muscles of the orbit. — The non-striated muscles are very
sparingly supplied with nerves ; and these are derived (for the most part, if
not entirely), from the Sympathetic system, rather than from the Cerebro-
Spinal.

241. We have, lastly, to consider the structure, composition, actions, and
mode of growth and regeneration of the Nervous Tissue ; the one which is
most distinctive of the Animal fabric, and which serves as the instrument of
the operations that are most peculiar to it. Wherever a distinct Nervous Sys-
tem can be made out (which has not yet been found possible in the lowest of
those beings, that, from their general structure and habits of life, are unques-
tionably to be ranked in the Animal Kingdom), it consists of two very different
forms of structure ; the presence of both of which, therefore, is essential to
our idea of it as a whole. We observe, in the first place, that it is formed of
trunks, which are distributed to different parts of the body, and especially to
the muscles and to the sensory surfaces ; and of ganglia, or masses with
which the central terminations of those trunks come into connexion. It is
easily established by experiment, that the trunks themselves have no power
of originating changes ; and that they only serve to conduct or convey the in-
fluence of operations which take place at their central or peripheral extremi-
ties. For if a trunk be divided in any part of its course, all the parts to which
the portion thus cast off from the ganglion is distributed, are completely para-
lyzed ; that is, no impression made upon them is felt as a sensation ; and no
motion can be excited in them by any act of the mind. Or, if the substance
of the ganglion be destroyed, all the parts which are exclusively supplied by
nervous trunks proceeding from it, are in like manner paralyzed. — But if,

Fig. 109.

Dorsal ganglion of Sympathetic nerve of Mouse ; a, 6, cords of connection with adjacent sympathetic
ganglia ; c, c, c, c, branches lo the viscera and spinal nerves ; d, ganglionic globules or cells j e, nervous
fibres traversing the ganglion.

when a trunk is divided, the portion still connected with the ganglion be pinched
or otherwise irritated, sensations are felt which are referred to the points sup-
plied by the separated portion of the trunk ; which shows that the part re-
maining in connexion with the ganglion is still capable of conveying impres-
18

206

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

sions, and that the ganglion itself receives these impressions, and makes them
felt as sensations. On the other hand, if the separated portion of the trunk
be irritated, motions are excited in the muscles which it supplies ; showing
that it is still capable of conveying the motor influence, though cut oft" from
the usual source of that influence.

242. In the ordinary Nerve-trunks, we find only one form of Nervous tis-
sue;— that which may be designated as the fibrous or tubular. In the Gan-
glia, we find, in addition to this, a substance made up of peculiar cells or
vesicles ; which may be distinguished as the vesicular nervous matter. In
fact, the character of a Ganglionic centre (which is frequently not otherwise
clearly distinguished as such) is derived from the presence of this vesicular
substance.

243. The ultimate Nerve-fibre, in its most complete form, — such as is pre-
sented to us in the ordinary spinal nerves, — is distinctly tubular ; being com-
posed of an external cylindrical membranous sheath, within which the peculiar
nervous matter is contained. This membranous tube, like the Myolemma of
muscular fibre, is extremely delicate and transparent ; and is nearly or quite

c 6 c d

A. Diagram of tubular fibre of a spinal nerve ;— a. Axis cylinder. 6. Inner border of white substance,
c, c. Outer border of white substance, d, d. Tubular membrane. B. Tubular fibres ; e, in a natural
slate, showing the parts as in A. f. The white substance and axis cylinder interrupted by pressure,
while tin; tubular membrane remains, g. The same, with varicosities. h. Various appearances of the
wliite substance and axis cylinder forced out of the tubular membrane by pressure. ('. Broken end of a
tubular fibre, with the white substance closed over it. k. Lateral bulging of wliite substance and axis
cylinder, from pressure. I. The same more complete, g'. Varicose fibres of various si/.es, from the
cerebellum, r. Gelatinous fibres from the solar plexus, treated with acetic acid, to exhibit their cell-
nuclei. B and c magnified 320 diameters.]

homogeneous. It is not penetrated by blood-vessels ; nor is it ever seen to
branch or anastomose with others ; so that there is reason to regard it as form-

TUBULAR NERVOUS TISSUE.

207

ing one continuous sheath, that isolates the contained matter from the surround-
ing tissue, along the whole course of the nerve-trunk, from its central to its
peripheral extremity. When the nerve-fibres are examined in a very fresh
state, their contents appear pellucid and homogeneous, and of a fluid consist-
ence ; so that each tube or fibre looks like a cylinder of clear glass, with sim-
ple, well-defined, dark edges. But a kind of coagulation soon takes place in
the contained substance, making it easily distinguishable from the tube itself;
for the latter is then marked by a double line, as shown in Fig. Ill, A. The
substance which is in immediate contact with the inner wall of the nerve-tube,
is more opaque than that which occupies its centre, and of a different refract-
ing power; and thus it forms a hollow cylinder, which surrounds the latter,
and which is known under the name of the White substance of Schwann. The
centre or axis of the tube is occupied by a substance that preserves its trans-
parency; and this is the axis-cylinder of Rosenthal and Purkinje. It may be
surmised that the White substance of Schwann, which exhibits much variety
in thickness in different parts of the nervous system, chiefly serves, like the
membranous investment, to isolate the interior matter ; which last seems to be
the essential constituent of the nervous fibre. The whole of the matter con-
tained in the tubular sheath is extremely soft; yielding to very slight pressure,
and readily escaping from the cut extremities of the tubes. The tubular sheath
itself varies in density in different parts ; being stronger in the nervous trunks
than in the substance of the brain and spinal cord. In the former, it is not
difficult to show that the regular form of the nerve-tube is a perfect cylinder;
though a little disturbance will cause an alteration in this, — a small excess of
pressure in one part forcing the contents of the tube towards another portion,

Fig. 111.

Structure of nerve-tubes, magnified 350 diameters. A. Cylindrical tubuli from nerve. B, Varicose
tubuli from brain, c, Nerve-tubes, of which one exhibits the remains of nuclei in its walls.

where they are more free to distend it, and thus producing a swelling. The
greater delicacy of the tubular sheath in the latter, causes this result to take
place with yet more readiness ; so that a very little manipulation exercised
upon the fibres of the Brain or Spinal Cord, or on those of special sense, occa-
sions them to assume a varicose or beaded appearance (Fig. Ill, B), which,
when first observed by Ehrenberg, was thought to be characteristic of them.
When the fibres of these parts are examined, however, without any such pre-
paration, they are found to be as cylindrical as the others. — The diameter of the
tubular fibres of the cerebro-spinal nerve-trunks in Man, usually varies from
about l-2000th to l-4000th of an inch, being sometimes as great, however,
as 1-1 500th of an inch ; and sometimes much below the least of the above

208

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

dimensions. The fibres decrease in size as they approach the brain, either
directly, or through the medium of the spinal cord ; and in the brain itself they
continue to diminish, as they pass through the medullary towards the cortical
portion ; so that they are very commonly found of no more than 1 -7000th or
l-8000th of an inch in diameter, and sometimes as little as 1-14, 000th. Like
most other elementary structures, they are of considerably larger dimensions
in Reptiles and Fishes ; varying, according to Dr. Todd, from 1-1 260th to
l-2280th of an inch in the Frog; being in the Eel as much as the l-1040th
of an inch ; and in the optic nerve of the Cod, no less than l-650th of an inch
in .diameter.*

244. Besides these proper tubular nerve-fibres, — of which, in combination
with areolar and fibrous tissue, blood-vessels, &c., a large proportion of the
cerebro-spinal nerve-trunks are made up, — there are certain other fibres, which
are peculiarly abundant in the trunks of the Sympathetic system, and which
are of different character from the preceding. They are chiefly distinguished
by their small size, their diameter not being above half or one-third of that of
the ordinary nervous tubuli. They are destitute of the double contour, which
has been shown to result in the preceding case from the presence of two dis-
tinct substances within the tubular investment; and their contents appear to
be homogeneous. And when they are aggregated in bundles, they possess a
yellowish-grey colour. — Although these fine fibres exist in greater proportion
in the Sympathetic system than in the Cerebro-spinal, yet they are present
in great numbers in some of the nerves of the latter; and it is even question-

Primitive fibres and ganglionic vesicles of human brain, after Piirkinje. A, ganglionic vesicles lying
amongst nerve-tubes and blood-vessels, in substance of optic thalamus; a, vesicle more enlarged; b,
vascular trunk. B, B, vesicles with variously-formed processes, from dark portion of cruscerebri. Mag-
nified 350 diameters.

able, whether they may not be continuous with the ordinary tubular fibres.
They may be traced into the ganglia of the Sympathetic, into the ganglia on
the posterior roots of the Spinal nerves, and even to the ganglionic matter of
the Brain and Spinal Cord.f

* Cyclopaedia of Anatomy and Physiology, Vol. HI., p. 593.

f Much controversy li;is recently taken place in Germany, regarding the existence of a
set of fibres peculiar to the Sympathetic system. The grey or gelatinous fibres, described by
Remak, and (following him) by Al filler and others, :is essentially constituting the Organic
system of Nerves, are now generally admitted not to be entitled to the designation of nerve-

VESICULAR NERVOUS TISSUE.

209

113.

245. The second primary element of the Nervous system, without which
the fibrous portion would seem to be totally inoperative, is composed of nu-
cleated cells, consisting of a finely granular substance, and lying somewhat
loosely in the midst of a minute plexus of blood-vessels. Their original form
may be regarded as globular ; whence they have been called ganglion-globules.
This, however, is liable to alteration; sometimes, perhaps, from external com-
pression ; but more commonly through their own irregular mode of growth.
They frequently extend themselves into long processes, which may give
them (according to the number thus projecting) a caudate or a stellate aspect,
resembling that of the pigment-cells of the Batrachia. These processes are
composed of a finely-granular substance, resembling that of the interior of the
vesicle, with which they seem to be distinctly continuous. They are very
liable to break off near the vesicle ; but if traced to a distance, they are found
to divide and subdivide, and at last to

give off some extremely fine transpa-
rent fibres ; some of which seem to in-
terlace with those of other stellate cells,
whilst others become continuous with
the axis-cylinders of the nerve-tubes.
Such vesicles have been seen alike in
the ganglionic masses of the Cerebro-
spinal, and in those of the Sympathetic
system.* Besides the finely-granular
substance just mentioned, these cells
usually contain a collection of pigment-
granules, which especially cluster round
the nuclei, and give them a reddish or
yellowish-brown colour. This pigment
seems to have some resemblance to
the haematine of the blood ; and it is

Usually, if not invariably, deficient

among the Invertebrata, as well as less
abundant in Reptiles and Fishes. The
vesicles are sometimes covered with a
layer of a soft granular substance, which adheres closely to their exterior and
to their processes ; this is the case in the outer part of the cortical substance
of the human brain. In other instances, each cell is inclosed in a distinct en-
velope composed of smaller cells, closely adherent to each other, and to the
contained cell ; such an arrangement is common in the smaller ganglia, and
in the inner portion of the cortical substance of the brain. — The diameter of
the vesicles is extremely variable, owing to the changes of form above de-
scribed; that of the globular ones is usually between l-300th and l-1250th of
an inch.

246. In the central or ganglionic masses of the Nervous system, we find
these vesicles aggregated together, and imbedded in a finely-granular matter;
the whole being traversed by a minute plexus of capillary blood-vessels.
The entire substance, made up of these distinct elements, is commonly known
as the cineritious or cortical substance ; being distinguished by its colour, in

fibres, but to be a form of simple fibrous tissue. The peculiar fibres described above, were
first pointed out by Bidder and Volkmann; whose statements in regard to them have re-
cently been confirmed by the laborious anil impartial researches of Kiilliker. (See his work
"Die Selbstiindigkeit und Abhangigkeit des Sympathischen Nervensystems," 1844; and the
abstract of his results in Mr. Paget's able Report, in Brit, and For. Med. Review, July, 1840,
p. 271.)

: See Todd and Bowman's Physiological Anatomy, Vol. i., p. 214. See also Kfllliker, loc.
cit.; and Dr. Radclyffe Hall, in Edinburgh Med. & Stirg. Journal, April, 1S46.

13*

Nerve-vesicles from the Gasserian ganglion of
the human subject :— a. A globular one with de-
fined border; 6, its nucleus; c, its nucleolus. rf.
Caudate vesicle, e. Elongated vesicle, with two
groups of pigment particles, f. Vesicle surround-
ed by its sheath, or capsule, of nucleated panicles.
g. The same, the sheath only being in focus. —
Magnified 31)0 diameters.]

210

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

[Fig. 114.

a>

115.

Ganglion globules, with their processes, nuclei, and nucleoli: — o. a. From the deeper part ol" the gray
mutter of the convolutions of the cerebellum. The larger processes are directed towards the surface
of the organ, b. Another from the cerebellum, c. d. Others from the post, horn of gray matter of the dor-
sal region of the cord. These contain pigment, which surrounds the nucleus in c. In all these specimens
the processes are more or less broken. — Magnified 200 diameters.]

Man and the higher animals at least, from the white substance composed of
nerve-tubes, of which the trunks of the nerves, as well as a large part of the
brain and spinal cord, are made up ; and occupying in the brain a position
external to the latter, which is often termed the medullary substance. This
position, however, is quite an exceptional one; for in the spinal cord and in
the scattered ganglia of Vertebrated animals, and in all the ganglionic centres
of (Invertebrata, — everywhere, in fact, except in the Brain, — the vesicular
nerve substance occupies the centres of the ganglia; consequently the terms

cortical and medullary, as applied to the vesi-
cular and tubular substances respectively, are
quite inappropriate. Nor are the designations
that have reference to their colour, much more
uniformly correct: for, as we have seen,
the vesicular substance may be destitute of
internal pigment-granules, and the blood in
its capillary plexus may be pale or colourless,
so that the reddish-grey hue, which is ex-
pressed by the term cineritious, may be entirely
wanting; whilst, on the other hand, we have
seen that certain of the nerve-fibres, making
up what is commonly termed the white sub-
stance, are of a grey colour. Hence the only
valid distinction between these two kinds of
nervous matter, is that which has reference to
their constitution ; — as consisting of cells or
vesicles on the one hand; or of tubes or fibres,
on the other.

247. The connection between the fibrous and

A small piece of the otic ganglion of
the sheep, slightly compressed; show-
ing the interlacement of the internal
fibres, and the vesicular matter. —
(After Valentin.)]

CONNECTION OF FIBROUS AND VESICULAR SUBSTANCES.

211

vesicular nervous elements, in the nervous centres, has not yet been tho-
roughly elucidated. It seems certain, on the one hand, that some of the

[Fig. 116.

[Fig. 117.

A. Blending; of the vesicular and fibrous nervous
matter in the dentate body of the cerebellum: — a,
Ganglion globule, with its nucleus and nucleolus.
b. Nerve-tube, slightly varicose, in close contact
with the ganglion globule, b'. Smaller nerve-tubes.
These parts all lie in a finely granular matrix in-
terspersed with nuclei, c. B. Vesicular and fibrous
matter of the lamince of the cerebellum, a. Gan-
glion globule, b. Very minute nerve-tubes tra-
versing a finely granular matrix, in which are
numerous rounded nuclei, c.]

From the Gasserian ganglion of an adult:— a. a.
Ganglion globules with their nucleus, nucleated
capsule, and pigment, t. Tubular fibres, running
among the globules in contact with their capsule.
§•. Gelatinous fibres also in contact with the gan-
glion globules.— Magnified 320 diameters.]

fibres come into direct continuity with caudate prolongations of the ganglionic
corpuscles, and may thus be said to originate from them. This appears to

Fig. 118.

Primitive fibres and ganglionic vesicles. A, from sympathetic ganglion ; * a separate vesicle, show-
ing its pellucid nucleus and nucleolus. B, from grey substance of human cerebellum ; a, b, plexus of
primitive fibre? ; c, nucleated globules ; * a separate globule from human Gasserian ganglion. Magni-
fied 350 diameters.

be especially the case, with regard to the class of fine fibres (§ 244). On the

212

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

other hand, it seems equally certain that there are many nerve-tubes which
simply enter the ganglionic masses, pass round and amongst the cells, and
then emerge from them, without having undergone any distinct change, save
that they present a soft and varicose appearance, whilst threading their way
through the cells. And it is equally certain that there are many ganglionic
corpuscles, which never acquire the caudate prolongations, and which appear
specially destined to act upon this class of nerve fibres. — Some observations
•which have been made upon the nervous system of foetuses, in which the
brain and spinal cord were wanting, present a remarkable confirmation of this
view.* The nervous cords were for the most part developed ; and at their
(so called) origins or central extremities, they were found to hang as loose
threads in the cavities of the cranium and spine. On examining these threads,
it was found that the nerve-tubes, of which they consisted, formed distinct
loops ; each of which was composed of a fibre that entered the cavity, and
then returned from it. These loops were imbedded in granular matter,
resembling that interposed between the vesicles in the cortical substance of
the brain; and perhaps to be regarded as vesicular matter in an early stage
of its formation. All that is known of the laws regulating the formation of
such irregular productions, leads to the belief, that we may rightly consider
this arrangement of the nerve-tubes as one which exists in the nervous cen-
tres, when they are normally developed. But it may not be the only one;
for, as already pointed out, some of the nerve-fibres appear to originate from
the filamentous prolongations of certain ganglionic cells. Additional informa-
tion is much needed upon this point.

248. The arrangement of the nerve-fibres, at their peripheral extremities,
seems to be essentially of the same character. It has been already shown
that the motor fibres, which are distributed to the muscles, have no proper
terminations ; a series of loops, returning into themselves or joining others,
being formed by the ultimate ramifications of the main trunks. The arrange-
ment of the sensory fibres seems to be usually of the same nature. The
principal trunks subdivide into numerous anastomosing branches, forming a
sort of plexus in the substance of the skin ; and from this, single filaments
detach themselves at intervals, rising up into the papillary elevations of its
surface, and then returning again into the plexus, after making a series of

Fisr. 119.

Distribution of the tactile nerves at the extremity of the. human thumb, as seen
in a tliin perpendicular section of the skin.

loops, ill which a sort of varicose enlargement of the fibre may often be
noticed. Similar looped terminations have been traced in the nerves supply-

* Dr. Lonsdalc, in Edinb. Mnl. ;iml Surg. Journal, No. CLTII.; and Mr. Fagot in Brit, and
For. Med. Rev., No. XLIII. p. 273.

CONNECTION OF FIBROUS AND VESICULAR SUBSTANCES.

213

Terminal nerves on the sac of the second
molar tooth of the lower jaw in the sheep,
showing the arrangement in loops. — (After
Valentin.)]

ing the dental saceuli, in the expansions of [Fig. 120.

the auditory nerve distributed upon the de-
licate membrane lining the cavities of the
internal ear, and elsewhere. It would yet,
however, be premature to say, that this ar-
rangement is universal. — The peripheral
extremities may be really considered as
the origins of the sensory nerves ; since
it is in them that those changes are ef-
fected which it is the office of the trunks
to conduct towards the centres ; and it may
be reasonably inquired, whether anything
like the vesicular substance of the ganglia
can be detected in them. In examining
the retina microscopically, it is found to
be almost entirely made up of a layer of
ganglionic cells, very closely resembling
those of the grey matter of the brain; and
these are in apposition with the vascular
layer; so that we have here precisely the
same provision for exciting a change, that
is to be conducted towards the centres, as
we have in the brain for exciting a change,
whose influence is to be conveyed towards
the periphery. Something of the same
kind has been seen in connection with the
corresponding expansions of the olfactive
and auditory nerves ; and it is probable
that similar elements exist in the papillae

of the skin and tongue, to which the nerves of taste and touch are distributed.
In these papillae we find loops of capillary vessels in close contiguity with
the extremities of the nerve-tubes. — Hence we may state it as a general fact,
that wherever a change is to be originated, we find some form of Vesicular
matter, with capillary blood-vessels ; whilst for the conduction of such a
change to distant parts, the Fibrous structure is alone required.

249. The Chemical constitution of the Nervous matter is peculiar ; and
an acquaintance with its general features is of importance, in leading us to
recognize in the excretions the results of its decomposition.

a. The following, according to L'Heritier, is the relative proportion of the different con-
stituents in individuals of different classes : —

Aged

Infants. Youths. Adults. '.
Water
Albumen
Fat .

Osmazome (?) and Salts
Phosphorus

It appears from the researches of M. Fremy, that the Phosphorus is combined with part of
the fatty matter; and forms with it two peculiar fatty acids, termed by him the Cerebric and
Oleophosphoric. — Cerebric acid, when purified, is white, and presents itself in crystalline
grains. It contains a small proportion of Phosphorus ; and differs from the ordinary fatty
matter, in being partly composed of Nitrogen. It consists of 66-7 per cent, of Carbon, 10-6
of Hydrogen, 2-3 of Nitrogen, 19-5 of Oxygen, and O9 of Phosphorus; and thus differs from
ordinary fat, not only in containing Phosphorus and Nitrogen, but in possessing more than
twice their proportion of Oxygen.* — Oleophosphoric acid is separated from the former by its

* It is probable that, in the above analysis of L'Heritier, the Cerebric acid, which is not
soluble in ether, is included under the head of Osmazome ; for the analyses of Denis and

Infants.

Youths.

Adults.

Persons.

Idiots.

82-79

74-26

72-51

73-85

70-93

7-00

10-20

9-40

8-65

8-40

3-45

5-30

6-10

4-32

5-00

5-96

8-59

10-19

12-18

14-82

0-80

1-65

1-SO

1-00

0-85

214

ON THE ELEMENTARY PARTS OF THE HUMAN FABRIC.

solubility in ether : it is of a viscid consistence ; but when boiled for a long time in water or
alcohol, it gradually loses its viscidity, and resolves itself into a fluid oil, which is pure
Oleine, whilst phosphoric acid remains in the liquor. The proportion of Phosphorus which
this oil contains is about 2 per cent. — Cholesterine has also been extracted from the brain by
M. Fremy in considerable quantity. — The proportion of Fixed Salts is small; not being
above 3^ parts in 100 of Dry Cerebral matter ; which is less than half the proportion that
exists in Muscle. — According to Lassaigne, the chemical composition of the Cortical and
Medullary substances of the brain is essentially different; the former containing 85 per
cent, of water, whilst the latter has only 73 ; the cortical substance having also 3'7 per cent.
of a red fatty matter, of which the medullary has scarcely any; and being almost entirely
destitute of the white fatty matter, which exists in large proportion in the latter.

The Albuminous matter in the above analyses, is probably that of which
the walls of the nerve-cells and nerve-tubes, and of the capillary blood-vessels
are composed. The contents of these cells and tubes are represented chiefly,
if not entirely, by the phosphorized fats ; and there are many reasons for re-
garding these as the active agents in the operations of the Nervous system.
It will be remarked, that the amount of phosphorus is the greatest at the
period of greatest mental vigour ; and that in infancy, old age, and idiocy, the
proportion is not above half that which is present during the adolescent and
adult periods.

250. The Nervous System is very copiously supplied with blood-vessels ;
the arrangement of which varies according to the form of the elementary parts,
in which they are distributed. Thus in the Vesicular substance of the ner-
vous centres, the capillaries form a minute net-work, in the interstices of which
the ganglionic cells are included. In the tubulo-fibrous substance, the capilla-
ries are distributed much on the same plan as in Muscular tissue ; the net-
work being composed of straight vessels, which run along the course of
the fibres, passing between the nerve-tubes, and which are connected at
intervals by transverse branches. And at the sensory extremities of the

Fig. 121.

Fig. 122.

Capillary net-work of Nervous Centres.

Distribution of Capillaries at the sur-
face of the skin of the finger.

nerves we find loops of Capillaries arching over their terminal and probably
looped filaments. — The Brain of Man, taken en masse, has been estimated to
receive one-sixth of the whole amount of blood, although its weight is not
usually more than a-fortieth part of that of the entire body. Whether or not
this estimate be precisely correct, there can be no doubt that it receives far
more blood, than any other part containing the same amount of solid matter.
Now this copious supply of blood evidently has reference to two distinct ob-
jects ; first, to supply the necessary conditions for the action of the Nervous
system ; and, secondly, to maintain its nutrition. Many circumstances lead
to the conclusion that, in the Nervous as in the Muscular system, every vital
operation is necessarily connected with a certain change of composition, so

other chemists give a much higher proportion to the phosphori/ed f;it, and a much smaller
one to the ill-delined compounds represented l>y the designation Osmazome.

SUPPLY OF BLOOD TO NERVOUS TISSUE.

215

that no manifestation of nervous power can take place, unless this change can
be effected. There is strong reason to believe, further, that this change es-
sentially consists in the union of oxygen conveyed by the arterial blood, with
the elements of the proper nervous matter ; and that this union consequently
involves the death and disintegration of a certain amount of the nervous tis-
sue,— the reproduction of which will be requisite, in order that the systsm
may be maintained in a state fit for action. This reproduction is effected by
the nutritive process, which takes place at the expense of other constituents
of the blood; and it will proceed most vigorously in the intervals, when the
active powers of the nervous system are not being called into operation (§§ 292
—296).

251. The proofs of this continual waste and reproduction of the Nervous
substance, will be partly found in the appearance of the products of its de-
composition in the excretions, and in the demand which is set up for the ma-
terials for its reparation ; these being found to accord in amount, as will be
shown hereafter, with the degree of its functional activity. But evidence of
another kind may be drawn from the microscopic appearances observable in
the cortical substance of the Brain. It seems probable, from the observations
of Henle, that there is as continual a succession of nerve-cells, as there is of
epidermic cells; their development commencing at the surface, where they
are most copiously supplied with blood-vessels from the pia mater; and pro-
ceeding as they are carried towards the inner layers, where they come into
more immediate relation with the tubular portion of the nervous tissue. This
change of place is probably due- to the continual death and disintegration of
the mature cells, where they are connected with the fibres, and the equally
rapid production of new generations at the external surface ; — the newly-
formed epidermic cells being thus carried inwards, in precisely the same man-
ner that the epidermic cells are carried outwards.

252. The first development of the Nerve-tubes appears to take place, likg
that of Muscular fibre, by the coalescence of a number of primary cells into
a continuous tube ; for although the primary nervous cell has not yet been
made out with precision, the nuclei of what seem to be the original cells may
frequently be seen in the fullv-

formed tube, lying between their
membranous walls, and the white
substance of Schwann (111, c).
When first a nerve-fibre can be re-
cognized as such, it has a strong re-
semblance to the gelatinous fibres
of the sympathetic trunks ; being a
cord of small diameter, without any
clear distinction between the tube
and its contents, of granular consist-
ence, and havingf nuclei at no great
distance from each other. The
substance of the fibre, at this pe-
riod, seems to correspond with the
axis-cylinder of the fully-formed
nerve-tube ; the white substance of
Schwann is subsequently deposited
around it, separating it from the
membranous

[Fig. 123.

Various stages of the development of nerve ;— a.
Earliest stage, b. Detached fibre, c. Nucleated fibre
in the lower part of which, d, the white substance of
Schwann has begun to be deposited, e. Nucleus in a
more fully-formed fibre between the white substance
and tubular membrane. /.Displays the tubular mem-
brane, the contained matter having given way.— (After
Schwann.)]

tubular envelope. —
The first development of the vesi-
cular substance appears to take place on the same plan with its subsequent
renewal.

216 GENERAL VIEW OF THE FUNCTIONS.

253. The regeneration of Nervous tubuli that have been destroyed, takes
place in continuity with that which has been left sound. This may be more
easily proved by the return of the sensory and motor endowments of the part
whose nerves have been separated, than by microscopic examination of the
reunited trunks themselves, which is not always satisfactory. All our know-
ledge of the functions of the Nervous System leads to the belief, that perfect
continuity of the nerve-tubes is requisite for the conduction of an impression
of any kind, whether this be destined to produce motion or sensation ; and
various facts, well known to Surgeons, prove that such restoration may be
complete. In the various operations which are practised for the restoration
of lost parts, a portion of tissue removed from one spot, is grafted as it were
upon another; its original attachments are more or less completely severed,
frequently altogether destroyed, and new ones are formed. Now in such a
part, so long as its original connections exist, and the new ones are not com-
pletely formed, the sensation is referred to the spot from which it was taken ;
thus, when a new nose is made, by partly detaching and bringing down a piece
of skin from the forehead, the patient at first feels, when anything touches the
tip of his nose, as if the contact were really with the upper part of his fore-
head. After time has been given, however, for the establishment of new
connections with the parts into whose neighbourhood it has been brought, the
old connections of the grafted portion are completely severed, and an interval
ensues, during which it frequently loses all sensibility ; but after a time its
power of feeling is restored, and the sensations received through it are referred
to the right spot. — A more familiar case is the regeneration of Skin, contain-
ing sensory nerves, which takes place in the well-managed healing of wounds
involving loss of substance. Here there must obviously be, not merely a pro-
longation of the nerve-tubes from the subjacent and surrounding trunks, but
also a formation of new sensory papillae. — A still more striking example of
the regeneration of Nervous tissue, however, is to be found in those cases (of
which there are now several on record), in which portions of the extremities,
that have been completely severed by accident, have been made to adhere to
the stump, and have, in time, completely recovered their connection with the
Nervous as with the other systems, — as indicated by the restoration of their
motor and sensory endowments.

CHAPTER IV.

GENERAL VIEW OF THE FUNCTIONS.

1. Of Vital Actions, their conditions, and their mutual dependence.

254. THE idea of Life, in its simplest and most correct acceptation, is that
of Vital Action; and obviously, therefore, involves that of change. We do
not consider any being as alive, which is not undergoing some continual alte-
ration, that may be rendered perceptible to the senses. This alteration may
be evidenced only by the growth and extension of the organic structure, or
the development of new parts ; and it may take place so slowly as to be im-
perceptible, except by comparing observations made at long intervals. Thus
the scaly Lichen, that forms the grey or yellow spots upon old walls, might
be thought an inert substance, did we not know that a sufficiently-prolonged

CONDITIONS OF VITAL ACTIONS. 217

acquaintance with its history would detect its progressive though tardy exten-
sion, and would ascertain that it multiplies its race by an humble yet effectual
process of fructification. — Or the change may be rather evidenced, by the
performance of some kind of movement, for which the ordinary physical
laws of matter will not account ; yet, for the detection of this, a close and
careful scrutiny will be frequently required. Thus the Oyster that is lying
motionless in its massive bed, or the Ascidia that clusters upon the faces of
sea-beaten rocks, may seem totally destitute of activity ; yet it would be found
upon close examination, that their internal surfaces are covered with cilia
which are in continual vibration, — that by this means water is drawn into
the stomach and caused to traverse the respiratory organs, yielding to the
former the animalcules it may contain, and to the latter the oxygen dissolved
in it, — that the food thus introduced into the stomach undergoes digestion, and
is converted into materials adapted to nourish the body, which are then con-
veyed to its different parts by a circulating apparatus, — that in due time em-
bryos are produced, which are endowed with powers of active motion, and
which swim forth from within the parent-envelopes and locate themselves
elsewhere, — and that, apathetic as these creatures may seem, they may be
excited by certain kinds of stimuli to movements which seem to evince sen-
sation ; the Oyster closing its shell, and the Ascidia contracting its muscular
tunic, when it receives any kind of mechanical irritation ; and the former,
whilst lying undisturbed in its native haunts, drawing together its valves, if a
shadow passes between itself and the sun. — From what has been already
stated, regarding the nature of the actions of the Nervous and Muscular sys-
tems, by which the movements of Animals are chiefly effected, it would ap-
pear that these, in common with the Vegetative functions, involve a chemical
alteration in the structure performing them ; so that it may be stated as a
general proposition, that a change in Chemical composition is an essential
condition of every Vital phenomenon.

255. If change be essential to our idea of Life, it may be asked, what is
the condition of a seed, which may remain unaltered during a period of many
centuries ; vegetating at last, when placed in favourable circumstances, as
if it had only ripened the year before. Such a seed is not alive; for it is not
performing any vital operations. But it is not dead, for it has undergone no
decay ; and it is still capable of being aroused into active life, when the proper
stimuli are applied. And the most correct designation of its state seems to
be that of dormant vitality. — The condition of an animal reduced to a state of
complete torpidity and inaction, is precisely similar ; into such a condition,
the Frog may be brought by cold, and the Wheel-Animalcule by deprivation
of moisture. And the condition of a Human being, during sleep, is precisely
similar, so far as his psychical powers are concerned ; he is not then a feel-
ing, thinking Man ; but he is capable of feeling and thinking, when his
brain is restored to a state of activity, and its powers are called into operation
by the impressions of external objects.

256. There can be no doubt whatever, that, of the many changes which
take place during the life, or state of vital activity, of an Organised being,
and which intervene between its first development and its final decay, a large
proportion are effected by the direct agency of those forces which operate in
the Inorganic world; and there is no necessity whatever for the supposition,
that these forces have any other operation in the living body, than they would
have out of it under similar circumstances. — But after every possible allowance
has been made for the operation of Physical and Chemical forces in the living
Organism, there still remain a large number of phenomena, which cannot be
in the least explained by them ; and which we can only investigate with suc-
cess, when we regard them as resulting from the agency of forces, as distinct

19

218 GENERAL VIEW OF THE FUNCTIONS.

from those of Physics and Chemistry, as these are from each other. It is to
such phenomena, that the name of Vital is properly restricted ; the forces
from whose operation we assume them to result, are termed vital forces ; and
the properties, which we must attribute to the substances exerting those forces,
are termed vital properties. — Thus we say that the contraction of Muscle is
a Vital phenomenon ; because its character and conditions appear to be to-
tally distinct from those of Chemical or Physical phenomena. The act is
the manifestation of a certain Force ; the possession of which is peculiar to
the muscular structure, and which is named the Contractile force. Further,
that force may remain dormant (as it were) in the muscular structure ; not
manifesting itself for a great length of time, and yet resting capable of being
called into opera ion at any moment. This dormant force is termed a Pro-
perty ; thus we regard it as the essential peculiarity of living muscular tissue,
that it possesses the vital property of Contractility. Or, to reverse the order,
the Muscle is said to possess the property of Contractility ; the property,
called into operation by the appropriate stimulus, gives rise to the Contractile
force ; and the force produces, if its operation be unopposed, the act of Con-
traction.

257. These distinctions, though apparently verbal only, are of importance
in leading us to the correct method of investigating Vital Phenomena, and of
comparing them with those of the Inorganic world. It is now almost uni-
versally admitted by intelligent Physiologists, that we gain nothing by the
assumption of some general controlling agency, or Vital Principle, distinct
from the organized structure itself; and that the Laws of Life are nothing else
than general expressions of the conditions under which Vital operations take
place, — expressions analogous to those which constitute the laws of Physics
or Chemistry, — and to be arrived at in the same manner, namely, by the col-
lection and comparison of phenomena. The difficulty of thus generalising in
Physiology results merely from the complex nature of the phenomena, and
the consequent difficulty of precisely determining their conditions. We have
as much ground for believing in the fixity and constancy of Physiological
phenomena, when the causes and conditions are the same, as we have in those
of any other department of science ; and the apparent uncertainty of the
actions of the living body, results merely from the influence of differences in
those conditions, so trivial in appearance as frequently to elude observation,
and yet sufficiently powerful in reality to produce an entire change in the
result.

258. All Vital phenomena are dependent upon at least two sets of condi-
tions;— an Organized structure, possessed of peculiar properties ; — and certain
Stimuli, by which these properties are called into action. Thus, to revert to
the example just cited, the Contraction of a Muscle is due to the inherent
Contractility of the Muscular tissue, called into operation by the stimulus of
innervation ; — other conditions, as a certain elevated temperature, a supply of
oxygen, &c., being at the same time requisite. The Microscopical and
Chemical researches of recent years, have given increased stability to the
position, that the peculiar properties, which we term Vital, are dependent
upon those peculiar modes of combination and aggregation of the elementary
particles, which are characteristic of Organized structures. We have no evi-
dence of the existence of Vital properties in any other form of matter than
that which we term Organized; whilst, on the other hand, we have no reason
to believe that Organized matter can possess its normal constitution, and be
placed in the requisite conditions, without exhibiting Vital Actions. The
advance of Pathological science renders it every day more probable (indeed,
the probability may now be said to amount almost to positive certainty), that
derangement injunction, — in other words, an imperfect or irregular action, —

CONDITIONS OF VITAL ACTIONS. 219

always results, either from some change of structure or composition in the
tissue itself, or from some corresponding change in the external conditions,
under which the properties of the organ are called into action. Thus, when
a Muscle has been long disused, it can scarcely be excited to contraction by
the usual stimulus, or may even be altogether powerless ; and minute exami-
nation of its structure shows it to have undergone a change, which is obvious
to the Microscope (the fibres being as it were shrunken, and the fibrillae in-
distinct), though it may not be perceptible to the naked eye, and which results
from imperfect nutrition. Or, again, convulsive or irregular actions of the
Nervous System may be produced, not by any change in its own structure
or composition, but by the presence of various stimulating substances in the
blood (such as urea or strychnine), although their quantity may be so small,
that they cannot be detected without great difficulty. Further, whenever the
peculiar properties of an Organized structure can no longer be excited by the
requisite stimuli, we find that it has undergone some incipient change of com-
position, or that some of the other conditions are wanting. Thus, the depar-
ture of the contractility from the muscles of warm-blooded animals, at no long
period after the cessation of the circulation, is due in part to the lowering of
their temperature, and in part to the cessation of the supply of oxygen to the
elementary parts of their substance ; either of which would alone suffice to
prevent their respondence to the stimuli, that would ordinarily produce ener-
getic contractions. — Lastly, we find special properties constantly associated
witli distinct forms of organized tissue ; thus we never find contractility exist-
ing in the fibres of Nerve ; nor do we ever find the power of conducting
impressions to exist in the fibres of Muscle. The details given in the pre-
ceding Chapter make it evident that each tissue, distinguished from others by
its peculiar composition, and by the form of its elementary parts, has some-
thing peculiar in its properties ; and this is true, as well of properties that are
simply physical, as of those that belong to a different category: thus the
Yellow Fibrous tissue is distinguished from the White as much by its elas-
ticity, as by its peculiar composition ; and it does not lose its elasticity, until
it is in a state of evident decay.

259. By the study of the various forms of Elementary Tissue, of which
the Human fabric (or any other of similar complexity) is made up, we are led
to the very same conclusion, with that which we should derive from the
observation of the simplest forms of organized being, or from the scrutiny
into the earliest condition of the most complex ; — namely, that the simple
Cell may be regarded as the type of Organization; and that its actions
constitute the simplest idea of Life. Between the humblest Confervoid Plant,
and the highest Animal, there is originally no perceptible difference ; they may
be said to have a common starting-point ; and the subsequent difference of
their course consists essentially in this, — that the successive generations of
cells, which are the descendants of the former, are all similar to it, each cell
being capable of existing by itself, and therefore ranking as an independent
individual ; whilst the subsequent generations, which originate from the
latter, undergo various departures from the primary type, and lose the power
of independent existence, their several actions being mutually dependent upon
each other, so that the integrity of the whole fabric is essential to the con-
tinued life of any individual cell. Every individual part, however, even in
the most complex and highly-organized fabric, has its own power of develop-
ment ; and the properties which it possesses are the result of the exercise of
that power. But instead of the power of cell-growth being exerted, as in the
Plant, upon the inorganic elements around, it can only be put in action, in
the Animal, upon certain peculiar compounds, having the same chemical com-
position with its own substance ; and it is for the reception of these, for their

220 GENERAL VIEW OF THE FUNCTIONS.

preparation, and for their maintenance in the requisite state of purity, that a
large part of the fabric of the Animal is destined. But if we could imagine
its several tissues to be supplied with nutriment in any other manner, and
maintained in other respects in their normal circumstances (as regards warmth,
air, &c.), we have every reason to believe that their independent vitality would
manifest itself by their continued development, and by the regular exhibition
of their ordinary properties. An approach to this condition is made, in the
experiment of entirely detaching a limb from the body, but keeping up the
circulation of blood through it, by means of tubes connecting its main artery
and vein with those of the stump. Notwithstanding the prejudicial effect of
such severe injuries, the increased duration of the muscular irritability in the
separated part, is a sufficient proof of the continuance of the normal actions of
nutrition, although of course in a diminished degree. And the occasional
reunion of a member which has been entirely separated, when decomposing
changes have not yet commenced in it, most clearly shows, that nothing but
the restoration of its supply of nutriment is requisite for the preservation of
its vitality, and that its powers of growth and renovation are inherent in itself,
only requiring a due supply of the nutrient material, with certain other con-
current conditions.

260. In every living structure of a complex nature, therefore, we see a great
variety of actions, resulting from the exercise of the different properties of its
several component parts. If we take a general survey of them, with reference
to their mutual relations to each other, we shall perceive that they may be
associated into groups; each consisting of a set of actions, which, though
different in themselves, concur in effecting some positive and determined pur-
pose. These groups of actions are termed Functions. Thus, one of the
most universal of all the changes necessary to the continued existence of a
living being, is the exposure of its nutritious fluid to the air; by the action of
which upon it, certain alterations are effected. For the performance of this
aeration, simple as the change appears, many provisions are required. In the
first place, there must be an aerating surface, consisting of a thin membrane,
permeable to gases; on the one side of which the blood may be spread out,
whilst the air is in contact with the other. Then there must be a provision
for continually renewing the blood which is brought to this surface; in order
that the whole mass of fluid may be equally benefited by the process. And,
in like manner, the stratum of air must also be renewed, as frequently as its
constituents have undergone any essential change. We include, therefore, in
speaking of the Function of Respiration, not only the actual aerating process,
but also the various changes which are necessary to carry this into effect, and
which obviously have it for their ultimate purpose.

261. On further examining and comparing these Functions, we find that
they are themselves capable of some degree of classification. Indeed the dis-
tinction between the groups into which they may be arranged, is one of essen-
tial importance in Animal Physiology. If we contemplate the history of the
Life of a Plant, we perceive that it grows from a germ to a fabric of sometimes
gigantic size, — generates a large quantity of organised structure, as well as
many organic compounds, which form the products of secretion, but which do
not undergo organization, — and multiplies its species, by the production of
germs similar to that from which it originated; — but that it performs all these
complex operations, without (so far as we can perceive) either feeling or think-
ing, without consciousness or will. All the functions of which its Life is com-
posed, are, therefore, grouped together under the general designation of Func-
tions of Organic or Vegetative life: and they are subdivided into those con-
cerned in the maintenance of the structure of the individual, which are termed
functions of Nutrition; and those to which the Reproduction of the species

CLASSIFICATION OF VITAL ACTIONS INTO FUNCTIONS. 221

..

is due. — The great feature of the Nutritive operations in the Plant, is their
constructive character. They seem as if destined merely for the building-up
and extension of the fabric; and to this extension there may be no definite
limit. But it is very important to remark, that the growth of the more per-
manent parts of the structure is only attained by the continual development,
decay, and renewal of parts, whose existence is temporary. No fact is better
established in Vegetable Physiology, than the dependence of the formation of
wood upon the action of the leaves. It is in their cells, that those important
changes are effected in the sap, by which it is changed, from a crude watery
fluid containing very little solid matter, to a viscid substance including a great
variety of organic compounds, destined for the nutrition of the various tissues.
The "fall of the leaf" results merely from the death and decay of its tissue;
as is evident from the fact, that, for some time previously, its regular functions
cease, and that, instead of a fixation of carbon from the atmosphere, there is a
liberation of carbonic acid (a result of their decomposition) in large amount.
The process takes place in evergreens equally with deciduous trees; the only
difference being, that the leaves in the latter are all cast off and renewed to-
gether, whilst in the former they are continually being shed and replaced, a
few at a time. It appears as if the nutritious fluid of the higher Plants can
only be prepared by the agency of cells, whose duration is brief; for we have
no instance, in which the tissue concerned in its elaboration possesses more
than a very limited term of existence. But by its active vital operations, it
produces a fluid adapted for the nutrition of parts which are of a much more
solid and permanent character, and which undergo little change of any kind
subsequently to their complete development ; — the want of tendency to decay
being the result of the very same peculiarity of constitution as that which
renders them unfit to participate in the proper vital phenomena of the organism.
Thus the final cause or purpose of all the Nutritive functions of the Plant, so
far as the individual is concerned, is to produce an indefinite extension of the
dense, woody, almost inert, and permanent portions of the fabric, by the con-
tinued development, decay, and renewal of the soft, active, and transitory
cellular parenchyma. — The Nutritive functions, however, also supply the
materials for the continuance of the race, by the generation of new individuals;
since a new germ cannot be formed, any more than the parent structure can
be extended, without organizable materials, prepared by the assimilating pro-
cess, and supplied to the parts where active changes are going on.

262. On analyzing the operations which take place in the Animal body, we
find that a large number of them are of essentially the same character with the
foregoing, and differ only in the conditions under which they are performed ;
so that we may, in fact, readily separate the Organic functions, which are
directly concerned in the development and maintenance of the fabric, from the
Animal functions, which render the individual conscious of external impres-
sions, and capable of executing spontaneous movements. The relative de-
velopment of the organs destined to these two purposes, differs considerably
in the several groups of Animals, as we have already in part seen (Chap. I.).
The life of a Zoophyte is upon the whole much more vegetative than animal ;
and we perceive in it, not merely the very feeble development of those powers
which are peculiar to the Animal kingdom, but also that tendency to indefinite
extension which is characteristic of the Plant. In the Insect we have the
opposite extreme; the most active powers of motion, and sensations of which
some (at least) are very acute, with a low development of the organs of nutri-
tion. In Man, and in the higher classes generally, we have less active powers
of locomotion, but a much greater variety of Animal powers ; and the instru-
ments of the organic or nutritive operations attain their highest development,
and their greatest degree of mutual dependence. "We see in the fabric of all

19*

222 GENERAL VIEW OF THE FUNCTIONS.

things, in which the Animal powers are much developed, an almost entire
want of that tendency to indefinite extension, which is so characteristic of the
Plant; and when the large amount of food consumed by them is considered,
the question naturally arises, to what purpose this food is applied, and what
is the necessity for the continued activity of the Organic functions, when once
the fabric has attained the limit of its development.

263. The answer to this question lies in the fact, that the exercise of the
Animal functions is essentially destructive of their instruments ; every ope-
ration of the Nervous and Muscular systems requiring, as its necessary con-
dition, a disintegration of a certain part of their tissues, probably by their ele-
ments being caused to unite with oxygen. The duration of the existence of
those tissues (as stated in the preceding Chapter) varies inversely to the use
that is made of them ; being less as their functional activity is greater. Hence,
when an Animal is very inactive, it requires but little nutrition ; if in mode-
rate activity, there is a moderate demand for food ; but if its Nervous and
Muscular energy be frequently and powerfully aroused, the supply must be
increased, in order to maintain the vigour of the system. In like manner, the
amount of certain products of excretion, which result from the disintegration
of the Nervous and Muscular tissues, increases with their activity, and dimin-
ishes in proportion to their freedom from exertion.* We are not to measure
the activity of the Nervous system, however, like that of the Muscular, only
by the amount of movement to which it gives origin. For there is equal evi-
dence, that the demand for blood in the brain, the amount of nutrition it re-
ceives, and the degree of disintegration it undergoes, are proportional likewise
to the energy of the purely psychical operations ; so that the vigorous exercise
of the intellectual powers, or a long-continued state of agitation of the feelings,
produces as great a waste of Nervous matter, as is occasioned by active bodily
exercise. From this and other considerations, we are almost irresistibly led
to the belief, that every act of Mind is inseparably connected, in our present
state of being, with material changes in the Nervous System; a doctrine not
in the least inconsistent with the belief in the separate immaterial existence of
the Mind itself, nor with the expectation of a future state, in which the com-
munion of Mind with Mind shall be more direct and unfettered.

264. Thus in the Animal fabric, among the higher classes at least, the func-
tion or purpose of the organs of Vegetative life is not so much the extension
of the fabric, for this has certain definite limits, as the maintenance of its in-
tegrity, by the reparation of the destructive effects of the exercise of the
purely Animal powers. Thus, by the operations of Digestion, Assimilation,
and Circulation, the nutritious materials are prepared and conveyed to the
points where they are required ; the Circulation of Blood also serves to convey
oxygen, which is introduced by the Respiratory process ; and it has further
for its office to convey away the products of the decomposition of the Muscular
and Nervous tissues that results from their functional activity, — these products
being destined to be separated by the Respiratory and other Excreting opera-
tions. In the performance of the Organic functions of Animals, as in those
of Plants, there is a continual new production, decay, exuviation, and renewal,
of the cells, by whose instrumentality they are effected ; which altogether effect
a change not less complete than of the leaves in Plants. But it takes place in
the penetralia of the system, in such a manner as to elude observation, except
that of the most scrutinizing kind; and it has been in bringing this into view,
that the Microscope has rendered most essential service in Physiology.

* This doctrine, though propounded in general terms by previous •writers, was first point-
edly stated by Prof. Liubig, so far as regards Muscular tissue, iu his Treatise on Animal
Chemistry. It will be hereafter shown, however, to be equally applicable to the Nervous
substance.

\

MUTUAL DEPENDENCE OF VITAL OPERATIONS. 223

265. The regular maintenance of the functions of Animal life is thus entirely
dependent upon the due performance of the Nutritive operations; a considera-
tion of great importance in practice, since a very large proportion of what are
termed functional disorders (of the Nervous system especially) are immediately
dependent upon some abnormal condition of the Blood. But there also exists
a connection of an entirely reverse kind, between the Organic and Animal func-
tions; for the conditions of Animal existence render the former in great degree
dependent on the latter. Thus, in regard to the acquisition of food, the Animal
has to make use of its senses, its psychical faculties, and its power of locomotion,
to obtain that which the Plant, from the different provision made for its support,
can derive without any such assistance. Moreover, the propulsion of the food
along the alimentary canal is effected by a series of operations, in which the
Nervous and Muscular systems are together involved at the two extremes;
though simple Muscular contractility is alone employed through the greater
part of the intestinal canal. Thus, the change in the conditions required for
the ingestion of food by Animals, has rendered necessary the introduction of
an additional element in the apparatus, to which nothing comparable was to
be found in Plants. Again, in the function of Respiration as performed in the
higher Animals, the Nervous and Muscular systems are alike involved; for the
movements, by which the air in the lungs is being continually renewed, are
dependent upon the action of both ; and those by which the blood is propelled
through the respiratory organs, are chiefly occasioned by the contractility of a
muscular organ, — the heart. But in regard to the simple contractility of mus-
cular fibre, upon the direct application of a stimulus to it, which is the agent
in the movements of the heart and of the alimentary canal, it may be remarked,
that it does not differ in any essential particular from that which is witnessed
in many Vegetables : so that it strictly belongs to the functions of Organic life.
And with respect to those concerned in the act of Respiration, as well as those
which govern the two orifices of the alimentary tube, it will hereafter appear
that they result, equally with the former, from the application of a stimulus ;
and that they may be performed without any consciousness on the part of the
individual (though ordinarily accompanied by it) : — the difference being, that
in the former the stimulus is applied to the contractile part itself, whilst in the
latter it is applied to an organ with which this is connected by nerves only.
Now we have, even in Vegetables, instances of the propagation of an irritation
from one part to another, so that a motion results in a part distant from that
stimulated, — as in the case of the Sensitive Plant or Venus's Fly-trap. The
only essential difference, therefore, between those movements of Animals,
which are thus closely connected with the maintenance of the organic func-
tions, and those of Plants, consists in the medium through which they are
performed, — this being in Animals a distinct Nervous and Muscular apparatus,
whilst in Plants it is only a peculiar modification of the ordinary structure.

266. From what has been said, then, it appears that all the functions of the
Animal body are so completely bound up together, that none can be suspended
without the cessation of the rest. The properties of all the tissues and organs
are dependent upon their regular Nutrition, by a due supply of perfectly-ela-
borated blood ; this cannot be effected unless the functions of Circulation,
Respiration, and Secretion, be performed with regularity, — the first being ne-
cessary to convey the supply of nutritious fluid, and the two latter to separate
it from its impurities. The Respiration cannot be maintained without the in-
tegrity of a certain part of the nervous system; and the due action of this,
again, is dependent upon its regular nutrition. The materials necessary for
the replacement of those which are continually being separated from the blood,
can only be derived by the Absorption of ingested aliment ; and this cannot
be accomplished without the preliminary process of Digestion. The intro-

224 GENERAL VIEW OF THE FUNCTIONS.

duction of food into the stomach, again, is dependent, like the actions of Re-
spiration, upon the operations of the muscular apparatus and of a part of the
nervous centres; and the previous acquirement of food necessarily involves
the purely Animal powers. Now it will serve to show the distinction between
these powers, and those which are merely subservient to Organic life, if we
advert to the case, which is of no unfrequent occurrence, of a human being,
deprived, by some morbid condition of the brain, of all the powers of Animal
life, — Sensation, Thought, Volition, &c.; and yet capable of maintaining a
vegetative existence, — all the organic functions going on as usual, the morbid
condition not having affected the division of the nervous system, that is con-
cerned in the movements on which some of them depend. It is evident that
we can assign no definite limits to such a state, so long as the necessary food
is placed within reach of the grasp of the muscles, that will convey it into the
stomach ; as a matter of fact, however, it is seldom of long continuance ;
since the disordered state of the brain is sure to extend itself, sooner or later,
to the rest of the nervous system. This condition may be experimentally
imitated, however, by the removal of the brain in many of the lower animals,
whose bodies will sustain life for many months after such a mutilation; but
this can only take place when that food is conveyed by external agency
within the pharynx, which they would, if in their natural condition, have ob-
tained for themselves. A similar experiment is sometimes made by Nature
for the Physiologist, in the production of foetuses, as well of the human as of
other species, in which the brain is absent ; these can breathe and suck and
swallow, and perform all their organic functions ; and there is no assignable
limit to their existence, so long as they are duly supplied with food. Hence
we may learn the exact nature of the dependence of the Organic functions
upon those of purely Animal life ; and we perceive that, though less imme-
diate than it is upon the simple organic operations of the nervous and muscu-
lar systems, it is not less complete. On the other hand, the functions of
Animal life are even more closely dependent upon the Nutritive actions than
are those of organic life in general ; for many tissues will retain their several
properties, and their power of growth and extension, for a much longer pe-
riod after a general interruption of the circulation, than will the Nervous
structure ; which is, indeed, instantaneously affected by a cessation of the due
supply of blood, or by the depravation of its quality.

267. It is of little consequence, then, with which group of functions we
commence the detailed study of the phenomena, which in their totality make
up the life of Man. In viewing him merely as one of the widely-extended
group of organized beings, it would be natural to commence with those phe-
nomena which are common to all ; and to make, therefore, the Organic func-
tions the first object of our consideration. On the other hand, regarding Man
as a being in some degree isolated from all these by his peculiar character-
istics, it seems right to inquire into the latter in the first instance; more
especially as, in a general view of his life, these occupy the most prominent
place. It will be necessary, however, previously to entering upon them, to
take a more detailed survey than we have hitherto done, of the vital opera-
tions performed by his several organs, and of their connections with each
other. We shall commence with those of Vegetative Life.

2. Functions of Vegetative Life.

268. It is one of the most peculiar characteristics of Organized structure,
that its elements have a constant tendency (under ordinary circumstances at
least) to separate into more simple combinations ; and although it has been
ordinarily considered, that their living state prevents such a change, and that

FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE. 225

they have no tendency to it except when dead, reason will hereafter he given
for the belief that no such distinction exists (Chap. XIV., Sect. 4). The
maintenance of the vital properties of all organized structure then, requires
either that this structure should be completely secluded from air, moisture,
warmth, and other agents which tend to its decomposition; or that it should
be renewed as fast as it decays. Now the exclusion of these decomposing
agents would prevent any vital actions from being called into operation;
since they are the ordinary stimuli which are necessary to them. For
instance, a seed which is buried so deep in the soil as to be excluded from
the contact of air, and from the warmth of the sun, will not vegetate, although
it may retain its power of germinating when placed in more favourable cir-
cumstances ; and it will not decay, because secluded from the air and warmth
which are necessary to its decomposition. But as a certain change of com-
position appears to be a necessary condition of its vital activity, it is obvi-
ously requisite that a provision should be made, for removing from the
organism all those particles which are manifesting an incipient tendency to
decay, and are thus losing their vital properties; and for replacing these by
newly-combined particles, which in their turn undergo the same process.
Thus we find that, in the softest parts of the Animal frame-work, as in those
of the Plant, there is much less permanency than there is in those harder and
more solid portions, which often seem altogether to defy the lapse of time.
Now it is in the former that the most active vital changes take place, — those
of the nervous system, for example; whilst of the latter, the function is
chiefly, if not entirely, that of giving mechanical support to the structure.
The former organs are renewed many times, whilst the fabric of the latter is
not once completely changed; and thus a very interesting correspondence is
shown between the degree in which the action of any organized structure is
removed from, or is similar to, that of a mere inorganic substance, and the
amount of tendency to decomposition which that structure exhibits ; since
this constant renewal can scarcely serve any other purpose than that of
making up for the effects of decay.

269. One of the most important purposes of the supply of aliment, there-
fore, which all living beings continually require, is the replacement of the
portions of the fabric that are thus lost. The effects of the process of decay,
when uncompensated by that of renovation, are remarkably seen in cases of
starvation ; for it is a very constant indication of this condition, that the body
exhales a putrescent odour, even before death, and that it subsequently passes
very rapidly into decomposition. This, it may be considered, is the reason
why a constant supply of aliment is still required for the maintenance of
every organic structure, though it may have arrived at its full growth; and it
also affords one source of explanation of the fact, that old people require less
food than adults, since their tissues are more consolidated, and thus become
at the same time unable to perform their usual actions with their pristine
energy, whilst their tendency to decomposition is less. In the growing state,
however, an additional important source of demand for food obviously exists,
in the extension which the tissues themselves are constantly receiving ; yet
this, perhaps, does not make so great a difference, as it appears to do, in the
supply which is requisite. For if the addition which is made by growth to
the body in any given time, be compared with the amount of exchange which
has taken place in the same time, — the latter being judged of by the quantity
of matter excreted from the lungs, liver, kidneys, skin, &c., — it will be found
to bear but a very small proportion to it; except during fetal life, when the
growth is very rapid, and a large proportion of the effete particles are com-
municated to the maternal blood, to be excreted from it. The real cause of
the increased demand for nutriment, during the early part of life, is rather

226 GENERAL VIEW OF THE FUNCTIONS.

this, — that the tissues are far from having acquired that firmness and consoli-
dation which they gain at adult age; and that they are, therefore, more prone
to decomposition, at the same time that their vital activity is greater, as is well
known to be the case. — The feeling of hunger or desire for food originates,
we shall hereafter find reason to believe (Chap. X., Sect. 1), not so much in
the stomach itself, as in the system at large; of whose condition, in regard to
the requirement of an increased supply of aliment, it may, during the state of
health, be considered as a pretty faithful index. The same may be said of
thirst. The feeling of hunger, then, is the stimulus to the mental operations,
which have for their object the acquisition of food; whether these be of a
voluntary or of a purely instinctive kind. In Man they are obviously the
former, during all but infant life.

270. The food received into the mouth, and prepared there by the acts of
mastication and insalivation (the movements concerned in which are dependent
upon the brain, and can only be performed when it is in a condition of some
activity), is brought by them within reach of the pharyngeal muscles, whose
contraction cannot be effected by the will, but is purely excito-motor, — result-
ing merely from the impression made upon the fauces by the contact of the
substance swallowed, which impression is conveyed to the medulla oblongata
and reflected back to the muscles (§ 383). By these it is propelled down
the oesophagus ; and, after their action has ceased, it is taken up (as it were)
by the muscular coat of the oesophagus itself, and conveyed into the stomach.
How far the movements of the lower parts of the oasophagus and of the
stomach are in Man dependent upon reflex action, is uncertain ; the facts
which have been ascertained on this point, by experiment on animals, will be
detailed in their proper place (§ 390). In the stomach the food is subjected
to the gastric secretion ; the chemical action of which, aided by the con-
stantly-elevated temperature of the interior of the body, and by the continual
agitation effected by the contractions of the parietes of the organ, effects a
more or less complete solution of it. The mixture of the biliary and pan-
creatic secretions with the chyme thus produced, occasions a separation of its
elements into those adapted for nutrition, and those of which the character is
excrementitious; and this separation can scarcely be regarded in any other
light than as a chemical precipitation. By the agency of the biliary secre-
tion, moreover, certain elements of the food that would otherwise be rejected,
are reduced to a form in which they can be absorbed. The nutritious por-
tion is taken up by the Blood-vessels and by the Absorbent vessels (or Lac-
teals), which are distributed on the walls of the alimentary canal; whilst the
remainder is propelled along the intestinal tube by the simple contractility of
its walls, undergoing at the same time some further change, by which the
nutritive materials are still more completely extracted from it. And at last,
the excrementitious matter, — consisting not only of a portion of the food
taken into the stomach, but also of part of the secretion of the liver, and of
that of the mucous surface of the intestines and of their glandulrc, — is avoided
from the opposite extremity of the canal, by a muscular exertion, which is
partly reflex, like that of deglutition, but is partly voluntary, especially (as it
would appear) in Man.

271. There seems no doubt that fluid containing saline, albuminous, or
other soluble matters, may be absorbed by the Blood-vessels, with which the
mucous membrane of the alimentary canal is so copiously supplied ; and this
simple process of Imbibition probably takes place according to the physical
laws of Endosmose. But the Selection and Absorption of certain nutritious
elements appear to be performed, not by vessels, but by the growth and de-
velopment of cells (§ 181); which, by their subsequent disintegration, give it
up to the Lacteals. The absorbed fluid, which now receives the name of

FUNCTIONS OF ORGANIC Oil VEGETATIVE LIFE. 227

Chyle, is propelled through the Lacteals, by the contractility of their walls ;
aided in part, perhaps, by a vis a tergo derived from the force of the absorp-
tion itself. With the reception of the nutritious fluid into the absorbent ves-
sels, commences its real preparation for Organization. Up to that period, it
cannot be said to be in any degree vitalised; the changes which it has under-
gone being only of a chemical and physical nature, and such as merely prepare
it for subsequent assimilation. But in its passage through the long and tor-
tuous system of absorbent vessels and glands, it undergoes changes which,
with little chemical difference, manifest themselves by a decided alteration in
its properties ; so that the chyle of the thoracic duct is evidently a very dif-
ferent fluid from the chyle of the lacteals, approaching much nearer to blood
in its general characters. These characters are such as indicate that the pro-
cess of organization and vitilization has commenced; as may be known alike
from the microscopic appearance of the fluid, and from the actions it per-
forms when removed from the body. There is reason to believe that the
changes, which the Chyle undergoes in its progress through the lacteals, are
due to the action of certain cells which are seen to be diffused through the
liquid (§ 155) ; these, by their own independent powers of growth, are con-
tinually absorbing into themselves the fluid in which they float ; whilst, by
bursting or liquefying, as soon as their term of life is completed, they give
this back in an altered state. The Chyle thus modified is conveyed into the
Sanguiferous system of vessels, and flows directly to the heart; by which it is
transmitted with the mass of the blood, to the lungs. It there has the oppor-
tunity of excreting its superfluous carbonic acid, and of absorbing oxygen ;
and probably acquires gradually the properties, by which the blood previous-
ly formed is distinguished, — thus becoming the pabulum vitse for the whole
system.

272. The Circulation of the Blood through the tissues and organs which
it is destined to support, is a process evidently necessary for the conveyance
to them of the nutritious materials, which are provided for the repair of their
waste ; and for the removal of those elements of their fabric, which are in a
state of incipient decomposition. In the lowest classes of organized beings,
every portion of the structure is in direct relation with its nutritive materials ;
it can absorb for itself that which is required ; and it can readily part with
that of which it is desirable to get rid. Hence in such, no general circulation
is necessary. In Man, on the other hand, the digestive cavity occupies so
small a portion of the body, that the organs at a distance from it have no other
means, than their vascular communication affords, of participating in the re-
sults of its operations ; and it is moreover necessary that they should be
continually furnished with the organizable materials, of which the occasional
operation of the digestive process would otherwise afford only an intermitting
supply. This is especially the case, as already mentioned, with the Nervous
system, which is so predominant a feature in the constitution of Man ; and
we accordingly find both objects provided for, in the formation of a large
quantity of a semi-organized product, which contains within itself the mate-
rials of all the tissues, and is constantly being carried into relation with them.
Blood has been not unaptly termed chair coulante, or liquid flesh ; and al-
though it has been heretofore much questioned, whether it could be regarded
as either organized or endowed with vital properties, there now appears to be
sufficient reason for admitting, that this is the case to a very considerable
extent. The propulsion of the blood through the large trunks, which subse-
quently divide into capillary vessels, is due to the contractions of a hollow mus-
cular organ, the Heart; but these, like the peristaltic movements of the ali-
mentary canal, are quite independent of (though frequently influenced by) the

228 GENERAL VIEW OF THE FUNCTIONS.

agency of the Nervous system ; and are therefore to be referred to the class
of Organic movements, such as occur in Vegetables.

273. Upon the circulation of the blood through all parts of the fabric, de-
pends, in the first place, the Nutrition of the tissues. Upon this subject, for-
merly involved in the greatest obscurity, much light has recently been thrown
by Microscopic discovery ; it being now understood (as explained in the
preceding Chapter), that the continued growth and renewal of each tissue are
effected by a continuation of a process of cell-growth, similar to that by which
it was first developed. Even where the primary cells have changed their
character, their nuclei remain persistent; and may be regarded (in the lan-
guage of Mr. J. Goodsir) as so many "germinal centres," for giving origin to
new products. The greatest difficulty, in the present condition of our know-
ledge of this most interesting subject, is to comprehend the reason why such a
variety of products should spring up ; when the cells in which they all origi-
nate, appear to be so exactly alike. The important discoveries now referred
to are not confined to healthy structures ; for it has been ascertained, that dis-
eased growths have a similar origin and mode of extension ; and that the ma-
lignant character, assigned to Cancer, Fungus Haematodes, and other such
productions, is to be traced to the fact, that they are composed of cells which
undergo little metamorphosis, and retain their reproductive power ; so that
from a single cell, as from that of a Vegetable Fungus, a large structure may
rapidly spring up, the removal of which is by no means attended with any
certainty that it will not speedily re-appear, from some germs left in the sys-
tem.

274. The independent character of the cells in which all organized tissues
originate, might be of itself a satisfactory proof that, in Animals, as in Plants,
the actions of Nutrition are performed by the powers with which they are
individually endowed ; and that, whatever influence the Nervous system may
have upon them, they are not in any way essentially dependent upon it. More-
over, there is an evident improbability in the idea, " that any one of the solid
textures of the living body should have for its office, to give to any other the
power of taking on any vital actions :" and the improbability becomes an im-
possibility, when the fact is made known, that no formation of nervous matter
takes place in the embryonic structure, until the processes of Organic life
have been for some time in active operation. The influence which the Nerv-
ous System is known to have upon the Function of Nutrition, is probably ex-
erted, rather through the medium of its power of regulating the diameter of the
arteries and capillaries, by which it controls in some degree the afflux of blood,
and of affecting those preliminary actions on which the quantity and quality of
the nutritious fluid depend ; than in any more direct manner. At any rate,
it may be safely asserted, that no such proof of its more direct influence, as
is required to counterbalance the manifest improbability which has been shown
to attend it, has yet been given ; — all the facts which have been adduced in
support of this hypothesis being equally explicable on the other, which, being
in itself more probable, ought to be preferred.

275. The renewal which the various tissues of the body are continually
undergoing, has for its chief object the counteraction of the decay into which
they would otherwise speedily pass; and it is obviously required, that a means
should be provided for conveying away the waste, as well as for supplying
the new material. This is partly effected by the Venous circulation ; which
takes up a large part of the products of incipient decomposition, and conveys
them to organs of Excretion, by which they may be separated and cast forth
from the body. The first product of the decay of all organized structures,
is carbonic acid; and this is the one which is most constantly and rapidly
accumulating in the system, and the retention of which, therefore, within the

FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE. 229

body, is the most injurious. Accordingly, we find two large organs — the
Lungs and the Liver — adapted to remove it ; and to both these Venous blood
passes, before it is again sent through the system. The function of the Lungs
is so important in warm-blooded animals, that a special heart is provided for
propelling the blood through them ; in addition to the one possessed by most
of the lower animals, the function of which is the propulsion of the blood
through the system. In these organs, the blood is subjected to the influence
of the atmosphere, by which the carbonic acid with which it was charged, is
removed and replaced by oxygen ; and this change takes place, through the
delicate membrane that lines the air-cells of the lungs, according to the physi-
cal law of the mutual diffusion of gases. The introduction of oxygen into
the blood is necessary for the maintenance of those peculiar vivifying powers,
by which the Nervous and Muscular systems are kept in a state fit for activity ;
and its union with their elements appears to be a necessary condition of the
manifestation of their peculiar powers. Of this union, carbonic acid is one
of the chief products ; and we shall find that the demand for oxygen, and the
excretion of carbonic acid, vary according to the amount of nervous and mus-
cular action. The continual formation of carbonic acid, in this and other in-
terstitial changes, appears to have a most important purpose in the vital eco-
nomy,— that of keeping up its temperature to a fixed standard; for the union
of carbon and oxygen in this situation may be compared to a process of slow
combustion ; and it is well known that, the more energetic this is, the higher
is the temperature. Thus, in Birds, whose muscular and nervous activity is
so great, and whose respiration is so energetic, the temperature is constantly
maintained at a point higher than that which other animals ever attain, in the
healthy state at least ; whilst in Reptiles, which present a condition exactly
the reverse of this, the temperature is scarcely above that of the surrounding
medium. — The function of the Liver is, like that of the lungs, twofold ; it
separates from the blood a large quantity of the superfluous hydro-carbon,
which it acquires by circulating through the tissues ; and it combines that
carbon with other elements, into a secretion, which, as we have seen, is of
great importance in the digestive process. The hepatic circulation, however,
is not kept up by a distinct impelling organ ; but the venous blood from the
abdominal viscera (and, in the lower Vertebrata, that from the posterior part
of the body) passes through the Liver on its return to the heart.

276. All animal substances have a tendency, during their decomposition,
to throw off nitrogen, as well as carbon ; and this nitrogen may take the form
either of cyanogen, by going off in combination with carbon, or of ammo-
nia, by uniting at the time of its liberation with hydrogen. The chief function
of the Kidneys is evidently to separate the azotized products of decay from
the circulating fluid ; for the secretion which is characteristic of them, — namely
urea, — contains a larger proportion of nitrogen than is found in any other
organic compound ; it is identical in its chemical nature with cyanate of am-
monia, and maybe considered as the result of the union of these two products
of animal decomposition. The action of the kidneys is equally essential to
the continued performance of the other vital functions, with that of the lungs
and liver; since death invariably follows its suspension, unless some other
means be provided by Nature (as occasionally happens), for the separation of
its characteristic excretion from the circulating blood.

277. There seems reason to believe, however, that, of the products of
decomposition which are set free in the various tissues and organs of the
body, only a part is destined to be immediately excreted ; and that it is this
part, which is taken up by the Veins, and conveyed, by the general vascular
apparatus, to the several glands which are to separate it. The remainder,
consisting of substances which are fit to be re-assimilated, appears to be

20

230 GENERAL VIEW OF THE FUNCTIONS.

taken up by a distinct system of vessels, termed Lymphatics; which may be
considered as an extension of the Lacteal system through the fabric at large.
There is good reason to believe, that the special function of the Lymphatics
is, like that of the Lacteals, to minister to Nutritive absorption (although
other substances may find their way into them, by the mere physical process
of imbibition); the latter being especially destined to take up assimilable
matter from the digestive cavity, whilst the former absorb the products of the
secondary digestion, which seems to be continually going on in every part of
the body. (See Chap. XL, Sects. 1 and 2.) Of these, however, a portion
may still be destined to immediate excretion.

278. The various Secretions which have not already been adverted to,
appear for the most part to have for their object the performance of some
special function in the system, rather than the conveyance out of it of any
substances which it would be injurious to retain. This is the case, for
example, in regard to the secretion of the Lachrymal, Salivary, and Mam-
mary Glands, as well as with that of the Mucous and Serous Membranes.
The Excretion of fluid from the cutaneous surface, however, appears to
answer two important purposes, — the removal from the body of a portion of
its superfluous fluid, — and the regulation of its temperature. Just as, by the
action of the Lungs, the conditions are supplied, by which the temperature of
the body is kept up to a certain standard, so, by that of the Skin, it is pre-
vented from rising too high; for by the continual excretion from its surface,
of fluid which has to be carried oft' by evaporation, a degree of cold is gene-
rated, which keeps the calorific processes in check; and this excretion is
augmented, in proportion to the elevation of the external temperature, which
seems, in fact, the direct stimulus to the process. — In all forms of true Secre-
tion, the selection of the materials to be separated from the blood, is accom-
plished, like selective Absorption, by the agency of cells. These are de-
veloped in the interior of the secreting organ ; and when they are distended
with the fluid they have imbibed, their term of life appears to have expired,
so that they burst or liquefy, yielding their contents to the ducts, by which
the secreted product is conveyed away. In the case of Adipose tissue, we
have an instance in which the secreted product (separated from the blood by
the cells of which this tissue essentially consists) is not carried out of the
body, but remains to form a constituent part of it. — The regulation of the
amount of fluid in the vessels, is provided in a kind of safety-valve structure,
which has been lately shown to exist in the Kidneys. This readily permits
the escape of aqueous jftwid from the capillary vessels, into the urinary canals,
by a process altogether distinct from the secretion of the solid matter, which
it is the office of the kidneys to separate from the circulating fluid. Hence,
if the excretion of fluid from the skin be checked by cold, so that an accumu-
lation would take place in the vessels, the increased pressure within them
causes an increased escape of water through the kidneys. The relation
between the true process of Secretion, which is performed by the selective
power of cells, and that of simple Transudation, is the same as that which
has been already pointed out, between Selective Absorption and simple
Imbibition (§ 271).

279. There is no sufficient reason to believe, that the Nervous System has
any more direct influence on the process of Secretion, than it has been stated
to have on that of Nutrition. That almost every secretion in the body is
affected by slates of mind, which must operate through the nerves, daily
experience teaches; but the very remarkable degree of control, which the
Nervous system possesses over the Circulation, appears sufficient to explain
any of these e fleets, whether they be local or general. The flow of the
secreted fluids through their efferent ducts, seems to be principally caused by

FUNCTIONS OF ORGANIC OR VEGETATIVE LIFE. 231

the proper contractility of these, which (like that of the heart and alimentary
canal) is directly stimulated by the contact of their contents; but there is
also evidence that this contractility may be affected (as it is in those two
instances) by the nervous system; and thus we have an additional means of
influence, by which the nervous system can operate on these processes, since
its power is probably not confined to the large ducts, but extends to their
ultimate ramifications. Where, as happens in the case of the urinary excre-
tion, there is a reservoir into which it is received as fast as it is formed, for
the purpose of preventing the inconvenience which its constant passage from
the body would otherwise occasion, — the power of emptying this reservoir is
usually placed in some degree under the dominion of the will, although
chiefly governed by reflex action. It is obvious that such a provision is by
no means essential to the function; and that it has for its object the adapta-
tion, merely, of that function, to the conditions of Animal existence.

280. Thus we see that, when we enter, as it were, into the penetralia of
the Animal system, and study those processes, of which the development and
maintenance of the material fabric essentially consist, we find them performed
under conditions essentially the same as those which obtain in Plants ; and
we observe that the operations of the Nervous System have none but an
indirect influence or control over them. It is, therefore, quite philosophical
to distinguish these Organic Functions, or phenomena of Vegetative Life,
from those concerned in the Life of Relation, or Animal Life. The distinc-
tion is, indeed, of great practical importance, and lies at the foundation of all
Physiological Science; yet it is seldom accurately made, and a very confused
notion on the subject is generally prevalent. It is commonly said, for ex-
ample, that the function of Respiration is the connecting link between the
two: — the fact being, however, that the true process of Respiration is no
more a function of Animal life, than is any ordinary process of secretion ; but
that, in order to secure the constant interchange of air, which is necessary to
its performance, the assistance of the nervous and muscular systems is called
in, though not in a manner which necessarily involves either consciousness
or will.

281. The process of Reproduction, like that of Nutrition, has been until
recently involved in great obscurity ; and although it cannot be said to be _vet
fully elucidated, it has been brought, by late investigations, far more within
our comprehension, than was formerly deemed possible. The close connec-
tion between the Reproductive and Nutritive operations, both as regards their
respective characters, and their dependence upon one another, has long been
recognized; and it is now rendered still more evident. Nutrition has not been
unaptly designated " a perpetual reproduction;" and the expression is strictly
correct. In the fully-formed organism, the supply of alimentary material to
every part of the fabric, enables it to produce a tissue resembling itself; thus
we only find true bone produced in continuity with bone, nerve with nerve,
muscle with muscle, and so on. Hence it would appear that, when a group
of cells has once taken on a particular kind of development, it continues to
reproduce itself on the same plan. But in the Reproductive process it is
different. A single cell is generated by certain preliminary actions, — from
which single cell, all those which subsequently compose the embryonic struc-
tures, take their origin ; and it is not until a later period, that any distinction
of parts can be traced, in the mass of vesicles which spring from it. Hence
the essential character of the process of Reproduction consists in the forma-
tion of a cell, which can give origin to others, from which again others spring ;
— and in the capability of these last to undergo several kinds of transforma-
tion, so as ultimately to produce a fabric, in which the number of different
parts is equal to that of the functions to be performed, every separate part

232 GENERAL VIEW OF THE FUNCTIONS.

having a purpose distinct from that of the rest. Such a fabric is considered
as a very heterogeneous one ; and is eminently distinguished from those homo-
geneous organisms, in which every part is but a repetition of the rest. Of all
Animals, Man possesses, as already shown, the greatest variety of endow-
ments,— the greatest number of distinct organs ; and yet Man, in common with
the simplest Animal or Plant, takes his origin in a single cell. It is in the
almost homogeneous fabrics of the Cellular Plants, that we find the closest
connection between the function of Nutrition, and that of Reproduction ; for
every one of the vesicles which compose their fabric, is endowed with the
power of generating others similar to itself; and these may either extend the
parent structure, or separate into new and distinct organisms. Hence it is
sca'rcely possible to draw a line, in these cases, between the Nutrition of the
individual, and the Reproduction of the species.

282. But, it will be inquired, how and where in the Human body (and in
the higher Animals in general) is this embryonic vesicle produced, and what
are the relative offices of the two sexes in its formation ? This is a question
which must still be answered with some degree of doubt; and yet observed
phenomena, if explained by the aid of analogy, seem to lead to a very direct
conclusion. The embryonic vesicle itself, like other cells, must arise from a
germ ; and reasons will be hereafter given for the belief, that the germ is sup-
plied by the male parent, and that the female supplies only the materials for
its development. Here, as in the Nutritive processes, we find that the opera-
tions immediately concerned in this function, — namely, the act of fecundation,
and the development of the ovum, — are not directly influenced in any way by
the nervous system ; and that the functions of Animal Life are called into play,
only in the preliminary and concluding steps of the process. In many of the
lower Animals, there is no sexual congress, even where the concurrence of
two sets of organs (as in the Phanerogamic Plants) is necessary for the pro-
cess; the ova are liberated by one, and the spermatozoa by the other; and
the accidental meeting of the two produces the desired result. In many Ani-
mals higher in the scale, the impulse which brings the sexes together is of a
purely instinctive kind. But in Man, it is of a very compound nature. The
instinctive propensity, unless unduly strong, is controlled and guided by the
will, and serves (like the feelings of hunger and thirst) as a stimulus to the
reasoning processes, by which the means of gratifying it are obtained; and a
moral sentiment or affection of a much higher kind is closely connected with
it, which acts as an additional incitement. Those movements, however,
which are most closely connected with the essential part of the process, are,
like those of deglutition, respiration, <fec., simply reflex and involuntary in their
character; and thus we have another proof of the constancy of the principle,
that, where the action of the apparatus of Animal Life is brought into near
connection with the Organic functions, it is not such as requires the operation
of the purely animal powers, — sensation and volition. Thus, then, as it has
been lucidly remarked, "the Nervous System lives and grows within an Ani-
mal, as a parasitic Plant does in a Vegetable ; with its life and growth, certain
sensations and mental acts, varying in the different classes of Animals, are
connected by nature in a manner altogether inscrutable to man; but the ob-
jects of the existence of Animals require, that these mental acts should exert
a powerful controlling influence over all the textures and organs of which they
are composed."

3. Functions of Animal Life.

283. The existence of consciousness, by which the individual (le moi, in
the language of French physiologists) becomes sensible of impressions made

FUNCTIONS OF ANIMAL LIFE. 233

upon its bodily structure, — and the power of spontaneously exciting contrac-
tions in its tissues, by which evident motions are produced, — have been already
stated to be the peculiar attributes of the beings composing the Animal king-
dom. The evident motions exhibited by some Plants, cannot be regarded as
indicating the existence of any psychical endowments in the beings included
in the Vegetable kingdom ; for they are usually to be referred without difficulty
to the action, either direct or indirect, of an external stimulus, upon a contrac-
tile tissue ; and even where no such action evidently takes place, there is good
reason to suppose its existence. To refer, therefore, the movements of Vege-
tables to a Nervous system, of which no traces can be found, — still more to
suppose them endowed with consciousness and will, as some have done, — is
to violate most grossly a well-known rule in philosophy, which cannot be too
steadily kept in view in prosecuting physiological inquiries — nonjingerc hy-
potheses.

284. There are in Animals, however, many movements which are equally
dependent upon direct stimuli for their production ; such are (as we have
seen), even in the highest, the actions of the heart and of the alimentary canal.
These, in the lowest tribes, probably bear a much greater proportion to the
whole amount of those exhibited by the beings, than they do in the higher;
whilst those, which we may regard as specially dependent on a nervous sys-
tem, appear to constitute but a small part of their general vital actions. The
life of such beings, therefore, bears a much closer resemblance to that of the
Vegetable, than to that of the higher Animal. Their organic functions are
performed with scarcely more of sensible movement, than is seen in plants ;
and of the motions which they do exhibit (nearly all of them immediately
concerned in the maintenance of the organic functions), it is probable that
many are the result of the simple contractility of their tissues, called into
action by the stimuli directly applied to them. It is scarcely possible to ima-
gine that such beings can enjoy any of those higher mental powers, which
Man recognizes by observation on himself, and of which he discerns the ma-
nifestations in those tribes, which, from their nearer relation to himself, he
regards as more elevated in the scale of existence. — If we direct our attention
on the other hand, to the psychical* operations of Man, as forming part ot
his general vital actions, we perceive that the proportion is completely re-
versed. So far from his organic life exhibiting a predominance, it appears
entirely subordinate to his animal functions, and seems destined only to afford
the conditions for their performance. If we could imagine his nervous and
muscular systems to be isolated from the remainder of his corporeal structure,
and endowed in themselves with the power of retaining their integrity and
activity, we should have all that is essential to our idea of Man. But, as at
present constituted, these organs are dependent, for the maintenance of their
integrity and functional activity, upon the nutritive apparatus ; and the whole
object of the latter appears to be the supply of those conditions, which are
necessary to the exercise of the peculiarly animal functions. That his men-
tal activity should be thus made dependent upon the due supply of his bodily
wants, is a part of the general scheme of his probationary existence ; and the
first excitement of his intellectual powers is in a great degree dependent upon
this arrangement.

285. The most simple or elementary function of the Nervous System is, as
already observed, the establishment of a communication between a part which
is susceptible of impressions, and another which can perform contractile move-

* Here and elsewhere this terra will be employed in its most extended sense, to designate
all the mental operations, — whether intellectual, emotional or instinctive, — of which Man's
nervous system is the instrument.

20*

234 GENERAL VIEW OF THE FUNCTIONS.

merits ; so that a stimulus applied to one may immediately excite a respondent
action in the other, however great may be its distance. Hence it may be said
to have an internuncial function ; but this, so far as it is performed without
the necessary participation of the consciousness or will of the individual, is
not essentially higher in character, than the corresponding function in Plants,
although the latter is affected by a different apparatus. The ministration of
the nervous system to purely Animal life, obviously consists in its rendering
the mind cognizant of that which is taking place around, and in enabling it to
act upon the material world, by the instruments with which the body is pro-
vided for the purpose. It is important to observe, that every method at pre-
sent known, by which Mind can act upon Mind, requires muscular contraction
as its medium, and sensation as its recipient. This is the case, for example,
not only in that communication which takes place by language, whether
written or spoken ; but in the look, the touch, the gesture, which are so fre-
quently more expressive than any words can be ; and thus we trace the limi-
tation, which, even in communication that appears so far removed from the
material world, constantly bounds the operations of the most powerful intel-
lect, ami the highest flights of the imagination. That in a future state of being,
the communion of mind with mind will be more intimate, and that Man will
be admitted into more immediate converse with his Maker, appears to be alike
the teaching of the most comprehensive Philosophical inquiries, and £| the
most direct Revelation of the Divinity.

286. The Organs of Sense are instruments, which are adapted to enable
particular nerves to receive impressions from without; of a kind, and in a de-
gree, of Avhich they would not otherwise be sensible. Thus, although the
simple contact of a hard body with the nerve may be readily conceived to
produce a material change in it, of such a kind as would be easily propagated
to the central sensorium, it is evident that a nerve must be peculiarly modi-
fied, to receive and conduct sonorous impressions from the undulations of the
air ; still more — to be susceptible of the impressions produced by those un-
dulations, to which most Natural Philosophers now attribute the transmission
of light. And, even when this difficulty has been provided for, by some mo-
dification in the structure of the nerve itself, there is evidently another still
remaining, — that of understanding how distinct images of the form, colour,
&c., of external objects can be communicated to the nerve of sight; or ideas
of the direction, pitch, quality, &c., of sonorous undulations, can be obtained
through the auditory nerve. There is reason to believe that many among
the lower Animals, which do not see objects around them, are conscious of
the influence of light ; and thus the distinction between the mere reception of
the impression, and the communication of the optical image, becomes evident.
The former may take place through the intervention of nerves, whose sensory
extremities offer no peculiarities : the latter can only be received through the
medium of an instrument, which shall, from the mixture of rays tailing
equally upon every part of a surface, produce an optical image, and then
impress it upon the expanded surface of the nerve ; so that each fibril may
receive a distinct impression, the image presented to the mind being formed
by the combination of the whole. That this is, in fact, the share which the
organs of special sense bear in the general endowments of the whole appa-
ratus, may be inferred especially from the conformation of the Eye ; which
is in every respect a merely optical instrument, of the greatest beauty and
perfection, adapted to present to the nerve, in the most advantageous manner,
the images of surrounding objects in all their variations. And we might con-
ceive that, if it were possible for the interior of the living eye to be replaced
by one constructed of inorganic materials by the hand of man, without de-
stroying the functional power of the retina, the sense of sight would be but

FUNCTIONS OF ANIMAL LIFE. 235

little impaired, — except through the incapability, on the part of any piece of
human mechanism, to imitate those wondrous contrivances of Infinite Skill,
which have for their object the adaptation of the instrument to varieties of dis-
tance, of intensity of light, &c. There can be little doubt, that the structure
of the Ear is arranged to do the same for the sonorous vibrations, which the
eye does for the rays of light; that is, through its means, the undulations
which strike upon the external surface of the organ are separated and distin-
gished, those of a like kind being brought together upon one division of the
nerve, and those of another order upon a different set of fibres ; so that the
different kinds of sound, and the peculiar quality and direction of each, may
be discriminated ; whilst, by the concentration of all the impressions of the
same character, a higher amount of force is given to them. Of the sense of
Smell, no similar account can be given ; since the medium by which odours are
propagated is not known. If, as is generally believed, this is accomplished by
the diffusion through space, of minute particles of the odoriferous body itself
(which supposition seems to derive support from the general fact, that the
most volatile substances are usually most odoriferous), smell may be regarded,
— as taste also is probably to be considered, — in the light of a refined kind of
touch.

287. Thus, the general rule holds good, here as elsewhere, that the pro-
cesses, by which the organism is immediately brought into relation with the
external world, are performed in obedience to physical laws ; the living struc-
ture only affording certain peculiar conditions, which may be imitated in a
great degree by other means. This is the case, for example, with regard to
Digestion, which is in itself a simply Chemical process, that will take place
out of the body as well as in it, if the materials and the necessary solvent be
submitted to the same circumstances, as those to which they are exposed in
the stomach ; and in regard also to the act of Respiration, which depends
upon the physical tendency to mutual diffusion, inseparable from the exist-
ence of gases : and we notice the prevalence of the same general fact in the
Animal as in the Organic functions. We cannot become cognizant of the
changes, or even of the existence, of the external world, unless some mate-
rial effect be produced by it on our organs of sense ; nor can we produce any
alteration in its condition, except by powers which act according to purely
mechanical principles.

288. In regard to the Muscular System, it has already been sufficiently
explained that it forms a part of the apparatus of Animal life, no otherwise
than as the instrument by which nervous energy operates upon external
objects. The contractility which it manifests on the application of a stimulus,
is an endowment which it derives from its own structure, and not from the
nervous system ; for it will be clearly proved in its appropriate place, that
the presence of this contractility is connected with the healthy nutrition of
the tissue, and with its due supply of arterial blood ; and that the complete
separation of any muscular part from all its nervous connections, has none
but an indirect influence on its properties.

236

CHAPTER V.

FUNCTIONS OF THE NERVOUS SYSTEM.

1. General Summary.

289. OUR fundamental idea of a Nervous System includes a central or^an
or ganglion, essentially composed of vesicles or cells, with a plexus of capil-
lary vessels distributed amongst these ; and a set of trunks and ramifying
branches, composed of tubular fibres, and connecting the ganglion with differ-
ent parts of the fabric. These branches are for the most part distributed, on
the one hand, to the sensory surfaces and organs ; and, on the other, to the
muscles or motor organs. The former serve for the conveyance of impres-
sions, made upon the periphery, towards the centre ; and they may thence
be denominated afferent fibres.* The latter, on the other hand, serve to con-
vey an influence, originating in the central ganglion, to the muscles, which
are thereby thrown into contraction; and these are distinguished as efferent
or motor fibres. Although the distinctness of these two sets of fibres has
only been proved in the Vertebrata, yet there can be no reasonable doubt of
its universality. Now this fundamental idea of a Nervous apparatus, which
is based upon what are believed to be the relative offices of its several com-
ponent parts (as formerly explained § 248), is found to be exactly realized in
the simple forms of that system, which we find in the lowest animals in which
Nervous structure can be discovered at all ; and even where the apparatus
has, to all appearance, a character of much greater complexity, it may still be
reduced to the same simple idea, by taking it to pieces (so to speak) and exa-
mining its component parts. For it will then be found, that the multiplica-
tion of ganglia and trunks is principally due to the multiplication of the
organs to be supplied ; as in the case of the nervous ring of the Star-fish,
where the ganglia, — all of them apparently identical in function, and similar in
the distribution of their branches, — are repeated in conformity with the num-
ber of the radiating parts of the body ; or in the case of the ventral nervous
cord of an Articulated animal, in which the ganglia are in like manner re-
peated longitudinally, in accordance with the number of segments of the body,
and of the pairs of members connected with them. In other instances, the
multiplication of ganglia is due to the increased complexity of the functions
performed by a set of organs; of this we shall see numerous examples in
the higher Vertebrata. In all cases, the individual ganglia remain to a great
extent independent of each other; so that the removal of any one (if it can
be accomplished without injury to the rest) affects only the particular organ
with which it may be connected, and the special function of that organ to
which alone it ministers.

290. Uefore proceeding to inquire into the operations of the Nervous Sys-
tem as a whole, it is desirable that we should stop to consider the conditions

* Such arc commonly denominated sensory fibres; but this designation is objectionable,
in as much as many of them serve to excite reflex actions, without necessarily producing
sensations.

DEPENDENCE OF NERVOUS POWER ON SUPPLY OF BLOOD. 237

on which its functional activity is dependent. — The chief of these, is a con-
stant supply of oxygenated blood ; which is more necessary for the mainte-
nance of the Nervous power, than it is for that of any other tissue whatever.
This supply is peculiarly required at those points at which changes originate ;
not being, it would appear, so necessary for the mere conduction of impres-
sions. Consequently we find that the greatest supply of blood is afforded to
the nervous centres, and to the peripheral extremities or origins of the affe-
rent nerves ; and that the effects of any interruption to the supply are mani-
fested in an immediate and most striking manner. Thus, if the circulation
through the Brain be suspended but for an instant, insensibility and loss of
voluntary power supervene, and continue until it is restored. This was
shown by the following experiment of Sir A. Cooper's. After having tied
both carotid arteries in a dog, he compressed the Vertebral trunks ; and im-
mediate insensibility came on, the animal at the same time falling powerless.
But convulsive movements occurred at the same time ; showing that the func-
tions of the spinal cord were not suspended, but only deranged. As soon as
the blood was re-admitted to the brain, the animal recovered its consciousness
and voluntary power, and stood on its legs again ; the convulsive movements
ceased at the same time. — In Syncope, the circulation through the Spinal
cord is weakened, by the failure of the heart's action, to the same extent as
the flow of blood through the Brain ; and a general cessation, not merely of
muscular movement, but of all power of exciting it, is the immediate result.
No sooner, however, is the circulation fully re-established, than the power of
the Nervous centres is restored. — Again, the influence of diminished circula-
tion, at the origins of the afferent nerves, is shown in the deficient impressi-
bility of the nerves, at the part affected. Thus, if the movement of blood
through the capillaries of a limb be stagnated, — whether by pressure on the
arterial trunks, by cold, or by any other cause, — it is at once made apparent
by the numbness of the surface ; and a complete stagnation produces com-
plete insensibility. The power of receiving impressions, that are to excite
reflex movements, is diminished in the same degree.

291. On the other hand it is found, that increased circulation through the
same parts, is attended with an exaltation of their function. This is particu-
larly noticed in those affections of the brain and spinal cord, closely border-
ing on inflammation, to which the terms active congestion and determination
of blood have been applied. We have, in such cases, extreme acuteness of
sensation, excessive activity of the mental functions, or violent excitement of
the motor powers ; according (it would seem) to the particular division of the
nervous centres most affected. Again, we find that an increase in the circu-
lation through any organ, from which afferent nerves arise, increases their
readiness to receive impressions ; thus the sensibility of the genital organs of
animals during the period of heat, and of those of man in a state of venereal
excitement, are greatly augmented ; and the tendency of impressions, made
upon them, to excite reflex movements, is similarly exalted.

292. The due activity of the Nervous System is not merely dependent
upon a constant and ample supply of Blood ; but it requires that this blood
should be in a state of extreme purity, and more especially that it should
contain a due supply of oxygen, and should be depurated of its carbonic acid,
and of other products of the decomposition of the body. The final cessa-
tion of nervous power, in death by Asphyxia, is partly due (as will be shown
hereafter, Chap. XIII., Sect. 3), to a positive deficiency in the supply of blood ;
but the obtuseness of sensibility which gradually increases until a state of
unconsciousness comes on, may be clearly traced in the first instance to the
deficient aeration of the blood, which is gradually deprived of its oxygen, and
charged with more and more carbonic acid. Corresponding but less severe

238 FUNCTIONS OF THE NERVOUS SYSTEM.

symptoms occur, when the excretion of carbonic acid is not checked, but only
slightly impeded ; provided the impediment be in operation for a sufficient
length of time, as in the case of an ill-ventilated apartment ; an indisposition
to mental exertion, a deficiency of muscular power, and an obtuseness of the
intellectual and moral faculties, being the general result. — These facts are
readily explained upon the hypothesis (which seems now to have a sufficiently
wide foundation, to be entitled to rank as physiological truth, although no
very direct proof of it can be given), that the functional activity of the nerv-
ous system is mainly dependent upon the combination of the oxygen sup-
plied by the blood, with its elements; the production of the nervous force,
whatever be its nature, being a result of this change of composition. The
chief grounds for this doctrine will now be enumerated.

293. In the first place, the dependence of nervous energy upon the con-
stant circulation of blood through the tissue, is much more close and imme-
diate than can be accounted for on the idea that the relation is one of mere
nutrition or development. On the contrary, where these last changes are
taking place most actively, we often find rather a disposition to stagnation of
the current, to give time for the elaboration of the nutrient materials that are
to be withdrawn from it ; and in no case does the process so instantaneously
cease, when the flow is suspended. From this it would appear, that some
combination takes place between the elements of the nervous tissue, and some
material supplied by the blood ; which is much more rapid in its character,
than the process of cell-development ; and which is essentially concerned in
the production and maintenance of the active condition of the nervous sys-
tem.— Again, that the material supplied by the blood for this purpose is Oxy-
gen, would appear from a variety of considerations. A general survey of
the Animal kingdom shows, that oxygen, is essential to the maintenance of
animal life, as distinct from vegetative; and a more particular comparison
of different tribes demonstrates most unequivocally, that the consumption of
oxygen is in direct relation to the development of the animal powers in each.
These facts harmonize completely with what has been just stated, respecting
the effects of a suspension of the oxygenating process.

294. Further, in proof that the activity of the Nervous system is immedi-
ately dependent, not upon a process of development or nutrition, but upon
one of disintegration or destruction, it may be urged, 'that it is impossible for
this state of activity to be maintained, in a large portion of it, without an in-
terval of repose, which we know to be favourable to the vegetative or repa-
rative processes. There are certain parts of the Nervous System, particularly
those that put in action the respiratory muscles, which are in a state of un-
ceasing though moderate activity ; and in these, the constant nutrition is suffi-
cient to repair the effects of the constant decay. But those parts winch
operate in a more powerful and energetic manner, and which are therefore
more rapidly disintegrated when in action, need a season of rest for their re-
paration. Hence the sense of fatigue which is experienced when the mind
has been long acting through its instrument, — the Brain ; and the irresistible
tendency to sleep, which usually supervenes after any unusual exertion of this
kind. In the healthy state of the body, when the exercise of the nervous system
by day does not exceed that which the repose of the night may compensate,
the Nervous System is maintained in a condition which fits it for constant
moderate exercise ; but unusual demands upon its powers,— whether by long-
continued and severe exercise of the intellect, by excitement of the emotions,
or by the combination of both, in that state of anxiety which the circum-
stances of man's condition too frequently induce, — occasion an unusual waste,
and require a prolonged repose and uninterrupted nutrition, for the complete
restoration of its powers. There can be no doubt that (from causes which

DISINTEGRATION OF NERVOUS MATTER WITH USE. 239

are not known) the amount of sleep required by different persons, for the
maintenance of a healthy condition of the Nervous. System, varies consider-
ably ; some being able to dispense with it to a degree which would be exceed-
ingly injurious to other individuals, who do not surpass them in mental activity.
Where a prolonged exertion of the mind has been made, and the natural tend-
ency to sleep has been habitually resisted, by a strong effort of the will,
injurious results are sure to follow. The bodily health breaks down; and too
frequently the mind itself is permanently enfeebled. It is obvious that the
Nutrition of the Nervous System becomes completely deranged ; and that the
tissue is no longer formed in a manner requisite for the discharge of its healthy
functions. The same may be said of the state of Mania ; in which there is,
for a time, an extraordinary degree of activity (though manifested in an irregu-
lar manner) of the cerebral functions, and an absence of disposition to sleep.
Such a state may continue for some time ; but the subsequent exhaustion of
nervous power is proportioned to the duration of the excitement, and frequent
attacks of mania almost invariably subside at last into imbecility.

295. Additional evidence for the belief that the functional activity of the
Nervous tissue involves disintegration of its tissue by the agency of Oxygen,
is found in the increase of plwsphalic deposits in the urine, — and especially
of those having alkaline bases, — when there has been any unusual demand
upon the nervous power. No others of the soft tissues contain any large
amount of phosphorus ; and the marked increase in these deposits, which has
been continually observed to accompany long-continued wear of mind, whether
by intellectual exertion, or by the excitement of the feelings, — and which fol-
lows any temporary strain upon its powers, can scarcely be set down to any
other cause. The most satisfactory proof is to be found in cases, in which
there is a periodical demand upon the mental powers ; as, for example, among
Clergymen, in the preparation for and discharge of their Sunday duties. This
is found to be almost invariably followed by the appearance of a large quantity
of the alkaline phosphates in the urine. And in cases in which constant and
severe intellectual exertion has impaired the nutrition of the brain, and has
consequently weakened the mental power, it is found that any premature at-
tempt to renew the activity of its exercise, causes the re-appearance of the
excessive phosphatic discharge indicative of an undue waste of nervous mat-
ter.*

296. There is not the same evidence of constant change, however, in re-
gard to \hefibrous element of the Nervous System; and its conducting power
appears to be much less dependent upon the supply of blood, than is the ori-
ginating power of the vesicular matter. It remains, with little decrease, for
some time after death ; especially in cold-blooded animals ; for we can, by
pinching, pricking, or otherwise stimulating the motor trunks, give rise to con-
tractions in the muscles supplied by them, exactly as during life. Its earlier
departure in warm-blooded animals, may be partly due to the cooling of the
body.

297. Of the actual nature of the changes by which impressions are received
upon the peripheral origins of the afferent nerves, or are communicated to the

* A large amount of evidence confirmatory of the above views, and showing the im-
portance of carefully distinguishing between the alkaline and earthy phosphates, has been
adduced by Dr. Bence Jones, in a Paper lately read to the Royal Society. The quantity of
the latter, which is present in the urine, is found to bear a constant relation to that which is
contained in the food. On the other hand, the amount of the former varies with dull-rent
conditions of the nervous system, in such a manner as to warrant the inference that its pro-
duction is a result of the disintegration of nervous matter; being due to the union of the
phosphoric acid thus set free, with alkaline bases present in the blood in a state of feeble
combination.

240 FUNCTIONS OF THE NERVOUS SYSTEM.

central origins of the motor, and by which they are conducted along each to
their opposite extremities, Physiologists have no certain knowledge. That
they are Electrical in their character, has been, and still continues to be, a
favourite theory with some; and the idea seems to derive support from the
marked degree in which Electricity, transmitted along the Nervous trunks,
can excite the changes to which those nerves are ordinarily subservient.
Tjjus, a feeble galvanic current, transmitted along the motor nerves of an ani-
mal recently killed, will call the muscles supplied by it into contraction ; whilst,
on the other hand, a similar current transmitted along an afferent nerve, shall
excite reflex movements through its ganglionic centre. Further, if the cur-
rent be transmitted along an afferent nerve, in a living animal, it will excite
sensations which are referred to the part whence the nerve arises ; and, as
will be shown hereafter (Chap. VI., Sect. 1), Electricity is capable of thus
producing sensations of a special kind, as well as those of a general nature.
Moreover, in the instantaneousness of the transmission of Nervous agency
from one part of the system to another, there is more analogy to Electricity,
than to any other known force. But these and similar arguments do not prove
the identity of Nervous agency with Electricity; since the effects of the for-
mer may be imitated to a certain extent, not merely by Electricity, but by
mechanical and chemical stimulation of various kinds. Further, there are
powerful arguments against such a supposition, the validity of which cannot
be easily set aside. All attempts to prove the existence of an Electric current,
in a Nervous trunk that is actively engaged in conveying motor influence,
have completely failed, though made with the greatest precaution. Thus, Mat-
teucci has lately experimented upon the very large crural nerve of a Horse,
which was caused, by stimulating its roots, to throw the muscles of the leg
into violent contraction ; nevertheless, although he used instruments of such
delicacy, as to be capable of detecting an infinitesimally-small disturbance of
the electric equilibrium, no such disturbance was apparent. Further, it is well
known that the conducting power of the nerves is destroyed, not merely by
dividing the trunk, but also by putting a ligature round it ; which last opera-
tion does not diminish its powers as a conductor of Electricity. Moreover,
the various fibrils are not as completely insulated from each other in regard to
Electricity, as we know them to be with respect to nervous agency ; 1'or the
first of these forces, when transmitted along a nervous trunk, cannot be re-
stricted to any fibre or fasciculus of fibres, but spreads through the entire
trunk, and even to the neighbouring parts in which it is imbedded; whilst the
latter is continually restricted to a small portion of the trunk, as is manifested
by its results. Again, if a small piece of nervous trunk be cut out, and he
replaced by an electric conductor, electricity will still pass along the nerve;
but no nervous force, excited by stimulus above the section, will be propa-
gated through the conductor to the parts below. And lastly, the conducting
power of Nerve for Electricity is stated by Matteucci to be not more than
one-fourth that of Muscle ; whilst Messrs. Toild and Bowman give it as the
result of their experiments, that both Nerve and Muscle are both infinitely
tvorse conductors than copper ; their power of conduction not ranking above
that of water holding in solution a small quantity of saline matter.

a. Although, fur the sake of convenience, Electricity ami Xervous power are spoken of,
here and elsewhere, as actual nili/ies or agents, traveling along tlic \vhvs or cords that con-
duct them, it rnnst not he lorgolteii that the. present tendency <i(' M-ieiitilii: inquiry leads us
to abandon .such an idea, in the funner ease at li-a.-t ; what is commonly termed the trans-
tniision of electricity lieing the result of a molecular change, instantaneously occurring along
the \vhole length ol'tlie conducting body, in virtue of a diMurhaiiee, in the polar arrangement
of its particles, at one extremity, \vhich causes a similar disturbance to manifest itself at the
other. Thus if

ab ab ab ab ab ab ab ab

LAWS OF NERVOUS TRANSMISSION. 241

represent the arrangement of the particles, in the condition of equilibrium or quiescence, and
this condition be disturbed at one extremity, by the operation of a new attraction upon the
first particle a, a new arrangement will instantaneously take place throughout: this may be
represented by

a ba ba ba ba ba ba ba b

which shows b in a free state at the opposite end, ready to exert its influence upon anything
submitted to it. It is probable that in this respect there is an analogy between the Nervous
and electrical forces ; and that, instead of speaking of the "transmission of nervous influence"
along a nerve, we should describe the change as the production of a "polar state" in the
nervous trunk; as first pointed out by Messrs. Todd and Bowman (Physiological Anatomy,
vol. i. p. 240).

298. Every fibre, there is reason to believe, runs a distinct course between
the central organ, in which it loses itself at one extremity, and the muscle or
organ of sense in which it terminates at the other. Each Nervous Trunk is
made up of several fasciculi of these fibres ; and each fasciculus is composed
of a large number of the ultimate fibres themselves. Although the fasciculi
occasionally intermix and exchange fibres with one another (as occurs in what
is termed a plexus), the fibres themselves never inosculate. Each fibre would
seem, therefore, to have its appropriate office, which it cannot share with
another. The objects of a plexus are twofold. In some instances it serves
to intermix fibres, which have endowments fundamentally different: for
example, the Spinal Accessory nerve, at its origin, appears to be exclusively
motor, and the roots of the Par Vagum are as exclusively afferent; but by
the early admixture of these, a large number of motor fibres are imparted to
the Par Vagum, and are distributed in variable proportion, with its different
branches ; whilst few of its sensory filaments seem to enter the Spinal Acces-
sory.— In other instances, the object of a plexus appears to be, to give a more
advantageous distribution to fibres, which all possess corresponding endow-
ments. Thus the Brachial plexus mixes together the fibres arising from five
segments of the spinal cord, and sends off five principal trunks to supply the
arm. Now if each of these trunks had arisen by itself, from a distinct seg-
ment of the spinal cord, so that the parts on which it is distributed had only
a single connection with the nervous centres, they would have been much
more liable to paralysis than at present. By means of the plexus, every part
is supplied with fibres arising from each segment of the spinal cord ; and the
functions of the whole must therefore be suspended, before complete paralysis
of any part can occur, from a cause which operates above the plexus. Such
a view is borne out by direct experiment; for it has been ascertained by
Panizza that, in Frogs, whose crural plexus is much less complicated than
that of Mammalia, section of the roots of one of the three nerves which enter
into it, produces little effect on the general movements of the limb ; and that,
even when two are divided, there is no paralysis of any of its actions, all
being weakened in a nearly similar degree. — It is not unlikely also that, by
this arrangement, a consentaneousness of action is in some degree favoured, as
is supposed by Sir C. Bell; for comparative anatomy shows that something
resembling it may be traced, wherever a similar purpose has to be attained.
Thus, in the Hymenoptera, there is a similar interlacement between the nerves
of the anterior and posterior pairs of wings, which act very powerfully to-
gether; whilst in the Coleoptera, in which the anterior wings are converted
into elytra, and are motionless during flight, the nerves supplying each pair
run their course distinctly. In the Octopus, or Poulp, again, the trunks which
radiate from the cephalic mass to the eight large arms surrounding the head,
are connected by a circular band ; forming a kind of plexus, which seems to
contribute to the very powerful and harmonious movements of the arms of
this Cephalopod.

299. The following statements, in which the language of Mtiller is adopted
21

242 FUNCTIONS OF THE NERVOUS SYSTEM.

with some modification, embody the general principles ascertained by ex-
periment, respecting the transmission of sensory and motor impressions.
Their rationale will be at once understood, from the facts already mentioned
in regard to the isolated characters of each fibril, and the identity of its
endowments through its whole course, i. When the whole trunk of a sensory
nerve is irritated, a sensation is produced, which is referred by the mind to
the parts to which its branches are ultimately distributed ; and if only part of
the trunk be irritated, the sensation will be referred to those parts only, which
are supplied by the fibrils it contains. — This is evidently caused by the pro-
duction of a change in the sensorium, corresponding with that which would
have been transmitted from the peripheral origins of the nerves, had the
impression been made upon them. Such a change only requires the integrity
of the afferent trunk, between the point irritated and the sensorium ; and is
not at all dependent upon the state of the extremity, to which the sensations
are referred : for this may have been paralyzed by the division of the nerve ;
or altogether separated, as in amputation; or the relative position of its parts
may have been changed. — It results from the foregoing, that, when different
parts of the thickness of the same trunk are separately subjected to irritation,
the sensations are successively referred to the several parts supplied by these
divisions. This may be easily shown by compressing the ulnar nerve, in
different directions, where it passes at the inner side of the elbow-joint.

ii. The sensation produced by irritation of a branch of the nerve, is con-
fined to the parts to which that branch is distributed, and does not affect the
branches which come off from the nerve higher up. The rationale of this
law is at once understood: but it should be mentioned that there are certain
conditions, in which the irritation of a single nerve will give rise to sensations
over a great extent of the body. This seems due, however, to a particular
state of the central organs ; and not to any direct communication among the
sensory fibres.

in. The motor influence is propagated only in a centrifugal direction, never
in a retrograde course. It may originate in a spontaneous change in the
central organs : or it may be excited by an impression conveyed to them
through afferent nerves ; but in both cases its law is the same.

iv. When the whole trunk of a motor nerve is irritated, all the muscles
which it supplies are caused to contract: but when only a part of the trunk
or a branch is irritated, the contraction is confined to the muscles, which
receive their nervous fibres from it. This contraction evidently results from
the similarity between the effect of an artificial stimulus applied to the trunk
in its course, and that of the change in the central organs by which the motor
influence is ordinarily propagated. In this instance, as in the other, there is
no lateral communication between the fibrils.

300. Various methods of determining the functions of particular nerves
present themselves to the Physiological inquirer. One source of evidence is
drawn from their anatomical distribution. For example, if a nervous trunk
is found to lose itself entirely in the substance of muscles, it may be inferred
to be chiefly, if not entirely, motor or efferent. In this manner, Willis long
ago determined that the third, fourth, sixth, portio dura of the seventh, and
ninth cranial nerves, are almost entirely subservient to muscular movement;
and the same had been observed of the fibres proceeding from the small root
of the fifth pair, before Sir C. Bell experimentally determined the double
function of that division of the nerve, into which alone it enters. Again,
where a nerve passes through the muscles, with little or no ramification among
them, and proceeds to a cutaneous or mucous surface, on which its branches
are minutely distributed, there is equal reason to believe that it is of a sensory,
or rather of an afferent, character. In this manner Willis came to the con-

DETERMINATION OF FUNCTIONS OF NERVES. 243

elusion, that the fifth pair of cranial nerves differs from those previously
mentioned, in being partly sensory. Further, where a nerve is entirely dis-
tributed upon a surface adapted to receive impressions of a special kind, — as
the Schneiderian membrane, the retina, or the membrane lining the internal
ear, — it may be inferred that it is not capable of transmitting any other kind
of impressions; for experiment has shown, that the special sensory nerves do
not possess common sensibility. The case is different, however, in regard to
the sense of taste, which originates in impressions not far removed from those
of ordinary touch; and it is probable that the same nerves minister to both. —
Anatomical evidence of this kind is valuable also, not only in reference to the
functions of a principal trunk, but even as to those of its several branches,
which, in some instances, differ considerably. Thus, some of the branches of
the Par Vagum are especially motor, and others almost exclusively afferent; and
anatomical examination, carefully prosecuted, not only assigns the reasons for
these functions, when ascertained, but is in itself nearly sufficient to determine
them. Thus the superior laryngeal branch is distributed almost entirely upon
the mucous surface of the larynx, the only muscle it supplies being the erico-
thyroid ; whilst the inferior laryngeal or recurrent is almost exclusively dis-
tributed to the muscles. From this we should infer, that the former is an
afferent, and the latter a motor nerve ; and experimental inquiries (hereafter to
be detailed) fully confirm this view. In like manner it may be shown, that
the Glosso-pharyngeal is chiefly an afferent nerve, since it is distributed to the
surface of the tongue and pharynx, and scarcely at all to the muscles of those
parts ; whilst the pharyngeal branches of the Par Vagum are chiefly if not
entirely, motor. Lower down, however, the branches of the glosso-pharyn-
geal cease, and the ossophageal branches of the par vagum are distributed both
to the mucous surface and to the muscles ; from which it may be inferred that
they are both afferent and motor — a deduction which experiment confirms.

301. We perceive, therefore, that much knowledge of the function of a
nerve may be obtained, from the attentive study of its ultimate distribution:
but it is necessary that this should be very carefully ascertained, before it is
made to serve as the foundation for physiological inferences. As an example
of former errors in this respect, may be mentioned the description of the
Portio Dura of the seventh, at first given by Sir C. Bell: he stated it to be
distributed to the skin as well as to the muscles of the face, and evidently
regarded it as in part an afferent nerve, subservient to respiratory impressions
as well as to motions. In the same manner, from inaccurate observation of
the ultimate distribution of the Superior Laryngeal nerve, it was long re-
garded as that which stimulated to action the constrictors of the glottis. — But
the knowledge obtained by such anatomical examinations alone is of a very
general kind; and requires to be made particular, — to be corrected and modi-
fied by other sources of information. One of these relates to the connection
of the trunks with the central organs. The evidence derived from this
source, however, is seldom of a very definite character; and, in fact, the
functions of particular divisions of the nervous centres have rather been
hitherto judged of, by those of the nerves with which they are connected,
than afforded aid in the determination of the latter. Still, this kind of
examination is not without its use, when there is reason to believe that a
particular tract of fibrous structure has a certain function, and when the office
of a nerve whose roots terminate in it is doubtful. Here again, however,
very minute and accurate examination is necessary, before any sound physio-
logical inferences can be drawn from facts of this description; and many
instances might be adduced to show, that the real connections of nerves and
nervous centres are often very different from their apparent ones.

302. Experimental inquiries into the functions of particular nerves are also

244 FUNCTIONS OF THE NERVOUS SYSTEM.

liable to give fallacious results, unless they are prosecuted with a full know-
ledge of all the precautions necessary to insure success. Some of these will
be here explained. Suppose that, upon irritating the trunk of a nerve, whilst
still in connection with its centre, muscular movements are excited ; it must
not be hence concluded that the nerve is an efferent one, for it may have no
directly motor powers. The next step would be to divide the trunk, and to
irritate each of the cut extremities. If, upon irritating the end separated
from the centre, muscular contractions are produced, it may be safely inferred
that the nerve is, in part at least, of an efferent character. Should no such
result follow, this would be doubtful. If, on the other hand, muscular move-
ment should be produced by irritating the extremity in connexion with the
centre, it will then be evident, that it is occasioned by an impression conveyed
towards the centre by this trunk, and propagated to the muscles by some
other; in other words, to use the language of Dr. M. Hall, this nerve is an
excitor of motion, not a direct motor nerve. The glosso-pharyngeal nerve
has been satisfactorily determined to be chiefly, if not entirely, an efferent
nerve, by experiments of this kind, performed by Dr. J. Reid.

303. It has been from the want of a proper mode of experimenting, that
the functions of the posterior roots of the Spinal nerves have been regarded
as in any degree motor. If they be irritated, without division of either root,
motions are often excited; but if they be divided, and their separated trunks
be then irritated, no motions ensue ; nor are any movements produced by
irritation of the roots in connexion with the spinal cord, if the anterior roots
have been divided. Hence it appears that the motor powers of these fibres
are not direct, but that they convey an impression to the centre, which is
reflected to the muscles through the anterior roots. Another source of fallacy
is to be guarded against, arising from the communication to a nerve, in its
course, of properties it did not possess at its root, by inosculation with an-
other nerve. Of this many instances will hereafter present themselves.

304. The same difficulties do not attend the determination of the sensory
properties of nerves. If, when the trunk of a nerve be pricked or pinched,
the animal exhibits signs of pain, it may be concluded that the nerve is sen-
sible to ordinary impressions at its peripheral extremity. But not unfre-
quently this sensibility is derived by inosculation with another nerve; as is
the case with the portio dura, which is sensory after it has passed through
the parotid gland, having received there a twig from the fifth pair. A similar
inosculation explains the apparent sensibility of the anterior roots of the
spinal nerves. If these be irritated, the animal usually gives signs of uneasi-
ness; but if they be divided, and the cut ends nearest the centre be irritated,
none such are exhibited ; whilst they are still shown, when the farther ends
are irritated, but not if the posterior roots are divided. This seems to indi-
cate that, from the point of junction of the two roots, sensory fibres derived
from the posterior root pass backwards (or towards the centre) in the anterior;
and thus its apparent sensory endowments are entirely dependent upon its
connexion with the posterior column of the spinal cord, through the posterior
roots.

305. The fallacies to which all experiments upon the nerves are subject,
arising from the partial loss of their powers of receiving and conveying im-
pressions, and of exciting the muscles to action, after death, are too obvious
to require particular mention here; yet they are frequently overlooked. Of
a similar description are those arising from severe disturbance of the system,
in consequence of operations; which also have not been enough regarded by
experimenters.

306. All our positive knowledge of the functions of the Nervous System
in general, save that which results from our own consciousness of what passes

DETERMINATION OF FUNCTIONS OF NERVES. 245

within ourselves, and that which we obtain from watching the manifestation's
of disease in Man, is derived from observation of the phenomena exhibited
by animals made the subjects of experiments; and it is desirable to preface
our general summary of the results of these, by some remarks upon the in-
ferences to be drawn from them. — In the first place it must be constantly
borne in mind that, except through the movements consequent upon them,
we have no means of ascertaining, whether or not particular changes in the
Nervous System, whose character we are endeavoring to determine, are
attended with Sensation; since we have no power of judging whether or not
this has been excited, save by the cries and struggles of the animal made the
subject of experiment. Now although such cries and struggles are ordinarily
considered as indications of pain, yet it is not right so to regard them in every
instance; and the only unequivocal evidence is derived from observation of
the corresponding phenomena in the Human subject; since we can there
ascertain, by the direct testimony of the individual affected, what impressions
produce sensation, and what excite movements independently of sensation.
Further, we are not justified in assuming that consciousness is excited by an
irritation, — still less that the intelligence and will are called into exercise by
it, — merely because movements, evidently tending to get rid of this, are per-
formed in respondence to it. We know that the contractions of the heart
and alimentary tube are ordinarily excited by a stimulus, without any sensa-
tion being involved; and these movements, like all that are concerned in the
maintenance of the Organic functions, have an obvious design, when con-
sidered either in their immediate effects, or in their more remote consequences.
The character of adaptiveness, then, in Muscular movements excited by
external stimuli, is no proof that they are performed in obedience to sensa-
tion ; much less, that they have a voluntary character. In no case is this
adaptiveness more remarkable, than in some of those actions, which are not
only performed without any effort of the will, but which the will cannot
imitate. This is the case, for example, with the act of Deglutition; the
muscles concerned in which cannot be thrown into contraction by a voluntary
impulse, being stimulated only by impressions conveyed from the mucous
surface of the fauces to the medulla oblongata, and thence reflected along the
the motor nerves. No one can swallow without producing an impression of
some kind upon this surface, to which the muscular movements will imme-
diately respond. Now it is impossible to conceive any movements more
perfectly adapted to a given purpose than those of the parts in question ; and
yet they are independent, not only of Volition, but of Sensation, — being still
performed in cases in which consciousness is completely suspended, or
entirely absent.

307. There is much difficulty, then, in ascertaining the really elementary
functions of the Nervous System, by experiments upon animals ; and it is
only when their results are corrected and explained by pathological observa-
tion on Man, — the sole case in which we can obtain satisfactory evidence of
the presence or absence of sensation, — that they have much value to the phy-
siological inquirer. From these combined sources, however, a vast amount
of knowledge of the functions of the nervous system has recently been gained;
and the general purposes to which it is subservient, may be advantageously
stated in a systematic form, before we enter upon any detailed examination of
them.

i. The Nervous System receives impressions, which, being conveyed by
its afferent fibres to the Sensorium, are there communicated to the conscious
Mind, and thus give origin to Sensations. The Nervous structure is further
subservient, in some way, to the acts of that mind ; as the result of which, a
motor impulse is transmitted along the efferent trunks, to particular Muscles,

246 FUNCTIONS OF THE NERVOUS SYSTEM.

exciting them to contraction. There is reason to believe, however, that this
motor impulse may proceed from at least two distinct sources; being either
the direct consequence of the sensation, acting involuntarily as an emotional
or instinctive impulse ; or resulting from a more or less complicated series
of intellectual operations, which terminate in an act of volition or will. — To
these functions, taken collectively, the Encephalon, and the nerves connected
with it, are alone subservient ; and we may probably assign the group of sim-
ple consensual or involuntary actions to the ganglia which receive the nerv-
ous trunks from the organs of sense, and which make up nearly the whole
of the Cephalic masses of ganglia in the Invertebrata ; whilst the Cerebral
hemispheres of Vertebrata are the instruments of the intellectual operations
and of the mandates of the will.

ii. Certain parts of the Nervous System receive impressions which are
propagated along afferent fibres, that terminate in ganglionic centres distinct
from the sensorium; and in these a reflex motor impulse is excited, which,
being conveyed along the efferent trunks proceeding from them, excites mus-
cular contraction, without any necessary intervention of sensation or volition.
Of this function (called by Dr. Hall, to whom the discovery of it is in a great
part due, the reflex function), we shall find that the portion of the Spinal
Cord of Vertebrata, which is not continuous with the fibrous structure of the
brain, together with the portion of the nervous trunks which are connected
with it alone, is the instrument : whilst, in the Invertebrata, the same office
is performed by ganglia still more obviously disconnected from the cephalic
mass.

in. Another division of the Nervous System appears to have for its object,
to combine and harmonize the muscular movements immediately connected
with the maintenance of Organic life ; and to bring these into relation with
certain conditions of the mind. There is reason to believe (though this is
less certain) that it also influences, and brings into connection with each other,
the processes of Nutrition. Secretion, &c. ; though these, like the muscular
movements just mentioned, are essentially independent of it. This portion
of the nervous apparatus is commonly known under the name of the Sympa-
thetic system.

308. Now, in reference to the first of these classes of operations, it is well
to explain that though the Physiologist speaks of the intellectual powers,
moral feelings, &c., as functions of the Nervous System, they are not so in
the sense in which the term is employed in regard to other operations of the
bodily frame. In general, by the function of an organ, we understand some
change which may be made evident to the senses ; as well in our own sys-
tem, as in the body of another. Sensation, Thought, Emotion, and Volition,
however, are changes imperceptible to our senses, by any means of observa-
tion we at present possess. We are cognizant of them in ourselves, without
the intervention of those processes by which we observe material changes
external to our minds ; but we judge of them in others, only by inferences
founded on the actions to which they give rise, when compared with our own.
When we speak of sensation, thought, emotion or volition, therefore, as func-
tions of the Nervous System, we mean only that this system furnishes the
conditions under which they take place in the living body ; and we leave the
question entirely open, whether the "^vxn has or has not an existence independ-
ent of that of the material organism, by which it operates in Man, as he is
at present constituted.

309. In regard to the second class of actions, it may be remarked, that they
are nearly all connected, more or less closely, with the maintenance of the
Organic junctions, or with the protection of the body from danger. Thus
the movements of the pharynx supply to the stomach the alimentary materi-

COMPARATIVE ANATOMY AND PHYSIOLOGY. RADIATA. 247

als, which it has to prepare for the nutrition of the body ; and those of the
muscles of the thorax, &c., maintain that constant interchange of air in the
lungs, which is necessary for the aeration of the blood : whilst those, by
which a limb is involuntarily retracted from any cause of pain or irritation, are
obviously adapted to the latter of these two ends.

2. Comparative Anatomy and Physiology of the Nervous System in

Invertebrated Animals.

310. Although the structure and distribution of the Nervous System in the
different classes of Animals have been, until recently, but little appealed to
in the determination of its functions, they are capable of supplying evidence
regarding some of these, not less important in its character than that which
Comparative Anatomy affords to other departments of Physiology. Some of
the principal of these contributions will now be pointed out.

311. In the lowest tribes of the RADIATED division of the animal kingdom,
no Nervous System has yet been discovered. These have, therefore, been
separated by some naturalists into a new primary group, to which the desig-
nation of Merita has been given, on account of the (supposed) "indistinct,
diffused, or molecular character of their nervous system." This idea of a
"diffused nervous system" seems to be regarded by many — Physiologists as
well as Naturalists — as the necessary alternative, resulting from the want of
any definite indications of its presence. It may be said, however, to be based
on very erroneous notions, as to the true offices of the nervous apparatus.
Its influence is not required to endow the tissues with contractility ; a pro-
perty possessed in a high degree by the structures of many Plants, to which
these beings present a much greater general resemblance, than they bear to
the higher Animals; and, even in the latter (as will be shown hereafter), this
property is independent of nervous agency, although generally called into
exercise by it. That a nervous system is not required by them for the per-
formance of the functions of Nutrition and Reproduction, otherwise than to
supply, by its locomotive actions, the conditions of those functions, would
also appear from its absence in Plants. It is on the sensible movements of
these beings, that our belief in their possession of a nervous system must be
founded, when we cannot render it cognizable by our senses. But we must
be careful not to draw hasty inferences from such phenomena. Sensible move-
ments are, as we have seen, performed by the Dionaea and Sensitive plant, in
respondence to external stimuli acting on distant organs ; and they are also
exhibited, in a very remarkable manner, by the reproductive particles of many
of the simpler Plants, as well as by numerous beings now generally referred
to the Vegetable kingdom. It is to be remarked, however, that such motions
are of a very simple description. In objects of the latter class, they are of
a rhythmical character, and do not seem to be in direct dependence on any
external influences. And even where they are performed solely in respond-
ence to external stimuli, there is usually such a uniformity in their character,
as indicates that the means by which the influence is propagated are of a very
mechanical nature. On the other hand, those movements of Polypes, which
are performed in respondence to external stimuli, are of a much more varied
character; and there are others, which seem to indicate a certain degree of
voluntary power, and therefore to display a consciousness of impressions made
upon the body. These phenomena, then, would lead us to suspect the ex-
istence of a Nervous System in the beings which exhibit them ; not, however,
in a "diffused" condition, but in the form of connected filaments. For, what
consentaneousness of action can be looked for in a being whose nervous
matter is incorporated in the state of isolated globules with its tissues? How

248 FUNCTIONS OF THE NERVOUS SYSTEM.

should an impression made on one part be propagated by these to a distance ?
And how can that consciousness and will, which are one in each individual,
exist in so many unconnected particles ? If, then, we allow any sensibility,
consciousness, and voluntary power, to the beings of this group of Acrita —
to deny which would be in effect to exclude ihem from the Animal Kingdom
— we must regard these faculties as associated with nervous filaments, of such
delicacy as to elude our means of research. When the general softness of
the textures, and the laxity of structure that characterizes the nervous fibres,
in the lowest animals in which they can be traced, are kept in view, little
difficulty need be felt in accounting for their apparent absence. The case is
very different from that of Vegetable structure ; the greater consistency of
which enables us to place much more reliance upon the negative evidence
afforded by anatomical research.

312. The correctness of this view (which has been here dwelt on the longer,
because it involves a fundamental question in Nervous Physiology), is borne
out by the fact, that, in those members of the group whose size and consist-
ency allow their structures to be sufficiently examined, a definite nervous
system has been detected ; in the position which it might, « priori, be ex-
pected to occupy, according to the type of the individual. Thus, in the large
fleshy isolated polype, commonly known as the Sea-Anemone (Jlctinia), a
nervous ring has been discovered, surrounding the mouth as in other Radiata,
and sending off branches to the tentacula, with a minute ganglionic enlarge-
ment at the base of each. In the higher Radiata, as the Star-Fish, the nerv-
ous system has the same regular form as that which prevails through the
other organs. The mouth is surrounded by a filamentous ring, which presents
a regular series of ganglionic enlargements, one of them corresponding with
each segment of the body. From every one of these, a branch is transmitted
to the corresponding ray ; and two smaller ones proceed to the viscera included
in the central disk.

313. The POLYPIFERA being the lowest of the Radiated classes, in which
there is a regularly-organized digestive apparatus, and which perform move-
ments of a character ascribable only to a Nervous System, it will be desir-
able to inquire a little more particularly into the phenomena they exhibit, and
the degree in which these necessarily involve the possession of the higher
mental endowments. In this inquiry we shall refer principally to the little
Hydra, or fresh-water Polype; the habits of which are better known than
those of any other species. Although no nervous filaments have been de-
tected in this, we have a right to infer their presence for the reasons already
given; and they probably form a ring around the mouth, as in the Actinia,
sending filaments to the tentacula. This interesting little being may be re-
garded as essentially a stomach; and the orifice of this is provided with
tentacula, which contract when irritated by the touch of any adjacent body,
and endeavour to draw it towards the entrance Now, the action in the Hu-
man body, to which this is most allied, is evidently that of the muscles of
Deglutition ; which lay hold, as it were, of the food that has been conveyed
to the fauces, and carry it into the stomach. These muscles are called into
action, not by an effort of the will, but by the contact of the food with the
lining membrane of the pharynx. This impression is propagated by the
glosso-pharyngeal nerve to the medulla oblongata. where a respondent motor
impulse is excited, which is transmitted through the pharyngeal branches of
the par vagum to the muscles of deglutition, and causes their contraction.
This phenomenon will be more fully examined hereafter ; it is here adduced
simply as an instance of the important class of re/lex movements, which are
independent of the brain (though, to a certain extent, controlled by it), which
are altogether involuntary, and which do not necessarily involve the produc-

MOVEMENTS OF POLYPES. 249

tion of sensation. There would appear to be little difference in the character
of this movement, between the simple Hydra and the most perfect Vertebrated
animal. In the latter, however, another set of muscles are superadded to
these, for the purpose of preparing the aliment by mastication for the opera-
tion of the stomach, and of bringing it within reach of the pharyngeal con-
striction.— But, it has been urged, the inactivity of the tentacula when the
Hydra is gorged with food, proves that they are excited to action by the will
of the animal. This inference, however, may be easily disproved. The
muscles of deglutition in Man are not called into action with nearly the same
readiness and energy, when the stomach is distended, as when it is empty; a
fact of which any one may convince himself, by observing the relative facility
of swallowing, at the commencement and the termination of a full meal. No
one will assert that this variation is an effect of the will; indeed, it is often
opposed to it; being one of those beautiful adaptations, by which the welfare
of the economy is provided for, but which the indulgence of the sensual appe-
tites opposes. Most of the movements of this animal, and of others of the
class, appear to be equally the result of external stimuli, with that already
described; and it is only in a few instances, principally those of absolute
locomotion or change of place, that any evidence of voluntary action can be
discerned. It may be occasionally remarked, however, that one or more of
the tentacula are retracted or extended, without the slightest appreciable
change in any of those external circumstances, which seem ordinarily to
affect the motions of the animal ; and this action we can scarcely regard as
otherwise than voluntary.

314. Thus in the Nervous System of Radiated Animals, we have an in-
stance of that community of function, which is so remarkable in the organism
of the lower tribes, when contrasted with the separation, which is perceptible
in those at the opposite extremity of the scale. The visceral nerves of the
Asterias are not isolated at their central terminations from those which are
connected with the sensorial and locomotive functions : nor are the nerves
which minister to the instinctive actions separable from those which convey
the influence of the will. Every segment of the body appears equal in its
character and endowments to the remainder; each has a ganglion appropriated
to it; and, as the ganglia, like the segments, are all alike, neither of them can
be regarded as having any presiding character.

315. From the Radiated we now pass to the MOLLUSCOUS classes; the
general character of which, as a natural group, is the remarkable predomi-
nance of the Nutritive system over that of Animal life. There is not in the
Mollusca, as in the Radiata, any repetition of parts around a common centre;
and we do not therefore meet in them with a number of ganglia, nearly or
altogether alike in endowments. In some of the higher species, there is a
conformity between the two sides of the body, or a lateral symmetry; which
involves a subdivision of some of the ganglia, that are single in the inferior
tribes, into two masses, which always remain in connexion with each other.
With this exception, it may be observed, that all the principal ganglia, to the
number of four or five, which we meet with in the higher Mollusca, appear
to have distinct functions; as may be determined by tracing the distribution
of their nerves. Thus we find a pair of cephalic ganglia, situated above the
esophagus, connected with the organs of special sensation, and sending motor
nerves (as we shall see reason to believe) to all parts of the body. This is
obviously analogous to the brain of Vertebrata. Below the oesophagus there
is generally a small ganglion, connected with the apparatus of deglutition,
which may be called the stomato- gastric ganglion. In connexion with the
gills we have always one ganglion, sometimes a pair, which may be termed
the branchial ganglion. Another is found at the base of the foot, which may

250 FUNCTIONS OF THE NERVOUS SYSTEM.

be called the pedal ganglion. And there is sometimes another, which espe-
cially supplies the mantle with nerves ; and this may be called the palleal
ganglion. — The distribution of their nerves to the different organs, would
alone indicate the respective functions of these ganglia; but these are placed
beyond doubt, by that very great variety in the disposition of these organs,
which is characteristic of the Mollusca. The development of the sensory
organs, the situation of the gills, the structure and position of the foot, the
conformation and uses of the mantle, are well known to differ in the most
obvious manner, in genera which are closely allied to each other. Hence
the anatomist is enabled, by the discovery of corresponding changes in the
nervous system, to satisfy himself of the particular functions of its different
centres.*

316. It is only in the higher tribes, however, that this separation of function
is evident ; for in the lowest, we find the Nervous System in its least deve-
loped form. This is the case in the class TUNICATA; composed of animals,
in which the whole body is enclosed in a tunic or bag, having two orifices,
through one of which the water is drawn in by ciliary action, whilst through
the other it is expelled. This bag incloses a large chamber, the lining of
which is devoted to the respiratory function ; and at the bottom of it lies the
mass of the viscera, on which is the entrance to the stomach. A part of the
water which is taken into the respiratory chamber flows into this, and passes
through the intestinal canal ; being discharged along with that, which has
only served the purpose of aerating the blood. These animals have no power
of motion, but such as is effected by the general contraction of the respiratory
sac; this is effected by a single ganglion placed between its orifices, which is
therefore chiefly a branchial ganglion, and is the only nervous centre they
possess. The trunks connected with it send branches over the muscular
envelope of the respiratory sac, and to the sphincters which surround its
orifices ; whilst other branches proceed to the membrane lining the orifices,
and especially to the tentacula, or lips, which are situated at the oral entrance.
The maintenance of the regular current is effected, as just stated, by ciliary
action; but when any substance is being drawn in, the entrance of which
would be injurious, its contact with the tentacula excites a general contraction
of the muscular envelope, and causes a jet of water to issue from one or both
orifices, which carries the offending body to a distance. And, in the same
manner, if the exterior of the body be touched, the mantle suddenly and vio-
lently contracts, and expels the contents of the sac. — These are the chief, if
not the only actions, which the Nervous System of these animals is destined
to perform ; and they are evidently of a reflex character ; bearing a close
correspondence with the acts of coughing and sneezing in Man, which are in
like manner destined to expel injurious substances from the respiratory pas-
sages. By the contact of such substances with the tentacula that guard the
oral orifice, or with the lining of the respiratory sac, or by irritation of the
external surface of the body, an impression is produced on the afferent fibres ;
which, being conveyed to the central ganglion, excites there a reflex motor
impulse ; and the propagation of this impulse along the afferent fibres, to the
muscular fibres of the contractile sac, and to the sphincters, produces the
movements in question.

317. la the CONCHIFERA, or Mollusks inhabiting bivalve shells, there are
invariably two ganglia, having different functions. The larger of these (Fig.
124, c), corresponding to the single ganglion of the Tunicata, is situated towards
the posterior end of the body (that is, the end most distant from the mouth),

* See Mr. Garner on the Nervous System of the Mollusca, in the Linnaean Transactions,
Vol. xvn.

NERVOUS SYSTEM OF THE LOWER MOLLUSCA.

251

in the neighbourhood of the posterior adductor muscle ; and its branches are

distributed to that muscle, to the mantle,
through which the water is introduced
and carried off. But we find another
ganglion, or rather pair of ganglia, a,
a, situated near the front of the body,
either upon the o?sophagus, or at its
sides ; these ganglia are connected
with the very sensitive tentacula
which guard the mouth ; and they
may be regarded as presenting the
first approach, both in position and
functions, to the brain of higher ani-
mals. In the Oyster, and others of
the lower Conchifera which have no
foot, — which is a muscular tongue-
like organ, — we find an additional
ganglion (b) connected with it. — This
is the case in the Solen, or animal of
the Razor-shell ; whose foot is a very
powerful boring instrument, enabling
it to penetrate deeply into the sand.
Here, then, we have three distinct
kinds of ganglionic centres ; every one
of which may be doubled, or repeated
on the two sides of the body. First,
the cephalic ganglia, a, a, which are
probably the sole instruments of sen-
sation and of consensual movements;
as well as of whatever voluntary
power the animal may possess : these
are almost invariably double, being
connected together by a transverse
band, which arches over the oesopha-
gus. Second, the pedal ganglion, b,
which is usually single, in conformity
with the single character of the organ
it supplies ; but in one very rare Bi-
valve Mollusk, the foot is double, and
the pedal ganglion is double also. —
Third, the respiratory ganglion, c,
which frequently presents a form that
indicates a partial division into two
halves, corresponding with the repe-
tition of the organs it supplies, on the
two sides of the body. Besides these
principal centres, we meet with nu-
merous smaller ones upon the nervous

to the gills, and to the siphons

Fiz. 124.

Nervous system of Solen; a, a. cephalic ganglia,
connected by a transverse band passing over the
oesophagus ; b, pedal ganglion, the branches of
which are distributed to the powerful muscular
foot; c, branchial ganglion, the branches of which
proceed to the gills g, the siphons t, (', and other
parts ; h, anus : e, trunks connecting cephalic and
branchial ganglia; f.f.f.f, minute ganglia on the
branches distributed to the mantle.

cords (f,f, and g, g], which proceed from them to the different parts of the
general muscular envelope or mantle.

318. Now it will be observed, that the two cephalic ganglia a, a, are con-
nected with the pedal ganglion, 6, by means of a pair of trunks, e, proceeding
from the former to the latter ; and that they are, in like manner, separately
connected with the respiratory or branchial ganglion c. It is found, upon

252 FUNCTIONS OF THE NERVOUS SYSTEM.

careful dissection, that these cords do not serve merely to bring the ganglia
into relation : but that a part of them pass through the ganglion into the trunks
proceeding from it. Thus, of the nerves which supply the large fleshy foot,
and which appear to proceed from the pedal ganglion, 6, a part are undoubt-
edly connected with that ganglion alone, coming into relation with its vesicu-
lar substance ; but a part also pass on to the cephalic ganglia, by the connecting
trunks, — so that these, rather than the pedal ganglion, constitute their centre.
The same may be said of the nerves proceeding from the branchial ganglion:
a portion of them having their centre in the vesicular matter of that ganglion;
whilst another portion has no relation to it whatever (beyond that of prox-
imity), but passes through or over it, to become connected with the cephalic
ganglia. There is good reason to believe, that the pedal and branchial gan-
glia minister to the purely reflex actions of the organs they respectively sup-
ply; and that they would serve this purpose as well, if altogether cut off from
connection with the cephalic ganglia : whilst the latter, being the instruments
of the actions which are called forth by sensation (whether these be of a con-
sensual or of a voluntary nature), exert a general control and direction over
the movements of the animal.

319. The animals of the class GASTEROPODA, whether furnished with uni-
valve shells, or entirely destitute of such protection, are, for the most part,
much more highly organized than the preceding; possessing not merely
greater locomotive power, but organs of special sense, which are situated in
the neighbourhood of the mouth, upon a projecting part of the body, which is
thus constituted a head. Their nervous system consists of at least three dis-
tinct centres ; the relative position of which varies with that of the organs
supplied by them. The anterior or cephalic ganglia are larger in proportion
to the rest, than they are in the Conchifera ; and they exhibit a tendency to
gain a position anterior to the oesophagus, and to approximate towards each
other, so as to meet and form a single ganglionic mass on the median line.
The branchial ganglion is constantly to be met with ; but its position is ex-
tremely variable. This centre, however, always bears a close relation with
the gills, both in situation and in degree of development; and even where
conjoined, as it frequently is, with the pedal ganglion, it may be distinguished
from it by the distribution of its nerves, as well as by its separate connection
with the cephalic ganglia, which is always noticed in such cases. This may
be observed in the Patella (limpet) and Limax (slug). Sometimes the func-
tions of this ganglion are subdivided between two ; of which one is still ap-
propriated to the branchiae ; whilst the other is connected with the general
surface of the mantle, and with the respiratory passages which are prolonga-
tions of it, and hence may be called the pallcal ganglion. The position of
the pedal ganglion (which is generally double in the Gasteropoda, though the
foot is single), also varies, but in a less degree, since it is generally in the
neighbourhood of the head. — Besides these nervous centres, we find, in many
of the Gasteropoda, a separate system connected with a very important set
of organs, the gustatory and manducatory, which are but slightly shadowed
out among the Conchifera. In these higher tribes, the oesophagus is dilated
at its commencement into a muscular cavity (Fig. 3, a]; containing a curious
rasp-like tongue, often supported upon cartilages, which serves to reduce the
food; and sometimes furnished with horny maxilla?. The nerves which sup-
ply these do not proceed directly from the cephalic ganglia, but from a dis-
tinct centre; and their ramifications proceed along the oesophagus and sto-
mach, and are occasionally connected with the other nerves by inosculating
filaments. This set of ganglia and nerves, which is even more important
from its relative development in some other classes, and into the analogies of

NERVOUS SYSTEM OF HIGHER MOLLUSCA. 253

which in the nervous system of Vertebrata we shall hereafter inquire, may be
called, from its distribution, the stomato- gastric system.

320. The ganglia first described may be regarded as corresponding with
those parts of the nervous centres in the Vertebrata, the distribution of whose
nerves is analogous. Thus the branchial ganglion obviously corresponds
with that portion of the Medulla Oblongata which is the centre of their respi-
ratory actions ; and the pedal ganglion is analogous to that division of the
Spinal Cord from which the nerves of the anterior or posterior extremities
pass off. It is well known that such portions of the spinal cord may be com-
pletely isolated, without destroying the functions to which they minister.
Thus, the brain and lower part of the spinal cord may be removed, — that
portion only of the cerebro-spinal axis being left, which is connected with the
principal respiratory nerves, in fact the respiratory ganglion, — and yet the
animal may continue to exist for some time. It is then reduced to a condi-
tion similar to that of the Tunicata; whose single ganglion, though combining
in some degree the functions of those which exist separately in the higher
tribes, has evidently the regulation of the respiratory movements for its chief
object. In the same manner, the integrity of the segment of the cord, with
which the nerves of the extremities are connected, will enable them to execute
those movements of a reflex character, which depend upon its power as their
centre; even though it be isolated from every other part of the nervous ap-
paratus.— The cephalic ganglia must be regarded as chiefly analogous to those
portions of the Encephalon of Vertebrata, which are immediately connected
with the nerves of sense. We find nerves of special sensation proceeding
from them, certainly to eyes and an auditory apparatus, perhaps als%> to
olfactive organs ; as well as others of common sensation, supplying the ten-
tacula and mouth. Hence we must admit, that they perform the functions of
the optic ganglia of Vertebrata, and perhaps also of the olfactory lobes ; as
well as of the portion of the medulla oblongata, in which the sensory portion
of the fifth pair terminates. Moreover, they certainly give origin also to
motor nerves ; and must thus perform the functions of the Medulla Oblongata,
from which the corresponding nerves arise in Vertebrata ; as well as, perhaps,
of the Cerebellum. — It is obvious that the portion of the Nervous system of
the Gasteropod Mollusca, into the analogies of which we have thus inquired,
cannot in the least be compared as a whole with the Sympathetic system of
the Vertebrata, which it was formerly imagined to resemble. The distribu-
tion of some of its nerves to the viscera, however, may indicate that it partly
performs the functions of that system; with which it is structurally inter-
mixed, even in Vertebrata. But the stomato-gastric system may, perhaps,
with more probability, be considered as executing its offices. Into the pecu-
liar character of that system we shall be more competent to inquire when we
have traced it through other classes of Invertebrata.

321. Having thus separately considered the nervous centres of the Gaste-
ropoda, and determined their special functions by their structural relations, we
shall inquire into the mode in which these functions are combined, so as to
enable them to act in harmony. This is an inquiry of much interest, in re-
ference to the determination of the offices of the different parts of the nervous
centres in Articulated and Vertebrated animals. If we examine the mode in
which the different ganglia are united by connecting trunks, we are led to per-
ceive the important fact, that, while they have little or no communication with
each other, they are all directly connected with the cephalic ganglia ; which
seem thus to harmonize and control their individual actions. Frequently a
communication with one another appears to exist, where there is really none.
Thus, in the Jlplysia,z cord passes from the branchial ganglion (Fig. 125, D),

22

254

FUNCTIONS OF THE NERVOUS SYSTEM.

which is situated in the posterior part of the body, to the pedal ganglion of
each side, (c, c). Where such is the case, the trunk is not united with that

Fig. 125.

proceeding from the ganglion through
which it passes; but the two remain
distinct, though running in the same
direction. Moreover, the double func-
tion of a ganglion may be sometimes
recognized, by its being connected
with the cephalic mass by a double
trunk. Thus, in the Aplysia, that
which has been termed the pedal gan-
glion is really made up of a pedal and
palleal ganglion, as is proved by the
distribution of its branches; and in
conformity with this double function,
we find it communicating with the
cephalic mass by two cords, besides
the one which has been just mentioned
as passing through it, and which ap-
pears as a third. In the Bullsea,
whose nervous system is disposed on
the same general plan, the pedal and
palleal ganglia are separately connected
with the cephalic ; the cord from the
branchial ganglion passing through the
palleal.

322. Further, a careful examination
of these ganglia, and of their connecting
cords, discloses this important fact,
which is peculiarly evident in the case
of the pedal ganglia — that the cords
proceeding from the cephalic mass do
not lose themselves in the grey matter
of these ganglia; but divide themselves
into filaments, which mix with those
proceeding from them, to form the
nervous trunks which they distribute.
We can scarcely, then, fail to infer,
that the pedal ganglion, with the nerv-
ous fibrils proceeding from itself, is the
source of the reflex actions of this or-
gan; whilst the filaments which are con-
tinuous with those of the connecting
trunk, and which are thus connected
with the nucleus of the cephalic gang-
lia, are the channels of sensory impres-
sions, and of the motor impulses prompted by them. — This is well illustrated
in the curious disposition of parts, which we find in the arms of the Cuttle-fish.
These are provided, it is well known, with a series of suckers, which are to
the animal important instruments of locomotion and prehension. It has been
observed by Dr. Sharpey, that the nerves which supply these arms are fur-
nished with ganglionic enlargements, of which one corresponds with each
sucker; and that each trunk consists of two tracts, in one of which the gan-
glionic enlargements exist; whilst the other passes continuously over these,
but sends off nervous filaments, which help to form the branches going to the

Nervous system of Aplysia. A. pharyngeal gan-
glion ; B, cephalic ganglion. The cephalic is con-
nected, by three distinct cords on each side, with
the lateral masses, c c, which combine the functions
of pedal and palleal ganglia; these are united with
each other by two transverse bands, between which
the aorta passes. From the lateral ganglia, a con-
necting cord passes backwards on each side to the
branchial ganglion, D ; this cord is continuous with
one of the three proceeding from the cephalic gan-
glion.

NERVOUS SYSTEM OF MOLLUSCA AND ARTICULATA. 255

several suckers. When the animal endeavours to embrace any object firmly
with its arm, it brings all the suckers simultaneously to bear upon it. There
can be little doubt that this action is occasioned by a motor impulse, propa-
gated from the cephalic masses by the non-ganglionic portion of the cord,
which supplies all the suckers alike. On the other hand, any individual
sucker may be made to attach itself, by placing a substance in contact with
it alone ; this action is independent of the cephalic ganglia, as is evident from
the fact, that it will take place when the arm is severed from the body, or even
in a small piece of the arm, if recently separated; and it can scarcely be doubted,
that it is due to the reflection of the impression made upon the sucker, through
the small ganglion in its own neighbourhood, where it excites a motor impulse.
The operation of these independent centres appears, in the entire living animal,
to be controlled, directed, and combined, by the cephalic ganglia ; through the
medium of the fibrous band which passes over them, and which mixes its
branches with theirs. A very similar arrangement will be presently shown
to exist in the double nervous column of the Articulata.

323. Upon reviewing all the anatomical facts hitherto stated, it will be per-
ceived that ganglionic masses, characterized by nuclei of grey matter, or of
something equivalent to it, seem to exist, wherever it is desirable that impres-
sions made upon the afferent nerves should excite motions ; and that, as we
rise in the scale, there is an increase in the number of centres possessing a
diversity of functions. We have seen that sometimes these centres are, for
the sake of convenient disposition, united into one mass; whilst on the other
hand, when the organs are multiplied, they also are repeated to a like extent ;
especially when it is desirable that they should be able to act independently
of one another, as in the case of the suckers of the Cuttle-fish. It may further
be remarked, that wherever the presence of special sensory organs, confined
to one part of the body, gives to that part a predominance over the remainder
(the entrance to the alimentary canal being always in this neighbourhood), we
find the ganglia with which they are connected possessing a special relation
with all the rest, which these do not possess with each other. It is obvious
that, where visual organs are developed, the impressions made upon these will
determine the movements of the animal, more than those of any other kind ;
and it would seem to be chiefly owing to the information they communicate,
that the cephalic ganglion has such an evident presiding influence over the rest,
even when smaller than any of them. This is, however, more the case in
animals whose movements are rapid, and in which, therefore, the perception
of distant objects is more important — as in the Insect tribes. Except in the
Cephalopoda, the subservience of the nervous system to the nutritive functions
of the Mollusca is so great that it might almost be regarded as an appendage to
the digestive organs, destined for the selection and prehension of aliment.
But in the more active members of that class it derives a more elevated cha-
racter, from the development of organs of special sensation and of active loco-
motion.

324. The animals composing the group ARTICULATA all present, in a more
or less evident degree, a division into segments, which have an obvious tend-
ency to resemble one another, as in the Radiata ; these are disposed, however,
not in a circle, as in the Radiata, but in a continuous line. In those in which
these segments differ but little (as in the Centipede, or the Caterpillar of the
Insect), the nervous system is a repetition of similar parts; the most anterior
of the ganglia, however, has an evident predominating influence over the
rest, for the reason just specified ; and this influence will be found, by com-
parison in other classes, to diminish with the loss, and to increase with the de-
velopment, of the faculties of special sensation, which have their seat there.
The locomotive powers are just as predominant in the Articulated series, as

256

FUNCTIONS OF THE NERVOUS SYSTEM.

Fig. 126.

Nervous System of Larva of Sphinx ligus-
tri, after Newport; A, cephalic ganglia; 1-11,
ganglia of tlie trunk, disposed at nearly equal
distances ; the last is formed by the consoli-
dation of the llth and lt>th.

are the nutritive functions among the Mol-
lusca. Accordingly, we rind the deve-
lopment of the Nervous system to bear a
special reference to them ; and the sensori-
motor divisions of it can be more distinctly
separated, than in the Mollusca, from the
portion which ministers to the organic func-
tions.

325. The general arrangement of the
Nervous System differs so little, except as
to the degree of concentration of the ganglia,
in the different classes of this sub-king-
dom, that it is of little consequence what
example we select. It will be convenient
to take for illustration that of the Larva of
the Sphinx ligustri, or Privet Hawk-Moth,
which has been minutely described by Mr.
Newport. Here we observe a chain of
ganglia running from one extremity of the
body to the other, along the ventral sur-
face, and in the median line. These gan-
glia are connected by trunks, which, on
close examination, are seen to consist of
two cords closely united. The cephalic
ganglion is bilobed ; evidently consisting
of two masses, which are united on the
median line. These receive the nerves of the
eyes and antennae ; but they are still of small
size, in accordance with the low develop-
ment of the sensory organs. The ganglia
of the longitudinal cord are nearly equal
from one extremity of the body to the
other. Each sends off nerves to its re-
spective segments ; and the branches pro-
ceeding from the different ganglia have
little communication with each other. The
highest of them, situated just beneath the
oesophagus, is connected with the cephalic
masses by two cords ; between which that
canal passes, encircled, as it were, in a ring.

326. The most detailed account of the
conformation of the Nervous Centres in
the Articulata, is that recently given by
Mr. Newport, in regard to the lulus, and
other animals of the class MYRIAPODA.*
Their general arrangement corresponds
with that which has been just described
in the larva; of the Sphinx ligustri ; but
the number of ganglia is much greater. In
each lateral half of the cord, two distinct
tracts or layers of librcs can be detected :
of these, one — known as the fibrous tract
— is continuous with the cephalic ganglia,

* Philosophical Transactions, 1843.

NERVOUS SYSTEM OF ARTICULATA.

257

Portion of the gang] ionic tract of Po-
lydesnuis maculatus ; b, inter-ganglionic
cord ; c, anterior nerves ; d, posterior
nerves; f, k, fibres of reinforcement;
g. h, commissural fibres ; i, longitudinal
fibres, softened and enlarged, as they
pass through ganglionic matter.

and contains no vesicular matter ; whilst the other known as the ganglionic
tract — has vesicular matter deposited at intervals amongst its fibres, some of
which are continuous with the brain, whilst others do not reach it. (Fig. 128,
A.) Every nerve that is given off from this ventral column, is connected with
both tracts ; and thus it has two sets of roots, one proceeding to the brain, the
other entering the ganglion near which it arises. Of this last division, a part
crosses to the opposite side, forming the
commissural fibres which unite together the
lateral halves of the cord ; whilst another
bundle of fibres runs along the side of the
ganglionic tract, for a greater or less propor-
tion of its length, and then emerges again
forming part of another nervous trunk. In
Fig. 127 is seen Mr. N.'s representation of
one of the ventral ganglia, and part of the
cord, of Polydesmus maculatus; showing
the longitudinal and commissural fibres, to-
gether with those to which he has given the
name of fibres of reinforcement. These
lateral fibres, which do not pass on to the
brain, but issue again from the ventral cord
at a point a little distant from their entrance,
seem to be more numerous in the hinder part
of the body of the Centipede tribe, than in
its front portion : and thus it is, that the whole
size of the cord remains nearly the same
along its entire length ; whilst that of the por-
tion which passes backwards from the brain, must be continually diminishing,
as it gives off fibres to the nerves.

327. After what has been said of the offices which the ganglia perform in
the Mollusca, and of the relation which they bear to the cephalic mass, we
shall have little difficulty in understanding the character of the nervous appa-
ratus in the Articulata, if our minds be unoccupied by any preconceived
notion. When we examine into the actions of the ventral cord, we perceive
that those of all its ganglia are similar to each other ; being related only to
the movements of their respective segments, and of the members which belong
to them. In fact, these ganglia may be regarded as so many repetitions of
the pedal or locomotive ganglion of the Mollusca. It is easily proved, that
the movements of each pair of feet may be produced by that ganglion alone,
with which it is connected ; since a single segment, isolated from the rest,
will continue to perform these movements for some time, under favourable
circumstances. But it is evident that they must be placed, in the living ani-
mal, under some general control ; by which the consentaneousness of action,
that is essential to regular locomotion, may be produced. This is proved by
the experiments to be presently quoted. We can scarcely account for the
exercise of such a general control, otherwise than by attributing it to the
fibrous portion of the cord,* which directly connects each of the nervous

* It is believed by Mr. Newport, that the fibrous portion of the ganglionic trad, which lies
nearest the surface of the body, may be the channel by which sensory impressions are con-
veyed to the brain; whilst the fibrous tract itself may convey downwards the motor impulses
which originate in the cephalic ganglia. The chief reason for this supposition, is the corre-
spondence in position, — relatively to each other, and to the rest of the body, — between the
fibrous and ganglionic columns in Articulata, and the portions of the Spinal Cord of Verte-
tebrata, from which the anterior or motor roots, and the posterior or sensory, respectively
arise. — But the fibres which are peculiar to the ganglionic tract, obviously form a distinct
system.

22*

258 FUNCTIONS OF THE NERVOUS SYSTEM.

trunks with the cephalic ganglia, as in the Mollusca ; and this must, there-
fore, conduct to the sensorium (whose seat is probably in the latter) the im-
pressions which there produce sensations, and must convey downwards the
locomotive impulse; whilst the ganglion of each segment, with the filaments
connected with its nucleus, will form the circle necessary for the simply-
reflex actions of its members. The independence of the segments of the
Articulata, as far as their reflex actions are concerned, and their common sub-
ordination to one presiding centre of the will, are fully explained on this sup-
position. It is also quite conformable to the analogy, both of Mollusca, and
of Vertebrata.

328. The number and variety of the reflex actions, which take place in the
Articulata after decapitation, are very remarkable ; and they seem to have a
consentaneousness, proportioned to the closeness of the relation between the
nervous centres in the respective species. Thus, in the Centipede, w,e find
the ganglia of the several segments distinct, but connected by a commissural
trunk. Here an impression made equally upon the afferent nerves of all the
ganglia, will produce a consentaneous action. Thus, if the respiratory ori-
fices on one side of a decapitated Centipede be exposed to an irritating vapour,
the body will be immediately flexed in the opposite direction ; and if the
stigmata of the other side be then similarly irritated, a contrary movement
will occur. But different actions may be excited in different parts of the
cord, by the proper disposition of the irritating cause. In the higher classes,
however, where the ganglia of the locomotive organs are much concentrated,
the same irritation will produce consentaneous motions in several members,
similar to those which the unmutilated animal performs. In the Mantis
religiosa, for example, — which ordinarily places ilself in a very curious
position, especially when threatened or attacked, resting upon its two pos-
terior pairs of legs, and elevating its thorax with the anterior pair, which are
armed with powerful claws, — if the anterior segment, of the thorax, with its
attached members, be removed, the posterior part of the body will still remain
balanced upon the four legs which belong to it, resisting any attempts to over-
throw it, recovering its position when disturbed, and performing the same
agitated movements of the wings and elytra, as when the unmutilated animal
is irritated: on the other hand, the detached portion of the thorax, which con-
tains a ganglion, will, when separated from the head, set in motion its long
arms, and impress their hooks on the fingers which hold it. These facts
prove unequivocally, that the combined automatic movements of these parts,
which are performed in direct respondence to external expressions, are only
dependent lor their stimulation upon that ganglionic centre, with which the
nerves that excite them are immediately connected. Another instance, related
by Burmeister, is still more satisfactory in regard to the manner in which
these movements are excited. A specimen of the Dytiscits Sulcatus, from
which the cephalic ganglia had been removed, and which remained in a
motionless condition whilst lying with its abdomen on a dry hard surface,
executed the usual swimming motions, when cast into water, with great
energy and rapidity, striking all its comrades to one side by its violence, and
persisting in this for half an hour.

329. These conclusions are also fully confirmed by the experiments of
Mr. Newport, upon various Insects and Myriapoda; the results of which
have been recently made public.* The following, upon the lulus terrestris,
is particularly interesting. " The cord was divided in the fourteenth, and
also the twentieth segment; and the intervening portion was destroyed, by
breaking it down witli a needle. The animal exhibited in the anterior part.

* Philos. Trans., 1843, p. 267.

REFLEX ACTIONS OF ARTICULATA.

259

of its body all the evidences of perfect volition. It moved actively along,
turning itself back on either side repeatedly, as if to examine the anterior
wounded portion, which it felt again and again with its antennas: and when
attempting to escape, frequently turned back as if in pain and aware of some
hindrance to its movements ; but it seemed perfectly unconscious of the
existence of the posterior part of its body, behind the first incision. In those
segments, in which the cord was destroyed, the legs were motionless ; while
those of the posterior division, behind the second incision, were in constant
but involuntary motion, the movements being similar to those of walking or
running, uniformly continued, but without any consentaneous action with
those of the anterior part, by which locomotion was performed, dragging the
posterior divisions of the body after them. When the animal was held by
the posterior segments, reflex actions were excited in the legs, and powerful
contractions and gyrations of the whole animal were performed in those seg-
ments; but these movements appeared to be entirely the result of reflex
actions of the muscles, since exactly similar ones took place in the whole
body of decapitated specimens. At the expiration of twelve hours, the most
perfectly voluntary acts were performed by the head and anterior division of

*

Fig. 128.

Parts of Nervous System of Articulata. A. single ganglion of Centipede, much enlarged, showing the
distinctness of the purely fibrous tract, b. from the ganglionic column, a. B, portion of the double cord
from thorax of Pupa of Sphinx ligustri, showing the respiratory ganglia and nerves, between the gan-
glia (2, 3, 4), and the separated cords of the symmetrical system, c, view of two systems combined,
showing- their arrangement in the Larva ; a, ganglion of ventral column ; b, fibrous tract passing over
it 5 cc, respiratory system of nerves distinct from both.

the body, such as locomotion forwards or to either side, avoidance of any
obstacle, touching it with the antenna?, (which were in rapid action, as in an
uninjured animal,) and attempting to reach and to climb up an object pre-

260 FUNCTIONS OF THE NERVOUS SYSTEM.

sented to it, but not in immediate contact with it. But reflex movements
alone existed in the posterior division, in which the legs were very slowly
moved, even when the animal was not progressing. Brisk actions were now
more easily excited in them than at first, either by contact with the segments,
by irritation of one or two of the legs themselves, or by a sudden current of
air. By these means, when the animal was lying still, actions were imme-
diately excited in all ihe legs of the posterior parts of the body, anterior and
posterior to those which were irritated ; and these actions were induced in
those of both sides of the body, but appeared to commence on the opposite
side, in the legs corresponding to those which were first irritated. In eighteen
hours, the anterior part of the body was quite dead, so that no motions what-
ever could be excited in it, either voluntary or reflex; but reflex actions were
then readily excited in the posterior, and also slightly so by mechanical irrita-
tion, even at twenty-four hours." It would appear, then, that we may obtain
more decided proof, in the Articulated series, of the real character of reflex
actions, and of their dependence upon a distinct system of nerves, than we
can draw from any other class of animals. In the Vertebrata, it is easy to
distinguish the sensory from the motor — the afferent from the efferent —
fibres; but the distinctness of the excito-motor system from the sensori-voli-
tional, is not so clearly made out. Here, however, the afferent and efferent
fibres cannot be readily distinguished; but it is obvious that the reflex actions,
which manifest themselves when the communication with the cephalic ganglia
is cut off, are to be attributed to those fibres, which enter the cord under the
afferent character, — pass into the edge of the ganglion as ihe fibres of rein-
forcement, or cross it as conVmissural fibres, — and then emerge again as
efferent fibres, either in the nerves of the same segment, or in those of another
more or less distant. By traversing the cord along a part of its length, and
thus placing the several segments in communication with each other, the
fibres of reinforcement thus constitute a part of the longitudinal filaments of
the cord, — the remainder consisting of the fibres continuous with the cephalic
ganglia.

330. Hitherto we have spoken only of that division of the nervous system
of the Articulata, which may be regarded as corresponding with the sensory
and locomotive ganglia of the Mollusca ; we have next to inquire what we
find corresponding with the branchial ganglion. It is to be recollected, that the
respiratory apparatus of Insects is diffused throughout the whole body, so that its
presiding system of nerves must be proportionally extended; and we are, there-
fore, prepared to find the branchial ganglion of the Mollusca repeated, like
the pedal, in each segment. Besides the nervous trunks proceeding from the
ventral cord at its ganglionic enlargement, we find, in most of the Articulated
classes, a series of smaller nerves, given off at intermediate points, without
any apparent swelling at the points of divergence. The connections of these
are most distinctly traced in the thoracic region, just as the Larva is passing
into the Pupa state ; for the cords of the ventral column then diverge, so that
an additional tract may be seen which occupies the central line. By a close
scrutiny, this tract may be found in the perfect Insect, on the superior or vis-
ceral aspect of the cord ; and its nerves are given off from minute ganglionic
enlargements upon it. It seems to be quite unconnected, along its whole
course, with the column upon which it lies. Its nerves, however, communi-
cate with those of the sensori-motor system ; but they have a separate distri-
bution, being transmitted especially to the tracheae, on the parietes of which
they ramify minutely, and also to the muscles concerned in the respiratory
movements. (The latter, however, being a part of the general locomotive
apparatus, are also supplied from the principal ganglionic column.) These
nerves, then, which are evidently analogous to those of the gills and siphonic

RESPIRATORY AND STOMATO-GASTRIC SYSTEMS OF INSECTS.

261

apparatus in the Mollusca, may be regarded as corresponding with the pneu-
monic "portion of the Par Vagum in Vertebrata (which is in like manner dis-
tributed on the air passages), and with its associated motor nerves.

331. In comparing the nervous system of Insects with that of the higher
Mollusca, it will be seen that they differ more in the arrangement and in the
relative proportion of their parts, than in their essential character. In both
there is a Cephalic division of the ganglionic centres, in which sensibility and
psychical power appear to reside more particularly, if not entirely. In both
there is a division specially appropriated to the Locomotive apparatus, differ-
ing only in the multiplication of the centres in Insects, conformably with the
arrangement of the members they supply ; and sometimes consolidated to
nearly the same degree. In both, also, we find a division appropriated to the
Respiratory apparatus, in which there is a corresponding multiplicity of
centres in the Articulata, in harmony with the universal distribution of their
tracheal system. And in both, as we shall now see,

there is a separate system of nerves, distributed to the Fig. 129.

alimentary apparatus, and supplying the organs of mas-
tication (with the salivary glands), of deglutition, and of
digestion.

332. Of the stomato-gastric system, some traces may
be found in nearly all the Articulated classes. Thus,
in the Leech, we find a minute ganglion existing at the
base of each of the three teeth which form the mouth ;
these ganglia are connected together, and, to the cephalic
by slender filaments ; and they seem also to be in con-
nection with other filaments, which maybe traced on the
alimentary canal. As a specimen of its highly-deve-
loped form, we shall describe that of the Gryllotulpa
vulgaris (Common Mole-Cricket). Here we find it con-
sisting of two divisions; one placed on the median
line, which may hence be called the median system ;
the other running on each side at some little distance,
and hence called the lateral system. — The median sys-
tem appears to originate in a small ganglion, situated an-
teriorly and interiorly to the cephalic mass, with which
it communicates by a connecting branch on each side.
From this ganglion, nerves proceed to the walls of the
buccal cavity, the mandibles, &c. Its principal trunk,
however, (the recurrent of authors,) is sent backwards
beneath the pharynx. The ramifications of this are
distributed along the oesophageal tube and dorsal ves-
sel; whilst the trunk passes downwards to the stomach,
where its branches inosculate with those supplied by
the lateral system, and seem to assist in forming a
pair of small ganglia, from which most of the visceral
nerves radiate. — The ganglia of the lateral system are
two on each side, lying behind and beneath the cephalic

masses. The anterior pair are the largest, and meet on Of Gryiiotaipa vulgaris;
the median line, just behind the cephalic ganglia, with AA, cephalic ganglia; a,
which they communicate. Posteriorly to these lie the anterior median ganglion
second pair, which are in connection with them. Two ^^/ownwwdJftem
cords pass backwards on each side ; one derived from ft"™faa ^."lateral ga™
the anterior, the other from the posterior, of these gan- gi'ia; 'd, visceral ganglia.
glia. They run along the sides of the oesophagus and
dorsal vessel ; and, after inosculating with the branches of the central system,

Stomato-gastric system

262 FUNCTION'S OF THE NERVOUS SYSTEM.

enter the two coeliac ganglia, from which branches radiate to the abdominal
viscera.

333. This system of ganglia and nerves has an evident affinity with the
Sympathetic system of Vertebrata, as well as with some parts of the Cerebro-
spinal system, more especially with the Par Vagum. It is to be remembered,
that the Pneumogastric nerve of Vertebrata is distributed to three separate
systems — the respiratory, the circulating and the digestive. As we know
that the ultimate fibrils of nerves never anastomose, there can be no doubt
that these branches might be separately traced backwards into their ganglionic
centres ; and they may thus be regarded as functionally three distinct nerves,
though bound up in a single trunk. There is no difficulty, then, in under-
standing that the respiratory system of nerves, in Insects, and other In-
vertebrata, may be analogous with the pneumonic portion of the Par Vagum ;
although it bears no relation with the cardiac and gastric divisions of the
nerve. To the latter divisions, the analogy of the recurrent nerve becomes
sufficiently plain, when we look at its distribution upon the dorsal vessel,
cesophagus, and stomach ;* but its commencement in the anterior ganglion,
which also supplies the mouth and pharynx, might seem to place it on a dif-
ferent footing, until we have determined the true analogy of this last centre.
It may be inferred from its situation, and from the distribution of its nerves,
that this anterior ganglion is analogous both to the labial and pharyngeal
ganglia of the higher Mollusca. These appear to form a division of the
nervous system, by which the actions immediately concerned in the prehen-
sion of food are performed ; and these seem almost as independent of the
cephalic ganglia, as are those of respiration. There is evidently, however,
a greater tendency towards the union of these centres with the resophageal
collar, than of those presiding over the respiratory function, which is more
independent of the will.

334. The division of the nervous system of Vertebrata with which the
central portion of this system corresponds, is a question of some apparent
difficulty; but, if we bring into comparison not only the highest but the
lowest forms of the cerebro-spinal apparatus, the chief difficulties will be
removed. The analogies drawn from the distribution of the nervous branches
would lead us to infer, that the third division of the Fifth pair (including its
sensory and motor origins), the Glosso-Pharyngeal, and the gastric portion of
the Par Vagum, would most nearly represent its central portion. Now, when
the fifth pair is traced back to its true origin, it is found to be not a cerebral
but a spinal nerve; and it is then seen to arise from the Medulla Oblongata,
in such close approximation with the par vagum and glosso-pharyngeal, as to
show that, if this portion of the nervous centres were isolated from the rest,
the nerves which proceed from it would form, anatomically as well as func-
tionally, a natural group. The fifth pair, like other spinal nerves, may act in
a simply-reflex character; although, in Man, it is usually under the dominion
of the will. In the lower animals we find these reflex actions bearing a much
larger proportion to the voluntary, than in Man; and even in him we not
unfrequently meet with cases, in which the functions of the cerebral hemi-
spheres seem suspended, whilst those of the spinal cord are unimpaired; so
that the prehension of food by the lips may take place without any effort of
the will. This lias been observed in anencephalous foatuses, in puppies from
which the brain has been removed, and in profound apoplexy. Further, the
connection between the fifth pair and par vagum is very intimate in fishes; the
class which approaches nearest, in the character of its nervous system, to
Invertebrata. We may reasonably infer, then, that the anterior ganglion is

* See Newport, in Phil. Trans., 1832, p. 386.

STOMATO-GASTRIC SYSTEM OF INVERTEBRATA. 263

the principal centre of the reflex actions of those nerves, which correspond to
the third branch of the fifth pair, to the glosso-pharyngeal, and to the gastric
portion of the par vagum, in Vertebrata; whilst the branches which connect
them with the cephalic ganglia, bring these nerves more or less under the
influence of the latter. — The lateral ganglia seem more analogous to the
centres of the Sympathetic system in Vertebrata; especially in the connection
of their branches with all the other systems of nerves; and in the share
which they have in the formation of the co?liac ganglia. This view of the
relative functions of these two divisions of the stomato-gastric system, is
strengthened by the fact, that the connection between the Sympathetic system
of Fishes and the Par Vagum is much more intimate than in the higher
Vertebrata; although, even in the latter, as will be shown hereafter, it is by no
means so slight as it appears.*

335. Upon taking a general review of the facts which have been stated,
and of the inferences which have been erected upon them, we perceive that
a gradual elevation may be traced, in the character of the actions to which the
Nervous System is subservient, as we ascend from the lower to the higher
parts of the Animal Scale. In the Radiata and lower Mollusca, in which no
organs of special sensation exist, all, or nearly all, of the movements which
are witnessed, may be legitimately regarded as simply reflex in their character ;
being analogous to those, which are unquestionably so in the higher animals ;
and being performed by the instrumentality of a nervous apparatus, that
seems to have little else than an intermmcial purpose. But when, as in
the higher Mollusca and in nearly all the Articulata, we meet with distinct
organs of special sensation, it becomes evident that the consciousness of the
animal must be concerned in the direction of its actions; since no impressions
upon these organs (the eyes, for example) can exert any motor influence on
the muscles, except by producing sensations ; — that is, if we may apply to
the lower tribes the laws deduced from the study of the higher. Whilst,
therefore, a large proportion of the actions of the higher Invertebrata still
continues to be reflex (as we have especially seen in the Articulata), a new
group is superadded to these; and this, consisting of actions, which are
directly stimulated by sensations, and in which no Reasoning powers nor
Will appear to have any direct participation, may be termed consensual.
They require, as their instruments, a set of ganglia to receive the trunks which
originate in the organs of sense, and to issue motor nerves to the several parts
of the body. These last are distributed along with the trunks, which are
connected with the ganglia belonging to each particular organ ; thus the legs
and wings of an Insect appear to derive their motor nerves, partly from the
ganglia of the ventral cord, which minister to their reflex actions, and partly
from the cephalic ganglia, which seem to harmonize, to control, and even to
antagonize, the influence of the former. In like manner, the parts of the
body, which are capable of receiving sensory impressions, appear to have a
double connection ; one with the ganglia of the ventral cord, for the purpose
of conveying thither those impressions which are destined to excite reflex
actions; and the other with the cephalic ganglia, in order to originate sensa-
tions.— Of this double system of nerves and ganglia, the one connected solely

* The view given above of the comparative structure and offices of the Nervous System,
in the Invertebrated animals, is chiefly abridged from the Author's Prize Thesis on this
subject; in which additional details will be found, as well as many other illustrative figures
and references to authorities. He has there, also, discussed the physiological explanation
which had been previously given of the double nervous cord of the Articulata ; and having
shown that it is neither consistent with itself, nor capable of being applied to the other
Invertebrata, he has deemed it unnecessary to complicate the present sketch by introducing it.

264 FUNCTIONS OF THE NERVOUS SYSTEM.

with the reflex actions, and the other with the consensual, the existence in
Articulata seems to be clearly established by Mr. Newport's researches
(§ 326) ; and although the distinction between the afferent and motor fibres,
of each system respectively, has not here been clearly made out, there can be
no reasonable doubt of its existence.

336. The class of consensual actions evidently becomes more predominant,
in proportion as the special sensory organs are more evolved, and as the
ganglia in immediate connection with them (and altogether forming the cephalic
mass) present an increase in their proportionate development. This is
especially the case in the higher Arliculata ; in which the Instinctive group of
actions attains its highest perfection and predominance. The propriety of
referring these to the consensual group, will be obvious upon a little considera-
tion. They are as evidently prompted by particular sensations, as are the
reflex actions by particular impressions; and the respondence is as uniform
in the one case, as in the other. Although in these movements, there is a
most remarkable adaptation of means to ends, (as in the construction of
habitations by various Insects, and especially by the social Hymenoptera,)
yet few persons will maintain that this adaptation is performed by the reason
of the animal; since, on this supposition, every Bee solves a problem which
has afforded scope for the laborious inquiries of the acutest human mathe-
matician.* The adaptation is in the original construction of a nervous system,
which should occasion particular movements to be performed under the in-
fluence of particular sensations; and the constancy with which these are
performed by different individuals of the same species, when placed in the
same conditions, leads at once to the belief, that they must be independent of
any operations so variable as those of judgment and voluntary exertion.

337. On the other hand, in the Vertebrata, we shall find the purely reflex
and consensual movements forming a smaller proportion of their actions, and
brought under a more complete subjection to the Volitional system. This is
evident, from the greater variety which the actions exhibit ; from the mode in
which they are adapted to peculiar circumstances ; from the degree in which
they may be modified by education ; and from various other indications of a
superior kind of Intelligence. At last, in adult Man, we perceive that all the
movements, which are elsewhere involuntary, but which are not immediately
requisite (as are those of deglutition, respiration, &c.) for the maintenance of

* The hexagonal form of the cell is the one in which the greatest strength, and the nearest
approach to the cylindrical cavity required for containing the larva, are attained, with tin;
least expenditure of material. But the instinct which directs the Bees in the construction
of the partition that forms the bottom or end of the cell, is of a nature still more wonderful
than that which governs its general shape. The bottom of each cell rests upon three parti-
tions of cells upon the opposite side of the comb; so that it is rendered much stronger, than
if it merely separated the cavities of two cells opposed to one another. The partition is not
a single plane surface; but is formed by the union of three rhomboidal planes, uniting in the
centre of each cell. The angles ibrnied by the sides of these rhombs, were determined by
the measurements of Maraldi to be 109° yS' and 72° 32'; and these have been shown, by
mathematical calculation, to be pwiscly the angles, at which the greatest strength and capa-
city can be attained, with the least expenditure of wax. The solution of the problem was
lirst atiempted by Koenig, a pupil of the celebrated Bernouilli; and as his result proved to
differ lioin the observed angle by only two minutes of a degree, it was presumed that the
discrepancy was due to an error of observation, which it was easy to account for by the
finallness of the surfaces whose inclination had to be measured. The question has been
since taken up, however, by Lord lin Hicham (Appendix to his Illustrated edition of Paley's
Natural Theology) ; wlio has worked it out afresh, and has shown that, when certain small
quantities, neglected by Koenig, are properly introduced into the calculation, the result is
exactly accordant with observation, — the Ikes being thus proved to be riglit, and the Mathe-
matician 'wrong.

NERVOUS SYSTEM OF VERTEBRATA. 265

the Organic functions, are placed under the control of the Will, guided by the
reasoning faculties. This is especially true of the locomotive organs, whose
rellex actions are entirely governed by the will ; being only distinguishable as
such, when, from peculiar states of the system, the immediate influence of
the controlling power is suspended. — We shall find ground to believe, that
the exercise of the Reasoning faculties, and the resulting operations of the
Will, take place through the instrumentality of another division of the nervous
centres ; to which there is nothing distinctly analogous among the Inverte-
brata ; but which seems to bear a constant proportion in size and importance,
among Vertebrated animals, to the development of the Intelligence and its
influence on the movements of the body : — namely, the Cerebral ganglion.

338. There is another aspect, however, under which we are to consider
the Nervous System ; and this becomes more important in the highest division
of the Animal kingdom, on which we are now about to dwell. We have
hitherto spoken only of its influence on the contractile properties of the tis-
sues, to which it is distributed. It has, however, an important and direct
connection with the purely organic functions of Nutrition and Secretion; and
we shall see reason to regard it as the means, not only of placing the animal
in relation with the external world, but of harmonizing and controlling the
organic changes taking place in its own structure, and of bringing these under
the influence of particular mental conditions. The opinion is entertained by
many, that all the Organic Functions are dependent upon the innervation,
supplied to them by the system of nerves, which has been termed Sympathetic
or visceral. It is incumbent, however, on those who uphold the necessity of
this nervous power, to prove it definitively; since all analogy leads to an
opposite conclusion. We may regard the capability of separating a particular
secretion from the blood, as a peculiar property inherent in the glandular cells,
just as contractility is the inherent property of muscular fibre. But as the
peculiar arrangement of the excitable and contractile tissues in Animals,
requires a nervous system to act as a conductor between them, and to blend
their actions ; so may the complicated Organic functions of Animals require
to be harmonized and kept in sympathy with each other, by some mode of
communication more direct and certain than that afforded by the circulating
system, which is their bond of union in Plants. We have seen, in the fore-
going sketch, that the Visceral system does not exist in a distinct form in the
lower classes of Invertebrated animals ; and also that the nervous system of
these classes cannot, as a whole, be compared with it, although it may be
regarded as containing some rudiments of it. As the divisions of this system
become more evident, however, and the organic functions more complicated,
some appearance of a separate Sympathetic system presents itself; but this is
never so distinct as in Vertebrata. Hence, it may fairly be inferred that, — as
the Sympathetic system is not developed in proportion to the predominant
activity of the functions of organic life (which is so remarkable in the Mol-
lusca when contrasted with the Articulata), but in proportion to the develop-
ment of the higher divisions of the nervous system, — its office is not to
contribute to these functions anything essential to their performance ; but
rather to exercise that general control over them which becomes the more
necessary as they become more independent of one another; and to bring
them into relation with the system of Animal life.

3. Nervous System of Vertebrata.

339. When we direct our attention to the Nervous System of the Verte-
brated classes, we are immediately struck by two remarkable differences which
its condition presents, from that under which we have seen it to exist in the

23

266 FUNCTIONS OF THE NERVOUS SYSTE3I.

Invertebrata. In the latter it has seemed but a mere appendage to the rest of
the organism, — a mechanism superadded for the purpose of bringing its various
parts into more advantageous relation. On the other hand, in the Vertebrata
the whole structure appears subservient to it, and designed but to carry its
purposes into operation. Again, in the Invertebrata, we do not find any
special adaptation of the organs of support, for the protection of the Nervous
System. It is either inclosed, with the other soft'parts of the body, in one
general hard tegumentary envelope, as in the Echinodermata and Articulata;
or it receives a still more imperfect protection, as in the Mollusca. In the
latter, the naked species are destitute of any means of passive resistance, and
the Nervous System shares the general exposed condition of the whole body ;
and it is not a little remarkable that, in the testaceous kinds, the portion of
the body containing the most important nervous centres should be protruded
beyond the shell, whilst the principal viscera are retained within it. Now,
in the Vertebrata, we find a special and complex bony apparatus, adapted in
the most perfect manner for the protection of the Nervous System ; and it is,
in fact, the possession of a jointed spinal column, and of its cranial expansion,
which best characterizes the group.

340. When we look more particularly at the Nervous Centres themselves,
we perceive that they combine the general characters of those of the Articulata
with those of the Mollusca ; the locomotive powers of the former (compara-
tively reduced, however, in activity) being united with the complex nutritive
system of the latter ; and we find this combination manifested, not only in
the organs themselves, but in the Nervous System, which stands in so close
a relation with them. The Spinal Cord of Vertebrata is evidently the ana-
logue of the ventral columns of Articulata. It is a continuous ganglion, con-
taining two portions as distinct as the two tracts in the Articulata; — a fibrous
structure, which is continuous between the Brain and the spinal nerves, and
thus resembles the white tract in Insects ; — and a ganglionic portion, princi-
pally composed of gray matter. Into this gray matter, as in the ventral gan-
glia of Insects, a part of the roots of the spinal nerves may be traced; whilst
others seem to pass on continuously to the brain. At the upper extremity of
the Spinal cord (commonly termed the Medulla Oblongata) we find the
ganglia and nerves of special sensation ; and the organs which these supply
are placed in immediate proximity with the entrance to the alimentary canal,
holding the same relation to it as in the Mollusca. But in addition to these
we find two ganglionic masses in all Vertebrata, to which we have no distinct
analogue in the lower classes — the Cerebral Hemispheres, and the Cerebel-
lum. With the development of the former of these, as already remarked,
the perfection of the reasoning powers appears to hold a close relation ; that
of the latter seems connected with the necessity which exists, for the adjust-
ment and combination of the locomotive powers, when the variety of move-
ments performed by the animal is great, and the harmony required among
them is more perfect. Upon these points, however, we shall hereafter
dwell.

341. The Visceral system of nerves now assumes a more distinct form.
It docs not share the protection of the Spinal column; hut its ganglia lie for
the most part in the general cavity of the trunk. These ganglia, which
are doubtless the independent centres of some of the nerve-fibres proceed-
ing from them, arc much more numerous than is commonly supposed. It
appears from recent researches, that we are to regard as belonging to the
Visceral or Sympathetic system, not only the Semilunar and Cardiac ganglia
(which seem to be its principal centres), with the chain of cranial, cervical,
thoracic, lumbar, and sacral ganglia, which are in nearer proximity to the

XERVOUS SYSTEM OF VERTEBRATA.

267

[Fig. 130.

Cerebro-spinal system, but also nu-
merous minute ganglia, which are
to be found on its branches in vari-
ous parts, and, in addition, the gan-
glia upon the posterior roots of the
Spinal nerves. If, indeed, we are
to regard the fine nerve - fibres,
wherever they present themselves,
as belonging to the Visceral sys-
tem, we must regard this as still
largely interwoven with the Cere-
bro-spinal system, notwithstanding
that the former has its own set of
ganglionic centres ; since, as already
mentioned (§ 244), these peculiar
fibres are found in considerable
numbers in all the Cerebro-spinal
nerves, and maybe shown to origi-
nate in the caudate corpuscles of
the Brain and Spinal Cord. On
the other hand, there unquestion-
ably exist numerous fibres in the
Visceral system, which proceed
into it from the Cerebro-spinal sys-
tem; these, however, are not uni-
formly distributed, for some of the
Visceral nerves contain few or none
of them, whilst in others they are
numerous. The branches by which
the Sympathetic system communi-
cates with the Cerebro-spinal, and
which were formerly considered as
the roots of the Sympathetic sys-
tem, contain fibres of both kinds : —
i. e., Cerebrc-spinal fibres passing
into the Sympathetic, and Sym-
pathetic fibres passing into the
Cerebro - spinal. The latter are
chiefly, if not entirely, transmit-
ted into the anterior branches of
the Spinal nerves ; the posterior
branches being principally supplied
with fine fibres, from the ganglia on

A view of the Great Sympathetic Nerve. — 1, the plexus on the carotid artery in the carotid foramen :
2, sixth nerve (motor externus); 3, first branch of the fifth or ophthalmic nerve ; 4, a branch on the sep-
tum narium going to the incisive foramen; 5. the recurrent branch or vidian nerve dividing into the
carotid and petrosal branches; 6, posterior palatine branches; 7, the lingual nerve joined by the corda
tympani; 8, the portio dura of nie seventh pair or the facial nerve; 9, the superior cervical ganglion;
10, the middle cervical ganglion ; 11, the inferior cervical ganglion ; 12, the roots of the great splanchnic
nerve arising from the dorsal ganglia; 13, the lesser splanchnic nerve; 14, the renal plexus; 15. the solar
plexus; 1C, the mesenteric plexus; 17, the lumbar ganglia; 18, the sacral ganglfe; 19, the vesical plexus;
20, the rectal plexus; 21, the lumbar plexus (cerebro-spinal) ; 22, the rectum; 23. the bladder; 24. the
pubis; 25, the crest of the ileum; 26, the kidney ; 27, the aorta; 28. the diaphragm; 29, the heart; 30. the
larynx; 31, the sub-maxillary gland ; 32, the incisor teeth; 33, nasal septum; 34, globe of the eye; 35,
36, cavity of the cranium.]

268

FUNCTIONS OF THE NERVOUS SYSTEM.

[Fig. 131. their posterior roots. Some of these

last fibres also pass, with the ordi-
nary large nerve-tubes, from the
Cerebro-spinal into the Sympathetic
system. By these communications
the two systems of fibres are so
blended with each other, that it is
impossible to isolate them ; and all
that can be said is, that the large
tubular fibres predominate in the
former, and the fine homogeneous
fibres in the latter.

342. The branches proceeding
from the Semilunar ganglia are dis-
tributed upon the abdominal viscera;
and those of the Cardiac ganglia
upon the heart and the vessels pro-
reeding from it. The latter seem
to accompany the arterial trunks
through their whole course, rami-
fying minutely upon their surface;
and it can scarcely be doubted, that
they exercise an important influ-
ence over their functions. What
the nature of that influence is, how-
ever, will be a subject for future
inquiry. It is so evidently con-
nected with the operations of nutri-
tion, secretion, &c., that the de-
signation of "nervous system of
organic life," as applied to this sys-
tem does not seem objectionable,
provided that we do not understand

it as denoting the dependence of these functions upon it. — Even in Vertebrata,
however, we do not always find the distribution of the visceral trunks distinct
from those of the cerebro-spinal. In the Cyclostome Fishes, the par vagum
supplies the intestinal canal along its whole length, as well as the heart; and
no appearance of a distinct sympathetic can be discovered. In Serpents,
again, the lower part of the alimentary canal is supplied from the spinal cord,
and the upper part by the par vagum ; and though the lateral cords of the
sympathetic may be traced, they are almost destitute of ganglia. Even in
the highest Vertebrata, some of the glands, of which the secretion is most
directly influenced by the condition of the mind, are supplied with most of
their nerves from the cerebro-spinal system ; thus, the lachrymal and sublin-
guul glands receive large branches from the fifth pair, and the mammary
glands from the intercostal nerves. But it appears probable, from what has
just been stated, that the influence is conveyed through the visceral fibres,
contained in these nerves, and either originating in the ganglia at their roots,
or derived from the Sympathetic system.

343. The Spinal Cord, witli its encephalic continuation — the Medulla Ob-
longata, — may be regarded as constituting the essential part of the nervous
system of Vertebrata. Although the Cerebral Hemispheres in Man bear so
large a proportion to it in size, that the Spinal Cord seems but a mere ap-
pendage to them, the case is reversed when we look at the other extremity of
the scale; the Cerebral Hemispheres, in many Fishes, being but ganglionic

Roots of a dorsal spinal nerve, and its union with
sympathetic : — e, c. Anterior fissure of the spinal cord.
a. Anterior root. p. Posterior root, with its ganglion.
a'. Anterior branch, p' . Posterior branch, s. Sympa-
thetic, e. Its double junction with the anterior branch
of the spinal nerve by a white and a grey filament.]

NERVOUS SYSTEM OF VERTEBRATA. 269

protuberances from the Medulla Oblongata. Moreover, the fact that animals
are capable of living- without the brain, whilst they at once die if deprived of
the spinal cord, sufficiently demonstrates this. The spinal cord, then, when
viewed in relation to the nervous system of the Invertebrata, may be regarded
as including their respiratory, stomato-gastric, and pedal ganglia. That these
should be associated together, can scarcely be considered remarkable. It is
obviously convenient that they should all be inclosed in the bony sheath pro-
vided for their protection ; and their closer relation favors that sympathy of
action, which is so important in animals of such complex structure and
mutually dependent functions, as the higher Vertebrata. An animal either
congenially or experimentally deprived of its cerebral hemispheres, is very
much in the condition of one of the Acephalous Mollusca. It can perform
those respiratory movements, on which depend the maintenance of its circu-
lation, and consequently its whole organic life; it can swallow food brought
within its reach, and it can, in some degree, exert its locomotive powers to
obtain it; but it is unconscious of the direction in which these can be best
employed, and is dependent upon the supplies of food that come within its
grasp. The Acephalous Mollusca are so organized, that they find support
from the particles brought in by their respiratory current; but the more
highly-organized Vertebrata are not capable of so existing, and they must
have their food provided for them by an exertion of the mental powers. So
long as an anencephalous Vertebrated animal is duly supplied with its requi-
site food, so long may it continue to exist, although in a state analogous to
that of profound sleep; and thus it is seen, that the operations of the Brain
are not immediately connected with the maintenance of the organic functions ;
the movements requisite for these being carried on, as in the lower animals,
through the instrumentality of ganglionic centres and nerves specially appro-
priated to them.

344. It is only in the Vertebrata, that the difference between the afferent
and efferent fibres of the nerves, has been satisfactorily determined. The
merit of this discovery is almost entirely due to Sir C. Bell. He was led to
it by a chain of reasoning of a highly philosophical character; and though
his first experiments on the Spinal nerves were not satisfactory, he virtually
determined the respective functions of their two roots, by experiments and
pathological observations upon the cranial nerves, before any other physiolo-
gist came into the field.* Subsequently his general views were confirmed
by the very decided experiments of Miiller ; but, until very recently, some
obscurity hung over a portion of the phenomena. It was from the first main-
tained by Magendie, and has been subsequently asserted by other physiolo-
gists, that the anterior and posterior roots of the nerves were both concerned
in the reception of sensations and in the production of motions ; for that,
when the anterior roots were touched, the animal gave signs of pain, at the
same time that convulsive movements were performed ; and that, on touching
the posterior roots, not only the sensibility of the animal seemed to be affected,
but muscular motions were excited. These physiologists were not willing,
therefore, to admit more, than that the anterior roots were especially motor,
and the posterior especially sensory. But the recently attained knowledge of
the reflex function of the spinal cord, enables the latter portion of these phe-
nomena to be easily explained. The motions excited by irritating the pos-
terior root are entirely dependent upon its connection with the spinal cord,
and upon the integrity of the anterior roots and of the trunks into which they
enter; whilst they are not checked by the separation of the posterior roots
from the peripheral portion of the trunk. It is evident, therefore, that excita-

' See British and Foreign Medical Review. Vol. ix., p. 140, &c.

23*

270

FUNCTIONS OF THE NERVOUS SYSTEM.

Fis. 132.

lion of the posterior root does not act immediately upon the muscles through
the trunk of the nerve, which they contribute to form; but that it excites a
motor impulse in the Spinal Cord, which is propagated through the anterior
roots to the periphery of the system. The converse phenomenon, the appa-
rent sensibility of the anterior roots, has been still more recently explained
by the experiments of Dr. Kron'enberg;* which seem to prove, that it is de-
pendent upon a branch of the posterior root passing into the anterior root at
their point of inosculation, and then directing itself towards the cord (§ 304).
345. On the other hand, the distinctness of the system of nerves concerned
in the simply-reflex actions, from those which minister to sensation, emotion,
and volition by their connection with the brain, is by no means so obvious as
in the Invertebrated classes. When first pointed out by Dr. Marshall Hall,
Avho had grounded his opinion more upon physiological phenomena than
upon anatomical facts, the statement did not command general assent; since,
Avhile the phenomena were admitted, the inferences which he drew from them
were not regarded as necessary results. When, however, the anatomy of
the Nervous centres in Vertebrata was more closely inquired into (by Mr.
Grainger, who had been partly anticipated by Bellingeri), it was found to
present certain phenomena which might be regarded as supporting Dr. M.
Hall's views; and when the inquiry was extended to the Invertebrated classes,
the confirmation was found to be still more decisive. In our previous sketch
these doctrines have been treated as established; since they have been found
not only to correspond with the facts disclosed by anatomical research, but to
be required by them. We shall now apply them to the nervous apparatus of
the Vertebrata.

346. The Spinal Cord consists of two lateral halves ;
these are partially separated, in the higher classes, by
the superficial anterior and posterior fissures ; and in
Fishes by an internal canal, which is continuous with the
fourth ventricle.! This canal is evidently the indication
of that complete separation of the two columns, which
exists in the lower Articulata; and the fourth ventricle,
which in many Fishes remains unclosed (the cerebellum
not being sufficiently developed to overlap it), corre-
sponds with the passage between the cords uniting the
cephalic ganglia, with the first sub-oesophageal, through
which the oesophagus passes in all the Invertebrata.
The two lateral halves have little connection with each
other in Fishes, and the pyramidal bodies at their apex
scarcely decussate ; but in ascending toward'^ the higher
classes, the communication between the two sides is more
intimate, and a larger proportion 6f the pyramidal fibres,
crosses to the opposite side. In all the Vertebrata, the
true Spinal Cord contains grey substance, or something
equivalent to it; thus possessing the character of a con-
tinuous ganglion. The proportion of the vertebral column
which this ganglionic portion occupies, is, however, ex-
tremely variable ; depending principally on the position
of the chief organs of locomotion. Thus, in the Eel,
and other Vermiform Fishes, it is continued through
the whole spinal canal ; whilst in the Lophius and
Tetraodon, whose body is less prolonged, and more
dependent for its movements upon the anterior extremi-

* Miiller's Archiv., 1S39, Heft v.: and Brit, and For. Med. Rev., vol. ix. p. 547.
t Tins canal may be traced in the Spinal Cord of Man and other Mammalia; but it is
nearly obliterated.

\i-rvous centres in
Frog; A, olfactive ganglia;
B, cerebral hemispheres ;
c, optic ganglia; D, cere-
bellum, so small as not to
cover the 4th ventricle, or
cavity left by the diver-
gence of the columns of
the Spinal Cord.

SPIJCAL CORD OF VERTEBRATA.

271

ties, the true Spinal Cord scarcely passes out of the cranium. The quan-
tity of grey matter is nearly uniform in every part of the cord, where
there is no great diversity in the functions of the nerves which originate
from each portion. In most Fishes, for example, the body is propelled
through the water more by the lateral action of the flattened trunk (whose
surface is extended by the dorsal and caudal fins erected upon prolonga-
tions of its vertebrae), than by the movements of its extremities, which serve
principally to guide it. Hence we usually find the amount of grey mat-
ter varying but little in different parts of the cord. But in the Flying-fish,
and others whose pectoral fins are unusually powerful, a distinct ganglionic
enlargement of the cord takes place where the nerves are given olf. In Ser-
pents, again, the spinal cord is nearly uniform throughout its entire length;
whilst in Amphibia it is so during the Tadpole condition, but presents enlarge-
ments corresponding to the anterior and posterior extremities, when these are
developed; at the same time becoming much shortened, as the tail is less im-
portant to locomotion, or is altogether atrophied. In Birds, the ganglionic
enlargements are generally very perceptible ; and bear a close relation in
size, with the development of the locomotive organs with which they are
connected. Thus, in birds of active flight, and short powerless legs, the an-
terior enlargement is the principal ; but in those which are more adapted to
run on hand than to wing their way through the air, such as the whole tribe
of Struthious birds, the size of the posterior enlargement is very remarkable.
Hence we have a right to infer, that the increase in the quantity of grey mat-
ter in the cord has some connection with the amount of power to be supplied ;
and this exactly corresponds with what has been observed in the Articulated
classes, and especially in watching the metamorphosis of Insects. In Birds
and Mammalia, however, the whole amount of the grey matter in the spinal
cord does not bear so large a proportion to the bulk of the nerves proceeding
from it, as in the lower Vertebrata ; and the reason of this seems obvious.
The actions of the locomotive
organs are less and less of a
reflex character, and are more
directly excited by the will,
and consequently by the brain
than in the inferior tribes ; and
just in proportion, therefore,
to the development of the
Brain, will it become the cen-
tre of all the actions performed
by the animal, and the Spinal
Cord a mere appendage to it.
Still, in all the Mammalia, even
in Man, do we find these gan-
glionic enlargements of the
spinal cord; and in Man it is
the posterior one (or rather the
inferior), which contains the
largest quantity of grey mat-
ter. In the cord of this class,
too, the lateral halves are much
more intimately united, than in
the classes below ; for not only is the central canal for the most part absent,
but the two crescent-shaped plates of grey matter are united by a transverse
lamella, which connects their centres like a commissure.

347. The Cord is transversed, not only by the anterior and posterior fis-

Fisr. 133.

Transverse sections of human Spinal Cord at different
points, showing the proportional quantity and arrangement
of grey and white matter at each: 1. opposite llth dorsal ver-
tebra; 2, opposite 10th dorsal ; 3, opposite 8th dorsal; 4, op-
posite 5th dorsal ; 5, opposite 7th cervical ; 6, opposite 4th
cervical; 7, opposite 3d cervical; 8, section of medulla ob-
longata through centre of corpus olivare. •

272

FUNCTIONS OF THE NERVOUS SYSTEM.

sures, but by two furrows on each side, marking out three columns upon it.
We have, therefore, on each half of the cord, an anterior middle or lateral
and posterior column. The points of the crescentic lamellae of grey matter
approach these furrows pretty closely ; but elsewhere the grey matter is
covered deeply by the fibrous columns. Each spinal nerve arises from two
sets of roots. The anterior roots join the spinal cord, near the anterior fur-
row ; and the posterior, near the posterior furrow. Respecting their intimate
connection with the principal divisions of the cord, a considerable diversity
has existed among the statements of anatomists ; but it seems to be now
generally admitted, that, as in the Articulata, a part of each root enters the

[Fig. 134.

Fist. 135.

Transverse section of human spinal cord, close to
the third and fourth cervical nerves ; magnified ten
diameters, (from Stilling;)-/. Posterior columns, ii.
Gelatinous substance of the posterior horn. k. Pos-
terior root. I. Supposed anterior roots, a. Anterior
fissure, c. Posterior fissure, b. Grey commissure, in
which a canal is contained, which, according to these
writers, extends through the length of the cord. g.
Anterior horn of grey matter containing caudate vesi-
cles, e. Anlero-lateral column (from k to a)].

Passage of Nerve-fibres through the
Spinal Cord, according to Stilling; A,
posterior fibres continuous with the
anterior of the same side, through the
nucleus of the cord ; B, posterior fibres
continuous with the anterior of the
opposite side.

grey matter or ganglionic portion of the cord, whilst a part is continuous
with its white or fibrous columns. — The course of the fibres which enter the
grey matter, has been lately displayed, in part, at least, by the researches of
Dr. Stilling.* It appears that of the fibres of the posterior roots, some form
loops in the grey matter, and become continuous with those of the anterior
roots of the same side, as seen at A, fig. 135. Others cross the grey matter,
and become continuous with those of the anterior roots of the opposite side,
as seen at B. It can scarcely be doubted that these fibres, being unconnected,
with the brain, constitute the system to which reflex actions are due. Although
Dr. Stilling's inquiries have not proved the fact,t yet it may be inferred from
physiological phenomena, as well as from the facts recently shown by Mr.
Newport (§ 326), that there are other fibres, which pass from' the posterior

* Ueber die Textur und Function der Medulla Oblonirnta.

f It may be thought that the mode of examination which he adopted, — that of making
very thin transverse sections of the Spinal Cord, — is not well fitted to display the connections
of the roots with longitudinal fibres. The subsequent observations of Budge (Muller's Ar-
chiv., 1844, p. 160), seem to have established the fact of the continuity of a portion of each
root with the longitudinal fibres of the cord.

SPINAL CORD OF VERTEBRATA. 273

roots into the anterior roots of other nerves above and below, both on the
same side and on the opposite. — Of the portions of the roots which are con-
tinuous with the fibrous columns, the anterior would seem to have a connec-
tion with both the anterior and lateral columns ; and the posterior cannot be
said to be restricted to the lateral column, some of their fibres entering the
posterior division of the cord.

348. If the white or fibrous portion of the Spinal Cord be really continu-
ous with the medullary matter of the Brain, the roots of the nerves which
enter it are in reality thus brought into connection with the Cerebral Hemi-
spheres and Cerebellum ; and the posterior division of these may, therefore,
be regarded as conducting to the Sensorium those impressions, which there
become sensations ; whilst the anterior roots convey the motive influence,
which has been propagated, by a voluntary or emotional impulse, down the
tract of the Spinal Cord with which they are continuous. On the other hand,
the passage of one portion of each set of roots through the grey matter of
the Cord, completes the nervous circle required for the performance of reflex
actions ; and by this they would seem to take place in Vertebrated animals,
just as through the distinct system of excito-motor fibres in the Articulata
(§ 328.) The fibres which pass continuously from the posterior to the ante-
rior roots of the nerves on the same side, probably constitute the channel of
those reflex actions, which can be excited in apart supplied by any compound
nerve, by stimulating its afferent fibres, and thus causing a motor impulse to
be transmitted from the Spinal Cord along its afferent portion. The "fibres
which cross to the opposite side, will produce similar movements in its cor-
responding parts. And the fibres, if such there be, that pass from the pos-
terior (afferent) roots of each nerve, into the anterior (motor) roots of distant
nerves, would convey to a great variety of muscles, the influence of a stimulus
applied to a single afferent nerve. It follows, then, on this view of the cha-
racter of the Spinal Cord, that the continuity of the fibrous tracts is all that
is required, to convey the influence of the brain to the parts below ; whilst
the completeness of the nervous circle is all that is necessary, for the perform-
ance of reflex actions excited through it. This is found to be strictly true ;
the former having been observed in cases of disease, and the latter having
been proved by experiment. As far as simple reflex actions are concerned,
there is as much segmental independence in Vertebrata, as in the Articulata ;
but these actions seldom have so completely the character of adaptation, ami
are of a more irregular and convulsive nature. Still, however, there is an
essential correspondence between them ; and we may, therefore, regard the
distinction between the reflex and voluntary movements as the same in each
group ; the former predominating in Articulata ; the latter in Vertebrata. On
this view, then, each spinal nerve contains at least four sets of fibres.

i. A sensory bundle passing upwards to the Brain.

ii. A motor set, conveying the influence of volition and emotion down-
\vardsfrom the Brain.

in. A set of excitor or centripetal fibres, terminating in the true Spinal
Cord or ganglion, and conveying impressions to it.

iv. A motor or centifrugal set, arising from the same Ganglionic centre,
and conveying the motor impulse reflected_/V0w it to the muscles.

Of these, the first and third are united in the posterior or afferent roots ;
the second and fourth in the anterior or efferent roots.

349. It is difficult to trace the course of the fibres within the Spinal Cord;
but it is now proved, that Sir C. Bell was not altogether correct in his idea,
that the functions of the columns of the Cord are respectively similar to those
of the roots connected with them. Cases, indeed, are of no (infrequent oc-
currence, in which a portion of one of the columns has been almost entirely

274 FUNCTIONS OF THE NERVOUS SYSTEM.

destroyed by injury or disease, without any corresponding loss of the func-
tion attributed to it.* Such cases have kept alive, in the minds of many emi-
nent practical men, a considerable distrust of the accuracy of Sir C. Bell's
conclusions. We have seen that, in regard to the roots of the nerves, his
first statements have been confirmed, and rendered more precise, by subse-
quent researches ; but it is not so in regard to the functions of the anterior
and posterior divisions of the Spinal Cord. — Bellingeri was led, by experi-
ments on the spinal cord, to the conclusion, that the anterior roots of the
nerves were for the flexion of the various articulations, and the posterior for
their extension. He also was wrong, in extending an inference, founded on
experiments on the Cord, to the roots of the nerves. — The recent experiments
of Valentin, whilst they fully confirm Sir C. Bell's determination of the func-
tions of the roots of the nerves, coincide, to no small degree, with Bellingeri's
opinion, in regard to the offices of the anterior and posterior divisions of the
Cord. He obtained reason to believe that, in the Frog, neither the superior
nor inferior strand of the cord (posterior and anterior columns in Man) solely
possesses motor functions ; but he found that, when the former were irritated,
sensations predominated ; and when the latter, motions were chiefly excited.
He further states that, if the superior strand (posterior column) be irritated
at the point at which the nerves of either extremity are given ofl', that ex-
tremity is extended ; and that if the inferior strand (anterior column) be irri-
tated, the extremity is flexed. At their entrance into the spinal cord, there-
fore, it would appear that the motor fibres of the extensors pass towards the
superior stratum (posterior column in Man), whilst those of the flexors are
continuous with the inferior stratum (inferior column) ; their course being
more altered, however, when they are examined far from the point of issue.
This doctrine was confirmed by experiments on Mammalia ; and is borne out
(according to Valentin) by pathological phenomena observed in Man. Accord-
ing to this eminent physiologist, also, relaxation of the sphincters is analogous
to the extended state of the extremities ; and he has noticed a manifest relaxa-
tion of the sphincter ani in the frog, when the superior part of the spinal
cord was irritated, so as to produce extension of the limbs. These state-
ments are entitled to considerable weight, on account of the quarter from
which they come ; but they are not, perhaps, to be received altogether with-
out hesitation, until confirmed by other physiologists, especially whilst the
phenomena of reflex action are still so imperfectly known. For it is quite
possible that, whilst stimulation of the anterior part of the cord may excite
direct motions of flexion, in preference to those of extension, the movements
of extension produced by stimulating the posterior column may be of a reflex
character.

350. There is no reason to believe, that the functions of the Spinal Cord
are essentially different along its whole length. Everywhere it appears to
consist of a ganglionic centre, supplying nerves to its particular segment ;
and of connecting fibres, by which the nerves proceeding from any one divi-
sion are brought into relation with distant portions of the organ, and with the
large ganglionic masses at its anterior extremity. In this respect, then, it
corresponds precisely with the double nervous cord of the Articulata ; the
only prominent difference between the two being, that in the former the gan-
glionic matter is continuous from one extremity of the organ to the other;
whilst in the latter it is interrupted at intervals ; and in the Mollusca, the
centres are still further separated from each other. The connection of the

* Sec especially a case recorded by Dr. Webster (Medico-Chinirgical Transactions, vol.
xxvi.), in which there was complete destruction of the posterior columns in the lower p;irt
of the cervical region ; which was not attended with loss of sensibility in the parts below,
but, on the contrary, with loss of power of voluntary motion.

SPINAL CORD OF VERTEBRATA.

275

Spinal Cord with the large ganglia
contained within the cavity of the
cranium, is effected by means of
processes from its superior extre-
mity, the arrangement of which is
somewhat complex. This portion
of the cord, which also lies within
the cavity of the cranium, has been
termed the Medulla Oblongata.
It has been supposed to be the
peculiar seat of vitality ; but the
only real foundation of this idea
is, that it is the great centre of the
Respiratory actions, on the conti-
nuance of which all the other
functions are dependent. The
Brain may be removed from above,
and nearly the whole Spinal Cord
from below, without an immediate
check being put upon all the phe-
nomena of life. In this Medulla
Oblongata,ybz<r different parts may
be distinguished on each side: — 1,
The Anterior Pyramids, or Cor-
pora Pyramidalia ; 2, The Oli-
vary Bodies, or Corpora Oliva-
ria; 3, The Restiforrn bodies, or
Corpora Restiformia ; otherwise
called Processus a Ccrebello ad
Medullam Oblongatam; 4, The

[Fig. 137.

[Fig. 136.

A posterior superior view of the Pons Varolii, the
Cerebellum, and the Medulla Oblongata and Spinalis.
1, 1, the crura cerebri; 2, the pons varolii or tuber-
annularis; 3, its middle fossa; 4, an oblique band of
medullary matter seen passing from its side ; 5, the
external surface of the crus cerebelli in its natural
state ; 6, the same portion deprived of outer layer; 7,
the nervous matter which united it to 4; 8, the trige-
minus or fifth pair of nerves ; 9, portion of the audi-
tory nerve— the while neurine is seen passing from
the oblique band which comes from the corpus resti-
forme to the trigeminus nerve in front, and the auditory
nerve behind ; 10, 11, the superior portion of the hemi-
spheres of the cerebellum; 12, lobulus amygdaloides ;
13, corpus olivare; 14, corpus pyramidale ; 15, medulla
spinalis.]

[Fig. 138.
s

Front view of the medulla oblon-
gata:— p, p. Pyramidal bodies, de-
cussating at d. 0,0. Olivary bodies.
r,r. Restiform bodies, a, a. Arci-
form fibres, v. Lower fibres of the
Pons Varolii.]

Posterior view of the medulla oblongata :—pp. Posterior
pyramids, separated by the posterior fissure, rr. Restiform
bodies, composed of cc, posterior columns, and dd, lateral
part of the antero-lateral columns of the cord. aa. Olivary
columns, as seen on the floor of the fourth ventricle, sepa-
rated by s, the median fissure, and crossed by some fibres
of origin of nn, the seventh pair of nerves.]

276

FUNCTIONS OF THE NERVOUS SYSTEM.

Posterior Pyramids, or Corpora Pyramidalia Posteriora. The connections
of these with the Brain above, and with the Spinal Cord below, will be now
traced.*

[Fig. 139.

IV

Transverse section of the medulla oblongata through the lower third of the olivary bodies. (From Stil-
ling.) Magnified 4 diameters.

a. Anterior fissure. 6. Fissure of the calamus scriplorius. c. Raphg. d. Anterior columns, e. La-
teral columns, f. Posterior columns, g. Nucleus of the hypoglossal nerve, containing large vesicles.
h. Nucleus of the vagus nerve, i, i. Gelatinous substance, k, k. Roots of the vagus nerve. /. Roots of
the hypoglossal, or ninth nerve, in. A thick bundle of white longitudinal fibres connected with the root
of the vagus, n. Soft column (Zartstrang, Stilling), o. Wedge-like column (Keelstrang, Stilling), p.
Transverse and arciform fibres, q. Nucleus of the olivary bodies, r. The large nucleus of the pyramid.
s, s, s. The small nuclei of the pyramid, it. A mass of grey substance near the nucleus of the olives
(Oliven-Nebenkern). u, q, r, are traversed by numerous fibres passing in a transverse semicircular direc-
tion, v, w. Arciform fibres, x. Grey fibres.]

351. As our object, however, is rather Physiological than purely Anato-
mical, we shall commence with a description of the motor and sensory tracts,
which may, according to Sir C. Bell,t be very distinctly separated in the Pons

* Great diversities will be found in the accounts given of those connections by different
Authors; some of which are attributable to a variation in the use of terms, which must not
pass unnoticed. By the majority of Anatomists, the name of Corpora Uestilbrmia is given to
the Ccrebdlar Columns; and its designation, therefore, it seems advisable to retain. Some,
however, and amongst them Dr. .1. Reid, in his late very excellent description of the Ana-
tomy of the .Medulla Oblongata (Kdinb. Mod. & Surg. Journal, Jan. 1841), give the name to
the columns that pass up from the posterior division of the spinal cord into the crus cerebri,
— which are here called (alter Sir C. Bell) the posterior pyramids; and apply the terms
Posterior Pyramids to the Cerebellar column. The truth is that, as Sir C. Bell has justly
observed, all the tracts of fibrous mailer connecting the Drain with the Spinal Cord, have a
somewhat jii/nnniilul Jbrm ; and it might be added that all have something of a restiform or
cord-like-aspect

f Philosophical Transactions, 1835.

STRUCTURE AND CONNECTIONS OF MEDULLA OBLONGATA.

277

Varolii. The Pons has been correctly designated as the great Commissure
of the Cerebellum, inclosing the Crura Cerebri; and its transverse fibres not
only surround the longitudinal bands which connect the Cerebrum with the
Spinal Cord, but pass through them ; so as in some degreee to isolate the

Fis?. 140.

Course of the Motor tract, according to Sir C. Bell. A, A, fibres of the hemispheres, converging to form
the anterior portion of the cms cerebri ; B, the same tract where passing the crus cerebri ; c, the right
pyramidal body, a little above the point of decussation ; D, the remaining part of the pons Varolii, a por-
tion having been dissected off to expose B. — 1, olfactory nerve, in outline; 2, union of optic nerves;
3. motor oculi; 4, 4, patheticus ; 5, 5, trigeminus; 6, 6, its muscular division ; 7, 7, its sensory root ; 8, ori-
gin of sensory root from the posterior part of the medulla oblongata ; 9, abducens oculi ; 10, auditory
nerve ; 11, facial nerve ; 12, eighth pair ; 13, hypoglossal ; 14, spinal nerves ; 15, spinal accessory of right
side, separated from par vagum and glosso-pharyngeal.

two lateral halves from one another, and to form a complete septum between
the anterior and posterior portions of each. The Motor tract is brought into
view, by simply raising the superficial layer of the Pons, and tracing upwards
and downwards the longitudinal fibres which then present themselves. It is
24

278

FUNCTIONS OF THE NERVOUS SYSTEM.

then found, that these fibres may be traced upwards, chiefly into the Corpora
Striata, whence they radiate to the Hemispheres ; and downwards, chiefly into
the Anterior Pyramids. From this tract arise all the Motor nerves usually
reckoned as Cranial; as will be seen in the accompanying Figure. — The
Sensory tract is displayed, by opening the Medulla Oblongata on its posterior
aspect ; and then separating and turning aside the Restiform Columns, so as
to bring into view the Posterior Pyramids, which lie on the outside of the ca-
lamus scriptorius. On tracing their fibres upwards, it is found that they form
a part of the posterior layer of the Crura Cerebri, ultimately passing on to the
Thalami optici, whence they radiate to the Hemispheres. From this tract,
no motor nerves arise ; but on tracing it downwards into the Spinal Cord, it
is found that the sensory root of the fifth pair terminates in it, and that the

Fig. 141.

= o

Course of the Sensory tract according to Sir C. Bell. A. Pons Varolii ; B, B, sensory tract separated ;
c, union and decussatiou of posterior columns ; D, D, posterior roots of spinal nerves ; E, sensory roots of
fifth pair.

posterior roots of the spinal nerves are evidently connected with its continua-
tion. Also forming part of the posterior division of the crus cerebri, and se-
parated from the anterior by the transverse septum, is a layer of fibres which
ascends from the Olivary bodies, some of which terminate in the Corpora
Quadrigemina.

352. On tracing upwards the four divisions of the Medulla Oblongata, the
following are found to be their chief connections with the Brain. — 1. The
fibres of the Anterior Pyramids for the most part enter the Crura Cerebri,
passing through the Pons Varolii, and traversing the Optic Thalami (which,
it must be carefully borne in mind, have scarcely any real connection with
the Optic Nerves, or with the sense of sight) ; after which they diverge and
become intermingled with grey matter, thus forming the Corpora Striata, and
finally radiate to the convolutions of the Cerebrum. — 2. The fibres of the
Olivary body also pass into the Pons Varolii, and there divide into two bands ;

STRUCTURE AND CONNECTIONS OF MEDULLA OBLONGATA.

279

of which one proceeds upwards and forwards to join the Crus Cerebri,
thence to pass to the Optic Thalami ; whilst the other passes upwards and
backwards into the Corpora Qnadrigemina. — 3. Of the true Restiform bodies,
the fibres pass entirely into the Cerebellum. — 4. Finally, of the Posterior
Pyramids, the fibres pass directly onwards through the Crura Cerebri into
the Thalami, whence they radiate to the convolutions.

353. The downward course of these fibres into the Spinal Cord now re-
mains to be traced; and their arrangement is by no means a simple one. — 1.
The Anterior Pyramids decussate, as is well known, at their lower extremity ;

[Fig. 142.

Analytical diagram of the encephalon— in a vertical section. (After Mayo.)

i. Spinal cord. r. Restiform bodies passing to, c the cerebellum, d. Corpus dentatum of the cerebel-
lum, o. Olivary body. /. Columns continuous with the olivary bodies and central part of the medulla
oblongata, and ascending to the tubercular quadrigemina and optic thalami. p. Anterior pyramids, v.
Pons Varolii. n, b. Tubercular quadrigemina. g. Geniculate body of the optic thalamus. t. Pro-
cessus cerebelli ad testes. a. Anterior lobe of the brain, q. Posterior lobe of the brain.]

the principal part (but not the whole) of the fibres on each side, passing over
to the other. The decussating fibres pass backwards as well as downwards,
and enter, not the anterior column of the spinal cord, (as commonly stated,)
but the lateral column. The smaller bundle of fibres, which do not decus-
sate, passes downwards, along with those of the olivary bodies, to form the
anterior column. — 2. The fibres descending from the Olivary bodies converge

280 FUNCTIONS OF THE NERVOUS SYSTEM.

as those of the pyramids pass backwards from between them, until they meet
on the median line, forming the greater part of the anterior column. — 3. The
fibres of the Restiform, or Cerebellar columns, — -which, like those of the
Olivary columns, do not decussate, mostly pass downwards into the posterior
columns ; but a band (which has been termed, from its curved aspect, the
arciform layer) passes forwards into the anterior columns : and another
small fasciculus enters the lateral columns. — 4. The fibres of the Posterior
Pyramids are stated by Sir C. Bell to decussate like those of the anterior;
they pass down chiefly into the posterior part of the lateral column, forming
part also of the posterior.

354. The following tabular view may assist, better than any delineations
could do, in the comprehension of this very intricate piece of Anatomy; the
knowledge of which can be readily applied to the explanation of many curious
pathological phenomena, and cannot but assist in the elucidation of others,
whose rationale is as yet obscure.

SPINAL CORD. MEDULLA OBLONGATA. BRATS'.

( Arciform fibres of Cerebellar Columns . . ) Cerebellum
Anterior Column •? Olivary Columns . . . . . . $ Corpora Quadrigeinina

( Non-decussating portion of Ant. Pyramids • ? /-. Ci • .

; T^. . l ~ . . , > Corpora otriata

TV/T-JJI r< i S Decussating portion of Ant. Pyramids . . \

Middle Column < r -j , o'i • ^\

{ Post. Pyramidal Columns (decussating?) . 1 . .

PosteriorColumn \ P°rti°n °f Post' Pyamids (non-decussating?) . \

\ Restiform Columns Cerebellum

355. The Medulla Oblongata is not to be viewed, however, solely as a series
of connecting bands or commissures, between the Brain and Spinal Cord; for
it contains vesicular matter of its own, in virtue of which it serves as a gan-
glionic centre to nerves that are specially connected with it. The vesicular
matter is partly found in a situation corresponding to that which it occupies
in the spinal cord ; and it forms a tract, which is continuous above with the
grey nucleus of the Corpora Quadrigemina, and below with that of the Spinal
Cord ; and which is opened out to view (as it were) on the floor of the fourth
ventricle, forming the calamus scriptorius. Besides this central portion,
there are other outlying masses, which are continuous with it. Thus the
bulk of the Olivary body is principally due to the presence of a ganglionic
mass in its interior ; inclosed in the fibres of which the olivary column is
composed, and which, for the most part, pass over and around it without en-
tering it. This mass consists of a layer of grey matter, spread in a thin pli-
cated stratum over a centre of white substance, and altogether forming what
is known as the corpus dentatum. There is a considerable amount of ve-
sicular substance in the Restiform bodies also ; and this is continuous with
the grey matter forming the posterior cornua in the Spinal Cord.

356. We have now to inquire into the character of the ganglionic masses,
which form, with the Medulla Oblongata, the Encephalon of Vertebrated ani-
mals. We should be liable to form a very erroneous conception of the rela-
tive importance, and of the real nature, of these, if we were to study them
only in the Brain of Man and of the higher animals ; for the great develop-
ment of their Cerebrum and Cerebellum throws into the shade (so to speak)
certain other ganglionic centres, which constitute yet more essential parts of
the nervous apparatus. It is one of the most interesting results of the com-
parison of the Human Brain with that of the lower tribes of Vertcbrata, that
the great change in the relative proportions of the parts, which we encounter
in the latter, makes evident the real nature and importance of what would
otherwise have been considered as subordinate appendages: whilst, at the
same time, they afford us the connecting links, by which we are enabled
to trace the real analogies of the different parts of the Encephalon with the
ganglionic masses which represent it among Invertebratcd animals.

ENCEPHALON OF FISHES.

281

357. Commencing with FISHES, we find a series of four distinct ganglionic
masses, arranged in a line which is nearly continuous, from behind forwards,
with that of the Spinal Cord; of these, the posterior is usually single, and
on the median plane, whilst the others are in pairs. The posterior, from its
position and connections, is evidently to be regarded in the light of a Cere-
bellum ; and it bears a much larger proportion to the rest, in this class, than
in any other. The pair in front of this are not the hemispheres of the Ce-
rebrum, as their large size in some instances (the Cod for instance) might
lead us to suppose; but they are immediately connected with the Optic nerve,
which, in fact, terminates in them, and are therefore to be considered (like the
chief part of the cephalic masses of Invertebrated animals) as Optic Ganglia.
In front of these are the Cerebral Hemispheres, which are small, generally
destitute of convolutions, and possess no ventricle in their interior, — except
in the Sharks and Rays, in which they are much more highly developed than
in the Osseous Fishes. Anterior to these is another pair of ganglionic en-
largements, from which the Olfactory nerves arise ; and these are, therefore,
correctly designated as the Olfactive tubercles or ganglia. In some instances,
these ganglia are not immediately seated upon the prolonged spinal cord, but
are connected with it by long peduncles ; this is the case in the Sharks ; and
we are thus led to perceive the real nature of the portion of the trunk of the
Olfactory nerve in Man, which lies within the cranium, and of its bulbous
expansion on the Ethmoid bone. Besides these principal ganglionic enlarge-
ments, there are often smaller ones, with which other nerves are connected.
Thus, in the Shark, we find a pair of tubercles of considerable size, at the
origin of the Trifacial nerves ; and another pair, in most Fishes, at the roots
of the Vagi. In some instances, too, distinct Auditory ganglia present them-
selves ; as in the Carp.

Pike.

Cod.

Fig. 143.

Fox-shark.

Brains of Fishes. A, olfactive lobes or ganglia; B, cerebral hemispheres; c, optic lobes; D, cerebel-
lum ; ol, olfactory nerve ; op, optic nerve ; pa, patheticus ; mo, motor oculi ; ab, abducens ; tri, trifacial ;
fa, facial; vag, vagus ; tt, tubercles or ganglia of the trifacial ; tc, tubercles of the vagus.

358. The Optic Lobes of Fishes have no analogy whatever with the Tha-
lami optici of Mammalia ; the connection of which, with the Optic nerves, is

24*

282

FUNCTIONS OF THE NERVOUS SYSTEM.

Fig. 144.

very slight. They are rather to be compared with the Tubercula Quadri-
gemina, which are the real ganglia of the Optic nerve. Their analogy is not
so complete, however, to these bodies in the fully formed Brain of Man, as
it is to certain parts which occupy their place at an earlier period. The Third
Ventricle, which is quite distinct from the Corpora Quadrigemina, is hollowed
out, as it were, from the floor of the Optic Lobes of Fishes; and the Anterior
Commissure bounds its front; hence these must be considered as analogous
to the parts surrounding the Third Ventricle, as well as to the Corpora Quad-
rigemina. This is made evident by the fact, observed by Miiller, that, in the
Lamprey, there is a distinct Lobe of the third ventricle, replacing the Optic
Lobes of other Fishes, and partly giving origin to the optic nerves ; and a
separate vesicle, analogous to the Corpora Quadrigemina. With this condition,
the early state of the Brain in the embryo of the Bird and Mammiferous ani-
mal, and even in Man himself, bears a very close correspondence. The En-
cephalon consists at this time of a series of vesicles, arranged in a line with

each other, of which those that represent
the Cerebrum are the smallest, whilst that
which represents the Cerebellum is the
largest. The latter, as in Fishes, is single,
covering the fourth ventricle on the dorsal
surface of the Medulla Oblongata. Ante-
rior to this, is the single vesicle of the
Corpora Quadrigemina, from which the
Optic nerve chiefly arises; this has in its
interior a cavity, the ventricle of Sylvius,
which exists even in the adult Bird, where
the Corpora Quadrigemina are pushed, as
it were, from each other by the increased
development of the Cerebral hemispheres.
In front of this is the vesicle of the Third
Ventricle, which contains also the Thala-
mi; as development proceeds, this, like
the preceding, is covered by the enlarged
hemispheres ; whilst its roof becomes
cleft anteriorly on the median line, so as
to form the anterior entrance to the cavity.
Still more anteriorly is the double vesicle,
which represents the hemispheres of the
Cerebrum ; this has a cavity on each side, the floor of which is formed by the
corpora striata. The cavity of the cerebral vesicles has at first no opening,
except into that of the third ventricle; at a later period is formed that fissure
on the inferior and posterior side, which (under the name of the fissure of
Sylvius)enables the membranes enveloping the brain to be reflected into the
lateral ventricles.

359. Thus it will be seen that the real analogy between the brain of the
Human foetus, and that of the adult Fish, is not so close as, from the resem-
blance in their external form, might have been supposed. In the small pro-
portion which the Cerebral Hemispheres bear to the other parts, there is evi-
dently a very close correspondence ; and this extends also to the general
simplicity of their structure, the absence of convolutions, and the deficiency of
commissures. But there is a much nearer analogy between the foetal brain
of the Fish, and \\icfoetal brain of the Mammal ; indeed, at the earliest period
of their formation, they could not be distinguished ; during their advance to the
permanent condition, however, each undergoes changes, which are so much more
decided in the higher animals than in the lower, that in the latter there seems
but little departure from the fcetal condition, whilst in the former the condition

Human Embryo of sixth week, enlarg-
ed about three limes; a, vesicle of corpora
cjuadrigemina ; 6, vesicle of cerebral hemi-
spheres; c, vesicle of thalami optici and
third ventricle ; d, vesicle for cerebellum
and medulla oblongata; e, auditory vesicle ;
f, olfactory fossa ; h, liver ; ** caudal extre-
mity.

ENCEPHALON OF REPTILES AND BIRDS.

283

appears entirely changed. Hence it is not correct to assert, as is frequently
done, — that the Brain, or any other organ, in the higher animals, passes
through a series of forms, which are parallel to the permanent forms of the
same organ in different parts of the animal scale ; since the fact is rather, that
the more nearly all are traced back to their first origin, the closer will their
conformity be found to be ; the subsequent development of each taking place
not only in various degrees, but in different modes or directions ; so that the
resemblances presented by the higher, at different epochs of their evolution,
to the permanent conditions of the lower, are often far from being complete.*
This we have seen to be the case in the present instance ; the vesicle of the
Corpora Quadrigemina, and that of the third Ventricle, uniting to form the
Optic Lobes of Fishes, whilst in the higher Vertebrata they remain distinct ;
so that there is no single part, with which the Optic Lobes can be properly
compared, either in the foetal or perfect state of the Human Brain.

360. The Brain of REPTILES does not show any considerable advance in
its general structure above that of Fishes; but the Cerebral Hemispheres are
usually much larger in proportion to the Optic lobes ; whilst the Cerebellum
is smaller. The very low development of the Cerebellum is especially seen
in the Frog (Fig. 132), in which it is so small as not even to cover-in the
Fourth Ventricle; but it is common to nearly the whole group. The defi-
ciency in commissures still exists to a great extent. The anterior Commissure
in front of the third ventricle, is the only uniting band which can be distinctly
traced in Fishes ; and Reptiles have, in addition to this, a layer of uniting
fibres which may be compared to the Fornix ; but as yet, there is no vestige
of a true Corpus Callosum, or great transverse commissure of the hemi-
spheres. The distinction between the tubercula quadrigemina, and the parts
inclosing the third ventricle, is more obvious than in Fishes ; in fact the Optic
ganglia of Reptiles correspond pretty closely with the Vesicle of the tubercula
quadrigemina in the brain of the fcetal Mammal.

Fig. 145.

Fig. 146.

Brain of Turtle ; A. olfactive
ganglia; B, cerebral hemi-
spheres: c, optic ganglia: r,
cerebellum.

Brain of Buzzard ; the olfactive ganglia
are concealed beneath B, the hemispheres;
c, optic ganglia; B, cerebellum; g, pineal
gland

* For a fuller examination of this interesting question, see General and Comparative Phy-
siology, § 244.

284

FUNCTIONS OF THE NERVOUS SYSTEM.

361. This is still more evident in BIRDS, in whose Encephalon the Tuber-
cula Quadrigemina or Optic Ganglia, and the Thalami with their included
ventricle, are obviously very distinct parts. The Cerebral Hemispheres
attain a great increase of development, and arch backwards, so as partly to
cover the Optic ganglia ; and these are separated from one another, and thrown
to either side. The Cerebellum also is much increased in size, proportion-
ably to the Medulla Oblongata and its ganglia ; and it is sometimes marked
with transverse lines, which indicate the intermixture of grey and white mat-
ter in its substance ; there is as yet, however, no appearance of a division
into hemispheres. On drawing apart the hemispheres of the Cerebrum, the
Corpora Striata, Optic Thalami, and Tubercula Quadrigemina or Optic Gan-
glia, are seen beneath them ; the size of the last still bears a considerable pro-
portion to that of the whole Encephalon. The Optic Ganglia are still hollow,
as they are in the embryo condition of Man. Indeed the Brain of the Human
foetus about the twelfth week will bear comparison, in many respects, with
that of the Bird. The Cerebral hemispheres, much increased in size, and
arching back over the Thalami and Optic ganglia, but destitute of convolutions,
and imperfectly connected by commissures, — the large cavity still existing in

Fig. 147.

Fig. 148.

cs..

t/ivl

Brain of Human Embryo at twelfth week. A, seen from behind ; B, side view; c, sectional view; a,
corpora quadrigemina; bb, hemispheres; d, cerebellum; e, medulla oblongata; ./, optic thalamus; g-,
floor of third ventricle; I, olfactory nerve.

the Optic ganglia, and freely communicating with the third ventricle, — and
the imperfect evolution of the Cerebellum, — make the correspondence in the
general condition of the two very considerable.

362. The Brain of the lowest MAMMALIA presents but a slight advance

upon that of Birds, in regard both to the rela-
tive proportions of its parts, and to their degree
of development. Thus, in the Marsupialia, the
Cerebral hemispheres exhibit no convolutions ;
and the great transverse commissure. — the
Corpus Callosum, — is deficient. There is gra-
dually to be noticed, however, in ascending the
scale, a backward prolongation of the Cerebral
hemispheres ; so that first the Optic ganglia,
and then the Cerebellum, are covered by them.
The latter partly shows itself, however, in all
but the Quadrumana, when we look at the
brain from above downwards; in the Rabbit,
which is in this respect among the lowest of
the true Viviparous Mammalia, nearly the
whole of the Cerebellum is uncovered. In
proportion to the increase of the Cerebral
hemispheres, there is a diminution in the size
of the ganglia immediately connected with the
organs of sense ; and this in comparison, not
only with the rest of the Encephalon, but even

Brain of Squirrel, laid open ; the
hemispheres, B, being drawn to either
side to show the subjacent parts;— c,
the optic lobes ; D, cerebellum ; thai,
thalamus opticus; cs, corpus striatum.

ENCEPHALON OF MAMMALIA.

285

with the Spinal Cord ; so that in Man the Tubercula Quadrigemina are abso-
lutely smaller than they are in many animals of far inferior size. The inter-

Fiz. 149.

feSB**

• ' F*™*\/YIf

•••J^CL

ff Mf ^

VU,

Upper and under surface of Brain of Rabbit. A, B, r, as before ; ol, olfactive lobes ; op, optic nerve ;
mo, motor oculi ; cm, corpora mamillaria; cc, crus cerebri ; pv, pons varolii ; pa, patheticus ; tri, trifa-
cial ; ab, abducens; fac, facial ; aw, auditory ; rag-, vagus ; s, spinal accessory ; hyp, hypoglossal.

nal structure of the hemispheres becomes more complex, in the same propor-
tion as their size and the depth of the convolutions increase; and in Man all
these conditions present themselves in a far higher degree, than in any other
animal. In fact it is only among the Ruminantia, Pachydermata, Carnivora,
and Quadrumana, that regular convolutions can be said to exist. The cor-
respondence between the bulbous expansion of the Olfactive Nerves in Mam-
malia, and the Olfactive lobes of the lower Vertebrata, is made evident by the
presence, in both instances, of a cavity which communicates with the lateral
ventricle on each side ; it is in Man only that this cavity is wanting. The
external form of the Corpora Quadrigemina of Mammalia, differs from that of
the Optic ganglia of Birds, owing to the division of the former into anterior
and posterior eminences, (the nates and testes;) and there is also an internal
difference, occasioned by the contraction of the cavity or ventricle, which now
only remains as the Aqueduct of Sylvius. The Cerebellum is chiefly re-
markable for the development of its lateral parts or hemispheres ; the central
portion, sometimes called the vermiform process, is relatively less developed
than in the lower Vertebrata, in which it forms the whole of the organ.

4. General Functions of the Spinal Cord. — Reflex Action.

363. The functions of the Nervous System in Vertebrated Animals are so
complex in their nature, and our means of analyzing them are so imperfect,
that the inquiry is confessedly one of the greatest difficulty, and needs all the
light which can be thrown upon it from any source. The great accession to
our knowledge of them, which has been made within the last few years,
chiefly by the labours of Sir C. Bell, and Dr. M. Hall, has so far changed
the aspect of this department of Physiological Science, as to render it neces-
sary for those who had previously studied it, to begin de novo. This is espe-
cially the case in regard to the actions dependent on the Spinal Cord ; which
it seems desirable to consider in the first instance, in order that it may be

286 FUNCTIONS OF THE NERVOUS SYSTEM.

clearly defined what the Brain does not do. By many, even in recent times,
the Spinal Cord has been considered as a mere appendage to the Brain ; but
the phenomena of its independent action render such an idea quite inadmis-
sible. These phenomena have been especially pointed out by Dr. M. Hall;
and it is mainly owing to his arguments, that Physiologists are now for the
most part agreed in the general fact, — that the Spinal Cord constitutes a dis-
tinct centre, or rather a collection of centres, of nervous influence, and that
its operations are carried on through the nervous trunks with which it is con-
nected. It is further generally admitted that its functions are independent of
the will; and that they are in effect frequently opposed to those of the Brain,
which operates on the muscles, either by a volitional, or by an emotional
impulse. And lastly, its actions are always (except when excited by a physi-
cal irritation directly applied to itself) entirely of a reflex character ; that is
to say, the motor impulses which originate in it are not spontaneous, but re-
sult from the stimulus of impressions, conveyed to it by the afferent trunks, and
operating upon it, to use the expression of Prochaska, according to certain
"peculiar laws written, as it were, by nature on its medullary pulp." It is
not, however, universally admitted that these actions are independent of sen-
sation; and some eminent physiologists, among whom may be named Dr.
Alison, still hold that the intervention of sensation is necessary — in the case
at least, of the ordinary associated movements, which have definite ends in
view, and follow one another in regular succession, as those of Respiration, —
for an impression to give rise to that organic change in the Spinal Cord, which
shall terminate in a muscular motion.* It will be desirable, therefore, to con-
sider the evidence upon which the statement rests, that reflex actions are in-
dependent of sensation, though ordinarily accompanied by it.

364. In the first place, then, it has long been well known that, in the
Human being, the Spinal Cord does not by itself possess, in the remotest
degree, the power of communicating sensory impressions to the mind; since,
when its lower portion has been severed from the brain by injury or disease,
there is complete anaesthesia of all the parts of the body, which derive their
nerves exclusively from it. Hence it might be inferred, that throughout the
Vertebrated classes, the spinal cord is equally destitute of sensibility ; and
that any movements produced by stimuli acting through it, are the results of a
physical, and not of a sensorial change. This inference, however, has been
disputed ; and, if unsupported by other evidence, it would not, perhaps, be
entitled to rank as an ascertained truth. The very performance, by decapi-
tated animals of inferior tribes, of actions which had not been witnessed in
Man under similar circumstances, has been held to indicate, that the spinal
cord in them has an endowment which his does not possess. The possibility
of such an explanation — however unconformable to that analogy throughout
organized nature, which the more it is studied, the more invariably is found
to guide to truth — could not be disproved. Whatever experiments on decapi-
tated animals were appealed to, in support of the doctrine that the brain is
the only seat of sensibility, could be met by a simple denial that the spinal
cord is everywhere as destitute of that endowment, as it appears to be in Man.
The cases of profound sleep and apoplexy might be cited, as examples of
reflex action without consciousness ; and these might be met by the assertion,
that in such conditions sensations are felt, though they are not remembered.
It is difficult, however, to apply such an explanation to the case of anence-

* See Outlines of Physiology, 3d edit., 211. By many of the German Physiologists, also,
it is maintained that Sensation is a necessary link in the chain of reflex actions ; but as they
employ the term sensation in a sense which does not involve consciousness, it is obvious that
their dissent from Dr. Hall's views is chiefly verbal.

FUNCTIONS OF THE SPINAL CORD. REFLEX ACTION. 287

phalous human infants (in which all the ordinary reflex actions have been ex-
hibited, with an entire absence of brain), without supposing that the Medulla
Oblonguta is the seat of a sensibility which we know that the lower part of
the Spinal Cord does not possess ; and of this there is no evidence whatever.

365. Experiments on the lower animals, then, and observation of the phe-
nomena manifested by apoplectic patients and anencephalous infants, might
lead to the conclusion, that the Spinal Cord does not possess a sensibility,
and that its reflex actions are independent of sensation. At this conclusion,
Prochaska, Sir G. Blane, Flourens, and other physiologists, had arrived ; but
it was not until special attention was directed to the subject by Dr. M. Hall,
that facts were obtained by which a positive statement of it could be supported.
For the question might have been continually asked, — If the spinal cord in
Man is precisely analogous in function to that of the lower Vertebrata, why
are not its reflex phenomena manifested, when a portion of it is severed from
the rest by disease or injury ? The answer to this question is twofold. In
the first place, simple division of the cord with a sharp instrument leaves the
separated portion in a state of much more complete integrity, and therefore
in a state much more fit for the performance of its peculiar functions, than it
ordinarily is after disease or violent injury ; and as the former method of di-
vision is one with which the Physiologist is not likely to meet in Man as a
result of accident, and which he cannot experimentally put in practice, the
cases in which reflex actions are manifested, are likely to be comparatively few.
But, secondly, anumberof such instances have now been accumulated, sufficient
to prove that the occurrence is by no means so rare as might have been sup-
posed; and that nothing is required but patient observation, to throw great
light on this interesting question, from the phenomena of disease. A most
valuable collection of such cases, occurring within his own experience, has
been published by Dr. W. Budd ;* and the leading facts observed by him will
be now enumerated.

366. In the first case, paraplegia was the result of angular distortion of the
spine in the dorsal region. The sensibility of the lower extremities was ex-
tremely feeble, and the power of voluntary motion was almost entirely lost.
" When, however, any part of skin is pinched or pricked, the limb that is
thus acted on jumps with great vivacity; the toes are retracted towards the
instep, the foot is raised on the heel, and the knee so flexed as to raise it off
the bed ; the limb is maintained in this state of tension for several seconds
after the withdrawal of the stimulus, and then becomes suddenly relaxed."
" In general, while one leg was convulsed, its fellow remained quiet, unless
stimulus was applied to both at once." "In these instances, the pricking and
pinching were perceived by the patient; but much more violent contractions
are excited by a stimulus, of whose presence he is unconscious. When a
feather is passed lightly over the skin, in the hollow of the instep, as if to
tickle, convulsions occur in the corresponding limb, much more vigorous than
those induced by pinching or pricking; they succeed one another in a rapid
series of jerks, which are repeated as long as the stimulus is maintained."
"When any part of the limb is irritated in the same way, the convulsions
which ensue are very feeble, and much less powerful than those induced by
pricking or pinching." " Convulsions, identical with those already described,
are at all times excited by the acts of defecation and micturition. At these
times, the convulsions are much more vigorous than under any other circum-
stances, insomuch that the patient has been obliged to resort to mechanical
means to secure his person while engaged in these acts. During the act of
expulsion, the convulsions succeed one another rapidly, the urine is discharged

* Medico-Chirurgical Transactions, vol. xxii.

288 FUNCTIONS OF THE NERVOUS SYSTEM.

in interrupted jets, and the passage of the faeces suffers a like interruption."
The convulsions are more vigorous, the greater the accumulation of urine ;
and involuntary contractions occur whenever the bladder is distended, and
also when the desire to relieve the rectum is manifested. "In all these cir-
cumstances, the convulsions are perfectly involuntary ; and he is unable, by
any effort of the will, to control or moderate them." The patient subse-
quently regained, in a gradual manner, both the sensibility of the lower ex-
tremities, and voluntary power over them ; and as voluntary power increased,
the susceptibility to involuntary movements, and the extent and power of these,
diminished.

367. This case, then, exhibits an increased tendency to perform reflex actions,
when the control of the brain was removed; and it also shows that a slight
impression upon the surface, of which the patient was not conscious, was
more efficacious in exciting reflex movements, than were others that more
powerfully affected the sensory organs. This is constantly observed in ex-
periments upon the lower animals ; and it harmonizes, also, with the important
fact, that, when the trunk of an afferent nerve is pinched, pricked, or other-
wise irritated, the reflex function will not be nearly so strongly excited, as
when a gentler impression is made on a surface supplied by the branches of
this nerve. The former produces pain, whilst the latter does not; the amount
of sensation, therefore, does not at all correspond with the intensity of reflex
action, but rather bears a converse relation to it. Mr. Grainger found, that
he could remove the entire hind leg of a Salamander with the scissors, with-
out the creature moving, or giving any expression of suffering, if the spinal
cord had been divided : yet that, by irritation of the foot, especially by heat,
in an animal similarly circumstanced, violent convulsive actions in the leg and
tail were excited. — It should be added that, in the foregoing case, the nutrition
of the lower extremities was not impaired, as in most cases of paraplegia.
The rationale of this phenomenon, which is to be constantly observed when
the reflex actions of the part remain entire, will be hereafter noticed (Chap.
VII.).

368. In another case, the paralysis was more extensive, having been pro-
duced by an injury (resulting from a fall into the hold of a vessel) at the lower
part of the neck. There was at first total loss of voluntary power over the
lower extremities, trunk, and hands ; slight remaining voluntary power in the
wrists, rather more in the elbows, and still more in the shoulders. The
intercostal muscles did not participate in the movements of respiration. The
sensibility of the hands and feet was greatly impaired. There were retention
of urine, and involuntary evacuation of the faeces. Recovery took place very
gradually; and during its progress, several remarkable phenomena of reflex
action were observed. At first, tickling one sole excited to movement that
limb only which was acted upon ; afterwards, tickling either sole excited both
legs, and, on the 26th day, not only the lower extremities, but the trunk and
other extremities also. Irritating the soles, by tickling or otherwise, was at
first the only method, and always the most efficient one, by which convulsions
could be excited. From the 26th to the 69th day, involuntary movements in
all the palsied parts continued powerful and extensive, and were excited by
the following causes: — In the lower extremities only, by the passage of flatus
from the bowels, or by the contact of a cold urinal with the penis; convulsions
in the upper extremities and trunk, attended with sighing, by plucking the
hair of the pubes. On the 41st day, a hot plate of metal was applied to the
soles, and found a more powerful excitor of movement than any before tried.
The movements continued as long as the hot plate was kept applied; but the
same plate, at the common temperature, excited no movements after the first
contact. The contact was distinctly felt by the patient; but no sensation of

FUNCTIONS OF THE SPINAL CORD. REFLEX ACTION. 289

heat was perceived by him, although the plate was applied hot enough to
cause vesication. At three different intervals, the patient took one-eignth of
a grain of strychnia three times a day. Great increase of susceptibility to
involuntary movements immediately followed, and they were excited by the
slightest causes. No convulsions of the upper extremities could ever be pro-
duced, however, by irritating their integument; though, under the influence of
strychnia, pulling the hair of the head, or tickling the chin, would occasion
violent spasmodic actions in them. Spontaneous convulsions of the palsied
parts, which occurred at other times, were more frequent and more powerful
after the use of strychnia. On the first return of voluntary power, the
patient was enabled to restrain in some measure the excited movements ; but
this required a distinct effort of the will ; and the first attempts to walk were
curiously affected, by the persistence of the susceptibility to excited involun-
tary movements. When he first attempted to stand, the knees immediately
became forcibly bent under him ; this action of the legs being excited by
contact of the soles with the ground. On the 95th day this effect did not
take place, until the patient had made a few steps ; the legs then had a
tendency to bend up, a movement which he counteracted by rubbing the
surface of the belly: this rubbing excited the extensors to action, and the legs
became extended with a jerk. A few more steps were then made; the
manoeuvre repeated, and so on. This susceptibility to involuntary movements
from impressions on the soles, gradually diminished ; and on the 141st day,
the patient was able to walk about, supporting himself on the back of a chair
which he pushed before him ; but his gait was unsteady, and much resembled
that of chorea. Sensation improved very slowly: it was on the 53d day
that he first slightly perceived the heat of the metal plate.

369. This important case suggests many interesting reflections. Common
sensation was not so completely abolished as in the former instance; but of
the peculiar kind of impression, which was found most efficacious in exciting
reflex movements, no consciousness whatever was experienced. Not less
interesting was the circumstance, that convulsions could be readily excited by
impressions on surfaces above the seat of injury; as, by pulling the hair of
the scalp, a sudden noise, and so on. This proves two important points:
first, that a lesion of the cord may be such, as to intercept the transmission of
voluntary influence, and yet may allow the transmission of that reflected from,
incident nerves. Secondly, that all influences from impressions on incident
nerves are'diffused through the cord; for, in the instance adduced, the reflected
influence was undoubtedly not made to deviate into the cord by the morbid
condition of that organ, but followed its natural course of diffusion, being
rendered manifest in this case by the convulsions which were excited, in con-
sequence of increased activity of the motor function of the cord. It is further
interesting to remark, that, in the foregoing case, the reflex actions were very
feeble during the first seven days, in comparison with their subsequent energy;
being limited to slight movements of the feet, which could not always be
excited by tickling the soles. In another case of very similar character, it was
three days after the accident, before any reflex actions could be produced. It
is evident, then, that the spinal cord must have been in a state of concussion,
which prevented the manifestation of its peculiar functions, so long as this
effect lasted; and it is easy, therefore, to perceive, that a still more severe
shock might permanently destroy its power, so as to prevent the exhibition of
any of the phenomena of reflex action.

370. It seems well established, then, by such cases, that the Spinal Cord,

or small segments of it, may serve in Man as the centre of very energetic

reflex actions ; when the voluntary power exercised through the Brain, over

the muscular system, is suspended or destroyed. And it is further evident,

25

290 FUNCTIONS OF THE NERVOUS SYSTEM.

that these movements are produced by a mere physical change in the nervous
centres; the consciousness of the individual not being affected in their per-
formance, and sensation having therefore no necessary participation in them.
As the movements witnessed in the lower animals, under the same circum-
stances, are altogether of a similar character, there seems no good reason to
attribute to their Spinal Cord an attribute, of which it is certainly destitute in
Man. There is no essential difference, either in structure, or in the nature of
the actions performed by them, between the Spinal Cord and the Medulla
Oblongata, which can warrant us in assigning to the latter a function that the
former does not possess : and if the reflexions of the Spinal Cord do not
involve sensation, there is good reason for concluding, that this change is not
a necessary element in those of the Medulla Oblongata. It is perfectly true,
that it usually accompanies in us the greater number of actions, to which that
division of the centre is subservient; for example, those of respiration and
deglutition : and it is scarcely possible for such an accident to occur in the
Human being, as the separation of the Medulla Oblongata from the brain,
without the destruction of the independent functions of both. It is not likely
that we can ever have the power of ascertaining, by the testimony of a patient
so affected, that the Respiratory movements are performed without the neces-
sary intervention of sensation ; as we have been able to do in regard to other
reflex movements. But as the general fact is, that there is no positive ground
whatever for regarding any part of the Spinal Cord as a serisorium independent
of the brain, and that the Respiratory movements certainly correspond in all
their conditions with the actions denominated reflex, — there would seem no
good reason for maintaining that sensation is an element in their production,
whilst it is admitted to be not essential in the case of the less regular con-
vulsive actions already described. The character of adaptiveness to a designed
end, in regard to their combination and succession, which the movements of
respiration and deglutition exhibit, has been shown to be no proof of their
dependence on sensation.

371. The question has been often put to those who advocate this view, —
why the sensation should be so constantly associated with these changes, if
not essential to produce the motion? An objection might fairly be made to
any reasoning from final causes, in a question of facts; but the inquiry may
be easily answered. In many instances the production of sensations is the
stimulus necessary for the excitement of other actions, which are required
for the continued maintenance of those in question. This may be rendered
more comprehensible by a simple illustration. — A cistern filled with water
may be speedily emptied by a cock occasionally opened at the bottom ; but,
if it communicate with a reservoir, by means of a valve opened by a ball
floating on the surface of the water it contains, it may be kept constantly full.
The lower cock is opened, and the water flows out; and, in consequence of
the lowering of the surface thus produced, the floating valve above is opened,
and the cistern is refilled from the reservoir. Now here the action of the ball-
cock at the top is not essential to the flow of water at the bottom, but is
rather consecutive upon it. — Just so is it with regard to those movements of
Animals, which are concerned in the ingestion of their food. The muscular
contractions required to propel it along the alimentary canal, from the stomach
downwards, are provided for, without even the intervention of the nervous
system. To bring it within reach of these, a muscular apparatus is provided,
by which anything that comes within its grasp is conveyed downwards,
through a reflex operation, originating in the impression made upon the sur-
face of the pharynx. Now this action, in the ordinary condition, may be
considered as attended with sensation, in order that the Animal may be called
upon to execute those other movements, which will bring food within the

FUNCTIONS OF THE SPINAL CORD. REFLEX ACTION. 291

reach of the apparatus of deglutition. The Polype is dependent for its sup-
plies of aliment, upon what the currents in the surrounding fluid, or other
chances, bring into its neighbourhood; but anything which touches its ten-
tacula, is entrapped and conveyed into its stomach. The anencephalous
Infant, again, can swallow, and even suck; but it can execute no other move-
ments adapted to obtain the supply of food continually necessary for mainte-
nance, because it has not a mind which sensations could awake into activity.

372. The sensation connected with reflex actions has not only this import-
ant end, but it frequently contributes to enjoyment, as in suction and ejaculatio
seminis. Now there is evidence that the latter of these processes, involving
though it does the combined action of a number of muscles, and dependent
as it seems upon sensation of a very peculiar kind, may take place without
consciousness on the part of the individual. Brachet mentions a case of this
kind in the Human subject, in which the patient's own testimony could be
adduced ; and he ascertained that emission could be produced in dogs, in
which the spinal cord had been divided in the back, and in which, therefore,
it can scarcely be doubted that the sensibility of the genital organs was de-
stroyed. Such cases, it might be thought, are sufficient to prove, that the
Reflex power, operating independently of sensation, is not confined to such
irregular convulsive movements as are seen in Man after disease or injury;
but is exercised in producing the regular combined actions which are neces-
sary for the maintenance of the organic functions. The sensation accompa-
nying these actions, moreover, frequently affords premonition of danger, or
gives excitement to supplementary actions destined to remove it, as in the
case of respiration; for where anything interferes with the due discharge of
the function, the uneasy sensation that ensues occasions unwonted move-
ments, which are more or less adapted to remove the impediment, in propor-
tion as they are guided by judgment as well as by consciousness. Again,
sensation often gives warning against inconvenience, as in the excretory func-
tions; and here it is very evident, that its object is not only (if it be at all) to
excite the associated muscles necessary for the excretion, but actually to make
the Will set up the antagonizing action of the sphincters, as will be hereafter
explained (§ 391). There is one unequivocal case, in the ordinary condition
of the human body, of reflex action without sensation; this is the muscular
contraction, by which the food is propelled from the bottom of the pharynx
to the stomach. Unless the morsel be very bulky, so as to press on the sur-
rounding parts, or be very different in temperature from the surface it touches,
or have any peculiar irritating quality, we are not more conscious of its pre-
sence, whilst it is passing down the lower part of the oesophagus, than when
it is being propelled along the intestinal tube; and yet, as Dr. J. Reid's ex-
periments* have shown, this contraction is of a reflex character, not being
stimulated by direct contact, but requiring the completeness of the nervous
circle for its performance.

373. We shall now separately consider the chief operations, in which the
Spinal Cord and its system of nerves are usually concerned, in the ordinary
course of the vital actions of the Human body. Upon taking a general sur-
vey of these, it will be found that their principal function is, to supply the
conditions requisite for the maintenance of the various Organic processes.
Thus, the aeration of the blood, which takes place whenever that fluid is
placed in relation with the atmosphere, can only be carried on, by the regular
exchange of the small quantity of the gas contained in the lungs ; if this
cease, the circulation is soon brought to a stand, and loss of vitality of the
whole system speedily results. Hence this is the most constantly necessary

* Ediub. Med. and Surg. Journ., vol. xlix.

292 FUNCTIONS OF THE NERVOUS SYSTEM.

of all the actions of the Spinal Cord; and we find its maintenance, in spite
of accident or disease of the spine, remarkably provided for, in the location of
the centre of the respiratory movements, which occupies a position where it
receives the greatest possible amount of protection. The supply of the di-
gestive apparatus, again, is immediately dependent upon the Spinal system ;
and this, being another essential function, has its centre equally protected.
The outlets of the cavities are also controlled by the Spinal system; but this
control, although essential to the comfort of life, is less necessary to its main-
tenance ; and we find it dependent upon a portion of the Cord, which is
more liable to lose its powers by disease or injury. It is possible, as will
hereafter be shown, that several actions, which are at first voluntary, may be
effected, when so frequently performed as to ^become habitual, through the
medium of the Spinal system ; of this kind seem to be the movements of
locomotion, which are continued involuntarily, when the whole attention of
the mind is given to other objects, but which the Will can check at any time.
We shall commence our particular survey of the Reflex movements in Man,
with the consideration of those of Respiration, which are well adapted for
illustrating their general character.

374. Respiratory Movements. — The centre of these is the upper part of
the Medulla Oblongata; into this may be traced the excitor nerves, that con-
vey the stimulus on which the movements are dependent; and from it pro-
ceed, either directly or indirectly, the motor nerves by which they are carried
into effect. The chief Excitor of the respiratory movements is unquestion-
ably the Par Vagum. When this is divided on both sides, according to the
experiments of Dr. Reid,* the number of respiratory movements is considera-
bly diminished, usually about one-half. Now if this nerve excites the motions
of respiration by its powerful action in producing sensation, we should ex-
pect to find its trunk endowed with considerable sensibility, which is not the
case; for all experimenters agree in stating that, when its trunk is pinched or
pricked, the animal does not exhibit signs of pain nearly so acute, as when
the trunks of the ordinary spinal nerves, or of the fifth pair, are subjected to
similar treatment. It cannot be questioned, however, that its power as an
excitor of respiration is very great; since, besides the fact of the diminution
in the number of inspirations which occurs immediately on section of it,
irritation of its trunk in the neck is instantly followed by an act of inspira-
tion. It is evident that this power must arise from impressions made upon
its peripheral extremities. The impression is probably due to the presence
of venous blood in the capillaries of the lungs; or, as Dr. M. Hall thinks, to
the presence of carbonic acid in the air-cells. Either or both may be true. —
The Pneumogastric nerve, however, is not the only excitor of the respiratory
movements ; since, when the nerve is cut on each side, they still continue.
Dr. Reid has satisfactorily shown the statement of many experimenters, that
the inspirations are increased in frequency after this operation, to be erroneous ;
this idea having originated in their very prolonged and laborious character.
The removal of the Encephalon, also, diminishes the frequency of the respi-
ratory movements, whether it be performed before or after the section of the
Vagi. Dr. Reid found that, in a kitten of a day old, in which the inspira-
tions were 100 per minute, they fell to 40 when the Encephalon was re-
moved ; and on subsequently cutting the Pneumogas tries, the number of
inspirations instantly fell to between 3 and 4 in the minute, and continued so
for some time. Hence it appears that the respiratory movements are partly
dependent upon sensation, and a motor influence excited by it; and this may
also be learned from the prolonged and laborious character of the inspirations

* Edinb. Mecl. and Surg. Journ., vol. li.

REFLEX ACTIONS. RESPIRATORY MOVEMENTS. 293

during sleep or profound attention, when the influence of the Encephalon is
more or less suspended.

375. But why (it may be asked) do the movements continue, when the
Pneumogastrics have been divided, and the Encephalon has been removed ?
It is evident that there must be other exciters to the action of the respiratory
muscles. Amongst these, the nerves distributed to the general surface, and
particularly to the face, probably perform an important part; and in exciting
the first inspiration, the Fifth pair seems the principal agent. It has long
been a well-known fact, that the first inspiratory effort of the new-born infant
is most vigorously performed, when the cool external air comes into contact
with the face ; and that impressions on the general surface, such as a slap of
the hand on the nates, are often effectual in exciting the first inspiratory
movements, when they would not otherwise commence. Dr. M. Hall relates
an interesting case, in which the first inspiration was delayed, simply because
the face was protected by the bed-clothes from the atmosphere; and, on lift-
ing up these, the infant immediately breathed. Dr. M. Hall has recently
mentioned the important fact, that if the cerebrum be removed, and the pneu-
mogastrics be divided, in a young kitten, the number o*f acts of respiration
will be reduced to four in a minute; but by directing a stream of air on the
animal, or by irritating various parts of the general surface, we may excite
twenty or thirty acts of respiration within the same space of time. He
further remarks, that in the very young warm-blooded animal, as in the cold-
blooded animal, the phenomena of the excito-motor power are far more vividly
manifested, than in the older and the warm-blooded. In the very young
kitten, even when asphyxiated to insensibility, every touch, contact, or slight
blow, — every jar of the table, any sudden impression of the external air, or
that of a few drops of cold water, induces at once energetic reflex movements,
and acts of inspiration. This may be looked upon as Nature's provision for
the first establishment of the acts of inspiration in the new-born animal. —
But the influence of the nerves of the general system is by no means want-
ing in the adult; as the following experiment of Dr. J. Reid's demonstrates.
After dividing the pneumogastrics, and removing the cerebrum and cerebel-
lum, he divided the spinal cord high up in the neck, so as to cut off the com-
munication between the spinal nerves and the Medulla Oblongata ; and he
found that the frequency of the respiratory movements was still further
diminished, although they were not even then entirely suspended. — Every
one knows the fact, that the first plunge into cold water, the first descent of
the streams of the shower-bath, or even the dashing of a glass of cold water
in the face, will produce inspiratory efforts ; and this fact has many important
practical applications. Thus in the treatment of Asphyxia, whether congeni-
tal, or the result of narcotic poisoning, drowning, &c., the alternate applica-
tion of cold and heat is found to be one of the most efficacious means of
restoring the respiratory movements; and a paroxysm of hysteric laughter
may be cut short, by dashing a glass of cold water in the face. — It may be
surmised that the Sympathetic nerve, which derives many filaments from the
Cerebro-Spinal system, and which especially communicates with the Pneu-
mogastric nerves, is one of the excitors to this function; and this, perhaps,
not only through its ramifications in the lungs, which are considerable, but
also by its distribution on the systemic vessels; so that it may convey to the
Spinal Cord the impression of imperfectly-arterialized blood, circulating in
these, such as the Pneumogastric is believed to transmit from the lungs. It
will hereafter be shown, that an impression of a corresponding kind is more
probably the cause of the sense of Hunger and Thirst, than any which origi-
nates in the stomach alone (Chap. X., Sect. 1).

376. The Motor or Efferent nerves concerned in the function of Respira-

26*

294 FUNCTIONS OF THE NERVOUS SYSTEM.

tion, are those which Sir C. Bell has grouped together in his respiratory
system. The most important of these, the Phrenic, arises from the upper
part of the Spinal Cord; the Intercostals much lower down; whilst the Facial
nerve and the Spinal Accessory, to the latter of which, as will hereafter be
stated (§ 408), the motor powers of the par vagum are chiefly due, take their
origin in the Medulla Oblongata itself. But we must not decide upon the
connection of a particular nerve with a particular segment of the Spinal Cord,
simply because it diverges from it at that point. It has been shown that, in
the Mollusca, a nerve passing to, or proceeding from, one ganglion, frequently
passes through or over another which lies in its course ; and in the Articulata,
this is a still more constant occurrence. It is by no means improbable, then,
that the connection of the intercostal nerves is really in part with the grey
matter of the Medulla Oblongata; at any rate, such a connection has not been
disproved. The white columns of the Spinal Cord consist of fibres, which
bring the spinal nerves into connection, not only with the brain, but also with
other segments of the ganglionic portion of the cord ; being analogous in func-
tion, not merely to the distinct fibrous tract of the ventral column of the Arti-
culata, but also to the fibrous bands that connect the ganglia themselves. And
as the Medulla Oblongata, in Vertebrated animals, is the chief centre of the
actions of Respiration, it can scarcely be doubted that all the nerves concerned
in that function have a direct structural connection with it.

377. That the Respiratory movements, as ordinarily performed, are essen-
tially independent of the Will, appears not only from our own consciousness,
but also from cases of paralysis; in some of which, the power of the will over
the muscles has been lost, whilst the movements have been kept up by the
reflex action of the Medulla Oblongata or respiratory ganglion ; whilst in
others, some of the respiratory muscles have been motionless during ordinary
breathing, and yet have remained under the power of the will. Such cases
are mentioned by Sir C. Bell, in the Appendix to his work on the Nervous
System. That consciousness is not a necessary link in the chain of causes,
which produce the respiratory movements, we are enabled to judge from the
phenomena presented by the human being in sleep and coma, by anencephalous
foetuses, and by decapitated animals. Further, Dr. Ley* has put on record a
case, which confirms this particular inference, just in the same manner as the
cases already related confirm the general doctrine of the non-existence of sen-
sibility in the Spinal Cord. He had under his care a patient, in whom the
par vagum appeared to be diseased; the lungs suffered in the usual way in
consequence, and the patient had evidently laborious breathing; but he dis-
tinctly said that he felt no uneasiness in his chest. — The experience of every
one informs him, that Respiratory movements are partly under the control
and direction of the will, though frequently unrestrainable by it. In ordinary
circumstances, when the blood is being perfectly aerated, and there is a suffi-
cient amount of arterial blood in the system to carry on the functions of life
for a short time, we can suspend the respiratory actions during a few seconds
without any inconvenience. If, however, we endeavour to prolong the sus-
pension, the stimulus conveyed by the excitor nerves to the Medulla Oblon-
gata becomes too strong, and we cannot avoid making inspiratory efforts ; and
if the suspension be still further prolonged, the whole body becomes agitated
by movements, which are almost of a convulsive nature ; and no effort of the
will can then prevent the ingress of air.t It is easy to understand why, in

* On Laryngismus Stridulus, p. 417.

t It is asserted by M. Bourdon (Recherches sur le MeVanisme de la Respiration, p. 81),
that no person ever committed suicide, though many havo attempted to do so, by simply
holding the breath; the control of the will over the respiratory muscles not being suHieiently
great, to antagonize the stimulus of the " besoin de respirer," when this has become aggru-

REFLEX ACTIONS. RESPIRATORY MOVEMENTS. 295

the higher animals at least, and more especially in Man, the respiratory actions
should be thus placed under the control of the will : since they are subser-
vient to the production of those sounds, by which individuals communicate
their feelings and desires to each other; and which, when articulate, are capa-
ble of so completely expressing what is passing in the mind of the speaker.
If the respiratory mucles of Man were no more under his control, than they
appear to be in the Insect or Molluscous animal, he might be provided with
the most perfect apparatus of speech, and yet he would not be able to employ
it to any advantage.

378. The motor power of the Respiratory nerves is exercised, however,
not only on the muscles which perform the inspiratory and expiratory move-
ments, but on those which guard the entrance to the windpipe, and also on
certain other parts. The movements of the internal respiratory apparatus
are chiefly, if not entirely, effected through the medium of the motor fibres,
which the Par Vagum contains. These motor fibres exist in very different
amount in its different branches. For example, the pharyngeal and cesopha-
geal branches, by which (as will hereafter appear) the muscles of deglutition
are excited to contraction, possess a much larger proportion of them, and
exhibit much less sensibility when irritated, than do other divisions of the
trunk. Between the superior and inferior laryngeal nerves, again, there is an
important difference, which anatomical and experimental research has now
very clearly demonstrated. It has long been known, that section of the Par
Vagum in the neck, above the inferior laryn'geals, is frequently followed by
suffocation, resulting from closure of the glottis ; and hence it has been in-
ferred, that the office of the inferior laryngeals was to call into action the
dilators of the larynx, whilst the superior laryngeals were supposed to stimu-
late the constrictors. This view, however, is incorrect. It is inconsistent
with the results, just stated, of anatomical examination into the respective
distribution of these two trunks ; and it has been completely overthrown by
the very careful and satisfactory observations and experiments of Dr. J. Reid,
which have established that, whilst the inferior laryngeal is the motor nerve
of nearly all the laryngeal muscles, the superior laryngeal is the excitor or
afferent nerve, conveying to the Medulla Oblongata the impressions by which
muscular movements are excited. Its motor endowments are limited to the
crico-thyroid muscle, to which alone of all the muscles its filaments can be
traced, the remainder being distributed beneath the mucous surface of the
larynx; and its sensibility is very evident, when it is pinched or irritated
during experiments upon it. On the other hand, the motor character of the
inferior laryngeal branch is shown by its very slight sensibility to injury, its
nearly exclusive distribution to muscles, and its influence in exciting contrac-
tion of these when its separated trunk is stimulated.

379. It has been ascertained by Dr. Reid that, if the inferior laryngeal
branches be divided, or the trunk of the par vagum be cut above their origin
from it, there is no constriction of the glottis, but a paralyzed state of its mus-
cles. After the first paroxysm occasioned by the operation, a period of qui-
escence and freedom from dyspnoea often supervenes, the respirations being
performed with ease, so long as the animal remains at rest; but an unusual
respiratory movement, such as takes place at the commencement of a struggle,
induces immediate symptoms of suffocation, — the current of air carrying in-
wards the aryterund cartilages, which are rendered passive by the paralyzed

vated by the temporary cessation of the action. But such persons have succeeded better, by
holding the face beneath the surface of water; because here another set of muscles is called
into action, which are much more under the control of the will, than are those of respiration;
and a strong volition applied to these can prevent all access of air to the lungs, however
violent may be the inspiratory efforts.

296 FUNCTIONS OF THE NERVOUS SYSTEM.

state of their muscles; and these, falling upon the opening of the glottis, like
valves obstruct the entrance of air into the lungs. The more effort is made,
the greater will be the obstruction: and accordingly, it is generally necessary
to counteract the tendency to suffocation, when it is desired to prolong the life
of the animal after this operation, by making an opening into the trachea. Dr.
Reid further ascertained that the application of a stimulus to the inferior
laryngeal nerves, when separated from the trunk, would occasion distinct
muscular contractions in the larynx; whilst a corresponding stimulus applied
to the superior laryngeal occasioned no muscular movement, except in the
crico-thyroid muscle. But when the superior laryngeals were entire, irritation
of the mucous surface of the larynx, or of the trunks themselves, produced
contraction of the glottis and efforts to cough ; effects which were at once pre-
vented by dividing those nerves, and thereby cutting off their communication
with the Medulla Oblongata. There can be no doubt, then, that the superior
and inferior laryngeal branches constitute the circle of incidents and motor
nerves, by which the aperture of the glottis is governed, and by which any
irritation of the larynx is made to close the passage, so as to prevent the
entrance of improper substances; whilst the superior laryngeal nerve also ex-
cites the muscles of expiration, so as to cause the violent ejection of a blast of
air, by which the offending gas, fluid, or solid, may be carried off'. The effect
of carbonic acid in causing spasmodic closure of the glottis is well known ;
and affords a beautiful exajnple of the protective character of this system of
nerves. The mucous surface" of the trachea and bronchi appears, from the
experiments of Valentin, to be endowed with excitability, so that stimuli ap-
plied to it produce expiratory movements; and this evidently operates through
the branches of the par vagum distributed upon the membrane. Here, as
elsewhere, we find that a stimulus applied to the surface has a much more
decided influence than irritation of the trunk of the nerve supplying it.

380. The actions of sighing, yawning, sobbing, laughing, coughing, and
sneezing, are nothing else than simple modifications of the ordinary movements
of respiration, excited either by mental emotions, or by some stimulus originat-
ing in the respiratory organs themselves. — Sighing is nothing more than a very
long-drawn inspiration, in which a larger quantity of air than usual is made to
enter the lungs. This is continually taking place to a moderate degree ; and
we notice it particularly, when the attention is released, after having been
fixed upon an object, which has excited it strongly, and which has prevented
our feeling the insufficiency of the ordinary movements of respiration. Hence
this action is only occasionally connected with mental emotion. — Yawning is
a still deeper inspiration, which is accompanied by a kind of spasmodic con-
traction of the muscles of the jaw, and also by a very great elevation of the
ribs, in which the scapulae partake. The purely involuntary character of this
movement is sometimes seen, in a remarkable manner, in cases of palsy ; in
which the patient cannot raise his shoulder by an effort of the will, but does
so in the act of yawning. Nevertheless this act may be performed by the
will, though not completely; and it is one that is particularly excited by
an involuntary tendency to imitation; as every one must have experienced,
who has ever been in company with a set of yawners. — Sobbing is the con-
sequence of a series of short convulsive contractions of the diaphragm ; and it
is usually accompanied by a closure of the glottis, so that no air really enters.
In Hiccup, the same convulsive respiratory movement occurs ; and the glottis
closes suddenly in the midst of it; the sound is occasioned by the impulse of
the column of air in motion, against the glottis. — In Laughing, a precisely
reverse action takes place; the muscles'of expiration are in convulsive move-
ment, more or less violent, and send out the breath in a series of jerks, the
glottis being open. This sometimes goes on, until the diaphragm is more

REFLEX ACTIONS. RESPIRATORY MOVEMENTS. 297

arched, and the chest is more completely emptied of air, than it could be by
an ordinary movement of expiration. — The act of Crying, though occasioned
by a contrary emotion, is, so far as the respiration is concerned, very nearly
the same as the last. Every one knows the effect of mixed emotions, in pro-
ducing an expression of them, which is " between a laugh and a cry." — The
greater part of the preceding movements seem to belong as much to the con-
sensual or emotional, as to the purely reflex group of actions ; for whilst they
are sometimes the result of peculiar states of the respiratory organs, or of the
bodily system in general, they may also be called forth by influences, which
operate directly through the senses, or which excite the emotions. Thus,
whilst Sighing and Yawning often occur as simple results of deficient aeration,
they may be brought on, — the former by a depressed state of the feelings, —
the latter by the mere sight of the act in another person. The actions of
Laughter and Crying never seem to originate in the respiratory system ; but
to be always either expressions of the emotions, or simple results of sensa-
tions,— crying being connected with the sense of pain, — and laughter with that
of tickling. The origin of the act of Hiccup does not seem very clear; but
the movement is probably of a purely reflex nature.

381. The purposes of the acts of Coughing and Sneezing are, in both
instances, to expel substances from the air-passages, which are sources of irri-
tation there; and this is accomplished in both, by a violent expiratory effort,
which sends forth a blast of air from the lungs. — Coughing occurs, when the
source of irritation is situated at the back of the mouth, in the trachea, or
bronchial tubes. The irritation may be produced by acrid vapours, or by
liquids or solids, that have found their way into these passages ; or by secre-
tions which have been poured into them in unusual quantity, as the result of
disease; or by the simple entrance of air (especially if cold), when the mem-
brane is in a peculiarly irritable state. Any of these causes may produce an
impression upon the excitor fibres of the Par Vagum, which, being conveyed
to the Medulla Oblongata, shall give rise to the transmission of motor impulses
to the several muscles, that shall combine them in the act of coughing. This
act consists, — 1st, in a long inspiration, which fills the lungs; 2d, in the
closure of the glottis at the moment when expiration commences ; and 3d, in
the bursting open (as it were) of the glottis, by the violence of the expiratory
movement; so that a sudden blast of air is forced yp the air-passages, carrying
before it anything that may offer an obstruction. — The difference between
coughing and Sneezing consists in this, — that in the latter, the communication
between the larynx and the mouth is partly or entirely closed, by the drawing
together of the sides of the velum palati over the back of the tongue; so that
the blast of air is directed, more or less completely, through the nose, in such
a way as to carry off any source of irritation that may be present there. — It is
difficult to say how far these actions are simply reflex; or how far they -may
require the stimulus of sensation for their performance.

382. Deglutition and Defecation. — Another very important function of the
Spinal Cord (and of the ganglia corresponding to it in the Invertebrata), is the
control which it exercises over the entrance and termination of the Alimentary
Canal; and this reflex action might probably be traced in some animals, in
which the necessity for that of Respiration does not exist. In all beings which
are unequivocally of an animal character, a stomach or digestive cavity exists;
and a means must be provided for the introduction of food into it. This is
partly accomplished by the power, with which its entrance is endowed, of
contracting upon, and of attempting to draw inwards, whatever comes in con-
tact with it; as we may readily observe in the Star-Fish, or Sea-Anemone,
where what is commonly regarded as the mouth, is really the aperture of the
stomach. But we almost always find some more special apparatus, for bring-

298 FUNCTIONS OF THE NERVOUS SYSTEM.

ing food within reach of this orifice. In the Sea-Anemone, the Hydra, and
other Polypes, for example, we find that aperture surrounded by tentacula;
which have an evident tendency to lay hold of anything that touches them, so
as to bring it, by their contraction, within reach of the muscles immediately
surrounding the aperture. This is just the purpose of the pharyngeal muscles
of Man. The lower part of the oesophagus, near its termination in the sto-
mach, has the same simple tendency to contraction from above downwards
(so as to convey into the stomach anything which is brought within its reach),
as have the muscles surrounding the mouth of the Polype; but there is need
of some more complex apparatus, for the purpose of laying hold of the food,
and of conducting it into its grasp. This is provided for, in the higher animals,
in the muscles of that funnel-like entrance to the oesophagus, which is called
the Pharynx. The actions of these are most distinctly reflex; and it is inte-
resting to remark, that the movements can neither be caused nor controlled by
the direct influence of the will. In the case of the movements of respiration,
we found sufficient provision made for their constant maintenance; and yet,
for secondary purposes, they were placed in a considerable degree under the
control of the brain. But here there are no secondary purposes to be an-
swered ; the introduction into the stomach of food, brought by the will within
reach of the pharyngeal muscles, is the only object contemplated by them;
and they are accordingly placed under the sole government of the Spinal Cord.

383. No attempts, on our own part, will succeed in producing a really
voluntary act of Deglutition. In order to excite it, we must supply some
stimulus to the fauces. A very small particle of solid matter, or a little fluid
(saliva, for instance), or the contact of the back of the tongue itself, will be
sufficient ; but without either of these we, cannot stvallow at will. Nor can
we restrain the tendency, when it is thus excited by a stimulus ; every one
knows how irresistible it is, when the fauces are touched in any unusual man-
ner ; and it is equally beyond the direct control of the will, in the ordinary
process of eating, — voluntary as we commonly regard this. The only mode
in which the will can influence it, is by regulating the approach of the stimu-
lus necessary to excite it ; thus, we voluntarily bring a morsel of food, or a
little fluid, into contact with the surface of the fauces, and an act of deglutition
is then involuntarily excited : or we may voluntarily keep all stimulus at a
distance ; and no effort of the will can then induce the action. Moreover,
this action is performed, like that of respiration, when the power of the will
is suspended, as in profound sleep, or in apoplexy affecting only the brain;
and it does not seem to be at all affected by the entire removal of the brain,
in an animal that can sustain the shock of the operation ; being readily ex-
citable, on stimulating the fauces, so long as the nervous structure retains its
functions. This has been experimentally proved by Dr. M. Hall ; and it
harmonizes with the natural experiment sometimes brought under our notice
in the case of an anencephalous infant, in which the power of swallowing
seems as vigorous as in the perfect one. But, if the nervous circle be de-
stroyed, either by division of the trunks, or by injury of any kind to the por-
tion of the nervous centres connected with them, the action can no longer be
performed; and thus we see that, when the effects of apoplexy are extending
themselves from the brain to the spinal cord, whilst the respiration becomes
stertorous, the power of Deglutition is lost, and then respiration also speedily
ceases.

384. Our knowledge of the nerves specially concerned in this action is
principally due to the very careful and well-conducted experiments of Dr. J.
Reid.* The distribution of the Glosso-Pharyngeal evidently points it out as

* Edinb. Med. and Surg. Journ., vol. xlix.

ACTIONS PRELIMINARY TO DEGLUTITION. 299

in some way connected with it ; and this, when carefully examined, discloses
the important fact, that the nerve scarcely sends any of its branches to the
muscles which they enter ; but that these mostly pass through them, to be
distributed to the superjacent mucous surface of the tongue and fauces.
Further, when the trunk is separated from the nervous centres, irritation
scarcely ever produces muscular movements. Hence it is not in any great
degree an efferent or motor nerve ; and its distribution would lead us to sup-
pose its function to be, the conveyance of impressions from the surface of the
Fauces to the Medulla Oblongata. This inference is fully confirmed by the
fact, that, so long as its trunk is in connection with the Medulla Oblongata,
and the other parts are uninjured, pinching, or other severe irritation of the
Glosso-Pharyngeal, will often excite distinct acts of deglutition. Such irrita-
tion, however, may excite only convulsive twitches, instead of the regular
movements of swallowing; and it is evident that, here, as elsewhere, the
impressions made upon the extremities of the nerves are much more power-
ful excitors of reflex movement, than those made upon the trunk, though the
latter are more productive of pain. It was further observed by Dr. Reid, that
this effect was produced by pinching the pharyngeal branches only ; no irrita-
tion of the lingual division being effectual to the purpose.

385. If, then, the muscles of deglutition are not immediately stimulated to
contraction by the Glosso-Pharyngeal nerve, it remains to be inquired, by
what nerve the motor influence is conveyed to them from the Medulla Oblon-
gata ; and Dr. Reid has been equally successful in proving, that this function
is chiefly performed by the pharyngeal branches of the Par Vagum. Ana-
tomical examination of their distribution shows, that they lose themselves in
the muscles of the pharynx ; and whilst no decided indications of suffering
can be produced by irritating them, evident contractions are occasioned, when
the trunk, separated from the brain, is pinched or otherwise stimulated. It
appears, however, that neither is the Glosso-Pharyngeal the sole excitor
nerve, ,nor are the pharyngeal branches of the Par Vagum the sole motor
nerves, concerned in deglutition ; for after the former has been perfectly di-
vided on each side, the usual movements can still be excited, though with less
energy; and, after the latter have been cut, the animal retains the means of
forcing small morsels through the pharynx, by the action of the muscles of
the tongue and neck. From a careful examination of the actions of degluti-
tion, and of the influence of various nerves upon them, Dr. Reid draws the
following conclusions : — The excitor impressions are conveyed to the Me-
dulla Oblongata chiefly through the Glosso-Pharyngeal, but also along the
branches of the Fifth pair distributed upon the fauces, and probably along the
branches of the Superior Laryngeal distributed upon the pharynx. The
motor influence passes chiefly along the pharyngeal branches of the Vagus ;
along the branches of the Hypo-glossal, distributed to the muscles of the
tongue, and to the. sterno-hyoid, sterno-thyroid, and thyro-hyoid muscles ;
along the motor filaments of the Recurrents, ramifying upon the larynx ;
along some of the branches of the Fifth, supplying the elevator muscles of the
lower jaw; along the branches of the Portio Dura, ramifying upon the digas-
tric and stylo-hyoid muscles, and upon the muscles of the lower part of the
face ; and probably along some of the branches of the Cervical plexus, which
unite themselves to the descendens noni.

386. When the food has been propelled downwards by the Pharyngeal
muscles as far as their action extends, its further progress through the (Eso-
phagus is effected by the peristaltic movement of the muscular coat of the
tube itself. This movement is not, however, due only to the direct stimulus
of the muscular fibre by the pressure of the food, as it seems to be in the
lower part of the alimentary canal ; for Dr. J. Reid has found, by repeated

300 FUNCTIONS OF THE NERVOUS SYSTEM.

4

experiment, that the continuity of the cesophageal branches of the Par Vagum
with the Spinal Cord, is necessary for the rapid propulsion of the food; so
that it can scarcely be doubted, that an impression made upon the mucous
surface of the oesophagus, conveyed by the afferent fibres of these nerves to
the Medulla Oblongata, 'and reflected downwards along the motor fibres, is
the real cause of the muscular contraction. If the Par Vagum be divided in
the rabbit, on each side, above the cesophageal plexus, but below the pharyn-
geal branches, and the animal be then fed, it is found that the food is delayed
in the oesophagus, which becomes greatly distended. Further, if the lower
extremity of the par vagum be irritated, distinct contractions are seen in the
O3sophageal tube, proceeding from above downwards, and extending over the
cardiac extremity of the stomach. We have here, then, a distinct case of
reflex action without sensation, occurring as one of the regular associated
movements in the natural condition of the animal body ; and it is very inte-
resting to find this following upon a reflex action with sensation (that of the
pharynx), and preceding a movement which is altogether unconnected with
the Spinal Cord (that of the lower part of the alimentary canal). The use of
sensation in the former case will presently appear. The muscular fibres of
the oesophagus are also excitable, though usually in a less degree, by direct
stimulation ; for it appears that, in some animals (the Dog, for example),
section of the pneumogastric does not produce that check to the propulsion of
the food, which it occasions in the Rabbit ; and even in the Rabbit, as Dr.
M. Hall* has remarked, the simple contractility of the muscular fibre occa-
sions a distinct peristaltic movement along the tube, after its nerves have been
divided; causing it to discharge its contents, when cut across. Such a move-
ment, indeed, seems to take place in something of a rhythmical manner (that
is, at short and tolerably regular intervals), whilst a meal is being swallowed;
but as the stomach becomes full, the intervals are longer, and the wave-like
contractions less frequent. — These movements are reversed in Vomiting; and
this reversion has been .observed, even after the separation of the stomach
from the oesophagus, as a consequence of the injection of tartar emetic into
the veins.

a. It will be desirable here to revert for a short time to the actions, which, in the higher
animals, precede those of Deglutition. There can be no doubt that, in the Human being,
the motions adapted to the Ingestion and Mastication of aliment originally result, in part at
least, from distinct operations of the Will ; but it would appear almost equally certain that,
in time, they come to be of so habitual a character, that the will only exerts a general con-
trolling influence over them, each individual act being directly excited by sensation. Every
one is conscious that the act of mastication may be performed as well, when the mind is
attentively dwelling on some other object, as when directed to it ; but, in the former case,
one is rather apt to go on chewing and rechewing what is already fit to be swallowed,
simply because the will does not exert itself to check the action, and to carry the food back-
wards within the reach of the muscles of deglutition. We now see why sensation should
be associated with the latter process, though not essential to it. The conveyance of food back-
wards to the fauces is a distinctly voluntary act; and it is necessary that it should bo guided
by the sensation, which there results from the contact it induces. If the surlace of the
pharynx were as destitute of sensation, as is the lower part of the "oesophagus, we should not
know when we had done what was necessary to excite its muscles to operation. — The
muscles concerned in the Mastication of food are nearly all supplied by the third branch of
the Fifth pair, a large proportion of which is well known to have a motor character. Many
of these muscles, especially those of the cheeks, are also supplied by the Portio Dura of the
Seventh; and yet, if the former be paralyzed, this cannot stimulate them to the necessary
combined actions. Hence we see that the movements are of an associated character, their
due performance being dependent on the part of the nervous centres, from which the motor
influence originates. It' t!u> Fifth pair, on the other hand, he uninjured, whilst the Portio
Dura is paralyxed, the movements of Mastication are porliirmod without difficulty; whilst
those connected in any way with the Respiratory function, or with Expression, are para-
lyzed.

* Third Memoir on the Nervous System, § 201.

ACTIONS PRELIMINARY TO DEGLUTITION. » 301

b. Comparative Anatomy supplies us with the key to the explanation of these phenomena.
It has been seen that, in the lower animals, the Respiratory organs are completely uncon-
nected with the mouth, and that a very distinct set of muscles is provided to keep them in
action. These muscles have distinct ganglia as the centres of their operations ; and these
ganglia are only connected indirectly with those of the sensori-motor system. The same
would appear to be the case, in regard to the introduction of the food into the digestive
apparatus. It has been shown that the muscles concerned in this operation have their own
centres. — the Stomato-gastric and Pharyngeal ganglia, which are not very closely connected
with the cephalic, or with the respiratory, or with those of general locomotion. Now in the
Vertebrata, the distinct organs have been so far blended together, that the same muscles
serve the purposes of both; but the different sets of movements of these muscles are excited
by different nerves; and the effect of division of either nerve, is to throw the muscle out of
connection with the function, to which that nerve previously rendered it subservient, — as
much as if the muscle were separated from the nervous system altogether. There is an
apparent exception to this view of the matter, in the case of the Portio Dura; this being the
source of those movements of the upper lip, which, in many animals, are essential to the
prehension of food. These movements, however, are dependent upon sensations conveyed
through the Fifth pair.* being completely checked by division of its infra-orbital trunk; and
it can scarcely be doubted, from their general character, that they are of a strictly voluntary
nature, and are not to be regarded as part of the reflex associated movements in which that
nerve is concerned.

c. Now although, in the adult Human being, the movements required to convey the food
to the pharynx are under the control of the Will, if not constantly dependent upon it, there
is good reason to believe that this is not the case in regard to those remarkable associated
movements, which constitute the act of suction in the Infant. The experiments provided
for us by nature, in the production of anencephalous monstrosities, fully prove that the
nervous connection of the lips and respiratory organs with the Spinal Cord, is alone sufficient
for its execution; and Mr. Grainger has sufficiently established the same, by experiment
upon puppies whose brain had been removed. He adds that, as one of the puppies lay on
its side, sucking the finger which was presented to it, it pushed out its feet in the same
manner as young pigs exert theirs against the sow's dugs. On the whole, however, the act
of suction belongs more to the Respiratory ganglion (so to speak) than to the Stomato-gastric
system of nerves; and hence we can understand why, even in the highest animals, it should
be purely reflex; the movements of Respiration being so from the first, whilst those ordi-
narily concerned at a later period in the Ingestion of the food are more directed by sensa-
tion and volition. The actions of the mammary foetus of the kangaroo, described by Mr.
Morgan, furnish a very interesting exemplification of the same function of the Spinal Cord ;
this creature, resembling an earth-worm in appearance, and only about fourteen lines in
length, with a brain corresponding in degree of development to that of a human fcetus of
the ninth week, executes regular, but slow, movements of respiration, adheres firmly to the
point of the nipple, and moves its limbs when disturbed. The milk is forced into the oeso-
phagus by a compressor muscle, with which the mamma of the parent is provided. . " Can it
be imagined," very justly asks Mr. Grainger, '-that in this case there are sensation and vo-
lition, in what can be proved anatomically to be a fostus?"

387. The Sphincter muscle, which guards the Cardiac orifice of the
stomach, appears to be under the influence of the Spinal system of nerves.
It is usually closed; but it opens when there is a sufficient pressure on it,
made by the accumulated food propelled by the movements of the oesophagus
above ; and it then closes again, so as to retain the food in the stomach.
That this closure is due to reflex action appears from the fact that, when the
nerves supplying the muscle are divided, the sphincter no longer contracts,
and the food regurgitates into the oesophagus. The opening of the cardiac
orifice is one of the first of the changes, which occur in the act of vomiting. —
With regard to the degree, in which the movements of the Stomach, that have
so important a share in the Digestive operation, are dependent upon the Spinal
system, and are consequently of a reflex nature, it is difficult to speak with

* Hence originated one of Sir C. Bell's early errors. He found that an ass, in which the
infra-orbital branch of the fifth was divided, would not pick up oats with its lip, although
they were in contact with it; hence he concluded that its power of motion was destroyed, —
when it was in reality only the sensation necessary to excite the will to cause the motion,
that was deficient.

26

302 FUNCTIONS OF THE NERVOUS SYSTEM.

i

certainty, owing to the contradictory results obtained by different experi-
menters. These contradictions, however, seem partly due to a diversity in
the nature of the animals experimented on. It seems to be well established,
by the researches of Reid, Valentin, and others, that distinct movements may
be excited in the Stomach of the Rabbit, if distended with food, by irritating
the Par Vagum soon after the death of the animal; these movements seem to
commence from the cardiac orifice, and then to spread themselves in a sort
of peristaltic manner along the walls of the stomach; but no such movements
can be excited if the stomach be empty. Various experiments upon living
animals have led to a similar conclusion ; food taken in shortly before or sub-
sequently to its division, having been found to be only dissolved on the sur-
face of the mass, where it was in contact with the mucous membrane. But
these experiments have been made for the most part upon Herbivorous
animals, such as horses, asses, and rabbits ; whose food is bulky and difficult
of solution, requiring to be constantly changed in its position, so that every
part of it may be successively brought to the exterior. On the other hand,
Dr. Reid found, in his experiments upon Dogs, that, after the first shock of
the operation had gone off", solution of the food in the stomach, and absorp-
tion of chyle, might take place; and hence it may be inferred, that no influ-
ence of this nerve upon the muscular parietes of the stomach is essential to
digestion in that species. This conclusion harmonizes well, therefore, with
the fact already stated respecting the absence of such influence in the lower
parts of its oesophagus; and it may, perhaps, be explained by the considera-
tion, that the natural food of the dog is much less bulky and more easy of
solution, than that of the animals already named; so that there is not so much
need of the peculiar movement, which is in them so important an aid to the
process of reduction. — The muscular walls of the stomach appear to be called
into reflex contraction in the act of Vomiting; the mechanism of which will
be considered hereafter (§ 505).

388. That the ordinary peristaltic movements of the Intestinal canal, from
the stomach to the rectum, may take place without any connection with the
nervous system, being due to the direct stimulation of the contact of food,
there is now ample evidence ; and though some may yet be found to deny the
Hallerian doctrine, that muscular fibre possesses in itself the property of con-
tractility, so much additional evidence of its truth has been recently adduced
whilst the doctrine itself is so conformable to the analogy supplied by other
vital phenomena, that it will be here unhesitatingly adopted. (See Chapter V.)
Some Physiologists still suppose, that the peristaltic movements of the ali-
mentary canal are due to a sort of reflex action, taking place through the
ganglia of the Sympathetic system of nerves, especially, of course, the semi-
lunar. This supposition, however, has little or no evidence to support it; for
it has been fully proved that the muscular contractions will continue, long
after the tube has been separated from its nervous connections through its
whole extent ; and the only evidence in its favour is derived from the con-
tractions, which may sometimes be induced in parts of the tube which are at
rest, when the Sympathetic nerves supplying them are irritated. The ex-
periments of Valentin, however, — by which the fact that such contractions
may be induced (which has been denied by some) is clearly substantiated, —
also show that the motor influence does not originate in the Sympathetic gan-
glia, but in the Spinal Cord. The following are the general results of up-
wards of three hundred experiments, so far as they apply to this subject. —
The pharynx may not only be excited to contraction by irritation of the pha-
ryngeal branches of the Par Vagum, or of the roots of the Spinal Accessory,
from which their motor power is derived (as will be hereafter explained), but
also by stimulating the roots of the first two Cervical nerves ; and the lower

REFLEX ACTIONS. MOVEMENTS OF STOMACH. 303

part of the oesophagus in the neck is made to contract peristaltically from
above downwards, by irritation of the roots of the first three Cervical nerves,
and of the cervical portion of the Sympathetic, through which last the former
evidently operate. The thoracic portion of the oesophagus is made to con-
tract, by irritation of the lowest Sympathetic ganglion of the neck, and of
the higher thoracic ganglia, and also of the roots of the lower Cervical spinal
nerves. Muscular contractions of the stomach are produced, by irritation of
the roots of the 4th, 5th, 6th, and 7th Cervical nerves, and of the first tho-
racic in the rabbit ; so that a distinct furrow is evident between the cardiac
and pyloric portion of the viscus ; and the lower the nerve irritated, the
nearer the pylorus do the contractions extend. Irritation of the first thoracic
ganglion of the Sympathetic produces the same effect. Contractions of the
intestinal tube, varying in place according to the part of the Spinal Cord ex-
perimented on, may be excited by irritation of the roots of the dorsal, lumbar,
and sacral nerves, and of the trigeminus ; and similar effects are produced by
irritation of the lower part of the thoracic portion, of the lumbar, and of the
sacral portions of the Sympathetic, — also of the splanchnic, and of the gastric
plexus.

389. From these facts it is evident, that the movements of the Intestinal
tube may be influenced by the Spinal Cord ; and that what is commonly
termed the Sympathetic nerve, is the channel of that influence, by the fibres
which it derives from the Spinal system. But it by no means thence follows,
that the ordinary peristaltic actions of the muscles in question are dependent
on a stimulus reflected through the spinal cord, rather than on one directly
applied to themselves. It is clear that, although these movements are of the
first importance to the welfare of the system, such means of sustaining them
are feeble, compared to those which we find provided for the maintenance of
the distinctly-reflex actions of deglutition, respiration, &c. The difficulty
with which any evidence can be obtained of the connection, is a sufficient
proof of this. On the other hand, we do know that these peristaltic move-
ments are influenced by particular states of mind, or by conditions of the bodily
system ; and the connection just traced satisfactorily accounts for this, and is
itself sufficiently explained. The intestinal tube, then, from the stomach to
the rectum is not dependent upon the Spinal cord for its contractility, but is
enabled to propel its contents by its own inherent powers ; still we find that
here, as in other instances, the nervous centres exert a general control over
even the Organic functions, — doubtless for the purpose of harmonizing them
with each other, and with the conditions of the organs of Animal life.

390. The Muscular Coat of the Bladder appears, like that of the Intestinal
tube, to be ordinarily excited to contraction, rather by direct stimulation than
by the agency of the Spinal nerves. It is not, however, altogether removed
from the influence of the Spinal Cord ; for the experiments of Valentin have
shown that a connection exists, as in the former case, through the Sympathetic
nerve, affecting not only the bladder but also the ureters. That physiologist
states, that a very distinct and powerful peristaltic action of the ureter, pro-
ceeding from the kidneys to the bladder, may be produced, by irritating the
abdominal ganglia of the Sympathetic, or the roots of the superior abdominal
Spinal nerves ; and that strong contractions of the bladder are excited, by irri-
tation of the inferior portion of the abdominal Sympathetic, but especially of
its sacral portion, and of the roots of the middle and inferior nerves of the
Spine. In these, as in former cases, no effect is produced by irritation of the
Spinal Nerves, unless the portion of the Sympathetic connected with the par-
ticular organ be entire.

391. On examining the outlets by which the excretions are voided, we find
that they are placed, like the entrances, under the guardianship of the Spinal
Cord; subject, however, to some control on the part of the Will. In the

304 FUNCTIONS OF THE NERVOUS SYSTEM.

lowest animals, the act of discharging excrementitious matter is probably as
involuntary, as are the acts immediately concerned in the introduction of nu-
triment; and it is performed as often as there is anything to be got rid of.
In the higher classes, however, such discharges are much less frequent ; and
reservoirs are provided, in which the excrementitious matter may accumulate
in the intervals. The associated movements required to empty these, are
completely involuntary in their character; and are excited by the quantity,
or stimulating quality, of the contents of the reservoir. But, had volition no
control over them, great inconveniences would ensue ; hence sensation is ex-
cited by the same stimulus, which produces the movements ; in order that,
by arousing the will, the otherwise involuntary motions may be restrained
and. directed.. — There can be little doubt, from the experiments of Dr. M.
Hall, as well as from other considerations, that the associated movements, by
which the contents of the rectum and bladder are discharged, correspond
much with those of Respiration ; being in their own nature excito-motor, but
capable of a certain degree of voluntary restraint and assistance. The acts
of Defecation and Urination chiefly depend upon the combined contraction
of the abdominal muscles, similar to that which is concerned in the expiratory
movement ; but, the glottis being closed, and the diaphragm fixed, the expulsor
power is restricted to the contents of the abdominal cavity ; and so long as the
sphincter of the cardia remains closed, the force must act downwards, upon
the walls of the rectum and bladder, — the contents of the one or the other of
these cavities, or of both, being expelled, according to the condition of their
respective sphincters. These actions are doubtless assisted by the contrac-
tion of the walls of the rectum and bladder themselves; for we sometimes find
their agency sufficient to expel the contents of the cavities, when there is a
total paralysis of the ordinary expulsors, — provided that the sphincters be at
the same time sufficiently relaxed. This is more especially the case, when
their power is augmented by increased nutrition. For example, in many
cases of disease or injury of the Spinal Cord, the bladder ceases to expel
its contents, through the interruption of the circle of reflex actions ; but after
a time, the necessity for drawing off the urine by the catheter is found to
exist no longer; the fluid is constantly expelled as soon as it has accumulated
in small quantities. In such cases, the mucous coat is found after death to
be thickened and inflamed; and the muscular coat to be greatly increased in
strength, and contracted upon itself. It would seem, then, that the abnormal
irritability of the mucous membrane, and the increased nutrition of the mus-
cular substance which appears consequent upon it, enable the latter to expel
the urine without the assistance of the ordinary expulsors.

392. On the other hand, the sphincters which antagonize the expellent ac-
tion, are usually maintained in a state of moderate contraction, so as to aflord
a constant check to the egress of the contents of the cavities ; and this con-
dition has been fully proved by Dr. M. Hall, to result from their connection
with the Spinal Cord, ceasing completely when this is interrupted. But the
sphincters are certainly in part controlled by the will, and are made to act in
obedience to the warning given by sensation ; and this voluntary power .is
frequently destroyed by injuries of the Brain, whilst the Spinal Cord remains
able to perform all its own functions, so that discharge of the urine and
ffeces occurs. — In their moderate action, the expulsors and the sphincters
may be regarded as balancing one another, so 1'ar as their reflex action is
concerned, — the latter having rather the predominance, so as to restrain the
operation of the former. But, when the quantity or quality of the contents
of the cavity gives an excessive stimulus to the former, their action pre-
dominates, unless the will is put in force to strengthen the resistance of
the sphincter ; this we are frequently experiencing, sometimes to our great

REFLEX ACTIONS. MOVEMENTS OF GENITAL ORGANS, ETC. 305

discomfort. On the other hand, if the stimulus is deficient, the will must
aid the expulsors, in order to overcome that resistance which is due to the
reflex contraction of the sphincters; of this also we may convince ourselves,
when a sense of propriety, or a prospective regard to convenience, occasions
us to evacuate the contents of the rectum or bladder without a natural call to
do so.

393. Movements of the Genital Organs. — The muscular contractions in-
volved in the Emissio Seminis are clearly of a reflex nature ; being inde-
pendent of the will and not capable of restraint by it, when once fully excited;
and being producible in no other way, than (like those concerned in Degluti-
tion) by a particular local irritation. That this irritation need not amount to
a sensation, is proved by cases already referred to (§ 372) ; and it has been
also shown by experiment, that section of the Spinal Cord in the lumbar
region does not prevent the act from being performed, the lower division only
being concerned in the reflexion of the impression. It further appears, from
the experiments of Valentin, that the Spinal Cord may operate on the Genital
organs through the Sympathetic system. Contractions were excited in the
vas deferens vesiculae seminales, especially of the Guinea Pig at the time of
heat, by irritation of the inferior lumbar and highest sacral portions of the
Sympathetic; and the Fallopian tubes, as well as the Uterus itself, may be
excited to contraction, by irritation of the same nerves as those which excite
the rectum, — namely, the lower lumbar and first sacral nerves of the Spine.
This last fact is important, in regard to the rationale of the operation of certain
medicines, such as aloes, which are known to have an influence on both
parts. — In regard to the act of Parturition, there would seem reason to believe,
from the evidence of cases of paraplegia, that, of the muscles whose operation
is associated in it, the diaphragm, abdominal muscles, &c., are called into
action (as in defecation) through the Spinal Cord ; but that the contractions
of the Uterus itself are but little dependent on its connection with the nervous
centres. Of the reason why the muscles, which were up to that time inert,
should then combine in this extraordinary manner, and with such remarkable
energy, Physiology can afford no certain information. There can be little
doubt, however, that the stimulus usually originates in the uterus, or in some
of the neighbouring organs which are incommoded by the pressure ; but it
may also result from some condition of the general system, in which the
uterus itself is but little concerned. It is an interesting fact, which has been
more than once observed, that the foetus may be expelled from the dying body
of the mother, even after the respiratory movements have ceased. This would
appear due to the contraction of the Uterine fibres alone, which, like those of
the heart and alimentary canal, retain their irritability longer than those of
the muscles supplied by the cerebro-spinal nerves ; and the power of these
would be unopposed by the resistance which they ordinarily have to en-
counter; since the tension of all the muscles surrounding the outlet would be
destroyed, by the cessation of the activity of the Spinal system of nerves
(§ 398).

394. Protecting Agency of the Spinal Cord. — From the foregoing details
it appears, that one of the chief functions of the Spinal Cord is to control the
orifices of the various open cavities of the body; and this function evidently
has safety, as well as convenience, in view. It has been manifestly designed
by the All-wise Creator, that the Glottis should close against agents injurious
to the organs within; and that the effort to vomit should be excited by the
attempt to swallow substances so nauseous as to induce loathing. — There is
another protective influence exerted by it, of a still more remarkable nature.
It has been ascertained by Dr. M. Hall that, if the functions of the Brain be
suspended or destroyed, without injury to the Spinal system of nerves, the

26*

306 FUNCTIONS OF THE NERVOUS SYSTEM.

Orbicularis muscle will contract, so as to occasion the closure of the eyelids,
upon the tarsal margin being touched with a feather. This fact is interesting
in several points of view. In the first place, it is a characteristic example of
pure reflex action ; occurring under circumstances in which volition cannot be
imagined to guide it, and in which there is no valid reason to believe that sen-
sation directs it. Further, it explains the almost irresistible nature of the tend-
ency to winking, which is performed at short intervals by the contraction of the
Orbicularis muscle; this is evidently a Spinal action, capable of being in some
degree restrained (like that of respiration) by the will, but only until such time
as the stimulus (resulting perhaps from the collection of minute particles of
dust upon the eyes, or from the dryness of its surface in consequence of
evaporation), becomes too strong to be any longer resisted. Again, we have
in sleep or in apoplexy an example of this purely spinal action, unbalanced
by the influence of the will, which, in the waking state, antagonizes it by
calling the levator palpebrae into action. As soon as the will ceases to act, the
lids droop, and close over the eye in order to protect it; and if those of a
sleeping person be separated by the hand, they will be found presently to
return. Here, as in studying the respiratory and other movements, we are
led to perceive, that it is the Brain alone, which is torpid during sleep, and
whose functions are affected by this torpidity. As Dr. M. Hall very justly
remarks, the Spinal system never sleeps ; it is constantly in activity ; and it is
thus that, in all periods and phases of Life, the movements which are essential
to its continued maintenance are kept up without sensible effort.

395. The closure of the Pupil against a strong light, is another movement
of the same protective tendency. The channel, through which that just
named is performed, is completed by the first branch of the Fifth and the
Portio Dura of the seventh. The contraction of the pupil is immediately
caused by the Third pair, or Motor Oculi; as is easily shown by irritating the
trunk of that nerve and observing the result. But it is not easy to speak with
certainty as to the afferent nerve, by which the motor influence is excited.
Although the contraction of the pupil is usually in close accordance with the
sensation occasioned by the impression of light upon the retina, yet there is
no want of evidence to prove that the sensation of light is not always neces-
sary; for, even when the sight of both eyes has been entirely destroyed by
amaurosis, the regular actions have been witnessed in the pupil, in accordance
with varying degrees of light impinging on the retina. This fact may be
explained in two ways. It may either be imagined that the requisite stimulus
is not that of light conveyed through the Optic nerve; but that of heat con-
veyed through the ophthalmic branch of the Fifth pair. Or it may be still
supposed, that the motion results from an impression upon the retina, which
impression, being conducted to the Sensorium, ordinarily produces a sensation;
whilst in these curious cases, no sensation is produced, on account of a dis-
ordered state of the part of the ganglionic centre in which the Optic nerve
terminates; though some filaments of that nerve, being connected with the
Third pair by means of a distinct tract of vesicular matter, can produce a
reflex action through it, although no sensation intervene. In either view, the
rarity of the occurrence is at once accounted for; since in most cases of
amaurosis, the disease lies in the trunk of the nerve, and thereby checks both
its spinal and its encephalic actions.

396. The Physiologist has not at present any knowledge of any similar
protective movements, in the Human being, designed to keep the organ of Hear-
ing from injury ; but there can be little doubt that those which we are constantly
witnessing in other animals, possessing large external ears, are reflex actions
excited by the irritation applied to them. In regard to the Nose, we find a
remarkably complex action — that of Sneezing — adapted to drive off any cause

REFLEX ACTIONS. MOVEMENTS OF LOCOMOTION. 307

of irritation (§ 381). It Avill hereafter be shown that the stimulus is conveyed,
in this case, not through the Olfactory nerve, but through the Fifth pair; so
that it is not dependent upon the excitement of the sensation of Smell. The
act of Coughing, also, may be regarded as of a protective character ; being
destined to remove sources of irritation from the air-passages. The automatic
movements, performed by the limbs of Frogs and other animals, when their
connection with the brain has been cut oft" (§§ 306, 370) appear destined to
remove these parts from sources of irritation or injury; and they may thus be
rightly placed under the same category.

397. Movements of Locomotion. — Lastly, we have to inquire how far the
Reflex function of the Spinal Cord is concerned in the locomotive actions of
the lower extremities in Man. It will be remembered that, in the Dytiscus
whose head had been removed (§ 328), the stimulus of the contact of water
immediately excited regular and continued locomotive actions which lasted
for some time. So in the cases already quoted (§§ 366 — 368), when the con-
trol of the will over the lower extremities was lost, powerful muscular actions
were excited in them, through the Spinal Cord alone. In the healthy con-
dition of the Human system, when the Will is controlling all the movements,
which are not immediately concerned in the maintenance and regulation of
the organic functions, no such actions can be excited : but in proportion as its
control is lost, does the independent power of the Spinal Cord manifest itself.
The more such actions are of a simple rhythmical character, similar to those
of Respiration, the more does it seem that they may with probability be re-
ferred to the Spinal system; and if we attribute to this (as we can scarcely
help doing) the rapid vibration of the wings of Insects, there seems no reason
why we should not extend the same view to the wings of Birds. Such an
explanation of their movements will account for their occasional continuance,
without apparent fatigue, during a period through which no known voluntary
effort can endure ; for it is one of the attributes of the Spinal system of
nerves, well pointed out by Dr. M. Hall, that the exercise of the muscles
excited by it does not occasion fatigue, the sense of which is Cerebral only.
It would seem to the A.uthor more probable, however, that those movements
which guide the body, and which must themselves be directed by Sensation,
are to be referred to a class intermediate between the Voluntary and the Re-
flex, which may be properly termed Consensual. Numerous actions, in Man,
which were at first Voluntary, appear at last to be performed as instinctively
or intuitively, as they are in the lower animals from the commencement of
their existence. (See the next Section.)

398. Influence on Muscular Tension. — The various muscles of the body,
even when there is the most complete absence of effort, maintain, in the
healthy state of the system, a certain degree of firmness, by their antagonism
with each other ; and if any set of muscles be completely paralyzed, the op-
posing muscles will draw the part on which they act, out of its position of
repose ; as is well seen in the distortion of the face, which is characteristic
of paralysis of the facial nerve on one side. This condition has been desig-
nated as the tone of the Muscles ; but this term renders it liable to be con-
founded with their tonic contraction, which is also concerned in maintaining
their firmness, but which operates in a very different manner. The latter is
dependent upon the simple contractility of the muscle ; and is exhibited alike
by the striated and the non-striated forms of muscular fibre, but more espe-
cially by the latter (§ 593). On the other hand, the condition now alluded to,
which may perhaps be appropriately termed their tension, is the result of a
moderate though continued excitement of that contractility, through the nerv-
ous centres. It has been proved by Dr. M. Hall, that the Muscular Tension
is not dependent upon the influence of the Brain ; but upon that of the Spinal

308 FUNCTIONS OF THE NERVOUS SYSTEM.

Cord ; as the following experiments demonstrate. — " Two Rabbits were taken ;
from one the head was removed ; from the other also the head was removed,
and the spinal marrow was cautiously destroyed with a sharp instrument : the
limbs of the former retained a certain degree of firmness and elasticity;
those of the second were perfectly lax." Again : — "The limbs and tail of a
decapitated Turtle possessed a certain degree of firmness or tone, recoiled on
being drawn from their position, and moved with energy on the application of
a stimulus. On withdrawing the spinal marrow gently out of its canal, all
these phenomena ceased. The limbs were no longer obedient to stimuli, and
became perfectly flaccid, having lost all their resilience. The sphincter lost
its circular form and contracted state, becoming lax, flaccid, and shapeless.
The tail was flaccid, and unmoved on the application of stimuli." It is further
remarked by Messrs. Todd and Bowman, that ' a decapitated frog will con-
tinue in the sitting posture through the influence of the spinal cord ; but im-
mediately this organ is removed, the limbs fall apart."

399. This operation of the Spinal Cord is doubtless but a peculiar mani-
festation of its ordinary reflex function. We shall hereafter see (Section 5)
how much the influence of the will in producing the active contraction of a
muscle, is connected with sensations received from it; and it seems highly
probable, that the impression of the state of the muscle, conveyed by the
afferent fibres proceeding from it to the spinal cord, is sufficient to excite this
state of moderate tension through the motor nerves, arising from the latter.
Such a view derives probability from the fact, which must have fallen under
the observation of almost every one, that most reflex actions become increased
in energy if resistance is made to them. Of this we have familiar examples
in the action of the expulsor muscles, which operate in defecation, urination,
and parturition, if, when they are strongly excited, their efforts be opposed
by the will acting on the sphincters, or by mechanical means. Many forms
of convulsive movement exhibit the same tendency ; their violence being pro-
portional to the mechanical force used to restrain them.* Here it is evident
that the impression of resistance, conveyed to the Spinal Cord, is the source
of the increased energy of its motor influence ; — from which we may fairly
infer that the moderate resistance, occasioned by the natural antagonism of the
muscles, is the source of their continued and moderate tension, whilst they
are under the influence of the Spinal Cord. This constant though gentle
action serves to keep up the nutrition of the muscles, which are paralyzed to
the will ; and this is still more completely maintained, if the portion of the
nervous centres, with which they remain connected, is so unduly irritable,
that the muscles are called into contraction upon the slightest excitation, and
are thus continually exhibiting twitchings, startings, or more powerful convuls-
ive movements. It is upon the state of nutrition of the muscles, that their
contractility depends, as will be shown hereafter (§ 588) ; and hence the
Spinal Cord has an indirect influence upon this peculiar property, which is
more likely to be retained, when the muscle is still subject to the influence of
the Spinal Cord, though cut off from that of the Brain, than when it is com-
pletely paralyzed by the entire cessation of the influence of the nervous
centres.

400. Pathological Phenomena. — It would not be right to conclude this
account of the principal functions of the Spinal Cord, without adverting to
some of the leading Pathological applications of the physiological doctrines

* Hence the absurdity of the common practice of endeavouring to prevent the move-
ments of the limbs and body, in convulsive paroxysms, by mechanical constraint Nothing
should be attempted but what is requisite to prevent the sullercr from doing himself an in-
jury-

REFLEX ACTIONS. PATHOLOGICAL PHENOMENA. 309

which have been developed in it; although they will hereafter be passed
under a more general review (Section 8). A large part of these were first
pointed out by Dr. M. Hall;* and they are receiving continual and important
extensions from his own labours and those of other practical inquirers. It
may be remarked, in the first place, that the power of the whole Spinal sys-
tem is capable of being morbidly diminished or augmented. It may even be
for a time almost completely suspended, as in Syncope; which state may be
induced by sudden and violent impressions, either of a mental or physical
nature, that operate upon the whole nervous system at once, — commencing,
however, in the brain. It is to be remarked that, in recovering from these, it
is the Spinal system of which the activity is first renewed, — the respiratory
movements recommencing, and the power of swallowing being restored,
before any voluntary actions can be performed. A corresponding state may
be induced in particular portions of the system by concussion ; as is seen in
severe injuries of the Spinal Cord, which are almost invariably followed for
a time by the suspension of its functions. Again, the power of the whole
Spinal Cord may be diminished by various causes, such as enfeebled circula-
tion, pressure, &c. ; and then we have torpidity of the whole muscular sys-
tem. If oppression exists in the Brain, the functions of the Medulla oblon-
gata will be especially affected; and if it be prolonged and sufficiently severe,
Asphyxia will result from the interruption of the respiratory movements which
it occasions.

401. On the other hand, the excitability of the whole Cord, or of particu-
lar parts of it, may be morbidly increased. This is especially seen in ordi-
nary Tetanus and the artificial Tetanus induced by Strychnine; in which the
slightest external stimulus is sufficient to induce reflex actions in their most
terrific forms. It is interesting to remark, that in this formidable disease the
functions of the muscles controlling the various orifices are those most affected ;
and it is by the spasms affecting the organs of respiration or deglutition, that
life is commonly terminated. — Various remedial agents will probably be found
to operate, by occasioning increased excitability in some particular segments
of the Cord; so that the usual stimuli applied to the parts connected with
these, will occasion increased muscular tension. This seems to be the case,
for example, in regard to the influence of aloes on the rectum and uterus,
cantharides on the neck of the bladder and adjoining parts, and secale cornu-
tum on the uterus. The mode of influence of cantharides is illustrated by a
curious case, related by Dr. M. Hall, of a young lady who lost the power of
retention of urine, in consequence of a fatty tumour in the spinal canal, which
gradually severed the Spinal Cord, and induced paraplegia. The power of
retaining the urine was always restored for a time by a dose of tincture
of cantharides, which augmented the excitability of the segment of the cord,
with which the sphincter vesicae is connected. — The researches of Valentin,
when grafted (as it were) on the doctrines of Dr. M. Hall, afford the key to
the explanation of the numberless sympathetic influences of the organs of
nutrition, &c., upon one another; by showing that they are all connected with
the Spinal Cord ; and that the muscular structure, with which they are all
provided, may be excited to contraction through it. And, lastly, the more
recent observations of Dr. M. Hall, in regard to the peculiar excitor power
that belongs to the nervous fibres distributed on various serous and fibrous
membranes, will probably lead, when they have been fully carried out, to the
explanation of the various convulsive actions, that result from pressure or
irritation affecting these parts.

See especially his Treatise on the Diseases and Derangements of the Nervous System.

310 FUNCTIONS OF THE NEIIVOUS SYSTEM.

a. It lias been pointed out by Messrs. Todd and Bowman (Physiological Anatomy, Vol. I.
p. 315), that the Spinal Cord of the male frog, at the season of copulation, naturally pos-
sesses a state of most extraordinary excitability. The thumb of each anterior extremity at
this season, becomes considerably enlarged; as is well known to Naturalists. "This enlarge-
ment is caused principally by a considerable development of the papillary structure of the
skin which covers it; so that large papillas are formed all over it. A male frog, at this
season, has an irresistible propensity to cling to any object, by seizing it between his anterior
extremities. It is in this way that he seizes , upon, and clings to the female ; fixing his
thumbs to each side of her abdomen, and remaining there for weeks, until the ova have been
completely expelled. An effort of the Will alone could not keep up the grasp uninterrupt-
edly for so long a time, yet so firm is the hold, that it can with difficulty be relaxed. What-
ever is brought in the way of the thumbs, will be caught by the forcible contraction of the
anterior limbs; and hence we often find frogs clinging blindly to a piece of wood, or a dead
fish, or some other substance which they may chance to meet with. If the finger be placed
between the anterior extremities, they will grasp it firmly; nor will they relax their grasp
until they are separated by force. If the animal be decapitated, whilst the finger is within
the grasp of its anterior extremities, they still continue to hold on firmly. The posterior half
of the body may be cut away, and yet the anterior extremities will still cling to the finger;
but immediately that the segment of the cord, from which the anterior extremities derive
their nerves, has been removed, all their motion ceases. This curious instinct only exists
during the period of sexual excitement; for at other periods the excitability of the anterior
extremities is considerably less than that of the posterior."

402. Nerves of the Spinal System. — The nerves which minister to the
functions of the Spinal Cord, conveying to it the impressions made on the
periphery, and transmitting its motor influence to the muscles, — are not those
alone which are ordinarily designated as Spinal nerves; for several of those,
which pass forth through the base of the cranium, and which are commonly
described as Cephalic nerves, belong to the same category. The general
characters of the Spinal nerves, their mode of connection with the Spinal
Cord by two sets of roots, and the presence of ganglion upon the posterior
root, have already been adverted to (§ 344). The anterior roots are usually
the smaller ; and this is particularly the case with those of the cervical nerves,
in which the posterior roots are of remarkable comparative size. In the First
Cervical or Sub-occipital pair, the anterior roots are sometimes wanting ; but
there is then a derivation of fibres from the Spinal Accessory, or from the
Hypoglossal, or from both. The two roots of the ordinary Spinal nerves
unite immediately beyond the ganglion, which is situated on the posterior one;
and the trunk thus formed separates immediately into two divisions, — the an-
terior and posterior,' — each of which contains both afferent and motor fibres.
These divisions, of which the anterior is by far the larger, proceed to the ante-
rior and posterior parts of the body respectively; and are chiefly distributed to
the skin and the muscles. The anterior branch is that which communicates
with the sympathetic nerve.

403. The pair of nerves commonly designated as the Fifth of the Cephalic
series, or as the Trifacial, is the one which more nearly resembles the ordi-
nary Spinal nerves (as was long since pointed out by Sir C. Bell), than docs
any other of those originating within the cranium. It possesses two distinct
sets of roots, of which one is much larger than the other ; on the larger root,
as on the posterior and larger root of the Spinal nerves, is a distinct ganglion;
and the fibres arising from the smaller root do not blend with the others, until
after the latter have passed through this ganglion. The trunk of the nerve
separates, as is well known, into three divisions, — the Ophthalmic, the Supe-
rior Maxillary, and the Inferior Maxillary ; and it can be easily shown, by
careful dissection, that the fibres of the smaller root pass into the last of these
divisions alone. When the distribution of this nerve is carefully examined,
it is found that the first and second divisions of it proceed almost entirely to
the skin and mucous surfaces; a very small proportion, only, of their fibres
being lost in the muscles : whilst of the branches of the third division, a large
number are distinctly muscular. Hence analogy, and the facts supplied by

SPINAL NERVES. FIFTH PAIR, OR TRIFACIAL.

311

anatomical research, would lead to the conclusion, that the first two divisions
are nerves of sensation only, and that the third division combines sensory and
motor endowments. Such an inference is fully borne out by experiment.
When the whole trunk is divided within the cranium by the penetration of a
sharp instrument (which Magendie, by frequent practice, has been able to ac-
complish), evident signs of acute pain are given. After the incision has been
made through the skin, the animal remains quiet until the nerve is touched ;
and when it is pressed or divided, doleful cries are uttered, which continue
for some time, showing the painful effect of the irritated state of the cut ex-
tremity. The common sensibility of all the parts supplied by this nerve is
entirely destroyed on the affected side. The jaw does not hang loosely, be-
cause it is partly kept up by the muscles of the other side ; but it falls in a
slight degree ; and its movements are seen, when carefully observed, to be
somewhat oblique. If the trunk be divided on each side, the whole head is
deprived of sensibility ; and the animal carries it in a curious vacillating man-
ner, as if it were a foreign body.

Fig. 150.

A diagram showing the Fifth pair of nerves with its branches. 1. The origin of the nerve by two roots.
2. The nerve escaping from the crus cerebelli. 3. The Gasserian ganglion. 4. Its ophthalmic division.
5. The frontal nerve, giving off the supra-trochlear branch, and escaping on the forehead through the
supra-orbital foramen. 0. The lachrymal nerve. 7. The nasal nerve, passing at 8 through the anterior
ethmoidal foramen, and giving off the infra-trochlear branch. 9. The communication of the nasal nerve
with the ciliary ganglion. 10. A small portion of the third nerve with which the ganglion is seen com-
municating; the ganglion gives off the ciliary branches from its anterior aspect. 11. The superior maxil-
lary nerve. 12. Its orbital branch. 13. The two branches communicating with Meckel's ganglion; the
three branches given off from the lower part of the ganglion are the posterior palatine nerves. 14, 14.
The superior dental nerves, posterior, middle, and anterior. 15. The infra-orbital branches distributed
upon the cheek. 16. The inferior maxillary nerve. 17. Its anterior or muscular trunk. IS. The pos-
terior trunk; the two divisions are separated by an arrow. 19. The gustatory nerve. 20 The corda
tympani joining it at an acute angle. 21. The submaxillary ganglion. 22. The inferior dental nerve.
23. Its mylo-hyoidean branch. 24. The auricular nerve, dividing behind the articulation of the lower
jaw, to reunite and form a single trunk. 25. Its branch of communication with the facial nerve. 26. Its
temporal branch.

404. If the anterior or Ophthalmic branch only be divided, all the parts
supplied by it are found to have lost their sensibility, but their motions are
unimpaired ; and all experiments and pathological observations concur in at-

312

FUNCTIONS OF THE NERVOUS SYSTEM.

tributing to it sensory endowments only. The only apparent exception is in
the case of the Naso-Ciliary branch; since there is good reason to believe that
the long root of the ciliary ganglion, and the long ciliary nerves, possess motor

[Fig. 151.

A view of the distribution of the Trifacial or Fifth
pair; 1, orbit; 2, antrum highmorianum ; 3, tongue;
4, lower jaw-bone; 5, root of the fifth pair, forming
the ganglion of Gasser ; 6, first branch of the fifth pair,
or ophthalmic ; 7, second branch of the fifth pair, or
superior maxillary ; 8, third branch of the fifth pair, or
inferior maxillary ; 9, frontal branch, dividing into ex-
ternal and internal frontal nerves ; 10, lachrymal
branch of the fifth pair ; 11, nasal branch ; just under
the figure is the long root of the lenticular or ciliary
ganglion and a few of the ciliary nerves; 12, internal
nasal nerve, disappearing through the anterior eth-
moidal foramen; 13, external nasal nerve; 14, external
and internal frontal nerve; 15, infra-orbitary nerve ;
16, posterior dental branches; 17, middle dental
branch ; ,18, anterior dental nerve : 19, terminating
branches of the infra-orbital nerve, called the labial
and palpebral nerves; 20, subcutaneous malse, or or-
bitar branch ; 21, pterygoid, or recurrent nerve, from
Meckel's ganglion; 22, five anterior branches of the
third branch of the fifth pair; 23, lingual branch of the
fifth, joined by the chorda tympani ; 24. inferior dental
nerve ; 25, its menial branches ; 26, superficial tempo-
ral nerve ; 27, auricular branches ; 23, mylo-hyoid
branch.]

powers ; but these appear to be derived from the Sympathetic nerve. When
the whole nerve, or its anterior branch, is divided in the rabbit, the pupil is
exceedingly contracted, and remains immovable ; but in dogs and pigeons it
is dilated. The pupil of the other eye is scarcely affected ; or, if its dimen-
sions be changed, it soon returns to its natural state. The eyeball speedily
becomes inflamed, however; and the inflammation usually runs on to suppu-
ration and complete disorganization. The commencement of these changes
may be commonly noticed within twenty-four hours after the operation ; and
they appear to be due to the want of the protective secretion, which (as will
be explained when the direct influence of the nervous system upon the organic
functions is considered), is necessary to keep the mucous surface of the eye
in its healthy condition, and which is not formed when the sensibility of that
surface is destroyed.— The Superior Maxillary branch, considered in itself,
is equally destitute of motor endowments with the ophthalmic ; but its con-
nections with other nerves, through the spheno-palatine ganglion and its anas-
tomosing twigs, may introduce a few motor fibres into it. — The Inferior
Maxillary branch is the only one which possesses motor as well as sensory
endowments from its origin; but its different subdivisions possess these endow-
ments in varying proportions, some being almost exclusively motor, and others
as completely of a sensory character. The latter is probably the nature of
the Lingual branch ; and there seems good reason to believe, as will hereafter
be shown, that this ministers not only to the tactile sensibility of the tongue,
but to the sense of Taste. The muscles put in action by this division of the
Fifth pair, are solely those concerned in the masticatory movements.

405. The Third, Fourth, and Sixth pairs, together make up the appara-
tus of motor nerves, by which the muscles of the Orbit are called into ac-
tion. The Third pair supplies the greater number of the muscles ; the Fourth

CRANIAL NERVES. THIRD TO SEVENTH.

313

being confined to the superior ob- [Fig- 152-

lique, and the Sixth to the abdu-
cens. Of these nerves, the Third
pair is the only one which exhibits
any app.earance of sensibility, when
its trunk is irritated ; but this sen-
sibility is not nearly so great as
that of the Fifth pair ; and it may
be doubted whether it is really pos-
sessed by the Third, in virtue of
its direct connection with the nerv-
ous centres, or whether it is not
imparted by the anastomosis of that
nerve with the Fifth, — some fila-
ments of which may pass back-
wards as well as forwards, so as to
confer sensibility on tbe trunk of
the Third, above as well as beyond
their point of entrance. — The pe-
culiar mode in which these motor
nerves ordinarily excite the mus-
cles to action, will be considered
in the next Section. Although
commonly ranked as cephalic
nerves, they have no direct con-
nection with the Cerebrum ; their
real origin being from the upper
part of the Medulla Oblongata, and
those prolongations of it which are
known as the Crura Cerebri. The

roots of the Third pair may be traced into direct connection with the Cor-
pora Quadrigemina ; a fact of considerable physiological importance, as will
hereafter appear. The chief actions of a purely reflex nature, to which this
group of nerves ordinarily ministers, are the government of the diameter of
the pupil, which is accomplished through the Third pair ; and the rolling of
the eyeball beneath the upper lid during sleep, as well as in the efforts of
sneezing, coughing, &c. But irregular movements of the eyeballs^ which
must be referred to the same group, are continually seen to accompany various
other forms of convulsive action.

406. The Portia Dura of the Seventh pair, or facial nerve, has been
supposed, since the first researches of Sir C. Bell, to be a nerve of motion
only ; but some recent physiologists have maintained, that it both possesses
sensory endowments, and arises by a double root. According to Valentin,
however, who experimented on the roots exposed within the cranium, it pos-
sesses no sensory endowments at its origin ; since, when these roots were
touched, the animals gave no signs of pain, though violent muscular move-
ments were excited in the face. Subsequently to its first entrance into the
canal by which it emerges, however, it anastomoses with other nerves ; and
thus sensory fibres are introduced into it from many different sources, — ante-
riorly, from the Fifth pair, and posteriorly, from the Cervical nerves, — which
cause irritation of several of its branches to produce pain. The number
and situation of the anastomoses vary much in different animals ; so that it
is impossible to make any very comprehensive statement in regard to them.
— Experimental researches leave no doubt that the Portio Dura is the general
motor nerve of the face ; ministering to the influence of volition and Emo-
27

A view ofthe Third, Fourth and Sixth pairs of
Nerves; 1, ball ofthe eye and rectus externus muscle;
2, the superior maxilla ; 3, the third pair, or motores
oculi, distributed to all the muscles of the eye except
the superior oblique and external reclus; 4, the fourth
pair, or palhetici, going to the superior oblique muscle;
5, one of the branches of the seventh pair ; 6, the sixth
pair, or motor externus, distributed to the external
rectus muscle ; 7, spheno-palatine ganglion and
branches; 8, ciliary nerves from the lenticular gan-
glion, the short root of which is seen to connect it with
the third pair.]

314

FUNCTIONS OF THE NERVOUS SYSTEM.
Fig. 153.

The distribution of the Facial jierve, and the branches of the Cervical plexus. 1 .The facial nerve,
escaping from the stylo-mastoid foramen, and crossing the ramus of the lower jaw; the parotid gland
has been removed in order to see the nerve more distinctly. 2. The posterior auricular branch; the
digastric and stylo-mastoid filaments are seen near the origin of this branch. 3. Temporal branches,
communicating with (4) the branches of the frontal nerve. 5. Facial branches, communicating with
(f>) the infra-orbital nerve. 7. Facial branches, communicating with (S) the mental nerve. 9. Cervico-
facial branches, communicating with (10) the superficialis colli nerve, and forming a plexus (11) over
the sub-maxillary gland. The distribution of the branches of the facial in a radiated direction over the
side of the face, constitutes the pes anserinus. 12. The auricularius magnus nerve, one of the ascending
branches of the cervical plexus. 13. The occipitalis minor, ascending along the posterior border of the
sterno-mastoid muscle. 14. The superficial and deep descending branches of the cervical plexus. 15.
The spinal accessory nerve, giving off a branch to the external surface of the trapezius muscle. 16.
The occipitalis major nerve, the posterior branch of the second cervical nerve.

tion, and also being the channel of the Reflex movements concerned in respi-
ration and other associated movements of the muscles ; but not being in the
least concerned in the act of mastication.

a. The distinctness of the Spinal and Encephalic actions of this nerve, is made evident
by the not unfrequent occurrence of paralysis in either of them, without the other being
affected. — Thus we may see the mouth drawn to one side (in consequence of the loss of
tone, which the muscles have experienced), and all the Reflex, and Emotional actions of
the face performed only on one side; and yet Voluntary power may remain unaffected ; so
that, in ordinary winking, the lid of the affected side does not close ; though the patient can
shut the eye by an effort of the will. — On the other hand, the tension of the muscles may
remain unimpaired, and all their Reflex and Emotional actions may be performed as usual ;
and yet distortion may be at once apparent, when Voluntary actions are attempted j in con-
sequence of paralysis of the Cerebral portion of the nerve on one side.

407. The functions of the Glosso-Pharyngeal nerve have been heretofore
alluded to in part ; but there still remain several questions to be discussed in
regard to them. Reasons have been given for the belief that it is chiefly an
afferent nerve, — scarcely having any direct power of exciting muscular con-
traction, but conveying impressions to the Medulla Oblongata, which produce
reflex movements of the other nerves (§ 384). This view of its function has
been deduced by Dr. Reid from minute anatomical investigation, and from a
large number of experiments. Some experimenters assert, that they have
.succeeded in exciting direct muscular actions through its trunk ; but these ac-
tions seem to be limited to the stylo-pharyngei and to the palato-glossi mus-

FUNCTIONS OF THE PAR VAGUM. 315

cles. Much controversy has taken place on the question, whether this nerve is to
be regarded as ministering, partly or exclusively, to the sense of Taste ; and
many high authorities have ranged themselves on each side. The question
involves that of the function of the Lingual branch of the Fifth pair; and it is
partly to be decided by the anatomical relations of the two nerves respectively.
The glosso-pharyngeal is principally distributed on the mucous surface of the
fauces, and on the back of the tongue. According to Valentin, it sends a
branch forwards, on either side, somewhat beneath the lateral margin, which
supplies the edges and inferior surface of the tip of the tongue, and inosculates
with the Lingual branch of the Fifth pair. On the other hand, the upper sur-
face of the front of the tongue is supplied by this lingual branch. The experi-
ments of Dr. Alcock, whose conclusions are borne out by Dr. J. Reid, de-
cidedly support the conclusion, that the gustative sensibility of this part of
the tongue is "due to the latter nerve, being evidently impaired by division of
it. Moreover, cases are by no means rare, in which the gustative sensibility
of the anterior part of the tongue has been destroyed, with its tactual sensi-
bility; when there was no reason to suppose that any other than the Fifth
pair of nerves was involved.* On the other hand, it is equally certain, that
the sense of taste is not destroyed by section of the Lingual nerve on each
side; and it seems also well ascertained, that it is impaired by section of the
Glosso-pharyngeal nerve. Considering how nearly allied is the sense of
Taste to that of Touch, and bearing in mind the respective distribution of
these two nerves, it does not seem difficult to arrive at the conclusion, that both
nerves are concerned in this function ; but there seems good reason to believe
the Glosso-pharyngeal to be exclusively that through which the impressions
made by disagreeable substances taken into the mouth are propagated to the
Medulla Oblongata, so as to produce nausea, and to excite efforts to vomit.

408. Tlie functions of the Par Vagum at its roots have lately been made
the subject of particular examination by various experimenters; some of
whom (for instance, Bischoff, Valentin, Longet, and Morgan ti), have concluded
that it there possesses no motor power, but is entirely a sensory, or rather, an
afferent nerve. According to these, if the roots be carefully separated from
those of the Glosso-Pharyngeal, and (which is a matter of some difficulty)
from those of the spinal Accessory nerve, and be then irritated, no movements
of the organs supplied by it can be observed ; whilst, if the roots be irritated
when in connection with the nervous centres, muscular contractions, evidently
of a reflex character, result from the irritation ; and strong evidences of their
sensibility are also given. It has been further asserted that, when the roots
of the Spinal Accessory nerve are irritated, no indications of sensation are
given ; but that the muscular parts supplied by the Par Vagum, as well as by
its own trunk, are made to contract, even when the roots are separated from
the nervous centres; so that these roots must be regarded as the channel of
the motor influence, transmitted to them from the Medulla Oblongata. When
the Par Vagum swells into the jugular ganglion, an interchange of fibres takes
place between it and the Spinal Accessory; and it seems clear that the pha-
ryngeal branches, which are among the most decidedly motor of all those
given off from the Pneumogastric, may in great part be traced backwards into
the Spinal Accessory. These statements confirm the idea of Arnold and
Scarpa, — that the Par Vagum and Spinal Accessory are together analogous to
a spinal nerve, the former answering to the posterior roots, and the latter to
the anterior. — But, on the other hand, an equally numerous and trustworthy
set of experimenters (among whom may be mentioned J. Reid, Miiller, Volk-
mann, and Stilling) are opposed to this opinion ; maintaining that the Par Va-
gum has motor roots of its own, and that the Spinal Accessory possesses sen-

* Romberg, in Mailer's Archiv., 1838, Heft m.

316 FUNCTIONS OF THE NERVOUS SYSTEM.

Fig. 154. [Fig. 155.

1 3

Origin and distribution of the Eighth pair of nerves.
1, 3, 4, the medulla oblongata; 1, the corpus pyrami-
dale of one side ; 3, the corpus olivare ; 4, the cor-
pus restiforme ; 2, the pons Varolii ; 5, the facial
nerve ; 6, the origin of the glosso-pharyngeal nerve ;
7, the ganglion of Andersch ; 8, the trunk of the nerve;
9, the spinal accessory nerve ; 10, the ganglion of the
pneumogastric nerve; 11, its plexiform ganglion;
12, its trunk; 13, its pharyngeal branch forming the
pharyngeal plexus (14) assisted by a branch from the
glosso-pharyngeul (•-) and one from the superior la-
ryngeal nerve (15) ; 1C, cardiac branches; 17, recur-
rent laryngeal branch ; 18, anterior pulmonary
branches; 19, posterior pulmonary branches; 20,
cusophageal plexus ; 21, gastric branches; 22, origin
of the spinal accessory nerve; 23, its branches dis-
tributed to the sterno-mastoid muscle ; 24, its branches
to the trapezius muscle.

A view of the distribution of the Glosso-Pha
ryngeal Pneumogastrio and Spinal Accessory
Nerves, or the Eighth pair ; 1, the inferior max-
illary nerve ; 2, the gustatory nerve ; 3, the
chorda-tympani ; 4, the auricular nerve; 5, its
communication with the portio dura; G, the fa-
cial nerve coming out of the stylo-mastoid fora-
men ; 7, the glosso-pharyngeal nerve ; 8, branch-
es to the stylo- pharyngeus muscle; 9, the pha-
ryngeal branch of the pneumogastric nerve
descending to form the pharyngeal plexus; 10,
branches of the glosso-pharyngeal to the pha-
ryngeal plexus ; 11, the pneumogastric nerve ;
12, the pharyngeal plexus; 13, the superior la-
ryngeal branch ; 14, branches to the pharyngeal
plexus; 15, 15, communication of the superior
and inferior laryngeal nerves ; 16, cardiac
branches ; 17, cardiac branches from the right
pneumogastric nerve ; IS, the left cardiac gan-
glion and plexus; 19. the recurrent or inferior
liiryngeal nerve; 20, branches sent from the
curve of the recurrent nerve to the pulmonary
plexus; 21, the anterior pulmonary plexus; 22,
22, the oesophageal plexus.]

FUNCTIONS OF THE PAR VAGUM. 317

sory roots ; and affirming that irritation of the roots of the Spinal Accessory
produces little or no effect on the muscles supplied by the trunk of the Par
Vagum. The fact appears to be, that the roots of these two nerves are so
commingled, that it is difficult to say what belong exclusively to each. Some
of the fibres usually considered to belong to the Spinal Accessory, are occa-
sionally seen to connect themselves with the roots of the Par Vagum, even
before the ganglion is found upon it. And it seems most probable, that the
roots of the Spinal Accessory are chiefly motor, and those of the Par Vagum
chiefly afferent; that they inosculate with each other in a degree which may
vary in different species, and even in different individuals ; and that the Par
Vagum may thus derive additional motor fibres from the Spinal Accessory,
whilst it supplies that nerve with additional afferent fibres. — In regard to its
trunk, there can be no doubt that the Par Vagum is to be considered as a
nerve of double endowments ; although it is certain that these endowments
are very differently distributed amongst its branches. That the nerve is capa-
ble of conveying those impressions which become sensations when commu-
nicated to the sensorium, is experimentally proved by the fact that, when its
trunk is pinched, the animal gives signs of acute pain ; but it is also evident
from the painful consciousness we occasionally have of an abnormal condition
of the organs which it supplies. Thus, the suspension of the respiratory
movements gives rise to a feeling of the greatest uneasiness, which must be
excited by impressions conveyed through this nerve from the lungs ; and an
inflamed state of the walls of the air-passages causes the contact of cold and
dry air to produce distressing pain and irritation. Yet, of the ordinary im-
pressions conveyed from these organs, which are concerned in producing the
respiratory movements, and in regulating the actions of the glottis, we are not
conscious. The same may be said of the portion of the nerve distributed
upon the alimentary tube. The pharyngeal branches are almost exclusively
motor, the afferent function being performed by the Glosso-pharyngeal ; whilst
the oesophageal and gastric are both afferent and motor, conveying impressions
which excite reflex movements in the muscles of those parts, but which do
not become sensations except under extraordinary circumstances.

409. The section of the Par Vagum produces, as would readily be expected,
great disorder of the functions of Respiration and Digestion, to which it minis-
ters. It is an operation which has been very frequently performed ; and the
statements of its results vary considerably amongst each other, being generally
influenced, in some degree, by the preconceived views of the experimenter.*
The section of the Par Vagum, when practised with the view of ascertaining
the influence of the nerve upon the lungs and stomach, is usually made in the
neck, between the origins of the superior and inferior (or recurrent) laryngeal
branches. Hence the muscles of the larynx are paralyzed (§ 379) ; and, if the
animal should struggle violently, the ingress of air is likely to be obstructed
by the flapping down of the arytenoid cartilages, and by the closure of the
glottis. This is especially the case in young animals, in which the larynx is
small. But in those that are full grown, and have a large larynx, an adequate
quantity of air may still find its way through the aperture, if the animal refrain
from any violent effort. In a considerable number of Dr. Reid's experiments,
therefore, he did not find it necessary to introduce the trachea-tube, which
other experimenters have generally employed ; an opening was made into the
trachea, however, in those instances in which, from any cause, the entrance of
air was obstructed.

* The Author employs, as in his opinion the most worthy of confidence, the experiments
of Dr. J. Reid (Edinb. Med. and Surg. Journ., vols. xlix. and li.), on whose accuracy he has
strong personal reasons for placing reliance; and whose anatomical and pathological attain-
ments are such as to render him fully competent to the task.

27*

318 FUNCTIONS OF THE NERVOUS SYSTEM.

410. The functions of the Pharyngeal and Laryngeal branches of the Pneu-
mogastric having been already explained (§§ 378, 379, and 385), we may now
proceed to its Pulmonary division. In regard to this, we have to notice, that
its endowments are chiefly afferent ; its most important office being, to con-
vey to the Medulla Oblongata the impression produced by venous blood in
the capillaries of the lungs, or of carbonic acid in the air-cells. This impres-
sion may give rise, as we have seen, to respiratory movements, without pro-
ducing sensation; but if it be from any cause stronger than usual, the sense of
uneasiness which it occasions is very distressing. The impression may be
imitated by pressure on the nerve ; which occasions an immediate inspiratory
movement. Hence the -chief function of the afferent portion of the pulmonary
division of the Par Vagum, is to serve as an excitor to the respiratory move-
ments ; which are consequently diminished in frequency, when the trunk is
divided on both sides. — But this division also contains motor fibres, which
are distributed upon the muscular fibres surrounding the bronchial tubes ; and
the experiments of Dr. Williams, which have been recently confirmed by
Longet and Volkmann, agree in proving, that the calibre of the bronchial tubes
can be caused to contract in a very considerable degree, by stimuli applied to
this nerve, and especially by electricity.

411. Various alterations are produced in the Lungs, by section of the Pneu-
mogastric nerves. The order in which these arise, and the causes to which
they are immediately due, constitute very interesting subjects of investigation;
and the knowledge of them will probably throw light upon many ill-understood
morbid phenomena.

a. In the first place, it has been fully established by Dr. Reid, that section of the Vagus
on one side only does not necessarily, or even generally, induce disease of that lung; and
hence the important inference may be drawn, that the nerve does not exercise any immediate
influence on its functions. When both Vagi are divided, however, the animal rarely survives
long; but its death frequently results from the disorder of the digestive functions. Never-
theless, the power of digestion is sometimes restored sufficiently to re-invigorate the animals;
and their lives may then be prolonged for a considerable time. In fifteen out of seventeen
animals experimented on by Dr. Reid, the lungs were found more or less unfit for the
healthy performance of their functions. The most common morbid changes were a congested
state of the blood-vessels, and an effusion of frothy serum into the air-cells and bronchial tubes.
In eight out of the fifteen, these changes were strongly marked. In some portions of the
lungs, the quantity of blood was so great as to render them dense. The degree of conges-
tion varied in different parts of the same lung ; but it was generally greatest at the most
depending portions. The condensation was generally greater, than could be accounted for
by the mere congestion of blood in the vessels ; and probably arose from the escape of the
solid parts of the blood into the tissue of the lung. In some instances the condensation was
so great, that considerable portions of the lung sank in water, and did not crepitate ; but
they did not present the granulated appearance of the second stage of ordinary pneumonia.
In five cases in which the animals had survived a considerable time, portions of the lungs
exhibited the second, and even the third stages of pneumonia, with puriform effusion into
the small bronchial tubes; and in two, gangrene had supervened.

b. One of the most important points to ascertain, in an investigation of this kind, is the
first departure from a healthy state ; — to decide whether the effusion of frothy reddish serum,
by interfering with the usual change in the lungs, causes the congested state of the pulmo-
nary vessels and the laboured respiration • or whether the effusion is the effect of a pre-
viously congested state of the blood-vessels. The former is the opinion of many physiolo-
gists, who have represented the effusion of serum as a process of morbid secretion, directly
resulting from the disorder of that function produced by the section of the nerve; the latter
appears the unavoidable inference from the carefully-noted results of Dr. Reid's experiments.
In several of these, only a very small quantity of froihy scrum was found in the air-tubes,
even when the lungs were found loaded with blood, and when the respiration before death
was very laboured. This naturally leads us to doubt, whether the frothy serum is the cause
of the laboured respiration, and of the congested state of the pulmonary vessels, in those
cases where it is present; though there can be no doubt that, when once it is effused, it must
powerfully tend to increase the dilliculty of respiration, and still further to impede the cir-
culation through the lungs. Dr. R. has satisfied himself of an important point, which has

FUNCTIONS OF THE PAR VAGT7M. 319

been overlooked by others — that this frothy fluid is not mucus, though occasionally mixed
with it; but that it is the frothy serum so frequently found in cases where the circulation
through the lungs has been impeded before death. From this and other facts, Dr. R. con-
cludes " that the congestion of the blood-vessels is the first departure from the healthy state
of tin- lung, and that the effusion of frothy serum is a subsequent effect."

c. The next point, therefore, to be inquired into, is the cause of this congestion ; and this
is most satisfactorily explained, upon the general principles regulating the circulation of the
blood, by remembering that section of the Par Vagum greatly diminishes the frequency of
the respiratory movements, and that the quantity of air introduced into the lungs is, there-
fore, very insufficient for the due aeration of the blood. We shall hereafter see reason to
regard it as one of the best established principles in Physiology, that the activity of the
changes which the blood undergoes in the capillary vessels, does, in some way or other,
regulate its movement through them ; — that, when these changes are proceeding with ac-
tivity, the capillary circulation is proportionably accelerated ; — and that when they are ab-
normally low in degree, the movement of the blood in the capillaries is stagnated. There
is now abundant evidence, in regard to the Pulmonary circulation in particular, that, to pre-
vent the admission of oxygen in the lungs, either by causing the animal to breathe pure
nitrogen or hydrogen, or by occlusion of the air-passages, is to bring the circulation through
their capillaries to a speedy check. Hence we should at once be led to infer, that diminu-
tion in the number of Respiratory movements would produce the same effect; and as little
or no difference in their frequency is produced by section of one Vagus only, the usual ab-
sence of morbid changes in the lung supplied by it is fully accounted for. The congestion
of the vessels, induced by insufficient aeration, satisfactorily accounts not only for the effusion of
serum, but also for the tendency to pass into the inflammatory condition, sometimes pre-
sented by the lungs, as by other organs similarly affected. Dr. Reid confirms this view, by
the particulars of cases of disease in the human subject, in which the lungs presented after
death a condition similar to that observed in the lower animals after section of the Vagi ;
and in these individuals, the respiratory movements had been much less frequent than natu-
ral during the latter part of life, owing to a torpid condition of the nervous centres. The
opinion (held especially by Dr. Wilson Philip) that section of the par vagum produces the
serous effusion, by its direct influence on the function of Secretion, is further invalidated by
the fact stated by Dr. Reid, — that he always found the bronchial membrane covered with its
true mucus, except when inflammation was present.

" The experimental history of the Par Vagum," it is justly remarked by
Dr. Reid, "furnishes an excellent illustration of the numerous difficulties with
which the physiologist has to contend, from the impossibility of insulating
any individual organ from its mutual actions and reactions, when he wishes
to examine the order and dependence of its phenomena." In such investi-
gations, no useful inference can be drawn from one or two experiments only ;
in order to avoid all sources of fallacy, a large number must be made ; the
points in which all agree must be separated from others, in which there is a
variation of results ; and it must be then inquired, to what the latter is due.

412. These observations apply equally to the other principal subject of in-
quiry in regard to the functions of the Par Vagum, — its influence upon the
process of Digestion. The results obtained by different experimenters have
led to differences of opinion as to its action, no less remarkable than those
which have prevailed on the question just discussed. Thus, in regard to the
afferent fibres of the Gastric division of the nerve, some physiologists main-
tain it to be by impressions on them alone, that the sense of hunger or satiety
is excited; whilst others deny that they have any power of transmitting such
impressions, which, according to them, do not originate in the stomach at all.
Dr. Reid has arrived at the conclusion, from his numerous experiments, that
the Par Vagum is the channel through which the mind becomes cognizant of
the condition of the stomach ; but that it is not the sole excitor of the sense
of hunger. Animals, which have sustained section of the nerve on both sides,
will eagerly take food, if they have not received too great a shock from the
operation ; but they seem to experience no feeling of satiety when the sto-
mach is loaded. This inference is confirmed by Valentin, who mentions that
puppies after the operation will take three times the same quantity of milk,
as uninjured individuals of the same age, so as greatly to distend the abdomen.

320 FUNCTIONS OF THE NERVOUS SYSTEM.

The act of Vomiting has been proved to be excitable by impressions trans-
mitted through the Gastric branches of the Par Vagum ; although they con-
stitute by no means the only channel, through which the various muscles con-
cerned in it may be called into combined action (§ 505).

413. The question -of the influence of the motor fibres of the Pneumo-
gastric, upon the muscular walls of the stomach, has been already in part dis-
cussed (§ 387). Although it seems unquestionable that they have the power
of stimulating these muscles to contraction, yet there is evidence that the
movements of the stomach, which are most essential to digestion, may take
place without it. Thus Dr. Reid found, in several of his experiments, that
food was not only digested in the Stomach, but propelled into the Duodenum,
subsequently to the operation. It seems very probable, however, that a tem-
porary suspension of these movements (as of other independent functions of
the stomach) may be the first effect of the operation.

414. It is necessary here to stop to notice, on account of the currency
which it has obtained, the doctrine of Dr. Wilson Philip ; — that the Par Va-
gum controls the secretion of the Gastric fluid ; and that its division checks
the secretion. He further stated, that the influence of Galvanism propagated
along the nerve, would re-establish the secretion. This statement has been quoted
and re-quoted, as an established physiological position ; and, when united with
the well-known fact, that galvanism would excite muscular contraction, it has
seemed to Dr. W. Philip and other physiologists sufficient to establish the
important position, that galvanism and nervous influence are identical. It has
been disputed, however, by many other experimenters ; who have satisfied
themselves that the secretion of gastric juice continues after the operation;
and consequently, that the elaboration of this product cannot be dependent on
nervous influence supplied by the Par Vagum, though doubtless in part regu-
lated by it. The first effects of the operation, however, are almost invariably
found to be vomiting (in those animals capable of it), loathing of food, and
arrestment of the digestive process ; and it is not until after four or five days,
that the power seems re-established. In the animals which died before that
time, no indication of it could be discovered by Dr. R. ; in those which survived
longer, great emaciation took place ; but when life was sufficiently prolonged, the
power of assimilation seemed almost completely restored. This was the
case in four out of the seventeen dogs experimented on ; and the evidence of
this restoration consisted in the recovery of flesh and blood by the animals,
the vomiting of half-digested food permanently reddening litmus paper, the
disappearance of a considerable quantity of alimentary matter from the intes-
tinal canal, and the existence of chyle in the lacteals. It may serve to account
in some degree for the contrary results, obtained by other experimenters, to
state that seven out of Dr. R.'s seventeen experiments were performed before
he obtained any evidence of digestion after the operation ; and that the four
which furnished this followed one another almost in succession ; so that it is
easy to understand why those who were satisfied with a small number of
experiments, should have been led to deny it altogether.

[M. Bernard has instituted fresh experiments to determine this still-debated question,
ninking use of the artificial fistulous openings into the stomach, invented by M. Blondlot.
A dog's digestion had been thus watched for eight days, and had always been well effected.
On the ninth day, after a day's fast, M. Bernard sponged out the Stomach, which contracted
on the contact of the sponge, and at once secreted a large quantity of gastric fluid ; he then
divided the pneumogastric nerves in the' middle of the neck, and immediately the mucous
membrane, which had been turgid, became pale, as if exsanguine, its movements ceased,
the secretion of gastric fluid was instantaneously put a stop to, and a quantity of ropy neutral
mucus was soon produced in its place. Al'ter this, no digestion was duly performed, and
milk was no longer coagulated; raw meat remained unchanged, and the food (meat, milk,
bread and sugar, which the dog had before thoroughly digested) remained for a long time

FUNCTIONS OF THE PAR VAGUM. 321

neutral, and at last acquired acidity only from its own transformation into lactic acid. In
the stomachs of other dogs after the division of the nerves, he traced the transformation of
cane-sugar into grape-sugar in three or four hours; and in ten or twelve hours the trans-
formation into lactic acid was complete. In others, when the food was not capable of an
acid transformation, it remained neutral to the last. In no case did any part of the food pass
through the peculiar changes of chymification. In a last experiment, he gave to each of two
dogs, in one of which he had cut the nerves, a dose of emulsine, and half an hour after, a
dose of amygdaline (substances which are innocent alone, but when mixed produce hydro-
cyanic acid). The dog, whose, nerves were cut, died in a quarter of an hour, the sub-
stances being absorbed unaltered and mixing in the blood: in the other, the emulsine was
changed by the action of the gastric fluid before the amygdaline was administered, and it
survived. — Gazette Med., Juin 1, 1844,/rom the Report of the Jicad. dcs Sci., seance du 27 Mai,
1844.— M. C.]

a. Another series of experiments was performed by Dr. Reid, for the purpose of testing
the validity of the results obtained by Sir B. Brodie, relative to the effects of section of the
Par Vagura upon the secretions of the stomach, after the introduction of arsenious acid into
the system. According to that eminent Surgeon and Physiologist, when the poison was
introduced after the Par Vagum had been divided on each side, the quantity of the pro-
tective mucous and watery secretions was much less than usual, although obvious marks of
inflammation were present. In order to avoid error as much as possible, Dr. Reid made five
sets of experiments, employing two dogs in each, as nearly as possible of equal size and
strength, introducing the same quantity of the poison into the system of each in the same
manner, but cutting the Vagi in one, and leaving them entire in the other. This comparative
mode of experimenting is obviously the only one admissible in such an investigation. Its
result was in every instance opposed to the statements of Sir B. Brodie ; the quantity of the
mucous and watery secretions of the stomach being nearly the same, in each individual of
the respective pairs subjected to experiment; so that they can no longer be referred to the
influence of the Eighth pair of nerves. Moreover, the appearances of inflammation were, in
four out of the five cases, greatest in the animals whose Vagi were left entire ; and this seemed
to be referrible to the longer duration of their lives after the arsenic had been introduced.
The results of Sir B. Brodie's experiments may perhaps be explained, by the speedy occur-
rence of death in the subjects of them, consequent (it may be) upon the want of suffi-
ciently free respiration, which was carefully guarded against by Dr. Reid.

415. So far as the results of Dr. Reid's experiments may be trusted to,
therefore, (and the Author is himself disposed to rely on them almost im-
plicitly,) all the arguments which have been drawn in favour of the doctrine
that Secretion depends upon Nervous agency, from the effects of lesion of the
Vagi upon the functions of the Stomach, must be set aside. That this nerve
has an important influence on the gastric secretion, is evident from the defi-
ciency in its amount soon after the operation, as well as from other facts.
But this is a very different proposition from that just alluded to; and the
difference has been very happily illustrated by Dr. R. " The movements of
a horse," he observes, " are independent of the rider on his back, — in other
words, the rider does not furnish the conditions necessary for the movements
of the horse; — but every one knows how much these movements may be
influenced by the hand and heel of the rider." It may be hoped, then, that
physiologists will cease to adduce the oft-cited experiments of Dr. Wilson
Philip, in favour of the hypothesis (for such it must be termed) that secretion
is dependent upon nervous influence, and that this is identical with galvan-
ism.— Additional evidence of their fallacy is derived from the fact mentioned
by Dr. Reid, that the usual mucous secretions of the stomach were always
found; and they are further invalidated by the testimony of Miiller, who
denies that galvanism has any peculiar influence in re-establishing the gastric
secretion, when it has been checked by section of the nerves.

416. It only remains to notice the influence of section of the Vagi upon
the actions of the Heart. It has been asserted by Valentin and other experi-
menters, that mechanical irritation of these nerves, especially at their roots,
has a tendency to excite or accelerate the heart's action; other experimenters,
however, have obtained none but negative results. Admitting, what seems
probable, that the Cardiac branches of the Pneumogastric have some influence

322 FUNCTIONS OF THE NERVOUS SYSTEM.

upon the Heart's action, it remains to inquire whether that influence is essen-
tial to its movements ; and whether these nerves form the channel, through
which they are affected by emotions of the mind, or by conditions of the
bodily system. In regard to the first point, no doubt can be entertained;
since the regular movements of the heart are but little affected by section of
the Vagi. With respect to the second, there is more difficulty ; since the
number of causes, which may influence the rapidity and pulsations of the
heart, is very considerable. For example, when the blood is forced on more
rapidly towards the heart, as in exercise, struggling, &c., the stimulus to its
contractions is more frequently renewed, and they become more frequent;
and when the current moves on more slowly, as in a state of rest, their fre-
quency becomes proportionably diminished. If the contractions of the heart
were not dependent upon the blood, and their number were not regulated by
the quantity flowing into its cavities, very serious and inevitably fatal dis-
turbances of the heart's action would soon result. That this adjustment takes
place otherwise than through the medium of the nervous centres, is evident
from the fact that, in a dog, in which the par vagum and sympathetic had
been divided in the neck on each side, violent struggling, induced by alarm,
raised the number of pulsations from 130 to 260 per minute. It is difficult
to ascertain, by experiment upon the lower animals, whether simple emotion,
unattended with struggling or other exertion, would affect the pulsation of the
heart, after section of the Vagi; but when the large proportion of the Sympa-
thetic nerves proceeding to this organ is considered, and when it is also re-
membered that irritation of the roots of the upper cervical nerves stimulates
the action of the heart through these, we can scarcely doubt that both may
serve as the channels of this influence, especially in such animals as the dog,
in which the two freely inosculate in the neck.

417. In regard to the functions of the Spinal Accessory nerve, also, there
has been great difference of opinion; the peculiarity of its origin and course
having led to the belief, that some very especial purpose is answered by it.
The predominance of motor fibres in its roots, its inosculation with the Par
Vagum, and its probable reception of sensory fibres from the latter whilst
imparting to it motor filaments, have been already referred to (§ 408). As its
trunk passes through the foramen lacerum, it divides into two branches; of
which the internal, after giving off some filaments that assist in forming the
pharyngeal branch of the Par Vagum, becomes incorporated with the trunk of
that nerve; whilst the external proceeds outwards, and is finally distributed to
the sterno-cleido-mastoideus and trapezius muscles, some of its filaments
inosculating with those of the cervical plexus. When the external branch is
irritated, before it perforates the sterno-mastoid muscles, vigorous convulsive
movements of that muscle, and of the trapezius, are produced; and the animal
does not give any signs of pain, unless the nerve is firmly compressed between
the forceps, or is included in a tight ligature. Hence it may be inferred, that
the functions of this nerve are chiefly motor, and that its sensory filaments are
few in number. Further, when the nerve has been cut across, or firmly tied,
irritation of the lower end is attended by the same convulsive movements of
the muscles; whilst irritation of the upper end, in connection with the spinal
cord, is unattended with any muscular movement. Hence it is clear that the
motions occasioned by irritating it are of a direct, not of a reflex character.
The same muscular movements are observed on irritating the nerve in the
recently-killed animal, as during life.

a. According to Sir C. Bell, the Spinal Accessory is a purely Respiratory nerve, whose office
it is to excite the involuntary or automatic movements of the muscles it supplies, which
share in the a<-t of n-.-piration ; and he Mates that the division of it paralyzes the muscles to
which it is distributed, as muscles of respiration ; though they still perform the voluntary

HYPOGLOSSAL NERVE. 323

movements, through the medium of the spinal nerves. Both Valentin and Dr. Reid, however,
positively deny that this is the case. Dr. Reid's method of experimenting was well adapted
to test the truth of the assertion. Considering that, in the ordinary condition of the animal,
it might be difficult to distinguish the actions of particular muscles, beneath the skin, when
those in the neighbourhood were in operation ; and also that the usual automatic movements
might be simulated by voluntary action, when the breathing might be rendered difficult; he
adopted the following plan : — A small dose of prussic acid was given to an animal, in which
the Spinal Accessory had been previously divided on one side ; and after the convulsive
movements produced by it had ceased, the animal was generally found in a state similar to
mat which we sometimes see in apoplexy, — the action of the heart going on, the respirations
being slow and heaving, and the sensorial functions appearing to be completely suspended.
The Respiratory movements always ceased before the action of the heart; but they con-
tinued, in several of the animals experimented on, sufficiently long to allow the muscles of
the anterior part of the neck to be laid bare, so that accurate observations could be made
upon their contractions. In the clog and cat, the sterno-mastoid does not appear to have
much participation in the ordinary movements of respiration ; for in several instances it
could not be seen to contract on either side, though the head was forcibly pulled towards the
chest at each inspiratory movement, chiefly by the action of the sterno-hyoid and thyroid
muscles. In two dogs and one cat, however, in which the head was fixed, and these
respiratory movements were particularly vigorous, distinct contractions were seen in the
exposed sterno-mastoid muscles, synchronous with the other movements of respiration : these
were, perhaps, somewhat weaker on the side on which the nerve had been cut, but were
still decidedly present. In one of these dogs, similar movements were observed in the
trapezius, on the side on which the nerve had been divided. As the condition of the animal
forbade the idea that volition could be the cause of these movements, it can scarcely be ques-
tioned that Sir C. Bell's statement was an erroneous one. As far, therefore, as these experi-
ments afford any positive data, in regard to the functions of this nerve, it may be concluded
that they are the same as those of the cervical plexus, with which it anastomoses freely.
"Future anatomical researches," as Dr. Reid justly remarks, "may perhaps explain to us how
it follows this peculiar course, without obliging us to suppose that it has a reference to any
special function in the adult of the human species." Thus, the study of the history of
development has accounted satisfactorily for the peculiar course of the recurrent laryngeal,
which may be traced passing directly from the par vagum to the larynx, at a time when the
neck can scarcely be said to exist, and when that organ is buried in the thorax. As this
rises in the neck, the nerve, which at first came off below the great transverse blood-vessels,
has both its origin and its termination carried upwards ; whilst it is still tied down by these
vessels in the middle of its course.

418. The Hypoglossal nerve, or Motor Linguse, is the only one which,
in the regular order, now remains to be considered. That the distribution of
this nerve is restricted to the muscles of the tongue, is a point very easily
established by anatomical research ; and accordingly we find that, long before
the time of Sir C. Bell, Willis spoke of it as the nerve of the motions of
articulation, whilst to the Lingual branch of the fifth pair he attributed the
power of exercising the sense of taste ; and he distinctly stated, that the
reason of this organ being supplied with two nerves is its double function.
The inference that it is chiefly, if not entirely, a motor nerve, which has been
founded upon its anatomical distribution, is supported also by the nature of
its origin, which is usually from a single root, corresponding to the anterior
root of the Spinal nerves. Experiment shows that, when the trunk of the
nerve is stretched, pinched, or galvanized, violent motions of the whole tongue,
even to its tip, are occasioned; and also, that similar movements take place
after division of the nerve, when the cut end most distant from the brain is
irritated. In regard to the degree in which this nerve possesses sensory pro-
perties, there is some difference of opinion amongst physiologists, founded, as
it would seem, on a variation in this respect between different animals.
Indications of pain are usually given, when the trunk is irritated after its exit
from the cranium; but these may proceed from its free anastomosis with the
cervical nerves, which not improbably impart sensory fibres to it. But in
some Mammalia, the hypoglossal nerve has been found to possess a small
posterior root with a ganglion : this is the case in the ox, and also in the rabbit ;

324

FUNCTIONS OF THE NERVOUS SYSTEM.

and ill the latter animal, Valentin states that the two trunks pass out from the
cranium through separate orifices, and that, after their exit, one may be shown

[Fig. 156.

The course and distribution of the Hypo-Glossal or Ninth pair of nerves ; the deep-seated nerves ot
the neck are also seen; 1, the hypo-glossal nerve; 2, branches communicating with the gustatory nerve ;
3, a branch to the origin of the hyoid muscles ; 4, the descendens noni nerve ; 5, the loop formed with the
branch from the cervical nerves ; 6, muscular branches to the depressor muscles of the larynx j 7, a
filament from the second cervical nerve, and 8, a filament from the third cervical, uniting to form the
communicating branch with the loop from the descendens noni; 9, the auricular nerve; 10, the inferior
dental nerve ; 11, its mylo-hyoidean branch; 12, the gustatory nerve ; 13, the chorda-tympani passing to
the gustatory nerve; 14, the chorda-tympani leaving the gustatory, nerve to join the sub-maxillary
ganglion; 15, the sub-maxillary ganglion; 16, filaments of communication with the lingual nerve; 17,
the glosso-pharyngeal nerve; 18, the pneumogastric or par vagum nerve; 19, the three upper cervical
nerves; 20, the four inferior cervical nerves; 21, the first dorsal nerve; 22, 23, the brachial plexus ; 24,
25, the phrenic nerve; 26, the carotid artery; 27, the internal jugular vein.]

to be sensory, and the other to be motor. Hence, this nerve, which is the
lowest of those that originate in the cephalic prolongation of the spinal cord,
generally known as the medulla oblongata, approaches very closely in some
animals to the regular type of the spinal nerves; and though in Man it still
manifests an irregularity, in having only a single root, yet this irregularity is
often shared by the first cervical nerve, which also has sometimes an anterior
root only.

419. The Hypoglossal nerve is distributed not merely to the tongue, but to
the muscles of the neck which are concerned in the movements of the larynx ;
and the purpose of this distribution is probably to associate them in those
actions, which are necessary for articulate speech. Though all the motions
of the tongue are performed through the medium of this nerve, yet it would
appear, from pathological phenomena, to have at least two distinct connec-
tions with the nervous centres ; for in many cases of paralysis, the masticatory
movements of the tongue are but little affected, when the power of articula-
tion is much injured or totally destroyed : and the converse may be occasion-
ally noticed. When this nerve is paralyzed on one side, in hemiplegia, it
will be generally observed that the tongue, when the patient is directed to put

CEPHALIC NERVES IN GENERAL. 325

it out, is projected towards the palsied side of the face : this is due to the
want of action of the lingual muscles of that side, which do not aid in pushing
forward the tip ; the point is consequently directed only by the muscles of
the other side, which will not act in a straight direction, when unantagonized
by their fellows. It is a curious fact, however, that the hypoglossal nerve
seems not to be always palsied on the same side with the facial, but sometimes
on the other. This has been suggested to be due to the origination of the
roots of this nerve from near the point, at which the pyramids of the medulla
oblongata decussate ; so that some of its fibres come off, like those of the
spinal nerves, without crossing ; whilst others are transmitted to the opposite
side, like those of the higher cerebral nerves ; and the cause of paralysis may
affect one or other of these sets of roots more particularly. Whatever may
be the validity of this explanation, the circumstance is an interesting one, and
well worthy of attention.*

420. The general character and arrangement of the Cephalic nerves, as
distinguished from the ordinary Spinal, constitute a study of much interest,
when considered in relation to Comparative Anatomy, and to Embryology. It
appears, from what has been already stated, that the Par Vagum, Spinal
Accessory, Glosso-pharyngeal, and Hypoglossal nerves, may be considered
nearly in the light of ordinary Spinal nerves. They all take their origin ex-
clusively in the Medulla Oblongata ; and the want of correspondence in posi-
tion, between their roots and those of the Spinal nerves, is readily accounted
for by the alteration in the direction of the columns of the Spinal Cord,
which, — as long since pointed out by Rosenthal, and lately stated prominently
by Dr. Reid, — not only decussate laterally, but, as it were, antero-posteriorly
(§ 353). The Hypoglossal, as just stated, not unfrequently possesses a sen-
sory in addition to its motor root. The Glosso-pharyngeal, which is princi-
pally an afferent nerve, is stated by Arnold and others to have a small motor
root; at any rate, the motor fibres which answer to it are to be found in the
Par Vagum. That the Par Vagum and a portion of the Spinal Accessory
together make up a spinal nerve, has been already stated as probable.

421. Leaving these nerves out of the question, therefore, we proceed to the
rest. Comparative anatomy, and the study of Embryonic development, alike
show that the Spinal cord and Medulla Oblongata constitute the most essen-
tial part of the nervous system in Vertebrata ; and that the Cerebral Hemi-
spheres are superadded, as it were, to this. At an early period of develop-
ment, the Encephalon consists chiefly of three vesicles, which correspond
with the ganglionic enlargements of the nervous cord of the Articulata, and
mark three divisions of the cerebro-spinal axis ; and, in accordance with this
view, the Osteologist is able to trace, in the bones of the cranium, the same
elements which would form three vertebrae, in a much expanded and altered
condition. However improbable such an idea might seem, when the cranium
of the higher Vertebrata alone is examined, it at once reconciles itself to our
reason, when we direct our attention to that of Reptiles and Fishes ; in
which classes the size of the Cerebral or hemispheric ganglia is very small,
in comparison with that of the Ganglia of special sensation; and in which the
latter evidently form but a continuation of the Spinal Cord, modified in its
function ; so that, when we trace upwards the cavity of the spinal column
into that of the cranium, we encounter no material change, either in its size or

* It may be questioned, however, whether the Hypoglossal is really paralyzed on the op-
posite side from the facial in such cases. An instance has been communicated to the Author
by Dr. W. Budd, in which the hypoglossal nerve was completely divided on one side ; and
yet the tip of the tongue, when the patient was desired to put it out, was sometimes directed
from and sometimes towards the palsied side ; showing that the muscles of either half are
sufficient to give any required direction to the whole.
28

326 FUNCTIONS OF THE NERVOUS SYSTEM.

direction. The three pairs of nerves of special sensation make their way
out through these three cranial vertebrae respectively. At a later period of
development, other nerves are interposed between these ; which, being inter-
vertebral, are evidently more analogous to the Spinal nerves, both in situation
and function. A separation of the primitive fibres of these takes place, how-
ever, during the progress of development, so that their distribution appears
irregular. Thus the greater part of the sensory fibres are contained in the
large division of the Trigeminus ; whilst, of the motor fibres, the anterior
ones chiefly pass forwards as the Oculo-motor and Patheticus ; and of the
posterior, some form the small division of the Trigeminus, and others unite
with the first pair from the Medulla Oblongata to form the Facial. This last
fact explains the close union which is found in Fishes and some Amphibia,
between that nerve and those proceeding more directly from the Medulla Ob-
longata. According to Valentin, the Glosso-pharyngeal is the sensory por-
tion of the first pair from the Medulla Oblongata, of which the motor part is
chiefly comprehended in the Facial nerve. It is very interesting to trace this
gradual metamorphosis from the character of the Spinal nerves, which is ex-
hibited in the Cephalic, when they are traced upwards from the Medulla Ob-
longata ; and this is shown also, in some degree, in the nerves of special sen-
sation (§ 446, or). Although we are accustomed to consider the Fifth pair as
par eminence the Spinal nerve of the head, the foregoing statements, founded
upon the history of development, show that the nerves of the Orbit really
belong to its motor portion ; they may consequently be regarded as altogether
forming \\\e first of the inter vertebral or Spinal nerves of the cranium. The
Facial and Glosso-pharyngeal appear to constitute the second ; whilst the Par
Vagum and Spinal Accessory, forming the third pair, intervene between this
and the true spinal, of which the Hypoglossal may be considered as the first.

5. Of the Sensory Ganglia and their Functions. — Consensual Movements.

422. At the base of the Brain in Man, concealed by the Cerebral Hemi-
spheres, but still readily distinguishable from them, we find a series of gan-
glionic masses ; which are in direct connection with the nerves of Sensation;
and which appear to have functions quite independent of those of the other
components of the Encephalon. — Thus 'anteriorly we have the Olfactive
ganglia, in what are commonly termed the bulbous expansions of the Olfactive
nerve. That these are real ganglia, is proved by their containing grey or ve-
sicular substance ; and their separation from the general mass of the Encepha-
lon, by the peduncles or footstalks commonly termed the trunks of the Olfac-
tory nerves, finds its analogy in many species of Fish (§ 357). The ganglionic
nature of these masses is more evident in many of the lower Mammalia, in
which the organ of smell is highly developed, than it is in Man, whose olfac-
tive powers are comparatively moderate. — At some distance behind these, we
have the representatives of the Optic ganglia, in the Tubercula Quadrigemina,
to which the principal part of the roots of the Optic nerve may be traced.
Although these bodies are so small in Mail, in comparison to the whole En-
cephalic mass, as to be apparently insignificant, yet they are much larger, and
form a more evidently important part of it in many of the lower Mammalia;
though slill presenting the same general aspect. — The Auditory ganglia do
not form distinct lobes or projections ; but are lodged in the substance of the
Medulla Oblongata. Their real character is most evident in certain Fishes, as the
Carp ; in which we trace the Auditory nerve into a ganglionic centre as distinct
ns the Optic ganglion. In higher animals, however, and in Man, we are able
to trace the Auditory nerve into a small mass of vesicular matter, which lies
on each side of the Fourth Ventricle ; and although this is lodged in the midst

SENSORY GANGLIA. CONSENSUAL ACTIONS.

327

of parts whose function is altogether different, yet there seems no reason for
doubting that it has a character of its own, and that it is really the ganglionic

[Fig. 157.

A view of the base of the Cerebrum and Cerebellum, together with their nerves ; 1, anterior extremity
of the fissure of the hemispheres of the brain ; 2, posterior extremity of the same fissure ; 3, the anterior
lobes of the cerebrum ; 4, its middle lobe ; 5, the fissure of Sylvius ; 6, the posterior lobe of the cerebrum ;
7, the point of the infundibulum ; 8, its body ; 9, the corpora alhicamia; 10, cineritious matter ; 11, the
crura cerebri ; 12, the pons Varolii ; 13, the top of the medulla oblongata; 14. posterior prolongation of
the pons Varolii; 15, middle of the cerebellum ; 16, anterior part of the cerebellum; 17, its posterior part
and the fissure of its hemispheres ; 18, superior part of the medulla spinalis ; 19, middle fissure of the
medulla oblongata ; 20, the corpus pyramidale ; 21, the corpus restiforme ; 22, the corpus olivare ; 23, the
olfactory nerve ; 24, its bulb ; 25, its external root ; 26, its middle root ; 27, its internal root ; 29, the op-
tic nerve beyond the chiasm; 29, the oplic nerve before the chiasm; 30, the motor oculi, or third pair
of nerves ; 31, the fourth pair or pathetic nerves ; 32, the fifth pair, or trigernini nerves ; 33. the sixth
pair, or motor externus ; 34, the facial nerve ; 35. the auditory — the two making the seventh pair ; 36,
37, 38, the eighth pair of nerves. (The ninth pair is not here seen .)]

centre of the Auditory nerve. — In like manner, we may probably fix upon a
collection of vesicular matter, imbedded in the Medulla Oblongata, — which is
considered by Stilling to be the nucleus of the Glosso-pharyngeal nerve, and
to which a portion of the sensory root of the Fifth pair may be traced, — as
representing the Gustatory ganglion.

423. At the base of the Cerebral Hemispheres, we find two other large
ganglionic masses, on either side ; into which all the fibres appear to pass,
which connect the Hemispheres with the Medulla Oblongata. These are the
Thalami Optici, and the Corpora Striata. Now, although these are com-
monly regarded in the light of appendages, merely, to the Cerebral Hemi-
spheres, it is evident, from the large quantity of vesicular matter they contain,
that they have an independent character ; and that, even if the Cerebral fibres
simply pass through them, other fibres have their proper ganglionic centres

328 FUNCTIONS OF THE NERVOUS SYSTEM.

in them. Such an idea is further warranted by the history of their develop-
ment ; for we find, in the Human embryo of the sixth week, a distinct vesi-
cle for the Thalami Optici, interposed between the vesicle of the Corpora
Quadrigemina, and that which gives origin to the Cerebral Hemispheres;
whilst the Corpora Striata constitute the floor of the cavity or ventricle, which
exists in the latter. — Now, as already pointed out, we may distinguish in the
Medulla Oblongata and Crura Cerebri, a sensory and a motor tract ; by
the endowments of the nerves which issue from them. The sensory tract
may be traced upwards from the Olivary columns, until it almost entirely
spreads itself through the substance of the Thalamus. Moreover, the Optic
nerves, and the peduncles of the Olfactive, may be shown to have a distinct
connection with the Thalami ; the former by the direct passage of a portion
of their roots into these ganglia ; and the latter through the medium of the
Fornix. Hence we may fairly regard the Thalami Optici as the chief focus
of the Sensory nerves ; and more especially as the ganglionic centre of the
nerves of common sensation, which ascend to it from the Medulla Oblongata
and Spinal Cord. — On the other hand, the Corpora Striata are implanted on
the motor tracts of the Crura Cerebri, which descend into the Pyramidal co-
lumns ; and their connection with the motor function is very generally admit-
ted, from the constancy with which paralysis is observed to accompany lesions
of these bodies, even when they are affected to a very trifling extent.

424. The Thalami Optici, and the Corpora Striata, as is well known, are
very closely connected with each other by commissural fibres ; and, if the
preceding account of their respective offices be correct, they may be regarded
as having much the same relation to each other, as that which exists between
the posterior and anterior peaks of vesicular matter in the Spinal Cord ; the
latter issuing motor impulses in respondence to sensations excited through
the former. They are also closely connected with other ganglionic masses
in their neighbourhood, such as the locus niger, and the vesicular matter of
the pons ; which again, are in close relation with the vesicular matter of the
medulla oblongata. — Altogether it is very evident, that an extensive tract of
ganglionic matter exists at the base of the Encephalon, which is really just as
distinct from either the Cerebrum or Cerebellum, as these are from each
other ; and we have next to inquire, what functions are to be assigned to it.

425. The determination of these may seem the more difficult, as it is im-
possible to make any satisfactory experiments upon the ganglionic centres in
question, by isolating them from the Cerebral Hemispheres above, and from the
Medulla Oblongata and Spinal Cord below. But the evidence derived from
Comparative Anatomy appears to be in this case particularly clear ; and,
rightly considered, seems to afford us nearly all the information we require.
In the series of " experiments prepared for us by nature," which is presented
to us in the descending scale of Animal life, we witness the effects of the
gradual change of the relative development of the Sensory ganglia and Cerebral
Hemispheres, which are presented to us in the Vertebratcd classes ; and the results
of the entire withdrawal of the latter, and of the sole operation of the former,
which are presented in the higher Invertebrata. In the sketch already given
of the Comparative Anatomy of the Encephalon in Vertebrata, it has been
shown that the Sensory ganglia gradually increase, whilst the Cerebral hemi-
spheres as regularly diminish, in relative size and importance, as we descend from
the higher Mammalia to the lower, — from these to Birds, — thence to Reptiles, —
from these, again, to the higher Fishes, in which the aggregate size of the
Sensory ganglia equals that of the Cerebrum, — thence to the lower Fishes,
in which the size of the Cerebral lobes is no greater than that of a single pair
of sensory ganglia, the Optic, and frequently even inferior, — and lastly, to the
•ftmphioxus or Lancelot, the lowest Vertebrated animal of which we have

FUNCTIONS OF SENSORY GANGLION. 329

any knowledge, in which there is not the rudiment of a Cerebrum, the En-
cephalon being only represented by a single ganglionic mass, which, from its
connection with the nerves of sense, must obviously be regarded as analogous
to the congeries of ganglia that we find in the higher forms of the class.

a. It has been supposed, from the results of an imperfect examination of this very remarka-
ble animal, that it is altogether destitute of Encephalon ; and that it possesses no ganglionic
centre, except the Spinal Cord and Medulla Oblongata. The researches of M. de Quatre-
fages, however, indicate that the most anterior of the ganglionic enlargements exhibited by
its Cerebro-Spinal axis, is of a more special character than the rest; uniting in itself the
characters of several distinct ganglionic centres. The ganglionic enlargements, arranged in
a linear series, which altogether represent the Spinal Cord, each give origin to a single pair
of nerves; but the cephalic ganglion is the centre of five pairs. Of these, the first pair is
distinctly an Optic nerve; being exclusively distributed to an organ, which has the structure
of a rudimentary Eye, though lodged within the dura mater; — reminding us, in its situation,
of the Auditory apparatus of the Gasteiopod Mollusks, which is actually imbedded in the
posterior part of the Cephalic ganglia. The second pair seems to correspond in its distribu-
tion with the Facial; whilst the third represents the Fifth pair and the Pneumogastric con-
jointly. The fourth find fifth pairs are distributed to the fin-like expansion, which forms the
margin of the head as well as of the body; and seem to hold the same relation to the two
preceding pairs, as the dorsal branches of the Spinal nerves bear to the ventral, — or, in Man,
the posterior to the anterior. Hence we see that this single ganglion is made up of at least
three centres; of which the first corresponds to the Optic ganglion of higher Vertebrata;
whilst the second and third are analogous to certain parts of the Medulla Oblongata in im-
mediate connection with them. Moreover, this little animal possesses an organ of Smell,
much more distinct than the rudimentary eye; and although its connection with the anterior
part of the cephalic ganglion has not yet been traced (owing to the extreme minuteness of
the parts, and the difficulty resulting from the interposition of the dura mater, which is in
equally close contact with the nervous mass which it incloses, and with the olfactive organ
which abuts upon its exterior), there can be little doubt that such a connection exists, and
that the Cephalic mass unites within itself also the characters of an Olfactive ganglion. But
no part whatever can be traced, which bears any resemblance to the Cerebral hemispheres;
and as these, wherever they exist, are completely isolated from the Sensory ganglia, their
absence may be stated as an almost certain fact. Hence, in this particular, the Amphioxus
evidently corresponds with the Invertebrata; to which its affinity is so close in other particu-
lars, that many Naturalists have hesitated to assign it a place in the Vertebrated series at all;
and, as will be seen in the next paragraph, the union of several really distinct ganglionic
centres into one Cephalic mass, is a fact which is capable of actual demonstration. (See
the Memoir on the Branchiostoma or Amphioxus, by M. de Quatrefages, in the Annales des
Sciences Naturelles, 3me Serie, Zoologie, torn, iv.)

426. Descending to the Invertebrated series, we find that, except in a few
of those which border most closely upon Vertebrata (such, for example, as
the Cuttle-Fish), the whole Cephalic mass appears to be made up of ganglia,
in immediate connection with the nerves of sense. These may appear to
form but a single pair ; yet they are in reality composed of several pairs,
fused (as it were) into one mass. Of this we may judge by determining the
number of distinct pairs of nerves which issue from them ; and also by the
investigation of the history of their development, the results of which bear a
close correspondence with those obtained in the preceding method.

a. Thus, Mr. Newport has shown, by studying the development of the head in certain
species of the class Myriapoda, that it is originally composed of no less than eight segments;
each having its peculiar appendages; and each possessing (like the segments of the body)
its own pair of ganglionic centres. These segments afterwards coalesce into two portions ;
of which the most anterior, made up by the union of four sub-segments, is termed the pro-
per cephalic; whilst the posterior, also made up of four sub-segments, is termed the basilar.
The four pairs of ganglia belonging to the cephalic portion coalesce into the one pair of
cephalic ganglia; whilst the other four pairs unite to form the first sub-assophageal ganglia. —
The first of the original sub-segments had, as its proper appendages, the antennae; and the
ganglia contained in it were evidently the proper centres of the antennal nerves. The
second had no movable appendages, but contained the eyes; and its ganglia were evidently
the proper centres of the optic nerves. To the third belonged the first pair of jaws, the
maxillae; and to the fourth, the maxillary palpi: and these organs derived nerves from their

28*

330 FUNCTIONS OF THE NERVOUS SYSTEM.

own ganglionic centres, belonging to their respective segments. Now as all these nerves
are found' to proceed, in the adult animal from the single pair of Cephalic ganglia, it is
obvious that these combine the functions of the ganglionic centres of the nerves of the
antenna;, eyes, and palpi, which are all sensory organs, as well as of the maxillary nerves,
which must be chiefly motor. And it is equally obvious, that there is nothing in such an
animal, which, can be compared to a pair of Cerebral hemispheres; since all the ganglia
of the original segments are directly connected with the appendages of those segments
respectively.

427. It is further to be remarked, that the development of the Cephalic
ganglia in the Invertebrata always bears an exact proportion to the develop-
ment of the eyes ; the other organs of special sense being comparatively
undeveloped ; whilst these, in all the higher classes at least, are instruments
of great perfection, and evidently connected most intimately with the direc-
tion of the movements of the animals. Of this fact we have a remarkable
illustration in the history of the metamorphoses of Insects ; the eyes being
almost rudimentary, and the Cephalic ganglia comparatively small, in most
Larvae; whilst both these organs attain a high development in the Imago, to
whose actions the faculty of sight is essential.

428. Now upon making a similar comparison of the psychical operations
of these different classes of animals, we are led to perceive that, as we de-
scend from the higher to the lower Vertebrata, we gradually lose the indica-
tions of Intelligence and Will, as the sources of the movements of the animal;
whilst we see a corresponding predominance of those, which are commonly
denominated Instinctive, and which are performed (as it would appear) in
immediate respondence to certain sensations, — without any intentional adapta-
tion of means to ends on the part of the individual, although such adaptive-
ness doubtless exists in the actions themselves, being a consequence of the
original constitution of the nervous system of each animal performing them.
It cannot be doubted by any person who has attentively studied the charac-
ters of the lower animals, that many of them possess psychical endowments,
corresponding with those which we term the intellectual powers and moral
feelings in Man; but in proportion as these are undeveloped, in that propor-
tion is the animal under the dominion of those Instinctive impulses, which,
so far as its own consciousness is concerned, may be designated as blind and
aimless, but which are ordained by the Creator for its protection from danger,
and for the supply of its natural wants. The same maybe said of the Human
infant, or of the Idiot, in whom the reasoning powers are undeveloped. In-
stinctive actions may in general be distinguished from those which are the
result of voluntary power guided by reason, chiefly by the two following
characters: — 1. Although, in many cases, experience is required to give the
Will command over the muscles concerned in its operations, no experience
or education is required, in order that the different actions, which result from
an Instinctive impulse, may follow one another with unerring precision. 2.
These actions are always performed by the same species of animal, nearly,
if not exactly, in the same manner; presenting no such variation in the means
adapted to the object in view, and admitting of no such improvement in the
progress of life, or in the succession of ages, as we observe in the habits of
individual men, or in the manners and customs of nations, that are adapted to
the attainment of any particular ends, by those voluntary efforts which are
guided by reason. The fact, too, that these instinctive actions are often seen
to be performed under circumstances rendering them nugatory, as reason
informs us, for the ends which they are to accomplish — (as when the Flesh-fly
deposits her egg on the Carrion-plant instead of a piece of meat, or when the
Hen sits on a pebble instead of her egg) — is an additional proof, that the
Instinctive actions of animals are prompted, like the consensual movements

SENSORY GANGLIA. CONSENSUAL ACTIONS. 331

we have been recently inquiring into, by an impulse which immediately
results from a particular sensation being felt, and not by anticipation of the
effect which the action will produce.

429. The highest development of the purely Instinctive tendencies, is to be
found in the class of Insects ; and above all in the order Hymcnoptera, and in
that of Neuroptera, which is nearly allied to it. It is in this division of the
class, that we find the highest development of the sensory organs and of the
cephalic ganglia, and the most active powers of locomotion. We may here
trace the operations of Instinct, with the least possible interference of Intelli-
gence. It is, of course, impossible to draw the line between the two sources
of action, with complete precision ; but we observe, in the habits of Bees and
other social Insects, every indication of the absence of a power of choice, and
of the entire domination of instinctive propensities called into action by sen-
sations. Thus, although Bees display the greatest art in the construction of
their habitations, and execute a variety of curious contrivances, beautifully
adapted to variations in their circumstances, the constancy with which indi-
viduals and communities will act alike under the same conditions, appears to
preclude the idea of their possessing any inherent power of spontaneously de-
parting from the line of action, to which they are tied down by the constitution
of their Nervous system. We do not find one individual or one community
clever, and another stupid; nor do we ever witness a disagreement, or any
appearance of indecision, as to the course of action to be pursued by the
several members of any republic.* For a Bee to be destitute of its peculiar
tendency to build at certain angles, would be as remarkable as for a Human
being to be destitute of the desire to eat, when his system should require
food. It may be doubted, on the other hand, whether there was ever a case,
in which an Insect of any kind could be taught to recognize any one, who had
been in the habit of feeding it; or to show any other unequivocal indications
of intelligence.

a. Such anecdotes have been related of Spiders; but these animals are the highest of the
Articulated series, having many points of approach to Vertebrata. It is probable, therefore,
that they may possess the rudiment of a Cerebrum ; a similar rudiment making its appear-
ance in the higher Cephalopoda, which occupy a corresponding place in the Molluscous
series.

b. The only manifestation of educability, which the Author has ever noticed, during a
pretty long familiarity with the habits of Bees, is the acquirement of a power of distinguish-
ing the entrance of their hive from that of others around. When a swarm is first placed in
a new box, and the Bees have gone forth in search of food, they often seem puzzled on their
return, as to which is their own habitation; more especially if there be several hives, with
similar entrances, in one bee-house ; and it has been proposed to paint these entrances of
different colours, in order to enable the Bee to distinguish them more readily. In a short
time, however, even without such aid, the Bees are seen to dart from a considerable height
in the air, directly down to their proper entrances ; showing that they have learned to dis-
tinguish these, by a memorial power. This the Author has observed most remarkably, in a
case in which a hive is placed in the drawing-room of a house, the entrance to it being be-
neath one of the windows ; the adjoining houses have windows precisely similar, except in
the absence of this small passage; and he has often noticed that, when a new stock has been
placed in this hive, the Bees are some days in learning the exact position of their house, con-
siderably annoying the neighbours by flying in at their windows.

The community of Bees, though commonly reputed to be a monarchy, governed by a
sovereign, is really a republic, in which every individual performs its own independent part.
The function of the queen is simply that of breeding ; and as (among the Hive-Bees at least)
she is the only female, the purpose of the instinct, which leads the workers to treat her with
peculiar attention, is very obvious. But the idea that she directs the operations of the hive,
or exerts any peculiar control over the ordinary Bees, is entirely destitute of foundation. The
actions of the latter all tend to one common end ; simply because they are performed in re-
spondence to impulses, which all alike share.

332 FUNCTIONS OF THE NERVOUS SYSTEM.

430. Thus the analysis of such of the actions of these animals, as are evi-
dently of a higher order than the simply-reflex, terminates in referring them to
the immediate directing influence of Sensations ; which, being received by the
cephalic ganglia through the sensory nerves, excite respondent motor impulses,
which are propagated to the various muscles of the body, through those por-
tions of the motor trunks that issue from them. As the term Instinctive has
been employed in a great variety of significations, and is very indefinite in its
character, we may more appropriately apply the designation Consensual to the
actions of this group. We have now to inquire, whether there is any class of
movements in Man and the higher Vertebrata, which seems to possess a simi-
lar character, and which may be regarded as the special function of the gangli-
onic centres under consideration. — By far the larger part of the movements of
these animals (putting aside the simply-reflex) are performed under the direc-
tion of the Intelligence ; to which the sensations are communicated ; by which
a reasoning process is founded upon them ; and from which, at last, issues
that mandate, which is called the Will. Consequently, there are compara-
tively few movements, in the adult at least, which can be clearly distinguished
as neither voluntary, on the one hand, nor reflex on the other. Such actions,
however, do exist ; and serve to show that, although the Instinctive propensities
are in great measure superseded by the Intelligence, they may still operate
independently of it. As examples of this group, we may advert to the act of
Vomiting, produced by various causes which act through the organs of sense;
such as the sight of a loathsome object, a disagreeable smell, or a nauseous
taste. The excitement of the act of Sneezing by a dazzling light, is another
example of the same kind; for even if it be granted, that the act of sneezing
is ordinarily excited through the reflex system alone (which is by no means
certain), there can be no doubt that in this instance it cannot be brought into
play without a sensation actually felt. The same may be said of the Laughter
which sometimes involuntarily bursts forth, at the provocation of some sight
or sound, to which no distinct ludicrous idea or emotion can be attached ; and
of that resulting from the act of tickling, in which case it is most certainly
occasioned by the sensation, and by that alone.

431. The direct influence of Sensations, in occasioning and governing move-
ments, which are neither reflex nor voluntary, is most remarkably manifested
in many phenomena of disease. Thus in cases of excessive irritation of the
retina, which renders the eye most painfully sensitive to even a feeble amount
of light, — the state designated as photophobia, — the eyelids are drawn together
spasmodically, with such force as to resist very powerful efforts to open them ;
and if they be forcibly drawn apart, the pupil is frequently rolled beneath the
upper lid (apparently by the action of the inferior oblique muscle), much fur-
ther than it could be carried by a voluntary effort. And in Pleuritis, Pericar-
ditis, and other painful affections of the parietes of the chest, we may observe
the usual movements of the ribs to be very much abridged ; the dependence of
this abridgement upon the painful sensation which they occasion, being most
evident in those instances in which the affection is confined to one side, — for
there is then a marked curtailment in its movements, whilst those of the other
side may take place as usual ; a difference which cannot be reflex, and which
the Will cannot imitate. Again, in some Convulsive disorders, we observe
that the paroxysms are excited by causes, which act through the organs of
special sense ; thus in Hydrophobia, we observe the immediate influence of
the sight or the sound of liquids, and of the slightest currents of air ; and in
many Hysteric subjects, the sight of a paroxysm in another individual is the
most certain means of inducing it in themselves.

432. The results of experiments, so far as any reliance can be placed upon
them, confirm these views ; by showing that any disturbance of the usual

SENSORY GANGLIA. CONSENSUAL ACTIONS. 333

actions of the organs of sense, and of the nervous centres with which they are
connected, in animals whose movements are directly governed by the sensations
received through these, is followed by abnormal movements. Thus it has
been ascertained by Flourens, that a vertiginous movement may be induced in
pigeons, by simply blindfolding one eye ; and Longet has produced the same
effect, by evacuating the humours of one eye. These vertiginous movements
are more decided and prolonged, when, instead of blinding one eye, one of
the tubercula quadrigemina is removed; the animal continuing to turn itself
towards the injured side, as if rotating on an axis. — The results of the experi-
ments of M Flourens upon the portion of the Auditory nerve proceeding to
the Semi-circular canals, are still more extraordinary. Section of the hori-
zontal semi-circular canal in Pigeons, on both sides, induces a rapid jerking
horizontal movement of the head, from side to side ; and a tendency to turn
to one side, which manifests itself whenever the animal attempts to walk for-
wards. Section of a vertical canal, whether the superior or inferior, of both
sides, is followed by a violent vertical movement of the head. And section of
the horizontal and vertical canals at the same time, causes horizontal and ver-
tical movements. Section of either canal on one side only, is followed by the
same effect as when the canal is divided on both sides ; but this is inferior in
intensity. The movements continue to be performed during several months.
In Rabbits, section of the horizontal canal is followed by the same movements,
as those exhibited by pigeons ; and they are even more constant, though less
violent. Section of the anterior vertical canal causes the animal to make con-
tinued forward somersets ; whilst section of the posterior vertical canal occa-
sions continual backward somersets. The movements cease when the animal
is in repose ; and they recommence when it begins to move, increasing in
violence as its motion is more rapid. — These curious results are supposed by
M. Flourens to indicate, that the nerve supplying the semi-circular canals does
not minister to the sense of hearing, but to the direction of the movements of
the animal: but they are fully explained upon the supposition that the normal
function of the semi-circular canals is to indicate to the animal the direction
of sounds, and that its movements are partly determined by these; so that a
destruction of one or other of them will produce an irregularity of movement
(resulting, as it would seem, from a sort of giddiness on the part of the animal),
just as when one of the eyes of a bird is covered or destroyed, as in the ex-
periments just cited.

433. But we may trace the influence of the Sensory ganglia, not merely in
their direct and independent operation on the muscular system, but also in the
manner in which they participate in all Voluntary actions. There can be no
doubt that, in every exertion of the will upon the muscular system, we are
guided by the sensations communicated through the afferent nerves, which
indicate to the Sensorium the state of the muscle. Many interesting cases
are on record, which show the necessity of this Muscular Sense, for determin-
ing voluntary contraction of the muscle. Thus, Sir C. Bell (who first promi-
nently directed attention to this class of facts, under the, designation of the
Nervous Circle), mentions an instance of a woman, who was deprived of it in
her arms, without losing the motor power; and who stated, that she could not
sustain anything in her hands (not even her child), by the strongest effort of
her will, unless she kept her eyes constantly fixed upon it; the muscles losing
their power, and the hands dropping the object, as soon as the eyes were
withdrawn from it. Here the employment of the visual sense supplied the
deficiency of the muscular ; but instead of being inseparably connected, as the
latter is in the state of health, with the action of the muscle, the former could
be only brought to bear by an effort of the will ; and the sustaining power was
therefore dependent, not upon the immediate influence of the will upon the

334 FUNCTIONS OF THE NERVOUS SYSTEM.

muscle, but upon the voluntary direction of the Sight towards the object to be
supported. Again, in the production of vocal sounds, the nice adjustment of
the muscles of the larynx, which is requisite to produce determinate tones,
can only be learned in the first instance under the guidance of the sensation
of the sounds produced, and can only be effected by an act of the will, in
obedience to a mental conception (a sort of inward sensation) of the tone to
be uttered, — which conception cannot be formed, unless the sense of hearing
has previously brought similar tones to the mind. Hence it is, that persons
who are born deaf, are also dumb. They may have no malformation of the
organs of speech ; but they are incapable of uttering distinct vocal sounds or
musical tones, because they have not the guiding conception, or recalled sen-
sation, of the nature of these. By long training, and by efforts directed by the
muscular sense of the larynx itself, some persons thus circumstanced have
acquired the power of speech ; but the want of a sufficiently definite control
over the vocal muscles, is always very evident in their use of the organ.

434. The conjoint movements of the two eyes, which concur to direct
their axes towards the same object, are among the most interesting of these
actions, in which Volition and Consensual action are alike concerned ; and
they afford an excellent illustration of the necessity for guiding sensations,
to determine the actions of muscles. The sensations, however, are not so
much those of the muscles themselves, as those received through the visual
organ; but the former appear capable of continuing to guide the harmonious
movements of the eyeballs, when the sense of sight has been lost. It 'is a
striking peculiarity of these movements, that, in the majority of them, two
muscles or combinations of muscles of opposite action are in operation at
once ; thus, when the eyes are made to rotate in a horizontal plane, the in-
ternal rectus of one side acts with the external rectus of the other. In most
other cases, there is a difficulty in performing two opposite movements, on
the two sides at the same time. Thus, if we move the right hand as if wind-
ing on a reel, and afterwards make the left hand revolve in a contrary direc-
tion, no difficulty is experienced; but if we attempt to move the two at the.
same time in contrary directions, we shall find it almost impossible. — As the
Consensual movements of the Eyes are of sufficient interest and importance,
to require a detailed consideration, they will be examined more fully at the
close of the present section (§§ 450 — 456).

435. If the preceding views be correct, we may regard the series of Gan-
glionic centres which have been enumerated (§§ 422, 423), as constituting the
real Sensorium ; each ganglion having the power of cummunicating to the
mind the impressions derived from the organ, with which it is connected, and
of exciting automatic muscular movements in respondence to these sensations.
If this position be denied, we must either refuse the attribute of consciousness
to those animals, which possess no other encephalic centres than these ; or
we must believe that the addition of the Cerebral hemispheres, in the Verte-
brated series, alters the endowments of the Sensory ganglia, — an idea which
is contrary to all analogy. So far as the results of experiments can be relied
on, they afford a corroboration of these views. The degree in which animals
high in the scale of organization can perform the functions of life, without
any other centre of action than the Ganglia of Special sense, the Medulla
Oblongata, and the Cerebellum, appears extraordinary to those who are accus-
tomed to regard the Cerebral Hemispheres as the centre of all energy. From
the experiments of Flourens, Hertwig, Magcndie, and others, it appears that
not only Reptiles, but Birds and Mammalia, may survive for many weeks or
months (if their physical wants be duly supplied) after the removal of the
whole Cerebrum. It is difficult to substantiate the existence in them of
actual Sensation; but some of their movements appear to be of a higher kind

SENSORY GANGLIA. CONSENSUAL AND EMOTIONAL ACTIONS. 335

than those resulting from mere Reflex action. One of the most remarkable
phenomena exhibited by such a being, is the power of maintaining its equili-
brium, which could scarcely exist without consciousness. If it be laid upon
the back, it rises again; if pushed, it walks. If a Bird thus mutilated be
thrown into the air, it Hies; if a Frog be touched, it leaps. It swallows food
and liquid, when they are placed in its mouth; and the digestive operations,
the acts of excretion, &c., take place as usual. In the case of a Pigeon ex-
perimented on by Malacorps, which is recorded by Magendie, there appears
sufficient proof of the persistence of a certain amount of sensation. Although
the animal was not affected by a strong light suddenly made to fall upon its
eyes, it was accustomed, when confined in a darkened or partially-illuminated
room, to seek out the light parts; and it avoided objects that lay in its way.
In the same manner, it did not seem to be affected by sudden noises; but at
night, when it slept with closed eyes and its head under its wing, it would
raise its head in a remarkable manner, and open its eyes, on the slightest
noise ; speedily relapsing into a state of complete unconsciousness. Its
principal occupation was to prune its feathers and scratch itself. — The con-
dition of such a being seems to resemble that of a Man, who is in a slumber
sufficiently deep to lose all distinct perception of external objects, but who is
yet conscious of sensations, as appears from the movements occasioned by
light or by sounds, or from those which he executes to withdraw the body
from an uneasy position.*

436. Among the ganglia of special sensation, the functions of the Optic
Lobes, or Corpora Quadrigemina, have been chiefly examined. The re-
searches of Flourens and Hertwig have shown, that their connection with
the visual function, which might be inferred from their anatomical relations,
is substantiated by experiment. The partial loss of the ganglion on one
side produces partial loss of power and temporary blindness on the opposite
side of the body, without necessarily destroying the mobility of the pupil;
but the removal of a larger portion, or complete extirpation of it, occasions
permanent blindness and immobility of the pupil, with temporary muscular
weakness, on the opposite side. This temporary disorder of the muscular
system sometimes manifests itself (as already stated) in a tendency to move on
the axis, as if the animal were giddy. No disturbance of consciousness ap-
pears to be produced; and Hertwig states that he never witnessed the con-
vulsions, which Flourens mentions as a consequence of the operation, and
which were probably occasioned by his incision having been carried too
deeply. These results are confirmed by pathological phenomena in Man;
for there are many instances on record, in which blindness has been one of
the consequences of diseased alterations in one or both tubercles ; and in
some of the cases, in which the lesion extended to parts seated beneath the
tubercles, disturbed movements were observed. — No definite conclusions can
be drawn, either from experiment or from pathological observation, in regard
to the functions of the Thalami Optici and Corpora Striata; but there is
nothing in these sources of information to oppose the views already offered,
which are based on other foundations.

437. Emotional fictions. — There appears strong reason for regarding the
Ganglionic tract, which is the instrument of Consensual actions, as the imme-
diate centre also of those movements which directfy result from the excite-
ment of the Emotions. Several considerations tend to establish this position.

It must not be forgotten that, in such experiments, the severity of the operation will of
itself occasion a suspension or disturbance of the functions of parts that remain ; so that the
loss of a power must not be at once inferred from the absence of its manifestations. But the
persistence of a power, after the removal of a particular organ, is a clear proof that it canuot
be the peculiar attribute of that organ.

336 FUNCTIONS OF THE NERVOUS SYSTEM.

In the first place, that the channel through which the direct impulses of the
Emotions are conveyed to the Muscles, is not the same with that which con-
veys to them the mandates of the Will, appears sufficiently established by
Pathological observation ; since cases of paralysis not unfrequently occur, in
which the muscles are obedient to an emotional impulse, though the will exerts
no power over them ; whilst, on the other hand, the will may have its due
influence, and yet the emotional state cannot manifest itself. This is espe-
cially remarkable in the different forms of paralysis of the Facial nerve ; since
the facial muscles manifest the ordinary influence of the Emotions, more evi-
dently than any others. But it is not, however, confined to them; thus, for
example, the arm of a man, which no effort of his will could move, has been
seen to be violently agitated at the sight of a friend. Dr. M. Hall has inferred
from cases of this kind, that the Spinal system of nerves constitutes the chan-
nel of the Emotional actions; but all which is proved by them is, that these
are not effected through the same agency with the Volitional ; and the idea
that they are of the same character with Reflex actions is distinctly negatived
by the fact, that in a great majority of instances, they are excited through the
organs of special sense, and that consciousness is a distinct element in the
series of changes which ends in their performance. These facts would lead
us to infer, that the Emotional actions are dependent on a set of centres, in-
termediate between the Cerebrum and the Spinal Cord ; a position which is
precisely that of the ganglionic tract under consideration. — In the next place
it may be remarked, that the Emotions are so closely linked with Sensations,
as to be regarded by many Metaphysicians as almost identical with them ; and
this connection is universally recognized in the term feelings popularly ap-
plied to both. Like the Instinctive tendencies of Animals, the Emotional
states follow directly and necessarily upon Sensations, without any interven-
ing process of ratiocination ; and there is such a marked correspondence in
the character of the actions, which flow from these sources, as to point to the
conclusion of the identity of the conditions on which they immediately de-
pend. Of this, an example will be presently given. We have seen that the
Sensory ganglia must necessarily be regarded as the instruments of the In-
stinctive actions ; and a probable inference may therefore be drawn from this
fact, in regard to their relation to those which (in Man) are designated as
Emotional.* — A* third argument in support of this view may be drawn from
the fact, of the very close connection of this division of the nervous centres,
with the nervous trunks, through which the emotional states are excited, and
the respondent muscular actions are stimulated. For the Sensory ganglia re-
ceive all those nerves, which communicate the Sensations through whose
immediate agency the Emotion is excited ; and the nerves of the Orbit, the
Face, and the Respiratory organs, — those most concerned in producing the
movements, by which the emotions are expressed or manifested, — arise in
their immediate proximity. It is chiefly through these nerves, too, that the

* It seems by no means certain, that we are always to attribute to the lower animals the
Emotions which we ourselves feel, because they perlonn movement* analogous to those by
•which we ordinarily express them: lor the move nts may lie tliinilij excited liy the Sen-
sations, without the intervention of the Emotion; just as in ourselves, involuntary laughter
is occasioned by tickling, although no ludicrotas emotion be exeited ; or as Vomiting results
from the si;;ht of a loathsome object, rather in resiiondenee to the sensation of nausea, than
to the emotion oi'di-^iist whicTi it concurrently excites. We miijht, on equally valid grounds,
assert, that the I See LTOCS through a process of mathematical ratiocination, before it commences
the construction of its cell. The purpose of the Emotion, in animals possessed of Intelligence,

may be rather to net upwards upon it .• and. altl uh e|o.-ely connected with the sensation

which excites it; it may lie no more necessary to the resulting muscular movement, than
sensation is to ivllex action/ — On this view, all actions of the directly Emotional character
Would be in reality purely Consensual.

EMOTIONAL*AND INSTINCTIVE ACTIONS. 337

abnormal movements are effected, in those disorders of the Nervous centres,
which may be most distinctly referred to the Emotional system ; such as
Chorea and Hysteria.

438. The correspondence between the purely Emotional actions in Man,
and those actions in the lower animals to which we give the name of Instinc-
tive, may be made evident by a very simple illustration. The Cuttle-fish is
well known to discharge its ink, when pursued, and to tinge the water around
with a colour so deep, as to enable it to escape under the cloud thus formed.
Now it is not to be supposed, that the Cuttle-fish has any notion of the pur-
pose which this act will serve; since its constancy and uniformity, and the
provision for its performance immediately on the emersion of the young ani-
mal from the egg, forbid our regarding it as the result of any act of reasoning.
Further, the ink is an excretion which corresponds to the urine (having been
found to contain .urea) ; and every one knows how strong an impulse to dis-
charge this, is frequently caused by mental emotion. The same may be said
of the strongly odorous secretions possessed by many Mammalia, which are
discharged under similar circumstances, and evidently with the same object:
though of that object, the animal itself be not conscious. The emotion of
fear involuntarily opens the sphincters, and causes the contraction of the recep-
tacle, in one case as in the other ; and the great difference between the condi-
tion of Man, and that of the lower animals, in this respect, is simply that, in
the former, the purely Emotional or Instinctive actions are few in comparison
with the whole, whilst in the latter they constitute by far the largest part ; and
also that Man has much greater power of controlling these actions by a volun-
tary effort, than that which the lower animals possess, although even he is not
unfrequently compelled by the strength of his Emotions to act against his
Will. Thus, we see or hear something ludicrous, which involuntarily pro-
duces laughter, although we may have the strongest motives for desiring to
restrain it.

a. It is a very interesting question, how far actions at first performed voluntarily by Man.
may by habit cease to require an effort of the Will; being prompted, like the movements of
the Consensual class, by the direct impulse of sensations. Thus we all know that, in walking
along an accustomed road, we frequently occupy our minds with some continuous train of
thought, and yet our limbs continue to move under us with regularity, until we are surprised
by finding ourselves at the place of our destination, or perhaps at some other which we had
not intended to visit, but to which habit has conducted us. Or we may read aloud for a
long time, without haying in the least degree comprehended the meaning of the words we
have uttered; our attention having been closely engaged by some engrossing thoughts or
feelings within. Or a Musician may play a well-known piece of music, whilst carrying on
an animated conversation: — the Author has known a skilful performer who could play at
sight whilst thus occupied. Now in such a case it would be said by some Metaphysicians
(acknowledging, as most do. that the mind cannot irill two different things at the same time)
that the Volition is in a sort of vibratory condition between the two sets of actions, now
prompting one, and now the other. But it would seem much more conformable to the
analogy afforded by other psychical phenomena, to refer the habitual series of actions to the
same operation of the Nervous System with the Instinctive; and perhaps the term .'ln/o/natic
may be fairly applied to the whole of this group. It is well known that in cases of severe
injury of the brain, in which Intelligence and Will seem completely in abeyance, habitual
actions may be often excited. Thus, Dr. Perceval, in his Essay on habit, mentions the case
of a snuff-taking Countess, in whom, when seized with apoplexy, irritation of the nose with
a feather produced contraction of the fore-finger and thumb of the right hand; and Mr.
Traverse has recorded a similar fact in the case of a boy, who, when apparently insensible
from depressed fracture of the skull, assisted in removing his clothes, preparatorily to the
required operation.

439. The purely Emotional actions are not always directly excited, however,
by external sensations; for they may result from the operations of the Mind
itself. Thus involuntary laughter may result from a ludicrous idea, called up
by some train of association, and havino- no obvious connection with the sen-

29

338 FUNCTIONS OF THE NERVOYS SYSTEM.

sation which first set this process in operation; and the various movements
of the face and person, by which Actors endeavour to express strong Emotions,
are only effectual in conveying their meaning, when they result from the actual
working of the emotions in the mind of the performer, who has, by an effort
of the will, identified himself (so to speak) with the character he personates.
A still more remarkable case is that, in which paroxysms of Hysterical con-
vulsion, in themselves beyond the power of the Will to excite or to control,
are brought on by a voluntary effort; which seems to act by "getting up," so
to speak, the state of feeling, which is the immediate cause of the disordered
movements. In all these instances, and others of like nature, it would seem
as if the agency of the Cerebrum produced the same condition in the Sensory
ganglia and their motor fibres, as that which is more directly excited by sen-
sations received through their own afferent nerves. It may be reasonably
surmised, that -the Sensory ganglia, like the Cephalic ganglia which are the
instruments of the Instinctive actions of the lower animals, can .only be excited
to action by stimuli immediately operating upon them ; but that these stimuli
may be either Sensations directly originating in external objects, or Concep-
tions resulting from the remembrance of those objects, of which there is strong
reason to believe that the Cerebrum is the storehouse.

440. The Emotions are concerned in Man, however, in many actions, which
are in themselves strictly voluntary. Unless they be strongly excited, so as
to get the better of the Will, they do not operate directly through the nervous
trunks, but are subservient to the intellectual operations; to which they supply
materials, or motives. Thus, of two individuals, with differently constituted
minds, one shall judge of everything through the medium of a gloomy morose
temper, which, like a darkened glass, represents to his judgment the whole
world in league to injure him; and all his determinations, being based upon
this erroneous view, exhibit the indications of it in his actions ; which are
themselves, nevertheless, of an entirely voluntary character. On the other
hand, a person of a cheerful, benevolent disposition, looks at the world around
as through a Claude Lorraine glass, seeing everything in its brightest and
sunniest aspect; and, with intellectual faculties precisely similar to those of
the former individual, he will come to opposite conclusions ; because the
materials, which form the basis of his judgment, are submitted to it in a very
different condition. Various forms of Moral Insanity exhibit the same con-
trast in a yet more striking light. We not unfrequently meet with individuals,
still holding their place in society, who are accustomed to act so much upon
feeling, and to be so little guided by reason, as to be scarcely regarded as
sane; and a very little exaggeration of such a tendency causes the actions to
be so injurious to the individual himself, or to those around him, that restraint
is required, although the intellect is in no way disordered, nor are any of the
feelings perverted. Not unfrequently we may observe similar inconsistencies
resulting from the habitual indulgence of one particular feeling, or a morbid
exaggeration of it. The mother \vho, through weakness of will, yields to her
instinctive fondness for her offspring, in allowing it gratifications which she
knows to be injurious to it, is placing herself below the level of many less
gifted beings. The habit of yielding to a natural infirmity of temper ol'tcn
lends into paroxysms of ungovernable rage, which, in their turn, pass into a
state of maniacal excitement. It is not unfrequently seen, that a delusion of
the intellect (constituting what is commonly known as Monomania) has in
reality resulted from a disordered state of the feelings, which have represented
every occurrence in a wrong light to the mind of the individual. All such
conditions are of extreme interest, when compared with those which are met
with amongst idiots, and animals enjoying a much lower degree of intelligence:
for the result is much the same, in whatever way the balance between the

NERVES OF SPECIAL SENSE. OLFACTIVE. 339

feelings and the judgment (which is so beautifully adjusted in the well-ordered
mind of Man) is disturbed; whether by a diminution of the intelligence, or
by an exaltation of the feelings. — These views will probably be found correct,
whatever be the truth of the speculation with which they have been here con-
nected, as to the part of the Nervous system concerned in the performance of
the purely Emotional actions. That their channel is alike distinct, however,
from that of the Voluntary movements, and from that of Reflex operations,
must be apparent to any one who fairly weighs the evidence.

441. Serves connected ivith the Sensory Ganglia. — That the First pair,
or Olfactory nerves, minister to the sense of smell, has long been known,
yet it could not be predicted without experimental inquiry, that it is not a
conductor of the impressions which produce ordinary sensation; nor that it
is destitute of all power of exciting muscular movement, either by direct or
reflex action. Anatomical examination of the distribution of this nerve, proves
that it is not one which directly conveys motor influence to any muscles ;
since all its branches are distributed to the membrane lining the nasal cavity.
Experimental inquiry leads to the same result ; for no irritation of the pedun-
cles or branches excites any muscular movement. Further, no irritation of
any part of this nerve excites reflex actions through other nerves. Again, it
is not a nerve of common sensation ; for animals exhibit no sign of pain,
when it is subjected to any kind of irritation. Neither the division of the
nerve, nor the destruction of the olfactive ganglia, seems to inconvenience
them materially. They take their food, move with their accustomed agility,
and exhibit the usual appetites of their kind. The common sensibility of the
parts contained in the olfactive organ is in no degree impaired, as is shown,
by the effect of irritating vapours ; but the animals are destitute of the sense
of smell, as is shown by the way in which these vapours affect them. At
first they appear indifferent to their presence, and then suddenly and vehe-
mently avoid them, as soon as the Schneiderian membrane becomes irritated.
Moreover, if two dogs, with the eyes bandaged, one having the olfactory
nerves and ganglia sound, and the other having had them destroyed, are
brought into the neighbourhood of the dead body of an animal, the former
will examine it by its smell ; whilst the latter, even if he touches it, pays no
attention to it. This experiment Valentin states that he has repeated several
times, and always with the same results. Further, common observation
shows that sensibility to irritants, such as snuff, and acuteness of the power
of smell, bear no constant proportion to one another ; and there is ample
pathological evidence, that the want of this sense is connected with some
morbid condition of the olfactory nerves or ganglia. — It is well known that
Magendie has maintained, that the Fifth pair in some way furnishes conditions
requisite for the enjoyment of the sense of smell; asserting that, when it is
cut, the animal is deprived of this. But his experiments were made with ir-
ritating vapours, which excite sternutation or other violent muscular actions,
not through the Olfactory nerve, but through the Fifth pair ; and the experi-
ments of Valentin, just related, fully prove that the animals are not sensitive
to odours, strictly so called, after the Olfactory has been divided. It is by
no means improbable, however, that the acuteness of the true sense of smell
may be diminished by section of the Fifth pair; since the olfactory mem-
brane is no longer duly moistened by its proper secretion; and, when dry, it is
not so susceptible of the impressions made by those minute particles of odori-
ferous substances, to which the excitement of the sensation must be referred.
442. That the Second pair, or Optic nerves, have an analogous character,
appears alike from anatomical and experimental evidence. No chemical or
mechanical stimulus of the nerve produces direct muscular motion ; nor does
it give rise, as far as can be ascertained, to indications of pain ; whence it may

340

FUNCTIONS OF THE NERVOUS SYSTEM.

[Fig. 158.

be concluded, that this nerve is not one of common sensation. That the ordi-
nary sensibility of the eyeball remains, when the functions of the Optic nerve
are completely destroyed, is well known ; as is also the fact, that division of
it puts an end to the power of vision. Valentin states that, although the Optic
nerve may, like other nerves, be in appearance completely regenerated, he has

never been able to obtain any evi-
dence that the power of sight has
been in the least degree recovered.
He remarks that animals suddenly
made blind exhibit great mental dis-
turbance, and perform many unaccus-
tomed movements ; and that the com-
plete absence of the power of vision
is easily ascertained. Morbid changes
are sometimes observed to take place
in eyes, whose Optic nerve has been
divided ; but these are by no means
so constant or so extensive, as when
the Fifth pair is paralyzed ; and they
may not improbably be attributed to
the injury, occasioned by the opera-
tion itself, to the parts within the or-
bit.— It is well known that, when
amaurosis is produced by a morbid
condition of the Optic nerve alone,
the eye retains its usual appearance ;
but, if the amaurosis be complete, the
texture of the Retina undergoes a re-
markable change, ceasing to exhibit
that peculiar structure which normally
characterizes it. Neither primitive
nervous fibrils, nor nucleated vesicles,
can be distinguished in it, and the
yellow spot of Soemmering becomes
paler, and is at last undistinguishable.
But if a very slight degree of sensi-
bility to light remain, these changes
are much less decided. Further, it is
well known that, Avhen the sight is
destroyed by a disease or injury,
which prevents the passage of light through the pupil, the whole eye becomes
more or less atrophied ; and the Retina and Optic nerve, although previously
sound, are found after death, (if the morbid condition have lasted sufficiently
long) to have lost their characteristic structure. It seems evident, then, that
the continuance of the functional operations of nerves, is a necessary condi-
tion of the maintenance of their normal organization; and we can very well
understand that this should be the case, from the analogy of other parts of the
system.

443. The Optic nerve, though analogous to the Olfactory in all the points
hitherto mentioned, differs from it in one important respect; — that it has the
power of conveying impressions which shall excite rc/Icx muscular motions.
This is especially the case in regard to the Iris, the ordinary actions of which
are regulated by the degree of light impinging on the retina. When the optic
nerve is divided, a contraction of the pupil takes place ; but this does not
occur, if the connection of this nerve with the third pair, through the new-

A view of the 3d pair or optic, and the origins of
seven other pairs. 1, 1. Globe of the eye, the one
on the left hand is perfect, but that on the right has
the sclerotic and choroid removed to show the
retina. 2. The chiasm of the optic nerves. 3. The
corpora albicantia. 4. The infundibulum. 5. The
Pons Varolii. 6. The medulla oblongata. The
figure is on the right corpus pyramidale. 7. The
3d pair, motores oculi. 8. 4th pair, pathetici. 9.
5th pair,trigernini. 10. 6th pair, abducentes. 11.
7th pair, auditory and facial. 12. 8th pair, pneumo-
gastric, spinal accessory, and Jglosso-pharyngeal.
13. 9th pair, hypoglossal. ]

NERVES OF SPECIAL SENSE. OPTIC. 841

ous centres, be in any way interrupted. After such division (if complete),
the state of the pupil is not affected by variations in the degree of light im-
pinging on the retina ; except in particular cases, in which it is influenced
through other channels. Thus, in a patient suffering under amaurosis of one
eye, the pupil of the affected eye is often found to vary in size, in accord-
ance with that of the other eye ; but this effect is produced by the action of
light on the retina of the sound eye, which produces a motor change in the
third pair on both sides. Further, as has been formerly stated (§ 395), the
impression only of light upon the retina may give rise to contraction of the
pupil, by reflex action, when the optic nerve is itself sound ; whilst no sen-
sations are received through the eye, in consequence of disease in the sen-
sorial portion of 'the nervous centres. Although the contraction of the pupil
is effected by the influence of motor fibres, which proceed to the sphincter
of the Iris from the third pair of nerves, through the Ophthalmic ganglion,
there is evidence that its dilatation depends rather upon the influence it de-
rived from that ganglion itself, and from the Sympathetic system, of which it
forms part. — Some have attempted to show, that the actions of the iris are in
a slight degree voluntary, because, by an effort of the will, they could occa-
sion contraction of the pupil ; but this so-called voluntary contraction is al-
ways connected with a change in the place of the eyeball itself, occasioned
by an action of some of its muscles. It is principally noticed under the two
following conditions : — 1. When an object is brought very near the eye, and we

J */ •

steadily lix our attention upon it, the axes of the two eyes are made to con-
verge ; and if this convergence be carried to a considerable extent, so that the
pupils of both eyes are sensibly directed towards the inner canthus, a con-
traction of the pupil takes place. The final cause or purpose of this contrac-
tion is very evident. When an object is brought near the eye, the rays pro-
ceeding from it would enter the pupil (if it remained of its usual size) at an
angle of divergence, so much greater than that which would allow them to
be properly refracted to a focus, that indistinct vision would necessarily re-
sult. By the contraction of the pupil, however, the extreme or most diver-
gent rays are cut off, and the pencil is reduced within the proper angle. The
principle is precisely the same as that on which the optician applies a stop
behind his lenses, which reduces their aperture in proportion to the shortness
of their focal distance. 2. Contraction of the pupil is also noticed, when the
eyeball is performing that rotation upwards and inwards, which, when per-
formed along with violent respiratory actions, or during sleep, must be regarded
as involuntary. This rotation also takes place, to a slight degree, when the
eyelid is depressed, as in ordinary winking ; and it is obvious that, in this
manner, the surface of the eye is more effectually swept free from impurities
which may have gathered upon it, than it would be by the downward motion
of the lid alone. But the pupil is not contracted, when the eyeball is volun-
tarily rotated upwards and inwards.

444. Besides the contractions of the pupil, another action, which has been
sometimes spoken of as reflex, is produced through the Optic nerve, — the
contraction of the Orbicularis muscle under the influence of strong lighf, or
when a foreign body is suddenly brought near the eye. But this cannot be
produced by any mechanical stimulation, and it evidently involves sensation ;
in fact, it is a movement of a consensual kind, produced by the painful effect
of light, which gives rise to the condition well characterized by the term
photophobia. The involuntary character of it must be evident to every one,
who has been engaged in the treatment of diseases of the eyes; and the effect
of it is aided by a similarly-involuntary movement of the eyeball itself, which
is rotated upwards and inwards, to a greater extent than the Will appears able
to effect.

29*

342

FUNCTIONS OF THE NERVOUS SYSTEM.

445. There is a further peculiarity, of a very marked kind, attending the
course of the Optic nerves ; this is the crossing or decussation which they

[Fig. 159.

[Fig. 160.

Plan of the oplic nerves on a
small scale, showing their diver-
gence from the chiasma. c, and
their junction with the globe, on
the inner side of the axis of the
humors.]

Course of fibres in the chiasma, as exhibited by
tearing; oft" the superficial bundles from a specimen
hardened in spirit, a. Anterior fibres, commissural
between the two retinrc. p Posterior fibres, com-
missural between the thalami. a', p'. Diagram of
the preceding.]

undergo, more or less completely, whilst proceeding from their ganglia to the
eyes. In some of the lower animals, in which the two eyes (from their lateral
position) have entirely different spheres of vision, the decussation is complete;
the whole of the fibres from the right optic ganglion passing into the left eye,
and vice versa. This is the case, for example, with most of the Osseous
Fishes (as the cod, halibut, &c.) ; and also, in great part at least, with Birds.
In the Human subject, however, and in animals which, like him, have the two
eyes looking in the same direction, the decussation seems less complete ; but
there is a very remarkable arrangement of the fibres, which seems destined to
bring the two eyes into peculiarly consentaneous action. The posterior border
of the Optic Chiasma is formed exclusively of commissural fibres, which pass
from one optic ganglion to the other, without entering the real optic nerve.
Again, the anterior border of the Chiasma is composed of fibres, which seem,
in like manner, to act as a commissure between the two retinae ; passing from
one to the other, without any connection with the optic ganglia. The tract
which lies between the two borders, and occupies the middle of the Chiasma,
is the true Optic Nerve ; and in this it would appear that a portion of the fibres
decussates, whilst another portion passes directly from each Optic ganglion
into the corresponding eye. The fibres which proceed from the ganglia to
the retina?, and constitute the proper Optic Nerves, may be distinguished into
an internal and an external tract. Of these, the external on each side, passes
directly onwards to the eye of that side; whilst the internal crosses over to
the eye of the opposite side. The distribution of these two sets of fibres in
the retina of each eye respectively, is such that, according to Mr. Mayo, the
fibres from either optic ganglion will be distributed to its own side of both
eyes ; the right optic ganglion being thus exclusively connected with the outer
part of the retina of the right eye, and with the inner part of the retina of the
left eye ; and the left optic ganglion being, in like manner, connected exclu-
sively with the outer side of the left retina, and with the inner side of the
right. Now as cither side of the eye receives the images of objects, which
are on the other side of its axis, it follows, if this account of their distribution
be correct, that in Man, as in the lower animals, each ganglion receives the
sensations of objects situated on the opposite sides of the body. The purpose
of this decussation may be, to bring UK: visual impressions, which are so im-
portant in directing the movements of the body, into proper harmony with the

NERVES OF SPECIAL SENSE. AUDITORY AND GUSTATORY.

343

[Fig. 101.

apparatus; so that, the decussation of the motor fibres in the pyramids being
accompanied by a decussation of the optic nerves, the same effect is produced
as if neither decussated, — which last is the case with Invertebrated animals in
general.

446. The functions of the Auditory nerve, or Portio Mollis of the Seventh,
are easily determined, by anatomical examination of its distribution, and by
observation of pathological phenomena, to be analogous to those of the two
preceding, Atrophy or lesion of the trunk destroys the sense of Hearing;
whilst irritation of it produces auditory sensations, but does not occasion pain.
From experiments made upon the
nerve before it leaves the cranial
cavity, it appears satisfactorily as-
certained, that this nerve is not
endowed either with common sen-
sibility, or with the power of di-
rectly stimulating muscular move-
ment. Nor can any obvious reflex
actions be executed by irritation of
this nerve; but it seems neverthe-
less by no means improbable, that
the muscles which regulate the ten-
sion of the tympanum, are called
into action by impressions made
upon it and reflected through the
auditory ganglion, in the same man-

ner as the diameter of the pupil is A view of ,he origin and distribution of the Portio

regulated through the Optic nerve. Mollis of the Seventh pair or Auditory Nerve ; 1, the

- It has been attempted by Flotl- medulla oblongata; 2, the pens Varolii; 3. 4. the crura

rens to show, that the division of cerebelli of the right side; 5,^6 eighth pairof nerves;

,, . i- i • i_ i 6, the ninth pair; 7, the auditory nerve distributed to

the Auditory nerve, which proceeds the cochlea and labyrinth; 8, th? sixth pair of nerves 5

to the Semi-Circular Canals, has 9, the portio dura of the seventh pair; 10, the fourth

functions altogether different from pair; n, the fifth pair.]

that portion which supplies the Ves-

tibule and Cochlea. This inference, however, is grounded only upon the

movements exhibited by animals, in which these nerves are irritated ; which

movements are capable of a different explanation (§ 432).

a. It is interesting to remark, that microscopic examination of the structure of the Audi-
tory nerve clearly indicates its intermediate character between the nerves of special sensa-
tion issuing from the anterior part of the cranium (namely, the Optic and Olfactory), and
those whose function is to minister, either to common sensation, or to that of Taste, which
approaches nearly to it, (namely, the Fifth pair and the Glosio-pliaryngeal,) which issue
from the posterior part of the Encephalon, and are more nearly analogous to the Spinal
nerves. The primitive fibres are not so soft as those of the Olfactive, nor so slender as
those of the Optic ; and they are softer than those of the Glosso-pharyngeal. Moreover, the
Auditory nerve forms a plexus with the Facial, to which there is no analogy in the Optic
and Olfactive nerves, but to which a similar one exists in the Glosso-pharyngeal. This
intermediate structural character is interesting, when we compare it with the intermediate
character of the function; for the impressions made upon the sense of Hearing are pro-
duced through vibrations of a material fluid, — instead of being, as in the case of Sight, the
result of changes so subtle as to be almost inscrutable to our means of research, — or, as in
the case of Taste and Touch, being produced by the direct contact of the substance which
rise to the sensation.

447. The nerves which minister to the sense of Taste, as already men-
tioned, are destitute of the peculiarities which distinguish the preceding;
being no other than certain branches of ordinary afferent nerves, — the Fifth
Pair and Glosso-pharyngeal, — the peculiar endowments of which seem to

344 FUNCTIONS OF THE NERVOUS SYSTEM.

depend rather upon the structure and actions of the papillae at their peripheral
extremities, than upon anything special in their own characters. — From the
recent observations and experiments of M. Ch. Bernard, it appears that the
Facial nerve (Portio Dura of the 7th) supplies some condition requisite for
the sense of Taste, through the branch known as the Chorda Tympani, which
is the motor nerve of the Lingualis muscle. When paralysis of the Facial
exists in Man, the sense of taste is very much impaired on the corresponding
side of the tongue, provided the cause of the paralysis be seated above the
origin of the Chorda Tympani from its trunk. Similar results have been ob-
tained from experiments upon other animals. The nature of the influence
afforded by this nerve is entirely unknown ; and it is the more obscure, as the
Chorda Tympani contains no sensory filament.

448. To the sense of Touch, all the afferent nerves of the body (save the
nerves of special sense) appear to minister; in virtue — according to the hypo-
thesis here upheld — of the direct connection of certain of their fibrils with the
Sensorium commune. But the degree in which they are capable of producing
Sensations, does not bear any constant relation to their power of exciting
Reflex actions. Thus, the Glosso-pharyngeal is not nearly so sensitive as
the Fifth pair; though more powerful as an excitor nerve. The Par Vagura
appears to have even less power of arousing sensory changes ; although it is
the most important of all the exciters to reflex action. So again, the afferent
nerves of the inferior extremities, in Man, are less concerned in ministering
to sensations, than are those of the superior; and yet they appear to be much
more efficient as excitors to muscular action. — These differences may be ac-
counted for, by supposing that the proportion which the fibres, having their
centre in the ganglionic matter of the Spinal Cord, bear to that of the fibres
which pass on to the Sensorium, is not constant, but is liable to variation ;
the former predominating in the Par Vagum and the Glosso-pharyngeal ;
whilst the latter are more numerous in the Fifth Pair, and in most of the Spi-
nal nerves.

449. It appears, from what has been already stated, that all the motor fibres
of the Cerebro-spinal system, not exclusively concerned in Reflex movements,
must be in connection with the Sensory ganglia ; since we find that their
actions, whether simply consensual, emotional, or volitional, are dependent
upon guiding sensations. Of these sensations, the greater proportion are
received from the muscles themselves ; but there are certain cases, as we have
seen, in which the guiding influence is communicated rather by the organs
and nerves of Special sense. Of these, a good example is afforded by the
movements of the Eyeball, presently to be examined in detail ; and another
is to be found in those of the Larynx, to be fully treated of hereafter (Chap,
viii.). The Emotions, in like manner, may operate upon all the motor nerves
of the body; as we see in the violent movements of unrestrained passion, or
in the increased power given to voluntary efforts, by the simultaneous excite-
ment of certain emotional states. But, as already remarked, their ordinary
action is most displayed through the motor nerves of the face and respiratory
organs.

450. Consensual Movements of the Eye. — It will be recollected that, in
the Human Orbit, six muscles for the movements of the eyeball are found, —
the four recti, and the two oblique muscles. The precise actions of these are
not easily established by experiment on the lower animals; for in all those
which ordinarily maintain the horizontal position, there is an additional mus-
cle, termed the retractor, which embraces the whole posterior portion of the
globe, and passes backwards to be attached to the bottom of the orbit. This
muscle is most developed in Ruminating animals, which, during their whole
lime of feeding, carry their heads in a dependent position. In most Carni-

CONSENSUAL MOVEMENTS OF THE EYE. 345

vorous animals, instead of the complete hollow muscular cone (the base inclos-
ing the eyeball, whilst the apex surrounds the optic nerve) which we find in
the Ruminants, there are four distinct strips, almost resembling a second set
of recti muscles, but deep-seated, and inserted into the posterior instead of the
anterior portion of the globe. It is obvious that the actions of these must
greatly affect the results of any operation, which we may perform upon the
other muscles of the Orbit; arid, as it is impossible to divide the former,
without completely separating the eye from its attachments, we have no means
of correcting such results, but by reasoning alone. Experiments upon ani-
mals of the order of Quadrumana, most nearly allied to Man, would be more
satisfactory ; as in them, the retractor muscle is almost or entirely absent. —
If the origin and insertion of the four Recti muscles be examined, however,
no doubt can remain that each of them, acting singly, is capable of causing
the globe to revolve in its own direction, — the superior rectus causing the pupil
to turn upwards, — the internal rectus causing it to roll towards the nose, — and
so on. A very easy and direct application of the laws of mechanics will fur-
ther make it evident to us, that the combined action of any two of the Recti
muscles will cause the pupil to turn in a direction intermediate between the
lines of their single action; and that any intermediate position may thus be
given to the eyeball by these muscles alone. This fact, which has not
received the attention it deserves, leads us to perceive, that the Oblique mus-
cles must have some supplementary function. It may be objected that this is
a theoretical statement only ; and that there may be some practical obstacle
to the performance of diagonal movements by the Recti muscles, which ren-
ders the assistance of the Obliques essential for this purpose. But to this it
may be replied, that no single muscle can direct the ball either downwards
and inwards, or upwards and outwards; and that, as we have good reason to
believe these movements to be effected by the combination of the Recti mus-
cles, there is no reason why the other diagonal movements should not also be
due to them.

451. The most probable account of the functions of the Oblique muscles of
the eye, seems to be that which was long ago suggested by John Hunter, and
which has received confirmation from the recent experiments of Dr. G. John-
son.*— It has been just shown that the action of the Recti muscles upon the
pupil, is such as to cause it to revolve in any given direction; and they are
put in action, not merely to alter the range of vision, the head remaining
stationary, but also to keep the range of vision the same, and to cause the
images of the objects, upon which our gaze is fixed, still to fall upon the
same parts of the retinre, by maintaining the position of the eyes when the
head is moved upwards, downwards, from side to side, or in any intermediate
direction. But these muscles are not able to rotate the eyeball upon its antero-
posterior axis; and such rotation is manifestly necessary to preserve the fixed
position, of the eyeball, and consequently to keep the image of the object un-
der survey upon the same part of the retina, when the head is inclined side-
ways, or bowed towards one shoulder and then towards the other. It appears
from the experiments of Dr. G. Johnson, that the action of the Oblique mus-
cles is exactly adapted to produce such a rotation; the Inferior oblique, in its
contraction, causing the eyeball to move upon its antero-posterior axis, in such
a manner that a piece of paper, placed at the outer margin of the cornea, passed
downwards and then inwards towards the nose; and the Superior oblique
effecting precisely the reverse action, the paper at the outer margin of the cor-
nea passing first upwards and then inwards. There was not the slightest
appearance, in these experiments, of elevation, depression, abduction, or ad-

* Cyclopedia of Anatomy and Physiology, vol. iii. p. 790.

346 FUNCTIONS OF THE NERVOUS SYSTEM.

duction, of the cornea, as a result of the action of the Oblique muscles ; all
these movements being attributable to the Recti alone.

452. On studying the conjoint movements of the Eyeball, we are led to
observe the very curious fact, that they are not so much symmetrical as har-
monious; that is to say, the corresponding muscles on the two sides are rarely
in action at once ; whilst such a harmony or consent exists between the ac-
tions of the muscles of the two orbits, that they work to one common purpose,
namely, the direction of both eyes towards the requirefl objects. In order to
study them properly, it is necessary to reduce them to some kind of classifica-
tion. We may divide them into the Voluntary and the Involuntary; and the
former, being numerous, require to be further classified. They may be ar-
ranged under two groups ; the first comprising those which are alike har-
monious and symmetrical ; the second including those which are harmonious
but not symmetrical. — To the first group belong the following: — 1. Both
eyeballs are elevated by the contraction of the two Superior Recti. — 2. Both
eyeballs are depressed by the conjoint action of the Inferior Recti muscles. —
3. Both are drawn directly inwards, or inwards and downwards, as when
we look at an object placed on or near the nose ; this movement is effected by
the action of the Internal Recti of the two sides, with or without the Inferior
Recti. It is evidently symmetrical, but might seem at first sight not to be
harmonious, because the eyes do not move together towards one side or the
other; it is, however, really harmonious, since their axes are directed towards
the same point. — Now it is to be observed, with regard to these movements,
that we can never effect them in antagonism with each other, or with those of
other muscles. We cannot, for example, raise one eye and depress the other;
nor can we raise or depress one eye, when we adduct or abduct the other.
The explanation of this will be found in the fact, that we can never, by so
doing, direct the eyes to the same point. — The harmonious but unsymmetrical
movements, forming the second class, are those in which the Internal and Ex-
ternal Recti of the two sides are made to act together, either alone, or in con-
junction with the Superior and Inferior Recti. They are as follows. — 4. One
eye is made to revolve directly imvards, by the action of its Internal Rectus,
whilst the other is turned outwards by the action of its External Rectus. — 5.
One eye is made to revolve upwards and inwards, by the conjoint action of
the Internal and Superior Recti ; the other, itpwards and outicards, by the
conjoint action of the External and Superior Recti. — 6. One eye is made to
revolve downwards and inwards, by the conjoint action of the Internal and
Inferior Recti ; the other, downwards and outivards, by the conjoint action
of the External and Inferior Recti. — In these movements, two different mus-
cles, the Abducens and Adducens, are called into action on the two sides ; but
they are so employed for the purpose of directing the axes of the eyes towards
the same point.

453. The normal Involuntary movements of the eyeballs are only of two
kinds. — 1. The rotation of the two eyeballs on their own axes, which takes
place when the head is moved in certain directions (§ 451) ; this is effected
in direct respondence to certain guiding sensations, and without any influ-
ence or control on the part of the will ; it is therefore a purely consensual
action. — 2. The revolution of both eyes n/i/rart/n and inward*, which takes
place in the acts of coughing, sneezing, winking, &c. ; this is altogether inde-
pendent of visual sensations, and is commonly, like the other movements
associated in these actions, of a reflex nature. — Many abnormal movements
of the eyeballs, in which there is neither harmony nor symmetry in the
actions of the muscles, present themselves in convulsive diseases.

454. It may be stated as a physiological fact, that Single Vision with two
eyes is dependent upon the formation of the image upon parts of the two

CONSENSUAL MOVEMENTS OF THE EYE. 347

retinae, which are accustomed thus to act with each other. In many physio-
logical works it is asserted, that single vision is the result of the impressions
being made on corresponding parts of the two retinae, — that is to say, on
parts equally distant from the axis, on one side or the other : but this seems
to be disproved by the fact, that patients who have been long affected with
Convergent Strabismus, and who see equally well with both eyes (as many
do), are not troubled with double vision. On the other hand, when a person
whose eyes look straight before him, is the subject of a disorder which
renders their motions in any degree irregular, he is at once affected with
double vision ; and the same has been noticed to be a common immediate
result of the successful operation for the cure of strabismus, where vision is
good in both eyes. Although the images were previously formed on parts of
the retinae which were very far from corresponding with each other, yet no
sooner is the position of the eyes rectified (so that the relation between the
situation of the images is the same as it would have been in a sound eye),
than the patient sees double. Now in these cases the difficulty very speedily
diminishes, and the patient soon learns to see single. It can scarcely be
imagined, then, that to any other cause than habit, is to be attributed the
long-discussed phenomenon of single vision with two eyes. The mind re-
ceives the two images, frequently combining them together (as Mr. Wheat-
stone's ingenious experiments with the Stereoscope have most satisfactorily
shown, § 547) to produce a picture in relief; and so long as these are con-
veyed to it in the accustomed manner, it reconciles them together, even if the
parts of the retinaa on which they are formed do not correspond; but if any
circumstance break this chain, and cause the images to be transmitted to the
sensorium through a new channel, the mind requires some little time to
adapt itself to this impression, as it does by habit to almost every other.

a. That there is a greater tendency to consent between the images, when they are formed
upon corresponding parts of the retinae, the Author readily admits ; and he thinks that this
is a principle of some importance, in explaining the re-adjustment of the eyes, after the
operation for Strabismus. Every one who has seen much of this operation is aware, that
the re-adjustment of the eye is not always immediate, but that, after the muscle has been
freely divided, the eye often remains somewhat inverted for a few days, gradually acquir-
ing its straight position. The Author has known one case, in which, after such a degree of
temporary inversion as seemed to render the success of the operation very doubtful, ever-
sion actually took place for a short time to a considerable extent ; after which the axes be-
came parallel, and have remained so ever since.

b. Another argument, derived from the results of this operation, in favour of the con-
sensual movement being chiefly dependent upon th^ place of the impressions on the retina,
is, that it is much more successful in those cases, in which the sight of the most displaced
eye is good, than in those in which, (as not unfrequently happens from long disuse) it is
much impaired. In cases of the latter class, the cure is seldom complete. There is another
curious fact, which may be adverted to in reference to this subject : Strabismus not unfre-
quently arises from the formation of an opaque spot on the centre of the cornea, which pre-
vents the formation of any images on the retina, except by the oblique rays ; and nature
seems to endeavour (so to speak) to repair the mischief, by causing the eye to assume the
portion most favourable for the reception of these.

c. To one more point only, connected with the subject of Strabismus, would the Author
now allude. He is well convinced, from repeated observation, that those Surgeons are in the
right, who have maintained, in a recent controversy, that, in a large proportion of cases,
strabismus is caused by an affection of both sets of muscles or nerves, and not of one only ;
and that it then requires, for its perfect cure, the division of the corresponding muscle on
both sides. Cases will be frequently met with, in which this is evident; the two eyes
being employed to nearly the same extent, and the patient giving to both a slight inward
direction, when desired to look straight forwards. In general, however, one eye usually
looks straight forwards, whilst the other is greatly inverted: and the sight of the inverted
eye is frequently affected to a considerable degree by disuse ; so that, when the patien;
voluntarily rotates it into its proper axis, his vision with it is far from being distinct. Some
Surgeons have maintained, that the inverted eye is usually the only one in fault, and con-
sider that the division of the tendon of its Internal Rectus is sufficient for the cure. They

348 FUNCTIONS OF THE NF.RVOUS SYSTEM.

would even divide its other tendons, if the parallelism be not restored, rather than touch
the other eye. The Author is himself satisfied, however, that the restriction of the abnor-
mal state to a single eye, is the exception, and not the rule, in all but very slight cases of
strabismus ; and to this opinion he is led both by the consideration of the mode in which
strabismus first takes place, and by the results of the operations which have come under his
notice. If the eyes of an infant affected with cerebral disease be watched, there will fre-
quently be observed in them very irregular movements; the axes of the two being some-
times extremely convergent, find then very divergent. This irregularity is rarely or never
see^i to be confined to one eye. Now, in a large proportion of cases of Strabismus, the
malady is a consequence of some cerebral affection during infancy or childhood, which we
can scarcely suppose to have affected one eye only. Again, in other instances we find the
Strabismus to have resulted from the constant direction of the eyes to very near objects, as
in short-sighted persons; and here, too, the cause manifestly affects both.

d. Now it is easy to understand, why one eye of the patient should appear to be in its
natural position, whilst the other is greatly inverted. The cause of strabismus usually
affects the two eyes somewhat unequally, so that one is much more inverted than the other.
We will call the least inverted eye A, and the other B. In the ordinary acts of vision, the
patient will make most use of the least inverted eye, A, because he can most readily look
straight forwards or outwards with it ; but to bring it into the axis, or to rotate it outwards,
necessitates a still more decided inversion of B. This remains the position of things, — the
patient usually looking straight forwards with A, which is the eye constantly employed for
the purposes of vision, — and frequently almost burying under the inner canthus the other
eye, B, the vision in which is of very little use to him. When, therefore, the tendon of the
internal rectus of B is divided, the relative position of the two is not entirely rectified.
Sometimes it appears to be so for a time; but the strabismus then begins to return, and it
can only be checked by division of the tendon of the other eye, A; after which the cure is
generally complete and permanent. That it has not been so, in many of the cases on
which operations have been performed, the Author attributes, without the slightest doubt in
his own mind, to the neglect of the second operation. As just now stated, the sight of the
most inverted eye is frequently very imperfect ; indeed it is sometimes impaired to such an
extent, that the patients speak of it as entirely useless. That this impairment results' in part
from disuse merely, seems very evident, from the great improvement which often succeeds
the rectification of the axes. The Author cannot help thinking it probable, however, that
the same cause which produced the distortion of the eye may, in some instances at least,
have affected the Optic nerve, as well as the Motor nerves of the orbit; and this idea is
borne out by the fact of the restoration of sight, in certain cases of Amaurosis, by division of
one or more tendons, where no Strabismus previously existed. (See Adams on Muscular
Amaurosis.) It is interesting to remark that, in these cases, Strabismus was usually the
first effect of the operation ; but that the eye generally recovered its ordinary position within
a short time, especially when the sight was improving.

455. If this be admitted, we gain an important step in the explanation of
the Consensual movements of the Eye. The object to be attained is evidently
this, — that the usual axes of the eye should always be directed towards the
object to be viewed; and this, asfve have seen, involves the necessity (in a
great majority of cases), of unsymmetrical movements being performed by
the two eyeballs. The combination of these movements is involuntary or
automatic ; and appears to be regulated by the sensations received through
the retinae. It is well known that, in children born blind, the movements are
not consensual ; they are frequently very far from being so, in cases of con-
genital cataract, where a considerable amount of light is evidently admitted,
but where no distinct image can be formed ; and in such cases, the movements
are most consensual where the object is bright and luminous, and a more vivid
impression therefore made upon the retina. It ie no objection to this theory
to say, that persons who have become blind may still move their eyes in a
consensual manner ; since, the habit of the association of particular move-
ments having been once acquired, the guidance of the muscles may be effected
by sensations derived from themselves, in the manner in which it takes place
in the laryngeal movements of the deal' and dumb ; and, as a matter of fact,
a want of consent may be often noticed where the blindness is total. The
peculiar vacant appearance, which may be noticed in the countenances of per-
sons completely deprived of sight by amaurotic or other affections, which do

FUNCTIONS OF THE CEREBELLUM. 349

not alter the external aspect of the eyes, seems to result from this, — that their
axes are parallel, as if the individual were looking into distant space, instead
of presenting that slight convergence which must always exist between them,
when the eyes are fixed upon a definite object. This convergence, which is
of course regulated by the Internal Recti, varies in degree according to the
distance of the object, and it is astonishing how minute an alteration in the
axes of the eyes is perceptible to a person observing them. For instance, A.
sees the eyes of B directed towards his face, but he perceives that B is not
looking at him ; he knows this by a sort of intuitive interpretation of the
fact, that his face is not the point of convergence of B's eyes. But if B, who
might have been previously looking at something nearer or more remote than
A's face, fix his gaze upon the latter, so that the degree of the convergence of
the axes is altered, without the general direction of the eyes being in the least
affected, the change is at once perceived by the person so regarded ; and the
eyes of the two then meet.

456. The foregoing considerations maybe summed up in this simple state-
ment : — that, when we voluntarily direct our eyes towards any object, the
actions of the several muscles concerned, are guided by the visual sensations,
rather than by the ordinary muscular sense, through which other voluntary
movements are regulated. In this manner are accomplished, not merely the
revolutions of the eyeballs from side to side, upwards and downwards, or in
any direction that is required to cause the image to fall most advantageously
upon the two retinae ; but also that rotation on their axes, which keeps the
images in the same position upon the retinae, when the head moves in a plane
perpendicular to their axes ; and likewise that exact convergence of the two
axes which shall cause them to meet in the object on which the attention is
fixed, and which consequently varies with its distance. Of all the movements
of the eyes, there is none which exhibits the necessity of the guiding visual
sensations so much as the revolution of both eyes inwards. Some persons
can effect this voluntarily to a greater extent than others ; but even then, they
can only accomplish it by fixing the gaze upon some object situated between
the eyes ; and cannot call the adductor muscles into combined action in per-
fect darkness, or if the lids be closed. Even those who have the least power
of effecting this extreme convergence, by at once directing the eyes towards
a very near object, can accomplish it by looking at an object placed at a mo-
derate distance, and gradually bringing this nearer to the nose, keeping the
eyes steadily fixed upon it. The unwonted character of the movement is
shown in this, — that it can only be maintained, even for a short time, by a
strong effort, producing a sense of fatigue. No effort whatever can call into
simultaneous action the two external Recti ; and this fact is an additional
proof of the necessity of a guiding visual sensation ; since it is evident, that
no object can ever be placed in such a position, as to require this action for
the direction of the axes of the eyes towards it.

6. Functions of the Cerebellum.

457. That the Cerebellum has some special function, distinct from that of
the Cerebral Hemispheres, can scarcely be doubted ; since its peculiar struc-
ture and position, its independent connections with the Medulla Oblongata,
and its extremely variable size relatively to the remainder of the Encephalon,
point it out as an instrument adapted to some particular purpose. We shall
inquire briefly into the nature of the evidence respecting its function, which
is supplied to us by Comparative Anatomy, by Experiment, and by Patholo-
gical phenomena. A Cerebellum is found in all Vertebrated animals; although
it is in some extremely small, looking like a little prominence on the Medulla
30

350

FUNCTIONS OF THE NERVOUS SYSTEM.

Oblongata. When this is the case, it is observed that the whole mass is not
a miniature (so to speak) of the large Cerebellum of Man, but that the central
portion (termed the vermiform process) is the part most developed; the lobes
not presenting themselves until the organ has acquired an increased dimension.
The following table, constructed from materials contained in M. Serres' most
valuable Comparative Anatomy of the Brain, will afford some idea of the ma-
terials for speculating on the nature of the function of the Cerebellum, which
we obtain from this source. The first column gives the diameter of the Spinal
Cord, at the second cervical vertebra ; in the two succeeding columns are
stated the transverse and the antero-posterior diameters of the Cerebellum ;
these dimensions are stated in hundred-thousandths of a metre. The fourth
column expresses, in round numbers, the proportion which the diameters of
the Cerebellum bear to that of the Spinal Cord ; the latter being reckoned as 1.

MAMMALIA.

Diam. of Spinal
Cord at 2d Cervical
Vertebra.

Transverse Diam.
of Cerebellum.

Amero-posterior
Diameter
of Cerebellum.

Proportions.

Man .
Simia Rubra .
Bear
Dog .
Dromedary .
Kangaroo

1.100
900
1,300
1.100
. 1,900
1.200

12,000
4,500
5;900
4^200

7^100
3.800

6,000
2,443
3,500
2,525
4,600
2J600

11 —5^

^ 9 t

OT~"™™"^ 2
Q 1 O 1

BIRDS.

Falcon .
Swallow

400
3,175

1,350
500

1,100
600

3 3 1

Turkey .
Ostrich .

500
700

1,350

1,750

1,600
2,500

22 o1

REPTILES.

Crocodile
Frog .

300
300

500
300

400
200

ii-ii

FISHES.

Shark .
Cod .
Turbot .

700
575

500

1,700
1.350
'750

3,100
1,700
900

Oi Q

Lamprey

275

225

100

f-i

458. This table affords us much scope for interesting speculation, and may
be applied to the correction of hypotheses erected upon other foundations.
Before we proceed to these, however, a few general remarks may be made
upon it. In the first place, the proportional development of the Cerebellum
is seen to be smallest in the Vermiform Fishes, which approach most nearly
to the Invertebrata; but it is much greater -in the higher Fishes than it is in
Reptiles. If we consider in what particular, that may be reasonably supposed
to have a connection with this organ, the former surpass the latter, we should
at once be struck with their superiority in activity and variety of movement.
Passing on to Birds, we remark that the average dimensions of the Cerebel-
lum greatly surpass those of the organ in Reptiles ; but that they do not exceed
those occasionally met with in Fishes. The greatest size is not found in those

FUNCTIONS OF THE CEREBELLUM. 351

species which approach most nearly to the Mammalia in general conformation,
such as the Ostrich ; but in those of most active and varied powers of flight.
Lastly, on ascending the scale of Mammiferous animals, we cannot but be
struck with the rapid advance in the proportional size of the Cerebellum, that
we observe, as we rise from the lowest, which are surpassed in this respect
by many Birds, towards Man, in whom it attains a development which appears
enormous, even when contrasted with that of the Quadrumana.

459. We have next to inquire what evidence can be drawn from Experi-
mental investigations on the same subject: and in reference to this it is desirable
to remark, in the first place, that the experimental mode of inquiry is perhaps
more applicable to this organ than to other parts of the Encephalon; inasmuch
as it can be altogether removed, with little disturbance of the actions imme-
diately essential to life; and the animals soon recover from the shock of the
operation, and seem but little affected, except in some easily-recognized par-
ticulars. The principal experimenters upon this subject have been Rolando,
Flourens, Magendie, Hertvvig, and Longet. It is not to be expected, that there
should be an exact conformity among the results obtained by all. Every one
who has been engaged in physiological experiments, is aware of the amount
of difference caused by very minute variations in their circumstances; in no
department of inquiry is this more the case than in regard to the Nervous
System ; and such differences are yet more likely to occur, in experiments
made upon the Nervous Centres, than in those which concern their trunks. —
The investigations of Flourens are the most clear and decisive in their results ;
and of these we shall accordingly take a general survey. He found that, when
the Cerebellum was mechanically injured, the animals gave no signs of sensi-
bility, nor were they affected with convulsions. When the Cerebellum was
being removed by successive slices, the animals became restless, and their move-
ments were irregular; and by the time that the last portion of the organ was cut
away, the animals had entirely lost the powers of springing, flying, walking,
standing, and preserving their equilibrium, — in short, of performing any com-
bined muscular movements, which are not of a simply-reflex character. When
an animal in this state was laid upon the back, it could not recover its former
posture; but it fluttered its wings and did not lie in a state of stupor. When
placed in the erect position, it staggered and fell like a drunken man, — not, how-
ever, without making efforts to maintain its balance. When threatened with a
blow, it evidently saw it, and endeavoured to avoid it. It did not seem that the
animal had in any degree lost voluntary power over its several muscles ; nor did
sensation appear to be impaired. The faculty of combining the actions of the
muscles in groups, however, was completely destroyed ; except so far as those
actions (as that of respiration) were dependent only upon the Reflex function
of the Spinal Cord. The experiments afforded the same results, when made
upon each class of Vertebrated animals; and they have since been repeated,
with corresponding effects, by Bouillaud and Hertwig. The latter agrees with
Flourens, also, in stating that the removal of one side of the Cerebellum affects
the movements of the opposite side of the body; and he further mentions
that, if the mutilation of the Cerebellum have been partial only, its function is
in great degree restored.

460. All these results are objected to by those who assert that the Cerebel-
lum is the seat of the sexual instinct; on the ground that the observed aberra-
tions of the motor functions are sufficiently accounted for, by the general
disturbance which an operation so severe must necessarily induce. The
fallacy of this objection, however, is shown by the fact, that the much more
severe operation of removing the Hemispheres does not occasion such an
aberration ; the power of performing the associated movements, and of main-

352 FUNCTIONS OF THE NERVOUS SYSTEM.

taming the equilibrium, being remarkably preserved after the loss of them
(§435).

461. Upon comparing these results with the preceding table, a remarkable
correspondence will be observed between them. The classes which have the
greatest variety of movements, and which require for them the most perfect
combination of a large number of separate muscular actions, have, taken col-
lectively, the largest Cerebellum. Of all classes of Vertebrata, Reptiles are
the most inert ; and their motions require the least co-ordination. The active
predaceous Fishes far surpass them in this respect ; and may be compared
with Birds, in the energy of their passage through the water, and in their
facility of changing their direction during the most rapid progression. The
Cerebellum, accordingly, bears to the Spinal Cord in them, very much the
same proportion as it does in Birds. On the other hand, the Flat Fish, which
lie near the bottom of the ocean, and which have a much less variety of move-
ment, have a very much smaller cerebellum : and the Vermiform Fishes, which
are almost all completely destitute of fins, and whose progression is accom-
plished by flexion of the body, have a Cerebellum so small as to be scarcely
discoverable: their motion being, like that of the Articulata, almost entirely of
a reflex character, — each segment being influenced by its own ganglionic cen-
tre, and the Spinal Cord constituting by far the largest proportion of the nervous
centres. On looking at the class of Birds, we observe that the active preda-
ceous Falcons, and the Swift-winged Swallows (the perfect control possessed
by which over their complicated movements must have been observed by every
one), have a Cerebellum much larger in proportion than that of the Gallina-
ceous birds, whose powers of flight are small, or than that of the Struthious
tribe, in which they are altogether absent. Lastly, on comparing its propor-
tional size in the different orders of Mammalia, with the number and variety
of muscular actions requiring combined movements, of which they are respect-
ively capable, we observe an even more remarkable correspondence. In the
hoofed Quadrupeds, in which the muscular apparatus of the extremities is
reduced to its greatest simplicity, and in which the movements of progression
are simple, the Cerebellum is relatively smaller than it is found to be in some
Birds ; but in proportion as the extremities acquire the power of prehension,
and together with this a power of application to a great variety of purposes, —
still more, in proportion as the animal becomes capable of maintaining the
erect posture, in which a constant muscular exertion, consisting of a number
of most elaborately-combined parts, is required, — do we find the size of the
Cerebellum, and the complexity of its structure, undergoing a rapid increase.
Thus, even between the Dog and the Bear there is a marked difference ; the
latter being capable of remaining for some time in the erect posture, and often
spontaneously assuming it; whilst .to the former it is anything but natural.
In the semi-erect Apes, again, there is a very great advance in the proportional
size of the Cerebellum ; and those which most approach Man in the tendency
to preserve habitually the erect posture, also come nearest to him in the di-
mensions of this organ.

462. Now it is evident that Man, although far inferior to many of the lower
animals in the power of performing various particular kinds of movement, far
surpasses them all, in the number and variety of the combinations which he
is capable of executing, and in the complexity of the combinations themselves.
Thus, if we attentively consider the act of tea Ik in ^ in man, we shall find that
there is scarcely a muscle of the trunk or extremities which is not actually
concerned in it; some being engaged in performing the necessary movements,
and others in maintaining the equilibrium of the body, which is disturbed by
them. On the other hand, in the horse or Camel, the muscular movements
are individually numerous, but they do not require nearly the same perfect

FUNCTIONS OF THE CEREBELLUM. 353

co-ordination. And in the Bird, the number of muscles employed in the
movements of flight, and in directing the course of these, is really comparatively
small ; as may at once be perceived, by comparing the rigidity of the skeleton
of the trunk of the Bird with that of Man, and by remembering the complete
inactivity of the lower extremities during the active condition of the upper.
In fact, the motions of the wings are so simple and regular, as to suggest the
idea, that, as in Insects, their character is more reflex than directly voluntary :
— an idea which is supported by the length of time during which they can be
kept up without apparent fatigue, and also by the important facts already men-
tioned, which experimental research has disclosed (§ 435). It is seen, then,
that Comparative Anatomy fully confirms the idea, which Experimental physi-
ology suggests, respecting the chief functions of the Cerebellum.

463. Some of Magendie's experiments indicate a further connection of
this organ with the motor function, the nature of which is still obscure. This
physiologist asserts that, if a wound be inflicted on the Cerebellum, the animal
seems compelled by an inward force 'to retrograde movement, although mak-
ing an effort to advance; and that, if the Crus Cerebelli on one side be injured,
the animal is caused to roll over towards the same side. Sometimes (if Ma-
gendie's statements can be relied on), the animals make sixty revolutions in a
minute, and continued this movement for a week without cessation. Division
of the second Crus Cerebelli restored the equilibrium. Hertwig observed the
same phenomenon, when the Pons Varolii (which is nothing more than the
commissure of the Cerebellum, surrounding the Crura Cerebri) was injured on
one side ; and he has also remarked, that the movements of the eyes were no
longer consensual.

464. On turning to Pathology for evidence of the functions of the Cerebel-
lum, we meet with much that seems contradictory. It must be remembered
that a sudden effusion of blood, even to a small extent, in any part of the En-
cephalon, is liable to produce the phenomena of apoplexy or paralysis ; and
inferences founded upon the phenomena exhibited after sudden lesions of this
description are, therefore, much less valid, than those based on the results of
more chronic affections. In regard to these last, however, it is to be observed,
that we are not yet in a condition to be able to state with precision, what
amount of morbid alteration in any part of the nervous centres, is compatible
with but slightly-disturbed performance of its function ; and that cases are
every now and then occurring, which would upset all our previous notions, if
we were not aware, that the same difficulty presents itself, even in regard to
the best-established results in Neurology. It is also to be remembered, that
the results of disease, occasioning pressure, will be peculiarly liable to affect
the Medulla oblongata, as well as the Cerebellum ; and will thus occasion a
greater loss of motor power than would be occasioned by the mere suspension
of the function of the latter.

465. Pathological phenomena, when examined with these reservations,
appear to coincide with the results of experiment, in supporting the conclu-
sion, that the Cerebellum is not in any way the instrument of psychical ope-
rations. Inflammation of the membranes covering it, if confined to that part,
does not produce delirium ; and its almost complete destruction by gradual
softening, does not appear necessarily to involve loss of intellectual power.
"But," remarks Andral, " whilst the changes of intelligence were variable,
inconstant, and of little importance, the lesions of motion, on the contrary,
were observed in all the cases [of softening which had come under his no-
tice] except one ; and in this it is not quite certain that motion was not inter-
fered with." In general, apoplexy of the Cerebellum is accompanied by para-
lysis ; but this is by no means usual in cases of chronic disease, in which
there is rather an irregularity of movement, with a degree of restlessness re-

30*

354 FUNCTIONS OF THE NERVOUS SYSTEM.

sembling that described by Flourens as resulting from partial injury of this
organ. In a few cases in which both lobes of the Cerebellum have been
seriously affected, the tendency to retrograde movement has been observed ;
and instances are also on record, of the occurrence of rotatory movement,
which has been found to be connected with lesion of the Crus Cerebelli on
the same side. So far as they can be relied on, therefore, the results of the
three methods of investigation bear a very close correspondence ; and it can
scarcely be doubted that they afford us some approximation to truth.

466. We have now to examine, however, another doctrine regarding the
functions of the Cerebellum, which was propounded by Gall, and which is
supported by the Phrenological school of physiologists. This doctrine —
that the Cerebellum is the organ of the sexual instinct — is by no means in-
compatible with the other ; and by some it has been held in combination with
it. The greater number of Phrenologists, however, regard this instinct as the
exclusive function of the Cerebellum ; and assert that they can judge of its
intensity, by the degree of development of the organ. We shall now exam-
ine the evidence in support of this position, afforded by the three methods of
inquiry which have been already indicated. The results of fair observation
as to the comparative size of the Cerebellum in different animals, can scarcely
be regarded as otherwise than very unfavourable to the doctrine in question.
In the greatest number of Fishes, it is well known that no sexual congress
takes place ; the seminal fluid being merely effused, like any other excretion,
into the surrounding water ; and being thus brought into accidental contact
with the ova, of which a large proportion are never fertilized. But there are
certain Fishes, as the Sharks, Rays and Eels, in Avhich copulation takes place
after the ordinary method. Now on contrasting these two groups, we find no
corresponding difference in the size of the Cerebellum. It is true that this
organ is of large size in the Sharks ; but it is very small in the Rays ; and
almost rudimentary in the Eels : — in this respect bearing a precise correspond-
ence with the variety and complexity of their movements. Further, in many
ordinary Fishes, which do not copulate, such as the Cod, the Cerebellum is
not only larger, but more complex in structure, than it is in the generality of
Reptiles, in which the sexual instinct is commonly strong ; — the whole spinal
system of the Frog possessing, at the season of reproduction, an extraordinary
degree of excitability, which is evidently destined to aid in the performance
of the function (§ 401, «). Again, in comparing the Gallinaceous Birds,
•which are polygamous, with the Raptorial and Insessorial tribes which live
in pairs, we find that the former, instead of having a larger cerebellum, have
one of inferior size. Further on looking at the Mammalia, the same dispro-
portion may be noticed. A friend who kept some Kangaroos in his garden,
informed the Author that they were the most salacious animals he ever saw ;
yet their Cerebellum is one of the smallest to be found in the class. Every
one knows, again, the salacity of Monkeys ; there are many which are excited
to violent demonstrations by the sight even of a human female; and there
are few which do not practise masturbation, when kept in solitary confinement:
yet in them the Cerebellum is much smaller than in Man, in whom the sexual
impulse is much less violent. It has been supposed that the large size of the
organ in Man is connected with his constant possession of the appetite, which is
only occasional in others ; but this does not hold good; since among domestic
animals, there are many Avhich are ready to breed throughout the year,— Cats
and Rabbits for instance ; and in these we do not find any peculiar difference
in the size of the Cerebellum. It is asserted, however, that the results of
observation in Man lead to a positive conclusion, that the size of the Cere-
bellum is a measure of the intensity of the sexual instinct in the individual.
This assertion has been met by the counter-statement of others, — that no

FUNCTIONS OF THE CEREBELLUM. 355

such relation exists. It is unfortunate that here, as in many other instances,
each party has registered the observations favourable to their own views,
rather than those of an opposite character ; so that until some additional
evidence of a less partial nature has been collected, we must consider the
question as sub judice. The Author is by no means disposed to deny
that such a correspondence may exist; but on contrasting the degree of sup-
port which this part of phrenology really derives from pathological evidence,
with that which the upholders of this view represent it to receive, he cannot
but look with much distrust at all their observations on the subject.

467. It is stated in Phrenological works, as an ordinary result of disease
of the Cerebellum, that there is an affection of the genital organs, manifest-
ing itself in priapism, turgescence of the testes, and sometimes in seminal
emissions. Now it is quite true that, in cases of apoplexy, in which these
symptoms manifest themselves, there is very commonly found to be effusion
upon the Cerebellum or in its substance ; but it is to be remembered, that in
all such lesions the Medulla Oblongata is involved, and these symptoms,
equally with paralysis, may be due to affection of that organ.* Further, the
converse does not by any means hold good ; for the proportion of cases of
disease of the Cerebellum, in which there is any manifest affection of the
sexual organs, is really very small, being, according to the calculations of
Burdach, not above one in seventeen. The same physiologist states that s^ich
affections do present themselves, although very rarely, when the Cerebrum is
the seat of the lesion. A large number of facts adduced by Phrenologists in
support of their views — such as the erections and emissions which often take
place during hanging — may be explained as well, or even better, on the hypo-
thesis that the Cerebro-spinal axis (that is, the Spinal cord with the Medulla
Oblongata) is the seat of this instinct. And this hypothesis is much more con-
formable to the results of experiment and disease, than that which locates it in
the Cerebellum. For it has been found that mechanical irritation of the Spinal
Cord, and disease in its substance, much more frequently produce excitement
of the genital organs, than do lesions of the Cerebellum. This view is en-
tertained by Miiller, and by most physiologists who have taken a compre-
hensive and unbiassed survey of the phenomena in question.

468. Among the arguments adduced by Gall and his followers in proof of
the connection between the Cerebellum and the sexual instinct, is one which
would deserve great attention, if the facts stated could be relied on. It has
been asserted, over and over again, that the Cerebellum, in animals which have
been castrated when young, is much smaller than in those which have retained
their virility, — being, in fact, atrophied from want of power to act. Now, it
is unfortunate that vague assertion, founded on estimates formed by the eye
from the cranium alone, is all on which this position rests ; and it will be pre-
sently shown, how very liable to error such an estimate must be. The fol-
lowing is the result of a series of observations on this subject, suggested by
M. Leuret,t and carried into effect by M. Lassaigne : — The weight of the
Cerebellum, both absolutely and as compared with that of the Cerebrum, was
adopted as the standard of comparison. This was ascertained in ten Stal-
lions, of the ages of from nine to seventeen years ; in twelve Mares, aged

* A case has been recently communicated to the Author, in which the sexual desire,
which had been always strong through life, but which had been controlled within the limits
of decency, manifested itself, during a period of some months preceding death, in a most
extraordinary degree: on post-mortem examination a tumour was found on the Pons Varolii.
This fact harmonizes with the view given in the text (§ 470), that the sexual instinct, if con-
nected with the Cerebellum at all, has its seat in the central lobe : but it also corresponds
equally well with the idea, that the Medulla Oblongata is its centre.

f Anat. Comp. du Systeme Nerveaux, torn, i., p. 427.

356 FUNCTIONS OF THE NERVOUS SYSTEM.

from seven to sixteen years ; and in twenty-one Geldings, aged from seven
to seventeen years. The average weight of the Cerebellum in the Stallions
was 433 grammes; the greatest heing 485 gr., and the least (which was in a
horse of ten years old) being 350. The average weight of the Cerebellum
was 61 gr. ; the greatest being 65 gr., and the least 56 gr. The average pro-
portion borne by the weight of the Cerebellum to that of the Cerebrum, was,
therefore, 1 to 7'07 ; the highest (resulting from a very small Cerebrum) being
1 to 6'25 ; and the lowest (resulting from an unusually large Cerebrum) being
1 to 7'46. Throughout it might be observed, that the variation in the size of
the Cerebellum was much less than in that of the Cerebrum. — In the twelve
Mares, the average weight of the Cerebrum was 402 gr. ; the highest being
432 gr., and the lowest 363 gr. That of the Cerebellum was 61 gr. ; the high-
est being 66 gr., (which was in the individual with the smallest Cerebrum),
and the lowest 58 gr. The average proportion of the weight of the Cerebel-
lum to that of the Cerebrum was 1 to 6'59 ; the highest being 1 to 5'09, and
the lowest 1 to 7. The proportion was, therefore, considerably higher in the
perfect female, than in the perfect male.— In the twenty-one Geldings, the
average weight of the Cerebrum was 419 gr. ; the highest being 566 gr., and
the lowest 346 gr. The average of the Cerebellum was 70 gr. ; the highest
being 76 gr., and the lowest 64 gr. The average proportion was, therefore,
1 to 5'97 ; the highest being 1 to 5'16, and the lowest 1 to 7'44. It is curi-
ous, that this last was in the individual which had the largest Cerebellum of
the whole ; but the proportional weight of the Cerebrum was still greater.

469. Bringing together the results of these observations, they are found to
be quite opposed to the statement of Gall. The weight of the Cerebrum,
reckoning the Cerebellum as 1, is thus expressed in each of the foregoing de-
scriptions of animals: —

Average. Highest. Lowest.

Stallions .... 7-07 7-46 G"25

Mares .... 6'59 7-00 5-09

Geldings . 5-97 7-44 5-16

The average proportional size of the Cerebellum in Geldings, therefore, is so
far from being less than that which it bears in entire Horses and Mares, that
it is positively greater ; and this depends not only on diminution in the rela-
tive size of the Cerebrum, but on its own larger dimension, as the following
comparison of absolute weights will show : —

Average. Highest. Lowest.

Stallions 61 65 56

Mares .... 61 66 58

Geldings .... 70 76 64

The difference is so remarkable, and appears, from examination of the indi-
vidual results, to be so constant, that it cannot be attributed to any accidental
circumstance, arising out of the small number of animals experimented on.
The average weight of the Cerebellum in the ten Stallions and twelve Mares,
is seen to be the same ; and the extremes differ but little in the two ; whilst
the average in the Gelding is more than one-seventh higher, and the lowest is
considerably above the average of the preceding, while the highest far exceeds
the highest amongst the entire Horses. It is curious that Gall would have
been much nearer the truth, if he had said that the dimensions of the Cere-
brum are usually reduced by castration ; for it appears from the following
table that this is really the case : —

Average. Greatest. Least.

Stallions ... 433 485 350

Mares .... 402 432 336

Geldings . . . . 419 566 346

FUNCTIONS OF THE CEREBRUM. 357

The weight of the largest Cerebrum of the Gelding is far above the highest of
the Stallions ; but it seems to be an extraordinary case, as in no other was the
weight above 490 gr. If this one be excluded, the average will be reduced
still further, being then about 412 ; this may be seen, by looking over the
whole table, to give a very fair idea of the usual weight in these animals,
which is therefore less, by about one-twentieth, than the average of the Stal-
lions.— The increased size of the Cerebellum in Geldings may perhaps be
accounted for by remembering that this class of horses is solely employed
for its muscular power, and that the constant exercise of the organ is not un-
likely to develop its size ; whilst Stallions, being kept especially for the pur-
pose of propagation, are much less applied to occupations which call forth
their motor faculties.

470. The Author is far from denying in toto, that any peculiar connection
exists between the Cerebellum and the Genital system ; but if the evidence
at present adduced in support of the Phrenological position be held sufficient
to establish it, in defiance of so many opposing considerations, we must bid
adieu to all safe reasoning in Physiology. The weight of testimony appears
to him to be quite decided, in regard to the connection of the Cerebellum with
the regulation of the motor function. How far this invalidates the moderate
phrenological view, which does not regard the function of the Cerebellum as
exclusively devoted to the sexual instinct, is a question well deserving of at-
tention. There is nothing opposed to such an idea in the results of the ex-
periments already adverted to (§ 459) ; since there is no evidence that sexual
instinct remained after the removal of the Cerebellum ; but, on the other hand,
there is no proof that it was destroyed. A circumstance which has been
several times mentioned to him, — that great application to gymnastic exercises
diminishes for a lime the sexual vigour, and even totally suspends desire, —
seems worthy of consideration in reference to such a view. If the Cerebellum
be really connected with both kinds of functions, it does not seem unreasona-
ble that the excessive employment of it upon one should diminish its energy
in regard to the other. Further, it would seem by no means improbable, that
the Lobes are specially connected with the regulation and co-ordination of
movements ; whilst the Vermiform processes, which are very large in many
animals in which the former scarcely present themselves, are the parts con-
nected with the sexual function. As an additional argument in favour of the
former part of this view, it may be stated, that in Man the lobes bear a larger
proportion to the Vermiform processes than in any other animal ; and that
they undergo their most rapid development during the first few years of life,
when a large number of complex voluntary movements are being learned by
experience, and are being associated by means of the muscular sensations
accompanying them : whilst in those animals which have, immediately after .
birth, the power of regulating their voluntary movements for definite objects,
witli the greatest precision, the Cerebellum is more fully developed at the
time of birth. In both instances it is well formed and in active operation (so
far as can be judged of by the amount of circulation through it), long before
the sexual instinct manifests itself in any perceptible degree.

7. Functions of the Cerebrum.

471. We come, in the last place, to consider the functions of that portion
of the Nervous Centres, which is evidently, in Man, the predominant organ
of his whole system ; being not merely the instrument of his reasoning facul-
ties, but also possessing a direct or indirect control over nearly all the actions
of his corporeal frame, save those purely vegetative processes, which are most

358 FUNCTIONS OF THE NERVOUS SYSTEM.

completely isolated from his animal powers. We should be in great danger,
however, of coming to an erroneous conclusion as to the real character of the
Cerebrum and of its operations, if we confined ourselves to the study of the
Human organism ; and the history of Physiological science shows, that every
advance of knowledge respecting its functions, has tended to limit them, whilst
at the same time rendering them more precise. Thus the Brain (this term, in
the older Anatomy, being chiefly appropriated to the Cerebrum) was accounted,
not merely the centre of all motion and sensation, but also the source of all
vitality ; the different processes of nutrition, secretion, &c., being maintained,
it was supposed, by a constant supply of " animal spirits," propagated from
the brain, along the nerves, to each individual part. The more modern doc-
trine, that the Sympathetic System has for its special function to supply the
nervous influence requisite for the maintenance of the functions of Organic
life, was the first step in the process of limitation ; still the Brain was regarded
as the centre of all the Animal functions ; and no other part was admitted to
possess any power independently of it. By experiments and pathological
observations, however, the powers of the Spinal Cord as an independent
centre of action were next established; and it was thus shown, that there is
a large class of motions, in which the Brain has no concern, and that the re-
moval of the Cerebral hemispheres is not incompatible (even among the higher
Vertebrata) with the prolonged maintenance of a sort of inert and scarcely
conscious life. Still, it has been usually maintained, and with great show of
reason, that the Cerebrum is the instrument of all psychical operations ; and
of all the movements which could not be assigned to the reflex action of the
Spinal Cord. An attempt has been made, however, in the preceding pages,
to show that this view is not altogether correct ; and that there is a class of
actions, neither reflex nor voluntary, but directly consequent upon Sensations
and upon the instinctive and emotional propensities associated with these,
which may be justly assigned to certain ganglionic centres, not less inde-
pendent of the Cerebrum than is the Spinal Cord itself. It has been advanced,
that the Cerebrum must be considered in the light of an organ siiperadded
for a particular purpose or set of purposes, and not as one which is essential
to life ; that it has no representative among the Invertebrata (except in a few
of the highest forms, which evidently present a transition towards the Verte-
brated series) ; and that, at its first introduction, in the class of Fishes, it evi-
dently performs a subordinate part in the general actions of the Nervous
System. Hence, whatever be the function, or set of functions, we assign to
the Cerebrum, we must keep in view the special character of the organ ; and
must never lose sight of the fact, that its predominance in Man does not de-
prive other parts of their independent powers, although it may keep the exer-
cise of those powers in check, and may considerably modify their manifesta-
tions.

472. Before proceeding to inquire into the Physiology of the Cerebrum,
we may advantageously take notice of some of the leading features of its struc-
ture.— In the first place, it forms an exception to the general plan, on which
the elements of ganglionic centres are arranged ; in having its vesicular sub-
stance on the exterior, instead of in the central part of the mass. The pur-
pose of this is probably to allow the vesicular matter to be disposed in such
a manner, as to present a very large surface, instead of being aggregated to-
gether in a more compact manner ; and by this means, to admit the more
ready access, on the one side, of the blood-vessels which are so essential to
the functional operations of this tissue, as well as the more ready communi-
cation, on the other, with the vast number of fibres, by which its influence is
to be propagated. There is no reason whatever to believe, that the functions

FUNCTIONS OF THE CEREBRUM. 359

of the vesicular and fibrous substances are in the least altered by this change
in their relative position ; indeed the results of observation upon the pheno-
mena of disordered Cerebral action are such, as to afford decided confirmation
to the idea already propounded, — that the action of the vesicular matter con-
stitutes the source of nervous power ; whilst the fibrous structure has for its
office, to conduct the influence generated in the preceding, towards the points
at which it is to operate. The purpose of this arrangement is further evi-
denced by the fact, that, in all the higher forms of Cerebral structure, we find
a provision for a still greater extension of the surface, at which the vesicular
matter and the blood-vessels may come into relation ; this being effected, by
the plication of the layer of vesicular matter into " convolutions," into the
sulci between which, the highly vascular membrane known as the pia mater
dips down, sending multitudes of small vessels from its inner surface into the
substance it invests. — In the fibrous or medullary substance of which the
great mass of the Cerebrum is composed, three principal sets of fibres may
be distinguished. These are, — -first, the radiating fibres, which connect the
vesicular matter of the cortical substance of the hemispheres with the Thala-
mi Optici, and which, if our view of the function of the latter be correct,
maybe regarded as ascending or sensory; — second, the radiating fibres,
which connect the vesicular matter of the cortical substance of the hemi-
spheres with the Corpora Striata, and which, on similar grounds, may be re-
garded as descending or motor ; — and third, the Commissural fibres, which
establish the connection between the opposite hemispheres, and between the
different parts of the vesicular substance of the same side, especially between
that disposed on the surface of each hemisphere, and those isolated patches
which are found in its interior. It is on the very large proportion which
the Commissural fibres bear to the rest, that the bulk of the Cerebrum of
Man and of the higher animals seems chiefly to depend ; and it is easy to
conceive, that this condition has an important relation with the operations of
the Mind, whatever be our view of the relative functions of different parts of
the Cerebrum. It appears from the late researches of M. Baillarger, that the
surface and the bulk of the cerebral hemispheres are so far from bearing any
constant proportion to each other, in different animals, that, notwithstanding
the depth of the convolutions in the Human Cerebrum, its bulk is 2£ times
as great in proportion to its surface, as it is in the Rabbit, the surface of whose
Cerebrum is smooth. The entire surface of the Human Cerebrum, when the
convolutions are unfolded, is estimated by him at about 670 square inches.*

473. With regard to the Radiating fibres, which connect the Corpora
Striata and Thalami Optici with the vesicular surface of the Cerebral hemi-
spheres, it must be admitted that no positive proof has yet been obtained of
their direct continuity with those, which enter into the composition of the
nerves proceeding from the Spinal Cord and Medulla Oblongata ; and how-
ever probable such a continuity may be regarded on some grounds, there are
certain phenomena, which may perhaps be better explained on the idea, that
these radiating fibres are of a Commissural nature only, serving to connect the
vesicular matter of the Cerebrum with that of the different portions of the Cranio-
Spinal Axis (under which term are included the Spinal Cord, the Medulla

The inference drawn by M. Baillarger from the facts he has collected. — namely, that
the proportional surface of vesicular matter in different animals, whether considered abso-
lutely, or relatively to the volume of the Cerebrum, has no correspondence with their intel-
lectual capability, — is far too sweeping an assumption ; since, as above shown, the increase
in the commissural fibres, causing an augmentation of the bulk of the Cerebrum, may be alike
the cause of increased intelligence and of a diminished proportional amount of vesicular mat-
ter ; though the latter still remains as the original source of power.

360 FUNCTIONS OF THE NERVOUS SYSTEM.

Oblongata, and the chain of Sensory Ganglia at the summit of the latter),
and thus brought, through the medium of the latter, into relation with the cen-
tral terminations of the afferent nerves, and the origins of the motor. On this
view, the Cerebrum would receive all its sensory impressions, by the commis-
sural fibres that connect it with the ganglia, which are the real centres of these
nerves ; whilst it would call the motor trunks into action, by exciting, through
another set of commissural fibres, the vesicular matter of the ganglionic cen-
tres from which they pass forth.* — This question cannot be determined until
it shall have been shown, whether there is, or is not, a direct continuity be-
tween any of the fibres of the trunks connected with the Cranio-Spinal Axis,
and any of the radiating fibres of the Cerebral hemispheres. But the latter
view is certainly favoured by the very remarkable fact, in which the results
of all experiments agree, that no irritation or injury of the Cerebral fibres
themselves, produces either sensation or motion. Even the Thalami and Cor-
pora Striata may be wounded, without the excitement of convulsive actions ;
but if the incisions involve the Tubercula Quadrigemina or the Medulla Ob-
longata, convulsions uniformly occur. These results are borne out by patho-
logical observations in Man ; for it has been frequently remarked, when it
has been necessary to separate protruded portions of the Brain from the
healthy part, that this has given rise to no sensation, even in cases in which
the mind has been perfectly clear at the time.

474. The Commissural fibres constitute two principal groups, the trans-
verse, and the longitudinal; the former connecting the two Hemispheres with
each other; the latter uniting the different parts of the same Hemisphere. —
Of the transverse commissures, the Corpus Callosum is the most important.
This consists of a mass of fibres very closely interlaced together; which may
be traced into the substance of the hemispheres on each side, particularly at
their lower part, where their connections are the closest with the Thalami
Optici and Corpora Striata. It is difficult, if not impossible, to trace its fibres
any further; but there can be little doubt that they radiate, with the fibres
proceeding from the bodies just named, to different parts of the cortical sub-
stance of the Hemispheres. This commissure is altogether wanting in Fish,
Reptiles, and Birds ; and it is partially or completely wanting in those Mam-
mals, whose Cerebrum is formed upon the least complex plan — the Rodents
and Marsupials. The anterior commissure particularly unites the Corpora
Striata of the two sides : but many of its fibres pass through those organs,
and radiate towards the convolutions of the Hemispheres, especially those of
the middle lobe. This commissure is particularly large in those Marsupials,
in which the Corpus Callosum is deficient. The posterior commissure is a
band of fibres which connects together the Thalami optici; crossing over from
the posterior extremity of one to that of the other. Besides these, there are
other groups of fibres, which appear to have similar commissural functions,
but which are intermingled with vesicular substance. Such are the soft
commissure, which also extends between the Thalami; the Pons Tarini,
which extends between the Crura Cerebri ; and the Tuber Cinereum, which
seems to unite the optic tracts with the thalarni, the corpus callosum, the for-
nix, &c., and to be a common point of meeting for several distinct groups of
fibres. — Of the longitudinal commissures, some lie above, and others below,
the Corpus Callosum. Upon the transverse fibres of that body, there is a
longitudinal tract on each side of the median line, which serves to connect

* See Messrs. Toilil ami Bowman's Physiological Anatomy, Chap. XI. for a fuller state-
ment of this view, and of the ni-Lruments in its favour. See also the General Summary at
the conclusion of the present Chapter.

FUNCTIONS OF THE CEREBRUM. 361

the convolutions of the anterior and posterior Cerebral lobes. Above this,
again, is the superior longitudinal commissure, which is formed by the fibrous
matter of the great convolutions nearest the median plane on the upper sur-
face of the Cerebrum, and which connects the convolutions of the anterior and
middle lobes with those of the posterior. Beneath the Corpus Callosum, we
find the most extensive of all the longitudinal commissures, the Fornix. This
is connected in front with the Thalami optici, the Corpora mammillaria, the
tuber cinereum, &c. ; and behind it spreads its fibres over the hippocampi
(major and minor), which are nothing else than peculiar convolutions that
project into the posterior and descending cornua of the lateral ventricles.
The fourth longitudinal commissure is the Tsenia semicircularis, which
forms part of the same system of fibres with the fornix ; connecting the cor-
pus marnmillare and thalamus opticus of each side with the middle lobe of
the cerebral hemisphere. If, as Dr. Todd has remarked,* we could take
away the corpus callosum, the grey matter of the internal convolution, and
the ventricular prominence of the optic thalami, then all these commissures
would fall together, and would become united in the same series of longitu-
dinal fibres. — Experiment does not throw any light upon the particular func-
tions of the Corpus Callosum and other Commissures; since they can
scarcely be divided without severe general injury. It would appear, how-
ever, that the partial or entire absence of these parts, reducing the Cerebrum
(in this respect at least) to the level of that of the Marsupial Quadruped, or of
the Bird, is by no means an unfrequent cause of deficient intellectual power.

a. The following case of deficient commissures, lately recorded by Mr. Paget, is of much
interest. The middle portion of the Foraix, and the whole of the Septum Lucidum, were
absent; and in place of the Corpus Callosum, there was only a thin fasciculated layer of
fibrous matter, l-4 inch in length, but of which the fibres extended to all the parts of the brain,
into which the fibres of the healthy corpus callosum can be traced. The Middle commissure
was very large ; and the lateral parts of the Fornix, with the rest of the Brain, were quite
healthy. The patient was a servant-girl, who died of pericarditis. She had displayed, during
her life, nothing very remarkable in her mental condition, beyond a peculiar want of forethought,
and power of judging of the probable event of things. Her memory was good ; and she possessed
as much ordinary knowledge as is commonly acquired by persons in her rank of life. She
was of good moral character, trustworthy, and fully competent to all the duties of her station,
though somewhat heedless ; her temper was good, and disposition cheerful. The mental de-
ficiencies in the few other cases of which the details have been recorded, seem to have been
of the same order; and this is exactly what might Irave been anticipated; since the depriva-
tion of these parts takes away that, which is most characteristic of the Cerebrum of Man and
of the higher Mammalia; and their intellectual operations are peculiarly distinguished by that
application of past experience to the prediction of the future, which constitutes the highest effort
of Intelligence.

475. The weight of the entire Encephalon in the. adult Male usually ranges
between 46 and 53 ounces; and in the Female, from 41 to 47 ounces. The
maximum of the healthy brain seems to be about 64 ounces, m four pounds;
and the minimum about 31 oz., or something less than two pounds. But in
cases of idiocy, the amount is sometimes much below this; as low a weight
as 20 oz. having been recorded. It appears, from the recent investigations
of M. Bourgery, that the relative sizes of the different component elements
of the Human Encephalon are somewhat as follows. Dividing the whole
into 204 parts, the weight of the Cerebrum will be represented by about 170
of those parts, that of the Cerebellum by 21, and that of the Medulla Oblon-
gata with the Optic Thalami and Corpora Striata at 13. The weight of the
Spinal Cord would be, on the same scale, 7 parts. Hence the Cerebral He-
mispheres of Man include an amount of nervous matter, which is four times

* Anatomy of the Brain, Spinal Cord, &c., p. 234.
31

362 FUNCTIONS OF THE NERVOUS SYSTEM.

that of all the rest of the Cerebro-spinal mass, more than eight times that of
the Cerebellum, thirteen times that of the Medulla Oblongata, &c., and twenty-
four times that of the Spinal Cord. — The average weight of the whole En-
cephalon, in proportion to that of the body, in Man, taking the average of a
great number of observations, is about 1 to 36. This is a much larger propor-
tion than that which obtains in most other animals; thus the average of Mam-
malia is stated by M. Leuret to be 1 to 186, that of Birds 1 to 212, that of
Reptiles 1 to 1321, and that of Fishes 1 to 5668. It is interesting to remark,
in reference to these estimates, that the Encephalic prolongation of the Me-
dulla Oblongata in Man (being about one-sixteenth of the weight of the whole
Encephalon) is alone more than twice as heavy in proportion to his body, as
the entire Encephalon of Reptiles, and ten times as heavy as that of Fish. —
But there are some animals in which the weight of the Encephalon bears a
higher proportion to that of the body than it does in Man; thus in the Blue-
headed Tit, the proportion is as 1 to 12, in the Goldfinch as 1 to 24, and in
the Field-Mouse as 1 to 31. It does not hence follow, however, that the Ce-
rebrum is larger in proportion; in fact, it is probably. not nearly so large ; for
in Birds and Rodentia, the sensory ganglia form a very considerable propor-
tion of the entire Encephalon. The importance of distinguishing between the
several parts of this mass, which are marked out as distinct, alike by their
structure and connections, as by the history of their development, has not been
by any means sufficiently attended to.

476. The Encephalon altogether receives a supply of Blood, the amount
of which is very remarkable, when its comparative bulk is considered ; the
proportion which it receives being, according to the estimate of Haller, as
much as one-fifth of the whole. The manner in which this blood is con-
veyed to the Brain, and the conditions of its distribution, offer some pecu-
liarities worthy of notice. The two Vertebral and two Carotid arteries, by
which the blood enters the cavity of the cranium, have a more free communi-
cation by anastomosis, than any similar set of arteries elsewhere ; and this is
obviously destined to prevent an obstruction in one trunk from interrupting
the supply of blood to the parts, through which its branches are chiefly dis-
tributed,— the cessation of the circulation through the nervous matter being
immediately productive (as formerly shown, § 290) of suspension of its
functional activity. — Not only must there be a sufficient supply of blood, but
it must make a regulated pressure on the walls of the vessels. Now the
Encephalon is differently circumstanced from other vascular organs, in being
inclosed within an unyielding bony case; and it has been supposed that the
total amount of blood circulating through it must consequently be invariable,
any disturbance of the circulation being due to an undue turgid ity of the
arteries and corresponding emptiness of the veins, or vice versa. But this is
by no means the case; for, independently of the fact that varying states of
functional activity will doubtless produce a considerable variation in the entire
bulk of the nervous mass, we find a special provision for equalizing the bulk
of the contents of the cranial cavity, and for counterbalancing the results of
differences in the functional activity of the brain and in its supply of blood.
This is the existence of a fluid, which is found beneath the arachnoid,
wherever pia mater exists in connection with the brain and spinal cord;
•whether on the surfaces of these organs, or in the ventricles of the latter.
The amount of this fluid seems to average about two ounces; but in cases of
atrophy of the brain, as much as twelve ounces of fluid may sometimes be
obtained from the crauio-spinal cavity; whilst in all instances, in which the
bulk of the brain has undergone an increase1, whether from the production of
additional nervous tissue, or from undue turgescence of the vessels, there is

FUNCTIONS OF THE CEREBRUM. 363

either a diminution or a total absence of this fluid. It appears from the ex-
periments of Magendie (to whom our knowledge of the importance of this
fluid is chiefly due), that its withdrawal in living animals causes great dis-
turbance of the cerebral functions, probably by allowing undue distention of
the blood-vessels ; it is, however, capable of being very rapidly regenerated ;
and its reproduction restores the nervous centres to their natural state.

477. As the cerebro-spinal fluid can readily find its way from the sub-
arachnoid spaces of the cranial cavity into those of the spinal, and as the
latter are distensible, to a very considerable extent, it evidently serves as an
equalizer of the amount of pressure within the cranial cavity ; admitting the
distention or contraction of the vessels to take place, within certain limits,
without any considerable change in the degree of compression to which the
nervous matter is subjected. That this uniformity is of the greatest import-
ance to the functional exercise of the brain, is evident from a few well-known
facts. If an aperture be made in the skull, and the protruding portion of the
brain be subjected to pressure, the immediate suspension of the activity of
the whole organ is the result ; in this manner, a state resembling profound
sleep can be induced in a moment; and the normal activity is renewed as
momentarily, as soon as the pressure is withdrawn. This phenomenon has
often been observed in the Human subject, in cases in which a portion of the
cranial envelope has been lost by disease or injury. The various symptoms
of Cerebral disturbance, which are due to a state of general Plethora, are
evidently owing to an excess of pressure within the vessels ; but an undue
diminution of pressure is no less injurious, as appears from the disturbance in
the Cerebral functions, which results from the very opposite cause, namely,
a depression of the power of the heart, or a deficiency of blood in the ves-
sels.— It is of peculiar importance to bear in mind the disturbance of the
Cerebral functions, which is occasioned by internal pressure, when we are
endeavouring to draw inferences from the phenomena presented by disease.

478. We shall now proceed with our Physiological inquiry into the func-
tions of the Cerebrum ; confining ourselves, in the present Section, to certain
general positions, with regard to which most Physiologists are agreed ; and
referring to the Appendix for a notice of the more detailed system of Cerebral
Physiology, first propounded by Dr. Gall. — We shall, as before, apply to
Comparative Anatomy, to Experiment, and to Pathology, for our chief data.
Any general inferences, founded only upon observation of the phenomena pre-
sented by Man, must be looked upon with suspicion; since every advance in
Comparative Physiology leads us to perceive, how close is the functional rela-
tion between organs, that are really of analogous nature in different classes of
animals ; and how necessary, therefore, it is, to examine and contrast all the
facts which we can attain in regard to them, in order to impart to our con-
clusions the utmost validity of which they are capable. — Our first general
proposition is, that the Cerebrum is the sole instrument of intelligence; by
which term is implied the intentional adaptation of means to ends, in a man-
ner implying a perception of the nature of both. The actions performed by
the lower animals are often such, as to leave us in doubt, whether they are
the result of a mere Instinctive impulse, or of an Intelligent adaptation of
means to ends ; and we are guided in our determinations, chiefly by the uni-
formity of these actions, in the several individuals of the same species. If
we analyze any of our own instinctive actions, we shall perceive the same
absence of design on our own parts, as that which we attribute to the lower
animals. No one would assert that the tendency to sexual intercourse is the
result of a knowledge of its consequences, and of a voluntary adaptation of
means to ends ; or that, if we can imagine a man newly coming into the

364 FUNCTIONS OF THE NERVOUS SYSTEM.

world in the full possession of all his powers, he would wait to eat when
hungry, until experience had taught him that the swallowing of food would
relieve the uneasy feeling. It has been already shown, that, in the infant,
the act of sucking may be performed even without a Cerebrum (§ 386, c) ;
and for this and other similar actions, therefore, it is doubtful whether con-
sciousness is a requisite condition. Adult animals, whose Cerebral hemi-
spheres have been removed, will eat food that is put into their mouths, although
they will not go to seek it; and this is the case with many Human idiots.
When the functions of the Brain are disturbed, or in partial abeyance, as in
fever, we often see a remarkable return to the instinctive propensities in
regard to food; and the Physician frequently derives important guidance as
to the patient's diet and regimen (particularly as to the administration of
wine), from the inclination or disinclination which he manifests.

479. The difference between actions of a purely Instinctive character, and
those which rather result from the Intellectual faculties prompted by the in-
stinctive propensities, is well seen in comparing Birds with Insects. Their
Instinctive tendencies are of nearly the same kind ; and the usual arts which
they exhibit in the construction of their habitations, in procuring their food,
and in escaping from danger, must be regarded as intuitive, on account of the
uniformity with which they are practised by different individuals of the same
species, and the perfection with which they are exercised on the very first
occasion. But in the adaptation of their operations to peculiar circumstances,
Birds display a variety and fertility of resource, far surpassing that which is
manifested by Insects ; and it is not doubted, by those who have attentively
observed their habits, that in such adaptations they are often guided by real
Intelligence. This must be the case, for example, when they make trial of
several means, and select that one which best answers the purpose ; or when
they make an obvious improvement from year to year in the comforts of their
dwelling ; or when they are influenced in the choice of a situation, by pecu-
liar circumstances, which, in a state of nature, can scarcely be supposed to
affect them. The complete domesticability of many Birds is in itself a proof
of their possessing a certain degree of intelligence ; but this alone does not
indicate the possession of more than a very low amount of it ; since many of
the most domesticable animals are of the humblest intellectual capacity, and
seem to become attached to Man, principally as the source on which they
depend for the supply of their animal wants. This is the case with most
Herbivorous quadrupeds, and with Rabbits, Guinea-pigs, &c. ; as well as with
the Gallinaceous Birds.

480. The attachment which is formed to Man, by certain Mammalia of
higher orders, such as the Dog, the Horse, and the Elephant, is evidently of
a more elevated kind, and involves a much larger number of considerations.
The Intelligence of such animals is peculiarly exhibited in their Edueability ;
— that is, in the facility with which their natural habits may be changed by
the new influences to which they are subjected, and the complication of the
mental processes which they appear to perform under their altered circum-
stances. Their actions are evidently the result, in many instances, of a com-
plex train of reasoning, differing in no essential respect from that which Man
would perform in similar circumstances ; so that the epithet, "half reason-
ing," commonly applied to these animals, does not express the whole truth ;
for their mental processes are of the same kind with those of Man, and differ
more in the degree of control which the animal possesses over them, than they
do in their own character. We have no evidence, however, that any of the
lower animals have a voluntary power of guiding, restraining, or accelerating
their mental operations, at all similar to that which Man possesses ; these

FUNCTIONS OF THE CEREBRUM. 365

operations, indeed, seem to be of very much the same character as those
which we perform in our dreams, different trains of thought commencing as
they are suggested, and proceeding according to the usual laws, until some other
disturb them. Although it is customary to regard the Dog and the Elephant as
the most intelligent among the lower animals, it is not certain that we do so
with justice; for it is very possible that we are misled by that peculiar attach-
ment to Man, which in them must be termed an instinct, and which enters as
a motive into a large proportion of their actions ; and that, if we were more
acquainted with the psychical characters of the higher Quadrumana, we should
find in them a greater degree of mental capability than we now attribute to
them. One thing is certain, — that, the higher the degree of intelligence
which we find characteristic of a particular race, — the greater is the degree of
variation which we meet with in the characters of individuals ; thus every one
knows that there are stupid Dogs and clever Dogs, ill-tempered Dogs and
good-tempered Dogs, — as there are stupid Men and clever Men, ill-tempered
Men or good-tempered Men. But no one could distinguish between a stupid
Bee and a clever Bee, or between a good-tempered Wasp and an ill-tempered
Wasp, simply because all their actions are prompted by an unvarying instinct.
481. It is important to bear in mind the view to which we have been con-
ducted,— in regard to the relative offices of the vesicular and fibrous matter, —
when forming our opinions upon the functions of the Cerebrum in general, or
of its several parts ; from the various data supplied to us by Comparative
Anatomy, by the comparison of the Cerebra of different individuals of the
Human race with each other and with their respective psychical manifestations,
and by experimental and pathological inquiry. For in regard to the first of
these sources it is to be remarked, that the size of the brain does not, con-
sidered alone, afford a means of judgment as to its power. The quantity of
vesicular matter on its surface should rather be our guide ; and this we may
judge of, not only by the depth of the layer, but by the complexity of the
convolutions by which the surface is extended. In no class, save in Mam-
malia, do we find the surface marked with convolutions; and in general
we do not meet with that fissure between the hemispheres, which greatly
increases the extent of surface. In forming comparisons as to the con-
nection between the size of the Cerebrum, and the Intelligence, in different
animals, we must not be at all guided by its simple proportional dimensions ;
since it is very evident, that it is rather the proportion of the bulk of the
brain to that of the whole body, upon which we should found our compari-
son. But even this is not altogether a safe guide; and many Physiologists
have endeavoured to compare the size of the brain, with the aggregate bulk
of the nerves proceeding from it. This is a much fairer measure; but it
cannot be taken without great difficulty. For all practical purposes, the
comparison of the bulk of the Cerebrum with that of the Spinal Cord will
probably answer very well. The following table, the materials of which
are drawn from M. Serres' Comparative Anatomy of the Brain, exhibits
the three diameters of the Cerebrum of a number of different animals,
and the diameter of the Spinal Cord at the second cervical vertebra. The
last three columns present in round numbers, the three diameters of the
Cerebrum, reckoning that of the Spinal Cord as 1, for the sake of easy com-
parison.

31*

366

FUNCTIONS OF THE NERVOUS SYSTEM.

Diameter
of Spinal
Cord.

DIMENSIONS OF CEKEKRUM.

Proportional Dimensions.

Anii.-post.

Transv.

Vertical.

Man

1,100

17,000

7.500

9,000

1—154

1-6|

i— 8i

Dolphin

1,100

9,500

5^850

8,200

1—9*

1-8*

Mandril

950

8,100

3,200

4,900

1 — 8*

1 — 3£

1—5

Tiger

1,600

9,400

4,250

6,400

1 — §1

i f) 5

1—4

Dromedary

1,900

10,500

5,050

5,800

1 — 5*

1 0 ^

1—3

Kangaroo

1,200

5,300

2,350

3,800

1— 4f

1—2

1— 3£

Vulture

800

3,200

2,200

1,550

1—4

1-2J

1—2

Falcon

500

1,900

1,450

1,200

1 — 3f

1—3

i 0_2

~ 5

Swallow

175

1,000

600

550

1—5$

1-3*

1-3^

Pie

450

2,000

1,400

1.200

1 — 4-|

1—3

1 — ^f

Turkey

500

1,750

1,250

l',200

1 — 3i

1 — 2£

l-2f

Parroquet

400

2,900

1,400

1.700

1—7$

1—34

1— 4i

Tortoise

300

1,600

500

1— 5£

1-lf

Crocodile

300

800

500

1-22 •

1-lf

Viper

200

600

300

1 O

Frog

300

500

400

1-lf

1—11

Shark

710

2,300

1,100

l_3i

1-lf

Cod

575

725

800

i— a

1-lf

Lamprey

275

400

300

i — i*

i-H

Angler

400

400

300

i— r

i- 1

482. As might be expected, the Cerebrum of Man bears by far the highest
proportion ; but this proportion is not so large in the transverse and vertical
diameters, as in the antero-posterior ; in fact, in the proportion of the vertical
diameter the Cerebrum of Man is equalled by that of the Dolphin, and nearly
so in that of the transverse diameter. In the complexity of the convolutions,
however, and in the thickness of the grey matter, the Cerebrum of Man
far surpasses that of this Cetaceous animal. In these respects the higher
Quadrumana present the nearest approach to it; but their brain is much infe-
rior in size. In descending the scale of Mammalia, there may be observed a
gradual simplification in the general structure of the Cerebrum, depending
upon a great diminution in the amount of commissural fibres ; until in the
Marsupialia the Brain presents nearly the same condition which it offers in
Birds (§ 361). These animals manifest a much lower degree of Intelligence
than many Birds evidently possess; and it is interesting to remark, that their
Cerebral hemispheres are proportionally smaller than those which we find in
many Birds: the diminution in their relative size not being counterbalanced
(as it is in some other instances) by increased complexity of structure. In
the class of Birds, we observe that the Vulture and the Falcon, whose prcda-
ceous instincts give them a considerable amount of general energy, are much
inferior in the size of their brains to the Insessorial Birds, which are more
intelligent; and that of all, there is none in which the brain is so proportion-
ably large, as it is in the Parrot tribe, the educability of which is familiar to
every one ; whilst the easily-domesticable, but unintelligent Turkey, has a brain
of scarcely half the proportional size. The very small size of the Cerebrum
in Reptiles and Fishes, completely harmonizes with the same view ; these
animals presenting for the most part but feeble indications of intelligence.
Among Reptiles, the Tortoise has a Cerebrum comparable in length to that
of Birds; but its breadth and deptli arc far less. The largest Cerebra among
Fishes are found in the Shark tribe ; the superior intelligence of which is

FUNCTIONS OF THE CEREBRUM. 367

well known to those who have had the opportunity of observing their habits :
and it is interesting to remark, that their surface occasionally presents an ap-
pearance of rudimentary convolutions.

483. Comparative Anatomy, then, fully bears out the general doctrine, that
the Cerebrum constitutes the organ ofvlntelligence, as distinguished from those
mere Instincts, by which many of the lower animals seem to be almost en-
tirely guided. By Intelligence, we do not mean, however, the reasoning
faculties only; but the combination of those powers which are of an educable
character, and which become the springs of voluntary action, in varying pro-
portions in different animals of the same tribe; as distinguished from those,
which have more immediate relation to the wants of the corporeal system,
and which are automatic and invariable in the several individuals of the same
species. — This definition does not leave out of view the operation of the Pas-
sions, Feelings, and Emotions; which are all but modifications of Instinctive
Propensities, to which different names are assigned. The true character of
these, however, can only be understood, by studying the mode of their action
on the bodily system. This action is of two kinds; — the one direct, irrational
and involuntary ; — the other indirect, rational, and voluntary. In the former,
the action is the immediate result of the Emotion, following closely upon the
Sensation which excited it, and consequently belongs to the Consensual group
already discussed (Sect. 5) ; it is executed without any consciousness of the
purpose to be answered by it; and the power of the Will is only exerted to direct
or restrain it. In the latter, as will be presently shown (§ 494), the action
is but remotely the result of the Emotion, being altogether of the Intelligent
class ; it is executed with a view to a distinct purpose, which has been deter-
mined on by the reasoning powers, and of which, therefore, the mind is fully
conscious; and it is purely an act of the Will, however strongly the Emotions
may have acted in supplying motives to it and exciting the intellectual powers
to action.

484. The general inferences drawn from Comparative Anatomy, are borne
out by observation of the Human species. When the Cerebrum is fully
developed, it offers innumerable diversities of form and size, among various
individuals ; and there are as many diversities of character. It may be doubted
if two individuals were ever exactly alike in this respect. That a Cerebrum
which is greatly under the average size, is incapable of performing its proper
functions, and that the possessor of it must necessarily be more or less idiotic,
there can be no reasonable doubt. On the other hand, that a large well-de-
veloped Cerebrum is found to exist in persons, who have made themselves con-
spicuous in the world by their attainments or their achievements, may be stated
as a proposition of equal generality. In these opposite cases, we witness most
distinctly the antagonism between the Instinctive and Voluntary powers. Those
unfortunate beings, in whom the Cerebrum is but little developed, are guided al-
most solely by their instinctive tendencies ; which frequently manifest them-
selves with a degree of strength that would not have been supposed to exist;
and occasionally new instincts present themselves, of which the Human being
is ordinarily regarded as destitute.* On the other hand, those who have obtained
most influence over the understandings of others, have always been themselves
persons of strong intellectual and volitional powers ; in whom the instinctive
tendencies have been subordinate to the reason and will, and who have given
their whole energy to the particular object of their pursuit. — It is very different,

* A remarkable instance of this has been recently published. A perfectly idiotic girl, in
Paris, having been seduced by some miscreant, was delivered of a child without assistance.
It was found that she had gnawed the umbilical cord in two, in the same manner as is prac-
tised by the lower animals. It is scarcely to be supposed that she had any idea of the object
of this separation.

368 FUNCTIONS OF THE NERVOUS SYSTEM.

however, with those who are actuated by what is ordinarily termed genius ;
and whose influence is rather upon the feelings, than upon the understandings,
of those around them. Such persons are often very deficient in the power of
even comprehending the ordinary affairs of life : and still more commonly,
they show an extreme want of judgment in the management of them, being
under the immediate influence of their passions and emotions, and not having
brought these under the control of their intelligent will. The life of a genius,
whether his bent be towards poetry, music, painting, or pursuits of a more
material character, is seldom one which can he held up for imitation. In
such persons, the general power of the mind being low, the Cerebrum is not
usually found of any great size. — The mere comparative size of the Cerebrum,
however, affords no accurate measure of the amount of mental power; we not
unfrequently meet with men possessing large and well-formed heads, whilst
their physical capability is not greater than that of others, the dimensions of
whose crania have the same general proportion, but are of much less absolute
size. Large brains, with deficient activity, are commonly found in persons of
what has been termed the phlegmatic temperament, in whom the general pro-
cesses of life seem in a torpid and indolent state ; whilst small brains and great
activity, betoken what are known as the sanguine and nervous temperaments.
These distinctions come to be very important, where we proceed further in
our inquiries, and attempt to determine the particular modes of development
of the Brain, which coincide with certain manifestations of the mind.

485. Having now inquired into the evidence of the general functions of the
Cerebrum, which may be derived from examination of its Comparative deve-
lopment, we proceed to our other sources of information ; Experiment, and
Pathological phenomena. From neither of these, however, is much informa-
tion to be derived. — The effects of the entire removal of the Cerebral Hemi-
spheres have been already stated (§ 435). So far as any inferences can be
safely drawn from them, they fully bear out the conclusion, that the Cerebrum
is the organ of Intelligence ; since the animals which have suffered this muti-
lation appear to be constantly plunged in a profound sleep, from which no
irritation ever seems able to arouse them into full activity. It may even be
argued, that the phenomena which they exhibit do not imply the persistence
of consciousness ; and that this also must be regarded as the attribute of the
Cerebral hemispheres, being destroyed by their ablation. But a careful ana-
lysis of them seems to show, that sensibility still exists, although it is much
deadened ; for in no other way can we legitimately explain the efforts made
by the animals to balance themselves and maintain their position, which are of
a much higher character than the mere reflex movements exhibited by the
same animals after the removal of the entire Encephalon, and which can
scarcely be explained without attributing to them a degree of sensation. That
their sensibility should be greatly blunted, however, is to be anticipated from
the fact, that it is almost impossible to remove the Hemispheres, without doing
great injury to the other ganglionic centres, especially to the Thalami Optici
and Corpora Striata ; which, if the preceding views be correct, form a most
important part of the Sensori-Motor apparatus, and which, in the experiments
referred to, appear to have been generally removed with the Cerebral Hemi-
spheres. The entire and permanent removal of all vascular pressure, top,
which is consequent upon the laying-open of the cranial cavity, is another
source of permanent disturbance in the functions of the parts which are left. —
So far as they go, therefore, the results of such experiments confirm the de-
ductions drawn from Comparative Anatomy, in regard to the general functions
of the Cerebrum ; but we must be careful not to infer too much from them, as
to the extent to which the animal functions are brought to a close by the
operation in question. In the most recent experiments, those of MM. Bouil-

FUNCTIONS OF THE CEREBRUM. 369

laud and Longet, it was the opinion of the observers, that sensibility was
retained, after the complete removal of the Cerebrum ; although the animals
appeared unable to attach any ideas to their sensations.* — The results of par-
tial mutilations are usually, in the first instance, a general disturbance of the
Cerebral functions; which subsequently, however, more or less subsides, leav-
ing but little apparent affection of the animal functions, except muscular weak-
ness. The whole of one Hemisphere has been removed in this way, without
any evident consequence, save a temporary feebleness of the limbs on the
opposite side of the body, and what was supposed to be a deficiency of sight
through the opposite eye. The former was speedily recovered from, and the
animal performed all its movements as well as before ; the latter, however,
was permanent, but the pupil remained active. — When the upper part, only,
of both Cerebral Hemispheres was removed by Hertwig, the animal was re-
duced, for fifteen days, to nearly the same condition with the one from which
they had been altogether withdrawn ; but afterwards, sensibility evidently re-
turned, and the muscular power did not appear to be much diminished.

486. The information afforded by Pathological phenomena is equally far
from being definite. Many instances are on record, in which extensive dis-
ease has occurred in one Hemisphere, so as almost entirely to destroy it,
without either any obvious injury to the mental powers, or any interruption
of the influence of the mind upon the body. But there is no case on record
of severe lesion of both hemispheres, in which morbid phenomena were not
evident during life. It is true, that in Chronic Hyclrocephalus, a very remark-
able alteration in the condition of the Brain sometimes presents itself which
might a priori have been supposed destructive to its power of activity ; — the
ventricles being so enormously distended with fluid, that the cerebral matter
has seemed like a thin lamina, spread over the interior of the enlarged cra-
nium. But there is no proof that absolute destruction of any part was thus
occasioned ; and it would seem that the very gradual nature of the change,
gives to the structure time for accommodating itself to it. This, in fact, is
to be noticed in all diseases of the Encephalon. A sudden lesion, so trifling
as to escape observation, unless this be very carefully conducted, will occasion
very severe symptoms ; whilst a chronic disease may gradually extend itself,
without any external manifestation. It will usually be found that sudden
paralysis, of which the seat is in the Brain, results from some slight effusion
of blood in the substance or neighbourhood of the Corpora Striata ; whilst,
if it follow disorder of the Brain of long standing, a much greater amount of
lesion will usually present itself. In either case, the paralysis occurs in the
opposite side of the body, as we should expect from the decussation of the
pyramids ; but it may occur either in the same, or on the opposite side of the
face, — the cause of which is not very apparent. If convulsions accompany
the paralysis, we may infer that the Corpora Quadrigemina, or the parts below,
are involved in the injury ; and in this case it is usually found, that the con-
vulsions are on the paralyzed side of the body, — the effect of the lesion, both
of the Cerebrum and of the Corpora Quadrigemina, being propagated to the
opposite side, by the decussation of the Pyramids. Where, as not unfre-
quently happens, there is paralysis of one side, accompanying convulsions on
the other, it is commonly the result of a lesion affecting the base of the Brain
and Medulla Oblongata, on the side on which the convulsions take place ; —
here the effect of the lesion has to cross from the Brain, whilst its influence

It is worthy of remark, also, that M. Flourens, who in the first instance maintained that
sensation is altogether destroyed by the removal of the Cerebrum, has substituted, in the
Second Edition of his Researches, the word perception for sensation : apparently implying ex-
actly what is maintained above. — See § 435.

370 FUNCTIONS OF THE NERVOUS SYSTEM.

on the Medulla Oblongata is shown on the same side. Many apparent ano-
malies present themselves, however, which are by no means easy of expla-
nation, in the present state of our knowledge. — The disturbance of the Cere-
bral functions, occasioned by those changes in its nutrition which are com-
monly included under the general term of Inflammation, presents a marked
diversity of character, according to the part it affects. Thus it is well known
that the delirium of excitement is usually a symptom of inflammation of the
cortical substance or of the membranes of the hemispheres. This is exactly
what might be anticipated from the foregoing premises, since this condition
is a perversion of the ordinary mental operations, which are dependent upon
the instrumentality of the vesicular matter ; and it is evidently impossible for
the membranes to be affected with inflammation without the nutrition of this
substance being impaired, since it derives all its vessels directly from them.
On the other hand, inflammation of the fibrous portion of the Cerebrum is
usually attended rather with a state of torpor than with excitement ; and with
diminished power of the will over the muscles. It is stated by Foville, that
in acute cases of Insanity, he has usually found the cortical substance in-
tensely red, but without adhesion to the membranes ; whilst in chronic cases,
it is indurated and adherent : but where the Insanity has been complicated
with Paralysis, he has usually found the medullary portion indurated and
congested.

487. The general result of such investigations is, that the Cerebrum is
the organ through which all those impressions are received which give rise to
the operations of the Intellect; and that it affords the power of occasioning
muscular contraction, in obedience to the influence of the Will, which is the
result of those operations. — That all the operations of the Intellect are ori-
ginally dependent upon the reception of Sensations, is a position that can
scarcely be denied. If it were possible for a Human being to come into the
world, with a Brain perfectly prepared to be the instrument of mental opera-
tions, but with all the inlets to sensation closed, we have every reason to be-
lieve that the Mind would remain dormant, like a seed buried deep in the
earth. For the attentive study of cases, in which there is congenital defi-
ciency of one or more sensations, makes it evident that the Mind is uttterly
incapable of forming any definite ideas, in regard to those properties of ob-
jects, of which those sensations are particularly adapted to take cognizance.
Thus the man who is born blind can form no conception of colour ; nor the
congenitally-deaf, of musical tones. And in those lamentable cases, in which
the sense of touch is the only one through which ideas can be introduced, it
is evident that the mental operations would remain of the simplest and most
limited character, if the utmost attention be not given by a judicious instructor,
to the development of the intellectual faculties, and the cultivation of the
moral feelings, through the restricted class of ideas which there is a possi-
bility of exciting. — The activity of the Mind, then, is just as much the result
of its consciousness of external impressions by which its faculties are called
into play, as the Life of the body is the consequence of the excitement of its
several vital properties by external stimuli. If these stimuli are prevented
from acting in the first instance, the state of inaction continues ; but when
once the mind has been aroused, the sensations which it receives are treasured
up by the Memory: and they may thus continue to be the sources of new
ideas, long after the complete closure of the inlets, by which new sensations
are ordinarily received. We have remarkable examples of this, in the vivid
conceptions which may be formed from the description of a landscape or a
picture, by those who have once enjoyed sight ; or in the composition of
music, even such as involves new combinations of sounds, by those who have
become deaf, — as in the remarkable case of Beethoven. The mind thus

FUNCTIONS OF THE CEREBRUM. 371

feeds, as it were, upon the store which has been laid up during the activity
of its sensory organs ; but instead of diminishing, like material food, these
sensations become more and more vivid, the oftener they are recalled to the
mind.

488. But the operations of the Intellect are immediately founded, not upon
Sensations, but upon the Ideas they excite in the Mind.* Some ideas are so
simple, and so constantly excited by certain sensations, that we can scarcely
do otherwise than attribute them to original or fundamental properties of the
mind, called into activity by the sensations in question ; others, however, are
of a much more complex nature, and vary according to the peculiar character
of the individual mind, the general habits of thought, and its particular condi-
tion at the time. In .either case, the formation in the mind of an elementary
notion respecting the object of the Sensation, is the first operation in which
the Cerebrum can be said to be necessarily concerned, and is introductory to
all the rest. The process, whether simple or complex, is termed Perception;
and the designation is applied, like Secretion, not merely to the act, but to its
result, — being used to indicate the notion thus produced, whether it be simple
and directly-excited, or more complex and the result of a succession of mental
operations.

489. The difference between Perception and Sensation maybe easily made
evident. In order that a sensation should be produced, a conscious state of
the mind is all that is required. Its whole attention may be directed towards
some other object, and the sensation calls up no new ideas whatever ; yet it
will produce some change in the Sensorium, which causes it to be (as it were)
registered there for a time, and which may become the object of subsequent
attention ; so that, when the mind is directed towards it, that idea or notion
of the cause of the sensation is formed, which constitutes a perception. For
example, a student, who is directing his thoughts to some object of earnest
pursuit, does not receive any intimation of the passage of time, from the
striking of a clock in his room. The sensation must be produced, if there
be no defect in his nervous system ; but it is not attended to, because the mind
is bent upon another object. It may produce so little impression on the mind,
as not to recur spontaneously, when the train of thought which previously
occupied the mind has been closed, leaving the attention ready to be directed
to any other object; or, the impression having been stronger, it may so recur,
and at once excite an idea in the mind. — Again, the individual may then be
able only to say, that he heard the clock strike ; or he may be able to retrace
the number of strokes. Now, in either case, a complex perception is formed,
without his being aware that any mental operation has intervened. He would
say that he remembers hearing the clock strike ; but this would not express
the truth. That which he remembers is a certain series of sonorous impres-
sions, which was communicated to his mind ; and he recognizes them as the
striking of a clock, by a process in which memory and judgment are com-
bined,— which process may further inform him, that the sounds proceeded
from his own particular clock. If he had never heard a clock strike, and the
sound produced by it had never been described to him, he would not have
been able to form that notion of the object giving rise to the sensation, which,
simple as it appears to be at the time, is the result of complex mental opera-
tions. But when these operations have been frequently performed, the per-

Some Metaphysicians have spoken of ideas as transformed sensations ; but this is a gross
absurdity. The idea is excited by the sensation, in accordance with the original properties of
the mind, and the laws of their operation, just as muscular contraction is excited by the sti-
mulus of electricity or innervation; but it would be just as correct to speak of a muscular
contraction as transformed electricity or innervation, because excited by either of these stimuli,
as it is to call an idea a transformed sensation.

372 FUNCTIONS OF THE NERVOUS SYSTEM.

ception or notion of the object becomes inseparably connected with the sen-
sation ; and thus it is excited by the latter, without any knowledge on the
part of the individual, that a mental operation has taken place.

490. Such Perceptions are termed acquired, in contradistinction to the in-
tuitive perceptions, of which the lower animals seem to possess a large num-
ber. The idea of the distance of an object, for example, is one derived in
Man from many sources, and is the result of a long experience ; the infant,
or the adult seeing for the first time, has to bring the senses of sight and of
touch to bear upon one another, in order to obtain it ; but, when once the
power of determining it is acquired, the steps of the process are lost sight of.
In the lower tribes of animals, however, in which the young receive no assist-
ance from their parents, there is an evident necessity for some immediate
power of forming this determination ; since they would not be able to obtain
their food without it. Accordingly, they manifest in their actions a percep-
tion or governing idea of distances, which can only be gained by Man after
long experience. A fly-catcher, for instance, just come out of its shell, has
been seen to peck at an insect, with an aim as perfect as if it had been all its
life engaged in learning the art. — In some cases, animals seem to learn that
by intuitive perception, at which Man could only arrive by the most refined
processes of reasoning, or by the. careful application of the most varied expe-
rience. Thus, a little fish, named the Chsetodon rostratus, is in the habit of
ejecting from its prolonged snout, drops of fluid, which strike insects that hap-
pen to be near the surface of the water, and causes them to fall into it, so as
to come within its own reach. Now, by the laws of refraction of light, the
place of the Insect in the air, will not really be that at which it appears to
the Fish in the water ; but it will be a little below its apparent place, and to
this point the aim must be directed. But the difference between the real and
the apparent place will not be constant ; for the more perpendicularly the rays
enter the water, the less will be the variation; and, on the other hand, the
more oblique the direction, the greater will be the difference. Now it is im-
possible to imagine but that, by an intuitive perception, the real place of the
Insect is known to the Fish in every instance, as perfectly as it could be to
the most sagacious Human mathematician, or to a clever marksman, who had
learned the requisite allowance in each case by a long experience.

490*. In Man, the acquirement of perceptions is clearly a Cerebral opera-
tion ; but their intuitional formation in the lower animals is probably to be
regarded as one of those processes to which the Sensory ganglia are subserv-
ient. The same may be said of many of the intuitive perceptions in Man ;
which, if analyzed, are found to be connected rather with the instinctive and
emotional tendencies, than with the intellectual powers ; — the perceptions
which minister to the exercise of these last, being the result of experience.
Thus, it has been well remarked by Dr. Alison, that the changes which Emo-
tions occasion in the countenance, gestures, &c., of one individual, are instinc-
tively interpreted by others ; for these signs of mental affection are very early
understood by young children, sooner than any associations can be supposed
to have been formed, by experience, of their connection with particular modes
of conduct; and they affect us more quickly and strongly, and with nicer
varieties of feeling, than when it is attempted to convey the same feelings in
words, which are signs addressed to the intellect.

491. By a certain retentive power, which appears to be peculiar to the
Cerebrum, Sensations and the simple ideas or Perceptions they excite, are
stored up (so to speak) in such a manner, as to become the subjects of further
mental operations at a time more or less remote. They then present them-
selves as renewed images of past sensations ; and these may recur, either
involuntarily, or by a special direction of the mind towards them by an effort

FUNCTIONS OF THE CEREBRUM. 373

of Recollection. In either case, the Memory of them is probably due to the
operation of the principle of Association ; by which sensations and the ideas
they excite become linked together, in such a manner that the recurrence of
one shall be the means of the recal of others which are connected with it. —
There seems much ground for the opinion, that every Sensation actually ex-
perienced may become the subject of a Perception at any future time, though
beyond the voluntary power of the memory to retrace ; and the phenomena of
dreams and delirium, in which these sensations often recur with extraordinary
vividness, afford much support to this doctrine. Some of the instances upon
record are remarkable, as proving that the sensations may be thus remembered,
without any perceptions being attached to them ; these sensations having been
of such a nature as not to excite any notion or idea in the mind of the indi-
vidual. A very extraordinary case of this kind has been recorded, in which a
woman, during the delirium of fever, continually repeated sentences in lan-
guages unknown to those around her, which proved to be Hebrew and Chal-
daic ; of these she stated herself, on her recovery, to be perfectly ignorant ; but
on tracing her former history, it was found that, in early life, she had lived as
servant with a clergyman, who had been accustomed to walk up and down,
the passage, repeating or reading aloud sentences in these languages, which
she must have retained in her memory unconsciously to herself. Of the
nature of the change, by which sensations are thus registered, it is in vain to
speculate ; and it does not seem likely that we shall ever become acquainted
with it. This is certain, however, — that disease or injury of the brain will
destroy this power, or will affect it in various remarkable modes. We not un-
frequently meet with cases in which the brain has been weakened by attacks
of epilepsy or apoplexy, in such a manner as to prevent the reception of any
neiv impressions ; so that the patient does not remember anything that passes
from day to day ; whilst the impressions of events, which happened long
before the commencement of his malady, recur with greater vividness than
ever. On the other hand, the memory of the long-since-past is sometimes
entirely destroyed ; whilst that of events which have happened subsequently
to the malady is but little weakened. The memory of particular classes of ideas
is frequently destroyed ; — that of a certain language, or some branch of science,
for example. The loss of the memory of words is another very curious
form of this disorder, which is not unfrequently to be met with : the patient
understands perfectly well what is said, but is not able to reply in any other
terms than yes or wo, — not from any paralysis of the muscles of articulation,
but from the incapability of expressing the ideas in language. Sometimes the
memory of a particular class of words only, such as nouns or verbs, is de-
stroyed ; or it may be impaired merely, so that the patient mistakes the proper
terms, and speaks a most curious jargon. These cases have a peculiar interest,
in reference to the inquiry into the functions of different parts of the Cere-
brum.

492. To the formation of vivid ideas of sensible objects, whether these have
actually presented themselves in the same form at some previous time, or are
modifications of the forms which had a real existence, the term Conception is
applied ; and this designation, like Perception, is also applied to the result of
the operation, that is, to the idea which is thus formed. The novelty of the
Conception may depend upon the new combination or correlation of the
objects it includes; or it may result from a sort of decomposition of former
complex ideas', and the re-assemblage of their elements under a different form.
These processes', like the Memory, of which they are modifications, may be
either spontaneous or voluntary; and in both forms they are continually em-
ployed by almost every one, — the tendency to the exact reproduction of former
32

374 FUNCTIONS OF THE NERVOUS SYSTEM.

ideas, however, being most evident in some minds, whilst the tendency to the
modification of them is more obvious in others. The latter is one source of
that faculty, to which the term Imagination is given.

493. The Mind, however, is not restricted to external sources, for objects
of perception ; since, when once in activity, it perceives its own operations,
and traces the various relations and connections among its objects of thought.
The power of doing this may be termed Internal Perception. The mind
often has internal perceptions without any direct effort of the will, just as it
receives perceptions from external objects ; but its power of cognizance is not
unfrequently directed inwards by express volition; and the act is then pecu-
liarly termed Reflection, or perhaps better, Introspection. — Now by this pro-
cess, a new class of ideas is excited, of a very different character from those
which are called up by external objects ; and these, being entirely dependent
upon the operation of the Intellectual powers, and having no dependence upon
Sensations except as the original springs of those operations, may be termed
Intellectual Ideas, in contradistinction to the Sensational Ideas. The former,
like the latter, become the subjects of the Associating tendency; and thus are
combined in Trains of Thought. Some of these intellectual ideas appear to
be so necessarily excited by mental operations, even of the simplest kind, and
to be so little dependent on individual peculiarities either inherent or acquired,
that they take rank as fundamental axioms or principles of Human Thought.
Such are, — the belief in our own present existence, or the faith which we re-
pose in the evidence of Consciousness ; this idea being necessarily associated
with every form and condition of mental activity, — the belief in our past ex-
istence, and in our personal identity so far as our memory extends, which is
necessarily connected with the act of Recollection ; with this, again, is con-
nected the general idea of Space: — the belief in the external and independent
existence of the causes of our sensations, which results from Perception, or
the direction of the mind to the ideas originating in them ; with this is con-
nected the general idea of Space : — the belief in the existence of an efficient
cause for the changes which we witness around us, which springs from the
Perception of those changes ; whence is derived our idea of Power, — the be-
lief in the stability of the order of nature, or in the invariable sequence of
similar effects to similar causes, which also springs directly from the Percep-
tion of external changes, and seems prior to all reasoning upon the results of
observation of them (being observed to operate most strongly in those whose
experience is most scanty, and in relation to subjects that are perfectly new
to them) ; but which is the foundation of all applications of our own experience
or that of others, to the conduct of our lives, or to the extension of our know-
ledge : — lastly, the belief in our own free tcill, involving the general idea of
Voluntary Power ; which is in like manner a direct result of our Internal
Perception of those mental changes which are excited by sensations. Hence
it is evident, that " the only foundation of much of our belief, and the only
source of much of our knowledge, is to be found in the constitution of our own
minds ;" but it must be steadily kept in view, that these fundamental axioms
are nothing else than expressions of the general fact, that the ideas in question
are uniformly excited (in all ordinarily-constituted minds, at least) by simple
attention to the changes in which they originate.

494. Upon the Sensational and Intellectual Ideas thus brought under the
cognizance of the Mind, all acts of reasoning are founded. These consist,
for the most part, in the aggregation and collocation of ideas ; the decompo-
sition of complex ideas into more simple ones, and the combination of simple
ideas into general expressions ; in which are exercised the faculty of Com-
parison, by which the relations and connections of ideas are perceived, — that

FUNCTIONS OF THE CEREBRVM. 375

of Abstraction, by which we fix our attention on any particular qualities of
the object of our thought, and isolate it from the rest, — and that of Generali-
zation, bv which we fix in our minds some definite notions in regard to the
general relations of those objects. These are the processes chiefly concerned
in the simple acquirement of Knowledge ; with which class of operations, the
Emotional part of our nature has very little participation. But in those
modes of exercise of our reasoning powers, which are chiefly concerned in
the determination of our actions, the Emotions, &c., are largely concerned.
As formerly explained (S 440), they chiefly (if not solely) act upon the reason-
ing powers, by modifying the form in which the ideas are presented to the
mind. — whether these ideas are directly excited by external sensations, or
whether they are called up by an act of the Memory, or result from the
exercise of the Imagination.^ If we closely scrutinize our Emotions, indeed,
we shall find that they consist chiefly, if not entirely, of feelings of pleasure
and pain, connected with certain classes of ideas ; the former producing a
desire of the objects to which they relate ; the latter a repugnance to them.
They thus have a most important influence upon the Judgment, which is
formed by the comparison of certain kinds of ideas; and they may conse-
quently modify the Volitional determination, or act of the Will, which is con-
sequent upon this, and which may either be directed towards the further
operations of the mind itself, or may exert an immediate influence on the
bodily frame, by the agency of the Xervous System. In either case, it is the
characteristic distinction of a Volitional operation, that means are intention-
ally adapted to ends, in accordance with the belief of the mind as to their
mutual relations. Upon the correctness of that decision, will depend the
power of the action to accomplish what the mind had in view.

495. The faculty of Imagination is in some respects opposed in its cha-
racter to that of Reason; being concerned about fictitious objects, instead of
real ones. Still it is in a great degree an exercise of the same powers, though
in a different manner. Thus it is partly concerned in framing new combi-
nations of ideas relating to external objects, and is thus an extended exercise
of Conception, — placing us, in idea, in scenes, circumstances, and relations,
in which actual experience never placed us, — and thus giving rise to a new
set of objects of thought. In fact, every Conception of that which has not
been itself an object of perception, may, strictly speaking, be regarded as the
result of the exercise of Imagination. Now the new Conceptions or mental
creations thus formed take their character, in great degree, from the Emo-
tional tendencies of the mind ; so that the previous development of particular
feelings and affections will influence, not merely the selection of the objects,
but the mode in which they are thus idealized. In the higher efforts of the
Imagination, the mind is concerned, not so much with the class of Sensa-
tional ideas, but with those of the Intellectual character; and the collocation,
analysis, and comparison of these, by which new forms of combinations are
suggested to the mind, involve the exercise of the same powers, as those con-
cerned in acts of Reasoning. — but they are exercised in a different way.
"V\ hilst the Imagination thus depends upon the Intellectual powers for all its
higher operations, the Understanding may be said to be equally indebted to
the Imagination ; for the ideal combinations, which are the results of the
action of the latter, do not merely engage the attention of the Artist, who
aims to develop them in material forms, but are the great sources of the im-

The recal of past sensations and ideas may produce purely Emotional actions ; by ex-
citing in the centres, from which those actions proceed, a condition corresponding with that
which would be excited by the present sensation (§ 439).

376 FUNCTIONS OF THE NERVOUS SYSTEM.

provement of the knowledge and happiness possessed by our race, — operat-
ing alike in the common affairs of life, by suggesting those pictures of the
future which are ever before our eyes, and are our animating springs of action,
with their visions of enjoyment never perhaps to be fully realized, and their
prospects of anticipated evil that often prove to be an exaggeration of the
reality, — prompting the investigations of Science, that are gradually unfolding
the sublime plan on which the Universe is governed, — and leading to a con-
tinual aspiration after those highest forms of Moral and Intellectual beauty,
which are inseparably connected with purity and love.

8. General Recapitulation and Pathological Applications.

496. A general Summary of the views here propounded, in regard to the
Functions of the Cerebro-Spinal division of the Nervous system, may proba-
bly be useful in assisting the Student to gain clear ideas regarding them. —
The fibres of the nervous trunks may be divided, according to the direction
of their influence, into two classes, — the afferent or centripetal, — and the effe-
rent or centrifugal. The afferent may be said to commence at the periphery,
especially on the skin, mucous surfaces, &c., and to terminate in the vesicu-
lar matter of the nervous centres ; whilst the efferent originate in that vesicu-
lar matter, and terminate in the muscles.* Every fibre runs a distinct course
from its origin to its termination ; and it is not improbable that there are
several distinct endowments in the different fibres composing each trunk.
There is no evidence that the fibrous structure serves any different purpose
than that of a mere conductor; and there seems good reason to believe that
all the active operations, of which the nervous system is the instrument, ori-
ginate in the vesicular matter. A mass of vesicular matter, connected with
nervous trunks, forms a ganglion. In the Invertebrata, the ganglia are fre-
quently numerous, and are scattered through the system, without much con-
nection with each other; — each having an independent action, although its
function may be but a repetition of that of others. In Vertebrated animals,
on the other hand, they are united into one mass ; partly, it would seem, for
the sake of the protection afforded them by the bony skeleton ; and partly,
in order that more complete consentaneousness of action may be attained.
Still, certain divisions may be traced in the central masses of the Cerebro-
Spinal system ; both by the determination of their respective functions, as
indicated by observation and experiment ; and by the study of the distribution
of the nerves proceeding from them. In this manner we arrive at the know-
ledge of several distinct ganglionic centres, of which the following may be
considered as a general account.

i. The True Spinal Cord, consisting of a nucleus of vesicular matter, re-
ceiving afferent fibres, and giving origin to efferent ; by these it is connected
with all parts of the body, but especially with the surface and muscles of the
extremities. The actions of this centre maybe performed without conscious-
ness on the part of the individual; and they consist in the reflexion of a motor
impulse along an efferent nerve, on the reception of a stimulus conveyed by an
afferent or excitor nerve. These reflex movements can be best excited, when
the muscles are removed from the control of the Will, which otherwise gene-
rally antagonizes them. Some of them are connected with the maintenance

* The terms originate and terminate cannot be used with strict correctness; since, as for-
merly explained (§ 2-18), many libres seen} to have no actual termination, either in the mus-
cles or in ve.-ienl:ir mutter: but they cease to rim in then previous direction, after forming
their terminal loops; and tlieir course as afferent or efferent fibres may consequently be said
to begin or to end at these points.

GENERAL SUMMARY.

377

of the Organic functions ; others with locomotion ; and others with the pro-
tection or withdrawal of the body from injury. Muscular movements may
also be excited by a stimulus directly applied to the Spinal Cord itself (§§
363—373).

ii. The .Medulla Oblongata, or cranial prolongation of the Spinal Cord.
The actions of this do not essentially differ from those of the true Spinal
Cord ; but they are connected with different organs. This part consists
chiefly of the centres of the nerves of Respiration and Deglutition, — two
functions, of which the continual maintenance is essential to the life of the
being; and it would seem as if these were placed within the cranium, to be
more secured from accidental injury. The movements concerned in Respira-
tion and Deglutition are, like those excited through the true Spinal Cord, of a
strictly reflex character, being in all instances due to an impression or stimulus
originating in the periphery of the system, which, being conveyed to the cen-
tre, excites there a motor impulse ; and they, also, are independent of Sensa-
tion (§§ 374—387).

in. The Ganglia of the nerves of Sensation, common and special, which
form, as it were, the continuation of the Medulla Oblongata. These appear
to minister to actions, which, like the Reflex, are almost necessarily excited
by certain stimuli, and are only in a degree controllable by the Will : but
which differ from those of which the Spinal Cord is the centre, in being only
excitable through Sensation. Reasons have been given for the belief, that
these ganglia are the centres of those actions, which are commonly termed
instinctive in the lower animals, and consensual and emotional in ourselves ;
these all correspond, in being performed without any idea of a purpose, and
without any direction of the Will, — being frequently in opposition to it (§§
422—460).

iv. The Cerebral Hemispheres or Ganglia, which are evidently the instru-
ments or organs of the intellectual faculties. It is probably by them alone,
that Ideas or notions of surrounding objects are acquired, and that these ideas
are made the groundwork of mental operations. They would seem, also, to
be the exclusive seat of Memory. The results of these operations are mani-
fested on the bodily frame, through the Will ; which is capable of acting, in
greater or less degree, on all the muscles forming part of the system of Ani-
mal life (§§ 471—495).

v. The Cerebellum, which appears to be concerned in the regulation and
harmonization of Muscular movements, especially those of a voluntary cha-
racter (§§ 457—470).

497. The arrangement and connections of these parts may be thus con-
cisely expressed : —

Tabular view of the Nervous Centres.

Cerebral Ganglia,

the centres of the operations

of Intelligence and Will.

Nerves of Special sen-")
sation. — Motor fibres !
mingled with general j
motor system (?). J

Sensory Ganglia,

the centres of Consensual,

Instinctive, and Emotional actions.

f Nerves of Special sen-
J sation. — Motor fibres
mingled with general
motor system (?) .

Cerebellic Ganglia,
for harmonization of general
muscular actions.

32*

378

FUNCTIONS OF THE NERVOUS SYSTEM.

Afferent and Motor Nerves
of Respiration, Deglutition,
&e.

Respiratory and
Stomato-gastric Ganglia,
in Medulla Oblonsata.

Afferent and Motor Nerves
of Respiration, Deglutition,
'&c.

Trunks of Spinal nerves, composed of
afferent and motor fibres from true
Spinal Cord and Medulla Oblongata ;
and probably also of sensory and
motor fibres, connected by the longi-
•tudinal strands of the Cord, with the
Sensory Ganglia.

c

Is

"Et

c
W

O

.S (U

I a

fli r^i

-
O rt

O

O

C

'5

Trunks of Spinal Nerves, composed of
afferent and motor fibres from true
Spinal Cord and Medulla Oblongata ;
and probably also of sensory and
motor fibres, connected by the longi-
tudinal strands of the Cord, with the
Sensory Ganglia.

I

M

o

The Spinal Cord, the Medulla Oblongata, and Sensory Ganglia, seem to
constitute one continuous group of ganglionic centres ; which must be regarded
as the fundamental portion of the Nervous System. In descending the Verte-
brated series, we find the Cerebrum and Cerebellum gradually diminishing in
size and importance, and at last, in the .flmphioxits, disappearing altogether ;
and the Cranio-Spinal axis, which then remains, differs in nothing but the
continuity of its vesicular structure, from the nervous system characteristic of
the Articulata, in which the vesicular matter is broken up (so to speak) into
distinct centres. In this Cranio-Spinal Axis, all the nerves have their termi-
nation ; and, from what has been ascertained of the anatomy of the gangliated
cord in the Articulata, there seems much reason to believe, that their fibres
may pass, in the longitudinal strands of the Cord, to great distances from their
points of entrance or emersion ; so that we may have, in the nerves connected
with every part of the Cord, sensory fibres, whose real termination is in the
Sensory ganglia at its summit, and motor fibres, which originate from these
centres, and are the instruments of all the actions to which they minister.
The great difficulty of tracing the individual fibres of the Spinal Cord, for any
considerable part of its length, renders it impossible, however, to say with
certainty that this is their real disposition ; but it is known that one at least
of the nerves, the Third pair, has this double connection with the Sensory
Ganglia and the Spinal Cord (or rather the Medulla Oblongata), and it is
likely that the same is true of the other motor nerves of the Orbit. Hence
there is no improbability in the idea, that of the afferent fibres of the Spinal
nerves, some are connected with the vesicular matter of the part of the Spinal
Cord through which they pass, and others with the Sensory Ganglia in the
Encephalon ; the relative numbers entering these centres being accordant with
the chief purposes of the trunk, whether as an excitor of reflex actions, or as
destined to arouse sensations: — and that the like is true of the motor fibres,
the relative proportions of those derived from the two sources having reference
to the character of the motions, whether simply-reflex or consensual, — to
which the trunk is destined to minister. But there is by no means the same
evidence, that any fibres contained in the nerves actually go on to the Cere-
brum and the Cerebellum; and the probability seems rather, that the fibres
which connect these masses with the Cranio-spinal Axis are of a commissural

GENERAL SUMMARY. 379

nature, and are destined to enable them to receive communications, and to act
on the muscular system, through the mediation of the latter, — than that they
are actually continuous with any of the fibres in the nerve-trunks connected
with it (see § 473).

498. According to these views, the following will be the mechanism of the
different classes of actions, in which the Cerebro-Spinal apparatus is directly
concerned.

i. In Reflex movements, a stimulus acting through the excitor fibres upon
the vesicular matter of certain parts of the Spinal Cord, causes the transmis-
sion of a reflex impulse through the motor fibres that proceed from it ; and
this gives occasion to muscular contraction. — With this operation, sensation
will be coincident, if the stimulus act upon any of the fibres that pass on to
the Sensory ganglia ; but this is not essential to it ; and will not be aroused
if the connection does not exist, or the Sensory ganglia be in a state of torpor.

ii. In Sensation, the stimulus acts upon fibres which have their termina-
tion in the chain of ganglia that lies at the base of the cranial cavity in Man,
and is closely connected with the Medulla Oblongata. The series is collect-
ively termed the Sensorium ; but it is probable that each is the instrument,
by which the animal becomes cognizant of Sensations of a particular class, —
the Olfactive, Optic, and Auditory ganglia, for those of Smell, Light, and
Hearing respectively, the Thalami Optici for those of Touch, and certain parts
of the Medulla Oblongata for those of Taste.

in. In Consensual movements, the stimulus conveyed by the Sensory fibres
becomes the direct source of motor impulses ; which are conveyed through the
agency of fibres that issue from the Sensory ganglia and Corpora Striata.
All the movements which are neither reflex nor voluntary, seem to belong to
this class; which will include, therefore, the instinctive actions of the lower
animals, with the automatic and purely emotional movements in Man.

iv. In the act of Perception, or the formation of ideas from Sensations, in
Memory, and in all the higher acts of Mind, the Cerebrum seems to be con-
cerned ; the vesicular matter which constitutes its active portion, receiving the
stimulus to its operations, through the ascending and commissural fibres that
connect its different parts with the Sensory Ganglia at its base. As the con-
ducting power of these fibres acisfrom, not towards, the Sensory ganglia, we
should not expect that irritation of them should produce Sensation ; and this
is precisely what experiment shows to be the case.

v. In the act of Voluntary movement, which results from mental operations,
the vesicular matter of the Cerebrum operates, through the descending and
commissural fibres, upon the motor portion of the Sensory ganglia ; the
stimulus transmitted downwards by Volition producing the same kind of state
in its vesicular matter, as that which is transmitted upwards by Sensation.
In the same manner, the recal of past Sensations and Ideas may reproduce, in
the Sensory ganglia, the condition which gives occasion to the purely Emo-
tional movements.

vi. The combination and harmonization of the separate acts of Voluntary
Muscular movement, which is the function here attributed to the Cerebellum,
appears to be prompted by the guiding sensations, of which the Sensory
ganglia are the seat; the influence of these will be propagated along the com-
missural fibres known as the processus a cerebello ad testes; and the motor
influence, resulting from the action thus excited in the vesicular matter of the
Cerebellum, will be propagated downwards by its connections with the various
columns of the Spinal Cord.

499. The distinctness of the operations of these several centres is shown
in various ways: but especially by conditions of the bodily system, in which
one or more of them is in a state of inaction, whether temporary or permanent;

380 FUNCTIONS OF THE NERVOUS SYSTEM.

or is prevented, by the interruption of the usual channel of communication,
from operating on particular parts. Thus, in ordinary profound Sleep, which
is a state of complete unconsciousness, it is evident that the Cerebral Hemi-
spheres, and the Sensory Ganglia, are at rest; as the Cerebellum, also, may be
considered to be: but the Medulla Oblongata and Spinal Cord must be in com-
plete functional activity. The same is the case in profound Coma, resulting
from effusion of blood, or from narcotic poisons, but not affecting the power
of breathing or swallowing. It may be frequently observed, that the sleep is
not so profound as entirely to suspend the consciousness of the individual ;
and that various movements of an adaptive character are performed, tending
to relieve uneasiness resulting from various causes. In this condition it seems
not improbable, that the Sensory ganglia are in some degree awake, and that
the movements are of an instinctive nature; — the mind of the individual not
being sufficiently active to discern the cause of the uneasiness, or to employ
his intelligence in the removal of it. Whenever Dreaming takes place, it is
evident that the Cerebrum is in a state of partial activity. The states of
Dreaming and Delirium, and many forms of Insanity, have considerable
analogy with each other; especially in the absence of the power which is so
characteristic of the well-regulated mind of Man, of controlling and regulating
the current of thought. One idea calls up another, according to their previous
associations; and the most incongruous combinations are frequently the result;
but it will generally, if not always, be found, that the ideas themselves have
been previously in the mind, and that no entirely new train of thought is
started. Of the degree in which, when the mind is thus closed to the external
\vorld, the hidden stores of Memory are opened to its search, many very
curious instances are recorded.

500. The state of Somnambulism appears to be nearer to that of wakeful
activity of the whole mind, than is that of Dreaming. In the latter condition,
the individual is unconscious of external objects ; for, if they produce an effect
upon him, it is in modifying the current of ideas, frequently in some very
extraordinary manner : and he does not form any true perception or idea of
their nature. But in Somnambulism, his senses are partly awake, so that im-
pressions made upon them may be properly represented to the mind, and
excite there the ideas with which they are connected ; moreover the Cere-
bellum is also awake, so that the movements which the individual performs,
are perfectly adapted to their object; indeed, it has frequently occurred, that
the power of balancing the body has been so remarkably exercised in this
condition, that sleep-walkers have traversed narrow and difficult paths, over
which they could not have passed in open day, when conscious of their danger.
In Somnambulism, as in Dreaming, there is an evident want of voluntary
control over the thoughts ; their succession is more influenced, however, by
impressions received from without, than it is in dreaming; and hence the mind
. may sometimes be easily guided into a particular train, by properly directing
the impressions made upon the sensory organs. It may often be remarked,
however, that impressions which do not in some degree harmonize with the
train of ideas, are not received by the mind ; or, at any rate, they are not
applied to the correction of the erroneous notions which possess it. But there
are many different shades in the condition of the mind, between Dreaming
and Somnambulism ; the individual being, in some cases, much less conscious
of external objects, than he is in others. In some instances it appears as if
the mind was so wholly engrossed in a particular train of thought, that it could
not be affected by any new sensations, so that there is even an unconsciousness
of those which produce pain ; this has its parallel in the waking state. A
very remarkable characteristic of the state of Somnambulism, is the complete
isolation which commonly exists, between the trains of thought which then

GENERAL SUMMARY. PATHOLOGICAL APPLICATIONS. 381

occupy the mind, and its operations during the waking hours; so that in neither
state is there a remembrance of what passes in the other. There is usually
this difference, however; — that the mental operations which take place in
Somnambulism are, like those o£ dreaming frequently suggested by what has
previously been occupying the mind; whilst these seem to leave no impression
to be retraced in the waking state, though all that passes in one fit of Som-
nambulism may be recollected in the next. This has been most remarkably
observed in the phenomena of that curious state, which is known under the
name of Double Consciousness ;* in this, the form of Somnambulism in which
there is a consciousness of external impressions, seems to alternate with the
condition of ordinary mental activity, and the individual leads (as it were) two
distinct'lives, recollecting in each condition what happened in previous states
of the same character, but knowing nothing of the occurrences of the other.
— In regard to the curious forms of these affections, which are produced by
the so-called Mesmeric influence, the present views of the Author will be
stated in the Appendix.

501. We have thus witnessed several varieties in the condition of the bo-
dily system, depending upon partial or complete suspension of the functional
activity of the Cerebrum, Cerebellum, and Sensory ganglia. There is no
normal condition of the Spinal system, which at all corresponds with these ;
since its operations are so closely connected with the maintenance of the Or-
ganic functions, that the suspension of them necessarily induces the cessation
of the latter. This is especially the case, however, in regard to the Respira-
tory ganglion; for the whole remainder of the Spinal Cord may be removed,
without the interruption of the movements which are dependent on that seg-
ment of it. Cases have occurred, however, in which the natural performance
even of these has been partially or entirely suspended ; and in which the
maintenance of life has for a time been effected, by a voluntary exertion of
the muscles of Respiration. The influence of the Will upon the general mo-
tor apparatus of Man, seems to predominate so greatly over the Reflex action
of the Spinal Cord, that few phenomena which are attributable to the latter
ordinarily present themselves ; these are manifested, however, when the in-
fluence of the Brain over any part is cut off, as is seen in certain cases of pa-
ralysis. These morbid conditions present us, also, with illustrations of other
effects of the interruption of the communication between the nervous centres
and particular sets of muscles. Thus, the influence of the Will may be cut
off, although that of the Instincts, Emotions, and Reflex Function may remain ;
or the respondence of the muscles to Emotion may be prevented, whilst they
are still capable of Voluntary control, or of Reflex action. Such cases seem
to point very clearly to three distinct primary centres of nervous agency ; —
and to these, the Cerebrum Sensory Ganglia, and Spinal Cord (including the
Medulla Oblongata) have been here assigned as the instruments. We shall
next inquire into some other morbid conditions of the system, which seem
due to the irregular action of these; and in this we shall be chiefly guided by
the researches of Dr. M. Hall, which have been already slightly glanced at
(§§ 400,401).

502. Of the Convulsive diseases, it appears that the greater part, if not the
whole, may be attributed to a morbid state of the Spinal System of nerves.
So completely does the power of producing convulsive movements appear
limited to that and to the Sensori-motor system, (no mechanical irritation of
the Cerebral substance being effectual in exciting such movements, § 473,)
that, where convulsions present themselves during diseases which appear

1 Much interesting information on this and other subjects, alluded to in this Section, may
be found in Dr. Abercrombie's Treatise on the Intellectual Functions.

382 FUNCTIONS OF THE NERVOUS SYSTEM.

limited to the Brain, we may infer that one of these systems is involved. Dr.
M. Hall has recently pointed out, that this complication is due to the impres-
sions made upon the fibres of the Spinal nerves distributed upon the Dura
Mater, and other serous and fibro^ membranes ; for convulsive actions may
be induced by pinching these membranes, or otherwise irritating them. — Of
the distinct forms or combinations, of which the class of convulsive disorders
is composed, Tetanus is one of the most interesting and instructive. This
disease is evidently dependent upon a state of undue excitability of the whofe
Spinal System ; and this may be produced by different causes. That which
is termed the idiopathic form of the disease has its origin in the centres ; it
may result in Man from the operation of various predisposing and exciting
causes: and may be artificially induced in Animals by the administration of
Strychnia. In the traumatic form of the disease, the morbid state has its
origin in a local injury; and the irritation propagated from this, and operating
through the Spinal Cord, may be itself a cause of many of the convulsive
movements. But, when the irritable state is once established in the nervous
centres, convulsive action of the muscles may be excited by any stimuli, and
even almost entirely without external causes. Hence it is that, whilst the
amputation of the injured part is not unfrequently the means of saving the
patient, if performed sufficiently early, it is attended with no benefit if delayed.
The Cerebral apparatus is entirely unaffected in this disorder; but the nerves
of deglutition are usually those first influenced by it; those of respiration,
however, being soon affected, as also those of the trunk in general. — The
condition termed Hydrophobia is nearly allied to that of traumatic Tetanus,
differing chiefly in the mode in which the cranio-spinal axis is affected. The
irritable state of the nervous centres results from a local injury of a peculiar
kind; and here, too, the early removal of the part is very desirable as a means
of prevention ; although, when the malady has once reached the centres, it is
of no use. The muscles of respiration and deglutition are, as in Tetanus,
those spasmodically affected in the first instance ; but there is this curious
difference in the mode in which they are excited to action, — that, whilst in
Tetanus the stimulus operates through the true Spinal Cord (either centrally, or
by being conveyed from the periphery), in Hydrophobia it is often conducted
from the ganglia of Special Sense, or even from the Cerebrum ; so that the
sight or sound of fluids, or even the idea of them, occasions — equally with their
contact, or with that of a current of air — the most distressing convulsions. It
would seem, therefore, as if the Serisori-motor system of nerves was involved
in it.* — In these and other general convulsive diseases, it is probable that the
whole vesicular matter of the centres involved is in so excitable a state, that
a stimulus applied to any part of it may produce a reaction through the whole.
In no other way would it be easy to explain the great number and variety of
movements, which a small degree of local irritation may excite.

503. Epilepsy is another convulsive disease, principally involving the Spinal
Cord, but partly affecting the Brain. The predisposition to convulsive move-
ments may depend upon many causes ; but the movements themselves are in
general immediately excited by some local irritation, as by the presence of
undigested matter in the stomach, of worms in the intestines, &c., although
frequently also from causes purely mental. The convulsive movements usually
affect the muscular system very extensively ; acting especially upon the mus-
cles of ingestion and egestion. The Brain is evidently much concerned in
the disease, however; as is evident from the numerous instances in which it
has been clearly traced to some local affection of that organ, as well as from

* For an interesting case of the excitement of involuntary muscular movements, by sen-
sations received through the eye and ear, see Dr. Cowan, in Lancet for 1840. Vol. II., p. 364.

GENERAL SUMMARY. PATHOLOGICAL APPLICATIONS. 383

the loss of consciousness which accompanies the convulsion.' — Many forms
of that protean malady, Hysteria, are attended with a similar irritability of
the Nervous Centres ; but there is this remarkable difference in the two cases,
— that the morbid phenomena of Hysteria, whilst they often simulate those
of Tetanus, Hydrophobia, Epilepsy, &c., are evidently dependent upon a state
of the system of a much less abnormal character, being frequently relieved
by very mild remedies, and being often capable of prevention by a strong
effort of the will. Dr. Hall has pointed out an important distinction between
Epilepsy and Hysteria, which materially influences the proximate danger of
the paroxysm of each respectively ; in the former, the larynx is convulsively
closed, and partial asphyxia is the necessary result, if the access of air be too
long prevented, so that venous congestion ensues, increasing the disorder of
the nervous centres even to a fatal degree ; in Hysteria, on the contrary, much
as the larynx is affected, it is not usually closed. Cases sometimes present
themselves, however, in which the Hysteric paroxysm assumes the Epileptic
character, the larynx being closed during expiration, so as to produce alarming
results. The disordered state of the Nervous Centres, to which these con-
vulsive actions are due, seems to be peculiarly connected with Emotional con-
ditions of the mind, and with functional derangements of the sexual organs.

504. The foregoing are the chief general spasmodic diseases in which the
Spinal system of nerves is evidently involved ;* but there are many others of
a more local character. Such are the various forms of Spasmodic Asthma,
the attacks of which generally result from some internal irritation, either in
the lungs themselves or in the digestive system, producing a reflex action upon
the muscular fibres of the bronchial tubes. The Croup-like Convulsion, or
Crowing Inspiration of Infants, again, is an obstruction to the passage of the
air through the glottis, by a spasmodic contraction of the constrictors of the
larynx. This spasmodic action may be induced by various kinds of irritation ;
such as that occasioned by teething, by the presence of undigested food, or by
intestinal disorder. In the crowing inspiration, the larynx is partially closed ;
when the spasm is severe, however, there is complete occlusion of the pas-
sage ; and forcible efforts at expiration are made, which induce, as in epilepsy,
a severe degree of venous congestion, and this reacts upon the nervous cen-
tres, aggravating the previous disorder of their condition. The present in-
creased knowledge of the functions of the laryngeal nerves, and of the symp-
toms of this disease, appears to render inadmissible the explanation of it given
not long since by Dr. H. Ley, who attributed it to paralysis of the pneumo-
gastric nerves occasioned by pressure. — Spasmodic closure of the larynx may
occur from other causes. When the rima-glottidis is narrowed, by effusion
of fluid into the substance of its walls, it is very liable to be completely closed,
by spasmodic action, to which the unduly irritable condition of the mucous
membrane will furnish many sources of excitement. Choking, again, does
not result so much from the pressure of the food on the air-passages them-

' Chorea is ranked by Dr. M. Hall as a disease of the Spinal System of nerves ; but this
can scarcely be regarded as a correct determination. It is true that there is considerable
irregularity in the ordinary Reflex actions ; but the irregularity is still greater in those, to
which Volition or Emotion are the stimuli. Moreover, the body is at rest during sleep ; and
"the Spinal system never sleeps." The frequent origin of the disease in causes which have
excited strong mental emotions, and the effect of even moderate excitement of the feelings
in greatly aggravating the movements of the body, seem to indicate the connection of this
disease with the Sensori-motor system of nerves. Stammering maybe regarded as a sort of
Chorea affecting the muscles of voice ; of this more hereafter (CHAP. TI). In Paralysis Agitans,
it may be usually observed, that the voluntary actions are much more affected than the reflex ;
the latter, indeed, not in general manifesting any disturbance. An interesting and well marked
case of this disease has been mentioned to the author by Dr. W. Budd, in which softening
was found in the Crura Cerebri.

384 FUNCTIONS OF THE NERVOUS SYSTEM.

selves, as from the spasmodic action of the larynx, excited by this ; and the
dislodgement of the morsel by an act of vomiting, is the most effectual means
of obtaining relief. — Tenesmus and Strangury are well-known forms of spas-
modic muscular contraction, excited by local irritation acting through the
Spinal system. The abnormal action which leads to Abortion is frequently
excited in the same manner ; how far the uterus itself is called into contrac-
tion by the ordinary spinal nerves, is a question as yet undecided ; but the
facts already stated leave no doubt, that stimuli operating on these may act
upon it through the Sympathetic, into which their fibres pass (§ 393). It will
be borne in mind, however, that, in abortion, as in ordinary parturition, many
muscles are called in, to aid the contractions of the uterus, which are strictly
under the dominion of the Spinal system. — There is a form of Incontinence
of urine, which is very analogous to the morbid action just described ; the
sphincter has its due power ; but the stimulus to the evacuation of the bladder
is excessive in strength and degree, owing to the acridity of the urine or other
causes. The part of the bladder upon which this appears chiefly to act, is
the trigonum (which is well known to be more sensitive to the irritation of
calculi, than the rest of the internal surface) ; and Sir C. Bell advises young
persons who suffer during the night from this very disagreeable complaint, to
lie upon the belly instead of the back, ,so that the contact of the urine with
the trigonum may be delayed as long as possible.

505. One of the most familiar examples of the pathological excitement of
the true Spinal system is the act of Vomiting; and, as Dr. M. Hall justly
remarks, the special function of this system nowhere receives better illustra-
tion. The act may be excited in various ways. Thus, it results from the
tickling of the fauces with a feather or with the finger ; but if the feather be
carried too far down, an act of deglutition is induced instead of vomiting.*
In this instance the glosso-pharyngeal, and perhaps also the fifth pair, are the
nerves by which the stimulus is conveyed to the Medulla Oblongata. Vomit-
ing, again, may be induced by substances introduced into the stomach ; and
here the pneumogastric is evidently the excitor. When it takes place as a
result of pregnancy, or of some intestinal irritation, the stimulus must be con-
veyed, either through one of the ordinary Spinal nerves, or through the Sym-
pathetic. But it may also be occasioned by the sight, smell, or taste of any
disagreeable object, or by the mere conception of it, or by mental emotion
simply. In this case, the stimulus appears to be received by the ganglia of
special sense, and to be transmitted by them to the muscles concerned, as by
the Spinal Cord or Medulla Oblongata in the former case. When Vomiting
is excited by the introduction of emetic substances into the blood, it is proba-
ble that their stimulation chiefly operates through the extended plexus of
nerves, spread out by the Sympathetic upon the walls of the blood-vessels ;
but the irritant action of the substance upon the nervous centres may be also
concerned. — In regard to the mechanism by which the act of Vomiting is
produced, considerable difference of opinion has existed. The old doctrine
was, that it was solely occasioned by the contraction of the stomach itself;
but Magendie proved that this could not be the case, by substituting a bladder
for the stomach of an animal, and then injecting a solution of tartarized anti-
mony into its blood, which immediately caused the emptying of the bladder,
by the pressure of the surrounding muscles ; these muscles he considered to

* This has been the cause of many accidents. Patients have tickled the fauces with a
feather in order to excite vomiting; and, having introduced it too far into the pharynx, it has
been Brawn out of their fingers by the muscles of deglutition, and carried into the oasophagus.
Similar accidents have occurred with the rectum-bougie, and female catheter, as well as with
probes, &c., introduced into the male urethra; all the orifices being furnished with a kind of
ingestive power, which isclearly the result of Reflex action.

OF SENSATION IN GENERAL. 385

be the diaphragm and abdominal muscles, the conjoint actions of which would
be a peculiarity observed in no other instance. By Dr. M. Hall, on the other
hand, it is maintained that the act of vomiting is, like the expulsion of the
foetus, urine, faeces, &c., an expiratory effort, modified in its effects by the pe-
culiar condition of the sphincters. It bears, indeed, great resemblance to the
act of coughing ; differing chiefly in this, that in vomiting, the larynx is closed
during the whole operation, whilst it is only closed momentarily in coughing ;
and also, that in coughing, the cardiac orifice of the stomach is closed, whilst
in vomiting it is opened. In this view, the accuracy of which has been proved
by experiment, the diaphragm is quite inert. — A curious case has been re-
corded by Drs. Graves and Stokes,* in which vomiting took place from the
stomach of a man, who was found after death to be the subject of a very re-
markable change in the relative position of the viscera, — the stomach lying in
the thorax, which cavity communicated with the abdomerf, by an opening in
the diaphragm, giving passage to the oesophagus and duodenum. This case
was regarded by its reporters as proving that vomiting might take place by
the action of the stomach alone ; but it can scarcely be held to justify this
conclusion ; since, the diaphragm being entirely passive, the abdominal mus-
cles would have the same power of emptying the stomach, as they would
possess over the lungs. There can be little doubt, however, that the walls of
the stomach participate in the action; for even the oesophagus is thrown into
a. state of reversed peristaltic movement.

CHAPTER VI.

ON SENSATION, AND THE ORGANS OF THE SENSES.

1. — Of Sensation in General.

506. BY the term Sensation is rightly understood that change in the con-
dition of the mind, by which we become aware of an impression made upon
some part of the body; or, in a briefer form of expression, it may be defined
to be the consciousness of an impression. Some physiologists have, it is
true, spoken of a sensation without consciousness ; but it seems very de-
sirable thus to limit the term ; since the word impression may be very well
applied to designate the change produced in the afferent nerves by an external
cause, up to the point at which the mind becomes conscious of it. We have
seen reason to believe, that the impressions communicated to the Spinal Cord
may there excite motor actions, without occasioning true Sensation ; and it
would seem to be with the Encephalon only, that the Mind possesses the
relation necessary for the production of such a change in it. Hence this
organ is spoken of as the Sensorium. For the reasons already given (§ 435),
it seems probable that the ganglia of Special Sensation are rather the essential
instruments of this function, than the Cerebral Hemispheres. The afferent
nervous fibres, which connect the various parts of the body with the Senso-
rium, are termed sensory. This term has also been applied to those which
terminate in the Spinal Cord ; but as the impressions which these convey do
not produce sensations, it seems desirable to avoid thus designating them ;

* Dublin Hospital Reports, Vol. v.
33

386 ON SENSATION, AND THE ORGANS OF THE SENSES.

and the term excitor, proposed by Dr. M. Hall, is much preferable. Every
afferent spinal nerve, therefore, is made up of sensory and of excitor fibres ;
and these may be distributed in very different proportions to different parts.
Of the excitor fibres, enough has been already said. Those parts of the body
which are endowed with sensory fibres, and impressions on which, therefore,
give rise to sensation, are ordinarily spoken of as sensible, and different parts
are spoken of as sensible in different degrees, according to the strength of the
sensation which is produced by a corresponding impression on each.

507. In accordance with what was formerly stated (§ 250) of the depend-
ence of all nervous action on the continuance of the capillary Circulation,
especially at the extremities of the fibres, it is found that the sensory nerves
are distributed pretty much in the same proportion as the blood-vessels ; that
is to say, in theTion-vascular tissues, — such as the epidermis, hair, nails, car-
tilage, and bony substance of the teeth, — no nerves exist, and there is an en-
tire absence of sensibility ; and in those whose vascularity is trifling, the sen-
sibility is dull, as is the case with bones, tendons, ligaments, fibrous mem-
branes, and other parts whose functions are simply mechanical, and even with
serous and areolar membranes. Many of these textures are acutely sensible,
however, under certain circumstances ; thus, although tendons and ligaments
may be wounded, burned, &c., with little or no consciousness of the injury,
they cannot be stretched without considerable pain ; and the fibrous, serous
and areolar tissues, when their vascularity is increased by inflammation, also
become extremely susceptible of painful impressions. All very vascular parts,
however, do not possess acute sensibility; the muscles, for instance, are fur-
nished with a large supply of blood, to enable them to perform their peculiar
function ; but they are not sensible in by any means the same proportion.
Even the substance of the brain and of the nerves of special sensation, ap-
pears to be destitute of this property ; and the same may be said of the mu-
cous membranes, lining the interior of the several viscera, which, in the ordi-
nary condition, are much less sensible than the membranes which cover those
viscera, although so plentifully supplied with blood for their especial purposes.
The most sensible of all parts of the body, is the Skin, in which the sensory
nerves spread themselves out into a minute net- work ; and even of this tissue,
the sensibility differs greatly in different parts. The organs of special sensa-
tion are, by the peculiar character of the nerves with which they are sup-
plied, rendered sensible to impressions of a particular kind : thus, the eye is
sensible to light, the ear to sound, &c. ; and whatever amount of ordinary
.sensibility they possess, is dependent upon other sensory nerves. The eye,
for example, contrary to the usual notions, is a very insensible part of the
body, unless affected with inflammation ; for though the mucous membrane
which covers its surface, and which is prolonged from the skin, is acutely
sensible to some kinds of impressions, the interior is by no means so, as is
well known to those who have operated much on the eye. And there are
many parts of the body, that are supplied with the common sensory nerves
which convey to the mind impressions of particular kinds, with much greater
readiness than they communicate those of a different description.

508. It appears, then, that the vascularity of a part is an essential condition
of its sensibility; but it does not follow that a tissue should be peculiarly sen-
sible, because it is highly vascular; since its large supply of blood may be
required for other purposes. It is not simple vascularity, however, which is
necessary, but rather an active capillary circulation; any cause which retards
tliis, deadens the sensibility, as is well seen in regard to cold ; and, on the
other hand, an increase in its energy produces a corresponding increase in the
sensibility, as is peculiarly evident in the active congestion which usually pre-
cedes inflammation. Acute sensibility to external impressions may arise,

OF SENSATION IN GENERAL. 387

however, not only from abnormal activity of the circulation in the organ or
part itself, but from the same condition affecting that part of the sensorium in
which the impressions are received. Thus in active congestion and inflam-
mation of the brain, the most ordinary external impressions produce sensations
of an unbearable violence ; and there are some peculiar conditions of the
nervous system, known under the name of hysterical, in which the patients
manifest the same discomfort, even when the circulation is in a feeble, rather
than an excited state. It is remarkable that the sensibility of the mucous
membranes lining the internal organs, is less exalted by the state of inflamma-
tion, than is that of most other parts ; and in this arrangement we may trace
a wise and beneficent provision ; since, were it otherwise, the functions neces-
sary to life could not be performed without extreme distress, with a very
moderate amount of disorder in the viscera. If a joint is inflamed, we can
give it rest ; but to the actions of the alimentary canal we can give little volun-
tary respite.

509. The feelings of Pain or Pleasure, which are connected with particular
sensations', cannot (for the most part at least) be explained upon any other
principle than that of the necessary association of these feelings, by an original
law of our nature, with the sensations in question. As a general rule, it may
be stated, that the violent excitement of any sensation is disagreeable, even
when the same sensation in a moderate degree may be a source of extreme
pleasure. This is the case alike with those impressions, which are communi-
cated through the organs of sight, hearing, smell and taste, as with those that
are received through the nerves of common sensation ; and there can be no
doubt that the final cause, or purpose, of the association of painful feelings
with such violent excitement, is to stimulate the individual to remove himself
from what would be injurious in its effects upon the system. Thus, the pain
resulting from violent pressure on the cutaneous surface, or from the proximity
of a heated body, gives warning of the danger of injury, and excites mental
operations destined to remove the part from the influence of the injurious
cause ; and this is shown by the fact, that loss of sensibility is frequently the
indirect occasion of severe lesions, — the individual not receiving the customary
intimation that an injurious process is taking place. Instances have occurred,
in which severe inflammation of the membrane lining the air-passages has re-
sulted from the effects of ammoniacal vapours, introduced into them during a
state of syncope, — the patient not receiving that notice of the irritation, which
would, in an active condition of his nervous system, have prevented him from
inhaling the noxious agent.

a. The following case, recorded in the "Journal of a Naturalist," affords a remarkable
instance of this general fact. The correctness of the statement having been called in question,
it was fully confirmed by Mr. Richard Smith, the late senior surgeon of the Bristol Infirmary,
under whose care the sufferer had been. "A travelling man, one 'winter's evening, laid
himself down upon the platform of a lime-kiln, placing his feet, probably numbed with cold,
upon the heap of stones, newly put on to burn through the night. Sleep overcame him in
this situation ; the fire gradually rising and increasing, until it ignited the stones upon which
his feet were placed. Lulled by the warmth, the man slept on ; the fire increased until it
burned one foot (which probably was extended over a vent-hole) and part of the leg above
the ankle entirely off, consuming that part so effectually, that a cinder-like fragment was
alone remaining, — and still the wretch slept on! and in this state was found by the kiln-man
in the morning. Insensible to any pain, and ignorant of his misfortune, he attempted to rise
and pursue his journey, but missing his shoe, requested to have it found; and when he was
raised, putting his burnt limb to the ground to support his body, the extremity of his leg-bone,
the tibia, crumbled into fragments, having been calcined into lime. Still he expressed no
sense of pain, and probably experienced none ; from the gradual operation of the fire, and his
own torpidity during the hours his foot was consuming. This poor drover survived his mis-
fortunes in the hospital about a fortnight ; but the fire having extended to other parts of his
body, recovery was hopeless.''

388 ON SENSATION, AND THE ORGANS OF THE SENSES.

510. It is a general rule, with regard to all sensations, that their intensity
is much affected by habit; being greatly diminished by frequent and continual
repetition. This is not the case, however, with regard to those sensations to
which the attention is peculiarly directed ; for these lose none of their acute-
ness by frequent repetition; on the contrary, they become much more readily
cognizable by the mind. — We have a good example of both facts, in the ef-
fects of sounds upon a sleeping person. If they are sounds which he has
been accustomed to hear, and to disregard, they may not awake him, however
loud they be : thus, the strokes of a forge-hammer, the firing of guns, the
shouts of a multitude, or the loudest music, may neither prevent the acces-
sion of sleep, nor arouse the already unconscious sleeper ; indeed, it oftener
happens that individuals are prevented from sleeping by the want of some
accustomed sound, or are awoke by its cessation. On the other hand, a very
slight sound, the nature of which excites the attention, is sufficient to prevent
sleep; thus, the buzz of a single musquito, in the stillness of the night, is
most effectual in dispelling repose ; — and, in like manner, a person in a state
of the profoundest unconsciousness maybe aroused by a whisper, if the sound
be one to which he has been accustomed to pay regard.

a. The following circumstance has been communicated to the Author by a Naval Officer
of high rank : — When a young man he was serving as signal-lieutenant under Lord Hood ;
and being desirous of obtaining the favourable notice of his commander, he devoted him-
self to his duty with the greatest energy and perseverance, often remaining on deck nineteen
hours out of the twenty-four, with his attention continually on the stretch. During the few
hours which he spent in repose, his sleep was so profound, that no noise of an ordinary
kind, however loud, would awake him. But if the word "signal" was softly uttered in his
ear, he was instantly aroused.

511. The general law, that Sensations, not attended to, are blunted by fre-
quent repetition, may perhaps be connected with certain other general facts,
which lie under the observation of every one. It is well known, that the
vividness of sensations depends rather on the degree of change which they
produce in the system, than on the absolute amount of the impressing cause;
and this is alike the case with regard to the special and the ordinary sensa-
tions. Thus, our sensations of heat and cold are entirely governed by the
previous condition of the parts affected ; as is shown by the well-known ex-
periment, of putting one hand in hot water, the other in cold, and then trans-
ferring both to tepid water, which will seem cool to one hand, and warm to
the other. Every one knows, too, how much more we are affected by a warm
day at the commencement of the summer, than by an equally hot day later
in the season. The same is the case in regard to light and sound, smell and
taste. A person going out of a totally dark room into one moderately bright,
is for the time painfully impressed by the light, but soon becomes habituated
to it ; whilst another, who enters it from a room brilliantly illuminated, will
consider it dark and gloomy. Those who are constantly exposed to very loud
noises, become almost unconscious of them, and are even undisturbed by them
in illness; and the medical student well knows, that even the elliuvia of the
dissecting-room are not perceived, when the organ of smell is habituated to
them, although an intermission of sufficient length would, in either instance,
occasion a renewal of the first unpleasant feelings, when the individual is
again subjected to the impression.

512. Again, it is a well-known fact, that impressions made upon the organs
of sense continue for a time, after the cause of the impression has ceased.
It is in this manner that a musical tone, which seems perfectly continuous,
results from a series of consecutive vibrations, following each other with a
certain rapidity ; and that a line or circle of light is produced by a luminous
body moving with a certain, velocity. Now there is reason to believe that

OF SENSATION IN GENERAL. 389

changes, of which the effects thus transiently remain upon the nerves of sense,
are more permanently impressed upon the Sensorium ; since, as formerly
shown (§ 491), we can only in this manner account for the phenomena of
Memory, and for the effects produced upon this power, by material changes
in the brain. Hence, the diminution in the force of sensations, which is the
consequence of their habitual recurrence, may be considered as resulting from
these two general facts, — the persistence of the impression made by them
upon the sensorium, — and the consequent absence of a change in its state.
when a sensory impression is brought to it, which is of the same nature with
one already registered there : the degree in which the consciousness is ex-
cited, being dependent, as just stated, not upon the absolute degree of the
impressing cause, but upon the amount of change which it produces in the
sensorial apparatus. In this respect there is a perfect conformity between
the law of sensation, and that of muscular contraction ; for stimuli which ex-
cite the latter, usually lose their force in proportion to the frequency of their
repetition. Indeed, both may be considered as results of the more general
laws of vitality ; for the actions of other tissues follow the same rule, as is
shown by the tolerance, that may be gradually established in the system, of
medicinal agents, poisons, &c., which would have at first produced the most
violent effects, when given in the same amount.

513. It is curious, also, that the feelings of Pain or Pleasure, which unac-
customed sensations excite, are often exchanged for each other, when the sys-
tem is habituated to them ; this is especially the case, in regard to impressions
communicated through the organs of smell and taste. There are many arti-
cles in common use among mankind, — such as Tobacco, Fermented Liquors,
&c., the use of which cannot be said to produce a natural enjoyment, since
it is at first unpleasant to most persons ; and yet it first becomes tolerable,
then agreeable; and at last the want of them is felt as a painful privation, and
the stimulus must be applied in an increasing degree, in order to produce
the usual effect.

514. It is through the medium of Sensation, that we acquire a knowledge
of the material world around us; and that its changes excite mental operations
in ourselves. The various kinds or modes of Sensation excite in us various
ideas regarding the properties of matter ; and these properties are known to
us, only through the changes which they produce in the several organs. Thus
a man totally blind from birth can form no idea of the nature of light or co-
lours; nor could one completely deaf have any just conception of musical
tones. It is well known that instances exist, in which, from some imperfection
of the organization, there is an incapacity for distinguishing colours or musi-
cal tones, whilst there is no want of sensibility to light or sound ; and that
some persons are naturally endowed with a much greater range of the sen-
sory faculties, than others possess. Hence it does not seem at all improbable,
that there are properties of matter, of which none of our senses can take
immediate cognizance ; and which other beings might be formed to perceive,
in the same manner as we are sensible to light, sound, &c. Thus, it is well
known, that many animals are affected by atmospheric changes, in such a
manner, that their actions are regarded by Man as indications of the probable
state of the weather ; and the same is the case in a less degree with some
of our own species ; who are peculiarly susceptible of the same influences.
Now the most universal of all the qualities or propensities of matter, —
that, in fact, on which our notion of it is founded, — is resistance ; and
it is this quality, of which the knowledge seems most universally diffused
throughout the Animal kingdom. In the lowest tribes, we find that contact,
between their surface and some material body, is required to produce sensa-

33*

390 ON SENSATION, AND THE ORGANS OF THE SENSES.

tion ; and beings which cannot be made conscious, in this manner, of the
existence of something external to themselves, do not deserve to be ranked
in the Animal kingdom. Our difficulty lies (as heretofore remarked, § 1),
in ascertaining what are to be regarded, in such beings, as unequivocal indi-
cations of consciousness. Those animals which are fixed to one spot, can
have few other ideas of matter than this most general one ; but in those
which have the power of locomotion, the general sensibility of the surface
doubtless communicates to them some notion of the character of the body
over which they move, in the same manner as we learn it by passing the
hand over its exterior. We shall presently see, however, that the idea of
the shape of a body which we form from the touch, results from a very com-
plex process ; which animals of the lowest grade can scarcely be supposed
to exercise. There can be no doubt that, next to the mere sense of resistance,
sensibility to temperature is the most universally diffused through the Ani-
mal kingdom ; and probably the consciousness of luminosity is the next in
the extent of its diffusion. There is good reason to believe, from observation
of their habits, that many animals are susceptible of the influence, and are
directed by the' guidance of light ; whilst their organs are not adapted to re-
ceive true visual impressions, or to form optical images ; and such would
seem to be the function of the red spots, frequently seen on prominent parts
of Animalcules, the lower Articulata and Mollusca, and even of some Radiata.
Wherever these are of sufficient size to allow their structure to be examined,
they are found to be largely supplied with nerves, but to be destitute of the
peculiar organization which alone constitutes a true eye. The sense of Taste
may be considered as a refined modification of that of Touch ; and it is
probable that this exists very low down in the animal scale, being obviously
of great importance in the selection of food ; but the Anatomist has no means
of ascertaining where this refinement exists, and where it does not ; since the
organs of taste and touch are so similar. The sense of Hearing does not
seem to be distinctly present among the Invertebrate animals, except in such
as approach most nearly to the Vertebrata ; it is not improbable, however,
that sonorous vibrations may produce an effect upon the system of those ani-
mals which do not receive them as sound; and this would appear, from a
fact subsequently to be mentioned (§ 526), to be not improbably the case,
with regard especially to aquatic animals. The sense of Smell, which is con-
cerned with one of the least general properties of matter, appears to be the
least widely diffused among the whole; being only possessed in any high
degree by Vertebrated animals, and being but feebly present in a large pro-
portion of these.

515. Besides the various kinds of sensibility which have been just enume-
rated, there are others which are ordinarily associated together, along witli
the sense of material resistance (and its several modifications), and the sense
of temperature, under the head of Common Sensation ; but several of them,
especially those which originate in the body itself, can scarcely be regarded
in this light. Such are the feelings of Hunger and Thirst; that of Nausea;
that of distress resulting from suspended aeration of the blood ; that of " sink-
ing at the stomach," as it is vulgarly but expressively described, which results
from strong mental emotion ; that of the venereal excitement, and perhaps
some others. Now in regard to all these, it is impossible in the present state
of our knowledge to say, whether their peculiarity results from the particular
constitution of the nerves that receive and convey them, or only from a modi-
fication in the impressing causes, and in the mode in which they operate.
Thus we have no evidence that the nervous fibrils, which convey from the
lungs the sense of distress resulting from deficient aeration, may not be of a
different character from those which convey from the surface of the air-pas-

OF SENSATION IN GENERAL. 391

sages the sense of the contact of a foreign body. But as we know that all
the trunks, along which these peculiar impressions travel, do minister to ordi-
nary sensation, whilst the nerves of truly special sensation are not sensible
to common impressions, it is evident that the probability is in favour of the
identity of the fibres, which minister to these sensations, with those of the
usual sensory character. For the sense of temperature, however, it is not by
any means certain that a special set of fibres does not exist ; for many cases
are on record, in which it has been lost, whilst the ordinary sense of tact
remained ; and it is sometimes preserved, when the anesthesia is in other
respects complete.

516. With regard to all kinds of Sensation it is to be remembered, that the
change of which the mind is informed, is not the change at the peripheral
extremities of the nerves, but the change communicated to the sensorium ;
hence it results, that external agencies can give rise to no kind of sensation,
which cannot also be produced by internal causes, exciting changes in the
condition of the nerves in their course. This very frequently happens in
regard to the senses of sight and hearing ; flashes of light being seen, and
ringing sounds in the ears being heard, when no external stimulus has pro-
duced such impressions. The production of odorous and gustative sensations
from internal causes, is perhaps less common ; but the sense of nausea is
more frequently excited in this manner, than by the direct contact of the nau-
seating substance with the tongue or fauces. The various phases of common
sensibility often originate thus ; and it is an additional evidence in favour of
the distinctness of the fibres which convey the impressions of temperature,
that these are frequently affected, — a person being sensible of heat or of chil-
liness in some part of his body, without any real alteration of its temperature,
— whilst there is no corresponding affection of the tactual sensations. The
most common of the internal causes of these subjective sensations (as they
have been termed, in contradistinction to the objective, which result from a
real material object), is congestion or inflammation ; and it is interesting to
remark that this cause, operating through each nerve, produces in the senso-
rium the changes to which that nerve is usually subservient. Thus, conges-
tion in the nerves of common sensation gives rise to feelings of pain or un-
easiness ; but when occurring in the retina and optic nerve it produces flashes
of light; and in the auditory nerve it occasions "a noise in the ears." — It
may be observed, also, of some external causes, that they may excite changes
in the sensorium through several different channels ; and that in each case the
sensation is characteristic of the particular nerve, on which the impression is
made. Thus pressure, which produces through the nerves of common sensa-
tion the feeling of resistance, is well known to occasion, when exerted on the
eye, the sensation of light and colours ; and, when made with some violence
on the ear, to produce tinnitus aurium. It is not so easy to excite sensations
of taste and smell, by mechanical irritation ; and yet, as Dr. Baly* has shown,
it may readily be accomplished in regard to the former. The sense of nau-
sea may be easily produced, as is familiarly known, by mechanical irritation
of the fauces. The stimulus of Electricity still more completely possesses
the power of affecting all the sensory nerves, with the changes which are pe-
culiar to them; for, by proper management, an individual may be made con-
scious at the same time of flashes of light, of distinct sounds, of a phosphoric
odour, of a peculiar taste, and of pricking sensations, all excited by the same
cause, the effects of which are modified, according to the respective peculi-
arities of the instruments through which it operates. — But although there are
some stimuli which can produce sensory impressions on all the nerves of

* Translation of Muller's Physiology, p. 1062, note.

392 ON SENSATION, AND THE ORGANS OF THE SENSES.

sensation, it will be found that those, to which any one organ is peculiarly
fitted to respond, produce little or no effect upon the rest. Thus the ear can-
not distinguish the slightest difference between a luminous and a dark object.
A tuning-fork, which, when laid upon the ear whilst vibrating, produces a dis-
tinct musical tone, excites no other sensation when placed upon the eye than
a slight jarring feeling. The most delicate touch cannot distinguish a sub-
stance which is sweet to the taste from one which is bitter; nor can the taste
(if the communication between the mouth and the nose be cut off) perceive
anything peculiar in the most strongly odoriferous bodies.

517. It may hence be inferred that no nerve of special sensation can, by
any possibility, take on the function of another. How far the nerves of com-
mon sensation, can, under any circumstances, perform the offices usually
delegated to those of special sense, we are not yet in a condition to deter-
mine. Comparative Anatomy seems to show that, in the lowest animals in
which the rudiments of eyes can be detected, there is no distinction between
the nerves proceeding to these organs, and the rest ; and there would appear
some ground for the belief that, as in other cases, the special organs of sensi-
bility are gradually elaborated, in ascending the Animal scale, from the more
general apparatus, and are not merely superadded to it. Hence we may con-
ceive the possibility (though there is no proof of the fact) that states of the
system might occur, in which a change in the common sensory nerves might
produce the sensation of light, sound, &c. But it is quite impossible (so far
at least as our present knowledge of physical phenomena permits us to decide
upon the impossibility of anything) that distinct visual impressions should be
communicated to a nerve, except through the mediation of such an optical
instrument as the eye; or distinct sonorous impressions, except through such
an acoustic instrument as the ear. Hence we must receive with the greatest
caution the wonderful accounts of transference of sensation, many of which
have undoubtedly been the offspring of deception. Still it may be objected
that, since we are so totally destitute of real knowledge, as to the mode in
which vision is ordinarily produced by inverted images upon the retina, we
have no right to assert that it may not take place in some other way ; and
perhaps this objection should lead us to consider the phenomenon rather as
extremely improbable, than as impossible. But the improbability may be
compared to that of a stone ascending like a balloon, or a piece of lead float-
ing on the water ; for we have no more knowledge of the ultimate cause of
that which we term the force of Gravitation, than we have of the nature of
Sensation.

518. The peculiar aptitudes of the different Sensory nerves, to receive
and convey impressions of various kinds, must be regarded as the result of
properties inherent in themselves; just as we consider the difference between
the afferent nerves in general, and the motor nerves, to be one belonging to
their own constitution. But it is probable that there are also different locali-
ties in the Sensorium, in which the changes to which they give rise are per-
formed. This may be judged of from the fact, that the phenomena of sub-
jective sensation frequently originate in peculiar conditions of the encephalon

itself, and not in the nervous trunks or organs of sense ; thus, in dreaming,
we have frequently very vivid pictures of external objects presented to our
minds; and we sometimes distinctly hear voices and musical tones, or have
perceptions (though this is less common) of tastes and odours. The phe-
nomena of spectral illusions are very nearly connected with those of dream-
ing; both may be in some degree influenced by external causes, acting upon
the organs of sensation, which arc misinterpreted (as it were) by the mind,
owing to its state of imperfect operation ; but both also may entirely originate
in the central organs. There seems to be no difference, in the feelings of the

OF SENSATION IN GENERAL. 393

individual, between the sensations thus originating, and those which are pro-
duced in the usual manner ; for we find that, unless otherwise convinced by
their own reason, persons who witness spectral illusions believe as firmly in
the reality of the objects that come before their minds, as if the images of
those objects were actually formed on their retinte. This is another proof, if
any were wanting, that the organ of sense, and the nerve belonging to it, are
but the instruments by which certain changes are produced in the sensorium;
of which changes, and not of the immediate impression of the object, the
sensation really consists. It seems to be by an innate law of our constitution,
that these subjective sensations, whether originating in the central organs, or
in the course of the nervous trunks, should be referred by the mind to the
ordinary situations of the peripheral terminations of those nerves ; even
though these should not exist, or should be destitute of the power of receiv-
ing impressions. Thus after amputations, the patients are for some time
affected with sensations (originating probably in the cut extremities of the
nerves), which they refer to the removed extremities; the same has been
noticed in regard to the eye, as well when it has been completely extirpated,
as when its powers have been destroyed by disease. The effects of the
Taliacotian operation also exhibit the operation of this law in a curious man-
ner; for until the flap of skin, from which the new nose is formed, obtains
vascular and nervous connections in its new situation, the sensation produced
by touching it is referred to the forehead. Another interesting illustration of
it may be obtained by the following very simple experiment: — if the middle
finger of either hand be crossed behind the fore-finger, so that its extremity is
on the radial side of the latter, and the ends of the two fingers thus disposed
be rolled over a marble, pea, or other round body, a sensation will be pro-
duced, which, if unconnected by reason, would cause the mind to believe in
the existence of two distinct bodies ; this is due to the impression being made
at the same time upon the radial side of the fore-finger, and the ulnar side of
the middle finger, — two joints which, in the natural position, are at a con-
siderable distance.

519. The acuteness of particular sensations is influenced in a remarkable
degree by the attention they receive from the mind. If the mind be entirely
inactive, as in profound sleep, no sensation whatever is produced by ordinary
impressions ; on the other hand, when the mind is from any cause strongly
directed upon them, impressions very feeble in themselves produce sensations
of even painful acuteness. Every one knows how much a slight itching of
some part of the surface may be magnified, by the direction of the thoughts
to it; whilst as soon as they are forced by some stronger impression into ano-
ther channel, the irritation is no longer felt. Every one is aware how vividly
sounds are perceived, when they break in upon the stillness of the night; being
increased in strength, not only by the contrast, but by absorbing the whole
attention. An interesting experiment is mentioned by Miiller, which shows
how completely the mind may be unconscious of impressions communicated
to it by one organ of sense, when occupied, even without a distinct effort of
the will, by those received through another. If we look at a sheet of white
paper through two differently-coloured glasses at the same time — one being
placed before each eye, — the resulting sensation is seldom that of a mixture
of the colours : if the experiment be tried with blue and yellow glasses, for
example, we do not see the paper of an uniform green; but the blue is pre-
dominant at one moment, and the yellow at another ; or blue nebulous spots
may present themselves on a yellow field, or yellow spots on a blue field.
We perceive from this experiment, that the attention may not only be directed
to the impressions made on either retina, to the complete exclusion of those of

394 ON SENSATION, AND THE ORGANS OF THE SENSES.

the other, but it may be directed to those made on particular spots of either.
This may be noticed, again, in the process by which we make ourselves ac-
quainted with a landscape or a picture ; if our attention be directed to the whole
field of vision at once, we see nothing distinctly ; and it is only by abstracting
ourselves from the contemplation of the greater part of it, and by directing
our attention to smaller portions in succession, that we can obtain a definite
conception of the details. The same is the case in regard to auditory impres-
sions ; and here the power of attention, in causing one sensation or series of
sensations to predominate over others which are really more intense, is often
most remarkably manifested. When we are listening to a piece of music
played by a large orchestra, for example, we may either attend to the combined
effect of all the instruments, or we may single out any one part in the har-
mony, and follow this through all its mazes; and a person with a practised ear
(as it is commonly but erroneously termed, it being not the ear but the mind
that is practised), can even distinguish the sound of the weakest instrument
in the whole band, and can follow its strain through the whole performance.
This attention to a single element can only be given, however, by withdrawing
the mind from the perception of the rest ; and a musician who thus listens,
will have very little idea of the rest of the harmonic parts, or of the general
effect. In fact, when the mind is thus directed, by a strong effort of the will,
into a particular channel, it may be almost considered as unconscious quoad
any other impressions.

520. The effects of this principle are manifested in regard to the sensations
which originate within the system ; as well as in respect to those which are
excited by external impressions. Every one is aware how difficult it is to
keep the body perfectly quiescent,* especially when there is a particular mo-
tive for doing so, and when the attention is strongly directed to the object.
This is experienced even whilst a Photogenic likeness is being taken, when
the position is chosen by the individual, and a support is adapted to assist
him in retaining it; and it is still more strongly felt by the performers in the
Tableaux Vivans, who cannot keep up the effort for more than three or four
minutes. Now it is well known that, when the attention is strongly directed
to an entirely different object (when we are listening, for example, to an elo-
quent sermon, or an interesting lecture), the body may remain perfectly mo-
tionless for a much longer period ; the uneasy sensations, which would other-
wise have occasioned the individual to change his position, not being felt; but
no sooner is the discourse ended, than a simultaneous movement of the whole
audience takes place, everyone then becoming conscious of some discomfort,
which he seeks to relieve. This is the case, also, in regard to the respiratory
sensation ; in general it may be observed, that the usual reflex movements are
not enough for the perfect aeration of the blood, and that a more prolonged
inspiration prompted by an uneasy feeling, takes place at intervals ; but under
such circumstances as those just alluded to, this feeling is not experienced, until
the attention ceases to be engaged by a more powerful stimulus, and then it
manifests itself by the deep inspirations which accompany, in almost every
individual, the general movement of the body.

521. It is curious that the constant direction of the attention to internal
sensations of a subjective kind, should sometimes occasion actual disorder of
the parts to which these sensations are referred ; and yet this seems the only
way of accounting for some of the phenomena of disease. Sometimes the
cause of the sensation may exist in the trunk of the nerve, in some part of its
course; whilst in other instances, it may be confined to the sensorium. Pain

* Of course the movements of respiration niul winking are left out of the question.

SENSE OF TOUCH. 395

of the testicle, for example, may be occasioned by irritation having its seat
in the lower part of the spine, the organ itself being perfectly sound ; yet if
that pain continue, it may become diseased. The following are some very
interesting remarks on this subject, from the able pen of Dr. Holland.*
" There is cause to believe the action of the heart to be quickened or other-
wise disturbed, by the mere centering of consciousness upon it, without any
emotion or anxiety." This is especially the case where its impulses are
irregular, or are so- loud as to be audible. "The same may be said of the
parts concerned in respiration. If this act be expressly made the subject of
consciousness, it will be felt to undergo some change; generally to be retarded
at first, and afterwards quickened." " The act of swallowing is manifestly
rendered more difficult, by the attention being fixed upon it ; and the same
cause will often be found to render articulation less distinct, especially when
there exists already some impediment to the function. A similar direction of
consciousness to the region of the stomach, creates in this part a sense of
weight, oppression, or other less definite uneasiness ; and, when the stomach
is full, appears greatly to disturb the due digestion of the food. The state
and action of the bowels are much influenced by the same cause." A pecu-
liar sense of weight and restlessness approaching to cramp, is felt in a limb,
to which the attention is particularly directed. " The attention concentrated,
for so by an effort of will it may be, on the head or sensorium, gives certain
feelings of tension and uneasiness, caused possibly by some change in the
circulation of the part ; though it may be an effect, however difficult to be
conceived, on the nervous system itself. Persistence in this effort, which is
seldom indeed possible beyond a short time without confusion, produces results
of much more complex nature, and scarcely to be defined by any common terms
of language." These phenomena have an evident affinity, on the one hand,
with the exaltation of external or objective sensations, to which the attention
is peculiarly directed ; and on the other with those of several morbid condi-
tions. The explanation of them all is probably to be sought in some change
in the circulation of the part, to which the sensation is referred. Thus the
hypochondriac patient, "in fixing his consciousness with morbid intentness on
certain organs, creates not merely disordered sensations, but often also disor-
dered actions in them. There may be palpitation of the heart, hurried or
choked respiration, flatulence and other distress of stomach, irritation of the
bladder ; all arising from this morbid direction of attention to the organs in
question." In hysteria, again, " the instances are frequent, of attacks brought
on by the mere expectation of them ; or by irritation ; or occasionally even a
sort of morbid solicitation of the organs to these singular actions." These
facts go a long way to explain the phenomena of Mesmerism, many of which
are obviously to be referred to the exaggerated operation of the same principle.
(See Appendix.) — We now proceed to consider in more detail the functions of
the several Organs of the Senses, and shall commence with that of the most
general character.

2. Sense of Touch.

522. By the sense of Touch, as commonly understood, is meant that mo-
dification of the common sensibility of the body, of which the Cutaneous sur-
face is the especial seat. It derives its peculiar power simply from the large
amount of sensory nervous fibres, which are distributed in its substance; and
especially through the terminations (or rather the origins) of these in the pa-
pillae, which are little elevations of the surface of the cutis, easily perceptible

* Medical Notes and Reflections, Chap. v.

396

ON SENSATION, AND THE ORGANS OF THE SENSES.

Fig. 162.

Capillary net-work at margin of
lips.

by the aid of a lens, and each chiefly composed of a vascular loop overlapping

the extremity of the nervous fibril. The pre-
cise arrangement of the nerve-fibres in the cuta-
neous papillae, has not been indisputably ascer-
tained ; but the opinion that they form loops
(Fig. 119) is the one most generally adopted.
The number of these papillae within any given
area, pretty closely corresponds with the degree
of sensibility of that part of the surface ; thus
we find them most abundant on the hands, es-
pecially towards the points of the fingers, and
on the lips and tongue. In some animals, es-
pecially those of the Feline tribe, the long vi-
brissse (commonly termed whiskers) evidently
minister to sensation; and it has been demonstrated that their pulps are
largely supplied with nerves from the fifth pair. Some interesting observa-
tions have been made by Prof. Weber, on the sensibility of different parts of
the skin. His mode of ascertaining this, was to touch the surface with the
legs of a pair of compasses, the points of which were guarded with pieces of
cork ; the eyes being closed at the time, the legs were approximated to each
other, until they were brought within the smallest distance, at which they
could be felt to be distinct from one another. The following are some of the
results of the experiments. With the extremities of the fingers and the
point of the tongue, the distance could be distinguished most easily in the
longitudinal direction ; on the dorsum of the tongue, the face, neck, and ex-
tremities, the distance could be recognized best when the points were placed
transversely.

5 of a line
tj of a line
1 line

Point of middle finger .
Point of tongue

Palmar surface of third finger

Red surface of lips . . 2 lines

Palmar surface of middle finger 2 „

Dorsal surface of third finger 3 „

Tip of the nose ... 3

Dorsum and edge of tongue 4

Part of lips covered by skin 4

Palm of hand ... 5

Skin of cheek ... 5

Extremity of great toe . . 5

Hard palate ... 6

Dorsal surface of forefinger . 7

Dorsum of hand , 8

Mucous Membrane of gums
Lower part of forehead .
Lower part of occiput
Back of hand .
Neck, under lower jaw .
Vertex ....
Skin over Patella
Sacrum

acromion

Dorsum of foot
Skin over sternum .
Skin beneath occiput
Skin over spine, in back
Middje of the arm .
thigh

9 lines

10 „

12 „

14 „

15 „

15 „

16 „
18 „
18 „
18 „
20 „
24 „
30 „
30 „
30

It is curious that the distance between the legs of the compasses seemed to
be greater (although really so much less), when it was felt by the more sensi-
tive parts, than when it was estimated by parts of less distinct sensibility. As
a general fact, it seems that the sensibility of the trunk is greater on the me-
dian line, both before and behind, and less at the sides. Differences of tem-
perature, and the weight of bodies, were, according to Prof. Weber's observa-
tions, most accurately recognized at the parts, which were determined to be
most sensible by the foregoing method of inquiry.

523. As already stated(§ 514), the only idea communicated to our minds by
the sense of Touch, when exercised in its simplest form, is that of Resistance;
but when the sensory surface and the substance touched are made to change
their place in regard to each other, we obtain the additional notion of Extension
or Space. By the various degrees of resistance which the sensory surface
encounters, we estimate the hardness or softness of the body; but in this we

SENSE OF TOUCH. 397

are assisted by the muscular sense (§ 433), which makes us conscious of the
degree of pressure we are employing. By the impressions made upon the
papillae, during the movement of the tactile surface over that which is being
examined, the roughness, smoothness, or other peculiar characters, of the lat-
ter are estimated. Our knowledge of form, however, is a very complex pro-
cess, requiring not merely the exercise of the sense of touch, but also great
attention to the muscular sensations. It is chiefly, as formerly remarked, in
the variety of movements of which the hand of Man is capable, that it is
superior to that of any other animal ; and it cannot be doubted that this affords
a very important means of acquiring information in regard to the external
world, and especially of correcting many vague and fallacious notions, which
we should derive from the sense of Sight, if used alone. On the other hand,
it must be confessed, that our knowledge would have a very limited range, if
this sense were the only medium, through which we could acquire ideas. It
is probably on the sensations communicated through the touch, that the idea
of the material world, as something external to ourselves, chiefly rests ; but
this idea is by no means a direct result of these sensations, being rather an
instinctive or intuitive perception excited by them. Every person who directs
the least attention to the subject must perceive, how completely different are
those notions of the primary or elementary properties of matter, which we
base upon the information thus communicated to us, from the sensations them-
selves ; and, as Dr. Alison has justly remarked, "a decisive proof of this being
the true representation of this part of our mental constitution, is obtained by
attending to the idea of extension or space ; which is undoubtedly formed
during the exercise of the sense of touch ; and is no sooner formed, than it
'swells in the human mind to Infinity,' to which certainly no human sensation
can bear any resemblance."

524. That the conditions under which certain of the modifications of com-
mon sensation operate, are in some respects different from those of ordinary
Touch, is very easily shown. Thus, the feeling of tickling is excited most
readily in parts, which have the least tactual sensibility, — the armpits, flanks,
and soles of the feet ; whilst in the points of the fingers it cannot be excited.
Moreover, the nipple is very moderately endowed with ordinary sensibility ;
yet by a particular kind of irritation, a very strong feeling may be excited
through it. Again, in regard to temperature, it is remarked by Weber, that
the left hand is more sensitive than the right ; although the sense of touch is
undoubtedly the most acute in the latter. He states that, if the two hands,
previously of the same temperature, be plunged into separate basins of warm
water, that in which the left hand is immersed will be felt as the warmest,
even though its temperature is somewhat lower than that of the other. In
regard to the sensations of heat and cold, he points out another curious fact, —
that a weaker impression made on a large surface, seems more powerful than
a stronger impression made on a small surface ; thus, if the forefinger of one
hand be immersed in water at 104°, and the whole of the other hand be
plunged in water at 102°, the cooler water will be thought the warmer;
whence the well-known fact, that water in which a finger can be held, will
scald the whole hand. Hence it also follows, that minute differences in tem-
perature, which are imperceptible to a single finger, are appreciated by plung-
ing the whole hand into the water ; in this manner, a difference of one-third
of a degree may readily be detected, when the same hand is placed succes-
sively in two vessels. The judgment is more accurate, when the temperature
is not much above or below the usual heat of the body; just as sounds are
best discriminated, when neither very acute nor very grave.

525. The improvement in the sense of Touch, in those persons whose de-
pendence upon it is increased by the loss of other senses, is well known ; this

34

398 ON SENSATION, AND THE ORGANS OF THE SENSES.

is doubtless to be in part attributed (as already remarked) to the increased
attention which is given to the sensations, and in part to an increased develop-
ment of the tactile organs themselves, resulting from the frequent use of them.
The case of Saunderson, who, although he lost his sight at two years old, be-
came Professor of Mathematics at Cambridge, is well known ; amongst his
most remarkable faculties, was that of distinguishing genuine medals from
imitations, which he could do more accurately than many connoisseurs in full
possession of their senses. The process of the acquirement of the power of
recognizing elevated characters by the touch, is a remarkable example of this
improveability. When a blind person first commences learning to read in this
manner, it is necessary to use a large type ; and every individual letter must
be felt for some time, before a distinct idea of its form is acquired. After a
short period of diligent application, the individual becomes able to recognize
the combinations of letters in words, without forming a separate idea of each
letter ; and can read line after line, by passing the finger over each, with con-
siderable rapidity. Now when this power is once thoroughly acquired, it is
found that the size of the type may be gradually diminished ; and this seems
to indicate, that the sensations themselves are rendered more acute, by the
frequent application of them in this direction. As an instance of the correct
notions which may be conveyed to the mind, of the forms and surfaces of a
great variety of objects, and of the sufficiency of these notions for accurate
comparison, the Author may mention the case of a blind friend of his own,
who has acquired a very complete knowledge of Conchology, both recent and
fossil ; and who is not only able to recognize every one of the numerous spe-
cimens in his own Cabinet, but to mention the nearest alliances of a Shell
previously unknown to him, when he has thoroughly examined it by his
touch. Many instances are on record, of the acquirement, by the blind, of
the power of distinguishing the colours of surfaces, which were similar in
other respects ; and, however wonderful this may seem, it is by no means
incredible. For it is to be remembered that the difference of colour depends
upon the position and arrangement of the particles composing the surface,
which render it capable of reflecting one ray whilst it absorbs all the rest ; and
it is quite consistent with what we know from other sources, to believe that
the sense of Touch may become so refined, as to communicate a perception
of such differences.

526. The examples of peculiar acuteness of this sense, which we occa-
sionally meet witn among the lower animals, are very interesting, when
viewed in connection with its improveability in Man. It was found by Spal-
lanzani, that Bats, when deprived of sight, and (as far as possible) of hearing
and smelling also, still flew about with equal certainty and safety, avoiding
every obstacle, passing through passages only just large enough to admit them,
and flying about places previously unknown, with the most unerring accuracy,
and without coming into collision with the objects near which they passed.
He also stretched threads in various directions across the apartment, with the
same result. So astonished was he at these curious facts, that he was led to
attribute the phenomenon to the possession of a sixth sense, unknown to Man.
Cuvier was the first to appreciate the real value of these experiments, as afford-
ing a proof of the existence of the most exquisite tactile sensibility, over the whole
surface of the flying membrane ; the naked surface and delicate structure of
which, appear well adapted to constitute the seat of so important a function.
From this view, tberefore, it would appear that it is by means of the pulsation of
the wings on the air, that the propinquity of solid bodies is perceived, through
the manner in which the air reacts on their surface. It is curious that the
instance which (so far as we at present know) is most analogous to this,
should be met with among the inhabitants of the deep. It is a fact well

SENSE OF TASTE.

399

known to Whale-fishers, especially to those who pursue the Spermaceti
Whale, that these animals have the power of communicating with each other
at great distances. It has often been observed, for example, that when a
straggler is attacked, at the distance of several miles from a shoal, a number
of its fellows bear down to its assistance, in an almost incredibly short space
of time. It can scarcely be doubted, then, that the communication must be
made through the medium of the vibrations of the water, excited by the
struggles of the animal, or perhaps by some peculiar movements especially
designed for this purpose, and propagated through the fluid to the large cuta-
neous surface of the distant Whales ; and this idea is fully confirmed by
the fact, that the nerves which proceed to the skin, pass through the inner
layers of blubber with scarcely any subdivision, but spread out into a net-
work of extreme minuteness, as soon as they arrive at the surface.

3. Sense of Taste.

527. That this sense may be really considered as a peculiar modification
of that of Touch, appears from several considerations. In the first place, the
actual contact of the object of sense, with the organ through which the im-
pression is received, is here necessary ; and this is the case in regard to no
other sense. Moreover the intimate

structure of the organ is nearly the [Fig. 163.

same in both instances. Again, it ap-
pears from the considerations formerly
alluded to (§ 407), that there is no
special nerve of taste ; the gustative
impressions made upon the front of
the tongue, being conveyed by the
lingual branch of the fifth pair ; whilst
those made upon the back of the organ,
are conveyed by the glosso-pharyngeal.
The first of these nerves also ministers
to ordinary tactile sensibility ; the se-
cond appears to convey the impres-
sions which produce nausea. The
papillae of the Tongue are essentially
the same in structure with those of
the Skin ; but many of them are of a
peculiarly complex nature.

a. The characters of the papillae of the
tongue have recently undergone a very careful
examination by Messrs. Todd and Bowman
(Physiological Anatomy, Chap. xv.). They
may be divided, in the first place, into the
simple and the compound; the former of which
had previously escaped observation, through
not forming any apparent projection. — The
Simple papillae are scattered in the intervals of
compound, over the general surface of the
tongue ; and they occupy much of the surface
behind the circumvallate variety, where no
compound papillae exist. They are com- Tongue, seen on iis upper surface: a. One of
pletely buried and concealed beneath the the circumvallate papillae, b. One of the fungi-
continuous sheet of epithelium, and can only form papilte. Numbers of the conical papillae
be detected, when this membrane has been are seen about rf, and elsewhere, e. Glottis, epi-
removed by maceration; they are then found 'glottis, and glosso-epiglottidean folds of mucous

membrane.— From Sffimmering.]

400

ON SENSATION, AND THE ORGANS OF THE SENSES.

to have the general characters of the cutaneous papillse, but nerve-tubes have not yet been
detected in them.

[Fig. 164.

Simple papillae near the base of the tongue:— A. a, concealed under the epithelium'; 6, uncovered by
it.— Magnified 10 diameters. B. a. Arterial twig, supplying their capillary loop?, v. Vein. The vessels
are all contained within the line 6, 6, of basement membrane, c, c. Deeper epithelial particles resting
on the basement membrane, d. Scaly epithelium on the surface. The granular interior of the papilla;
is represented at e. c. Papillae in which the basement membrane is not visible; and the deep layer of
epithelium seems to rest on the capillary loop.— Magnified 200 diam ]

[Fig. 165.

Vertical section of one of the circumvallate
papillce :— o. Central part. 6, b. Border, c, c.
Fissure between centre and border. The se-
condary papillae are seen covered by the epi-
thelium. Similar papilla? are seen, d, d, on the
membrane beyond.— Magn. S diam.]

[Fig. 1G6.

A. Compound papillae on the side of the foramen caecum, injected:— a, a. Arterial twigs, v, v. Veins.
The capillary loops indicate the simple papilla; ; in one of which, b, the injected matter has been extra-
vasated witliin the basement membrane of the papillx, the outline of which is thus distinguished, c.
Capillary plexus, where no papillaj exist, e, e. External surface of the epithelium of the papilla.—
Magn. 15 diam.

B. One of the simple papilte of A :— a, i>, v. Arterial and venous sides of the capillary loops. b,b.
Basement membrane, d. Deeper epithelial particles resting on the basement membrane, s. Scaly epi-
thelium on the surface.— Magnified 300 diameters.]

SENSE OF TASTE.

401

Fig. 167.

b. The Compound papillcr are visible to the naked eye ; and have been classified, accord-
ing to their shape, into the circumvallate, the fungiform, and the filiform. — The Circumvnl-
late or calyciform papillae are eight or ten in number, and are situated in a V-shaped line
at the base of the tongue. Each consists of a central flattened circular projection of the
mucous membrane, surrounded by a tumid ring of about
the same elevation, from which it is separated by a narrow
circular fissure. The surface of both centre and border
is smooth, and invested by scaly epithelium, which con-
ceals a multitude of simple papilla?. — The Fungiforrn pa-
pilke are scattered singly over the tongue, chiefly upon its
sides and tip. They project considerably from the surface,
and are usually narrower at the base than at their summit.
They contain a complex capillary plexus, the terminal
loops of which enter the numerous simple papillae that
clothe the surface of the fungiform body. They contain
nerve-tubes, in which a looped arrangement can be traced ;
and the epithelium which covers them is so thin, as to allow
the red colour of the blood to be seen through it. In this
manner they are readily distinguished from the filiform pa-

Capillary net- work of fungiform
papilla of the tongue.

pilla?, among which they lie. — The Filiform papilte, like the preceding, contain a plexus of

ig. 168.

v

A. Fungiform papilla, showing the secondary papillae on its surface, and at a its epithelium covering
them over.— Magnified 35 diameters.

B. Another, with the capillary loops of its simple papillae injected, a. Artery, v. Vein. The groove
around the base of some of the fungiform papillae is here represented, as well as the capillary loops, c, c,
of some neighbouring simple papillae.— Magnified 18 diameters.]

capillaries, and a bundle of nerve-fibres, both terminating in loops, which enter the simple
papillas that clothe the surface of the compound body; but instead of being covered with
a thin scaly epithelium, they are furnished with bundles of long pointed processes, some of
•which approach hairs in their stiffness and structure. These are immersed in the mucus of
the mouth, and may be moved in any direction, though they are generally inclined back-
wards.

[Fig. 169.

Various forms of the conical compound papillae deprived of their epithelium: — a, b, and especially c,
are the best marked, and were provided with the stiffest and longest epithelium; their simple papillae
are more acuminated, d, approaches the fungiform variety : e.f, come near the simple papillae.— Mag-
nified 20 diameters.]

34*

402

ON SENSATION, AND THE ORGANS OF THE SENSES.

c. The Simple papillae which occur in an isolated manner, with those which are aggre-
gated in the Circum valla te and Fungiform bodies, doubtless minister to the sense of Taste;
but there seems much reason to coincide in the opinion of Messrs. Todd and Bowman, with
regard to the different office of the Filiform papillse. " The comparative thickness of their

[Fig. 170.

A. Vertical section near the middle of the dorsal surface of the tongue : — a, a. Fungiform papillae. 6.
Filiform papillae, with their hair-like processes, c. Similar ones deprived of their epithelium.— Magni-
fied 2 diameters.

B. Filiform compound papillae :— a. Artery, v. Vein. c. Capillary loops of the secondary papilla1.
b. Line of basement membrane, d. Secondary papillae, deprived of e, e, the epithelium. /. Hair-like
processes of epithelium capping the simple papilla?.— Magnified 25 diameters, g. Separated nucleated
particles of epithelium, magnified 300 diameters.

1, 2. Hairs found on the surface of the tongue. 3, 4, 5. Ends of hair-like epithelial processes, showing
varieties in the imbricated arrangement of the particles, but inall a coalescence of the particles towards
the point. 5> encloses a soft hair.— Magnified 160 diameters.]

protective covering, the stiffness and brush-like arrangement of their filamentary productions,
their greater development in that portion of the dorsum of the tongue which is chiefly em-
ployed in the movements of mastication, all evince the subservience of these papilla? to the
latter function, rather than to that of taste; and it is evident that their isolation and partial
mobility on one another, must render the delicate touch with which they are endowed, more
available in directing the muscular actions of the organ. The almost manual dexterity of the
organ, in dealing with minute particles of food, is probably provided for, as far as sensibility
conduces to it, in the structure and arrangement of these papillre." It may be added, that
the filiform papillre of Man seem to be the rudimentary forms of those homy epithelial pro-
cesses, which acquire so great a development in the tongues of the Carnivora, and which are
of such importance in the abrasion of their food.

SENSE OF TASTE.
[Fig. 171.

403

A. Secondary papilla of the conical class, treated with acetic acid: — a. Its basement membrane, b.
Its nerve-tube forming a loop. c. Its curly elastic tissue. The epithelium in this instance is not abund-
ant; but the vertical arrangement of its particles over the apex of the papilla is well seen, d, and illus-
trates the mode of formation of the hair-like processes described in the test. — Mag. 160 diam.

B. A similar papilla, deprived of its epithelium : — a. Basement membrane. 6. Tubular fibre, probably
forming a loop, but its arch not clearly seen, c, c. Elastic fibrous tissue at its base and in its interior. —
Magnified 320 diameters.

c. Nerves of a compound papilla near the point of the tongue, in which their loop-like arrangement is
distinctly seen.— Magnified 160 diameters.]

528. As a general rule, it is a necessary condition of the sense of Taste,
that the object should either be in a state of solution, or should be soluble in
the moisture covering the tongue ; if this be not the case, or if the tongue be
dry, a simple feeling of contact is all that is produced. As in the case of
touch, the idea of the character of the sapid body is very imperfect, unless it
is made to move over the gustative surface ; and thus the taste is very much
heightened, by the compression and friction of the substance between the
tongue and the palate. From all these circumstances it appears indisputable,
that a very strong analogy exists between Taste and Touch ; indeed it may
be questioned, whether they are not in reality more closely allied, than is the
sense of Temperature with that of Resistance.

529. Although the Tongue seems to be the chief seat of Gustative sensi-
bility, yet this is also possessed, though in a less degree, by the palate. But
it is to be remarked that the sensations produced by most sapid substances
are of a complex kind; and are in great part due to the organ of Smell. Of
this any one may convince himself, by closing the nostrils, and inspiring and
expiring through the mouth only, when holding in the mouth, or even rub-
bing between the tongue and the palate, some sapid substance ; of which the
taste is then scarcely recognized, although it is immediately perceived, when
its effluvia are drawn into the nose. It is well known too, that, when the

404 ON SENSATION, AND THE ORGANS OF THE SENSES.

sensibility of the Schneiderian membrane is blunted by inflammation (as in
an ordinary cold in the head), the power of distinguishing flavours is very
much diminished. In fact, some Physiologists are of opinion that all our
knowledge of the flavor of sapid substances is received through the Smell ;
and this is not improbably true : but it is to be remembered, that, besides
flavor, a sapid body may excite various other sensations, as those of irritation
and pungency ; and of these, it seems to be the true function of the sensory
surface of the mouth, to take cognizance. Such sensations are evidently not
far removed from those of ordinary touch ; and correspond with those which
may be excited in the nostrils, through the medium of the Fifth pair. Taken
in its ordinary compound acceptation, the sense of Taste has for its object to
direct us in the choice of food, and to excite the flow of the mucus and saliva,
which are destined to aid in the preparation of the food for Digestion. Among
the lower Animals, the instinctive perceptions connected with this sense are
much more remarkable than our own ; thus an omnivorous Monkey will
seldom touch fruits of a poisonous character, although their taste may be
agreeable ; and animals, whose diet is restricted to some one kind of food,
will decidedly reject all others. As a general rule, it may be stated, that
substances of which the taste is agreeable to us, are useful in our nutrition ;
and vice versa: but there are many signal exceptions to this.

530. Like other senses, that of Taste is capable of being rendered more
acute by education ; and this on the principles already laid down in regard to
touch. The experienced wine-taster can distinguish differences in age, purity,
place of growth, &c., between liquors that to ordinary judgments are alike ;
and the epicure can give an exact determination of the spices that are com-
bined in a particular sauce, or of the manner in which the animal, on whose
flesh he is feeding, was killed. As in the case of other senses, moreover,
impressions made upon the sensory surface remain there for a certain period :
and this period is for the most part longer than that which is required for
the departure of the impressions made upon the eye, the ear, or the organ of
smell. Every one knows how long the taste of some powerful substances
remains in the mouth ; and even of those which make less decided impres-
sions, the sensation remains to such a degree that it is difficult to compare
them at short intervals. Hence if a person be blindfolded, and be made to
taste substances of distinct, but not widely different flavours (such as various
kinds of wine or of spirituous liquors), one after another in rapid succession,
he soon loses the power of discriminating between them. In the same man-
ner, the difficulty of administering very disagreeable medicines may be some-
times got over, by either previously giving a powerful aromatic, or by com-
bining the aromatic with the medicine ; its strong impression in both cases
preventing the unpleasant taste from exciting nausea.

4. Sense of Smell.

531. Of the nature of Odorous emanations, the Natural Philosopher is so
completely ignorant, that the Physiologist cannot be expected to give a defi-
nite account of the mode, in which they produce sensory impressions. Al-
though it may be surmised that they consist of particles of extreme minuteness,
dissolved as it were in the air, and although this idea seems to derive confir-
mation from the fact that most odorous substances are volatile, and vice versa,
— yet the most delicate experiments have failed to discover any diminution in
weight, in certain substances (as musk) that have been impregnating with their
effluvia a large quantity of air for several years ; and there are some volatile
fluids, such as water, which are entirely inodorous. The true Olfactory
nerves pass down from the Olfactory Ganglion (§ 422) in the form of very

SENSE OF SMELL.

405

numerous minute threads, which form a plexus upon the surface of the
Schneiderian or Pituitary membrane. Nothing satisfactory is known in re-
gard to their ultimate arrangement ; but it is probable that they form loops,

Fig. 172.

The Olfactory nerve, with its distribution on the septum nasi. The nares have been divided by a longi-
tudinal section made immediately to the left of the septum, the right nares being preserved entire. 1.
The frontal sinus. 2. The nasal bone. 3. The crista galli process of the ethmoid bone. 4. The sphe-
noidal sinus of the left side. 5. The sella turcica. G. The basilar process of the sphenoid and occipital
bones. 7. The posterior opening of the right nares. S. The opening of the Eustachian tube in the upper
part of the pharynx. 9. The soft palate, divided through its middle. 10. Cut surface of the hard palate.
a. The olfactory peduncle, b. Its three roots of origin, c. Olfactory ganglion, from which the filaments
proceed that spread out in the substance of the pituitary membrane, d. The nasal nerve, a branch of
the ophthalmic nerve, descending into the left nares from the anterior foramen of the cribriform plate, and
dividing into its external and internal branch, e. The naso-palatine nerve, a branch of the spheno-pala-
tine ganglion distributing twigs to the mucous membrane of the septum nasi in its course to (/) the ante-
rior palatine foramen, where it forms a smali gangliform swelling (Cloquet's ganglion) by its union with
its fellow of the opposite side. g. Branches of the naso-palatine nerve to the palate, h. Posterior pala-
tine nerves, i, i. The septum nasi.

similar to those of the cutaneous nerves. It would appear that every part of
the Schneiderian membrane is not equally endowed with the faculty of dis-
tinguishing odours, which is a very different power from that of becoming
sensible of irritation from them. The Olfactory nerves cannot be traced to
the membrane covering the middle and inferior spongy bones, or to that which
lines the different sinuses, these parts of the surface being supplied by the
Fifth pair only ; and it is a matter of common experience, that we cannot dis-
tinguish faint odours, unless, by a peculiar inspiratory effort, we draw the air
charged with them to the upper part of the nose. In animals living in the
air, it is a necessary condition of the exercise of the sense of Smell, that the
odorous matter should be transmitted by a respiratory current through the
nostrils; and that the membrane lining these should be in a moist state.
Hence, by breathing through the mouth, we may avoid being affected by
odours even of the strongest and most disagreeable kind; and in the first stage
of a catarrh, when the ordinary mucous secretion is suspended, the sense of
smell is blunted from this cause, as it afterwards is from the excess in the
quantity of the fluid, which prevents the odoriferous effluvia from coming
into immediate relation with the sensory extremities of the nerves. Hence
we may easily comprehend, that section of the Fifth pair, which exercises a

406 ON SENSATION, AND THE ORGANS OF THE SENSES.

considerable control over the secretions, will greatly diminish the acuteness of
the smell ; and it will have the further effect of preventing the reception of
any impressions of irritation from acrid vapours, which are entirely different
in their character from true odorous impressions, and which are not trans-
mitted through the Olfactory nerve (§ 441). The nasal passages may indeed
be considered as having, in the air-breathing Vertebrata, two distinct offices ;
they constitute the organ of smell, through the distribution of the olfactory
nerve upon a part of their surface; but they also constitute the portals of the
respiratory organs, having for their office to take cognizance of the aeriform
matter which enters them, and to give warning of that which would be inju-
rious ; this latter function is performed by the Fifth pair, as by the Par Vagum
in the glottis. It is through this nerve, that the act of sneezing is excitable :
the evident purpose of which, is the ejection of a strong blast of air through
the nasal passages, in such a manner as to drive out any offending matter
they may contain.

532. The importance of the sense of Smell among many of the lower
Animals, in guiding them to their food, or in giving them warning of danger
and also in exciting the sexual feelings, is well known. To Man its utility
is very subordinate under ordinary circumstances ; but it may be greatly in-
creased when other senses are deficient. Thus, in the well-known case of
James Mitchell, who was deaf, blind and dumb, from his birth, it was the
principal means of distinguishing persons, and enabled him at once to per-
ceive the entrance of a stranger. It is recorded that a blind gentleman, who
had an antipathy to cats, was possessed of a sensibility so acute in this re-
spect, that he perceived the proximity of one that had been accidentally shut
up in a closet adjoining his room. Among Savage tribes, whose senses are
more cultivated than those of civilized nations, more direct use being made of
the powers of observation, the scent is almost as acute as in the lower Mam-
malia; it is asserted by Humboldt, that the Peruvian Indians in the middle of
the night can thus distinguish the different races, — whether European, Ameri-
can-Indian, or Negro.* The agreeable or disagreeable character assigned to
particular odours, is by no means constant amongst different individuals.
Many of the lower Animals pass their whole lives in the midst of odours,
which are to Man (in his civilized condition at least) in the highest degree
revolting ; and will even refuse to touch food, until it is far advanced in pu-
tridity. It more frequently happens in regard to odours and savours, than
with respect to other sensory impressions, that habit makes that agreeable,
and even strongly relished, which was at first avoided; the taste of the epi-
cure for game that has acquired ihefumet, — for olives, — for assafoetida, &c.,
are instances of this. As to the length of time, during which impressions
made upon the organ of smell remain upon it, no certain knowledge can be
obtained. It is difficult to say that the effluvia have been completely removed
from the nasal passages ; since it is not improbable that the odorous particles
(supposing such to exist) are absorbed or dissolved by the mucous secretion ;
it is probably in this manner that we may account for the fact, well known to
every medical man, that the cadaverous odour is frequently experienced for
days after a post-mortem examination.t

The author has been assured by a competent witness, that a lad in the state of Som-
nambulism, had his sense of smell so remarkably heightened, as to be able to assign (with-
out the least hesitation) a glove placed in his hand, to its right owner, — in the midst of
about thirty persons, the boy himself being blindfolded.

f This may partly be attributed also to the effluvia adhering to the dress. It has been
remarked that dark cloths retain these more strongly than light.

SENSE OF VISION. 407

5. Sense of Vision.

533. The objects of this sense are bodies, which are either in themselves
luminous, or which become so by reflecting the light that proceeds from others.
"Whether their light is transmitted by the actual emission of rays, or by the
propagation of undulations analogous to those of sound, is a j^iestion at pre-
sent keenly debated amongst Natural Philosophers ; but it is of little conse-
quence to the Physiologist, which is the true solution ; since it is only with
the laws, which actually regulate the transmission of light, that he is concerned.
These laws it may be desirable here briefly to recapitulate.

534. Every point of a luminous body sends off a number of rays, which
diverge in every direction, so as to form a cone, of which the luminous point
is the apex. So long as these rays pass through a medium of the same dens-
ity, they proceed in straight lines ; but, if they enter a medium of different
density, they are refracted or bent. — towards the perpendicular to the surface
at the point at which they enter, if they pass from a rarer into a denser me-
dium, and from the perpendicular, when they pass from a denser medium
into a rarer. It is easily shown to be a result of this law, that, when parallel
rays passing through air fall upon a convex surface of glass, they will be
made to converge ; so as to meet at the opposite extremity of the diameter of
the circle, of which the curve forms part. If, instead of continuing in the
glass, they pass out again, through a second convex surface, of which the di-
rection is the reverse of the first, they will be made to converge still more, so
as to meet in the centre of curvature. Rays which are not parallel, but which
are diverging from a focus, are likewise made to converge to a point or focus ;
but this point will be more distant from the lens, in proportion as the object
is nearer to it, and the angle of divergence consequently greater. The rays
diverging from the several points of a luminous object, are thus brought to a
corresponding focus ; and the places of all these foci hold exactly the same re-
lation to each other, with that of the points from which the rays diverged; so
that a perfect image of the object is formed upon a screen held in the focus
of the lens. This image, however, will be inverted ; and its size, in pro-
portion to that of the object, will depend upon their respective distances from
the lens. If their distances be the same, their size will also be the same ; if
the object be distant, and the image near, the latter will be much the smaller;
and vice versa.

535. There are two circumstances, however, which interfere with the per-
fection of an image thus formed by a convex lens. The one is, that, if the
lens constitute a large part of the sphere from which it is taken, the rays
which fall near its margin are not brought to a focus at the same point with
those which pass through its centre ; but at a point nearer the lens. This
difference, which must obviously interfere greatly with the distinctness of the
image, is termed Spherical Aberration ; it maybe corrected by the combi-
nation of two or more lenses, of which the curvatures are calculated to ba-
lance one another, in such a manner that all the rays shall be brought to the
same focus ; or by diminishing the aperture of the lens by means of a stop
or diaphragm, in such a manner that only the central part of it shall be used.
The latter of these methods is the one employed, where the diminution in
the amount of light transmitted is not attended with inconvenience. The
nearer the object is to the lens (and the greater, therefore, the angle of diverg-
ence of its rays), the greater will be the spherical aberration, and the more
must the aperture of the diaphragm be contracted in order to counteract*!!.
The other circumstance that interferes with the distinctness of the image, is
the unequal refrangibility of the differently-coloured rays, which together

408 ON SENSATION, AND THE ORGANS OF THE SENSES.

make up white or colourless light ; the violet being more bent from their
course than the blue, the blue more than the yellow, and the yellow more
than the red ; the consequence of which will be, that the violet rays are
brought to a focus much nearer to the lens than the blue, and the blue nearer
than the red. If a screen be held to receive the image, in the focus of any
of the rays, the others will make themselves apparent as fringes round its
margin. This difference is termed Chromatic Aberration. It is corrected in
practice, by combining together lenses of different substances, of which the
dispersive power (that is, the power of separating the coloured rays) differs
considerably. This is the case with flint and crown glass, for instance, — the
dispersive power of the former being much greater than that of the latter,
whilst its refractive power is nearly the same : so that, if a convex lens of
crown glass be united with a concave of flint whose curvature is much less,
the dispersion of the rays effected by the former will be counteracted by the
latter, which diminishes in part only its refractive power.

536. The Eye may be regarded as an optical instrument of great perfec-
tion, adapted to produce, on the expanded surface of the optic nerve, a com-
plete image or picture of luminous objects brought before it; in which the
forms, colours, lights and shades, &c.., of the object are all accurately repre-
sented. By the different refractive powers of the transparent media, through
which the rays of light pass, and by the curvatures given to their respective
surfaces, both the Spherical and Chromatic aberrations are corrected in a de-
gree sufficient for all practical purposes : so that, in a well-formed eye, the
picture is quite free from haziness, and from false colours. The power by
which it adapts itself to variations in the distance of the object, — so as to
form a distinct image of it, whether it be six inches, six yards, or six miles
off, — is extremely remarkable, and cannot be regarded as hitherto completely
explained. It is obvious that, if we fix upon any distance as that for which
the eye is naturally adjusted (say 12 or 14 inches, the distance at which we

(Fig. 173.

' A longitudinal section of the globe of the Eye; 1, the sclerotic, thicker behind than in front; 8, the
cornea, received within the anterior margin of the sclerotic, and connected with it by means of a be-
veled edge; 3, the choroid, connected anteriorly with (4) the ciliary ligament, and (5) the ciliary pro-
cesses ; 6, the iris ; 7, the pupil ; S, the third layer of the eye, the retina, terminating anteriorly by an
abrupt border at the commencement of the ciliary processes ; 9, the canal of Petit, which encircles the
lens (12) ; the thin layer in front of this canal is the /onula ciliaris, a prolongation of the vascular layer
of the retina to the lens. 10, the anterior chamber of the eye, containing the aqueous humour; the
lining membrane by which the humour is secreted is represented in the diagram ; 11, the posterior; 12,
tlit lens more convex behind than before, and enclosed in its proper capsule; 13, the vitreous humour
enclosed in the hyaloid membrane, ami in cells formed in its interior by that membrane ; 14, a tubular
sheath of the hyaloid membrane, which serves for the passage of the artery of the capsule of the lens ;
15, the neurilemma of the optic nerve ; 1C, the arteria centralis retinae, imbedded in its centre.]

SENSE OF VISION".
[Fig. 174.

409

A Horizontal Section of the Eyeball ; 1, sclerotic coat ; 2, sheath or" the optic nerve, or canal of Fon-
tana; 3, circular venous sinus of the iris; 4, proper substance of the cornea; 5, arachnoidea oculi ; 6,
membrane of the anterior chamber of the aqueous humour ; of the two dotted lines one points to the

35

410 ON SENSATION, AND THE ORGANS OF THE SENSES.

supposed membrane of Descemet, the other to the supposed continuation of that membrane over the
anterior surface of the iris ; 7. choroid coat; 8, annulus albidus; 9, ciliary ligament ; 10. 10', ciliary body,
consisting of (10') a pars non-fimbriata, and (10) a pars fimbriata formed by the ciliary process; 11, ora
serrata of ihe ciliary body ; 12, iris ; 13, pupil; 14, membrane of the pigment ; 15, delicate membrane lining
the posterior chamber of the aqueous humour ; 16, membrane of Jacob ; 17, the optic nerve surrounded
by its neurilemma; 17', the fibres of the optic nerve consisting of fasciculi of primitive! ubules ; 18, cen-
tral artery of the retina ; 19, papilla cornica of the optic nerve ; 20, retina ; the situation of its vascular
layer is indicated by a dotted line ; 21, central transparent point of the retina; 22, vitreous humour; 23,
the hyaloid membrane j 24, canalis hyaloideus; 25, zonula ciliaris; in the plate, none of its fimbriated
part is seen, being concealed by the ciliary processes; 26, canal of Petit; 27, crystalline lens; 28, an-
terior wall of the capsule of the lens ; 29, posterior wall of the capsule of the lens ; 30, posterior chamber
of the aqueous humour ; 31, anterior chamber of the aqueous humour.]

ordinarily read), the rays proceeding from an object, placed nearer to the
eye than this, would not be brought to a focus upon the retina, but would
converge towards a point behind it ; whilst on the contrary, the rays from an
object at a greater distance would meet before they reached the retina, and
would have again diverged from each other when they impinge upon it ; so
that in either case, vision would be indistinct. Now two methods of adapta-
tion suggest themselves to the Optician. Either he may vary the distance
between the refracting surface and the screen on which the image is formed,
in such a manner, that the latter shall always be in the focus of the converg-
ing rays ; or, the distance of the screen remaining the same, he may vary the
convexity of his lens, in such a manner as to adapt it to the distance of the object.
It is not improbable, that both of these methods are employed in the Eye,
though no distinct evidence has been obtained of the operation of either. Seve-
ral hypotheses have been proposed, to account for the phenomenon : it is
easily proved that no one of them can alone be true ; but it cannot be readily
shown that any of them is entirely false : and it would not seem unlikely,
therefore, that all may participate, in various degrees, in the effect. The fol-
lowing are the principal of these. — 1. An alteration in the form of the globe
of the eye by the action of the muscles, so that its antero-posterior diameter
may be increased or diminished.* — 2. A change in the convexity of the cor-
nea. This might be very well connected with the last; since, if the globe
were converted into a spheroid, of which the antero-posterior diameter would
be the longest, the curvature of the cornea would be increased ; whilst, if the
antero-posterior diameter were shortened, the curvature would be diminished.

3. Change of position of the crystalline lens, by means of the ciliary processes.

4. Change of figure of the lens itself. That one or both of the last two are
concerned in the effect, would appear from the fact, well known to every Oculist,
that, after the removal of a cataract, the power of adapting the eye to dis-
tances is greatly diminished. — 5. Change in the aperture of the pupil ; the
mode in which this could assist in accommodating the eye to variations of
distance, is not very obvious.

537. Some curious circumstances, relative to the connection between the
optical adaptation of the eye to distances, and the changes in the direction of the
axes of the two eyes, have been pointed out by Miiller. When both eyes are
fixed upon an object, their axes must converge (as formerly explained, § 455)
so as to meet in it. The nearer the object, the greater must be the degree of
convergence ; and when the object is brought within the ordinary distance of
distinct vision, the convergence must very rapidly increase. Now this is
precisely what takes place, in regard to alterations in the focus of the eye; for
little change is required, when the object is made to approach from a considera-
ble distance to a moderate distance; but, when it is brought near the eye, the

* The influence of the muscles in altering the form of the globe may be better compre-
hended, now that we know the mode in which this is kept in its place in the front of the
orbit, by a fascia passing behind, it, and attached anteriorly to the lids.

SENSE OF VISION. 411

focus must be considerably lengthened, or the convexity of the eye increased,
to cause the rays to meet on the retina: and hence it may be surmised, that
the same cause is acting to produce both changes. But that the convergence
of the axes is not itself in any way the occasion of the alteration of the focus
of the eye, is shown by the fact, that the adaptation is as perfect, in a person
who only possesses or uses one eye, as it is when both are employed ; and
also by the power, which is possessed by some persons, of altering the focus
of the eye by an effort of the will, whilst the convergence remains the same.
In regard to the adaptation of the eyes to varying distances, it is further to be
remarked, that, when an object is being viewed as near to the eye as it can be
distinctly seen, the pupil contracts in a considerable degree.. The final cause
of this change, is evidently to exclude the outer rays of the cone or pencil,
which, from the large angle of their divergence, would fall so obliquely on the
convex surface of the eye, as to be much affected by the spherical aberration ;
and to allow the central rays only to enter the eye, so as to preserve the clear-
ness of the image. The channel through which it is effected is evidently the
same, as that by which the convergence of the eyes is produced, — namely,
the inferior branch of the third pair of nerves; to the action of which, the
sensations upon the retina form the stfmulus, in the same manner as they do
to the ordinary variation in the diameter of the pupil under the influence of
lisrlit. L--'i_-'''u~\_^u-'v''%— •»-"• ~fj

o

538. The ordinary forms of defective vision, which are known under the
names of myopia and presbyopia, or short-sightedness and long-sightedness,
are entirely attributable to defects in the optical adaptation of the eye. In the
former, its refractive power is too great; the rays from objects at the usual
distance are consequently brought too soon to a focus, so as to cross one
another and diverge, before they fall upon the retina; whilst the eye is adapted
to bring to their proper focus on the retina, only those rays which were pre-
viously diverging at a large angle, from an object in its near proximity. Hence
a short-sighted person, whose shortest limit of distinct vision is not above half
that of a person of ordinary sight, can see minute objects more clearly; his
eyes having, in fact, the same magnifying power, which those of the other
would possess, if aided by a convex glass, that would enable him to see the
object distinctly at the shorter distance. But as the myopic structure of the
eye incapacitates its possessor from seeing objects clearly, at even a moderate
distance, it is desirable to apply a correction ; and this is done, by simply inter-
posing a concave lens, of which the curvature is properly adapted to compen-
sate for the excess of that of the organ itself, between the object and the eye.
On the other hand, in the presbyopic eye, the curvature and refractive power
are not sufficient to bring to a focus on the retina, rays which were previously
divergent in a considerable or even in a moderate degree; and indistinct vision
in regard to all near objects is, therefore, a necessary consequence, whilst
distant objects are well seen. This defect is remedied by the use of convex
lenses, which make up for the deficiency of the curvature. We commonly
meet with myopia in young persons, and with presbyopia in old; but this is
by no means the invariable rule ; for even aged persons are sometimes short-
sighted; and long-sightedness is occasionally met with amongst the young.
In choosing spectacles, for the purpose of correcting the errors of the eye, it
is of great consequence not to make an over-compensation; for this has a
tendency to increase the defect, besides occasioning great fatigue in the employ-
ment of the sight. It may be easily found, when a glass of the right power
has been selected, by inquiring of the individual, whether it alters the apparent
size of the objects, or only renders them distinct. If it alter the size (in-
creasing it if it be a convex lens, and diminishing it if it be a concave), its
curvature is too great ; whilst if it do not disperse the haze, it is not sufficiently

412

ON SENSATION, AND THE ORGANS OF THE SENSES.

powerful. In general it is better to employ a glass which somewhat under-
compensates the eye, than one which is of a curvature at all too high ; since,
with the advance of years in elderly persons, a progressive increase in power
is required ; and, as young persons grow up to adult age, they should endeavour
to dispense with the aid of spectacles.

539. Many other interesting inquiries, respecting the action of the eye as
an optical instrument, suggest themselves to the physical philosopher ; but the
foregoing are the chief in which the Physiologist is concerned ; and we shall
now proceed, therefore, to consider the share, which the Retina and Optic

Fig. 175.

Fig. 176.

Part of the Retina of a Frog, seen
from the outer surface. Magnified 300
times.

Distribution of Capillaries in Vascu-
lar layer of Retina.

[Fig. 177.

Nerve perform in the phenomena of vision. — The optic nerve, at its entrance
into the eye, divides itself into numerous small fasciculi of ultimate fibrils;

and these appear to spread themselves out,
and to inosculate with each other by an ex-
change of fibrils, so as to form a net-like
plexus. There is considerable difficulty,
however, in the precise determination of the
course of the nerve-fibres in the Retina; on
account of their minute size, and the absence
of their distinctive characters. According to
Mr. Bowman, the tubular membrane and the
white substance of Schwann are deficient;
and only the central part of the nerve-fibre, or
axis-cylinder, is continued into this expansion.
The plexus of nerve-fibres comes into relation
with a plexus of capillary vessels, very minute-
ly distributed ; and also with a layer of cells,
so closely resembling those of the cortical sub-
stance of the brain, that there can be no rea-
sonable doubt of their correspondence in func-
tion. This layer of cells, constitutes the in-
ternal layer of the true retina. We have here,
then, all the elements of an apparatus for the
origination of changes in the nervous trunks,
in a fully displayed form ; and it can scarcely
be doubted that the essential parts of the same
structures exist in the papillae of the cutaneous
and other sensory surfaces. — The true Retina
is covered externally by a very peculiar in-
vestment, the Membrane of Jacob, which

A portion of the Retina of an Infant,
with its vessels injected and niagnilird
•_>5 diameters. An outline of ihe natural
si/e of this piece is seen just below the
main cut.]

SENSE OF VISION.

413

separates it from the pigmentary layer. This seems to be composed of cells
having a cylindrical form. These are sometimes arranged vertically to the

[Fig. 178.

as*

& W

771

i '—in

Vertical section of the Human Retina and Hyaloid Membrane, h. Hyaloid membrane, h'. Nuclei
on its inner surface, c. Layer of transparent cells, connecting the hyaloid and retina, c'. Separate
cell enlarged by imbibition of water, n. Gray nervous layer, with its capillaries. 1. Its fibrous lamina.
2. Its vesicular lamina. 1'. Shred of fibrous lamina detached. 2'. Vesicle and nucleus detached, g. Granu-
lar layer. 3. Light lamina frequently seen. g'. Detached nucleated particle of the granular layer.
m. Jacob's membrane, in'. Appearance of its particles, when detached, m" . Its outer surface. Mag-
nified 320 diameters.]

surface of the membrane, so that their extremities only are seen ; whilst in
other instances they are found to present an
imbricated arrangement, lying over each other
obliquely, in which case they are of conside-
rable length (Fig. 175). They are remarka-
ble for the rapidity with which they undergo
alterations after death ; and especially for the
changes in their form, which are produced
by the action of water.

540. The following statements on the
Limits of Human Vision, in regard to the
possible minuteness of the objects of which
it can take cognizance, comprehend the re-
sult of numerous inquiries made by Ehren-
berg, with the view of calculating the ulti-
mate power of the Microscope.* In opposi-
tion to the generally-received opinion, Ehren-
berg arrived at the conclusion that, in regard
to the extreme limits of vision, there is little difference amongst persons of
ordinarily good sight, whatever may be the focal distance of their eyes. The
smallest square magnitude usually visible to the naked eye, either of white
particles on a black ground, or of black upon a white or light-coloured ground,
is about the l-405th of an inch. It is possible, by the greatest condensation
of light, and excitement of the attention, to recognize magnitudes between the
l-405th and l-540th of an inch ; but without sharpness or certainty. Bodies
which are smaller than these, cannot be discerned with the naked eye when
single ; but may be seen when placed in a row. Particles which powerfully
reflect light, however, may be distinctly seen, when not half the size of the

Outer surface of the Retina, showing
the membrane of Jacob, partially detach-
ed. After Jacob.]

Taylor's Scientific Memoirs.
35*

Vol. i. p. 576.

414 ON SENSATION, AND THE ORGANS OF THE SENSES.

least of the foregoing ; thus, gold dust* of the fineness of 1-1 125th of an inch,
may be discerned with the naked eye in common daylight. The delicacy of
vision is far greater for lines than for single articles ; opaque threads of l-4900th
of an inch in diameter may be discerned with the naked eye, when held to-
wards the light. Such threads are about half the diameter of the Silk-worm's
fibre. The degree in which the attention is directed to them, has a great
influence on the readiness with which very minute objects can be perceived;
and Ehrenberg remarks that there is a much greater difference amongst indi-
viduals in this respect, than there is in regard to the absolute limits of vision.
Many persons can distinctly see such objects, when their situation is exactly
pointed out to them, who cannot otherwise distinguish them; and the same
is the case with persons of acuter perception, with respect to objects at dis-
tances greater than those, at which they can see most clearly. " I myself,"
says Ehrenberg, " cannot see l-2700th of an inch, black on white, at twelve
inches distance; but having found it at from four to five inches distance, I
can remove it to twelve inches, and still see the object plainly." Similar
phenomena are well known in regard to a balloon, or a faint star, in a clear
sky; or a ship in the horizon: we easily see them after they have been
pointed out to us; but the faculty of rapidly descrying depends on the habit
of using the eyes in search of such objects (§ 519).

541. The sense of Vision depends, in the first place, on the transference
to our minds of the picture which is formed upon the retina ; this picture puts
us in possession of the outlines, lights and shades, colours, and relative posi-
tions of the objects before us ; and all the ideas respecting the real forms,
distances, &c., of bodies, which we found upon these data, must be considered
in the light of perceptions, either instinctive or acquired. Many of these are
derived through the combination, in our minds, of the Visual sensations, with
those derived from the sense of Touch. Thus, to take a most simple illustra-
tion, the idea of smoothness is one essentially tactile ; and yet it constantly
occurs to us, on looking at a surface which reflects light in a particular man-
ner. But, if it were not for the association, which experience leads us to
form, of the connection between polish as seen by the eye, and smoothness
as felt by the touch, we should not be able to determine, as we now can do,
the existence of both these qualities from an impression communicated to us
through either sense singly. The general fact that, in Man, the greater part
of those notions of the external world by which his actions in the adult state
are guided, are acquired by the gradual association of the sensations commu-
nicated by the sight and by touch, is substantiated by amply-sufficient evidence.
This evidence is chiefly derived from observations made upon persons born
blind, to whom sight has been communicated by an operation, at a period of life
which enabled them to give an accurate description of their sensations. The
case recorded by Cheselden is one of the most interesting of these. The
youth (about 12 years of age), for some time after tolerably distinct vision had
been obtained, saw everything Jlat, as in a picture ; simply receiving the con-
sciousness of the impression made upon his retina ; and it was some time be-
fore he acquired the power of judging, by his sight, of the real forms and
distances of the objects around him. An amusing anecdote recorded of him,
shows the complete want of natural or intuitive connection which there is in
Man, between the ideas formed through visual and through tactile sensations.
He was well acquainted with a Dog and a Cat by feeling ; but could not re-
member their respective characters when he saw them. One day, when thus
puzzled, he took up the Cat in his arms, and felt her attentively, so as to as-

* Ehrenb?rg mentions thnt he obtained the finest particles of gold, by scraping gilt brass ;
by filing pure gold, he always obtained much coarser particles.

SENSE OF VISION. 415

sociate the two sets of ideas ; and then, setting her down, said, " So, puss, I
shall know you another time." A similar instance has come under the Au-
thor's own knowledge ; but the subject of it was scarcely old enough to pre-
sent phenomena so striking. One curious circumstance was remarked of him,
which fully confirms (if confirmation were wanting) the view here given.
For some time after the sight was tolerably clear, the lad preferred finding his
way through his father's house, to which he had been quite accustomed when
blind, by touch rather than by sight, — the use of the latter sense appearing to
perplex rather than to assist him ; but, when learning a new locality, he em-
ployed his sight, and evidently perceived the increase of facility which he de-
rived from it.

542. The question has been proposed, whether a person born blind, who
was able by the sense of Touch to distinguish a cube from a sphere, would,
on suddenly obtaining his Sight, be able to distinguish them by the latter
sense. This question was answered by Locke in the negative ; and probably
with justice. It is no real objection to such a reply, that a new-born animal
seeks the nipple of its mother, when informed of its proximity by sight ; for
all that is indicated by this fact is, that the sensation excites an intuitive feel-
ing of desire, which gives rise to movements adapted to gratify it. Such in-
stinctive actions, founded upon intuitive perceptions, are, as already pointed
out, much more numerous in the lower Animals than in the higher, and in the
young of the Human species than in the adult (§ 428) ; and they do not afford
any proof that definite notions, such as we acquire, of the forms and proper-
ties of external objects, are possessed by the animals which exhibit them.
We shall now examine, a little more in detail, into the means by which we
gain such notions, and the data on which they are founded.

543. The first point to be determined, is one which has been a fruitful
source of discussion, — the cause of erect vision, the picture upon the retina
being inverted. Many solutions of it have been attempted; but they are for the
most part rather specious than really satisfactory. That which has been of late
years the most in vogue, is founded upon what was styled the Law of Visible
Direction, which has been supported by Sir D. Brewster, and other eminent
Philosophers. This law affirms, that every object is seen in the direction of
the perpendicular to that point of the retina, on which its image is formed ;
or, in other words, that, as all the perpendiculars to the several points of the
inner surface of a sphere meet in the centre, the line of direction of any ob-
ject is identical with the prolonged radius of the sphere, drawn from the point
at which its image is made upon the retina. Upon close examination, how-
ever, it is found that this law cannot be optically correct ; since the lines of
direction cross each other at a point much anterior to the centre of the globe ;
as may be determined by drawing a diagram upon a large scale, and laying
down the course of the rays received by the eye, according to the curvatures
and refractive powers of its different parts. In this manner it has been deter-
mined by Volkmann, that the lines of direction cross each other in a point a
little behind the crystalline lens ; and that they will thus fall at such differ-
ent angles on different points of the retina, that no general law can be laid
down respecting them. It may be questioned, moreover, whether such a law
would afford any assistance in explaining the phenomenon ; since, after all,
it is requisite to assume an intuitive application of it, in supposing the mind
to derive its ideas of the relative situations of objects, from the imagined line
of direction. — A much simpler and more direct explanation may be given.
We must remember that, which we have had occasion to notice in regard to all
the other senses, — the broad line of distinction between the sensation and the
perception or elementary notion; and this is still more clearly shown by the
complete absence of any relation, but such as experience developes, between

416 ON SENSATION, AND THE ORGANS OF THE SENSES.

the perceptions derived through the sight, and those acquired from the touch.
Hence there is no more difficulty in understanding, that an inverted picture
upon the retina should convey to us a notion of the external world, which
harmonizes with that acquired through the sense of touch, than there is in
comprehending the formation of any of those intuitive perceptions of animals,
which are so much more removed from the teachings of our own experience
(§ 490). It is justly remarked by Muller that, " if we do see objects inverted [or
rather, if the picture on the retina is inverted] the only proof we can possibly
have of it, is that afforded by the study of the laws of Optics ; and, if everything
is seen reversed, the relative position of the objects remains unchanged. Hence
it is, also, that no discordance arises between the sensations of inverted vision
and those of touch, which perceives everything in its erect position ; for the
images of all objects, even of our own limbs, on the retina, are equally in-
verted, and therefore maintain the same relative position. Even the image of
our hand, when used in touch, is inverted." From what has been stated, it
would appear quite conceivable, that a person just endowed with sight, should
not at first know by his visual powers, whether a pyramid placed before his
eyes is the same body, and in the same position, as one with which he has
become acquainted by the touch ; and, if this be admitted, the inference ne-
cessarily follows, that the notion of erectness, which we form by the combined
use of our eyes and our hands, is really the product of experience in ourselves,
whilst it is probably innate or intuitional in the lower Animals.

544. The cause of single vision with the two eyes has, in like manner,
been the subject of much discussion; since the mode in which we are affected
by the two simultaneous impressions, is quite different from that, in which
we derive our knowledge of external things through the other senses. Some
have even asserted, that we do not really employ both eyes simultaneously,
but that the mind is affected by the image communicated by one only; and
this idea might seem to be confirmed by the fact heretofore mentioned (§ 519),
respecting the alternate use of the two eyes, when they are looking through
two differently-coloured media. But it is easily disproved in other ways. —
It will presently be shown, that all our estimates of the forms of bodies, de-
pend on the combination by the mind, of the images simultaneously transmit-
ted by the two eyes ; and our knowledge of distances is in great part obtained
in like manner. The condition of Single Vision has been already stated
(§ 454) to be probably this,' — that the two images of the object should be
formed on parts of the two retinae, which are accustomed to act in concert ;
and reasons were given for the belief, that habit is the chief means by which
this conformity is produced. There can be no doubt, however, that double
images are continually being conveyed to our minds ; but that, from their
want of force and distinctness, and from the attention being fixed on something
else, we do not take cognizance of them. This may be shown by a very
simple experiment. If two fingers be held up before the eyes, one in front
of the other, and vision be directed to the more distant, so that it is seen
singly, the nearer will appear double ; while, if the nearer one be regarded
more particularly, so as to appear single, the more distant will be seen double.
A little consideration will show, therefore, that our minds must be continually
affected with sensations, which cannot be united into the idea of a single
image ; since, whenever we direct the axes of our eyes towards any object,
everything else will be represented to us as double; but we do not ordinarily
perceive this, from our minds being fixed upon a clear and distinct image, and
disregarding, therefore, the vague undefined images formed by objects at a
different focus. Of this it is very easy to convince oneself. It is moreover
evident from this experiment, that double vision cannot result from want of
symmetry in the position of the images upon the retina, to which some have

SENSE OF VISION. 417

attributed it ; for it answers equally well, if the line of the two fingers be pre-
cisly in front of the nose, so that the inclination of both eyes towards either
object is equal ; the position of the images of the second object must then be
at the same distance on each side from the central line of the retina, and yet
they are represented to the mind as double. It is, moreover, easily shown,
that, in the lower animals whose orbits are not directed forwards as in us, but
sideways in a greater or less degree, whenever an object is so situated as to
be seen by both eyes, the points of the two retina? on which its images are
formed, must be very far from possessing this symmetry.

545. Many attempts have been made to explain the phenomena of Single
Vision by the peculiar decussation of the Optic nerves (§ 445) ; and an inte-
resting correspondence between the varieties in the degree of decussation, and
the position of the eyes, in several animals, has been pointed out by Mr. Solly
and Mr. Mayo. From these and other data, it has been concluded, that each
nerve is used in looking towards the opposite side. This is evidently true of
the Osseous Fishes, whose two eyes, being directed sideways, have two en-
tirely different spheres of vision. And it is also true of Man, if Mr. Mayo's
account of the distribution of the nerve be correct ; since, when we look at
an object held directly in front of the face, at the level of the eyes, and at the
nearest point for distinct vision, almost the whole of that portion of the right
retina, which lies to the outside of the entrance of the optic nerve, is directed
to the left; and the exactly different, complementary, or inner portion of the
left retina, which is supplied by the same nerve, is likewise directed to the
left. On this supposition, all the rays entering the two eyes from any one
point, will be brought to a focus on fibrils belonging to the nerve of the same
side ; though these are in Man, as in other animals whose spheres of vision
are nearly or partly coincident, distributed to distinct visual organs.* It is
obvious, however, that this or any similar explanation, must be insufficient to
explain the phenomenon of single vision ; since the images formed upon the
two retinae are necessarily different, and must be combined or harmonized by
an act of the mind, as will be shown in the succeeding paragraphs.

546. We shall next consider the mode, in which our notion of the solid
forms and relative projection of objects is acquired ; on which great light has

recently been thrown by the interesting experiments of Mr. Wheatstone.t It
is perfectly evident, both from reason and experience, that the flat picture upon
the retina, which is the only object of our sensation, could not itself convey to
our minds any notion, but that of a corresponding plane surface. In fact, any
notion of solidity, which might be formed by a person, who had never had
the use of more than one eye, would entirely depend upon the combination of
his visual and tactile sensations. This idea is fully confirmed by the case
already referred to, as recorded by Cheselden. The first visual idea formed
by the youth was, that the objects around him formed a flat surface, which
touched his eyes, as they had previously been in contact with his hands ; and
after this notion had been corrected, through the education of his sight by his
touch, he fell into the converse error of supposing that a picture, which was
shown to him, was the object itself represented in relief on a small scale. — But
where both eyes are employed, it has been ascertained by Mr. Wheatstone,

The late Dr. Wollaston was subject to a curious affection of vision, which consisted in
his not being able to see more than half an object, — the loss being sometimes on one side,
and sometimes on the other. The Author has met with several cases of this disorder, which
has been termed hemiopia. Dr. W. thought that they might be explained by the decussation
of the optic nerve; but Mr. Mayo states that he has known instances of a parallel affection,
involving alternately the centre and the circumference of the retina, and therefore not attribut-
able to any such structural arrangement,
-j- Philosophical Transactions, 1838.

418 ON SENSATION, AND THE ORGANS OF THE SENSES.

that they concur in exciting the perception of solidity or projection, which
arises from the combination of two different images in the mind. It is easily
shown, that any near object is seen in two different modes by the two eyes.
Thus let the reader hold up a thin book, in such a manner that its back shall
be exactly in front of his nose, and at a moderate distance from it ; he will
observe, by closing first one eye and then the other, that his perspective view
of it (or the manner in which he would represent it on a plane surface) is very
different, according to the eye with which he sees it. With the right eye he
will see its right side, very much foreshortened ; with the left, he will gain a
corresponding view of the left side ; and the apparent angles, and the lengths
of the different lines, will be found to be very different in the two views. On
looking at either of these views singly, no other notion of solidity can be
acquired from it, than that to which the mind is conducted, by the association
of such a view with the touch of the object it represents. But it is capable of
proof, that the mental association of the two different pictures upon the retina?,
does of itself give rise to the idea of solidity. This proof is afforded by Mr.
Wheatstone's ingenious instrument, the Stereoscope.

547. The Stereoscope essentially consists of two plane mirrors, inclined
with their backs to one another at an angle of 90°. If two perspective draw-
ings of any solid object, as seen at a given distance with the two eyes respect-
ively, be placed before these mirrors, in such a manner that their images shall
be made to fall upon the corresponding parts of the two retinae, in the same
manner as the two images formed by the solid object itself would have done,
the mind will perceive, not a single representation of the object, nor a confused
union of the two, but a body projecting in relief, — the exact counterpart of
that from which the drawings were made. Mr. Wheatstone further shows by
means of the Stereoscope, that similar images, differing to a certain extent in
magnitude, when presented to the corresponding parts of the two retina?, give
rise to the perception of a single object, intermediate in size between the two
monocular pictures. Were it not for this, objects would appear single, only
when at an equal distance from both eyes, so that their pictures upon the
retina are of the same size ; which will only happen, when they are directly
in front of the median line of the face. Again, if pictures of dissimilar objects
be simultaneously presented to the two eyes, the consequence will be similar
to that which is experienced, when the rays come to the eye through two
differently-coloured media ; — the two images do not coalesce, nor do they
appear permanently superposed upon one another : but at one time one image
predominates to the exclusion of the other, and then the other is seen alone ;
and it is only at the moment of change, that the two seem to be intermingled.
It does not appear to be in the power of the will, Mr. Wheatstone remarks,
to determine the appearance of either; but, if one picture be more illuminated
than the other, it will be seen during a larger proportion of the time. Many
other curious experiments with this simple instrument are related by Mr.
Wheatstone ; and they all go to confirm the general conclusion, that the com-
bination of the images furnished by the two eyes is a mental act, resulting
from an inherent law of our psychical constitution ; and that our perceptions of
the solidity and projection of objects, near enough to be seen in different views
with the two eyes, result from this cause. In regard to distant objects, how-
ever, the difference in the images formed by the two eyes is so slight, that it
cannot aid in the determination ; and hence it is, that, whilst we have no dif-
ficulty in distinguishing a picture, however well painted, from a solid object,
when placed near our eyes, (since the idea, which might be suggested by the
image formed on one eye, will then be corrected by the other,) we are very
liable to be misled by a delineation, in which the perspective, light and shade,
&c., are faithfully depicted, if we are placed at a distance from it, and are pre-

SENSE OF VISION. 419

vented from perceiving that it is but a picture. In this case, however, a slight
movement of the head is sufficient to undeceive us ; since by this movement
a great change would be occasioned in the perspective view of the object, sup-
posing it to possess an uneven surface ; whilst it scarcely affects the image
formed by a picture. In the same manner, a person who only possesses one eye,
obtains, by a slight motion of his head, the same idea of the form of a body,
which another would acquire by the simultaneous use of his two eyes.

548. The appreciation of the distance of objects, may be easily shown to
be principally derived from the association, in the mind, of visual and tactual
sensations ; assisted, in regard to near objects, by the muscular sensations de-
rived from the convergence of the eyes. Thus, an infant, or a person who
has but recently acquired sight, evidently forms very imperfect ideas regarding
the distance of objects ; and it is only after long experience that a correct no-
tion is formed. The assistance which is given by the joint use of both eyes,
is evident from the fact, that, if we close one eye, we are unable to execute
with certainty many actions, which require a precise appreciation of the dis-
tance of near objects, — such as threading a needle, or snuffing a candle. In
regard to distant objects, our judgment is chiefly founded upon their apparent
size, if their actual size be known to us ; but, if this is not the case, and if we
are so situated that we cannot judge of the intervening space, we principally
form our estimate from the greater or less distinctness of their colour and out-
line. Hence this estimate is liable to be greatly affected by varying states of
the atmosphere ; as is well known to every one who has visited warmer lati-
tudes. The extreme clearness of the air sometimes brings, into an apparently
near proximity, a hill that rises beyond some neighbouring ridge (the inter-
vening space being hidden, so as not to afford any datum for the estimate of
the distance of the remote hill) ; and which, by a slight haziness, is carried to
three or four times the degree of apparent remoteness. It is probable that, in
the lower Animals, the perception of distance is much more intuitive than it is
in ourselves.

549. Our estimate of the real size of an object is manifestly connected with
that of its distance. The apparent size is dependent upon the angle at which
its rays diverge, to impinge upon the cornea ; this angle increases with the
proximity, and diminishes with the remoteness, of the object. Our estimate
of the comparative size of near objects, of whose distances we can become
aware by the inclination of the optic axes, is much more correct than that
which we form, when one or both are far removed; since, when we are un-
certain as to its distance, we cannot form a judgment of the real size of a body,
from the angle at which its rays diverge. Hence our estimate of the size of
objects even moderately distant, is much influenced by states of the atmosphere.
Thus, if we walk across a common in a fog, a child approaching us appears
to have the size of a man, and a man seems like a giant; since the indistinct-
ness of the outline excites in the mind the idea of distance; and an object
seen under a given visual angle at a distance, must of necessity be much larger
than one, of which the apparent size is the same, but which is much nearer.
The want of innate power in Man to form a true conception of either size or
distance, is well shown by the effect produced on the mind unprepared for
such delusions, by a skilfully-painted picture; the view of which is so con-
trived, that its distance from the eye cannot be estimated in the ordinary man-
ner; the objects it represents are invested by the mind with their real sizes
and respective distances, as if their real image was formed upon the retina.*

> This delusion has been extremely complete, in some of those who have seen the pano-
ramic view of London in the Coliseum. A lively and interesting account of it is given in
the Journal of the Parsee Shipbuilders, who visited England some time ago.

420 ON SENSATION, AND THE ORGANS OF THE SENSES.

550. From all these considerations, we are led to perceive the truth of the
quaint observation made by Dr. Brown, — that "vision is, in fact, the art of
seeing things which are invisible ;" that is, of acquiring information, by means
of the eye, which is neither contained in the sensations of sight themselves,
nor logically deducible from the intimations which those sensations really
convey. We cannot too constantly bear in mind, in treating of this subject,
that we do not take cognizance by our optic nerves, as we do by the nerves
of touch, of material bodies themselves, but of the pictures or images formed
by those objects; and whatever be the notions suggested by the picture, that
can never be transformed into anything else. These notions appear to be, in
the lower Animals, entirely of an intuitional or instinctive character; in Man
they are so in a much less degree ; and although it is impossible to come to a
precise conclusion on the subject, from the want of sufficient data, it is indu-
bitable that a large part of the knowledge of the external world, which he de-
rives in the adult condition from the use of his eyes alone, is really dependent
upon the early education of his perceptive powers, in which process, the sen-
sations conveyed by different organs are brought to bear upon one another.

551. The persistence, during a certain interval, of impressions made upon
the retina, gives rise to a number of curious visual phenomena. The pro-
longation of the impression will be governed, in part, by its previous duration.
Thus, when we rapidly move an ignited point through a circle, the impression
itself is momentary, and remains but for a short time; whilst, if we have been
for some time looking at a window, and then close our eyes, the impression of
the dark bars traversing the illuminated space is preserved for several seconds.
Such phenomena can here be only briefly adverted to. One of these is the
combination, into one image, of two or more objects presented to the eye in
successive movements ; but these must be of a kind which can be united, other-
wise a confused picture is produced. Thus in a little toy, called the Thauma-
trope, which was introduced some years ago, the two objects were painted on
the opposite sides of a card, — a bird, for instance, on one, and a cage on the
other; and, when the card was made (by twisting a pair of strings) to revolve
about one of its diameters, in such a manner as to be alternately presenting
the two sides to the eye at minute intervals, the two pictures were blended,
the bird being seen in the cage. A far more curious illusion, however, was
that first brought into notice by Mr. Faraday ; who showed that, if two toothed
wheels, placed one behind the other, be made to revolve with equal velocity,
a stationary spectrum will be seen; whilst if one be made to revolve more
rapidly than the other, or the number of teeth be different, the spectrum also
will revolve. The same takes place when a single wheel is made to revolve
before a mirror ; the wheel and its image answering the purpose of the two
wheels in the former case. On this principle, a number of very ingenious
toys have been constructed; in some of these, the same figure or object is
seen in a variety of positions; and the impressions of these, passing rapidly
before the eye, give rise by their combination to the idea, that the object is
itself moving through these positions. Similar illusions may be produced in
regard to colour.

552. When the Retina has been exposed for some time to a strong im-
pression of some particular kind, it seems less susceptible of feebler impres-
sions of the same kind. Thus, if we look at any brightly luminous object,
and then turn our eyes on a sheet of white paper, we shall perceive a dark
spot upon it; the portion of the retina, which had been affected by the bright
image, not being able to receive an impression from the fainter rays reflected
by the paper. The dark spectrum does not at once disappear, but assumes
different colours in succession, — these being expressions of the states through
which the retina passes, in its transition to the natural condition. If the eye

SENSE OF VISION. 421

has received a strong impression from a coloured object, the spectrum exhibits
the complementary colour;* thus, if the eye be fixed for any length of time
upon a bright red spot on a white ground, and be then suddenly turned so as
to rest upon the white surface, we see a spectrum of a green colour. — The
same explanation applies to the curious phenomenon of coloured shadows.
It may not unfrequently be observed at sunset, that, when the light of the sun
acquires a bright orange colour from the clouds through which it passes, the
shadows cast by it have a blue tint. Again, in a room with red curtains, the
light which passes through these produces green shadows. In both instances,
a strong impression of one colour is made on the general surface of the retina ;
and at any particular spots, therefore, at which the light is colourless but very
faint, that colour is not perceived, its complement only being visible. The
correctness of this explanation is proved by the fact, that, if the shadow be
viewed through a tube, in such a manner that the coloured ground is excluded,
it seems like an ordinary shadow. It is not unlikely that, as Miiller suggests,
the predominant action of one colour on the retina disturbs (as it were) the
equilibrium of its condition, and excites in it a tendency to the development
of a state, corresponding to that which is produced by the impression of the
complementary colour; for the latter is, according to him, perceived even
where it does not exist; — as when the eye, after receiving a strong impression
from a coloured spot, and directed upon a completely dark surface or into a
dark cavity, still perceives the spectrum. — Upon these properties of the eye
are founded the laws of harmonious colouring, which have an obvious analogy
with those of musical harmony. All complementary colours have an agreeable
effect, when judiciously disposed in combination ; and all bright colours, which
are not complementary, have a disagreeable effect, if they are predominant : this
is especially the case in regard to the simple colours, strong combinations of
any two of which, without any colour that is complementary to either of them,
are extremely offensive. Painters who are ignorant of these laws, introduce
a large quantity of dull grey into their pictures, in order to diminish the glaring
effects, which they would otherwise produce; but this benefit is obtained by
a sacrifice of the vividness and force, which may be secured in combination
with the richest harmony, by a proper attention to physiological principles.

553. Some persons, who can perfectly distinguish forms, are deficient,
through some original peculiarity in the constitution of the retina, in the
power of discriminating colours. This is most commonly seen in regard to the
complementary colours, especially red and green ; such persons not being
able to perceive cherries amidst the leaves on a tree, except by the difference
of their form. Several distinct varieties of this affection may be distinguished,
however. These have been classified by Seebeck and Wartmann.t

554. Amongst other curious phenomena of Vision, is the vanishing of
images which fall at the entrance of the optic nerve ; as is shown in the fol-
lowing experiment. Let two black spots be made upon a piece of paper,
about four or five inches apart ; then let the left eye be closed, and the right
eye be strongly fixed upon the left-hand spot. If the paper be then moved
backwards and forwards, so as to change its distance from the eye, a point will
be found, at which the right-hand spot is no longer visible ; though it is clearly
seen, when the paper is brought nearer or removed further. In this position
of the eye and object, the rays from the right-hand spot cross to the nasal

* By tile complementary colour is meant that, which would be required to make white or
colourless light, when mixed with the original. As red, blue, and yellow are the primary
or elementary colours, red is the complement of green (which is composed of yellow and
blue); blue is the complement of orange (red and yellow) ; and yellow of purple (red and blue);
and vice versa in all instances.

f Miiller's Physiology, p. 1213; Taylor's Scientific Memoirs, Vol. iv. p. 156, et seq.
36

422 ON SENSATION, AND THE ORGANS OF THE SENSES.

side of the globe, and fall upon the point of the retina, which has just been
mentioned. The phenomenon is not confined to that spot, however ; nor is
it correct to say, as is sometimes done, that the retina is not sensible to light
at that point ; since, if such were the case, we should see a dark spot in our
field of view, whenever we use only one eye. The fact is, that a similar
phenomenon may occur under somewhat different conditions, in any division
of the retina, especially in its lateral parts. Thus, if we fix the eye for some
time, until it is fatigued, upon a strip of coloured paper lying upon a white
surface, the image of the coloured object will in a short time disappear, and
the white surface will be seen in its place ; the disappearance of the image,
however, is only of a few seconds duration. The truth seems to be, that
there is a tendency in the retina, to the propagation over neighbouring parts,
of impressions which occupy a large proportion of its surface ; and that this
tendency is the strongest, around the point at which the optic nerve enters,
so that the state of this part will generally become similar to that of the sur-
rounding portion of the retina. Hence, when we are using one eye only,
we do not perceive any dark spot in the field, but only a certain degree of in-
distinctness in a portion of the image.

555. Under particular circumstances, we may receive a visual representa-
tion of the retina itself; as is shown by the experiments of Purkinje. "If,
in a room otherwise dark, a lighted candle be moved to and fro, or in a circle,
at a distance of six inches before the eyes, we .perceive, after a short time, a
dark arborescent figure ramifying over the whole field of vision; this appear-
ance is produced by the vasa centralia distributed over the retina, or by the
parts of the retina covered by those vessels. There are, properly speaking,
two arborescent figures, the trunks of which are not coincident, but on the
contrary arise in the right and left divisions of the field, and immediately
take opposite directions. One trunk belongs to each eye, but their branches
intersect each other in the common field of vision. The explanation of this
phenomenon is as follows : — By the movement of the candle- to and fro, the
light is made to act on the whole extent of the retina, and all the parts of the
membrane which are not immediately covered by the vasa centralia are feebly
illuminated ; those parts, on the contrary, which are covered with those vessels
cannot be acted on by the light, and are perceived, therefore, as dark arbore-
scent figures. These figures appear to lie before the eye, and to be suspended
in the field of vision."* We have thus another demonstration of the fact
that, in ordinary vision, the immediate object of our sensation is a certain
condition of the retina, which is excited by the formation of a luminous
image.

6. Sense of Hearing.

556. In the Ear, as in the Eye, the impressions made upon the sensory
nerve are not at once produced by the body which originates the sensation ;
but they are propagated to it, through a medium capable of transmitting them.
Here too, therefore, we take cognizance by the mind, not of the sonorous ob-
ject, but of the condition of the auditory nerve ; and all the ideas we form of
sounds, as to their nature, intensity, direction, &c., must be based upon tin
changes which they produce in it. The complex contrivances, which we
meet with in the organ of Hearing among higher animals, are evidently in-
tended to give them greater power of discriminating sounds, than is possessed
by the lower tribes ; in which last it is reduced to a form so simple, that it may
be questioned whether they can be said to possess an organ of hearing, if
by this term we imply anything more than the mere consciousness of sono-

* Midler's Physiology, p. 1103.

SENSE OF HEARING.

423

rous vibrations. There is a considerable difference, however, between the
Eye and the Ear, in regard to the special purposes for which they are respect-
ively adapted. In the former we have seen, that the whole object of the in-
strument is to direct the rays of light received by it, in such a manner, as to
occasion them to fall upon the expansion of the optic nerve in a similar rela-
tive position, and with corresponding proportional intensity, to that which
they possessed when issuing from the object. We have no reason to believe
anything of this kind to be the purpose of the Ear; indeed, it would be in-
consistent with the laws of the propagation of sound. Sonorous vibrations
having the most various directions, and the most equal rate of succession, are
transmitted by all media without modification, however numerous their lines
of intersection ; and wherever these undulations fall upon the auditory nerve,
they must cause the sensation of corresponding sounds. Still it is probable
that some portions of the complex organ of hearing, in Man and in the higher
animals, are more adapted than others to receive impressions of a particular
character ; and that thus we may be especially informed of the direction of a
sound by one part of the organ, of its musical tone by another, and of some
other of its qualities by a third. In our inquiries into this ill-understood sub-
ject, we shall commence with a brief survey of the comparative structure of
the organ.

557. The essential part of an Organ of Hearing being obviously a nerve,
endowed with the peculiar property of receiving and transmitting sonorous
undulations, it is by no means indispensable that a special provision should
be made for this purpose; since the Auditory nerve, if merely in contact with
the solid parts of the head, will be affected by the vibrations, in which it is
continually participating. Hence we must not imagine the sense to be absent,
wherever we cannot discover a special organ. It is among the highest only
of the Invertebrate animals, that any such special organ presents itself; and
then only in a very simple form. Thus in the Crustacea and Cephalopoda,

[Fig. 180.

General view of the external, middle, and internal ear, as seen in a prepared section through a, the
auditory canal, b. The tympanum or middle ear. c. Eustachian tube, leading to the pharynx, rf. Coch-
lea; and e. Semicircular canals and vestibule, seen on their exterior, as brought into view by dissecting
away the surrounding petrous bone. The styloid process projects below; and the inner surface of the
carotid canal is seen above the Eustachian tube. From Scarpa.]

424

ON SENSATION, AND THE ORGANS OF THE SENSES.

the ear consists of a small cavity excavated in the solid frame-work of the
head ; this cavity is lined with a membrane, on which the nerve is distri-
buted ; and it is filled with a watery fluid. In some instances, the cavity is
completely shut in by its solid walls ; and the sonorous vibrations can then
only be communicated through these : but in the higher forms of this appa-
ratus, there is a small aperture covered with a membrane, upon which the
external medium can at once act. In tracing this most simple into the more
complex forms, it is at once seen, that the cavity corresponds with the vesti-
bule of the ear of higher animals, and its opening with the fenestra ovalis.
In the lowest Cyclostome Fishes, the organ is but little more complicated ;
from the vestibule proceeds a single annular passage, which may be consi-
dered as a semicircular canal ; and the auditory nerve is distributed minutely
upon its lining membrane, as upon that of the vestibule itself. In species
a little higher in the scale, two such canals exist ; these are present in the
Lamprey. And in all the rest of the class, three semicircular canals are
found; holding the same direction in regard to each other, as they do in Man.
Within the vestibular sac of Fishes are found calcareous concretions, which
are pulverulent in the Cartilaginous, but hard and stony in the Osseous tribes;
to these the name of Otolithes has been given. Some rudiments of a tympa-
nic cavity may be found in Fishes ; but there is no vestige of a cochlea : in
several tribes, the organ of hearing possesses a peculiar connection with the
air-bladder, which appears to be a foreshadowing of the Eustachian tube of
higher classes.

558. In the true Reptiles, a considerable advance is constantly to be found
in the character of the Ear; a tympanic cavity being added, with a drum and
a chain of bones ; and a rudiment of the cochlea being generally discoverable.
Among the Amphibia, however, which are in so many respects intermediate

ig. 181.

Diagram of the inner wall of the tympanun after maceration, the outer wall anil ossicles being re-
moved, o. Fenestra ovalis. b. Fenestra rotunda, c. Promontory. <l. Pn r:\mid, with the orifice at its
apex. e. Projection of the aqueductus Fallopii. f. Some of the mastoid cells communicating with the
tympanum, g. Processus cochleariformis, bounding i. the canal for the tensor lympani muscle : the an-
terior pyramid is broken off, if it existed, h. Commencement of the Bustacnian tube, j. Jugular-fossa,
immediately below the tympanum, k, k. Carotid canal, with the artery in outline, to show its course in
relation to the tympanum and Kustachian tube. I. Portio dura of the seventh pair of nerves, as it would
be seen in the terminal part of the aqueduct of Fallopius. m. Chorda tympani, leaving the portio dura,
and entering a short canal, which opens in the tympanum, at the base of the pyramid, n. Grooves for
the tympanic plexus.]

SENSE OF HEARING.

425

between the true Reptiles and Fishes, there is a remarkable variation in this
respect, — some having a tympanum, and some being completely destitute of
it. Wherever a tympanic cavity distinctly exists, there is an Eustachian tube
connecting it with the fauces. This cavity, in the true Reptiles, not only
possesses ihefenestra ovalis (or opening into the vestibule), but the fenestra
rotunda (or opening into the cochlea). The membrana tympani is usually

[Fig. 182.

A view of the axis of the Cochlea and the Lamina Spiralis, showing the arrangement of the three
Zones; the osseous zone and the membrane of the vestibule have been removed ; 1, the natural size of the
parts ; the other figure is greatly magnified ; 2, trunk of the auditory nerve ; 3, the distribution of its fila-
ments in the zona ossea ; 4, the nervous anastomosis of the zona vesicularis ; 5, the zona membranacea ;
6, the osseous tissue of the modiolus ; 7, the opening between the two scalae.]

visible externally ; but it is sometimes covered by the skin. — In Birds, the
structure of the ear is essentially the same as in the higher Reptiles. A dis-
tinct cochlea exists, though its form is not spiral but nearly straight : of its
character, however, there can be no doubt ; a division into two passages, by
a membranous partition on which the nerve is spread out, being evident.
Moreover the tympanum communicates with cavities in the cranial bones,
which are thus filled with air ; and these, by increasing the extent of surface,
produce a more powerful resonance. There is no external ear, except in a
few species of nocturnal Birds. — In Mammalia, the organ of hearing is usually

[Fig. 183.

Cochlea of a new-born infant, opened on the side towards the apex of the petrous bone. It shows the
general arrangement of the two scalae, the lamina spiralis, and the distribution of the cochlear nerve. At
the apex is seen the modiolus expanding into the cupola, where the spiral canal terminates in a cul-de-
sac. The helicotrema is not visible in this view. From Arnold.]

36*

426

ON SENSATION, AND THE ORGANS OF THE SENSES.

formed upon the same plan, as it presents in Man ; in the Monotremata, how-
ever, it more approaches that of Birds. The cochlea of the Mammalia in
general is a spiral, forming about two turns and a half; the partition which

[Fig. 184.

The Cochlea divided parallel with its axis, through the centre of the Modiolus ; after Breschet; 1, the
modiolus; 2, the infundibulum in which the modiolus terminates ; 3, 3, the cochlear nerve, sending its fila-
ments through the centre of the modiolus ; 4, 4, the scala tympani of the first turn of the cochlea; 5, 5, the
scala vestibulaof the first turn; 6, section of the lamina spiralis, its zonulaossea; one of the filaments of
the cochlear nerve is seen passing between the two layers of the lamina spiralis to be distributed upon the
membrane which invests the lamina; 7, the membranous portion of the lamina spiral!*; S, loops formed by
the filaments of the cochlear nerve; 9, 9, scala tympani of the second turn of the cochlea; 10, 10, scala
vestibula of the second turn ; the septum between the two is the lamina spiralis ; 11, the scala tympani of
the remaining half turn ; 12, the remaining half turn of the scala vestibula; the dome placed over this half
turn is the cupola: 13, the lamina of bone which forms the floor of the scala vestibula curving spirally
round to constitute the infundibulum (2) ; 14, the helicotrema through which a bristle is passed ; its lower
extremity issues from the scala tympani of the middle turn of the cochlea.]

divides its canal is partly osseous, partly membranous; and its two passages
communicate with the tympanic cavity and the vestibule respectively. The
cavity of the tympanum is very large in some species, extending even into the
contiguous bones. All the Mammalia, except the aquatic tribes, have an ex-
ternal ear ; and this is sometimes of an enormous size in proportion to the
dimensions of the body, as it is in the Bats. The labyrinth of the higher
Vertebrata contains no otolithes.

559. The ultimate terminations of the fibres of the Auditory nerve, are

Fig. 1S5.

[Fig. 186.

Papilla; (?) of the Auditory nerve,
on a segment of the spiral lamina of
the cochlea of a young Mouse ; the
lower portion is the osseous, and the
higher the membranous part of the
lamina. Magnified 300 times.

The Auditory Nerve taken out of the Cochlea; 1, 1, 1,
the trunk of the nerve; 2, 2. its filaments in the zona ossea
of the lamina spiralis; 3. 3. its anastomoses in the zona
vesicularis.]

SENSE OF HEARING.

427

best seen in the lamina spiralis of the cochlea, and its membranous prolon-
gation. Much diversity exists, however, as to the interpretation of the ap-

[Fig. 187.

[Fig. 188.

A highly magnified view of a small piece of the Lamina Spiralis,
showing the globular structure of the Nerves, and the manner in
which they leave their Neurilemma as they anastomose; the natural
size of the piece is seen on the side of the figure; 1, portion of the
auditory nerve, 2, 2. osseous canals in the zona ossea of the lamina
spiralis; 3, 3, anastomoses in the zona mollis; 4, 4, the neurilemma
leaving the nervous loops and interlocking to form the layer of the
zona membranacea.]

Plexiform arrangement of the
cochlear nerves seen in the basal
coil of the lamina spiralis, treated
with hydrochloric acid. There
are no ganglion globules in this
plexus, which consists of tubular
fibres, a. Twig of cochlear nerve
in the modiolus, its fibres diverging
and reuniting in 6, a band in the
plexus taking a direction parallel
to the zones. From this other
twigs radiate, and again and again
branch and unite as far as the mar-
gin of the osseous zone c, where
they terminate. From the sheep.
Magnified 30 diameters.]

pearances there seen ; some observers affirming that there are no free or
papillary terminations, and that the nervous fibres all return by loops ; whilst
others state that the papillae are clearly to be distinguished. The fact appears
to be that, as in the retina, the fibres do form a minute plexus ; but that fibres
are connected with this, which end, or rather commence in papillae. The
Auditory nerve is also very minutely distributed on the membrane lining the
vestibule and semicircular canals; and in the ampullae or dilated extremities
of the latter, there are little projections of this membrane internally, which
are largely supplied with nerves.

560. In order to gain any definite idea of the uses of different parts of the
Ear, it is necessary to bear in mind, that sounds may be propagated amongst
solid or fluid bodies in three ways, — by reciprocation, by resonance, and by
conduction. — 1. Vibrations of reciprocation are excited in a sounding body,
when it is capable of yielding a musical tone of definite pitch, and another
body of the same pitch is made to sound near it. Thus if two strings of the
same length and tension be placed along side of each other, and one of them
be sounded with a violin-bow, the other will be thrown into reciprocal vibra-
tion ; or if the same tone be produced near the string in any other manner,
as by a flute, or a tuning-fork, the same effect will result. — 2. Vibrations of
resonance are of somewhat the same character; but they occur when a sound-

428

ON SENSATION, AND THE ORGANS OF THE SENSES.

[Fig. 189.

The soft parts of the Vestibule taken out of their bony case, so as to show the distribution of the Nerves
-ii the Ampullae ; 1, the superior semicircular membranous canal or tube ; 2, the external semicircular
tube ; 3, the inferior semicircular tube ; 4, the tube of union of the superior and inferior canals ; 5, the
sacculus ellipticus ; 6, the sacculus sphericus ; 7, the portio dura nerve; 8, the anterior fasciculus of the
auditory nerve ; 9, the nerve to the sacculus sphericus ; 10, 10, the nervous fasciculi to the superior and
external ampullae; 11, the nerve to the sacculus ellipticus ; 12, the posterior fasciculus of the auditory
nerve, furnishing 13, the filaments of the sacculus sphericus, and 14, the filaments of the cochlea, cut off.]

iff. 190.

The Ampulla of the External Semicircular Membranous Canal, showing the Mode of termination of its
Nerve.]

ing body is placed in connection with any other, of which one or more parts
may be thrown into reciprocal vibration, even though the tone of the whole
be different, or it be not capable of producing a definite tone at all. This is
the case, for example, when a tuning-fork in vibration is placed upon a sound-
board ; for even though the whole board have no definite fundamental note,*

* The fundamental note of a body is the lowest tone which it will yield, when the whole
of it is in vibration together. By dividing the body into two or more distinct parts, it may

SENSE OF HEARING. 429

it will divide itself into a number of parts, which will reciprocate the original
sound, so as greatly to increase its intensity; and the same sound-board will
act equally well for tuning-forks of several different degrees of pitch. When
a smaller body is used for resonance, however, it is essential that there should
be a relation between its fundamental note and that of the sonorous body;
otherwise no distinct resonance is produced. Thus, if a tuning-fork in vibra-
tion be held over a column of air in a tube, of such a length that the same note
would be given by its vibration, its sound will be reciprocated. And if it be
held over a pipe, the column of air in which is a multiple of this, the column
will divide itself into that number of shorter parts, each of which will recipro-
cate the original sound, and the total action will be one of resonance. But if
the length of the pipe bear no such correspondence with the note sounded by
the tuning-fork, no resonance is given by the column of air it contains. — 3.
Vibrations of conduction are the only ones by which sounds can strictly be
said to be propagated. These are distinguishable into various kinds, into
which it is not requisite here to inquire. It should be remarked, however,
that all media, fluid, liquid, or solid, are capable of transmitting sound in this
manner, — a vacuum being the only space through which it cannot pass.
The transmission is usually much more rapid through solid bodies, than
through liquid ; and through liquid, than through gaseous. The greatest
diminution in the intensity of sound is usually perceived, when a change takes
place in the medium through which it is propagated, especially from the aeri-
form to the liquid.

561. The detailed application of these principles has been most elaborately
worked out by Miiller ; and the following statement of what may be regarded
as the present condition of our knowledge of the subject, is little more than
an abstract of his results. Considering it desirable, in the first place, to estab-
lish the conditions under which those animals hear that are constantly im-
mersed in water, he made a series of experiments, from which he draws the
following conclusions : — i. Sonorous vibrations, excited in water, are imparted
with considerable intensity to solid bodies. — n. Sonorous vibrations of solid
bodies are communicated with greater intensity to other solid bodies brought
in contact with them, than to water ; but with much greater intensity to
water, than to atmospheric air. — in. Sonorous vibrations are communicated
from air to water with great difficulty, — with very much greater difficulty
than they are propagated from one part of the air to another ; but their transi-
tion from air to water is much facilitated, by the intervention of a membrane
extended between them. — iv. Sonorous vibrations are not only imparted from
water to solid bodies with definite surfaces, which are in contact with the
water, but are also returned with increased intensity by these bodies to the
water ; so that the sound is heard loudly in the vicinity of those bodies, in
situations where, if it had its origin in the conducting power of the water
alone, it would be faint. — v. Sonorous undulations, propagated through water,
are partially reflected by the surfaces of solid bodies. — vi. Thin membranes
conduct sound in water without any loss of its intensity, whether they be
tense or lax. — From HI., iv., and vi., we learn the mode in which the sound

be made to give a great variety of sounds. Thus, if a stretched string be divided by a bridge
into two equal parts, each will sound the octavo of the fundamental note, or the 8th note
above it. If it be divided into three parts, each will give the 12th above the fundamental
note; if into four, the 15th or double, octave will be heard; if into five, the 17th; if into six,
the 1 9th ; if into seven, the 20£th (flat seventh above the second octave); if into eight, the
22d or triple octave. A string forcibly set in vibration has a tendency to sound these har-
monics with the fundamental note, by spontaneous division into several distinct segments of
vibration ; as may be easily made evident by striking one of the lower keys of the piano,
and listening to the sounds heard whilst the fundamental note is dying away.

430 ON SENSATION, AND THE ORGANS OF THE SENSES.

is conducted to the ear, in aquatic animals not breathing atmospheric air.
The labyrinth of such is either entirely inclosed witbin the bones of the head,
as in the Cephalopoda, and in the Cyclostome and Osseous Fishes ; or, its
cavity being prolonged to the surface of the body, it is there brought into
communication with the conducting medium, by means of a membrane, — be-
sides receiving the vibrations through the medium of the solids of the body,
as is the case in Cartilaginous Fishes and Crustacea. It would seem as if,
in the Osseous Fishes, the resonance of the cranial bones, in which the laby-
rinth is imbedded, were sufficient to give the requisite increase of intensity to
the sound ; whilst in the Cartilaginous orders, the softness of these bones
renders some other means necessary. In addition to this, we find in many
Fishes a communication with the air-bladder; which indeed seems to have,
in these, but little other use. The mode in which this increases by resonance
the intensity of the sounds, will appear from the following experimental con-
clusions.— vii. When sonorous vibrations are communicated from water to
air inclosed in membranes or solid bodies, a considerable increase in the in-
tensity of the sound is produced, by the resonance of the air thus circum-
scribed.— vin. A body of air inclosed in a membrane, and surrounded by
water, also increases the intensity of the sound by resonance, when the sono-
rous undulations are communicated to it by a solid body. From these ob-
servations, it may be concluded, that the air-bladder of Fishes, in addition to
other uses, serves the purpose of increasing by resonance the intensity of the
sonorous undulations, communicated from the water to the body of the Fish.
Moreover, as the conducting and resonant power of the air in the air-bladder
is greater in proportion to its density, the influence of this organ on the per-
ception of sounds will, of course, be greater in deep waters, where the pres-
sure upon it is considerably increased.

562. Most animals living in air, are provided with an opening into the ves-
tibule, covered by a thin membrane; and, in the majority of cases, with the
tympanic apparatus also. The following experimental results bear upon the
manner in which the Ear of such animals is affected by sound. — ix. Sono-
rous undulations, in passing from air directly into water, suffer a considerable
diminution in their strength; while, on the contrary, if a tense membrane
exists between the air and the water, the sonorous undulations are communi-
cated from the former to the latter medium with great intensity. — x. The so-
norous vibrations are also communicated without any perceptible loss of in-
tensity, from the air to the water ; when, to the membrane forming the me-
dium of communication, there is attached a short solid body, which occupies
the greater part of its surface, and is alone in contact with the water. — xi. A
small solid body, fixed in an opening by means of a border of membrane, so
as to be movable, communicates sonorous vibrations, from air on one side, to
water or the fluid of the labyrinth on the other, much better than solid media
not so constructed. But the propagation of sound to the fluid is rendered
much more perfect, if the solid conductor, thus occupying the opening, is by
its other end fixed to the middle of the tense membrane, which has atmo-
spheric air on both sides. — The fact stated in ix. is evidently one of great im-
portance in the physiology of hearing ; and fully explains the nature of the
process in those animals which receive the sonorous vibrations through air,
but which have no tympanic apparatus. In x. we have the elucidation of the
action of the fenestra ovalis, and of the movable plate of the stapes which
occupies it, in animals living in air, but destitute of tympanic apparatus; this
is naturally the case in many Amphibia ; and it may happen as the result of
disease in the Human subject. In xi. we have a very interesting demonstra-
tion of the purpose and action of the tympanum, in the more perfect forms of
the auditory apparatus. We are now prepared to inquire, in somewhat more

SENSE OF HEARING. 431

of detail, into the action of the different parts of this apparatus ; and it will be
better to commence with that of the Internal Ear, the accessory organs being
afterwards considered.

563. The object of the Membrana Tympani is evidently to receive the
sonorous undulations from the air, in such a manner as to be thrown by them
into a recriprocal vibration, which is to be communicated to the chain of bones.
This membrane is, in its usual state, rather lax than tense; and this laxity is
found by experiment to be, for a small membrane, the best condition for the
propagation of ordinary sounds. This is easily rendered sensible in one's
own person ; for an increased tension may be given to the membrana tym-
pani, either by holding the breath and forcing air into the Eustachian tube, so
as to distend it from within, or by exhausting the cavity, so as to cause the
external air to make increased pressure upon it. In either case the hearing is
found immediately to become indistinct. It is observed, however, that grave
and acute sounds are not equally affected by this action ; for the experimenter
renders himself deaf to grave sounds, whilst acute sounds are heard even more
distinctly than before. This fact is easily understood by referring to the laws
of Acoustics already mentioned. The greater the tension to which the mem-
brana tympani is subjected, the more acute will be its fundamental tone; and
as no proper reciprocation can take place in it, to any sound lower than its
fundamental tone, its power of repeating perfectly the vibrations proper to the
deeper notes will diminish. The nearer a sound approaches to the funda-
mental note proper to the tense membrane, the more distinctly will it be heard.
On the other hand, when the membrane is in its natural lax condition, its fun-
damental note is very low, and it is capable of repeating a much greater vari-
ety of sounds ; for, when it receives undulations of a higher tone, than those
to which the whole membrane would reciprocate, it divides itself into distinct
segments of vibration, which are separated by lines of rest; and every one of
these reciprocates the sound;* at the same time rendering it more intense by
multiplication. These facts enable us to understand the influence of the ten-
sor tympani muscle, in modifying the tension of the membrane, and thus caus-
ing it to vibrate in reciprocation to sounds having a great variety of funda-
mental notes. Moreover, the fact that some persons are deaf to grave sounds,
whilst they readily hear the more acute, is thus accounted for. The tensor
tympani, like the iris, is probably excited to operation by a reflex action ; and
it is by no means improbable that one of its functions may be, to prevent the
internal ear from being too violently affected by loud sounds, by putting the
membrana tympani into such a state of tension, as not readily to reciprocate
them.

564. The uses of the Tympanic cavity are very obvious. One of its pur-
poses is, to render the vibrations of the membrane quite free ; and the other,
to isolate the chain of bones, in such a manner as to prevent their vibrations
from being weakened, by diffusion through the surrounding solid parts. As to
the objects of the Eustachian tube, however, opinions have been much divided.
From the experiments of Muller it appears, that it does not increase the intens-
ity of sound, but that it prevents a certain degree of dulness, which would
attend it, if the cavity of the tympanum were completely closed ; of this dul-
ness we are conscious, when any tumefaction of the fauces causes an occlusion
of the extremity of the tube. It has been supposed that, among other uses,

This is very easily proved by experiments on a membrane stretched over a resonant
cavity ; if light sand be strewed upon it, and a strong musical tone be protluced in its vicinity,
the membrane will immediately be set in vibration, not as a whole (unless its fundamental note
be in unison with that sounded), but in distinct segments, of which every one reciprocates the
sound ; from the vibrating parts, the sand will be violently thrown off; but it will settle on the in-
termediate lines of rest, forming a variety of curious figures, which are known as the rcorfa/lines.

432 ON SENSATION, AND THE ORGANS OF THE SENSES.

this canal serves for the conduction of the speaker's voice to his ears ; but this
is certainly not the case in any considerable degree ; for, when the Eustachian
tubes are obstructed by disease, the patient hears his own voice well, though
other sounds are indistinct ; and it is easily shown, that its transmission is
chiefly accomplished in other ways. The common idea is, that it serves the
same purpose with the hole in an ordinary drum ; the effect of which is gene-
rally supposed to be, the removal of the impediment to the vibrations of the
membrane, that would be offered by the complete inclosure of the air within.
It does not appear, however, that any such impediment is really offered ; and
the effect of the hole in the drum seems rather to be the communication, to
the ear of the auditor, of the sonorous vibrations of the contained air ; which
are thus transmitted directly through the atmosphere, instead of being weak-
ened by transmission through the walls of the instrument. Hence there is no
real analogy in the two cases. The principal object of the Eustachian tube
(which is always found where there is a tympanic cavity), seems to be, the
maintenance of the equilibrium between the air within the tympanum and the
external air ; so as to prevent inordinate tension of the membrana tympani,
which would be produced by too great or too little pressure on either side,
and the effect of which would be imperfection of hearing. It also has the
office of conveying away mucus secreted in the cavity of the tympanum, by
means of cilia vibrating on its lining membrane ; and the deafness, conse-
quent on occlusion of this tube, is in part explicable by the accumulation,
which will then take place in the tympanum.

565. From what has been stated, it is evident that sonorous undulations
taking place in the air, will be propagated to the fluid contained in the laby-
rinth,— through the tympanum, the chain of bones, and the membrane of the
fenestra ovalis to which the stapes is attached, — without any loss, but rather
an increase, of intensity. Why water should be chosen as the medium through
which the impression is to be made upon the nerve, it is impossible for us to
say with anything like certainty, in our present state of ignorance as to the
physical character of that impression. But, the problem being, to communi-
cate to water the sonorous undulations of air, the experimental results already
detailed satisfactorily prove that, — whilst this may be accomplished, in a de-
gree sufficient for the wants of the inferior animals, by the simple interposition
of a tense membrane between the air and the fluid, — the tympanic apparatus
of the higher classes is most admirably adapted for this purpose. The fenes-
tra ovalis is not, however, the only channel of communication between the
tympanum and the labyrinth ; for there is, in most animals, a second aperture,
the fenestra rotunda, leading into the cochlea, and simply covered with a mem-
brane. It is generally supposed that, the labyrinth being filled with a nearly
incompressible fluid, this second aperture is necessary to allow of the free
vibration of that fluid, — the membrane of the fenestra rotunda being made to
bulge out, as that of the fenestra ovalis is pushed in. It may, however, be
easily shown by experiment, as well as by reference to comparative anatomy,
that no such contrivance is necessary ; for sonorous undulations may be ex-
cited in a non-elastic fluid, completely inclosed within solid walls at every
part, except where these are replaced by the membrane through which the
vibrations are propagated ; and this is precisely the condition, not only of the
Invertebrated animals, but even of Frogs ; in which last a tympanic apparatus
exists, without a second orifice into the labyrinth. Moreover it is certain, that
the vibrations of the air in the cavity of the tympanum, must of themselves
act upon the membrane of the fenestra rotunda ; and this is perhaps the most
direct manner in which the fluid in the cochlea will be affected; although it
will ultimately be thrown into much more powerful action, by the transmission
of vibrations from the vestibule. For it lias been satisfactorily determined by

SENSE OF HEARING.
[Fig. 191.

433

The labyrinth of the Left Ear, laid open in order to show its cavities and the Membranous Labyrinth;
after Breschet; 1, the cavity of the vestibule, opened from its anterior aspect in order to show the three-
cornered form of its interior, and the membranous labyrinth which it contains ; the figure rests upon the
common saccule of the membranous labyrinth— the sacculus communis; 2, the ampulla of the superior
or perpendicular semicircular canal, receiving a nervous fasciculus from the superior branch of the
vestibular nerve ; 3, 4, the superior or perpendicular canal with its contained membranous canal ; 5, the
ampullaof the inferior or horizontal semicircular canal, receiving a nervous fasciculus from the superior
branch of the vestibular nerve ; 6, the termination of the membranous canal of the horizontal semicircular
canal in the sacculus communis ; 7, the ampulla of the middle or oblique semicircular canal, receiving a
nervous fasciculus from the inferior branch of the vestibular nerve ; 8, the oblique semicircular canal
with its membranous canal ; 9, the common canal, resulting from the union of the perpendicular with
the oblique semicircular canal ; 10, the membranous common canal terminating in the sacculus com-
munis ; 11, the otoconite of the sacculus communis seen through the membranous parietes of that sac ; a
nervous fasciculus from the inferior branch of the vestibular nerve is seen to be distributed to the saccu-
lus communis near to the otoconite ; the extremity of the sacculus above the otoconite is lodged in the
superior ventricle of the vestibule, and that below it in the inferior ventricle ; 12, the sacculus proprius
situated in the anterior ventricle ; its otoconite is seen through its membranous parietes, and a nervous
fasciculus derived from the middle branch of the vestibular nerve, is distributed to it ; the spaces around
the membranous labyrinth are occupied by the aqua labyrinthi; 13, the first turn of the cochlea; the
figure is situated in the scala tympani ; 14, the extremity of the scala tympani corresponding with the
fenestra rotunda; 15, the lamina spiralis ; the figure is situated in the scala vestibuli; 16, the opening of
the scala vestibuli into the vestibule ; 17, the second turn of the cochlea ; the figure is placed upon the
lamina spiralis, and, therefore, in the scala vestibuli, the scala lympani being benealh the lamina; 18,
the remaining half turn of the cochlea ; the figure is placed in the scala tympani ; 19, the lamina spiralis
terminating in a falciform extremity ; the dark space included within the falciform curve of the extremity
of the lamina spiralis is the helicotrema; 20, the infuudibulum.]

experiment (xii.), that vibrations are transmitted with very much greater in-
tensity to water, when a tense membrane, and a chain of insulated solid bodies
capable of free movement, are successively the conducting media, than when
the media of communication between the vibrating air and the water are the
same tense membrane, air, and a second membrane : — or, to apply this fact
to the organ of hearing, the same vibrations of the air act upon the fluid of the
labyrinth with much greater intensity, through the medium of the chain of
auditory bones and the fenestra ovalis, than through the medium of the air of
the tympanum and the membrane closing the fenestra rotunda. — The fenestra
rotunda is not to be considered as having any peculiar relation with the cochlea;
since, in the Turtle tribe, the former exists without the latter.

566. In regard to the functions of particular parts of the labyrinth, no cer-
tainty can be said to exist. From the experimental results already stated, it
appears likely that, the greater the extension of the cavity into the dense sub-
stance of the bone, the greater will be the resonance communicated to the
fluid, and thence transmitted to the nerves exposed to its influence. — It is
37

434

ON SENSATION, AND THE ORGANS OF THE SENSES.

[Fig. 192.

A view of the labyrinth of the Left Side, laid open in1 its whole extent so as to show its Structure; these
figures are all magnified ; 1, the thickness of the outer covering of the cochlea; 2, 2, the scala vestibuli
or upper layer of the lamina spiralis ; 3, 3, the scala tympani or lower layer of the lamina spiralis ; 4, the
hamulus cochleae ; 5, centre of the infundibulum ; 6, the foramen rotundum communicating with the tym-
panum ; 7, the thickness of the outer layer of the vestibule ; S, the foramen rotundum ; 9, the fenestra
ovalis; 10, the orifice of the aqueduct of the vestibule ; 11, the inferior semicircular canal; 12. the superior
semicircular canal; 13, the external semicircular canal; 14, the ampulla of the inferior canal; 15, the
ampulla of the superior canal ; l(i, the common orifice of the superior and inferior canals; 17, the ampulla
of the external canal.]

commonly supposed that the Semicircular Canals have for their peculiar func-
tion, the reception of the impressions by which we distinguish the direction of
sounds; and it is certainly a powerful argument in support of this view, that,
in almost every instance in which these parts exist at all, they hold the same
relative position to each other as in Man, their three planes being nearly at
right angles to one another. The idea, however, must be regarded as a mere
speculation, the value of which cannot be decided without an increased know-
ledge of the laws, according to which sonorous vibrations are transmitted. —
Regarding the special function of the Cochlea, there is precisely the same un-
certainty. This part of the organ is peculiar in one respect, — that the expan-
sion of the auditory nerve is here spread out (upon the lamina spiralis) in
closer proximity with the bone itself, than it is in any other part of the laby-
rinth ; so that the vibrations of the bone will be more directly communicated
to the nerve. It is not easy to see, however, what can be the peculiar object
of this disposition, in regard to the function of hearing. By M. Duges it is
surmised, that by the cochlea we are especially enabled to estimate the pitch
of sounds, particularly of the voice ; and he adduces, in support of this idea,
the fact, that the development of the cochlea follows a very similar proportion
with the compass of the voice. This is much the greatest in the Mammalia:
less in liirds ; and in Reptiles, which have little true vocal power, the cochlea
is reduced to its lowest form, disappearing entirely in the Amphibia. That
there should be an acoustic relation between the voice and ear of each species
of animal, cannot be regarded as improbable ; but the speculation of M. Duges
can at present only be received as a stimulus to further inquiry.

567. We have now to consider the functions of the accessory parts, — the
External Ear, and the Meatus. The Cartilage of the external ear may pro-

SENSE OF HEARING.

435

pagatc sonorous vibrations in two ways, — by reflection, and by conduction.
In reflection, the concha is the most important part, since it directs the reflected
undulations towards the tragus, whence they are thrown into the auditory
passage. The other inequalities of the external ear cannot promote hearing
by reflection ; and the purpose of the extension of its cartilage is evidently to
receive the sonorous vibrations from the air, and to conduct them to its point
of attachment. In this point of view, the inequalities become of importance ;
for those elevations and depressions upon which the undulations fall perpen-
dicularly, will be affected by them in the most intense degree ; and in conse-

[Fig. 193.

[Fig. 194.

A view of the Left Ear in its natural state ; 1. 2,
the origin and termination of the helix ; 3, the anti-
helix ; 4, the anti-tragus ; 5, the tragus; G, the Jobus
of the external ear; 7, points to the scapha and is on
the front and top of the pinna ; 8, the concha; 9, the
meatus auditorius externus.]

An anterior view of the External Ear, as well
as of the Meatus Auditorius, Labyrinth, &c. ; 1,
the opening into the ear at the bottom of the con-
cha ; 2, the meatus auditorius externus or car-
tilaginous canal ; 3, the membrana tympani
stretching upon its ring ; 4, the malleus ; 5, the
stapes; 6. the labyrinth.]

quence of the varied form and position of these inequalities, sonorous undula-
tions, in whatever direction they may come, must fall advantageously upon
some of them. — The functions of the Meatus appear to be threefold. The
sonorous undulations entering from the atmosphere are propagated directly,
without dispersion, to the membrana tympani : — the sonorous undulations
received on the external ear, are conveyed along the walls of the meatus to
the membrana tympani: — the air which it contains, like all insulated masses
of air, increases the intensity of sounds by resonance. That, in ordinary
hearing, the direct transmission of atmospheric vibrations to the membrana
tympani, is the principal means of exciting the reciprocal vibrations of the
latter, is sufficiently evident ; the undulations which directly enter the passage,
will pass straight on to the membrane; whilst those that enter obliquely will
be reflected from side to side, and at last will fall obliquely on the membrane,
thus perhaps contributing to the notion of direction. The power of the lining
of the meatus to conduct sound from the external ear, is made evident by the
fact, that, when both ears are closely stopped, the sound of a pipe having its
lower extremity covered by a membrane, is heard more distinctly, when it is
applied to the cartilage of the external ear itself, than when it is placed in con-
tact with the surface of the head. The resonant action of the air in the tube
is easily demonstrated, by lengthening the passage by the introduction of

436 ON SENSATION, AND THE ORGANS OF THE SENSES.

another tube; the intensity of external sounds, and also that of the individual's
own voice, as heard by himself, is then much increased.

568. Many facts prove, however, that the fluid of the labyrinth may be
thrown into vibration in other ways, than by the tympanic apparatus. Thus
in Osseous Fishes, it is only by the vibrations transmitted through the bones
of the head, that hearing can take place. There are many persons, again,
who can distinctly hear sounds which are thus transmitted to them ; although,
through some imperfection of the tympanic apparatus, they are almost insen-
sible to those which they receive in the ordinary way. It is evident, where
this is the case, that the nerve must be in a state fully capable of functional
activity ; and, on the other hand, where sounds cannot thus be perceived,
there will be good reason to believe that the nerve is diseased. •

569. A single impulse communicated to the Auditory nerve, in any of the
foregoing modes, seems to be sufficient to excite the momentary sensation of
sound ; but most frequently a series of such impulses is concerned, there
being but few sounds which do not partake, in a greater or less degree, of
the character of a tone. Any continuous sound or tone is dependent upon a
succession of such impulses ; and its acuteness or depth is governed by the
rapidity with which they succeed one another.

a. It is not difficult to ascertain by experiment, what number of such impulses or undula-
tions are required, to give every tone which the ear can appreciate. Thus, if a circular plate,
with a number of apertures at regular intervals, be made to revolve over the top of a pipe
through which air is propelled, a succession of short puffs will be allowed to issue from this ;
and, if the revolution is sufficiently rapid, these impulses will unite into a definite tone. In
the same manner, if a spring be fixed near the edge of a revolving toothed wheel, in such
a mariner as to be caught by every tooth as it passes, a succession of clicks will be heard ;
and these too, if the revolution of the wheel be sufficiently rapid, will produce a tone. The
number of apertures in the plate, which pass the orifice of the pipe in a given time, or the
number of teeth which pass the spring, being known, it is easy to see, that this must be the
number of impulses required to produce the given tone. Each impulse produces a double
vibration, — forwards and backwards (as is seen when a string is put in vibration, by pulling
it out of the straight line); hence the number of impulses is always half that of the single
vibrations. The maximum and minimum of the intervals of successive pulses, still appre-
ciable by the ear as determinate sounds, have also been determined by M. Savart, more satis-
factorily and more accurately than had previously been done. If their intensity is great,
sounds are still audible which result from the succession of 24,000 impulses in a second;
and this, probably, is not the extreme limit to the acuteness of sounds perceptible by the ear.
From some observations of Dr. Wollaston's, it seems probable that the ears of different indi-
viduals are differently constituted in this respect, — some not being able to hear very acute
tones produced by Insects, or even Birds, which are distinctly audible to others. Again, the
sound resulting from 16 impulses per second, is not, as has been usually supposed, the lowest
appreciable note ; on the contrary, M. Savart has succeeded in rendering tones distinguisha-
ble, which are produced by only 7 or 8 impulses inji second; and continuous sounds of a
still deeper tone could be heard, if the individual pulses were sufficiently prolonged. In
regard, however, to the precise time during which a sonorous impression remains upon the
ear, it is difficult to procure exact information, since it departs more gradually th:m do visual
impressions from the eye. This is certain, however, — that it is much lotmer than the interval
between the successive pulses in the production of tones; since it was found by M. Savart,
that one or even several teeth might be removed from the toothed wheel, without a percep-
tible break in its sound, — showing that, when the tone was once established, the impression
of it remained during an intermission of some length.

570. The Ear may, like the Eye, vary considerably, as regards general
acuteness amongst different individuals; and its power may be much increased
by practice. A part of this increase depends, however, as in other instances,
upon the greater attention which its fainter indications receive ; but a part,
also, upon an increased use of the organ. The power of hearing very faint
sounds, is as different from the power of distinguishing musical tones, as the
power of discerning very minuto objects, or of seeing with very faint degrees
of light, is from that of distinguishing colours. Many persons are altogether

SENSE OF HEARING. 437

destitute of what is termed a musical ear ; whilst others are endowed with it
in a degree, which is a source of great discomfort to them, since every discord-
ant sound is a positive torment. The power of distinguishing the direction
of sounds appears to be, in Man, at least, for the most part acquired by habit.
It is some time before the infant seems to know anything of the direction of
noises, which attract his attention. Now although there can be no question,
that this perception is acquired by attention to certain variations in the impres-
sion made upon the nerve, through the medium either of the tympanic appa-
ratus, or of the bones of the head, yet it is equally evident, that there can be
nothing in these variations themselves adequate to excite the idea, and that it
must therefore be either intuitive or acquired by habit. This is a considera-
tion of some importance, in regard to the similar question as to the sense of
Visual direction. In some cases we are probably assisted by the relative in-
tensity of the sensations, communicated by the two ears respectively. The
idea of the distance of the sonorous body is another acquired perception, de-
pending principally upon the loudness or faintness of the sound, when we
have no other indications to guide us. In this respect, there is a great simi-
larity between the perception of the distance of an object, through the Eye,
by its size, and through the Ear, by the intensity of its sound. When we
know the size of the object, or are acquainted with the usual intensity of its
sound, we can judge of its distance ; and vice versa, when we know its dis-
tance, we can at once form an idea of its real from its apparent size, and of
its real strength of tone from that which affects our ears. In this manner,
the mind may be affected with corresponding deceptions through both senses;
thus, in the Phantasmagoria, the figure is gradually diminished whilst its dis-
tance remains the same, and it appears to the spectators to recede, — the illu-
sion being more complete, if its brightness be at the same time diminished;
and the effect of a distant full military band gradually approaching, may be
alike given by a corresponding crescendo of concealed instruments. It is upon
the complete imitation of the conditions which govern our ideas of the intensity
and direction, as well as of the character, of sounds, that the deceptions of the
Ventriloquist are founded.

571. Some facts of much interest have lately been ascertained, in regard to
an occasional variation in the rapidity of the perception of sensory impres-
sions, received through the Eye and through the Ear. These facts are the
result of comparisons made amongst different astronomical observers, who
may be watching the same visual phenomena, and timing their observations
by the same clock ; for it has been remarked, that some persons see the same
phenomenon, a third or even half of a second earlier than others. There is
no reason to suppose from this, however, that there is any difference in the
rate of transmission of the sensory impressions in the two nerves. The fact
seems rather to be, that the sensorium does not readily perceive two different
impressions with equal distinctness ; and that, when several impressions are
made on the nerves at the same time, the mind takes cognizance of one only,
or perceives them in succession. When, therefore, both sight and hearing are
directed simultaneously to one object, the communication of the impression
through one sense will necessarily precede that made by the other. The in-
terval between the two sensations is greater in some persons than in others ;
for some can receive and be conscious of many impressions, seemingly at
the same moment ; whilst in others a perceptible space must elapse.

572. Amongst other important offices of the power of Hearing, is that of
supplying the sensations by which the Voice is regulated. It is well known
that those who are born entirely deaf, are also dumb, — that is, destitute of the
power of forming articulate sounds ; even though not the least defect exist in
their organs of voice. Hence it appears that the vocal muscles can only be

37*

438 OF MUSCULAR CONTRACTION.

guided in their action by the sensations received through the Ears, in the same
manner as other muscles are guided by the sensations received through them-
selves (§ 433). On this point, more will be said hereafter (§611).

CHAPTER VII.

OF MUSCULAR ACTION.

1.— Of Contractility in General.

573. THE Nervous System has no power of occasioning movement in any
part of the body, save by exciting to contraction certain structures, to which
the term Muscular is given. That one tissue should possess within itself the
property of Contractility on the application of a stimulus, is no more wonderful,
than that another should be capable of conveying sensory or motor influences,
or another of separating a peculiar secretion from the blood. Such contractile
tissues are found in Vegetables, as well as in Animals ; and they appear to
consist, in both instances, of cells, whose peculiar property it is to change
their form, when subjected to certain kinds of irritation (§ 230). The only
essential difference in function, between the Contractility of the cells compos-
ing the ultimate fibrillre of Muscular Fibre, and that of the cells composing
the intumescence of the Sensitive Plant, consists in the susceptibility of the
former to a stimulus, which does not operate on the latter. Both can be made
to change their form by stimuli of various kinds, — mechanical, chemical,
electrical, &c., — directly applied to themselves ; but the contractility of Mus-
cular fibre is excited, in addition, by the stimulus of Innervation, which has
no operation in the Plant ; and it is when its peculiar property is thus excited,
that the Muscular tissue becomes the instrument of the operation of the Nerv-
ous system upon the external world, and thus performs an important part in
the purely Animal Functions. — The Muscular tissue, however, is not always
thus called into activity through the medium of the Nervous system ; for it is
employed to execute numerous movements, which are immediately connected
with the maintenance of the Organic functions, and in which the influence of
Innervation seems to be but little concerned; its contractility being excited to
action by stimuli directly applied to itself. — We have seen that there are two
forms of Muscular tissue, the striated and the non-striated, which are appro-
priated to these two purposes ; the former being the kind most readily acted
on through the Nervous System, and invariably employed in the Muscles that
are called into action by its influence ; whilst the latter (which seems a less
perfectly-developed form of the tissue) is with difficulty excited to contraction
through the Nervous System, and is usually employed in Muscles, whose
action is altogether uncontrollable by the will (§§ 225 — 234).

574. The general property of Contractility shows itself under two forms ;
which are alike distinct in the mode of their action, and in the conditions
requisite for its excitation. — Its most obvious and striking manifestations pre-
sent themselves in the Voluntary muscles and in the Heart ; which, when in
activity, exhibit powerful contractions tending to alternate with relaxations.
The modification of contractility which is concerned in producing these, is
distinguished as Irritability. — On the other hand, we find that the muscles

OF MUSCULAR IRRITABILITY. 439

exhibit a tendency to a moderate and permanent contraction, which is not
shown by them when they are dead, and which cannot, therefore, be the re-
sult of elasticity, or of any simple physical property ; and the contraction,
instead of being a result of stimulation through the nerves, is especially ex-
cited by changes of temperature in the tissue itself. This endowment, which
seems to exist in the greatest amount in certain forms of the non-striated
muscle, is called Tonicity. — These two modifications of Muscular Contract-
ility require a separate consideration.

2. — Of Muscular Irritability.

575. All Muscular Fibres, which are in possession of vital activity, may be
caused to contract by stimuli directly applied to themselves ; and these stimuli
may be of different kinds. The simplest is the contact of a solid substance,
especially if it be pointed ; thus we may excite contractions in Muscular
fibres, by simply touching them with the point of a needle or of a scalpel.
Most substances of strong chemical action, such as acids and alkalies, will ex-
cite the fibres to contraction, when directly applied to themselves; but the
most powerful agent of all is Electricity. — If we thus irritate a portion of a
muscle composed of striated fibre, the biceps, for example, the fasciculus of
fibres which is touched will immediately contract, and that one only ; and the
contracted fasciculus will soon relax, without communicating its movements
to any other. In fact, the only way to call the entire muscle into contraction
at once (since it would be impossible to apply direct irritation to every fasci-
culus), is to stimulate it through its nerves. On the other hand, if we apply
a similar irritation to a portion of non-striated fibre, as that of the Intestinal
canal, the fasciculus which is stimulated will contract less suddenly, but ulti-
mately to a greater amount ; its relaxation will be less speedy ; and, before it
takes place, other fasciculi in the neighbourhood begin to contract ; their con-
traction propagates itself to others ; and so on. In this manner, successive
contractions and relaxations may be produced through a considerable part of
the canal, by a single prick with a scalpel ; a sort of wave of contraction being
transmitted in the direction of its length, and being followed by relaxation.
Again, in the Muscular structure of the Bladder and Uterus (which is of the
non-striated kind), direct irritation excites immediate and powerful contractions,
which extend beyond the fasciculus actually irritated, and produce a great
degree of shortening; but they do not alternate in the healthy state with any
rapid and decided elongation. In the Heart, which is composed of a mixture
of striated and non-striated fibre, the Muscular substance of a large part of the
organ is thrown into rapid and energetic contraction, by a stimulus applied at
any one point; and this contraction is speedily followed by relaxation, which
is again succeeded by a number of alternating contractions and relaxations.
And in the muscular tissue of the middle coat of the Arteries, which is of the
non-striated character, the contraction takes place rather after the manner of
that of the bladder and uterus ; a considerable degree of shortening being
effected, by the contraction of other fasciculi than those directly irritated, and
this shortening not giving way speedily to relaxation ; but a prolonged appli-
cation of the stimulus is often necessary to produce the effect.

576. On the other hand, when the stimuli which excite Muscular Contrac-
tility are applied to the nerves, which supply any muscle composed of striated
fibre (the Heart only excepted), they produce a simultaneous contraction in the
whole muscle ; the effect of the stimulus being at once exerted upon every part
of it. The contraction speedily alternates with relaxation, unless the operation
of the stimulus be continued, — as when an electric current is propagated with-
out intermission along the nerve-trunks, — in which case the contraction lasts as

440 OF MUSCULAR CONTRACTION.

long as the stimulus is continuously applied, but ceases as soon as it is with-
drawn. But it has been lately stated by Volkmann,* that, if the electric
stimulus be applied to the central organs, from which the motor nerves arise,
the muscular contraction continues for some time after its renewal. If this
should prove to be a universal fact, it will afford a valuable means of distin-
guishing what are the real centres of the motor nerves of particular organs.
Further, when the continuous electric current was passed through incident or
excitor nerves, it produced alternating movements of contraction and relaxa-
tion, in the muscles which were thus called into play by reflex stimulation.
The ordinary actions of the non-striated fibre, on the other hand, are not
easily excitable by stimuli applied to their nerves ; indeed many Physiologists
have denied the possibility of producing them through this channel. Positive
evidence to this effeflt, however, has been already given (§ 388). The results
of Volkmann's recent electrical experiments upon the Heart and the Intesti-
nal Canal are of much interest. He found that neither of these organs is
thrown into fixed contraction, when the continuous electric current is applied
to the Brain and Spinal Cord ; whence he concludes that these organs are not
the centres of their motor nerves. On the other hand, alternating contrac-
tions and relaxations were produced on applying the continuous current to
the spinal cord, the par vagum, and the sympathetic nerves ; whence it may
be concluded that these parts contain afferent fibres, which excite motion
through centres that can scarcely be any others than the ganglia of the Sym-
pathetic system. When the Heart is removed from the body, and is left en-
tire, it may be thrown into a state of fixed contraction, which lasts after the
cessation of the current; whence it may be concluded, that it contains the
centre of its own motor nerves.t These experiments, however, by no means
warrant the conclusion, that the ordinary actions of these muscular organs are
dependent upon the agency of their nerves ; which is opposed by a variety of
evidence.

577. The general fact, that Muscular Contraction alternates with Relaxa-
tion at no longer intervals, — is most evident in the rhythmical movements of
the Heart, and in the peristaltic action of the Intestinal canal ; since in those
parts, the whole or a large proportion of the fibres seem to contract together,
and then shortly relax. But it is probably no less true, as formerly stated
(§ 232), of the individual fibres of those muscles, which are kept in a state
of contraction by a stimulus transmitted through their nerves; since none of
them appear, under ordinary circumstances at least, to remain in a contracted
state for any length of time, — a constant interchange of condition taking place
among the fibres, some contracting whilst others are relaxing, and vice versa.
It is difficult to speak with confidence, however, in regard to the condition of
the individual fibres of a muscle, that is thrown into a state of continued
spasmodic contraction ; such as that produced by the application of the elec-
tric current to the centre of its motor nerves (§ 576). A state of this kind is
often of considerable duration. Thus the Author has known a case of Hys-
teric Trismus, in which the jaws remained closed with the greatest violence
during five days. Whether the individual fibres, in such instances, maintain
a state of contraction without intermission, or whether the contraction of the
entire muscle is kept up by a continual interchange of the fibres actually en-
gaged, is a very curious subject for inquiry.

578. Muscles do not lose their Irritability immediately on the general
death of the system, which must be considered as taking place, when the cir-
culation ceases without a power of renewal ; in cold-blooded animals it is re-

* Muller's Arcbiv., 1844, No. 5, p. 407.

t Op. cit.; and Mr. Paget's Report for 1845, in Brit, and For. Med. Rev., July, 1S4U.

LOSS OF IRRITABILITY BY AFFECTIONS OF THE NERVOUS SYSTEM. 441

tained much longer after this period than in the higher Vertebrata, in some
of which it disappears within an hour. The muscles of young animals
generally retain their irritability for a longer time than those of adults ; on
the other hand, those of Birds lose their irritability sooner than those of Mam-
malia. Hence, as a general rule, the duration of the irritability is inversely
as the amount of respiration. From experiments on the bodies of executed
criminals, who were previously in good health, Nysten ascertained that, in
the.Humnn subject, the irritability of the several muscular structures departs
in the following time and order. — The left ventricle of the heart first; the in-
testinal canal at the end of 45 or 55 minutes ; the urinary bladder nearly at
the same time ; the right ventricle after the lapse of an hour ; the oesophagus
at the expiration of an hour and a half; the iris a quarter of an hour later ;
the muscles of Animal life somewhat later ; and lastly, the auricles of the
heart, especially the right, which in one instance contracted under the influ-
ence of galvanism 16j hours after death.

579. Muscular Irritability is deadened by many substances, especially by
those which have a narcotic or sedative action on the Nervous system. In
carbonic acid gas, hydrogen, carbonic oxide, or sulphurous acid gas, muscles
contract very feebly, or not at all, when stimulated ; whilst in oxygen they
retain their irritability longer than usual. Narcotic substances, such as a watery
solution of opium, when applied directly to the muscles, have an immediate
and powerful effect in diminishing or even destroying their irritability ; this
effect is also produced, though in a less powerful degree, by injecting these
substances into the blood. In the same manner, venous blood, charged with
carbonic acid, and deficient in oxygen, has the effect of a poison upon
muscles ; diminishing their irritability, when it continues to circulate through
them, to such a degree, that they sometimes lose it almost as soon as the cir-
culation ceases, as is seen in those who have died from gradual and therefore
prolonged Asphyxia. The unfavourable influence of venous blood is also
shown in the Morbus Creruleus ; patients affected with which are incapable
of any considerable muscular exertion. — Although most of the stimuli which
occasion the contraction of muscles, when directly applied to their fibres, ope-
rate also when applied to their motor nerves, the same does not hold good in
regard to those agents which diminish irritability. It is a fact of some im-
portance, in relation to the disputed question of the connection of muscular
irritability with the nervous system, that when, by the application of narcotic
substances to the Nerves, their vital properties are destroyed, the irritability
of the Muscle may remain for some time longer, — showing that the latter
must be independent of the former.

580. We find, however, that sudden and severe injuries of the Nervous
Centres have power to impair, directly and instantaneously, or even to destroy,
the Contractility of the whole Muscular system ; so that death immediately
results, and no irritability subsequently remains. It is in this manner, that
the sudden destruction of the Brain and Spinal Cord, especially of the latter,
occasions the immediate cessation of the Heart's action ; though they may be
gradually removed, without any considerable effect upon it. Severe concus-
sion has the same effect; hence the Syncope which immediately displays it-
self. It is sometimes an important question in Forensic Medicine, whether
an individual, who has died from the effects of a blow upon the head, could
have moved from the place where the blow was inflicted. If there be found,
as is frequently the case, no sensible disorganization of the Brain, the death
must be attributed to the concussion, and must have been in that case imme-
diate. If, on the other hand, effusion of blood has taken place within the
cranium, to any considerable extent, it is probable that the first effects of the
blow were in some degree recovered from, and that the circulation was re-

442 OF MUSCULAR CONTRACTION.

established. — It is not essential, however, that the impression should be prima-
rily made upon the Cerebro-Spinal system. The well-known fact of sudden
death not unfrequently resulting from a blow on the stomach, especially after
a full meal, without any perceptible lesion of the viscera, clearly indicates that
an impression upon the widely-spread coeliac plexus of Sympathetic nerves
(which will be much more extensively communicated to them, when the sto-
mach is full, than when it is empty), may cause the immediate cessation of
the Heart's action, in the same manner as a violent injury of the Braia or
Spinal Cord. — Now it is interesting to remark that, in all these cases, the
whole vitality of the system appears to be destroyed at once ; for the pro-
cesses which would otherwise succeed the injury, and which, after other kinds
of death, less sudden in their character, produce evident changes in the part
of the surface that has immediately received it, are here entirely prevented.
An instance is on record, in which a criminal under sentence of death deter-
mined to anticipate the law by self-destruction. Having no other means of
accomplishing his purpose, he stooped his head and ran violently against the
wall of his cell ; he immediately fell dead ; and no mark of contusion showed
itself on his forehead. The same absence of the usual results is to be noticed
in the case of blows on the stomach. Yet it is well known, that many of the
ordinary vital processes will take place in the injured parts, after death of a
more lingering nature ; the vitality of the individual organs not being destroyed
immediately on the severance of the chain which binds together the different
functions. Hence the Irritability of Muscle is not shown, by the foregoing
facts, to have any closer dependence upon the Nervous system, than have the
peculiar vital properties of any other tissue.

581. The influence of severe impressions on the Nervous System, in di-
minishing, where it does not altogether destroy, Muscular Irritability, is well
seen in the effect of severe injuries affecting vital organs, or extending over a
large part of the surface, in depressing the Heart's action. This is a well-
known result of severe burns, especially in children, whose nervous system
is more susceptible of such impressions than that of the adult; also of the
rupture of the alimentary canal, of the bladder or uretus; and of the shatter-
ing of one of the extremities, by violence affecting a large part of their sub-
stance. In all these cases, the sufferer is in the same condition with one who
has received a severe blow on the head, that does not quite stun him ; the
shock immediately diminishes the muscular contractility of the whole sys-
tem ; and its influence on the heart, which of course manifests itself most
conspicuously, produces a degree of depression which is frequently never re-
covered from, and which, at any rate, renders necessary the employment of
stimulants, for the purpose of counteracting this very dangerous effect.* — Ex-
cessive mental emotion, of a kind not in itself depressing, may occasion the
sudden cessation of the Heart's action, and a general loss of muscular Irrita-
bility; and it is well known that muscular power is greatly diminished by
emotions, which produce no other direct action.

582. There is no evidence that Muscular Irritability can be increased by
any cause operating through the Nervous system. It is quite true that, under

* The large quantity of stimulus which can be borne even by children, suffering under
severe burns, is very extraordinary. There can be no doubt that many lives have been
saved by the judicious administration of them, to an amount which would, ti priori, have
been judged in itself fatal ; but that many more have been sacriliced to neglect, even on the
part of those whose duty it is to watch the indications with the closest attention. The Au-
thor's observation leads him to believe, that Hospital-Nurses very commonly make up their
minds, that children, who have met with severe burns, must die ; and that, unless closely
watched, they neglect the means of which Science and Experience alike dictate the free em-
ployment.

INFLUENCE OF ARTERIAL BLOOD. 443

the stimulus of alcohol, nitrous oxide, &c., or of some purely mental excite-
ment, individuals can perform actions requiring a degree of strength, which
they cannot exert under any other circumstances. But it does not hence fol-
low, that the irritability is increased ; since the energy of the action may be
due solely to the power of the stimulus by which it is excited, and to the un-
usual number of fibres called into simultaneous contraction. It is well known
that stimulating agents, which thus temporarily increase Muscular power, pri-
marily excite the Nervous system ; as is shown by the increased mental acti-
vity which results from the moderate use of alcohol, nitrous oxide, opium,
&c. ; and it does not seem necessary, therefore, to go further in search of an
explanation of their effect on muscular action. — It is worthy of remark that,
whilst the influence of general depressing causes acting through the Nervous
System, is primarily manifested on the muscles of Organic life, that of stimu-
lants chiefly shows itself in the muscles subjected to the Will.

583. There can be no question that, in the living body, the energy of Mus-
cular contraction is determined (other things being equal), by the supply of
Arterial Blood, which the muscle receives. It is well known that, when a
ligature is applied to a large arterial trunk in the Human subject, there is not
only a deficiency of sensibility in the surface, but also a partial or complete
suspension of muscular power, until the collateral circulation is established.
The same result has been constantly attained, in experiments upon the lower
Animals ; the contractility of the muscle being impaired or altogether ex-
tinguished, when the flow of blood into it was arrested ; and being recovered
again, when the supply of blood was restored. The influence of this supply
of arterial blood is twofold ; — it affords the materials for the nutrition of the
tissue ; — and it furnishes (what is perhaps more immediately necessary) the
supply of oxygen required for that metamorphosis of the tissue, which seems
to be an essential condition of the generation of its contractile force. As this
oxygen is taken in through the lungs, and as the greater part of it is thrown
off — when united with carbon into carbonic acid — by the same channel, we
should expect to find a very close correspondence between the amount of
muscular power developed in an animal, and the quantity of oxygen consumed
in its Respiration : and this is in reality the case. We find, for example, that
in Birds and Insects, whose respiration is the highest, the muscular power is
greater in proportion to their size, than in any other animals. In the Mam-
malia, and certain Fishes that might be almost called warm-blooded, it is only
in a degree inferior. But in the cold-blooded Reptiles, Fishes, and Mollusca,
the muscular power is comparatively feeble ; though even here we trace gra-
dations, which accord well with the relative quantities of oxygen consumed.
But in proportion to the feebleness of the power, do we usually find its dura-
tion greater (§ 578) ; so that it is not so immediately dependent upon the
supply of oxygen, in cold-blooded, as in warm-blooded animals. Thus, it is
found that Frogs are still capable of voluntary movement, after the heart has
been cut out ; they can move limbs which are connected with the trunk by
the nerves alone : and that this power is not altogether due to the blood which
may remain in the capillary vessels, is shown by the experiment of Muller,
who found the muscles still contractile, after he had expelled all the blood,
by forcing a current of water into an artery, until it escaped from the divided
veins.

584. It seems probable that the Muscles of Organic life are less dependent
upon a supply of arterialized blood, than are those of Animal life ; for the
Heart will continue to contract, when the blood in its vessels is entirely ven-
ous, and when the circulation in it has come to a stand. Still the dependence
of its action upon a constant supply of arterial blood, is very close ; and in all
animals, however different the plans of their circulation, we find a provision

444 OF MUSCULAR CONTRACTION.

for this supply, by a special arrangement of the coronary arteries.* That the
heart's action comes to an end much sooner, after the destruction of animal
life by pithing, when the coronary arteries have been tied, than when they
are left untouched, has been proved by the experiments of Mr. Erichsen.t
In an animal that has been pithed, but whose heart has been left intact, artificial
respiration will easily keep up its action for an hour, or an hour and a half.
But when the coronary arteries were tied, a mean of six experiments gave a
duration, for the ventricular action, of only 23d minutes after the ligatures
were applied, and 32^- minutes after the pithing; and in no instance was it
prolonged more than 31 minutes after the application of the ligature, or 37
minutes after the pithing. On the other hand, when the aorta was tied, so
that the coronary arteries were distended with blood, the circulation being
carried on through them alone, the right ventricle continued to act up to the
82d minute.

585. There is a remarkable difference in the degree of Irritability in the two
sides of the heart, to which Dr. M. Hall has directed attention. In the warm-
blooded Vertebrata, the right side of the heart will act on the stimulus of ven-
ous blood ; whilst the left side requires the stimulus of arterial. In Fishes,
on the other hand, whose heart corresponds to the right side only of that of
Man, the whole is put in action by venous blood. In Reptiles, one auricle is
sufficiently stimulated by venous blood, whilst the other requires arterial ; and
the ventricle is excited to action by a mixed fluid. In all these cases, there
must be a marked difference in the properties of the several parts ; some being
sufficiently affected by a stimulus, which is totally inoperative on others.
This is still more remarkably exemplified by the fact, that the muscular fibre
of Frogs would be thrown into a state of permanent and rigid contraction
(through the powerful operation of its property of Tonicity), by the stimulus
of a fluid no hotter than the blood, which ordinarily bathes the muscles of
Birds. Now in those warm-blooded animals which pass the winter in a state
of torpidity, the respiration is very slow and imperfect, and the blood is very
imperfectly arterialized. There must, therefore, be a change in the properties
of the left ventricle, by which it becomes capable of action on a more feeble
stimulus, thus resembling the ventricle of Reptiles.

a. This change Dr. M. Hall designates as an increase of Irritability; considering that,
if muscular action be excited by a more feeble stimulus, the property to which that action is
due, must be itself more exalted. Physiologists have been so long accustomed, however, to
consider the irritability of the muscles in warm-blooded animals as greater than that of cold-
blooded, on account of the greater energy and rapidity of their contractions when excited,
that it seems undesirable to modify the term in the manner proposed by Dr. Hall. No one
will assert that the vitality of the Muscle is exalted, when it is reduced to the condition of that
of the Reptile; and, as Irritability is strictly a vital property, it cannot be correctly spoken of
in that manner. The general principle, however, laid down by Dr. M. Hall, — that the facility
with which the muscular system may be excited to contraction, or in other words the feeble-
ness of the stimulus required for the purpose, is inversely as the respiration of the animal, —
is, no doubt, generally correct.

586. The doctrine, now generally accepted as a Physiological truth, that the
active exercise of the Contractility of Muscle, is attended with a waste or dis-
integration of its tissue, rests upon a great variety of evidence. The increase
of the demand for food, occasioned by Muscular activity (§ 263), is an indica-
tion that the nutritive operations are excited by it ; and the purpose of these
can scarcely be anything else, than the reparation of the loss which the Mus-
cle has sustained. Again, it has been just shown, that the presence of Oxygen
is essential to the development of the Contractile force ; and there is evidence
that, in this development, a chemical change is effected in the substance of the

* Dr. M. Hall's Gulstonian Lectures, pp. 23, 24. f Medical Gazette, July 8, 1842.

DISINTEGRATION AND NUTRITION OF MUSCLE. 445

Muscle, which is of a nature destructive to its integrity as an organized tissue.
For, in the first place, the researches of Helmholtz, formerly referred to
(§ 238, 6), indicate such a change, from the comparative results of Chemical
analysis of the muscle, before and after the violent excitement of its contrac-
tility. But it is still more decidedly shown, by the increase in the excretions,
which is consequent upon Muscular activity; and especially by the augmenta-
tion of the Carbonic acid set free from the respiratory organs, and by that of
the Urea set free from the kidneys. The amount of the latter, indeed, may be
regarded, cseteris paribus, as an approximative indication of the quantity of
Muscular tissue which has undergone disintegration ; being increased or
diminished, in precise proportion to the degree of exertion to which the
Muscular system has been subjected. — It cannot but be regarded as a probable
inference from these facts, that the development of the Contractile force is in
some way dependent upon the Chemical change, which seems to be so essen-
tial a condition of it; just as the development of the Electric force of the
Galvanic battery is dependent upon the new chemical arrangements, which
take place between the bodies brought to act upon one another in its trough.

587. The frequently-renewed exercise of Muscles, by producing a deter-
mination of blood towards them, occasions an increase in their nutrition ; so
that a larger amount of new tissue becomes developed, and the muscles are
increased in size and vigour. • This is true, not only of the whole Muscular
system when equally exercised; but also of any particular set of muscles,
which is more exercised than another. Of the former we have examples in
those who practise a system of Gymnastics adapted to call the various mus-
cles alike into play ; and of the latter, in the limbs of individuals who follow
any calling, that habitually requires the exertion of either pair, to the partial
exclusion of the other, — as the arms of the Smith, or the legs of the Opera-
dancer. But this increased nutrition cannot take place, unless an adequate
supply of food be afforded ; and if the amount of nutritive material be insuffi-
cient, the result will be a progressive diminution in the size and power of the
muscles ; which will manifest itself the more rapidly, as the amount of exer-
tion, and consequently the degree of waste, are greater. Nor can it be effected,
if the exercise be too constant ; for it is during the intervals of repose that
the reparation of the muscular tissue occurs; and the Muscular system, like
the Nervous (§ 294), may be worn out by too constant use. The more violent
the action, the longer is the period of subsequent repose, which is required for
the reparation of the tissue : and the longest will, of course, be requisite, when
(as sometimes occurs) the contractility of the muscle is so completely ex-
hausted by excessive stimulation, that no new manifestation of it can be ex-
cited. Nevertheless it is certain, that there must be a provision in some Mus-
cles, for the continuance of their nutrition during their state of activity; for in
no other way could the Heart and Respiratory Muscles, which are in unceas-
ing action during the whole of life, be kept in a state fit for the discharge of
their functions.

588. On the other hand, Muscular Irritability, like the vital properties of
other parts, is diminished by want of action; and in this, as in other cases, it
is quite clear that the cause of its loss is to be found in the alteration of the
nutritive processes, which is the uniform result of the cessation of the usual
operations of any part. The Muscular tissue, like all other soft organized
substances, has a constant tendency to spontaneous disintegration, especially
at the high temperature of the body in warm-blooded animals ; and it is con-
sequently subject to a slow and regular waste, quite irrespectively of that pro-
duced by its vital activity.* Now when a Muscle or set of Muscles, in a

This does not occur with nearly the same rapidity in cold-blooded Animals, nor in the
38

446 OF MUSCULAR CONTRACTION.

warm-blood animal, is reduced to a state of prolonged inactivity, from what-
ever cause, its supply of blood is diminished, and its spontaneous decay is
not compensated by an equally active renewal ; so that, in time, the characters
of the structure are changed, and its distinguishing properties are no longer
presented. Thus in persons whose lower extremities have been long disused,
the muscles first become pale and flabby ; their bulk gradually diminishes ;
their contractile force progressively decreases, and at last departs altogether ;
and their proper structure is replaced by a deposit of fat, intermixed with
ordinary fibrous tissue, in which few or no characteristically-striated muscular
fibres can be detected.

589. The continual and evident influence of the Nervous System upon
Muscular Irritability, has led many Physiologists to the belief, that the latter
is dependent upon the agency of the former. Two views upon this question
have been commonly taught, to both of which it seems necessary to devote a
brief consideration. — The first of these is, that Muscular Irritability is derived
from some influence or energy communicated from the Brain or Spinal Cord.

a. This opinion is evidently analogous to that which attributes the vital properties of
other parts to the Nervous System alone ; and it is open to the same objection, in laming
•which has been applied to the latter, — the improbability that anyone of the solid textures of the
living body, should have for its office to give to any other the power of performing any vital
action. Moreover it is inconsistent with the fact that, in Vegetables, tissues endowed with
a high degree of contractility exist, and manifest their property 'when a stimulus is directly
applied to themselves; which, nevertheless, can have no dependence whatever upon a
nervous system. In the lower classes of Animals, too, there is good reason to believe, that
the property is much more universally diffused through their tissues, than nervous agency
can be. Again, the action of the heart may be kept up, in the highest Animals, by taking
care that the current of the circulation be not interrupted, for a long time after the removal
of the brain and spinal cord ; it may even continue when completely separated from the
body, which shows that the great centres of the ganglionic system cannot supply any influ-
ence necessary to it; and there are many instances, in which the human fcetus has come to
its full size, so that its heart must have regularly acted, without the existence of a brain or
spinal cord. Further, the irritability of muscles of the first class continues for a long time
after their nerves are divided, and may be called into action by stimuli directly applied to
the parts themselves, or to their nerves below the section, so long as their nutrition is unim-
paired.

6. The loss of the irritability of Muscles, within a few weeks after the section of their
nerves, — on which great stress has been laid by Miiller in support of a modified form of the
above doctrine, (it being maintained by this distinguished physiologist, that, if muscular irri-
tability is not dependent on the Brain and Spinal Cord, they supply some influence essential
to its exercise,) — is clearly due to the alteration in their nutrition', consequent upon their dis-
use. This has been recently proved to demonstration, by the very ingenious experiments of
Dr. J. Reid.* "The spinal nerves were cut across, as they lie in the lower part of the spinal
canal, in four frogs; and both posterior extremities were thus insulated from their nervous
connections with the spinal cord. The muscles of one of the paralyzed limbs were daily
exercised by a weak galvanic battery ; while those of the other limb were allowed to remain
quiescent. This was continued for two months; and at the end of that time, the muscles of
the exercised limb retained their original size and firmness and contracted vigorously, while
those of the quiescent limb had shrunk to at least one-half of their former bulk, and pre-
sented a marked contrast with those of the exercised limb. The muscles of the quiescent
limb still retained their contractility, even at the end of two months; but there can be little
doubt that, from their imperfect nutrition, and the progressing changes in their physical
structure, this would in no long time have disappeared, had circumstances permitted the
prolongation of the experiment."! This experiment satisfactorily explains the fact ob-

hybernating condition of certain warm-blooded Mammalia; indeed, when the temperature
i ihc luidy is ivdiirrd to within a few degrees of the freezing point, no chemical change
seems possible in muscle, — its spontaneous decay, and its vital activity, being alike checked.
* Kdinliiirgh Monthly .Ionni;il of .Medical Science, May, 1841.

~(~ A fact of an exactly parallel character has fallen under the Author's observation, in a

of Hysteric Paraplegia, in which one leg was occasionally affected with severe cramps.

The muscles of this leg suffered much less diminution of size and firmness, than those of

INHERENT IRRITABILITY OF MUSCULAR FIBRE. 447

served by Dr. M. Hall, and heretofore adverted to (§ 399), that in cases in which the
cause of the paralysis is situated in the Brain, and in which the Spinal Cord and its
nerves are unaiiivtcd, the irritability of the muscles of the paralyzed part is not destroyed,
even after a considerable lapse of time. For, if the capability of performing reflex actions
still exist, on the part of the nervous system, it is manifest that the muscles will be < »
sionally excited to action through this channel; and that their nutrition and vital prop*-,
will thereby be preserved, as they were in Dr. Reid's experiments by the artificial excite-
ment of galvanism. Hence Dr. M. Hall's opinion, that the property of Muscular contrac-
tility is derived from the Spinal Cord, is no more tenable than that which locates it in the
Brain.

c. The loss of irritability from section of the nerves, takes place more speedily in warm-
blooded Vertebrata, all whose vital operations are performed with a much greater activity,
than in Reptiles, and other cold-blooded animals. Dr. Reid found that, in a Rabbit, a por-
tion of whose sciatic nerve had been removed on one side, the muscles of that leg were but
very feebly excited to contraction by Galvanism, after the lapse of seven weeks. The change
in their nutrition was evident to the eye, and was made equally apparent by the balance.
The muscles of the paralyzed limb were much smaller, paler, and softer, than the corre-
sponding muscles of the opposite leg; and they scarcely weighed more than half, — being
only 170 grains, whilst the others were 327 grains. It was found, also, that a perceptible
difference existed in the size of the bones of the leg, even after so short an interval had
elapsed; the tibia and fibula of the paralyzed limb weighing only 81 grains, whilst those of
the sound limb weighed 89 grains. On examining the muscular fibres with the microscope,
it was found that those of the paralyzed leg were considerably smaller than those of the
sound limb, and presented a somewhat shrivelled appearance; and that the longitudinal and
transverse stria? were much less distinct.

d. Another equally satisfactory proof, that the loss of Irritability, which follows the sever-
ance of the connection between the Nervous centres and the Muscle, is not immediately due
to the interruption of any influence communicated by the former, has been given by the ex-
periments of Dr. J. Reid. He has proved, that if the irritability of Muscles be exhausted by
means, which have no tendency to impair their healthy nutrition, and the other conditions
favour the normal performance of the nutrient processes, the irritability is restored, and re-
mains for some time. His first experiments were on cold-blooded animals, and they would
in themselves be sufficiently satisfactory ; but he has since repeated them in the Rabbit, and
established the fact beyond all doubt.* " The sciatic nerve was divided in the Rabbit,
and a portion of it removed. One wire from two galvanic batteries consisting of thirty
pairs of plates, was applied over the course of the nerve ; and the other wire was applied
over the foot, which was kept moist, until the muscles had ceased to contract. Three
days after this, a weaker battery was used, and the muscles of the limb had recovered
their contractility, and contracted powerfully. The more powerful battery was used as
before, until the muscles had ceased to respond to the excitement; and three days after
this, they had again recovered their contractility." It seems scarcely possible to draw any
other inference from these experiments, than that Irritability is a property inherent in Mus-
cular tissue, and that the agency of the Nervous system upon it is merely to call it into
active operation.

•

590. The second doctrine referred to, as having been taught by some Phy-
siologists, is, that Muscles, though not dependent on nerves for their peculiar
vital power, are yet dependent upon them for the exercise of that power; —
all stimuli, which excite muscles to contraction, operating first on the nervous
filaments which enter muscles, and through them on the muscular fibres.

a. The facts which have been already stated, in regard to the ordinary action of the Mus-
cles of Organic life, furnish a sufficient answer to this hypothesis. It is with great difficulty
that these can be made to display their irritability, by any stimuli applied to their nerves ;
whilst they manifest it strongly, when the stimulus is directly applied to themselves. Even
in the Muscles of Animal life, individual fasciculi may be thrown into action in the same
manner; although the entire mass cannot be put into combined operation, except by a stimu-
lus simultaneously communicated to the whole, which the nerve affords the readiest means
of effecting. Perhaps the most satisfactory disproof of it, however, is to be found in the ob-

the other ; so that there was a difference of more than an inch in the circumference of the
limbs. But since the paraplegia has been recovered from, voluntary power having been es-
tablished in both limbs, and the muscles of both having been exercised in the same degree,
they have greatly improved in size and firmness, and there is no lon-rer any perceptibl'/
ference between them. * LOC. cit.

448 OF MUSCULAR CONTRACTION.

servation of Mr. Bowman already cited (§ 231), that a single fibre, completely isolated from
all its connections, may be seen with the microscope to pass into a state of contraction, under
the influence of direct irritation. Further, it has been experimentally ascertained, that there
are some chemical stimuli, which will produce the contraction of muscles when directly ap-
plied to them, but of which the influence cannot be transmitted through the nerves ; this is
especially the case with regard to acids.

591. When all these considerations are allowed their due weight, we can
scarcely do otherwise than acquiesce fully in the doctrine of Haller, which
involves no hypothesis, and which is perfectly conformable to the analogy of
other departments of Physiology. He regarded every part of the body which
is endowed with Irritability, as possessing that property in and by itself; but
considered that the property is subjected to excitement and control from the
Nervous System, the agency of which is one of the stimuli that can call it
into operation. — It may be desirable briefly to recapitulate the facts, by which
this doctrine is supported. 1. The existence in Vegetables of irritable tissues,
which are excited to contraction by stimuli directly applied to themselves,
and which can be in no way dependent upon, or influenced by, a Nervous
system. 2. The existence in Animals of a form of Muscular tissue, which
is especially connected with the maintenance of the Organic functions, and
which is much more readily excited to action by direct stimulation, than it is
by Nervous agency. 3. The fact that, by the agency of these, the Organic
functions may go on (as long as their other requisite conditions are supplied)
after the removal of the nervous centres, and when none were ever present ;
rendering it next to certain, that their ordinary operations are not dependent
upon any stimuli received through the nerves, but upon those directly applied
to themselves. 4. The persistence of irritability in muscles, for some time
after the nerves have ceased to be able to convey them the effects of stimuli;
this is constantly seen in regard to the Sympathetic system of nerves, and
the muscles of Organic life upon which they operate; and it may also be
shown to occur with respect to the Cerebro-Spinal system, and the muscles
of Animal life, by the agency of narcotics. 5. The persistence of irritability
in the muscles, after their complete isolation from the nervous centres, so
long as their nutrition is unimpaired; and the effects of frequent exercise, in
preventing the impairment of the nutrition and the loss of irritability. 6.
The recovery of the irritability of muscles, when isolated from the nervous
centres, after it has been exhausted by repeated stimulation; this also depends
upon the healthy performance of the nutritive actions. 7. The contraction
of muscular fibre under the microscope, when completely isolated from .all
other tissues. — In the words of Dr. Alison, then, "the only ascertained final
cause of all endowments bestowed on Nerves in relation to Muscles, in the
living body, appears to be, not to make Muscles irritable, but to subject their
irritability, in different ways, to the dominion of the acts and feelings of the
Mind," — to its volitions, emotions, and instinctive determinations.

592. A curious question has been lately raised, the decision on which is of
some importance in our determination of the nature of the force, by which
the contraction of muscles is occasioned. This is, — whether the power of a
muscle is greater or less at different degrees of contraction, the same stimulus
being applied. This seems to have been determined, by the ingeniously-de-
vised experiments of Schwann.* He contrived an apparatus, which should
accurately measure the length of the muscle, and, at the same time, the weight
which it would balance by its contraction. Having caused the muscle of a
Frog to shorten to its extreme point, by the stimulus of galvanism applied to
the nerve, so that no further stimulation could lift a weight placed in the oppo-
site scale, he allowed the muscle to relax until it was extended to a certain

* fuller's Physiology, p.

TONIC CONTRACTION OF MUSCLES. 449

point, and then ascertained the weight which would balance its power. The
same was several times repeated, as in the following manner : — The length of
the muscle in its extreme state of contraction, at which no additional force
could be exerted by it, being represented by 14, it was found that, when it
had been extended to 17, it would balance a weight of 60 ; when its length
increased to 19'6, it would balance a weight of 120; and at 22'5, it would
balance 180. In another experiment, the muscle at 13'5, balanced 0; at IS'S,
it balanced 100; and at 23'4, it balanced 200. Hence it appears that a uni-
form increase of force corresponds with a nearly uniform increase in the
length of the muscle ; or, in other words, that when the muscle is nearly at
its full length, its contractile power is the greatest. In later experiments upon
the same muscle, this uniform ratio seemed to be departed from ; but, by
comparing the results in a considerable number of instances, it was constantly
found that, in those experiments which were performed the soonest after the
preparation of the frog, and in which, therefore, the normal conditions of the
system were the least disturbed, the ratio was very closely maintained. It
has been ascertained by Valentin, on repeating these experiments, that, by
repeated equal irritations, the strength of the muscles in beheaded frogs de-
creases in a regular and corresponding ratio ; losing the same amount in each
successive period of time. He also found that, when all the Irritability has
ceased, the muscles tear with a far less weight, than they were previously
able, when galvanized, to draw.

a. It has been inferred by Miiller, from Schwann's experiments, that the power, which
causes the contraction of a Muscle, must be very different in its character, from any of the
forces of attraction known to us ; since these all increase in energy as the attracted parts ap-
proach each other, in the inverse ratio of the square of the distance ; so that the power of a
Muscle, if operated on by any of these, ought to increase, instead of regularly diminishing,
with its degree of contraction. But it is to be remembered that, as the observations of Mr.
Bowman have clearly shown, there must be a considerable displacement of the constituents
of every fibre during contraction (§ 231) ; so that it is easy to understand that, the greater
the contraction, the more difficult must any further contraction become. If, between a mag-
net and a piece of iron attracted by it, there were interposed a spongy elastic tissue, the iron
would cease to approach the magnet at a point, at which the attraction of the magnet would
be balanced by the force, needed to compress still further the intermediate substance.

3. — Of Muscular Tonidty.

593. We have now to consider the other form of Contractility, which pro-
duces a constant tendency to contraction (varying, however, as to its degree)
in the Muscular fibre ; but which is so far different from simple Elasticity,
that it abates after death, before decomposition has taken place. This Toni-
city is to be distinguished from the Muscular Tension, which is the result of
the reflex operation of the nervous centres (§ 398) ; being manifested as well
when the muscle is altogether removed from nervous influence, as when sub-
jected to it, and being, like Irritability, an inherent property of the tissue itself,
the presence of which is characteristic of its living state. It manifests itself
in the retraction which takes place in the ends of a living muscle, when it is
divided (as is seen in amputation) ; this retraction being permanent, and
greater than that of a dead muscle. But its effects are much more remarkable
in the non-striated, than in the striated form of Muscular Fibre ; and are par-
ticularly evident in the contractile coat of the Arteries, causing the almost
entire obliteration of their tubes, when they are no longer distended with
blood. The disposition to tonic contraction is increased by any considerable
change of temperature ; the power of Heat is well seen in the following ex-
periments of John Hunter's : — "As soon as the skin could be removed from
a sheep that was newly killed, a square piece of muscle was cut off, which

38*

450 OF MUSCULAR CONTRACTION.

was afterwards divided into three pieces, in the direction of the fibres ; each
piece was put into a basin of water, the water in each basin being of different
temperatures, viz., one about 125°, about 27° warmer than the animal; an-
other 98°, the heat of the animal; and the third 55°, about 43° colder than
the animal. The muscle in the water heated to 125° contracted directly, so
as to be half an inch shorter than the other two, and was hard and stiff. The
muscle in the water heated to 98° after six minutes began to contract and
grow stiff; and at the end of twenty minutes it was nearly, though not quite,
as short and hard as the above. The muscle in the water heated to 55° after
fifteen minutes, began to shorten and grow hard; after twenty minutes it was
nearly as short and as hard as that in the water heated to 98°. At the end
of twenty-four hours, they were all found to be of the same length and stiff-
ness."* The agency of Heat in producing this contraction is also remarkably
shown in the fact, that if a Frog be immersed in water of the temperature of
110°, the muscles of its body and limbs will be thrown into a state of perma-
nent and rigid contraction. — But it would seem that these effects are chiefly,
if not entirely, exerted upon the striated form of Muscular fibre ; and that the
tonicity of the non-striated fibre is called into play by Cold, rather than by
heat. For if a Tadpole or Frog be immersed in water, the temperature of
which is gradually raised, until this state of contraction comes on, the Heart
will be found to continue pulsating for many hours afterwards, not being
affected by the heat. On the other hand, if an artery in a living warm-blooded
animal be exposed to cold air for some time, the lowering of its temperature
occasions its contraction to such an extent, that its cavity becomes almost
obliterated. The influence of warmth in diminishing, and of cold in increas-
ing, the tonicity of the arterial system, will be adverted to hereafter (Chap.
xii., Sect. 3).

594. The distinctness of the Tonicity of Muscles from their Irritability, is
further shown by the fact that the former commonly survives the latter ; and
that it is not destroyed by treatment, which occasions the complete departure
of the Irritability. The first of these statements finds its proof in the pheno-
mena of the Rigor Mortis, presently to be adverted to. Of the latter, the fol-
lowing remarkable experiment of John Hunter's is an ample demonstration: —
" From a straight muscle in a bullock's neck, a portion, three inches in length,
was taken out immediately after the animal had been knocked down, and was
exposed between two pieces of lead, to a cold below 0°, for fourteen minutes ;
at the end of this time it was found to be frozen exceedingly hard, was be-
come white, and was now only two inches long; it was thawed gradually, and
in about six hours after thawing, it contracted so as only to measure one inch
in length ; but irritation did not produce any sensible motion in the fibres.
Here, then, were the juices of muscles frozen, so as to prevent all power of
contraction in their fibres, without destroying their life ; for when thawed,
they showed the same life which they had before ; this is exactly similar to
the freezing of blood too fast for its coagulation, which, when thawed, does
afterwards coagulate, as it depends in each on the life of the part not being
destroyed."!

595. The Rigor Mortis, or death-stiffening of the muscles, is probably to
be regarded as the final manifestation of tins property ; occurring after all the
Irritability of the muscles has departed, but before any putrefactive change
has commenced. This phenomenon is rarely absent ; though it may be so
slight, and may last for so short a time, as to escape observation. The period
which elapses before its commencement, is as variable as its duration ; and

* General Principles of the Blood, in Hunter's Works, Vo). iii., p. 110. .
t Op. cit., p. 109.

RIGOR MORTIS. 451

both appear to be in some degree dependent upon the vital condition of the
body at the time. of death. When the fatal termination has supervened on slow
and wasting disease, occasioning great general depression of the vital powers,
the rigidity usually developes itself very early, and lasts for a short time. In
diseases which powerfully affect the nervous energy, such as Typhus, this is
often the case ; even though they have not been of long duration. Thus,
after death from Typhus, the limbs have been sometimes known to stiffen
within fifteen or twenty minutes. The same is observed in infants and in old
people. On the other hand, where the general energy has been retained up
to a short period before death, the rigidity is much later in coming on, and
lasts longer; this happens, for example, in many cases of Asphyxia and Poi-
soning, in which it has been said not to occur at all. The commencement of
the rigidity, however, is not usually prolonged much beyond seven hours ;
but twenty or even thirty hours may elapse, before it shows itself. Its gene-
ral duration is from twenty-four to thirty-six hours ; but it may pass off much
more rapidly ; or it may be prolonged through several days. An attempt has
been made to connect it with the lowering of the temperature of the dead
body ; but with this it does not seem to have any relation. It occurs in cold-
blooded Vertebrata, and even in Invertebrata, as well as in warm-blooded ani-
mals ; and it has frequently been noticed to commence in the latter, long be-
fore the heat has entirely departed from the body. Moreover, it appears first
upon the trunk, which is the region last deserted by the caloric. It first affects
the neck and lower jaw, and seems gradually to travel downwards ; but ac-
cording to some observers, the lower extremities are stiffened before the upper.
In its departure, which is immediately followed by decomposition, the same
order is observed. It affects all the muscles nearly alike ; but the flexors are
usually more contracted than the extensors, so that the fingers are somewhat
flexed on the palm, and the fore-arm on the arm; and the lower jaw, if pre-
viously drooping, is commonly drawn firmly against the upper. It is remark-
able, that it is equally intense in muscles which have been paralyzed by He-
miplegia ; provided that no considerable change has taken place in their
nutrition. When very strong, it renders the muscles prominent, as in volun-
tary contraction.

596. The ordinary Irritability of the muscles appears to be almost invaria-
bly lost, or greatly diminished, before the Rigor Mortis commences. This
statement holds good in regard to animals of different classes, as well as with
respect to Man under various conditions. Thus, in Birds, whose muscles
most speedily lose their contractility, the cadaveric rigidity is most quickly
exhibited ; whilst in Reptiles it is much longer in commencing, the irritability
of the muscles being more persistent. The interval between the cessation of
the Irritability and the accession of the Rigidity, is sometimes very consider-
able ; and in such cases, the rigidity, when it does occur, is usually very de-
cided and prolonged. — An attempt has been made to show a correspondence
between the rigor mortis, and the coagulation of the blood in the vessels ; and
there is certainly evidence enough to make it appear, that some analogy exists
between these two actions, though they are far from being identical. After
those forms of death in which the blood does not coagulate, or coagulates
feebly, the rigidity commonly manifests itself least ; but this is by no means
an invariable rule. It seems probable that, as the coagulation of the blood
will be shown to be the last act of its vitality, so the stiffening of the muscles
is the expiring effort of theirs.

a. It is necessary to bear in mind, when the pftnomena of cadaveric rigidity are brought
into question in juridical investigations, that a state at first sight corresponding to it may
supervene immediately upon death, from some peculiar condition of the nervous and muscular
systems at the moment. This has been observed in some cases of Asphyxia; but chiefly
when death has resulted from apoplexy following chronic ramollissement of the brain or spinal

452 OF MUSCULAR CONTRACTILITY.

cord. This contraction, which is obviously of a tetanic character, ceases after a few hours,
and is then succeeded by a state of flexibility, after which the ordinary rigidity supervenes.
The following case illustrates the nature of the inquiries, to which this 'condition may give
rise.* The body of a man was found in a ditch, with the trunk and limbs in such a relative
position, as could only be maintained by the stiffness of the articulations. This stiffness must
have come on at the very moment when the body took that position; unless it could be
imagined that the body had been supported by the alleged murderers, until the joints were
locked by cadaveric stiffness. A post-mortem examination showed, that there was no neces-
sity for this supposition, — obviously a very improbable one in itself; — by affording sufficient
evidence, that apoplexy, resulting from chronic disease, was the cause of death. A case
occurred a few years since in Scotland, in which the same plea was raised. The body was
found in a position in which it could have only been retained by rigidity of the joints ; and
it was pleaded on the part of the prisoner, that death had been natural, and had resulted
from fracture of the processus dentatus, causing sudden pressure upon the spinal cord, whence
the spasmodic rigidity would naturally result. Proof was deficient, however, as 'to the
existence of this lesion before death ; and the position of the body rather resembled that into
which it might have been forced during the rigidity, than that in which it would probably
have been at the moment of death. There were also marks of violence, and many other
suspicious circumstances; but the prisoner was acquitted, chiefly from want of evidence
against him. What seemed to indicate that the rigidity was of the ordinary cadaveric nature,
Avas, that there was no evidence of the body having become flexible and again stiffened ; as
it would probably have done, had the rigidity been of the spasmodic character.

597. As the property of Tonicity manifests itself most decidedly in the non-
striated muscles in the living body, so do we find this post-mortem contraction
most remarkable in them. As soon as the muscular walls of the several cavi-
ties lose their irritability, they begin to contract firmly upon their contents,
and thus become stiff and firm, though they were previously flaccid. In this
manner the ventricles of the heart, which are the first parts to lose their
irritability, become rigid and contracted within an hour or two after death ;
and usually remain in that state for ten or twelve hours, sometimes for
twenty-four or thirty-six, then again becoming relaxed and flaccid. This
rigid contracted state of the heart, in which the walls are thickened and the
cavities diminished, was formerly supposed to be a result of disease, and
was termed concentric hypertrophy; but it is now known, from the inquiries
of Mr. Paget, to be the natural condition of the organ, at the period when the
rigor mortis occurs in it. — The contraction of the arterial tubes is so great, as
to produce for the time a great diminution in their calibre ; and this doubtless
contributes to the passage of the blood from the arterial into the venous sys-
tem, which almost invariably takes place within a few hours after death. The
arteries then enlarge again, and become quite flaccid, their tubes being emptied
of their previous contents ; and it was from this circumstance, that the ancient
Physiologists were led to imagine, that the arteries are not destined to carry
blood, but air.

4. — Energy and Rapidity of Muscular Contraction.

598. The energy of Muscular contraction is of course to be most remarkably
observed in those instances in which the continual exercise of particular parts
has occasioned an increased determination of blood towards them, and in con-
sequence a permanent augmentation in their bulk. This has been the case,
for example, with persons who have gained their livelihood by exhibiting
feats of strength. Much will, of course, depend on the mechanically-advantage-
ous application of muscular power ; and in this manner, effects may be pro-
duced, even by persons of ordinary strength, which would not have been
thought credible. In lifting a heavy weight in each hand, for example, a per-
son who keeps his back perfectly rigid, so as to throw the pressure vertically
upon the pelvis, and only uses thw powerful extensors of the thigh and calf,
by straightening the knees (previously somewhat flexed), and bringing the leg
to a right angle with the foot, will have a great advantage over one who uses

* Annalcs d'Hygiene, torn. vii.

ENERGY AND RAPIDITY OF MUSCULAR CONTRACTION. 453

his lumbar muscles for the purpose. A still greater advantage will be gained,
by throwing the weight more directly upon the loins, by means of a sort of
girdle, shaped so as to rest upon the top of the sacrum and the ridges of the
ilia ; and by pressing with the hands upon a frame, so arranged as to bring
the muscles of the arms to the assistance of those of the legs : in this manner,
a single Man of ordinary strength may raise a weight of 2000 Ibs. ; whilst few
who are unaccustomed to such exertions, can lift more than 300 Ibs. in the
ordinary mode. A man of great natural strength, however, has been known
to lift 800 Ibs. with his hands ; and the same individual performed several
other curious feats of strength, which seem deserving of being here noticed.
"1. By the strength of his fingers, he rolled up a very large and strong pewter
dish. 2. He broke several short and strong pieces of tobacco-pipe, with the
force of his middle finger, having laid them on the first and third finger. 3.
Having thrust in under his garter the bowl of a strong tobacco-pipe, his legs
being bent, he broke it to pieces by the tendons of his hams, without altering
the bending of the knee. 4. He broke such another bowl between his first
and second fingers, by pressing them together sideways. 5. He lifted a table
six feet long, which had half a hundred-weight hanging at the end of it, with
his teeth, and held it in that position for a considerable time. It is true, the
feet of the table rested against his knees ; but, as the length of the table was
much greater than its height, that performance required a great strength to be
exerted by the muscles of his loins, neck, and jaws. 6. He took an iron
kitchen poker, about a yard long, and three inches in circumference, and, hold-
ing it in his right hand, he struck it on his bare left arm between the elbow
and the wrist, till he bent the poker nearly to a right angle. 7. He took such
another poker, and, holding the ends of it in his hands, and the middle of it
against the back of his neck, he brought both ends of it together before him ;
and, what was yet more difficult, he pulled it straight again."* Haller men-
tions an instance of a man, who could raise a weight of 300 Ibs. by the action
of the elevator muscles of his jaw : and that of a slender girl, affected with
tetanic spasm, in whom the extensor muscles of the back, in the state of tonic
contraction or opisthotonos, resisted a weight of 800 Ibs., laid on the abdomen
with the absurd intention of straightening the body. It is to be recollected,
that the mechanical application of the power developed by muscular contrac-
tion, to the movement of the body, is very commonly disadvantageous as re-
gards force; being designed to cause the part moved to pass over a much
greater space, than that through which the muscle contracts. Thus the tem-
poral muscle is attached to the lower jaw, at about one-third of the distance
between the condyle and the incisors ; so that a shortening of the muscle to
the amount of half an inch, will draw up the front of the jaw through an inch
and a half; but a power of 900 Ibs. applied by the muscle, would be required
to raise 300 Ibs. bearing on the incisors. In the case of the forearm and leg,
the disproportion is much greater; the points of attachment of the muscles,
by which the knee and elbow-joints are flexed and extended, being much
closer to the fulcrum, in comparison with the distance of the points on which
the resistance bears.

599. The energy of muscular contraction appears to be greater in Insects,
in proportion to their size, than it is in any other animals. Thus a Flea has
been known to leap sixty times its own length, and to move as many times
its own weight. The short-limbed Beetles, however, which inhabit the
ground, manifest the greatest degree of muscular power. The Lucanus cer-
vus (Stag Beetle) has been known to gnaw a hole of an inch diameter, in the
side of an iron canister in which it had been confined. The Geotrupes ster-
corarius (Dung or shard-born Beetle) can support uninjured, and even elevate

* Desaguliers' Philosophy, Vol. ii.

454 OF MUSCULAR CONTRACTILITY.

a weight equal to at least 500 times that of its body. And a small Carabus
has been seen to draw a weight of 85 grains (about 24 times that of its body)
up a plane of 25° ; and a weight of 125 grains (36 times that of its body)
up a plane of 5° ; and in both these instances the friction was considerable,
the weights being simply laid upon a piece of paper, to which the insect was
attached by a string.

600. The rapidity of the changes of position of the component particles
of muscular fibres, may, as Dr. Alison justly remarks,* be estimated, though
it can hardly be conceived from various well-known facts. The pulsations of
the heart can sometimes be distinctly numbered in children, at more than 200
in the minute ; and as each contraction of the ventricles occupies only one-
third of the time of the whole pulsation, it must be accomplished in l-600th
of a minute, or l-10th of a second. Again, it is certain1 that, by the move-
ments of the tongue and other organs of speech, 1500 letters can be distinctly
pronounced by some persons in a minute : each of these must require a sepa-
rate contraction of muscular fibres ; and the production and cessation of each
of the sounds, imply that each separate contraction must be followed by a
relaxation of equal length ; each contraction, therefore, must have been ef-
fected in l-1000th part of a minute, or in the l-10th of a second. Haller
calculated that, in the limbs of a dog at full speed, muscular contractions must
take place in less than the l-200th of a second, for many minutes at least in
succession. — All these instances, however, are thrown into the shade, by those
which may be drawn from the class of Insects. The rapidity of the vibra-
tions of the wings may be estimated from the musical tone which they pro-
duce ; it being easily ascertained by experiments, what number of vibrations
are required to produce any note in the scale. From these data, it appears
to be the necessary result, that the wings of many Insects strike the air many
hundred, or even many thousand, times in every second. — The minute pre-
cision with which the degree of muscular contraction can be adapted to the
designed effect, is in no instance more remarkable than in the Glottis. The
musical pitch of the tones produced by it, is regulated by the degree of ten-
sion of the chordx vocales, which are possessed of a very considerable de-
gree of elasticity (§ 603). According to the observations, of Miiller,t the
average length of these, in the male, in a state of repose, is about 73-100ths
of an inch ; whilst, in the state of greatest tension, it is about 93-100ths ; the
difference being therefore 20-100ths, or one-fifth of an inch : in the female
glottis, the average dimensions are about 51-100ths, and 63-100ths respect-
ively; the difference being thus about one-eighth of an inch. Now the natu-
ral compass of the voice, in most persons who have cultivated the vocal
organ, may be stated at about two octaves, or 24 semitones. Within each
semitone, a singer of ordinary capability could produce at least ten distinct
intervals; so that of the total number, 240 is a very moderate estimate. There
must, therefore, be at least 240 different states of tension of the vocal cords,
every one of which is producible by the will, without any previous trial ; and
the ivhole variation in the length of the cords being not more than one-fifth
of an inch even in man, the variation required to pass from one interval to
another, will not be more than one twelve-hundredth of an inch. And yet
this estimate is much below that which might be truly made from the per-
formances of a practised vocalist. :(:

* Cyclopaedia of Anatomy and Physiology, Art. Contractility.

t Physiology, 1018.

j It is said tli:it the celebrated Made. Mara was able to sound 100 different intervals be-
tween each tone. The compass of her voice was at least three octaves, or 22 tones ; so that
the total number of intervals was 2200, all comprised within an extreme variation of one-
eighth of an inch ; so that it might be said that she was able to determine the contractions
of her vocal muscles to the seventeen-thousandth of an inch.

OF THE VOICE AND SPEECH. 455

601. Of the different associations of Muscular actions, which are em-
ployed for various purposes in the living body, it would be out of place here
to speak ; since these associations depend upon the Nervous rather than upon
the muscular system ; and the most important of them have already been con-
sidered in detail. It may be mentioned, however, that the aptitude which is
acquired by practice, for the performance of particular actions, that were at
first accomplished with difficulty, seems to result as much from a change,
which the continual repetition of them occasions in the Muscle, as in the
habit which the Nervous system acquires, of exciting their performance.
Tims almost every person learning to play on a musical instrument, finds a
difficulty in causing the two shorter fingers to move independently of each
other and of the rest ; this is particularly the case in regard to the ring-finger.
Any one may satisfy himself of the difficulty, by laying the palm of the hand
flat on a table, and raising one finger after the other, when it will be found,
that the ring-finger cannot be lifted without disturbing the rest, — evidently
from the difficulty of detaching the action of that portion of the extensor
commimis digitorum, by which the movement is produced, from that of the
remainder of tlje muscle. Yet to the practised musician, the command of the
will over all the fingers becomes nearly alike ; and it can scarcely be doubted
that some change takes place in the structure of the muscle, which favours the
isolated operation of its several divisions.

CHAPTER VIII.

OF THE VOICE AND SPEECH,

1. The Larynx, and its Actions.

602. THE sounds produced by the organ of Voice constitute the most im-
portant means of communication between Man and his fellows ; and the
power of speech has, therefore, a primary influence, as well on his physical
condition, as on the development of his mental faculties. Hence, although it
only depends on one particular application of muscular force, comparable
to that by which other volitional or emotional movements are effected, it
seems right, in treating of the Physiology of man, to make it an object of
special consideration. In order to understand the nature of the Organ of
Voice as a generator of Sound, it is requisite to inquire, in the first, instance,
into the sources from which sounds at all corresponding to the human voice
are elsewhere obtained. It is necessary to bear in mind, that Vocal Sounds,
and Speech or Articulate Language, are two things entirely different; and
that the former may be produced in great perfection, where there is no ca-
pability for the latter. Hence we should at once infer, that the instrument
for the production of Vocal Sounds was distinct from that by which these
sounds are modified into articulate speech ; and this we easily discover to be
the case, — the Voice being unquestionably produced in the Larynx, whilst
the modifications of it, by which language is formed, are effected for the most
part in the Oral cavity. The structure and functions of the former, then, first
claim our attention.

603. It will be remembered that the Windpipe is surmounted by a stout
cartilaginous annulus, termed the Cricoid cartilage ; which serves as a founda-

456

OF THE VOICE AND SPEECH.

tion for the superjacent mechanism. This is embraced (as it were) by the
Thyroid, which is articulated to its sides by its lower horns, round the ex-
tremities of which it may be regarded as turning, as on a pivot. In this man-

External and sectional views of the Larynx. A n B, the cricoid cartilage ; E c G, the thyroid cartilage ;
G, its upper horn ; c, its lower horn, where it is articulated with the cricoid ; F, the arytenoid cartilage ;
E, F, the vocal ligament ; A K, crico-thyroideus muscle ; F e m, thyro-arytenoideus muscle ; x e, crico-ary-
tenoideus lateralis ; s, transverse section of arytenoideus transversus ; m n, space between thyroid and
cricoid ; B L, projection of axis of articulation of arytenoid with thyroid.

ner the lower front border of the thyroid cartilage, which is ordinarily sepa-
rated by small intervals from the upper margin of the cricoid, may be made to
approach it or recede from it ; as any one may easily ascertain, by placing
his finger against the little depression which may be readily felt externally,
and observing its changes of size, whilst a range of different tones is sounded ;
it will then be observed that, the higher the note, the more the two cartilages
are made to approximate, — whilst they seperate in proportion to the depth of
the tones.* Upon the upper surface of the back of the cricoid, are seated
the two small Arytenoid cartilages ; these are fixed in one direction by a
bundle of strong ligaments, which tie them to the back of the cricoid ; but
they have some power of moving in other directions upon a kind of articulat-
ing surface. The direction of the surface, and the mode in which these car-
tilages are otherwise attached, cause their movement to be a sort of rotation
in a plane, which is nearly horizontal, but partly downwards ; so that their
vertical planes may be made to separate from each other, and at the same
time to assume a slanting position. This change of place will be better un-
derstood, when the action of the muscles is described. To the summit of
the arytenoid cartilages are attached the chordae vocalcs or Vocal Ligaments,
which stretch across to the front of the thyroid cartilage ; and it is upon the
condition and relative situation of these ligaments, that their action depends. It

* In milking this observation, it is necessary to put out of view the general movement to
the larynx itself, which the finger must be made to follow up and down.

STRUCTURE AND ACTIONS OF THE LARYNX.

457

!L

is evident that they may be rendered more or less tense by the movement of
the Thyroid cartilage just described ;

being tightened by the depression of Fig. 196.

its front upon the Cricoid cartilage, and
slackened by its elevation. On the
other hand, they may be brought into
more or less close apposition, by the
movement of the Arytenoicl cartilages ;
being made to approximate closely, or
to recede in such manner as to cause
the rima glottidis to assume the form
of a narrow V, by the revolution of
these cartilages. We shall now in- 3
quire into the actions of the muscles
upon the several parts of this apparatus;
and first into those of the larynx alone.
604. The depression of the front of
the Thyroid cartilage, and the conse-
quent tension of the Vocal Ligaments,
are occasioned by the conjoint action of
the Crico-thyroidei on both sides ; and
the chief antagonists to these are the „. ,, , ,

• , . i-i Bird's-eye view of larynx from above. G E H,

J hyro-arytenoidet, which draw the the thyroid cartilage, embracing the ring of the

front of the Thyroid back towards the cricoid r u x w, and turning upon the axis x z,

Ary tenoid Cartilages, and thus relax the which passes through the tower horns, c, Fig. 113,

VOCal ligaments. These tWO pairs of N F' N F' the arvtenoid cartilages, connected by

i . j j ill the arytenoideus transversus ; T v, T v, the vocal

muscles may be regarded as the prm- .

• ! . ligaments; N x, the right crico-arytenoideus late-

cipal governors of the pitch of the notes, raHs (lhe left being rem0ved) ; v t/, the left thyro-

whicll, as We shall hereafter See, is al- arytenoideus (the right being removed) ; N I, N I,
most entirely regulated by the tension the crico-arytenoidei postici; B, B, the crico-ary-

of the ligaments; their action is as- tenoid ligaments,
sisted, however, by that of other muscles

presently to be mentioned. — The Arytenoid cartilages are made to diverge
from each other, by means of the Crico-arytenoideus posticus of each side,
which proceeds from their outer corner, and turns somewhat round the edge
of the Cricoid, to be attached to the lower part of its back ; its action is to
draw the outer corner backwards and downwards, so that the points to which
the vocal ligaments are attached, are separated from one another, and the
Rima Glottidis is thrown open. This will be at once seen from the succeed-
ing diagram, in which the direction of traction of the several muscles is laid
down. — The action of this muscle is partly antagonized by that of the Crico-
arytenoideus lateralis, which runs forwards and downwards from the outer
corner of the Arytenoid cartilage ; and its action, with that of its fellow, will
be to bring the anterior points of the Arytenoid cartilages into the same
straight line, at the same time depressing them, and thus to close the Glottis.
This muscle is assisted by the Arytenoideus transversus, which connects
the posterior faces of the Arytenoid cartilages, and which, by its contraction,
will draw them together. By the conjoint action, therefore, of the Crico-ary-
tenoideus lateralis, and of the Arytenoideus transversus, the whole of the ad-
jacent faces of the Arytenoid cartilages will be pressed together; and the
points to which the vocal ligaments are attached, will be depressed. — But if
the Arytenoideus be put in action in conjunction with the Crico-arytenoidei
postici, the tendency of the latter to separate the Arytenoid cartilages being
antagonized by the former, its backward action only will be exerted ; and thus
it may be caused to aid the Crico-thyroideus in rendering tense the vocal
39

458

OF THE VOICE AND SPEECH.

ligaments. This action will be further assisted by the Sterno-fhyroideus,
which tends to depress the Thyroid cartilage, by pulling from a fixed point
below ;* and the Thyro-hyoideus will be the antagonist of this, when it acts

Part of Fig. 196 enlarged, to show the direction of the muscular forces, which act on the Arytenoid
cartilage. Q N v s, the right Arytenoid cartilage ; T v, ils vocal ligament ; B R s, bundle of ligaments unit-
ing it to Cricoid ; o p, projection of its axis of articulation ; h g-, direction of the action of the Thyro-ary-
tenoideus; N x, direction of Crico-arytenoideus lateralis ; N w, direction of Crico-arytenoideus posticus;
N Y, direction of Crytenoideus transversus.

from a fixed point above, the Os Hyoides being secured by the opposing con-
traction of several other muscles. — The respective actions of these muscles
will be best comprehended by the following Table.

Govern the pitch of the notes.

Depress the front of the Thyroid cartilage on the
Cricoid, and stretch the vocal ligaments; assisted
by the Arytenoideus and Crico-arytenoidei postici.

Elevate the front of the Thyroid cartilage, and draw
it towards the Arytenoids, relaxing the vocal liga-
ments.

>\ ,

% \ STERNO-THYROIDEI

5. C THYHO-ARYTENOIDEI
ST \ THYHO-HYOIDEI

> . . . .

Govern the Aperture of the Glottis.
5. CRICO-ARYTENOIDEI POSTICI ................. Open the Glottis.

CRTCO-ARYTEXOIDEI LATERALES
AHYTENOIDEUS

Press together the inner edges of the Ary-
tenoid cartilages, and close the Glottis.

605. The muscles which stretch or relax the Vocal ligaments, are entirely
concerned in the production of Voice ; those which govern the aperture of
the Glottis have important functions in connection with the Respiratory
actions in general, and stand as guards (so to speak) at the entrance to the
lungs. Their separate actions are easily made evident. We can close the
aperture of the Glottis, by an exertion of the will, either during inspiration or
expiration; and it is a kind of spasmodic movement of this sort, which is

* This is not usually reckoned as one of the principal muscles concerned in regulating the
voice; but that it is so, any our ni;iy convince himself by placing his finger just above the
sternum, whilst he is sounding high notes; a strong feeling of muscular tension is then at
once perceived.

STRUCTURE AND ACTIONS OF THE LARYNX. 459

concerned in the acts of Coughing and Sneezing (§ 381), as well as in the
more prolonged impediments to the ingress and egress of air, which have been
already noticed as resulting from disordered states of the Nervous system
(§ 504). A slight examination of the recent Larynx is sufficient to make it
evident that, when once the borders of the Rima Glottidis are brought toge-
ther by muscular action, the effect of strong aerial pressure on either side, —
whether produced by an expulsory blast from below, or by a strong inspiratory
effort, occasioning a-'partial vacuum below, and consequently an increased
pressure above, — will be to force them into closer apposition. With this
action, then, the muscles which regulate the tension of the vocal ligaments
have nothing to do. In the ordinary condition of rest, it seems probable that
the Arytenoid cartilages are considerably separated from each other ; so as to
cause a wide opening to intervene between their inner faces, and between the
vocal ligaments, through which the air freely passes ; and the vocal ligaments
are at the same time in a state of complete relaxation. In order to produce
a vocal sound, it is not sufficient to put the ligaments into a state of tension ;
they must also be brought nearer to each other. That the aperture of the
Glottis is greatly narrowed during the production of sounds, is easily made
evident to one's self, by comparing the time occupied by an ordinary expiration,
with that required for the passage of the same quantity of air during the sus-
tenance of a vocal tone. Further, the size of the aperture is made to vary in
accordance with the note which is being produced ; of this, too, any one may
convince himself, by noting the time during which he can hold out a low and
a high note ; from which it will appear, that the aperture of the Glottis is so
much narrowed in producing a high note, as to permit a much less rapid pas-
sage of air, than is allowed when a low one is sounded. This adjustment of
the aperture to the tension of the Vocal Ligaments, is a necessary condition
for the production of a clear and definite tone. It further appears that, in the
narrowing of the Glottis, which is requisite to bring the vocal ligaments into
the necessary approximation, the upper points of the Arytenoid cartilages are
caused to approximate, not only by being made to rotate horizontally towards
each other, but also by a degree of elevation; so that the inner faces of the
Vocal Ligaments are brought into parallelism with each other, — a condition
which may be experimentally shown to be necessary, for their being thrown
into sonorous vibration.

606. We have now to inquire what is the operation of the Vocal Ligaments
in the production of sounds; and in order to comprehend this, it is necessary
to advert to the conditions under which tones are produced, by instruments of
various descriptions, having some analogy with the Larynx.

a. These are chiefly of three kinds, — strings, flute-pipes, and reeds or tongues. The Vocal
Ligaments were long ago compared by Ferrein to vibrating Strings ; and at first sight there
might seem a considerable analogy, the sounds produced by both being elevated by increased
tension. This resemblance disappears, however, on more accurate comparison ; for it may
be easily ascertained by experiment, that no string so short as the vocal ligaments could give
a clear tone, at all to be compared in depth with that of the lowest notes of the human voice ;
and also, that the scale of changes produced by increased tension is fundamentally different.
When strings of the same length, but of different tension, are made the subject of comparison,
it is found that the number of vibrations is in proportion to the square roots of the extending
forces. Thus, if a string extended by a given weight produce a certain note, a string extended,
by four times that weight will give a note, in which the vibrations are twice as rapid, — and
this will be the octave of the other. If nine times the original weight be employed, the
vibrations will be three times as rapid as those of the fundamental note, producing the
twelfth above it. Now by fixing the larynx in such a manner, that the vocal ligaments can
be extended by a known weight, Miiller has ascertained that the sounds produced by a varia-
tion of the extending force will not follow the same ratio ; and therefore the condition of
these ligaments cannot be simply that of vibrating cords. Further, a cord of a certain length,
which is adapted to give out a clear and distinct note, equal in depth to the lowest of the

460 OF THE VOICE AND SPEECH.

human voice, may be made by increased tension to produce all the superior notes, which,
in stringed instruments, are ordinarily obtained by shortening the strings.* But it does not
follow that a short string, which, with moderate tension, naturally produces a high note,
should be able, by a diminution of the tension, to give out a deep one; for, although this
might be theoretically possible, yet it cannot be accomplished in practice; since the vibrations
become irregular on account of the diminished elasticity ."f" These considerations are in them-
selves sufficient to destroy the supposed analogy ; and to prove that the Chorda? Vocales can-
not be reduced to the same category with vibrating strings.

b. The next kind of instrument, with which some analogy ijpight be suspected, is the
Flute-pipe, in which the sound is produced by the vibration of an elastic column of air con-
tained in the tube ; and the pitch of the note is determined almost entirely by the length of the
column, although slightly modified by its diameter, and by the nature of the embouchure or
mouth from which it issues. This is exemplified in the German Flute, and in the English
Flute or Flageolet; in both of which instruments, the acting length of the pipe is determined,
by the interval between the embouchure and the nearest of the side apertures; by opening
or closing which, therefore, a modification of the tone is produced. In the Organ, of which
the greater number of pipes are constructed upon this plan, there is a distinct pipe for every
note: and their length increases in a regular scale. It is, in fact, with flute-pipes as with
strings, — that a diminution in length causes an increase in the number of vibrations, in an
inverse proportion ; so that of two pipes, one being half the length of the other, the shorter
will give a tone which is the octave above the other, the vibrations of its column of air being
twice as rapid. Now there is nothing in the form or dimensions of the column of air be-
tween the larynx and the mouth, which can be conceived to render it at all capable of such
vibrations, as are required to produce the tones of the Human voice; though there is some
doubt, whether it is not the agent in the musical tones of certain Birds. The length of an
open pipe necessary to give the lowest G of the ordinary bass voice, is nearly six feet ; and
the conditions necessary to produce the higher notes from it, are by no means those which
we find to exist in the process of modulating the human voice.

c. We now come to the third class of instruments, in which sound is produced by the
vibration of Reeds orTongues; these may either possess elasticity in themselves, or be made
elastic by tension. The reeds of the Mouth- EoLina, Accordion, Seraphine, &c., are examples
of instruments of this character, in which the lamina vibrates freely in a sort of frame, that
allows the air to pass out on all sides of it through a narrow channel, thus increasing the
strength of the blast: whilst in the Hautboy, Bassoon, &c., and in Organ-pipes of similar con-
struction, the reed is attached to one end of a pipe. In the former kind, the sound is pro-
duced by the vibration of the tongue alone, and is regulated entirely by its length and elasti-
city; whilst in the latter, its pitch is dependent upon this conjointly with the length of the
tube, the column of air contained in which is thrown into simultaneous vibration. Some
interesting researches on the effect produced on the pitch of a sound given by a reed, through
the union of it with a tube, have been made by M. W. Weber ; and, as they are important
in furnishing data, by which the real nature of the vocal organ may be determined, their
chief results will be here given. — i. The pitch of a reed may be lowered, but cannot be
raised, by joining it to a tube. u. The sinking of the pitch of the reed thus produced, is at
the utmost not more than an octave, in. The fundamental note of the reed thus lowered, may
be raised again to its original pitch, by a further lengthening of the tube; and by a further
increase is again lowered, iv. The length of tube, necessary to lower the pitch of the in-
strument to any given point, depends on the relation which exists between the frequency of
the vibrations of the tongue of the reed, anil those of the column of air in the tube, each
taken separately. — From these data, and from those of the preceding paragraph, it follows
that, if a wind-instrument can, by the prolongation of its tube, be made to yield tones of any
depth in proportion to the length of the tube, it must be regarded as a Bute-pipe; whilst, if
its pitch can only be lowered an octave or less (the emlxiiiehuiv remaining the <amc) by
lengthening the tube, we may be certain that it is a reed instrument. The latter proves to
be the case in regard to the Larynx.

607. It is evident from the foregoing considerations, that the action of the
Larynx has more analogy to that of reed instruments, than it has to that either

* Thus in the Piano-forte, where there are strings tin- each note, a gradual shortening is
seen from the lowest to the highest; and in the \ lolin the change of tone is produced by
slopping the strings with the linger, so as to diminish their acting length.

f Thus it would be impossible to produce good Bass notes on the strings of a Violin, by
diminishing their tension; the len-ih allorded l>y the Violoncello or Double Bass is requisite.
The striking dill'ereiiee between the tone of the Bass strings in the Grand Piano-forte and the
small upright Piccolo, is another e\eiiii>lilieaiii>n of the same principle; being chiefly due to
the length and tension of the former, as contrasted with the shortness and slackness of the
latter.

ACTIONS OF THE LARYNX.

461

of vibrating strings, or of flute pipes. There would seem, at first sight, to be
a marked difference in character, between the Chordae Vocales, and the tongue
of any reed instrument ; but this difference is really by no means considera-
ble. In a reed, elasticity is a property of the tongue itself, when fixed at one
end, the other vibrating freely ; but by a membranous lamina, fixed in the
same manner, no tone would be produced. If such a lamina, however, be
made elastic by a moderate degree of tension, and be fixed in such a manner
as to be advantageously acted on by a current of air, it will give a distinct
tone. It is observed by Miiller, that membranous tongues made elastic by
tension, may have either of three different forms, i. That of a band extended
by a cord, and included between two firm plates, so that there is a cleft for
the passage of air on each side of the tongue, u. The elastic membrane
may be stretched over the half or any portion of the end of a short tube, the
other part being occupied by a solid plate, between which and the elastic
membrane a narrow fissure is left. HI. Two elastic membranes may be ex-
tended across the mouth of a short tube, each covering a portion of the opening,
and having a chink left open between them. — This last is evidently the form
most allied to the Human Glottis ; but it may be made to approximate still more
closely, by prolonging the membranes in a direction parallel to that of the cur-
rent of air, so that not merely their edges, but their whole planes, shall be
thrown into vibration. Upon this principle, a kind of artificial Glottis has
been constructed by Mr. Willis ; the conditions of action, and the effects ot
which, are so nearly allied to that of the real instrument, that the similar cha-
racter of the two can scarcely be doubted. The following is his description
of it. "Let a wooden pipe be prepared of the form of Fig. 198 a, having a
foot, c, like that of an organ-pipe, and an upper opening, long and narrow, as
at B, with a point A, rising at one

end of it. If a piece of leather, or Fig. 198.

still better, of sheet India-rubber, be a b

doubled round this point, and secur-
ed by being bound round the pipe
at D with strong thread, as in Fig.
198, b, it will give us an artificial
glottis, with its upper edges G H,
which may be made to vibrate or
not, at pleasure, by inclining the
planes of the edges. A couple of
pieces of cork, E, F, may be glued
to the corners, to make them more
manageable. From this machine,
various notes may be obtained, by
stretching the edges in the direction
of their length, G H ; the notes rising
in pitch with the increased tension,
although the length of the vibrating
edge is increased. It is true, that a
scale of notes equal in extent to that
of the human voice, cannot be ob-
tained from edges of leather ; but

this scale is much greater in India-rubber than in leather ; and the elasticity
of them both is so much inferior to that of the vocal ligaments, that we may
readily infer that the great scale of the latter is due to its greater elastic pow-
ers." By other experimenters, the tissue forming the middle coat of the arte-
ries has been used for this purpose, in the moist state, with great success ;
with this, the tissue of the vocal ligaments is nearly identical. It is worthy

39*

Artificial Glottis.

462 OF THE VOICE AND SPEECH.

|

of remark that, in all such experiments, it is found that the two membranes
may be thrown into vibration, when inclined towards each other in various
degrees, or even when they are in the same plane, and their edges only ap-
proximate ; but that the least inclination from each other (which is the posi-
tion the vocal ligaments have during the ordinary state of the glottis, § 605,)
completely prevents any sonorous vibrations from being produced.

608. The pitch of the note produced by membranous tongues, may be
affected in several ways. Thus, an increase in the strength of the blast, which
has little influence on metallic reeds, raises their pitch very considerably ;
and in this manner the note of a membranous reed may be raised by semitones,
to as much as a fifth above the fundamental. The addition of a pipe has
nearly the same effect on their pitch, as on that of metallic reeds ; but it can-
not easily be determined with the same precision. The effect of the junction
of a pipe with a double membranous tongue, is well shown in the Trumpet,
Horn, and other instruments ; which require the vibration of the lips, as well
as a blast of air, for the production of their sound, having no reed of their
own. By some, these instruments have been classed with Flute-pipes ; but
the conditions of their action are entirely different. The mouth-piece of the
horn or trumpet is incapable of yielding any tone, when a current of air is
merely blown through it ; and the lips are necessary to convert it into a musi-
cal reed, being rendered tense by the contraction of their sphincter, partly
antagonized by the slightly-dilating action of other muscles. The variation
of the tension of the lips is effected by muscular effort ; and several different
notes may be produced with a pipe of the same length ; but there is a certain
length of the column of air, which is the one best adapted for each tone ; and
different instruments possess various contrivances for changing this. It has
been recently ascertained, that the length of the pipe prefixed to the reed, has
also a considerable influence on its tone, rendering it deeper in proportion as
it is prolonged, down to nearly the octave of the fundamental note ; but the
pitch then suddenly rises again, as in the case of the tube placed beyond the
reed. The researches of Mliller, however, have not succeeded in establishing
any very definite relation between the length of the two tubes, in regard to
their influence on the pitch of the reed placed between them.

609. From the foregoing statements it appears, that the true theory of the
Voice may now be considered as well established, in regard to this essential
particular, — that the sound is the result of the vibrations of the vocal ligaments,
which take place according to the same laws with those of metallic or other
elastic tongues : and that the pitch of the notes is chiefly governed by the
tension of these lamina?. With respect, however, to the modifications of these
tones, induced by the shape of the air-passages, both above and below the
larynx, by the force of the blast, and by other concurrent circumstances, little
is certainly known. Hence it is, that on the theory of the production of what
are called falsetto notes, there is much difference of opinion amongst Physi-
ologists. Some have contended, that these tones are produced by the vibra-
tion of the vocal ligaments along only a part of their length ; but this is cer-
tainly untrue. By Miiller it is believed, that in the falsetto notes merely the
thin border of the glottis vibrates, so that the fissure remains distinctly visible ;
whilst in the production of the ordinary vocal tones, the whole breadth of the
vocal ligaments is thrown into strong vibrations, which traverse a wider sphere,
so that a confused motion is seen in the lips of the glottis, rendering its fissure
obscure. That the tension of the vocal cords is not diminished (as it ought
to be if only a part of their length were being used), but is progressively in-
creased, as we pass from the ordinary to the falsetto scale, any one may con-
vince himself, by placing his finger on the interval between the thyroid and

ACTIONS OF THE LARYNX. 463

cricoid cartilages, as formerly described (§ 603).* — A very important adjunct
to the production of the higher notes, has been pointed out by Muller, as
being afforded by the modification in the space included between the two
sides of the thyroid cartilage, which is effected by the thyro-arytenoidei. He
had experimentally ascertained, that the introduction of a hollow plug into the
upper end of the pipe beneath his artificial larynx (and therefore just below
the reed), by diminishing its aperture, produced a considerable elevation of
the tone. The action may be imitated in the human larynx, when made the
subject of experiment, by compressing the thyroid cartilage laterally; and in
this manner, the natural voice could be made to extend through a range, that
could otherwise be only reached by a falsetto.

610. The strength of the tone produced in the larynx, is much increased
by the resonance of the elastic tissue, which it contains in various other parts ;
but still more, perhaps, by that produced by the air in the trachea, bronchi,
and pulmonary cells. This comes to be of great importance in the pheno-
mena of auscultation. The aerial resonance is loudest where any large body
of air is collected together, as in the trachea, the larger bronchi, an emphyse-
matous dilatation, or a cavity resulting from tubercular softening. On the
other hand, solidification of the pulmonary tissue will produce a resonance of
a somewhat different kind. The influence of the prefixed and superadded
tubes, in modifying the tones produced by the Human larynx, has been found
by Prof. Muller not to be at all comparable to that which they exercised
over the artificial larynx ; the reason of which difference does not seem very
apparent. It appears, however, that there is a certain length of the prefixed
tube, — as there is a certain distance of the vibrating laminae, and a certain
length or form of the tube above, — which is most favourable to the produc-
tion of each note ; and the downward movement of the whole vocal organ,
which takes place when we are sounding deep notes, and its rise during the
elevation of the tones, have been supposed to have the purpose of making this
adjustment in the length of the trachea; but this requires the supposition,
that the real length of the trachea is shortened whilst it appears extended, —
for which there seems no foundation. It is considered by Mr. Wheatstone,
that the column of air in the trachea may divide itself into harmonic lengths,
and may produce a reciprocation of the tone given by the vocal ligaments
(§ 560) ; and in this manner he considers that the falsetto notes are to be
explained. It may be added, that the partial closing of the epiglottis seems
to assist in the production of deep notes, just as the partial covering of the
top of a short pipe fixed to a reed will lower its tone ; and that something of
this kind takes place during natural vocalization, would appear, from the re-
traction and depression of the tongue which accompany the lowering of the
front of the head, when the very lowest notes are being sounded. The arches
of the palate and uvula become contracted during the formation of the higher
tones ; but no difference can be perceived in their state, whether these tones
be falsetto or not; hence it would appear that they have no concern in this
peculiarity ; and the purpose of their increased tension is probably to main-
tain their power of resonance. The experiments of Savart have shown, that
a cavity which only responds to a shrill note, when its walls are firm and dry,
may be made to afford a great variety of lower tones, when its walls are

° That the falsetto voice differs in some essential particular from the natural, is evident
from this, — that many persons who possess a considerable range of both, are yet unable to
unite them, so as to sing through the whole scale without a marked interruption. Thus a
gentleman of the Author's acquaintance has a bass voice, ranging from the lowest D of the
Square Piano to the second D above ; and a falsetto ranging from the A below this to the E
of the octave above, so as to give a compass of more than three octaves on the whole ; yet
the two registers cannot be smoothly blended.

464 OF THE VOICE AND SPEECH.

moistened and relaxed in various degrees. This observation may probably
be applied also to the trachea.

611. These and numerous other muscular actions, which are employed in
the production and regulation of the voice, are effected by an impulse which
can scarcely be termed Voluntary, and the nature of which is a curious sub-
ject for inquiry. It may be safely affirmed, that the production of sounds is
in itself an Instinctive action; although the combination of these, whether into
music or articulate language, is a matter of acquirement. Now it might be
supposed that the AVill has sufficient power over the vocal muscles, to put
them into any state requisite for its purposes, without any further condition :
but a little self-experiment will prove that this is not the case. No definite
tone can be produced by a Voluntary effort, unless that tone be present to the
mind, during however momentary an interval, either as immediately conveyed
to it by an act of Sensation, recalled by an act of Conception, or anticipated
by an effort of the imagination. When thus present, the Will can enable the
muscles to assume the condition requisite to produce it; but under no other
circumstances does this happen, except by a particular mode of discipline
presently to be adverted to. The action itself, therefore, must be reduced to
the class of consensual movements ; and we must suppose that the will is
exercised in preparing the conditions requisite for it, rather than in directly
exciting it. — That those who are unfortunately labouring under congenital
deafness, are thence debarred from learning the use of Voice in the ordinary
manner, is well known ; the consensual action cannot be excited, either
through sensations of the present, or conceptions of the past ; and the imagi-
nation is entirely destitute of power to suggest that which has been in no
shape experienced. But such persons may be taught to speak in an imperfect
manner, by causing them to imitate particular muscular movements, which
they may be made to see; and it is evident, that they must be guided in the
imitation and ordinary performance of those movements, by the common
muscular sensations which accompany them, and not by the sensations con-
veyed through the Auditory nerve, which are ordinarily by far the most pre-
cise guides. Many instances, indeed, are on record, in which persons entirely
deaf were enabled to carry on a conversation in the regular way; judging of
what was said, by the movements of the lips and tongue, which they had
learned to connect with particular syllables ; and regulating their own voices
in reply, by their voluntary power, guided by muscular sensation.*

[In the foregoing account of the Physiology of Voice, the author has been chiefly guided
by the excellent paper by Mr. Willis 'in the Transactions of the Cambridge Philosophical
Society, vol. iv. ; and by the elaborate investigations of Miiller and his coadjutors, as detailed
in the Fourth Book of his Physiology.]

2. — Of Articulate Sounds.

612. The larynx, as now described, is capable of producing those tones of
which Voice fundamentally consists, and the sequence of which becomes
Music : but Speech consists in the modification of the laryngeal tones, by
other organs, intervening between the Glottis and the Os Externum ; so as
to produce those articulate sounds, of which Language is formed. It cannot
be questioned that Music has its language ; and that it is susceptible of ex-
pressing the emotional states of the mind, among those at least who have
been accustomed to associate these with its varied modes, to even a higher
degree than articulate speech. But it is incapable of addressing the intellect,
by conveying definite ideas of objects, properties, actions, &c., in any other

* See Jolmstone on Sensation, p. 128.

OF ARTICULATE SOUNDS. 465

way than by a kind of imitation, which may be compared to the signs used
in hieroglyphic writing. These ideas it is the peculiar province of articulate
language to convey ; and we find that the vocal organ is adapted to form a
large number of simple sounds, which may be readily combined into groups,
forming words. The number of combinations which can be thus produced,
is so inexhaustible, that every language has its own peculiar series ; no dif-
ficulty being found in forming new ones to express new ideas. There is con-
siderable diversity in different languages, even with regard to the use of the
simplest of these combinations ; some of them are more easy of formation
than others, and these accordingly enter into the composition of all languages;
Avhilst of the more difficult ones, some are employed in one language, some
in another, — no one language possessing them all. Without entering into any
detailed account of the mechanism required to produce each of these simple
sounds, a few general considerations will be offered in regard to the classifi-
cation of them ; and the peculiar defect of Articulation, termed Stammering,
will be briefly treated of.

613. Vocal sounds are divided into Vowels and Consonants; and the dis-
tinctive characters of these are usually considered to be, that the Vowels are
produced by the Voice alone, whilst the sound of the Consonants is formed
by some kind of interruption to the voice, so that they cannot be properly
expressed, unless conjoined with a vowel. The distinction may be more
correctly Jaid down, however, in this manner: — the Vowel sounds are con-
tinuous tones, modified by the form of the aperture through which they pass
out ; whilst in sounding Consonants, the breath suffers a more or less com-
plete interruption, in its passage through parts anterior to the larynx. Hence
the really simple Vowel sounds are capable of prolongation during any time
that the breath can sustain them ; this is not the case, however, with the
real Diphthongal sounds (of which it will presently appear that the English i
is one) ; whilst it is true of some Consonants. It seems to have been for-
gotten by many of those who have written upon this subject, that the laryn-
geal voice is not essential to the formation of either vowels or consonants ; for
all may be sounded in a whisper. It is very evident, therefore, that the
larynx is not primarily concerned in their production ; and this has been fully
established by the following experiment. A flexible tube was introduced by
M. Deleau through his nostril into the pharynx, and air was impelled by it
into the fauces ; then, closing the larynx, he threw the fauces into the differ-
ent positions requisite for producing articulate sounds, when the air impelled
through the tube became an audible whisper. The experiment was repeated,
with this variation, — that laryngeal sounds were allowed to pass into the
fauces ; and each articulated letter was then heard double, in a proper voice
and in a whisper.

614. That the Vowels are produced by simple modifications in the form
of the external passages, is easily proved, both by observation and by imita-
tive experiment. When the mouth is opened wide, the tongue depressed,
and the velum palati elevated, so as to give the freest possible exit to the
voice, the vowel a in its broadest form (as in ah] is sounded.* On the other
hand, if the oral aperture be contracted, the tongue being still depressed, the
sound oo (the continental w) is produced. If attention be paid to the state of
the buccal cavity, during the pronunciation of the different vowel sounds, it
will be found to undergo a great variety of modifications, arisingfrom varieties
of position of the tongue, the cheeks, the lips, and velum palati. The posi-

This sound of the vowel a is scarcely used in our language, though very common in
most of the continental tongues; the nearest approach to it in English is the a in far : but
this is a very perceptible modification, tending towards aw.

466 OF THE VOICE AND SPEECH.

tion of the tongue is, indeed, one of the primary conditions of the variation
of the sound ; for it may be easily ascertained that, by peculiar inflexions of
this organ, a great diversity of vowel sounds may be produced, the other parts
remaining the same. Still there is a certain position of all the parts, which
is most favourable to the formation of each of these sounds ; but this could
not be expressed without a lengthened description. The following table,
slightly altered from that of Kempelen, expresses the relative dimensions of
the buccal cavity and of the oral orifice, for some of the principal of these ;
the number 5 expressing the largest size, and the others in like proportion : —

Vowel. Sound. Size of oral opening. Size of buccal cavity.

a as in ah 5 5

a as in name 4 2

e as in theme 3 1

o as in cold 2 4

oo as in cool 1 5

These are the sounds of the five vowels, a, e, i, o, u, in most Continental
languages ; and it cannot but be admitted, that the arrangement is a much more
natural one than that of our own vowel series. The English a has three dis-

O

tinct sounds capable of prolongation:* — the true broad a of ah, slightly modi-
fied in far; the a of fate, corresponding to the e of French; and the a of fall,
which should be really represented by au. This last is a simple sound, though
commonly reckoned as a diphthong. In Kempelen's scale, the dral orifice
required to produce it would be about 3, and the size of the buccal cavity 4.t
On the other hand, the sound of the English i cannot, like that of a true vowel,
be prolonged ad libitum; it is in fact a sort of Diphthong, resulting from the
transition from a peculiar indefinite murmur to the sound of e, which takes
its place when we attempt to continue it. The sound oy or oi, as in oil,
is a good example of the true diphthong; being produced by the transition
from au to e. In the same manner, the diphthong on, which is the same with
ow in owl, is produced in the rapid transition from the broad a of ah, to the
oo of cool. — Much discussion has taken place as to the true character of y,
when it commences a word, as in yet, yawl, &c. ; some having maintained
that it is a consonant, (for the very unsatisfactory reason, that we are in the
habit of employing a rather than an, when we desire to prefix the indefinite
article to such words,) whilst others regard it as a peculiar vowel. A slight
attention to the position of the vocal organs during its pronunciation, makes it
very clear, that its sound in such words really corresponds with that of the
long (English) c; the pronunciation of the word yawl being the same as that
of eaul, when the first sound is not prolonged, but rapidly transformed into
the second. — The sound of the letter iv, moreover, is really of the vowel
character, being formed in the rapid transition from oo to the succeeding
vowel; thus wall might be spelt ooall. Many similar difficulties might be
removed, and the conformity between spoken and written language might be
greatly increased (so as to render far more easy the acquirement of the former
from the latter), by due attention to the state of the vocal organs in the pro-
duction of the simple sounds.

* The short vowel sounds, as a in fat, e in met, o in pot, &c., are not capable of prolonga-
tion.

•)" The mode of making a determination of this kind may here be given, for the sake of
example. If the broad a be sounded, the mouth and fauces being opened wide, and we
contract the oral orifice by degrees, at the same time slightly elevating the point of the
tongue, we gradually come to the sound of au; by still further cnutraeting the orifice, and
again depressing the tongue, we form oo. On the other hand, in sounding e, the tongue is
raised nearly to the roof of the mouth; if it be depressed, without the position of the lips
being altered, aw is given.

OF ARTICULATE SOUNDS. 467

615. It is not very difficult to produce a tolerably good artificial imitation
of the Vowel sounds. This was accomplished l>y Kempelen, by means of an
India-rubber ball, with an orifice at each end, of which the lower one was
attached to a reed; by modifying the form of the ball, the different vowels
could be sounded during the action of the reed. He also employed a short
funnel-like tube, and obtained the different sounds by covering its wide open-
ing to a greater or less extent. This last experiment has been repeated by
Mr. Willis; who has also found that the vowel sounds might be imitated, by
drawing out a long straight tube from the reed. In this experiment he arrived
at a curious result: — with a tube of a certain length, the series of vowels, i, e,
a, o, u, was obtained, by gradually drawing it out; but, if the length was in-
creased to a certain point, a further gradual increase would produce the same
sequence in an inverted order, u, o, a, e, i; a still further increase would pro-
duce a return to the first scale, and so on. When the pitch of the reed was
high, and the pipe short, it was found that the vowels o and u could not be
distinctly formed, — the proper tone being injured by the elongation of the
pipe necessary to produce them ; and this, Mr. Willis remarks, is exactly the
case in the Human voice, most singers being unable to pronounce u and o
upon their highest notes.

616. The most natural primary division of the Consonants is into those
which require a total stoppage of the breath at the moment previous to their
being pronounced, and which, therefore, cannot be prolonged ; and those in
pronouncing which the interruption is partial, and which can, like the vowel
sounds, be prolonged ad libitum. The former have received the designation
of explosive; and the latter of continuous. — In pronouncing the explosive
consonants, the posterior nares are completely closed, so that the exit of air
through the nose is altogether prevented; and the current may be checked in
the mouth in three ways, — by the approximation of the lips, — by the approxi-
mation of the point of the tongue to the front of the palate, — and by the ap-
proximation of the middle of the tongue to the arch of the palate. In the first
of these modes, we pronounce the letters b, and p; in the second, d and t;
in the third, the hard g, and k. The difference between b, d, and g, on the
one hand, and p, t, and k,* on the other, seems to depend on this ; — that in
the former group the approximating surfaces are larger, and the breath is sent
through them more strongly at the moment of opening, than in the latter. —
The continuous consonants may be again subdivided, according to the degree
of freedom with which the air is allowed to make its exit, and the compression
which it consequently experiences, i. The first class includes those, in which
no passage of air takes place through the nose, and in which the parts of the
mouth that produce the sound are nearly approximated together, so that the
compression is considerable. This is the case with v andy, which are pro-
duced by approximating the upper incisors to the lower lip; and which stand
in nearly the same relation to each other, as that which exists between d and
t, or b and p. The sibilant sounds z and s, stand in nearly the same relation
to each other; they are produced by the passage of air between the point of
the tongue and the front of the palate, the teeth being at the same time nearly
closed. The simple sound sh is formed, by narrowing the channel between
the dorsum of the tongue and the palate; the former being elevated towards
the latter, through a considerable part of its length. If, in sounding s,
we raise the point of the tongue a very little, so as to touch the palate, the
sound of / is evolved; and in the same manner d is produced from z. This
class also includes the th ; which, being a perfectly simple sound, ought to be
expressed by a single letter, as in Greek; instead of by two, of which the

* For the sake of proper comparison, this letter should be sounded not as kay but as key.

468 OF THE VOICE AND SPEECH.

combination does not really produce anything like it. For producing this
sound, the point of the tongue is applied to the back of the incisors, or to the
front of the palate, as in sounding t ;* but, whilst there is complete contact of
the tip, the air is allowed to pass out around it. n. In the second class of
continuous consonants, including the letters m, n, /, and r, the nostrils are not
closed; and the air thus undergoes very little compression, even though the
passage of air through the oral cavity is almost or completely checked. In
pronouncing m and n, the breath passes through the nose alone; and the dif-
ference of the sound of these two letters, must be due to the variation in the
form of the cavity of the mouth, which acts by resonance. The letter m is a
labial, like b ; and the only difference between the two is, that in the former
the nasal passage is open, whilst the mouth remains closed; whilst in the
latter, the nose is entirely closed, and the sound is formed at the moment of
opening the mouth. The same correspondence exists between n and t, or n
and g (the particular part of the tongue approximated to the palate not being
of much consequence in the pronunciation of n} ; and hence it is that the
transition from n to t, or from n to g, is so easy, that the combinations nt and
ng are found abundantly in most languages. The sound of / is produced, by
bringing the tip of the tongue into contact with the palate, and allowing the
air to escape around it, at the same time that a vocal tone is generated in the
larynx ; it differs, therefore, from th in the position at which the obstruction
is interposed, as well as in the slight degree of the compression of the air
which it involves. The sound of the letter r depends on an absolute vibration
of the point of the tongue, in a narrow current of air forced between the tongue
itself and the palate, m. The sounds of the third class are scarcely to be
termed consonants, since they are merely aspirations, caused by an increased
force of breath. These are h, and the cAt of most foreign languages (the
Greek #). The first is a simple aspiration ; the second, an aspiration modified
by the elevation of the tongue, causing a slight obstruction to the passage of
air, and an increased resonance in the back of the mouth. This sound would
become either g or k, if the tongue, whilst it is being produced, were carried
up to touch the palate.J

617. These distinctions come to be of much importance, when we apply
ourselves to the treatment of defects of articulation. Great as is the number
of muscles employed in the production of definite vocal sounds, the number
is much greater for those of articulate language ; and the varieties of combina-
tion, which we are continually forming unconsciously to ourselves, would not
be suspected, without a minute analysis of the separate actions. Thus, in ut-
tering the explosive sounds, we check the passage of air through the posterior
narcs, in the very act of articulating the letter; and yet, this important move-
ment commonly passes unobserved. We must regard the power of forming
the several articulate sounds which have been adverted to, and their simple
combinations, as so far resulting from intuition, that it can in general be more
readily acquired by early practice, than other actions of the same complexity ;
so that we may consider these movements as having somewhat of the same
consensual character as that which has been attributed to the purely vocalizing
actions (§ 611). But there is in many individuals a deficiency of the power
of rightly combining them ; from which Stammering and other imperfections
result.

618. Many theories regarding the nature of Stammering have been pro-
posed ; and there can be little doubt, that the impediment may be attributed to

* Hence it is easy to understand the substitution of t or </, for the English th, by foreigners,
f Tlie English ch is merely a comlimatinn of/ \viih nh ; thus chime might be spelt Is/ii/iie.
j The general classification pn.pnscd by Dr. M. Hull is here adopted, with some modifica-
tion as to the details.

OF ARTICULATE SOUNDS. 469

a great variety of exciting causes. A disordered action of the nervous cen-
tres must, however, be regarded as the proximate cause ; though this may be
(to use the language of Dr. M. Hall) either of centric or of excentric origin,
— that is, it may result from a morbid condition of the ganglionic centre, or
from an undue excitement conveyed through its afferent nerves. When of
centric origin (and this is probably the most general case), the phenomena of
Stammering and Chorea have a close analogy to each other ; in fact, stammer-
ing is frequently one of the modes in which the disordered condition of the
nervous system in Chorea manifests itself. It is in the pronunciation of the
Consonants of the explosive class, that the stammerer experiences the greatest
difficulty. The total interruption to the breath which they occasion, frequently
becomes quite spasmodic ; and the whole frame is thrown into the most dis-
tressing semi-convulsive movement, until relieved by expiration.* In the pro-
nunciation of the continuous Consonants of the first class, the stammerer
usually prolongs them, by a spasmodic continuance of the same action; and
there is, in consequence, an impeded, but not a suspended respiration. The
same is the case with the / and r in the second class. In pronouncing the m
and n, on the other hand, as well as the aspirates and vowels, it is sometimes
observed that the stammerer prolongs the sound, by a full and exhausting ex-
piration. In all these cases, then, it seems as if the muscular sense, resulting
from each particular combination of actions, became the stimulus to the invo-
luntary prolongation of that action. In some instances, it is possible that the
defect may result from malformation of the parts about the fauces, producing
an abnormal stimulus of this kind, in some particular positions of the organ ;
and such cases may be really benefited by an operation for the removal of
these parts. But the effect of the operation is evidently for the most part upon
the Nervous System ; and it coincides with what may be frequently observed,
— that the Stammering is increased under any unusual excitement, especially
of the Emotional kind.

619. The method proposed by Dr. Arnott for the prevention of Stammer-
ing, consists in the connection of all the words by a vocal intonation, in such
a manner, that there shall never be an entire stoppage of the breath. It is
justly remarked by Muller, however, that this plan may afford some benefit,
but cannot do everything; since the main impediment occurs in the middle of
words themselves. One important remedial means, on which too much stress
cannot be laid, is to study carefully the mechanism of the articulation of the
difficult letters, and to practise their pronunciation repeatedly, slowly, and
analytically. The patient would at first do well to practise sentences, from
which the explosive consonants are omitted; his chief difficulty, arising from
the spasmodic suspension of the expiratory movement, being thus avoided.
Having mastered these, he may pass on to others, in which the difficult letters
are sparingly introduced ; and may finally accustom himself to the use of
ordinary language. One of the chief points to be aimed at, is to make the
patient feel that he has command over his muscles of articulation ; and this
is the best done, by gradually leading him from that which he finds he can
do, to that which he fears he cannot. The fact that stammering people are
able to sing their words better than to speak them, has been usually explained
on the supposition that, in singing, the glottis is kept open, so that there is
less liability to spasmodic action; if, however, as here maintained, the spas-
modic action is not in the larynx, but in the velum palati and the muscles of
articulation, the difference must be due to the direction of the attention rather

By Dr. Arnott this interruption is represented as taking place in the larynx ; that such is
not the case, the Author believes that a little attention to the ordinary phenomena of voice will
satisfactorily prove.

40

470 INFLUENCE OF THE NERVOUS SYSTEM

to the muscles of the larynx than to those of the mouth. Every one must
have noticed how much the impediment of Stammerers is increased, when
they are particularly anxious to speak fluently.

CHAPTER IX.

INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS.

620. OF the modes in which the Nervous System influences the Organic
Functions, a part have been already considered. It has been shown (§ 183)
that it is concerned in providing the conditions, either immediate or remote,
under which alone these functions can be performed ; so that, when its ac-
tivity ceases, they cannot be much longer maintained. The first mode in
which it operates upon them is, therefore, by producing sensible movements
in the Muscles or other contractile organs, which can be stimulated to action
through it ; and the contractions thus induced have usually an important effect
upon them, which varies, however, in each individual case. Thus, the pro-
cess of Nutritive Absorption, which is the very first stage in the operations of
Vegetative Life, and which is accomplished in Plants by the accidental con-
tact of the alimentary materials with the radical fibres, cannot take place in
Animals, until the muscular apparatus of prehension has been set in action by
the Will, that of deglutition by the Reflex Function, and that of the intestinal
canal by direct stimulation, — the two former kinds of contraction being ac-
complished entirely through the Nervous System, and the latter being influ-
enced by it. The Circulation of Blood, too, is chiefly effected, in the higher
Animals at least, by the contractions of a muscular organ of impulsion ; which
contractions, though not essentially dependent upon Nervous action, are
nevertheless greatly influenced by it. The function of Respiration, again,
cannot be maintained even for a short time, without muscular movement, ex-
cited through the Nervous System. The functions of Nutrition and Secre-
tion are more independent of it ; taking place, as in Plants, so long as the
conditions are supplied by other functions, without any sensible movements
being actually concerned in them. We shall presently see, however, that
they are subject to a peculiar kind of Nervous influence, which does not
manifest itself in obvious movement, but in altered performance of the inti-
mate processes themselves ; showing itself in the character of the organized
tissue, or of the secreted product. The act of Excretion is, like ingestion,
entirely performed by Muscular movement, dependent upon Nervous agency.
Now, wherever such movements of distant organs are usually performed in
connection with each other, there is an obvious channel for one kind of sym-
pathy between them ; an interesting example of this, is the contraction of the
Uterus, which may be frequently made to occur, when that organ is in a re-
laxed state at the conclusion of labour, by applying suction or other irritation
to the nipple.

G21. Sympathetic movements of this kind may be excited either through
the Cerebro-Spinal, or the Gangliouic systems; and we shall be guided in
our determination of their channel in each particular case, by the distribution
of these systems respectively to the organ aflectcd. The sympathetic move-
ments of the Muscles of Animal life appear to be chiefly, if not entirely, ex-

ON THE ORGANIC FUNCTIONS. 471

cited through the Cerebro-Spinal system ; whilst those of the contractile tis-
sues of the Viscera (§ 234) are probably excited through nerves, which,
though connected with the Cerebro-Spinal system, act under peculiar condi-
tions, and are commonly spoken of as forming part of the Sympathetic
system. It has been shown (§§ 388 — 393) that all the contractile organs,
which may be excited through the Sympathetic or Visceral system of nerves,
may also be made to act by stimuli applied to the roots of the Spinal nerves;
but that each Cerebro-Spinal fibre appears to pass through several Ganglia,
before being distributed to the organs which it supplies.

«. Many speculations have been hazarded, as to the reasons why the Visceral nerves
are destitute of sensibility; and, at the time when the Sympathetic was supposed to be
merely an offset from the Cerebro-Spinal system, it was imagined that the use of the gan-
glia upon the roots of the spinal nerves was to " cut off sensation'' from those concerned in
the " vital and involuntary motions." The influence of Bichat's ingenious hypothesis, — that
the Sympathetic system is complete and independent, ministering to the functions of Or-
ganic Life, as the Cerebro-Spinal does to those of Animal Life — for a time caused this idea
to be abandoned. Since, however, it has been anatomically proved, that a large proportion
of the filaments of the visceral nerves are derived from the Spinal cord, this opinion has
been revived, in a somewhat modified form.* Nevertheless the evidence in its support is
somewhat vague ; especially if the truth of the doctrine formerly urged, — that the Spinal
Cord is not itself a centre of sensation, — be admitted. For it is only necessary to suppose,
that the white fibres of the Sympathetic nerve terminate in the true Spinal Cord, without
proceeding to the Brain, to have an explanation of the absence of sensory endowments in
the organs to which they are distributed, and of the complete removal of the muscles sup-
plied by their motor nerves, from voluntary control. That a few fibres, of which the actions
cannot be excited under ordinary circumstances, pass on to the Brain, would seem probable
from the fact of the sensibility of some parts, in disease, which are totally insensible in their
normal condition ; — a fact in the explication of which, the hypothesis just alluded to affords
no assistance.

622. It appears, then, that it may be stated as a general proposition, that
all the evident movements which can be excited, by irritation applied to one
part of the body, in the contractile organs or tissues of another, are really
effected through the true Spinal Cord ; whether the contractile .organ be a
powerful muscle, or a thin and feeble layer of fibres around a blood-vessel or
duct. Upon the reasons why the fibres of the Visceral nerves should be so
peculiarly separated from the rest, we can at present only speculate ; but it
may not be considered improbable that, by their peculiar plexiform arrange-
ment in the various ganglia through which they pass, connections are estab-
lished between remote organs, which tend to bring their actions into closer
relation with each other, than would otherwise be the case. The existence
of such connections for the purpose of harmonizing the several movements
of the Viscera, which are concerned in the various and complex operations of
Digestion and its attendant processes, may be inferred from the perfect con-
formity which exists between them, during all their different states of regular
action; and still more, perhaps, from the phenomena of their disordered con-
ditions. The study of these Sympathies is one of those departments of Phy-
siology, in which it maybe expected that much will be gained by patient and
well-directed investigation.

623. The movements immediately concerned in the Organic Functions, how-
ever, are not influenced by Reflex action alone, but also by Emotional condi-
tions of the mind. This is most obvious in regard to the Heart. Every one
must have experienced the disturbance of its pulsations, consequent upon ex-
citement of the feelings, of almost any description. But other organs probably
experience similar changes, although of a less manifest character. It is well
known that the Sympathetic system is largely distributed upon the trunks of

* See Dr. Alison on the Nerves of the Orbit; Edin. Phil. Trans., vol. xv.; and Med. Gaz.
vol. xxviii. p. 378.

472 INFLUENCE OF THE NERVOUS SYSTEM

the blood-vessels, accompanying them to their minutest ramifications ; and it
will be hereafter shown (§ 732), that the fibrous (issue of the walls of the ar-
teries is probably susceptible of influence from these nerves. There can be
little doubt, therefore, that they constitute the channel through which Emo-
tions operate, in producing sudden distension of particular parts of the vascu-
lar system, as in blushing, erection, &c. And to the same kind of influence,
more gradually exerted, we may very probably attribute the regulation of the
supply of blood which passes to different secreting organs, in varying condi-
tions of the system.

624. But the Sympathetic System does not consist of Cerebro-Spinal fila-
ments alone; nor is its influence exerted only upon the motor or contractile
tissues of the body. There is good evidence, that the Nervous System has
an immediate action upon the molecular changes, which constitute the func-
tions of Nutrition, Secretion, &c. ; and the channel of such influence is pro-
bably to be found in that system of peculiar fibres formerly described (§ 244),
which constitutes a considerable proportion of the Visceral nerves, existing
much more sparingly in most of the Cerebro-Spinal, but being abundant in
the Fifth pair. There is no valid reason, however, to believe that any of the
processes of Nutrition and Secretion are dependent upon this, or any other,
kind of Nervous agency. These processes go on with great rapidity and
energy in the Vegetable kingdom, in which nothing approaching to a Nervous
System exists ; and in the Animal kingdom they take place with equal vigour,
long before the least vestige of it appears. The Embryological researches
of Dr. Barry have fully proved, that in the earliest condition of fffital life, the
germ consists but of a congeries of cells, which have all originated in a single
one ; and from this mass, the several tissues are gradually generated, by a
process which is technically called Mstolqgical* transformation, — one set of
cells being converted into muscular tissue, anther into nervous tissue, another
into mucous membrane, and so on. Now since this is the case, it is evident
that all these processes of development must take glace, in virtue of the inhe-
rent properties of the primary tissue itself; since no nervous influence can be
supposed to operate, before nerves are called into existence. Throughout the
Animal body, it may be observed that, the more Vegetative the nature of any
function, the less is it connected with the Nervous System ; and all the ex-
periments, which have been regarded as proving that the Organic functions
are dependent upon Nervous influence, are really explicable, fully as well,
upon the supposition that they are capable of being affected by it, either in
the way of excitement or retardation (see § 415). Moreover, there is abundant
evidence, that Secretion may take place after the death of the general system,
through the persistence of certain molecular changes, of which the essential
conditions are not immediately altered ; thus Mr. T. Bell mentions that, in
dissecting the poison apparatus of a Rattle-snake, which had been dead for
some hours, the poison continued to be secreted, so fast as to require being
occasionally dried off. This is precisely what might have been anticipated,
from the independent power of growth in the secreting cells ; and other acts
of Nutrition are recorded to have occurred under similar circumstances. In
such a case, the Animal body is reduced to the condition of a Plant; since
the influence of the Nervous system must then be entirely extinct. Upon
those Avho maintain that Nervous agency is a condition essential to those mo-
lecular actions, of which Nutrition and Secretion consist, it is incumbent,
therefore, to offer some more unexceptionable proof of their position than has
yet been given ; since their doctrine is opposed by so many considerations of
great weight.

* This term is used in contradistinction to morphological ', which applies to the alterations
in the/orm of the several parts of the embryo.

OX THE ORGANIC FUNCTIONS. 473

625. That many of the Organic Functions, however, are directly influenced
by the Nervous System, is a matter which does not admit of dispute ; and
this influence, exerted sometimes in exciting, sometimes in checking, and
sometimes in otherwise modifying them, may well be compared to that,
which the hand and heel of the rider have upon his horse, or which the en-
gine-driver exerts over a locomotive. It is most remarkably manifested in the
result of severe injury of the Nervous centres, — such as concussion of the
Brain, or of the Solar plexus (§ 580) ; for this does not merely produce a sus-
pension of the respiratory and other movements, which minister to the or-
ganic functions, and hence a gradual stagnation of the latter, — but a sudden
and complete cessation of the whole train of action ; which cannot be attri-
buted to any other cause than a positive depressing influence of some kind,
propagated through the Nervous System. It will hereafter appear (§ 701),
that in such cases even the vitality of the Blood is often affected; the usual
coagulation not taking place after death, so long, at least, as the blood remains
within the vessels. A similar general depression may result from Mental
Emotion, operating through the same channel ; but this more commonly
has rather a local action, or operates more gradually. — The influence of the
Nervous System is often especially exerted, in giving temporary excitement
to a Secreting process ; which need not be kept in constant activity, or of
which circumstances may occasionally require an increase. This is the
case, for example, in regard to the secretions connected with the process of
digestion, — the Saliva, Gastric fluid, Bile, Pancreatic fluid, &c. ; all of these
being excited by the contact of the substances on which they act, with the
surfaces on which their respective ducts open. The secretion of Milk, again,
in a nursing female, may be excited by irritation of the nipple ; and the de-
termination of blood to the Mammae during pregnancy, must be due to in-
creased action in the part, excited by the changes occurring in the Uterus,
which can scarcely operate otherwise than through the Nervous System. No
other channel of influence can be well imagined for most of these operations,
than the Sympathetic system of Nerves ; since the organs in question are for
the most part supplied by it. There is an apparent exception, however, in
the case of the Salivary and Lachrymal glands, which are supplied by the
Fifth pair ; but this nerve contains so many organic filaments, and is so inti-
mately connected with the Sympathetic, as evidently to supply (in the head)
the place of a separate ganglionic system. It is by Nervous influence, that
the mucous secretion covering the membranes is caused to be regularly formed
for their protection ; for it is shown, by pathological facts, that, when this
influence is interrupted, and the secretion is no longer supplied, the membrane
losing its protection, is irritated by the air or the fluids with which it may be
in contact, and passes into an inflammatory condition. This is the explana-
tion of the fact, which has been well ascertained, that the Eye is liable to
suppurate when the Fifth pair has been divided ; and that the mucous Mem-
brane of the bladder becomes diseased in Paraplegia.

626. The influence of particular conditions of the mind, in exciting various
Secretions, is a matter of daily experience. The flow of Saliva, for exam-
ple, is stimulated by the idea of food, especially that of a savoury character.
The Lachrymal secretion, again, which is continually being formed to a small
extent, for the purpose of bathing the surface of the eye, is poured out in
great abundance under the moderate excitement of the emotions, either o4'
joy, tenderness, or grief. It is checked, however, by violent emotions ; hence
in intense grief the tears do not flow. It is a well-known proof of moderated
sorrow, when this takes place ; tears, however, do not bring relief, as is com-
monly believed, but they indicate that it has been brought. Violent emotion
may also suspend the Salivary secretion ; as is shown by the well-known test.

40*

474 INFLUENCE OF THE NERVOUS SYSTEM

often resorted to in India, for the discovery of a thief amongst the servants of
a family, — that of compelling all the parties to hold a certain quantity of rice
in the mouth during a few minutes, — the offender being generally distin-
guished by the comparative dryness of his mouthful, at the end of the ex-
periment. The influence of the emotion of love-of-ofFspring, in increasing
the secretion of Milk, is well known. The formation of this fluid is con-
tinually going on during the period of lactation ; but it is greatly increased
by the sight of the infant, or even by the thought of him, especially when as-
sociated with the idea of suckling : this gives rise to the sudden rush of blood
to the gland, which is known by nurses as the draught, and which occasions
a greatly-increased secretion. The strong desire to furnish milk, together
with the irritation of the gland through the nipple, has often been effectual
in producing the secretion in girls and old women, and even in men (§ 853, d).
The quantity of the Gastric secretion is increased by exhilaration ; at least
if we may judge from the increase of the digestive powers, under such cir-
cumstances. Freedom from mental anxiety favours the secretion of fat ;
whilst continual solicitude effectually checks the disposition. It has been
stated that total despair has an equal tendency, with absence of care, to pro-
duce this effect ; persons left long to pine in condemned cells, without a shadow
of hope, frequently becoming remarkably fat in spite of their slender fare.*
The odoriferous secretion of the Skin, which is much more powerful in some
individuals than in others, is increased under the influence of certain mental
emotions (as fear or bashfulness), and commonly also by sexual desire. The
Sexual secretions themselves are strongly influenced by the condition of tne
mind. When it is frequently and strongly directed towards objects of passion,
these secretions are increased in amount to a degree which may cause them
to be a very injurious "drain on the powers of the system. On the other hand,
the active employment of the mental powers on other objects, has a tendency
to render less active, or even to check altogether, the processes by which they
are elaborated.!
i

* Fletcher's Physiology, Part II., b, p. 11.

•j- This is a simple physiological fact, but of high moral application. The Author would
say to those of his younger readers, who urge the wants of Nature as an excuse for the il-
licit gratification of the sexual passion: " Try the effects of close mental application to some
of those ennobling pursuits, to which your profession introduces you, in combination with
vigorous bodily exercise (for the effects of which see § 470), before you assert that the ap-
petite is unrestrainable, and act upon that assertion. Nothing tends so much to increase
the desire, as the continual direction of the mind towards the objects of its gratification. The
following observations, which the Author believes to be strictly correct, are extracted from
a valuable little work (anonymous) entitled, "Be not deceived, " addressed to Young Men;
they are directed to those who maintain that, the married state being natural to Man, illicit
intercourse is necessary for those who are prevented by circumstances from otherwise grati-
fying the sexual passion. "When the appetite is naturally indulged, that is, in marriage, the
necessary energy is supplied by the nervous stimulus of its natural accompaniment of love
before referred to, which prevents the injury which would otherwise arise from the in-
creased expenditure of animal power: and in like manner, also, the function being in itself
grateful, this personal attachment performs the further necessary office of preventing im-
moderate indulgence, by dividing the attention, through ilie numerous other sources of sym-
pathy and enjoyment which it simultaneously opens to the mind. But, \vheii the appetite
is irregularly indulged, that is in fornication, lor want of the healthful vigour of true love,
its energies become c.\h;m>tcd ; and from the want of the numerous other sympathetic;
sources of enjoyment in true love, in similar thoughts, common pursuits, and above all in
common holy hopes, the mere gross animal gratilieatiou of lust is resorted to with unnatural
frequency, and thus its powers become still further exhausted, and, therefore, still more
unsatisfying, u bile, ;it the same time, a habit is thus created, and these jointly cause an
increased craving; and the still greater deficiency in the satisfaction experienced in its indulg-
ence further, continually, ever in a circle, increases — the habit, demand, indulgence, conse-
quent exhaustion, illmini.-heil satisfaction, and again demand, — till the mind and body alike
become disorganized." Such considerations as these may, to some persons, appear misplaced

ON THE ORGANIC FUNCTIONS. 475

627. No secretion so evidently exhibits the influence of the depressing
Emotions, as that of the Mammae ; but this may be partly due to the fact, that
the digestive system of the Infant is a more delicate apparatus for testing the
qualities of that secretion, than any which the Chemist can devise ; affording
proof, by disorder of its function, of changes in the character of the Milk,
which no examination of its physical properties could detect. The following
remarks on this subject are abridged from Sir A. Cooper's valuable work on
the Breast. " The secretion of milk proceeds best in a tranquil state of
mind, and with a cheerful temper : then the milk is regularly abundant, and
agrees well with the child. On the contrary, a fretful temper lessens the
quantity of milk, makes it thin and serous, and causes it to disturb the child's
bowels, producing intestinal fever and much griping. Fits of anger produce
& very irritating milk, followed by griping in the infant, with green stools.
Grief has a great influence on lactation, and consequently upon the child.
The loss of a near and dear relation, or a change of fortune, will often so
much diminish the secretion of milk, as to render adventitious aid necessary
for the support of the child. Anxiety of mind diminishes the quantity, and
alters the quality of the milk. The reception of a letter which leaves the
mind in anxious suspense, lessens the draught, and the breast becomes empty.
If the child be ill, and the mother is anxious respecting it, she complains to
her medical attendant that she has little milk, and that her infant is griped,
and has frequent green and frothy motions. Fear has a powerful influence
on the secretion of milk. I am informed by a medical man who practices
much among the poor, that the apprehension of the brutal conduct of a
drunken husband, will put a stop for a time to the secretion of milk. When
this happens, the breast feels knotted and hard, flaccid from the absence of
milk, and that which is secreted is highly irritating, and some time elapses
before a healthy secretion returns. Terror, which is sudden and great fear,
instantly stops this secretion." Of this, two striking instances, in which the
secretion, although previously abundant, was completely arrested by this emo-
tion, are detailed by Sir A. C. " Those passions which are generally sources
of pleasure, and which, when moderately indulged, are conducive to health,
will, when carried to excess, alter, and even entirely check the secretion of
milk."

a. The following is perhaps the most remarkable instance on record, of the effect of strong
mental excitement on the Mammary secretion ; the event could hardly be regarded as more
than a simple coincidence, if it were^iot borne out by the less striking, but equally decisive
facts already mentioned. " A Carpenter fell into a quarrel with a Soldier billeted in his house,
and was set upon by the latter with his drawn sword. The wife of the carpenter at first
trembled from fear and terror, and then suddenly threw herself furiously between the combat-
ants, wrested the sword from the soldier's hand, broke it in pieces, and threw it away. During
the tumult, some neighbours came in and separated the men. While in this state of strong
excitement, the mother took up her child from the cradle, where it lay playing, and in the
most perfect health, never having had a moment's illness; she gave it the breast, and in so

in a Physiological Treatise — yet the Author feels sure that, by his well-judging readers, he
will not be blamed for adverting to this subject, or for the introduction of the above quota-
tion from a writer, of whom he has no personal knowledge, but whose object must be con-
fessed by all to be laudable. There seems to be something in the process of training young
men for the Medical Profession, which encourages in them a laxity of thought and expres-
sion on these matters, that generally ends in a laxity of action and of principle. It might
have been expected that those who are so continually witnessing the melancholy conse-
quences of the violation of the Divine law in this particular, would be the last to break it
themselves: but this is unfortunately very far from being the case. The Author regrets to
be obliged further to remark, that some recent works which have issued from the Medical
press, contain much that is calculated to excite, rather than to repress, the propensity ; and
that the advice sometimes given by practitioners to their patients is immoral as well as un-
scientific.

476 INFLUENCE OF THE NERVOUS SYSTEM ON THE ORGANIC FUNCTIONS.

doing sealed its fate. In a few minutes the infant left off sucking, became restless, panted,
and sank dead upon its mother's bosom. The physician who was instantly called in, found
the child lying in the cradle, as if asleep, and with its' features undisturbed ; but all his re-
sources were fruitless. It was irrecoverably gone.':* In this interesting case, the milk must
have undergone a change, which gave it a powerful sedative action upon the susceptible
nervous system of the infant.

b. The following, which occurred within the Author's own knowledge, is perhaps equally
valuable to the Physiologist, as an example of the similarly-fatal influence of undue emotion
of a different character; and both should serve as a salutary warning to mothers, not to
indulge either in the exciting or depressing passions. A Lady having several children, of
which none had manifested any particular tendency to cerebral disease, and of which the
youngest was a healthy infant a few months old, heard of the death (from acute hydroce-
phalus) of the infant child of a friend residing at a distance, with whom she had been on
terms of close intimacy, and whose family had increased almost contemporaneously with
her own. The circumstance naturally made a strong impression on her mind ; and she
dwelt upon it the more, perhaps, as she happened, at that period, to be separated from the
rest of her family, and to be much alone with her babe. One morning, shortly after having
nursed it, she laid the infant in its cradle, asleep and apparently in perfect health ; her atten-
tion was shortly attracted to it by a noise; and, on going to the cradle, she found her infant
in a convulsion, which lasted for a few minutes, and then left it dead. — Now, although the
influence of the mental emotion is less unequivocally displayed in this case than in the last,
it can scarcely be a matter of doubt; since it is natural that no feeling should be stronger in
the mother's mind under such circumstances, than the fear that her own beloved child
should be taken from her, as that of her friend had been ; and it is probable that she had
been particularly dwelling on it, at the time of nursing the infant on that morning.

c. Another instance, in which the maternal influence was less certain, but in which it was
not improbably the immediate cause of the fatal termination, occurred in a family nearly
related to the Author's. The mother had lost several children in early infancy, from a con-
vulsive disorder; one infant, however, survived the usually-fatal period; but whilst nursing
him. one morning, she had been strongly dwelling on the fear of losing him also, although
he appeared a very healthy child. In a few minutes after the infant had been transferred
into the arms of the nurse, and whilst she was urging her mistress to take a more cheerful
view, directing her attention to his thriving appearance, he was seized with a convulsion-fit
and died almost instantly. Now although there was here unquestionably a predisposing
cause, of which there is no evidence in the other cases, it can scarcely be doubted that the
exciting cause of the fatal disorder is to be referred to the mother's anxiety. This case offers
a valuable suggestion, — which, indeed, would be afforded by other considerations, — that an
infant, under such circumstances, should not be nursed by its mother, but by another woman
of placid temperament, who had reared healthy children of her own.

628. Other Secretions are in like manner vitiated by mental Emotions, al-
though the influence is not always so manifest. Thus, the halitus from the
lungs is sometimes almost instantaneously affected by bad news, so as to pro-
duce fffitid breath. A copious secretion of foetid gas not unfrequently takes
place in the intestinal canal, under the influence of any disturbing emotion ;
or the usual fluid secretions from its walls are similarly disordered. The
tendency to defecation which is commonly excited under such circumstances,
is not, therefore, due simply to the relaxation of the sphincter ani (as com-
monly supposed) ; but is partly dependent on the unusually stimulating cha-
racter of the faeces themselves. The same may be said of the tendency to
micturition, which is experienced under similar conditions : the change in its

* Dr. Von Ammon, in his treatise " Die ersten Mutterpflichten unddie erste Kindespflege,"
quoted in Dr. Combe's excellent little work on the Management of Infancy. Similar facts
are recorded by other writers. Mr. Wardrop mentions (Lancet, No. 516), that having re-
moved a small tumour from behind the ear of a mother, all went well, until she fell into a
violent passion; and the child, being suckled soon afterwards, died in convulsions. He was
sent for hastily, to see another child in convulsions, after taking the breast of a nurse who
had just been severely reprimanded; and he was informed by Sir Richard Croft, that he had
seen many similar instances. Three others are recorded by Burdach (Physiologic, § 5'22) ;
in one of them, the infant was seized with convulsions on the right side, and hemiplcgia on
the left, on sucking immediately after its mother had met with M>me distressing occurrence.
Another case was that of a puppy, which was seized with epilepsy, on sucking its mother
after a fit of rage.

SOURCES OF DEMAND FOR ALIMENT. 477

character becomes perceptible enough among many animals, in which it ac-
quires a powerfully-disagreeable odour under the influence of fear; and thus
answers the purpose, which is effected in others by a peculiar secretion. It
is a prevalent, and perhaps not an ill-founded opinion, that melancholy and
jealousy have a tendency to increase the quantity, and to vitiate the quality,
of the biliary fluid ; perhaps the disorder of the organic function is more com-
monly the source of the former emotion, than its consequence ; but it is cer-
tain that the indulgence of these feelings has a decidedly morbific effect, by
disordering the digestive processes, and thus reacts upon the nervous system
by impairing its healthy nutrition. On the influence of mental emotion in
the Mother, on the Foetus in utero, some remarks will be offered hereafter
(§ 938).

CHAPTER X.

OF FOOD, AND THE DIGESTIVE PROCESS.

1. — Sources of the Demand for JHiment. — Hunger and Thirst.

629. THE dependence of all Organized beings upon a supply of aliment, —
in the first place for the development of their fabric, and in the second for the
maintenance of their activity, — is a circumstance of such a familiar character,
that it might not seem worth while to dwell upon it. Nevertheless the in-
quiry into the purposes which the aliment serves in the economy, and into
the relative values of different articles of food, cannot be advantageously pro-
secuted, until we have first determined, with more precision, the causes
which occasion the demand to be set up. These will be now briefly enume-
rated.

630. In the first place, a due supply of aliment is required, for the fifct
development of the germ into the adult fabric. In all instances, the essen-
tial character of the act of Reproduction appears to be the liberation or setting-
free of a cell-germ ; which, according to the character of the being that gave
origin to it, may be destined to evolve, either a simple cell (as in the lowest
Cryptogamic Plants), a congeries of cells having a certain degree of variety
of form and of difference of function (as in the higher classes of the Vegetable
kingdom), or a complex fabric, composed of an immense variety of parts,
most of them departing widely, in appearance at least, from the original cellu-
lar type, and destined to perform a vast variety of actions, — as we see in the
perfectly developed organism of the higher Animals. The materials which
are subservient to this evolution, are all derived from the external world ;
either immediately, or through the medium of the parent. The germs of the
lowly Cryptogamia are thrown at once upon the world (so to speak), to obtain
their own livelihood ; and they themselves occasion the combination of the
inorganic elements, which they there meet with, into the organic compounds,
which are to be applied to the development of their simple organisms. In
the Flowering Plants, on the other hand, the germ is at first supplied with a
store of nutriment, which has already undergone this preparation, by the
agency of the parent ; and this store, laid up in the seed, is employed in the
development of the fabric of the young plant, until its organs are sufficiently
evolved to enable it to perform the same processes for itself. The same plan

478 OF FOOD, AND THE DIGESTIVE PROCESS.

is invariably followed in the development of the Animal ; the nutriment stored
up in the ovum being usually sufficient for the evolution of the fabric, until it
acquires the power of ingesting food for itself; and where this is not the
case (as in the Mammalia), a further provision being adopted, by which the
supply is continued during a lengthened period. Even when thrown upon
its own resources, the young Animal is often far from having attained even
the form of its parent; much less its size; and in the progress of its evolu-
tion, a greater or less degree of metamorphosis or change of form is observa-
ble. This is not usually so much the case in the higher animals, as in the
lower; because the supply of nutriment is proportionally greater in the
former, and serves to carry on the development to a later period ; but the
changes of condition which their germinal structure undergoes within the
ovum, are really as remarkable as those which are presented in the early em-
bryos of the latter after their emersion from the egg.

a. The phenomena of metamorphosis are most familiarly known in the case of Insects,
and Frogs, which were formerly thought to be exceptions to all general rules ; the Insect
coming forth from the egg in the state of a Worm; and the Frog in the condition of a Fish.
But it is now known that changes of form, as complete as these, occur in a large proportion
of the lower tribes of Animals ; so that the absence of them is the exception. The true
mode of viewing these early aspects of Animals of the inferior groups, seems to be to re-
gard them as foetal or embryonic ; thus, the Insect, in its larva state, is essentially a fcetus,
as regards the grade of development of its several tissues and organs; but it is a foetus
capable of obtaining its own nourishment. In this condition it attains its full growth as re-
gards size, though its form remains the same; but it then, in passing into the Chrysalis state,
re-assumes (as it were) the condition of the embryo within the egg, — the development of
various new parts takes place, at the expense of the nutriment stored up in its tissues, —
and it comes forth in the state of the perfect Insect, which henceforth takes no more food
than is requisite for the maintenance of the fabric thus evolved, or for the preparation of the
stores to be imparted to the offspring. — In many of the lower tribes, the animal quits the
egg at a still earlier period in comparison ; thus it has been lately shown by M. Milne Ed-
wards, that some of the long Marine Worms consist only of a single segment, forming a
kind of head, when they leave the egg ; and that the other segments, to the number it may
be of several hundred, are gradually developed from this ; the evolution continuing in some
instances during a considerable part of life. In some of the Radiated tribes, propagation
actually takes place whilst the animal is yet in its first or imperfect form ; thus the- Meduste
begin life as Polypes, and in this condition they increase by germination or budding, in the
manner of the true or permanent Polypes.

631. It is desirable to bear in mind, that the function of the Germ is sim-
ply that of occasioning the combination of the materials supplied by the
external world, and of directing the appropriation of those materials. The
several parts of the complex fabric of the higher Animals, contain a great
variety of materials ; and it is therefore requisite for its development, that it
should be duly supplied with all these. — The demand set up by the fabric,
whilst in course of development or evolution, for the materials of its growth,
constitutes, therefore, the primary source of the requirement of food ; and tin-
nature of this must be adapted to the wants of the being. Thus, the fabric
of Plants is essentially composed of Cellulose, a compound of Oxygen, Hy-
drogen, and Carbon ; and the materials required for the production of this are
simply Carbonic Acid and Water. But. nearly all Plants form some azotized
compound in the interior of their cells ; for the production of which, Ammo-
nia also is required. And in those species, whiclis like the Ccrealia, form a
large quantity of azotized compounds, and store them up in their seeds, a free
supply of Ammonia is requisite for the production of the greatest proportion
which they are capable of generating. — In Animals, again, whose tissue chiefly
consists of these very azotized compounds, or of modifications of them, a
constant supply of such is required during the whole period of the develop-
ment of the fabric, as well as subsequently; and if they be not afforded in

SOURCES OF DEMAND FOR ALIMENT. 479

sufficient amount, the evolution of the organism is either retarded or checked
altogether.* But there is one tissue, namely, Fat, the peculiar characters of
which are derived from the presence of a non-azotized substance in its cells ;
and this cannot be developed, unless there be in the food either oily, saccha-
rine, or amylaceous matters, from any of which the fatty compounds may be
generated.

632. The full development of the Animal fabric, however, does not by any
means involve the cessation of the demand for food ; in fact, during the whole
period of that development, it may be observed that the amount of nutriment
ingested is far greater than that which is applied to the simple extension of
the structure (§ 269). One source of this constant demand is to be found in
the continual ivaste or disintegration of the fabric, which goes on to a certain
extent under all circumstances, but which varies in degree according to cer-
tain conditions not difficult to be understood. — All organized substances are
liable, from the peculiarity of their chemical composition, to interstitial de-
cay ; and this operates in the living organism, as much as in the dead body
(§ 268). The difference is, that, in the living fabric, there is a provision for
at once removing the products of decay, so that they may be cast out of the
system as soon as possible ; whilst in the dead body they remain, and act as
ferments, accelerating the decomposition of other parts. Now the amount of
this interstitial decay varies with the temperature ; being increased by warmth,
and retarded by cold. It is consequently greatest in warm-blooded animals,
the temperature of whose bodies is constantly sustained at a high standard ;
it is reduced to its minimum in the torpid condition of cold-blooded animals,
which is brought on by the agency of cold; and will be lowered to nearly
the same degree in the hybernating state of certain Mammalia. — There is
another source of waste and decay, which is common to Animals, and all but
the simplest Plants ; this results from the limited duration of life in the indi-
vidual parts, which are most actively concerned in the Vegetative Functions.
We have seen that the essential instruments in the various functions of
Absorption, Assimilation, Respiration, Secretion, and Reproduction, are cells;
each of which goes through a certain series of processes and then dies and
decays, — just as do the isolated cells, which compose the entire fabric of the
simplest Cryptogamic Plants. This is evidenced to us in the Vegetable king-
dom by the " fall of the leaf;" which is nothing else than the result of the
death and decay of the component cells of that organ, after having fulfilled
their peculiar functions ; these consisting in the preparation or elaboration of
the nutritious sap, from which the various tissues and secretions of the plant
are subsequently generated. The same process is continually taking place,
though in a less obvious manner, in the Animal body ; the rate of death and
renewal of each group of cells being greater, as the functions to which it
ministers are energetically performed ; whilst the energy of these operations
is mainly dependent upon the demand set up by the exercise of the Minimal
functions, for the reparation of the Nervous and Muscular tissues.

633. The great source of waste and decay in the Animal body, and con-
sequently the chief source of the demand for food, is the disintegration of the
Nervous and Muscular tissues, which has been shown to be a necessary con-
dition of their functional activity. Every manifestation of Nervous power,
of whatever kind, seems to require the combination of Oxygen with the ele-
ments of Nervous matter ; the normal composition of which is thus destroyed,

The very curious discovery has lately been made, in regard to the integuments of the
Tunicated or Ascidian Mollusca (the lowest class of that sub-kingdom), that they contain a
considerable quantity of Cellulose • a substance which had not been previously supposed to
be a normal constituent of the Animal Fabric. See Annales des Sciences Naturelles ; 3me
Serie, Zool., torn. v. p. 193 et sea.

480 OF FOOD, AND THE DIGESTIVE PROCESS.

so that it ceases to be fit to form part of the body, and is cast out by the va-
rious processes of excretion. The same is the case in regard to the Muscu-
lar substance ; the waste of which is conformable to the use made of it. The
demand for the materials of reparation will follow the same proportion ; and
as the preparation of these materials can only be effected by the agency of
the Vegetative or nutritive functions, the rate at which these are performed
will be greatly influenced by the activity of the Animal functions. Hence
we see the necessity of regulating the supply of food, in accordance with the
state of the latter ; since a diet which would be superfluous and injurious to
an individual of inert habits, is suitable and beneficial to one who is leading a
life of continual exertion. This difference manifests itself remarkably in the
contrast between Animals of different tribes, whose natural instincts lead them
to different modes of life. The Birds of most active flight, and the Mammals
which are required to put forth the greatest efforts to obtain their food, need
the largest and most constant supplies of nutriment ; but even the least active
of these classes stand in remarkable contrast with the inert Reptiles, whose
slow and feeble movements are attended with so little waste, that they can
sustain life for weeks and even months, with little or no diminution of their
usual activity, without a fresh supply of food.*

634. Finally, there is a most important cause of demand for food, amongst
the higher Animals, which does not exist either amongst the lower Animals, or
in the Vegetable kingdom, at least to any great degree. In the classes of
Mammals and Birds, and in that of Insects also, we find a capability of sus-
taining the heat of the body at a fixed standard ; which is usually far above
that of the surrounding medium. This they are enabled to do, as will be
explained hereafter, by a process strictly analogous to ordinary combustion ;
the Carbon and Hydrogen, which are directly supplied by their food, or which
have been employed for a time in the composition of their living tissues and
then set free, being made to combine with Oxygen introduced by the respira-
tory process, and thus giving out the same heat, as if the same materials were
burned in a furnace. It will be hereafter shown that the immediate cause of
death in a warm-blooded animal, from which the food has been entirely with-
held, is the inability any longer to sustain the temperature which is requisite for
the performance of its vital operations (Chap. XVI., Sect. 2). Hence we see
the necessity for a constant supply of aliment, in the case of warm-blooded
animals, for this purpose alone ; and the demand will be regulated by the
external temperature. When the heat is rapidly carried off from the surface
by the chilling influence of the surrounding air or water, a much greater
amount of Carbon and Hydrogen must be consumed within the body, to main-
tain its proper heat, than when the medium is nearly as warm as the body
itself; so that a diet, which is appropriate in the former circumstances, is
superfluous and injurious in the latter; and the food which is amply sufficient
in a warm climate, is utterly destitute of power to enable it to resist the influ-
ence of severe cold. Substances rich in carbon and hydrogen, and having
little or no oxygen, afford the most efficient heat-sustaining materials ; but it
is an essential condition of their due action, that they should be of a kind
that renders them capable of being reduced by the solvent action of the sto-
mach, and of being absorbed into the system.

635. The demand for food is increased by any cause which creates an
unusual drain or waste in the system. Thus an extensive suppurating action

* The materials which are ret|uirecl for the reparation of the Muscular tissue, are chiefly
of a fibrinous nature; those employed for the renovation of the Nervous substance, would
seem to be iatty matter with I'lm-phorus. But from the peculiar composition of the fatty
matters of the Nervous substanoe (especially the presence of Azote in them), it seems quite
uncertain from which of the constituents of the i'<«>d they are really formed.

DEMAND FOR ALIMENT. SENSE OF HUNGER. 481

can be sustained only by a large supply of highly nutritious food. The
mother who has to furnish the daily supply of milk, which constitutes the
sole support of her offspring, needs an unusual sustenance for this purpose.
And there are states of the system, in which the solid tissues seem to possess
an unusual tendency to decomposition, and in which an increased supply of
aliment is therefore required. This is the case, for example, in Diabetes ; one
of the first symptoms of which disease is the craving appetite, that seems as
if it would be never satisfied. And there can be no doubt that, putting aside
all the other circumstances which have been alluded to, there is much differ-
ence amongst individuals, in regard to the rapidity of the changes which their
organism undergoes, and the amount of food consequently required for its
maintenance.

636. The want of solid aliment is indicated by the sensation of Hunger ;
and that of liquid by thirst. The former of these sensations is referred to
the stomach ; and the latter to the fauces : but although certain conditions of
these parts may be the immediate cause of the sensations in question, they
are really indicative of the requirements of the system at large. For the in-
tensity of the feelings bears no constant relation to the amount of solid or
liquid aliment in the stomach ; whilst, on the other hand, it does correspond
with the excess of demand in the system, over the supply afforded by the
blood ; and it is caused to abate by the introduction of the requisite materials
into the circulating fluid, even though this be not accomplished in the usual
manner by the ingestion of food into the stomach.

637. That the sense of Hunger, however, is immediately dependent upon
some condition of the Stomach, seems to follow from the fact, that it is abated,
if not arrested, by section of the Par Vagum (§ 412) ; and that it may be
temporarily alleviated, by introducing into the digestive cavity, matter which
is not alimentary. Of the precise nature of that condition, however, we have
no certain knowledge. It is easy to prove that many of the causes which
have been assigned for the sensation, are but little, if at all, concerned in pro-
ducing it. Thus, mere emptiness of the stomach cannot occasion it ; since,
if the previous meal have been ample, the food passes from its cavity some
time before a renewal of the uneasy feeling; and this emptiness may continue
(in certain disordered states of the system) for many hours or even days, with-
out a return of desire for food. It cannot be due, as some have supposed, to
the action of the gastric fluid upon the coats of the stomach themselves ; since
this fluid is not poured into the Stomach, except when the production of it is
stimulated by the irritation of its secreting follicles. By Dr. Beaumont it is
thought, that the distension of these follicles with the secreted fluid is the
proximate cause of hunger; but there is no more reason to believe that the
secretion of Gastric fluid is accumulating during the intervals when it is not
required, than there is in regard to Saliva, the Lachrymal fluid, or any other
secretions, which are occasionally poured out in large quantities under the in-
fluence of a particular stimulus; and, moreover, it is difficult to imagine how
mental emotion, or any impression on the nervous system alone (which is
able, as is well known, to dissipate the keenest appetite in a moment), can re-
lieve such distension. — It may, perhaps, be a more probable supposition, that
there is a certain condition of the Capillary circulation in the Stomach, which
is preparatory to the secretion, and which is excited by the influence of the
Sympathetic nerves, that communicate (as it were) the wants of the general
system. This condition may be easily imagined to be the proximate cause
of the sensation of hunger, by acting on the Par Vagum. When food is in-
troduced into the stomach, the act of secretion is directly excited ; the capil-
lary vessels are gradually unloaded ; and the immediate cause of the impres-
sion on the par vagum is withdrawn. By the conversion of the alimentary

41

482 OF FOOD, AND THE DIGESTIVE PROCESS.

matter into materials fit for the nutrition of the system, the remote de-
mand also if satisfied ; and thus it is that the condition of the stomach just
referred to, permanently relieved by the ingestion of substances that can
serve as food. But if the ingested matter be not of a kind capable of solution
and assimilation, the feeling of hunger is only temporarily relieved, and soon
returns in greater force than before. — The theory here given seems reconcile-
able with all that has been said of the conditions of the sense of hunger ; and
particularly with what is known of the effect produced upon it by nervous
impressions, which have a peculiar influence upon the capillary circulation.
It also corresponds exactly with what we know of the influence of the nerv-
ous system, and of mental impressions, upon other secretions (§ 624).

638. The sense of Hunger, like other sensations, may not be taken cogni-
zance of by the Mind, if its attention be strongly directed towards other ob-
jects; of this fact, almost every one engaged in active occupations, whether
mental or bodily, is occasionally conscious. The nocturnal student, who takes
a light and early evening meal, and, after devoting himself to his pursuits for
several hours uninterruptedly, retires to rest with a wearied head and an empty
stomach, but without the least sensation of hunger, is frequently prevented
from sleeping by an indescribable feeling of restlessness and deficiency ; and
the introduction of a small quantity of food into the stomach will almost in-
stantaneously allay this, and procure comfortable rest. Many persons, again,
who desire to take active exercise before breakfast, are prevented from doing
so by the lassitude and even faintness which it induces, — the bodily exercise
increasing the demand for food, whilst it draws off the attention from the sen-
sation of hunger.

a. The Author may be excused for mentioning the following circumstance, which some
years ago occurred to himself; and which seems to him a good illustration of the principle,
that the sense of hunger originates in the condition of the general system, and that its mani-
festation through a peculiar action in the stomach, is to be regarded as a secondary pheno-
menon,— adapted, under ordinary circumstances, to arouse the mind to the actions necessary
for the supply of the physical wants, — but capable of being overlooked if the attention of
the mind be otherwise directed. He was walking alone through a beautiful country, and
with much to occupy his mind ; and, having expected to meet with some opportunity of ob-
taining refreshment on his road, he had taken no food since his breakfast. This expectation,
however, was not fulfilled ; but, as he felt no hunger, he thought little of the disappointment.
It was evening before he approached the place of his destination, after having walked about
twenty miles, resting frequently by the way ; and he then began to feel a peculiar lassitude,
differing from ordinary fatigue, which rapidly increased, so that during the last mile he could
scarcely support himself. The "stimulus of necessity," however, kept him up; but on ar-
riving at his temporary home, he immediately fainted. It is obvious that, in this case, the
occupation of the mind on the objects around, and on its own thoughts, had prevented the
usual warning- of hunger from being perceived ; and the effect which succeeded was ex-
actly what was to be anticipated, from the exhaustion of the supply of food occasioned by
the active and prolonged exertion.

639. The conditions of the sense of Thirst appear to be very analogous to
those of hunger. This sense is not referred, however, to the stomach, but to
the fauces. It is generally considered that it immediately results from an im-
pression on the nerves of the stomach ; since, if liquids are introduced into
the stomach through an oesophagus-tube, they are just as effectual in allaying
thirst, as if they are swallowed in the ordinary manner. It may, however,
be doubted, whether the sense of thirst is not even more immediately connect-
ed with the state of the general system, than that of hunger ; for the imme-
diate relief afforded by the introduction of liquid into the stomach, is fully ac-
counted for by the instantaneous absorption of the fluid into the veins, which
is known to take place when there is a demand for it, not only from Dr. Beau-
mont's observations, but from many experiments made with reference to this
particular question. This demand is increased with almost equal rapidity,

NATURE AND DESTINATION OF FOOD. 483

by an excess in the amount of the fluid excretions ; and it may be satisfied
without the introduction of water into the stomach* (§ 677). Thirst may also
be produced, however, by the impression made by peculiar kinds of food or
drink upon the walls of the alimentary canal ; thus salted or highly-spiced
meat, fermented liquors when too little diluted, and other similarly irritating
agents, excite thirst ; the purpose of which is obviously to cause ingestion of
fluid, by which they may be diluted.

2. — Nature and Destination of the Food of Jlnimals.

640. The substances which are required by Animals for the development
and maintenance of their fabric, are of two kinds ; — the Organic and the In-
organic. The former alone are commonly reckoned as aliments; but the lat-
ter are really not less requisite for the sustenance of the body, which speedily
disintegrates, if the attempt be made to support it upon any organic com-
pounds in a state of purity. In all ordinary articles of diet, however, the in-
organic matters are present in the requisite proportion ; and hence they have
very commonly escaped notice. The nature of these substances, and the
mode in which they are introduced into the body, will be considered here-
after (§ 648). The Organic matters, used as food by Animals, are partly
derived from the Animal, and partly from the Vegetable kingdom ; and they
may be conveniently arranged under the four following heads :t — 1. The
Saccharine group, including all those substances, derived from the Vegetable
kingdom, which are analogous in their composition to Sugar ; — consisting of
oxygen, hydrogen, and carbon, alone ; and having the two first present in the
proportions to form water. To this group belong starch, gum, woody fibre,
and the various tissues of Plants ; which closely resemble each other in the
proportion of their elements, and which may be converted into Sugar by che-
mical processes of a simple kind. — 2. The Oleaginous group, including oily
matters, whether derived from the Vegetable kingdom, or from the fatty por-
tions of Animal bodies. The characteristic of this class, is the great pre-
dominance of hydrogen and carbon, the small proportion of oxygen, and the
entire absence of nitrogen. — 3. The Albuminous group, comprising all those
substances, whether derived from the Animal or Vegetable kingdom, which
are closely allied to Albumen, and therefore to the majority of the Animal
tissues, in their chemical composition. In this group, a large proportion of
azote is united with the oxygen, hydrogen, and carbon of the preceding. —
4. The Gelatinous group, consisting of substances derived from Animal bodies
only, which are closely allied to Gelatine in their composition. These also
contain azote ; but the proportion of their components differs from that of the
preceding.

641. The compounds of the Saccharine group cannot, without undergoing
a metamorphosis, form part of any Animal tissue ; as there is none which
they resemble in composition. It will be shown, however, that they are con-
vertible, within the Animal body, into those of the Oleaginous group; and,
like them, may be deposited in the form of Adipose matter. There is no
other tissue in the body, into which they can enter without considerable change ;
for all others are azotized; and it seems extremely improbable that non-azo-
tized compounds can, under any circumstances, be converted within the body
into compounds of the albuminous or gelatinous groups.

This was among die remarkable results of the injection of fluid into the veins, in the
Asiatic Cholera.

f Dr. Front's classification of alimentary substances is here adopted, with a slight modifi-
cation ; not as being altogether unexceptionable, but as being, in the Author's opinion, the
most convenient hitherto proposed..

484 OF FOOD, AND THE DIGESTIVE PROCESS.

642. The application of the substances forming the Albuminous group, to
the support of the Animal body, by affording the materials for the nutrition
and re-formation of its tissues, needs little explanation. The proportions of
the four ingredients of which they are all composed, are so nearly the same,
that no essential difference appears to exist among them ; and it is a matter of
little consequence, except as far as the gratification of the palate is concerned,
whether we feed upon the flesh of animals (fibrine), upon the white of egg
(albumen), the curd of milk (caseine), the grain of wheat (gluten), or the seed
of the pea (legumin). All these substances are reduced in the stomach to the
form of albumen; which resembles the gum of Plants, in being the raw ma-
terial, as it were, out of which the various fabrics of the body are constructed.
But the rule holds good, with regard to these also, that by being made to
feed constantly on the same substance,— boiled white of egg, for instance, or
meat deprived of the principle (osmazome) that gives it flavour, — an animal
may be effectually starved ; its disgust at the food being such, that even if it
be swallowed, it is not digested. It is very interesting to remark that, in the
only instance in which Nature has provided a single article of food for the
support of the animal body, she has mingled articles from the three first of
the preceding groups. This is the case in Milk, which contains a conside-
rable quantity of an albuminous substance, caseine, which forms its curd ; a
good deal of oily matter, the butter ; and no inconsiderable amount of sugar,
which is dissolved in the whey. The proportions of these vary in different
Mammalia ; and they depend in part upon the nature of the food supplied
to the Animal that forms the milk ; but the substances are thus combined in
every instance. — Although the greater part of the organized tissue of Animals
is formed at the expense of the Albumen and Fibrine of their blood, yet
many of them also contain a large quantity of Gelatine. It seems certain
that this gelatine may be produced out of fibrine and albumen ; since in ani-
mals that are supported on these alone, the nutrition of the gelatinous tissues
does not seem to be impaired. But it also appears, that gelatine taken in as
food may be applied to this purpose ; for ordinary experience shows, that be-
nefit is derived from jelly, soup, broth, &c. ; peculiarly by persons who have
been suffering under exhausting diseases, such as fevers. But it also ap-
pears certain, that it cannot be applied to the nutrition of the Albuminous
tissues. Some important experiments have been recently made in Paris on
this subject, with a view of determining how far the soup made from crushed
bones, which constituted a principal article of diet in the hospitals of Paris,
was adequate for the support of the patients. The result of these has been
quite confirmatory of previous conclusions, — namely, that Gelatine may be
advantageously mixed with albumen, fibrine, gluten, &c., and those other in-
gredients which exist in meat-soup and bread ; but that, when taken alone, it
has little more power of sustaining life than sugar or starch possesses ; and
that, even when bread is united with gelatine-soup, it does not give it the re-
quisite power of nutrition.

643. If the non-azotized compounds which exist so largely in the food of
Herbivorous animals, be not destined to form part (in any considerable degree
at least) of their tissues, the question arises, — what becomes of them ? It is
not enough to say that they are deposited as Fat; since it is only when a large
quantity of them is taken in, that there is any increase in the quantity of fat
already in the body. We shall hereafter see, that they are used up in the
process of Respiration; being burned-ofT within the body, for the purpose of
keeping up its temperature. The process will be hereafter considered more
in detail ; and at present we need only stop to remark upon the adaptation
between the food provided for animals in different climates, and the amount
of heat which it is necessary for them to produce. Thus the bears, and seals,

NATURE AND DESTINATION OF FOOD. 485

and whales, from which the Esquimaux and the Greenlander derive their sup-
port, have an enormous quantity of fat in their massive bodies: this fat is as
much esteemed as an article of food among these people, as it would be thought
repulsive by the inhabitants of southern climates; and by the large quantity of
it they consume, they are able to support the bitterness of an Arctic winter,
without appearing to suffer more from the extreme cold, than do the residents
in more temperate climates during their winter. On the other hand, the ante-
lopes, deer, and wild cattle, which form a large proportion of the animal food
of savage or half-cultivated nations inhabiting temperate or tropical regions, pos-
sess very little fat; and the comparatively small supply of carbon and hydro-
gen, whose combustion is required to keep up the bodily temperature of the
inhabitants of those regions, is derived from the flesh of those animals, in the
manner that will be presently explained. Every one knows how much less
vigorous the appetite becomes, during the heat of summer, than it is during
the colder portion of the year; and this is a natural result of the diminished
demand for the fuel required to maintain the temperature. And one great
means of preserving the health, during a prolonged residence in a hot climate,
is to attend to the dictates of Nature, in regard to the quantity of food ingested;
instead of endeavouring (as is the prevalent practice) to stimulate the appetite
by artificial provocatives.

644. The maintenance of the bodily temperature in Carnivorous animals,
appears to depend upon the combustion of the carbon and hydrogen set free
by the disintegration of their Nervous and Muscular tissues : this disintegra-
tion taking place with much more rapidity, in consequence of their almost
unceasing activity, than it does in the Herbivorous animals, which lead com-
paratively inactive lives. Every one who has visited a menagerie, must have
noticed the continual restlessness of the Tigers, Leopards, Hyasnas, &c., which
keep pacing from one end of their narrow cages to the other ; and it would
seem as if this restlessness were a natural instinct, impelling them to use mus-
cular exertion sufficient for the metamorphosis of an adequate amount of tissue,
that enough carbon and hydrogen may be set free for the support of the respi-
ratory process. And we see a corresponding activity in the Human hunters
of the swift-footed Antelope and agile Deer, which answers a similar purpose;
and which is remarkably contrasted with the stupid inertness of the inhabitants
of the frigid zone, which is only occasionally interrupted by the necessity of
securing the supplies of food afforded by the massive tenants of their seas. —
The nutrition of the Carnivorous races may, then, be thus described. The
bodies of the animals upon which they feed contain flesh, fat, &c., in nearly
the same proportion as their own; and all, or nearly all, the aliment they con-
sume, goes to supply the waste in the fabric of their own bodies, being con-
verted into its various forms of tissue. After having remained in this condition
for a certain time, varying according to the use that is made of them, these
tissues undergo another metamorphosis, which ends in restoring them to inor-
ganic matter; and thus give back to the Mineral world the materials which
were drawn off from it by Plants. Of these Materials, part are burned off, as
it were, within the body, by union with the oxygen of the air, taken in through
the lungs ; and are discharged from these organs, in the form of carbonic acid
and water: the remainder are carried off in the liquid form by other channels.
Hence we may briefly express the destination of their food in the following
manner: —

Food consisting of ^ T . . , f Carbonic acid and Water

albumen, fibrine, I Convert- \ ^m" .t An< I thrown off by respiration.

and other azotized f ed into i °rgamzed ( ™et™> 1 Urea and biliary matter, &c,
compounds J * ph mto [thrown off by other excretions.

41*

486 OF FOOD, AND THE DIGESTIVE PROCESS.

645. But in regard to the Herbivorous animals, the case is different. They
perspire much more abundantly, and their temperature is thus continually kept
down. They consequently require a more active combustion, to develope
sufficient bodily heat; and the materials for this are supplied, as we have
seen, by the non-azotized portions of their food, rather than by the metamor-
phosis of their own tissues, which takes place with much less rapidity than in
the Carnivorous tribes. Hence we may thus express the destination of this
part of their food; that of the azotized matter, here much smaller in amount,
will be the same as in the preceding case : —

Starch, oil, and} partly (AT ^ but chiefly C Carbonic acid and Water, dis-

other non-azotized > converted < > thrown off < engaged by the respiratory

compounds ) into ( ) directly as ( process.

The proportion of the food deposited as fat, will depend in part upon the sur-
plus which remains, after the necessary supply of materials has been afforded
to the respiratory process. Hence, the same quantity of food being taken, the
quantity of fat will be increased by causes that check the perspiration, and
otherwise prevent the temperature of the body from being lowered, so that
there is need of less combustion within the body to keep up its heat. This is
consistent with the teachings of experience respecting the fattening of cattle ;
for it is well known that this may be accomplished much sooner, if the animals
are shut up in a warm dwelling and covered with cloths, than if they are freely
exposed in the open air.

646. Now the condition of Man may be regarded as intermediate between
these two extremes. The construction of his digestive apparatus, as well as
his own instinctive propensities, point to a mixed diet as that which is best
suited to his wants. It does not appear that a diet composed of ordinary
vegetables only, is favourable to the full development of either his bodily or
mental powers ; but this cannot be said in regard to a diet of which bread is
the chief ingredient, since the gluten it contains appears to be as well adapted
for the nutrition of the animal tissues, as does the flesh of animals. On the
other hand, a diet composed of animal flesh alone is the least economical that
can be conceived ; for, since the greatest demand for food is created in him
(taking a man of average habits, in regard to activity and the climate he in-
habits), by the necessity for a supply of carbon and hydrogen to support his
respiration, this want may be most advantageously fulfilled by the employment
of a certain quantity of non-azotized food, in which these ingredients predomi-
nate. Thus it has been calculated, that, since fifteen pounds of flesh contain
no more carbon than four pounds of starch, a savage with one carcass and an
equal weight of starch, could support life for the same length of time, during
which another restricted to animal food would require five such carcasses, in
order to procure the carbon necessary for respiration. Hence we see the im-
mense advantage as to economy of food, which a fixed agricultural population
possesses over those wandering tribes of hunters, whicli still people a large
part both of the old and new continents. The mixture of the nzotized and
non-azotized compounds (gluten and starch), that exists in wheat flour, seems
to be just that which is most useful to Man ; and hence we see the explanation
of the fact, that, from very early ages, bread has been regarded as the "staff
of life." In regard to the nutritious properties of different articles of vegetable
food, these may be generally estimated by the proportion of azote they con-
tain ; which is in almost every instance less than that existing in good wheat
flour.

647. The following table represents the relative quantity of Nitrogen in
different articles used as food ; and thus shows their relative applicability to

NUTRITIVE POWER OF DIFFERENT KINDS OF FOOD.

487

the maintenance and reparation of the body.* Those which are poorest in
nitrogen, are richest in Carbon and Hydrogen ; and are, therefore, the best
adapted to serve as the pabulum for the heat-sustaining process. It is to be
borne in mind, however, that no table of this kind, founded simply upon the
Chemical composition of the various substances, can indicate their respective
fitness as articles of diet; since this depends also upon the facility with which
they are reduced by the digestive process, and afterwards assimilated. Thus
an aliment, abounding in nutritive matter, may be inferior to one which really
•contains a much smaller proportion, if only a part in the first case, and the
whole in the second, be readily taken up by the system. — In the following
table, Human Milk is taken as the standard ; and the quantity of Nitrogen it
contains is expressed by 100. But it must be borne in mind that this sub-
stance is intended for the nourishment of a being that passes nearly the whole
of its time in a quiescent state ; and must not be supposed to be adapted for
the sole maintenance of the Human body in a state of activity. In fact, it is
inferior in its proportion of Caseine (the substance of which alone the azote
forms a part) to the milk of most, if not all, other Mammalia ; their young
bringing their animal functions into exercise at a much earlier period than the
Human infant.

Vegetable.

Rice
Potatoes
Turnips
Rye .
Maize .
Barley

Human milk

Cow's milk .

Oyster

Yolk of eggs .

Cheese

Eel, raw

. boiled

Liver of crab
Mussel, raw

boiled

Ox liver, raw
Pork-ham, raw
boiled

. . 81

Oats

. 138

. 84

White bread .

. . 142

. . 106

Wheat

. 119-144

. 106

Carrots

. . 150

100-125

Brown Bread

. 166

. 125

Agaricus cantharellus 201

Jlnimal.

. 100 Salmon, raw . . 776

. . 237 • boiled . . 610

. 305 Liver of Pigeon . . 742

. . 305 Portable soup . . 764

331-447 White of Egg . .845

. . 434 Crab, boiled . . . 859

. 428 Skate, raw . . 859

. . 471 boiled . . . 956

. 528 Herring, raw . .910

. . 660 boiled . . 808

. 570 milt of . . 924

. . 539 Haddock, raw . . 920

. 807 boiled .816

Peas . . . . 239

Agaricus russula . 264

Lentils . . .276

Haricot beans . .283

Agaricus deiiciosus _ 289

Beans . 320

Flounder, raw . . 898

• .boiled . . 954

Pigeon, raw . .756

boiled . . 827

Lamb, raw . .833

Mutton, raw . . . 773

toiled . . 852

Veal, raw . . .873

boiled . .911

Beef, raw . . . 880

boiled . . 942

Ox lung . 931

648. Besides these substances, there are certain Mineral ingredients, which
may be said to constitute part of the food of Animals ; being necessary to their
support, in the same manner as other mineral substances are necessary to the
support of Plants. Of this kind are common salt, and also phosphorus, sul-
phur, and lime, either in combination or separate. The uses of Salt are very
numerous and important. It consists of two substances of opposite qualities,
muriatic acid and soda ; and the former is the essential ingredient in the gastric
juice ; whilst the latter performs a very important part in the production of
bile. Phosphorus is chiefly required to be united with fatty matter, to serve
as the material of the nervous tissue; and to be combined with oxygen and
lime, to form the bone-earth, by which the bone is consolidated. Sulphur
exists in small quantities in several animal tissues ; but its part is by no
means so important, as that performed by phosphorus. Lime is required for
the consolidation of the bones ; and for the production of the shells and other

* ^'chlossberger and Kemp, in Philosophical Magazine. Nov. 1S45.

488 OF FOOD, AND THE DIGESTIVE PROCESS.

hard parts, that form the skeletons of the Invertebrata. To these ingredients
we may also add Iron, which is -a very important element in the red blood of
Vertebrated animals. — These substances are contained, more or less abund-
antly, in most articles generally used as food ; and where they are deficient,
the animal sufFers in consequence, if they are not supplied in any other way.
Thus common Salt exists, in no inconsiderable quantity, in the flesh and
fluids of animals, in milk, and in the egg : it is not so abundant, however, in
plants ; and the deficiency is usually supplied to herbivorous animals by some
other means. Thus salt is purposely mingled with the food of domesticated
animals ; and in most parts of the world inhabited by wild cattle, there are spots
where it exists in the soil, and to which they resort to obtain it. Such are the
"buffalo licks" of North America. Phosphorus exists also in the yolk and white
of the Egg, and in Milk, — the substances on which the young animal subsists
during the period of its most rapid growth ; and it abounds, not only in many
animal substances used as food, but also (in the state of phosphate of lime or
bone-earth) in the seeds of -many plants, especially the grasses. In smaller
quantities it is found in the ashes of almost every plant. When flesh, bread,
fruit, and husks of grain, are used as the chief articles of food, more phosphorus
is taken into the body than it requires ; and the excess has to be carried out in
the excretions. Sulphur is derived alike from vegetable and animal substances.
It exists in flesh, eggs, and milk ; also in the azotized compounds of plants ;
and (in the form of sulphate of lime) in most of the river and spring-water that
we drink. Iron is found in the yolk of egg, and in milk, as well as in animal
flesh; it also exists in small quantities in most vegetable substances used as
food by Man, — such as potatoes, cabbage, peas, cucumbers, mustard, &c. ;
and probably in most articles, from which other animals derive their support.
Lime is one of the most universally diffused of all mineral bodies ; for there
are very few animal or vegetable substances, in which it does not exist. It
is most commonly taken in, among the higher animals, combined with Phos-
phoric acid ; and in this state it exists largely in the seeds of most grasses,
especially in wheat flour. If it were not for their deficiency in Phosphate
of lime, some of the Leguminous seeds would be more nutritious than wheaten
flour ; the proportion of azotized matter they contain being greater. A con-
siderable quantity of lime exists, in the state of carbonate and sulphate, in all
hard water.

649. The absolute quantity of food, required for the maintenance of the
Human body in health, varies so much with the age, sex, and constitution
of the individual, and with the circumstances in which he may be placed,
that it would be absurd to attempt to fix any standard which should apply to
every particular case. The appetite is the only sure guide for the supply of
the wants of each ; but its indications must not be misinterpreted. To eat
when we are hungry, is an evidently natural disposition; but to eat as long
as we are hungry, may not always be prudent. Since the feeling of hunger
does not depend so much upon the state of fulness or emptiness of the sto-
mach, as upon the condition of the general system, it appears evident that the
ingestion of food cannot at once produce the effect of dissipating it, though
it will do so after a short time ; so that, if we eat with undue rapidity, we
may continue swallowing food long after we have taken as much as will really
be required for the wants of the system ; and every superfluous particle is
not merely useless, but injurious. Hence, besides its other important ends,
the process of thorough mastication is important, as prolonging the meal,
and giving time to the system to become acquainted (as it were) that the sup-
ply of its wants is in progress ; so that its demand may be abated in due time
to prevent the ingestion of more than is required. It is very justly remarked
by Dr. Beaumont, that the cessation of this demand, rather than the positive

REQUISITE AMOUNT OF FOOD. 489

sense of satiety, is the proper guide. " There appears to be a sense of per-
fect intelligence conveyed to the encephalic centre, which, in health, invariably
dictates what quantity of aliment (responding to the sense of hunger and its
due satisfaction) is naturally required for the purposes of life ; and which, if
noticed and properly attended to, would prove the most salutary monitor of
health, and effectual preventive of disease. It is not the sense of satiety,
for this is beyond the point of healthful indulgence, and is Nature's earliest
indication of an abuse and overburden of her powers to replenish the system.
It occurs immediately previous to this ; and may be known by the pleasurable
sensations of perfect satisfaction, ease and quiescence of body and mind. It
is when the stomach says, enough ; and it is distinguished from satiety by
the difference of sensations, — the latter saying too much.'1'' Every medical
man is well aware how generally this rule is transgressed ; some persons
making a regular practice of eating to repletion ; and others paying far too
little attention to the preliminary operations, and thus ingesting more than is
good for them, even though they may actually leave off with an appetite.

650. Although no universal law can be laid down for individuals, however,
it is a matter of much practical importance to be able to form a correct ave-
rage estimate. It is from the experience afforded by the usual consumption
of food by large bodies of men, that our data are obtained ; and these data
are sufficient to enable us to predict with tolerable accuracy what will be re-
quired by similar aggregations, though they can afford no guide to the con-
sumption of individuals. — We shall first consider the quantity sufficient for
men in regular active exercise ; and then inquire how far that may be safely
reduced for those who lead a more sedentary life. — The Diet-scale of the
British Navy may be advantageously taken as a specimen of what is required
for the first class. It is well known that an extraordinary improvement has
taken place in the health of seamen during the last 80 years ; so that three
ships can now be kept afloat with only the same number of men, which were
formerly required for two. This is due to the improvement in the quality of
the food, in combination with other prophylactic means. At present it may
safely be affirmed, that it would not be easy to conceive of any diet-scale
more adapted to answer the required purpose. The health of crews that
have been long afloat, and have been exposed to every variety of external
conditions, appears to be preserved (at least when they are under the direc-
tion of judicious officers), to the full as well as that of persons subject to
similar vicissitudes on shore ; and there can be no complaint of insufficiency
of food, although the allowance cannot be regarded as superfluous. It con-
sists of from 31 to 35$ ounces of dry nutritious matter daily; of this 26 oz.
are vegetable; and the rest animal; 9 ;oz. of salt meat, or 4| oz. fresh,
being the allowance of the latter. This is found to be amply sufficient
for the support of strength ; and considerable variety is produced, by ex-
changing various parts of the diet for other articles. This, however, is some-
times done erroneously ; thus 8 oz. of fresh vegetables, which contain only
l£ oz. of solid nutriment, are exchanged for 12 oz. of flour, which is almost
all nutritious. Sugar and Cocoa are also allowed ; partly in exchange for a
portion of the Spirits formerly served out, the diminution of which, especially
in the case of boys, has been attended with great benefit.

651. A considerable reduction in this amount is of course admissible,
where little bodily exertion is required, and where there is less exposure to
low temperatures. In the case of Prisoners, the diet should of course be as
spare as possible, consistently with health ; but it should be carefully modi-
fied, in individual cases, according to several collateral circumstances, such
as depression of mind, compulsory labour, previous intemperate habits, and
especially the length of confinement. It has been supposed by some, that

490 OF FOOD, AND THE DIGESTIVE PROCESS.

prisoners require a fuller diet than persons at large ; this is probably erro-
neous ; but more variety is certainly desirable, to counteract, as far as possi-
ble, the depressing influence of their condition upon the digestive powers.
The circumstances which occurred at the Milbank Penitentiary in 1823, form
a lamentable warning against the reduction of the diet-scale to an insufficient
amount. The allowance to the prisoners had formerly been from 31 to 33
oz. of dry nutriment daily, and the prison was considered healthy; but in
1822, it was reduced to 21 oz. The health of the prisoners continued un-
broken for nearly six months ; but scurvy then showed itself unequivocally,
and out of 860 prisoners, 437, or 52 per cent., were affected with it. The
effect of previous confinement here became remarkable ; for those were chiefly
attacked, who had been in the prison for two years, a year, or six months.
Again, the prisoners employed in the kitchen, who had 8 oz. of bread addi-
tional per day, were not attacked, except three who had only been there a
few days. After the epidemic had spread to a great extent, it was found that
the addition of 8 oz. to the daily allowance of vegetable food, and 5 oz. to
the animal, facilitated the operation of the remedies which were used for the
restoration of the health of the prisoners. — The effects of confinement have
been further shown in the experience of the Edinburgh House of Refuge,
which was first established in 1832, for the reception of beggars during the
cholera, and which has been continued to the present time. The diet was at
first a quart of oatmeal porridge for each person, morning and evening ; and
at dinner 1 oz. of meat, in broth, with 7 oz. of bread ; making altogether
about 23 oz. of solid food a day. During some months, this diet seemed to
answer very well ; the people went out fatter than they came in, owing to
the diet being better than that to which they had been accustomed ; but after-
wards a proneness to disease manifested itself in those who had been resi-
dents there for a considerable time, and the diet was therefore somewhat in-
creased, with good effect. The quantity of animal food was probably here
too small ; and the total weight might still have been sufficient, if it had
been differently apportioned. — In a Convict-ship, which took out 433 prison-
ers to New Holland in 1802, the mortality was very trifling, and the general
health good; although these prisoners were supported on 16 oz. of vegetable
food, and 7 1 oz. of animal food per day ; a quantity which was found to be
perfectly sufficient for them. — The aged inmates of work-houses, especially
those who have been accustomed to poor food during their whole lives, re-
quire much less than this ; their vital functions being comparatively inactive,
and their amount of labour or exercise small. In the Edinburgh work-house,
of which the inmates usually have good health, they are fed upon oatmeal-
porridge morning and evening, with barley-broth at dinner ; the total allow-
ance of dry nutriment is about 17 oz. ; namely 13 oz. vegetable, and 4 oz.
animal.

652. It is a curious effect of insufficient nutriment, as shown by the recent
inquiries of Chossat,* that it produces an incapability of digesting even the
limited amount supplied. He found that, when turtle-doves were supplied
with limited quantities of corn, but with water at discretion, the whole amount
of food taken was scarcely ever actually digested ; a part of it being rejected by
vomiting, or passing off by diarrhoea, or accumulating in the crops. It seems
as if the vital powers were not sufficient to furnish the requisite supply of
gastric fluid, when the body began to be enfeebled by insufficient nutrition ;
or perhaps we might well say, the materials of the gastric fluid were wanting.
Hence the loathing of food, which is often manifested by those who have
been subjected to the influence of an insufficient diet-scale in our prisons and

* Recherches E.xperimcntales sur 1'Inanition, 1843.

REQUISITE AMOUNT OF FOOD. 491

poor-houses, and which has been set down to caprice or obstinacy, and pun-
ished accordingly, may be actually a proof of the deficiency of the supply
which we might expect to have been voraciously devoured, if really less than
the wants of the system require.

653. The smallest quantity of food upon which life is known to have been
supported with vigour, during a prolonged period, is that on which Cornaro
states himself to have subsisted. This was no more than 12 oz. a day,
chiefly of vegetable matter, for a period of 58 years. There is only one in-
stance on record, in which his plan was followed ; and there are probably few
who could long persevere in it, at least among those whose avocations require
much mental or bodily exertion. It is certain, however, that life with a mode-
rate amount of vigour may be preserved for some time, with a very limited
amount of food ; this appears from the records of shipwreck and similar dis-
asters. In regard, however, to those who have been stated to fast for a period
of months or even years, taking no nutriment, but maintaining an active con-
dition, it may be safely asserted that they were impostors, — probably possess-
ing unusual powers of abstinence, which they took care to magnify. The
instances in which the life of Man, or of other Mammalia, has been prolonged
to the greatest extent without water, are those in which, from the peculiarity
of the circumstances, the cutaneous exhalation must have been reduced to a
very small amount, or in which there may have been an actual absorption of
water by the skin and lungs. Thus, Fodere mentions that some workmen
•were extricated alive, after fourteen days' confinement in a cold damp cavern,
in which they had been buried under a ruin. And there is a well-known case
of a Hog, which was buried in its sty for 160 days, under thirty feet of the
chalk of Dover cliff, and was dug out alive at the end of that time, reduced in
weight from 160 Ibs. to 40 Ibs. : here the temperature would be kept up by the
non-conducting power of the chalk around ; and the air surrounding the ani-
mal would soon become sufficiently charged with fluid, to resist further evapo-
ration. The time during which life can be supported under total abstinence,
is usually stated to vary from 8 to 10 days : the period may be greatly
prolonged, however, by the occasional use of water, and still more by a very
small supply of food. In a case recorded by Dr. Willan, of a young gentle-
man who starved himself, under the influence of a religious delusion, life was
prolonged for 60 days ; during the whole of which time nothing else was
taken than a little orange-juice. In a somewhat similar case which occurred
under the Author's notice, in the person of a young French lady, more than
15 days elapsed between the time that she ceased to eat regularly, and
the time of her being compelled to take nourishment; during this period she
took a great deal of exercise, and her strength seemed to suffer but little, al-
though she swallowed solid food only once, and then in small quantity. If
the cessation of muscular exertion be complete, it seems that life is usually
more prolonged than where exercise of any kind is performed ; and this is
what might naturally be expected. — In certain states of the system commonly
known as Hysterical, there is frequently a very remarkable disposition for ab-
stinence, and power of sustaining it. In a case of this kind which occurred
under the Author's own notice, a young lady, who had suffered severely from
the tetanic form of Hysteria, was unable to take food for three weeks. The
slightest attempt to introduce a morsel of solid matter into the stomach, oc-
casioned very severe vomiting and retching ; and the only nourishment taken
during the period mentioned, was a cup of tea once or twice a day, — on many
days not even this being swallowed. Yet the strength of the patient rather
increased than diminished, during this period ; her muscles became firmer,
and her voice more powerful. — It may be well to remark that, under such
circumstances, the continual persuasions of anxious friends are very injurious

492 OF FOOD, AND THE DIGESTIVE PROCESS.

to the patient; whose return to her usual state will probably take place the
earlier, the more completely she is left to herself.

654. Of the quantity which can be devoured at a time, it is scarcely the
place to speak; since such feats of gluttony only demonstrate the extraordi-
nary capacity, which the stomach may be made to attain by continual practice.
Many amusing instances are related by Captain Parry in his Arctic Voyages ;
in one case, a young Esquimaux, to whom he had given (for the sake of cu-
riosity) his full tether, devoured in four-and-twenty hours, no less than 35lbs.
of various kinds of aliment, including tallow candles. A case has recently
been published of a Hindoo, who can eat a whole sheep at a time ; this pro-
bably surpasses any other instance on record. The half-breed voyageurs of
Canada, according to Captain Franklin, and the wandering Cossacks of Sibe-
ria, as testified by Capt. Cochrane, habitually devour a quantity of animal
food, which would be soon fatal to any one unused to it. The former are
spoken of as very discontented, when put on a short allowance of 81bs. of
meat a day; their usual consumption being from 12 to 201bs. — That a much
larger quantity of food than that formerly specified, may be taken, with per-
fect freedom from injurious consequences, under a particular system of exer-
cise, &c., appears from the experience, of those who are trained for feats of
strength, pugilistic encounters, &c. The ordinary belief, that the Athletic
constitution cannot be long maintained, appears to have no real foundation ;
nor does it appear that any ultimate injury results from the system being per-
severed in for some time. That trained men often fall into bad health, on
the cessation of the plan, is probably owing in part to the intemperance and
other bad habits of persons of the class usually subjected to this discipline.
The effects of trainers' regimen are hardness and firmness of the muscles,
clearness of the skin, capability of bearing continued severe exercise, and a
feeling of freedom and lightness (or " corkiness") in the limbs. During the
continuance of the system, it is found that the body recovers with wonderful
facility from the effects of injuries ; wounds heal very rapidly ; cutaneous
eruptions usually disappear. Clearness and vigour of mind, also, are stated
to be results of this plan ; and it is probable that, where persevering attention
and intense application are necessary, a modification of this system, in which
due allowance should be made for the diminished quantity of exercise, would
be found advantageous.*

3. — Of the Passage of Food along the Alimentary Canal.

655. The introduction of alimentary matter into the system, is accomplished
in Animals by the reception of the food into an internal cavity, where it is
subjected to a preparatory process, to which nothing analogous exists in Plants,
and which is termed Digestion. This process may be said to have three dif-
ferent purposes in view ; — the reduction of the alimentary matter to a fluid
form, so that it may become capable of absorption ; — the separation of that

The method of training employed by Jackson (a celebrated trainer of prize-fighters in
modern times), as deduced from his answers to questions put to him by John Bell, was to
begin on a clear foundation, by an emetic and two or three purges. Beef and mutton,
the lean of fat meat being preferred, constituted the principal food ; veal, lamb, and pork
were said to be less digestible (" the last purges some men"). Fish was said to be a " wa-
tery kind of diet:" and is employed by jockeys who wish to reduce weight by sweating.
Stale bread was the only vegetable food allowed. The quantity of fluid permitted was 3J
pints per diem; but fermented liquors were strictly forbidden. Two full meals, with a light
supper, were usually taken. The quantity of exercise employed was very considerable, and
such as few men of ordinary strength could endure. This account corresponds very much
with that which Hunter gave of the North American Indians, when about to set out on a long
inarch.

DIGESTIVE APPARATUS.

493

portion of it which is fit to be assimilated or converted into organized texture,
from that which cannot serve this purpose, and which is at once rejected ; —
and the alteration (when required) of the chemical constitution of the former,

[Fig. 199.

A view of the Org*ns of Digestion, opened in nearly their whole length; a portion of the oesophagus
has been removed on account of want of space in the figure ; the arrows indicate the course of sub-
stances along the canal ; 1. the upper lip, turned off the mouth; 2, its frrenum ; 3, the lower lip, turned
down ; 4, its franum ; 5, 5. inside of the cheeks, covered by the lining membrane of the mouth ; 6, points
to the opening of the duct of Steno; 7, roof of the mouth; 8, lateral half arches ; 9, points to the tonsils;
10, velum pendulum palati ; 11. surface of the tongue ; 12, papillae near its point ; 13, a portion of the
irachea ; 14, the oesophagus ; 15, its internal surface ; 16, inside of the stomach ; 17, its greater extremity
or great cul-de-sac : 18, its lesser extremity or smaller cul-de-sac ; 19, its lesser curvature ; 20, its greater
curvature; 21, the cardiac orifice; 2-2, the pyloric orifice; 23, upper portion of duodenum; 24, 25, the
remainder of the duodenum ; 26, its valvulse conniventes ; 27, the gall bladder; 28, the cystic duct ; 29,
division of hepatic ducts in the liver; 30, hepatic duct; 31, ductus communis choledochus ; 32, its open-
ing into the duodenum ; 33, ductus Wirsungii, or pancreatic duct: 34, its opening into the duodenum ;
35, upper part of jejunum; 36, the ileum ; 37, some of the valvuloe conniventes; 38, lower extremity
of the ileum; 39, ileo-colic valve; 40,41, ccecum, or caput coli ; 42, appendicula vermiformis; 43.44,
ascending colon ; 45, transverse colon ; 46, 47, descending colon ; 43, sigmoid flexure of the colon ;
49. upper portion of the rectum ; 50, its lower extremity ; 51, portion of the levator-ani muscle ; 52
the anus.]

42

494 OF FOOD, AND THE DIGESTIVE PROCESS.

which prepares it for the important changes it is subsequently to undergo.
The simplest conditions requisite for the accomplishment of these purposes
are the following: — a fluid capable of performing the solution and of effecting
the required chemical changes ; — a fluid capable of separating the unorganiz-
able matter, by a process analogous to chemical precipitation ; — and a cavity
or sac, in which these operations may be performed. In the lowest Animals,
we find this cavity formed on a very simple plan ; being evidently nothing
else than an inversion of the external integument, communicating with the
exterior by one orifice only, through which the food is drawn in and the ex-
crementitious matter rejected. The fliiid necessary to dissolve the food, which
is known by the name of gastric fluid or juice, and that required to separate
the portion which is to be thrown off, which is known as the bile, are secreted
in the walls of the stomach. In the Sea-Anemone, which affords a very charac-
teristic example of this type of structure, it cannot be ascertained that the very
rapid solution of food, which takes place in the digestive cavity, is assisted
by any movement of its walls. In Polypes of a higher conformation, how-
ever, the digestive cavity is provided with a second orifice ; the stomach opens
into an intestinal tube, through which the excrement is rejected in little pellets ;
and the food, before entering the true digestive cavity, is submitted to a pow-
erful gizzard or triturating apparatus. Still, the bile, like the gastric juice, is
secreted in the walls of the stomach; as may be distinctly perceived in many
of these animals, on account of their transparency, and the bright yellow co-
lour of the fluid. As we ascend the animal series, we find no essential change
in the character of the digestive apparatus. The biliary follicles are gradu-
ally collected into a glandular mass, which is altogether removed from the
walls of the stomach, and which pours its secretion into the intestinal tube,
at a short distance from its commencement; the gastric juice, however, is still
secreted in minute sacs imbedded in the substance of the membrane. Several
accessory glands are added, the uses of which are not accurately known; and
particular modifications of the apparatus are adapted to peculiarities in the
nature of the food, or in the mode of its ingestion. As a general rule it may
be stated, that the digestive apparatus is most simple in Carnivorous animals,
in which it has to effect little change upon the aliment except solution, in or-
der to bring it to the state fit for absorption ; whilst it is most complex in those
that feed upon Vegetable matter, which needs to undergo a greater change,
both in its chemical composition and in the mechanical arrangement of its
components, before it can be rendered subservient to animal nutrition.

656. Mastication and Deglutition. — The first step in the process of reduc-
tion, is the Mastication of the food, and the impregnation of its comminuted
particles with the Salivary secretion. Mastication is evidently of great im-
portance, in preparing the substances to be afterwards operated on, for the
action of their solvent; and it exactly corresponds with tire trituration to
which the Chemist would submit any solid matter, that he might present it in
the most advantageous form to a digestive menstruum. The complete disin-
tegration of the alimentary matter, therefore, is of great consequence ; and, if
imperfectly effected, the subsequent processes are liable to derangement. This
derangement we continually meet with: for there is not, perhaps, a more fre-
quent source of Dyspepsia than imperfect mastication, whether resulting from
the haste with which the food is swallowed, or from the want of the proper
instruments. The disintegration of the food by mechanical reduction, is mani-
festly aided by Insalivation : and the admixture of Saliva appears further to
have the effect of commencing the transformation of the amylaceous or starchy
particles into sugar. From recent experiments it would seem that Saliva, if
acidulated, possesses the same power of acting on azotized compounds, as that
which characterizes the gastric juice; and consequently, when introduced into

MASTICATION AND DEGLUTITION.

495

the stomach, the Saliva may afford important aid in the digestive process.
(See §§ 668 and 863.) When the reduction of the food in the mouth has
been sufficiently accomplished, it is carried into the oesophagus by the action
of Deglutition. The share which the nervous system has in this action has
been already stated (§ 382) ; and it here only remains to define more pre
cisely the different movements which are concerned in it. These were lirst
described in detail by Magendie; but his account requires some modification,
through the more recent observations of DzondL* Theirs? stage in the pro-
cess is the carrying back of the food, until it has passed the anterior palatine
arch; this, which is effected by the approximation of the tongue and the

[Fig. 200.

.30

29

28

A view of the Muscles of the Tongue, Palate, Larynx and Pharynx— as well as the position of the
upper portion of the CEsophagus, as shown by a vertical section of the head; 1, 1. the vertical section of
the head; 2, points to the spinal canal; 3, section of the hard palate; 4. inferior spongy bone ; 5. middle
spongy bone ; 6, orifice of the right nostril ; 7, section of the inferior maxilla; 8, section of the oshyoides;
9, sectionofthe epiglottis: 10. section of the cricoid cartilage ; 11. the trachea, covered by its lining mem-
brane; 12. section of sternum; 13, inside of the upper portion of the thorax; 14, genio-hyo-glossus muscle;
15, its origin ; 10, 17, the fan-like expansion of the fibres of this muscle; 18, superficialis lingua; muscle;
19, verticales linguae muscle; 20, genio-hyoideus muscle: 21. mylo-hyoideus muscle; 22, anterior belly
ofdigastricus; 23, section of platysma myoides; 24, levator menii : 25. orbicularis oris; 26. orifice of Eus-
tachian tube ; 27, levator palati ; 28, internal pterygoid ; 29, section of velum pendulum palati, and azy-
gos uvulas muscle; 30, stylo-pharyngeus ; 31, constrictor pharyngis superior; 32. constrictor pharyngis
medius; 33, insertion stylo-pharyngeus; 34, constrictor pharyngis inferior ; 35, 36, 37, muscular coat of
esophagus; 38, thyreo-arytenoid muscle and ligaments, and above is the ventricle of Galen :jS9, section
of arytenoid cartilage ; 40, border of sterno-hyoideus.]

palate, is a purely voluntary movement. In the second stage, the tongue is
carried still further backwards, and the larynx is drawn forwards under its
root, so that the epiglottis is depressed down over the rima glottidis. The
muscles of the anterior palatine arch contract after the morsel has passed it,
and assist its passage backwards; these, with the tongue, cut off completely
the communication between the fauces and the mouth. At the same time, the
muscles of the posterior palatine arch contract in such a manner, as to cause

* Miiller's Physiology, p. 501.

496 OF FOOD, AND THE DIGESTIVE PROCESS.

v

the sides of the arch to approach each other like a pair of curtains ; so that
the passage from the fauces into the posterior nares is nearly closed by them ;
and to the cleft between the approximated sides, the uvula is applied like a
valve. A sort of inclined plane, directed obliquely downwards and backwards,
is thus formed ; and the morsel slides along it into the pharynx, which is
brought up to receive it. Some of these acts may be performed voluntarily ;
but the combination of the whole is automatic. The third stage of the pro-
cess, — the propulsion of the food down the oesophagus, — then commences.
This is accomplished in the upper part by means of the constrictors of the
pharynx; and in the lower by the muscular coat of the oesophagus itself.
When the morsels are small, and are mixed with much fluid, the undulating
movements from above downwards succeed each other very rapidly ; this
may be well observed in Horses whilst drinking; large morsels, however, are
frequently some time in making their way down. Each portion of food and
drink is included in the contractile walls, which are closely applied to it during
the whole of its transit. The gurgling sound, which is observed when drink
is poured down the throat of a person in articulo mortis, is due to the want
of this contraction. The whole of the third stage is completely involuntary.
At the point where the oesophagus enters the stomach, — the cardiac orifice of
the latter, — there is a sort of sphincter, which is usually closed. This opens
when there is a sufficient pressure on it, made by accumulated food ; and after-
wards closes, so as to retain the food in the stomach. The opening of the
cardiac is one of the first acts which takes place in vomiting. When the
sphincter is paralyzed by division of the pneumogastric nerve, the food regur-
gitates into the oesophagus.

657. Action of the. Stomach. — A remarkable opportunity of ascertaining the
condition of the Stomach during Digestion, presented itself, some lime since,
in a case in which a large fistulous aperture remained after a wound that laid
open the cavity, but in which the general health was completely recovered ;
so that the process may be considered as having been normally performed.*
"The inner coat of the stomach, in its natural and healthy st.ate, is of a light
or pale pink colour, varying in its hues, according to its full or empty state.
It is of a soft or velvet-like appearance, and is constantly covered with a very
thin, transparent, viscid mucus, lining the whole interior of the organ. By
applying aliment or other irritants, to the internal coat of the stomach, and
observing the effect through a magnifying glass, innumerable lucid points, and
very fine nervous or vascular papilla?, can be seen arising from the villous
membrane, and protruding through the mucous coat, from which distils a pure,
limpid, colourless, slightly viscid fluid. The fluid thus excited is invariably
distinctly acid. The mucus of the stomach is less fluid, more viscid or albu-
minous, semi-opaque, sometimes a little saltish, and does not possess the slight-
est character of acidity. The gastric fluid never appears to be accumulated in
the cavity of the stomach while fasting; and is seldom, if ever, discharged
from its proper secerning vessels, except when excited by the natural stimulus
of aliment, mechanical irritation of tubes, or other excitants. When aliment
is received, the juice is given out in exact proportion to its requirements for
solution, except when more food has been taken than is necessary for the
wants of the system." That the quantity of the Gastric Juice secreted from

* Sec I!M' case of Alexis St. Martin, \vith tlic observations and experiments of Dr. Ben.il-
jnont, repuMi^lied in this country by Dr. A. Combe. [A \er\ extended examination of the

phenomena of ^a>iiic di^eMioti has been made by Al. Blondloi. The chief subject of ex-
periment \va.-a dot:, in v." I lie 1 1 lie maintained, \viihoMi a I led mi: the health, a li Minions opening
into the stomach Jin- more than two years. His examinations have furnished many new
and important facts, and have continued those of Dr. Beaumont made on Alexis St. Martin
in nearly every point. — Traite dnalytique dc la Digestion, Paris, 1844. — M. C.]

ACTION OF THE STOMACH. 497

the walls of the stomach depends rather upon the general requirements of the
system, than upon the quantity of food introduced into the digestive cavity, is
a principle of the highest practical importance, and cannot be too steadily kept
in view in Dietetics. A definite proportion only of aliment can be perfectly
digested in a given quantity of the fluid; the action of which, like that of
other chemical operations, ceases after having been exercised on a fixed and
definite amount of matter. "When the juice has become saturated, it refuses
to dissolve more ; and, if an excess of food has been taken, the residue remains
in the stomach, or passes into the bowels in a crude state, and becomes a
source of nervous irritation, pain, and disease, for a long time." The unfa-
vourable effect of an undue burthen of food upon the stomach itself, interferes
with its healthy action ; and thus the quantity really appropriate is not dis-
solved. The febrile disturbance is thus increased; and the mucous membrane
of the stomach exhibits evident indications of its morbid condition. The de-
scription of these indications, given by Dr. Beaumont, is peculiarly graphic,
as well as Hygienically important.

658. "In disease, or partial derangement of the healthy function, the mu-
cous membrane presents various and essentially-different appearances. In
febrile conditions of the system, occasioned by whatever cause, — obstructed
perspiration, undue excitement by stimulating liquors, overloading the sto-
mach with food; fear, anger, or whatever depresses or disturbs the nervous
system, — the villous coat becomes sometimes red and dry, at other times pale
and moist, and loses its smooth and healthy appearance ; the secretions be-
come vitiated, greatly diminished, or even suppressed ; the coat of mucus
scarcely perceptible, the follicles flat and flaccid, with secretions insufficient
to prevent the papillae from irritation. There are sometimes found, on the
internal coat of the stomach, eruptions of deep-red pimples, not numerous,
but distributed here and there upon the villous membrane, rising above the
surface of the mucous coat. These are at first sharp-pointed, and red, but
frequently become filled with white purulent matter. At other times, irre-
gular, circumscribed red patches, varying in size and extent from half an inch
to an inch and a half in circumference, are found on the internal coat.
These appear to be the effects of congestion in the minute blood-vessels of the
stomach. There are also seen at times small aphthous crusts, in connection
with these red patches. Abrasion of the lining membrane, like the rolling up
of the mucous coat into small shreds or strings, leaving the papillae bare for
an indefinite space, is not an uncommon appearance. These diseased appear-
ances, when very slight, do not always affect essentially the gastric apparatus.
When considerable, and particularly when there are corresponding symptoms
of disease, — as dryness of the mouth, thirst, accelerated pulse, &c. — no gas-
tric juice can be extracted by the alimentary stimulus. Drinks are imme-
diately absorbed or otherwise disposed of; but food taken in this condition of
the stomach remains undigested for twenty-four or forty-eight hours, or more,
increasing the derangement of the alimentary canal, and aggravating the gene-
ral symptoms of disease. After excessive eating or drinking, chymification is
retarded; and, though the appetite be not always impaired at first, the fluids
become acrid and sharp, excoriating the edges of the aperture, and almost
invariably producing aphthous patches and the other indications of a diseased
state of the internal membrane. Vitiated bile is also found in the stomach
under these circumstances, and flocculi of mucus are more abundant than in
health. Whenever this morbid condition of the stomach occurs, with the
usual accompanying symptoms of disease, there is generally a corresponding
appearance of the tongue. When a healthy state of the stomach is restored,
the tongue invariably becomes clean."

42*

498 OF FOOD, AND THE DIGESTIVE PROCESS.

a. Dr. A. Combe's commentary on the above passage is too apposite to be omitted.
" Many persons who obviously live too freely, protest against the fact, because they feel no
immediate inconvenience, either from the quantity of food, or the stimulants in which they
habitually indulge; or, in other words, because they experience no pain, sickness, or head-
ache,— nothing, perhaps, except slight fulness and oppression, which soon go off. Observa-
tion extended over a Mifh'cient length of time, however, shows that the conclusion drawn is
entirely fallacious, and that the real amount of injury is not felt at the moment, merely be-
cause, for a wise purpose, nature has deprived us of any consciousness of either the exist-
ence or the state of tile stomach during health. In accordance with this, Dr. Beaumont's
experiments prove, that extensive erythematic inflammation of the mucous coat of the sto-
mach was of frequent occurrence in St. Martin after excesses in eating, and especially in
drinking, even when no marked general symptom was present to indicate its existence.
Occasionally, febrile heat, nausea, headache, and thirst were complained of, but not always.
Had St. Martin's stomach, and its inflamed patches, not been visible to the eye, he too might
have been pleased that his temporary excesses did him no harm; but, when they presented
themselves in such legible characters, that Dr. Beaumont could not miss seeing them, argu-
ment and supposition were at an end, and the broad fact could not be denied."

b. The observations of Dr. Beaumont have been confirmed by those of M. Blondlot (Traite
Analytique de la Digestion), and of M. Ch. Bernard (Archiv. d'Anat. Gen. et de Physiol.,
Jan. 1S4G); which were made upon Dogs, in whose stomachs fistulous openings were main-
tained for a length of time. — They found that, although a slightmechanical irritation, applied
directly to the mucous surface of the stomach, excites at once an abundant flow of gastric
fluid, yet if this irritation be carried beyond certain limits, so as to produce pain, the secre-
tion, instead of being more abundant, diminishes or ceases entirely; whilst a ropy mucus is
poured out instead, and the movements of the stomach are considerably increased. The
animal at the same time appears ill at ease, is agitated, has nausea, and, if the irritation be
continued, actual vomiting; and bile has been observed to flow into the stomach, and es-
cape by the fistulous opening. Similar disorders of the functions of the stomach result from
violent pain in other parts of the body; the process of digestion in such cases being sus-
pended, and sometimes vomiting excited. When accidulated substances, as food rendered
acid by the addition of a little vinegar, were introduced into the stomach, the quantity of
gastric fluid poured out was much smaller, and the digestive process consequently slower,
than when similar food, rendered alkaline by a •weak solution of carbonate of soda, was in-
troduced. If, however, instead of a weak solution, carbonate of soda, in crystal or in pow-
der, was introduced into the stomach, a large quantity of mucus and bile, instead of gastric
fluid, flowed into the stomach ; and vomiting and purging very often followed. When very
cold water, or small pieces of ice, were introduced into the stomach, the mucous membrane
was at first rendered very pallid ; but soon a kind of reaction followed, the membrane be-
came turgid with blood, and a large quantity of gastric fluid was secreted. If, however, too
much ice was employed, the animal appeared ill, and shivered; and digestion, instead of
being rendered more active, was retarded. Moderate heat, applied to the mucous surface of
the stomach, appeared to have no particular action on digestion; but a high degree of heat
produced most serious consequences. Thus, the introduction of a little boiling water threw
the animal at once into a kind of adynamic state, which was followed by death in three or
four hours; the* mucous membrane of the stomach was found red and swollen, whilst an
abundant exudation of blackish blood had taken place into the cavity of the organ. Similar
injurious cHivis resulted in a greater or less degree, from the introduction of other irritants,
Mich ;is niinitc of silver or ammonia; the digestive functions being at once abolished, and
the mucous surface of the organ rendered highly sensitive.

659. The food which is propelled along the oesophagus, enters the Stomach
through its cardiac orifice, in successive waves: and it is immediately sub-
jected to a peculiar peristaltic movement, which has for its object to produce
the thorough intermixture of the gastric fluid with the alimentary mass, and
also to aid the solution of the latter by the gentle trituration to which it is thus
subjected. The fasciculi composing the muscular wall of the human stomach,
are so disposed as to shorten its diameter in every direction ; and by the al-
ternate contraction and relaxation of these bands, a great variety of motion is
induced in this organ, sometimes transversely, and at other times longitudi-
nally. "These motions," Dr. Beaumont remarks, "not only produce a con-
stant disturbance or churning of the contents of the stomach, but they compel
them, at the same time, to revolve about the interior from point to point, and
from one extremity to the other." In addition to these movements, there is

ACTION OF THE STOMACH.
[Fig. 201.

499

A front view of the Stomach, distended by flatus, with the Peritoneal Coat turned off; 1, anterior face
of the (Esophagus ; 2, the cul-de-sac, or greater extremity ; 3, the lesser or pylorie extremity ; 4, the duo-
denum ; 5, 5, a portion of the peritoneal coat turned back ; 6, a portion of the longitudinal fibres of the
muscular coat ; 7. the circular fibres of the muscular coat; 8, the oblique muscular fibres, or muscle of
Uavard ; 9. a portion of the muscular coat of the duodenum, where its peritoneal coat has been removed.]

[Fig. 202.

A view of the interior of the Stomach, as given by the removal of its anterior parietes ; I, oesophagus j
2, cardiac orifice of the stomach ; 3. its greater extremity, or cul-de-sac ; 4, the greater curvature , 5, line
of the attachment of the omentum majus; 6, the muscular coat ; 7, the anterior cut edge of the mucous
coat ; 8, the ruga; of the mucous coat ; 9, the lesser curvature ; 1 0. the beginning of the duodenum ; 11,
pylorie orifice, or valve ; 12. the first turn of the duodenum downwards.]

a constant agitation of the stomach, produced by the respiratory muscles.
The motions of the stomach itself are not performed on any very exact plan,
and are much influenced by the character of the ingesta, the state of the
general system, and by other circumstances. The following is the ordinary
course, however, of the revolutions of the food. " After passing the cesopha-
geal ring, it moves from right to left, along the small arch ; thence, through the
large curvature, from left to right. The bolus, as it enters the cardia, turns to
the left, passes the aperture,* descends into the splenic extremity, and follows
the great curvature towards the pylorie end. it then returns, in the course of
the smaller curvature, makes its appearance again at the aperture in its descent

The fistulous orifice in St. Martin's stomach, through which these observations were
made.

500 OF FOOD, AND THE DIGESTIVE PROCESS.

[Fig. 203.

A view of the interior of the Stomach and Duodenum in situ, the inferior portion of each having been
removed; 1, 1, the under side of the liver; 2, the gall bladder; 3. 3, the lesser curvature and anterior
faces, as seen from below ; 4, the rugte, about the cardiac orifice; 5, the pyloric orifice ; 6, the ruga;, and
thickness of this orifice ; 7, 7, the duodenum; S, lower end of the right kidney.]

into the great curvature, to perform similar revolutions. These revolutions
are completed in from one to three minutes. They are probably induced in
a great measure, by the circular or transverse muscles of the stomach. They
are slower at first, than after chymification has considerably advanced ;" at
which time also there is an increased impulse towards the pylorus. It is
probable that, from the very commencement of chymification, until the organ
becomes empty, portions of chyme are continually passing into the duode-
num ; for the bulk of the alimentary mass progressively diminishes, and this
the more rapidly as the process is nearer its completion. The accelerated
expulsion appears to be effected by a peculiar action of the transverse mus-
cles ; and especially of that portion of them which surrounds the stomach at
about four inches from its pyloric extremity. This band is so forcibly con-
tracted in the latter part of the digestive process, that it almost separates the
two portions of the stomach, into a sort of hour-glass form ; and Dr. B. states
that, when he attempted to introduce a long thermometer tube into the pyloric
portion of the stomach, the bulb was at first gently resisted, then allowed to
pass, and then grasped by the muscular parietes beyond, so as to be drawn
in: whence it is evident that the contraction has for its object, to resist the
passage of solid bodies into the pyloric extremity of the stomach, at this stage
of digestion ; whilst the matter which has been reduced to the fluid form is
pumped away (as it were) by the action of that portion of the viscus. These
peculiar motions continue, until the stomach is perfectly empty, and not a par-
ticle of food or chyme remains. Of the degree in which they are dependent
upon the influence of the Nervous System, some idea has been already given
(§ 387) ; there is yet much to be learned, however, especially in regard to the
degree in which the movements may be checked or altered, by impressions
transmitted through the nervous system. It is stated by Brachetthat, in some
of his experiments upon the Par Vagum some hours after section of the nerve
on both sides, the surface only of the alimentary mass was found to have un-
dergone solution, the remainder of the mass remaining in the condition in
which it was at first ingested ; and if this statement can be relied on, it would
appear that the movements of the stomach, like those of the heart, can be
readily affected by a strong nervous impression. It may be partly in this
manner, therefore, and not by acting upon the secretions alone, that strong
Emotions influence the digestive process, as they are well known to do. On
the other hand, the moderate excitement of pleasurable emotions may be fa-

ACTION OF THE INTESTINAL TUBE. 501

vourable to the operation ; not only by giving firmness and regularity to the
action of the heart, and thence promoting the circulation of the blood, and the
increase of the gastric secretion ; but also in imparting firmness and regularity
to the muscular contractions of the stomach.

660. Action of the Intestinal Tube. — The pulpy substance to which the
aliment is reduced, by the mechanical reduction and chemical solution it has
undergone in the mouth and stomach, is termed chyme. The consistence of
this will of course vary in some degree with the quantity of fluid ingested ;
in general it is greyish, semifluid, and homogeneous ; and possesses a slightly
acid taste, but is otherwise insipid. Dr. Beaumont describes it as varying in
its aspect, — from that of cream, which it presents when the food has been of
a rich character, — to that of gruel, which it possesses when the diet has been
farinaceous. The passage of the chyme through the pyloric orifice is at first
slow ; but when the digestive process is nearly completed, it is transmitted in
much larger quantities. From the time that the ingested matter enters the
intestinal canal, it is propelled by the simple peristaltic action of its muscular
coat, which is directly excited by the contact either of this matter, or of the
secretions which are mingled with it;* and all that is not absorbed is thus
conducted to the rectum, its expulsion from which is due to an action of a
distinctly reflex kind, excited through the nervous centres (§ 391). During
its progress through the intestinal tube, the product of the gastric operation
undergoes very important changes. The chyme is mingled in the duodenum
with the biliary and pancreatic secretions, which eft'ec't an immediate altera-
tion both in its sensible and chemical properties. The nature of this altera-
tion can be best estimated, by mingling bile with chyme removed from the
body. This has been done by several experimenters on the lower animals ;
and by Dr. Beaumont in the case already referred to, which afforded him the
means of obtaining not only chyme, but bile and pancreatic fluid. The effect
of this admixture was to separate the chyme into three distinct parts, — a red-
dish brown sediment at the bottom, — a whey-coloured fluid in the centre, —
and a creamy pellicle at the top. The central portion, with the creamy pelli-
cle, seems to constitute the chyle absorbed by the lacteals ; the creamy matter
being chiefly composed of oily particles; and the wheyey fluid having pro-
teine-compounds, saccharine and saline matters, in solution : the sediment,
partly consisting of the insoluble portion of the food, and partly of the biliary
matter itself, is evidently excrementitious. It is not until the food has passed
the orifice of the Ductus Choledochus, that the absorption of chyle begins, —
the lacteals not being distributed upon the Stomach, or the higher part of the
Duodenum.

661. By the gradual withdrawal of their fluid portion, the contents of the
alimentary canal are converted into a mass of greater consistence ; and this,
as it advances through the small intestines, assumes more and more of a faecal
character. A part of the faeces, however, may be derived from the secretions
of the enteritic mucous membrane, and of its glandules ; the surface of the for-
mer, with its simple follicles, probably secretes nothing else than mucus ; but
the glandidx, with which it is so thickly studded, appear to serve as the
channel for the elimination of putrescent matter from the blood. There can
be no doubt, that a large quantity of fluid is poured out by these glandulae,
when they are in a state of irritation from disease, or from the stimulus of a
purgative medicine ; since the amount of water discharged from the bowels is

' The bile seems to have an important share in producing this effect; since, when the
(1 net us choledochus is tied, constipation always occurs. The action of mercury as a purgative
appears to take place through the increase of the hepatic and other secretions which it in-
duces.

502

OF FOOD, AND THE DIGESTIVE PROCESS.

often much greater than that which has been ingested, and must be derived
from the blood. — The secretion of the ccecum has been ascertained to be, in
herbivorous animals, distinctly acid during digestion ; and there is reason to
believe, that the food there undergoes a second process, analogous to that to
which it has been submitted in the stomach, and fitted to extract from it what-
ever undissolved alimentary matter it may still contain. There is no evi-
dence, however, that this is the case in Man, whose ccecum (commonly termed
the appendix coeci vermiformis) is very small, compared to that of most her-
bivorous animals.

662. The act of Defecation having been already sufficiently considered
(§ 391), it only remains to notice the composition of the Faeces. These are
made up of certain parts of the food, which have not been reduced and ab-
sorbed ; together with that portion of the secretions poured into the aliment-
ary canal between the mouth and the anus, which has not been taken back
again into the system. Of the former portion, the constituents may be in
great part determined by the Microscope. Thus the cell-walls of the Vegeta-
ble tissues whose contents have been extracted, the entire woody fibres (on
which the digestive process has no influence), the granules of starch, when
they have undergone no preparation before being swallowed, — portions of
tendon, ligament, adipose tissue, and even of muscular fibre, — with other
substances constituting the undigested residue of the food, may be readily
detected. Besides these, the microscope enables us to recognize the brown
colouring-matter of the bile, epithelium-cells and mucus-corpuscles, and various
saline particles, especially those of the ammoniaco-magnesian phosphate, whose
crystals are well-defined ; most of which are derived from the secretions. —
The following is the result of the proximate analysis of the faeces of an in-
dividual in good health, who had taken the ordinary diet of this country, as
given by Dr. Percy : —

Substances soluble in ether (brownish yellow fat)

alcohol of -830

water (brown resinoid matter)
Organic matter insoluble in the above menstrua .
Salts soluble in water ....
Salts insoluble in water . . .

11-05
10-74
11-01'
49-33
4-70
11-61

Ultimate analysis of the same faeces gave the following as the proportion of
the components of the Organic constituents ; Carbon 46'20, Hydrogen 6'72,
Nitrogen and Oxygen 30'71. — The mineral ash of faecal matter has been ex-
amined by Enderlin ; who has given the following as the proportion of its
ingredients : —

Chloride of sodium and alkaline sulphates

Bibasic phosphate of soda

Phosphates of lime and magnesia

Phosphate of iron .

Sulphate of lime .

Silica

Soluble in water.

1-367?

2-033 5
80-372 ~\

~ ' > Insoluble in water.

4'OoU I

7-940 J

It further appears from the inquiries of Enderlin, that a portion of the or-
ganic matter taken up by alcohol, sometimes (but not constantly) consists of
Choleate of soda, the characteristic ingredient of bile ; and he thinks that this
is more likely to be present, when the faeces have remained for only a short
period in the large intestine, and when ihere has been less time for its re-
absorption. — In the faecal discharges which result from the action of mercu-
rials, large quantities of biliary matter may be detected, very little changed.

NATURE OF CHYMIFICATION. 503

4. Nature of Chymification and Chylification.

663. The causes of the reduction of the food in the Stomach, have long
been a fruitful source of discussion amongst physiologists ; and various hy-
potheses have heen devised to account for it. Some have compared the Sto-
mach of Man to the Gizzard of a fowl, and have supposed that the trituration
of the food between its walls was the essential element in the process ; but
this doctrine is completely incompatible with the fact, that digestible substances,
inclosed in metallic balls with perforations in their sides, are still dissolved by
the power of the gastric fluid, though the walls of the stomach do not come
in contact with them. Others, again, have imagined that the process of di-
gestion is one of putrefaction ; but this idea, putting aside its inherent ab-
surdity, is proved to be incorrect by the fact that the gastric juice has a de-
cidedly antiseptic quality. Others, in despair of obtaining any other solution,
have attributed the operation to the direct agency of the vital principle ; for-
getting that, as long as the aliment remains within the stomach and intestinal
canal, it can no more be the subject of any peculiarly vital process, than if it
were in contact with the skin, of which the mucous membrane is but an inter-
nal reflexion. The theory of chemical solution, which was at first regarded
by many as quite untenable, has been of late years so much strengthened by
new facts and arguments, that there now appears no valid reason for with-
holding our assent from it; even though it cannot yet give a complete expla-
nation of the complex phenomena in question. The chief opposition to this
theory has arisen from the difficulty of imagining, that any simply-chemical
solvent should have the power of acting on so great a variety of substances,
and of reducing them to a state so homogeneous. This difficulty, however,
seems now in a great degree removed, by the discovery of the close Chemical
relation that subsists, between the various substances of each of the groups
already enumerated (§ 639) ; which renders it easy to conceive, that the
changes involved in their reduction may be of a very simple character.

664. The first series of facts which will be here adduced, as throwing light
on the process of Chymification, is that which has been obtained by the ex-
periments of Dr. Beaumont upon the individual already alluded to (§ 658.)
By introducing a tube of India-rubber into the empty stomach, he was able
to obtain a supply of Gastric Juice whenever he desired it ; for the tube
served the purpose of stimulating the. follicles to pour forth their secretion,
and at the same time conveyed it away. This fluid, of which the existence
has been denied by some physiologists, is not very unlike saliva in its appear-
ance ; it is, however, distinctly acid to the taste ; and chemical analysis shows
that it contains a considerable proportion of free muriatic acid, and also some
acetic acid. The former must evidently be derived from the decomposition
of the muriate of soda contained in the blood, the remote source of which is
the salt ingested with the food. The latter is an organic compound, probably
formed at the expense of some of the saccharine matter of the previous ali-
ment. Of equal importance with the free acids, is an animal matter, soluble
in cold water, but insoluble in hot, bearing considerable resemblance to albu-
men. Of this more will be said hereafter. Besides these principal ingre-
dients, the gastric fluid contains muriates and phosphates of potass, soda,
magnesia, and lime. It possesses the power of coagulating albumen in an
eminent degree ; it is powerfully antiseptic, checking the putrefaction of meat ;
and it is effectually restorative of healthy action, when applied to old fetid
sores and foul ulcerating surfaces. It may be kept for many months, if ex-
cluded from the air without becoming fetid.

a. The Chemistry of the Gastric Juice has been greatly unsettled by the results of recent

504 OF FOOD, AND THE DIGESTIVE PROCESS.

inquiries ; which seem inconsistent Math the statement just given, especially in regard to the
presence of free muriatic acid. It may be well, in the first instance, to quote Professor
Dunglison's account of the analysis of the gastric fluid drawn from the stomach of Alexis
St. Martin, and supplied to him by Dr. Beaumont. " The quantity of free hydrochloric acid
was surprising ; on distilling the gastric fluid, the acids passed over, the salts and animal mat-
ter remaining in the retort ; the amount of chloride of silver thrown down, on the addition
of nitrate of silver to the distilled fluid, was astonishing. The author had many opportu-
nities of examining the gastric secretion obtained from the case in question. At all times,
when pure or unmixed, except with a portion of the mucus of the lining membrane of the
digestive tube, it was a transparent fluid, having a marked smell of hydrochloric acid ; and of
a slightly salt, and very perceptibly acid, taste." (Human Physiology, Sixth Edition, Vol. I.,
p. 54G.)

b. From the experiments of MM. Blondlot, Bernard, and Barreswill, and Dr. R. D. Thom-
son, on the other hand, it would seem that no free hydrochloric acid is present in the gastric
fluid; since the fluid which comes over, on distillation at a low temperature, contains none;
whilst the matter remaining in the retort becomes more and more acid with the progress of
the distillation, and may be subjected to a high temperature (300°) without giving off acid
fumes. It is difficult to account for the discrepancy between these carefully conducted ex-
periments, and the positive statement of Professor Dunglison. otherwise than by supposing
that the Human gastric fluid differs from that of the Dog and the Pig, which were employed
in the analyses last quoted. — The acid reaction was referred by Blondlot to the presence of
super-phosphate of lime; but this seems incorrect. Professor Thomson agrees with MM.
Bernard and Barreswill in attributing it chiefly to Lactic acid ; which, contrary to previous
opinions, they regard as generally if not universally present in the stomach during healthy
digestion, and it would seem that this acid may partially decompose the phosphates and
muriates, which are contained in the secretion : and may thus occasion the phosphoric and
muriatic acids to be set free. The presence of a small quantity of free Acetic acid, also,
seems to have been recognized by them.

665. The Gastric Juice obtained from the stomach, was found by Dr.
Beaumont to possess the power of dissolving various kinds of alimentary sub-
stances, when these were submitted to its action at a constant temperature of
100°, (which is about that of the stomach,) and were frequently agitated.
The solution appeared to be in all respects as perfect as that which naturally
takes place in the stomach ; but required a longer time. This is readily ac-
counted for when we remember, that no ordinary agitation can produce the
same effect with the curious movements of the stomach ; and that the conti-
nual removal from its cavity, of the matter which has been already dissolved,
must aid the operation of the solvent on the remainder. The following is
one out of many experiments detailed by Dr. Beaumont. "At 111 o'clock,
A.M., after having kept the lad fasting for 17 hours, I introduced a gum-elastic
tube, and drew off one ounce of pure gastric liquor, unmixed with any other
matter, except a small proportion of mucus, into a three-ounce vial. I then
took a solid piece of boiled recently-salted beef, weighing three drachms, and
put it into the liquor in the vial ; corked the vial tight, and placed it in a
saucepan filled with water, raised to the temperature of 100°, and kept at that
point on a nicely-regulated sand-bath. In forty minutes, digestion had dis-
tinctly commenced over the surface of the meat. In fifty minutes, the fluid
had become quite opaque and cloudy ; the external texture began to separate
and become loose. In sixty minutes, chyme began to form. At 1 o'clock,
P.M., (digestion having progressed with the same regularity as in the last half-
hour), the cellular texture seemed to be entirely destroyed, leaving the mus-
cular fibres loose and unconnected, floating about in fine small shreds, very
tender and soft. At 3 o'clock, the muscular fibres had diminished one-half,
since the last examination. At 5 o'clock, they were nearly all digested ; a
few fibres only remaining. At 7 o'clock, the muscular texture was completely
broken down, and only a few of the small fibres could be seen floating in the
fluid. At 9 o'clock, every part of the meat was completely digested. The
gastric juice, when taken from the stomach, was as clear and transparent as
water. The mixture in the vial was now about the colour of whey. After

NATURE OF CHYMIFICATION. 505

standing at rest a few minutes, a fine sediment, of the colour of the meat, sub-
sided to the bottom of the vial. — A piece of beef, exactly similar to that placed
in the vial, was introduced into the stomach, through the aperture, at the same
time. At 12 o'clock it was withdrawn, and found to be as little atFected by
digestion as that in the vial ; there was little or no difference in their appear-
ance. It was returned to the stomach; and, on the string being drawn out at
1 o'clock P.M., the meat was found to be all completely digested and gone.
The effect of the gastric juiee on the piece of meat suspended in the stomach,
was exactly similar to that in the vial, only more rapid after the first half
hour, and sooner completed. Digestion commenced on, and was confined to,
the surface entirely in both situations. Agitation accelerated the solution in the
vial, by removing the coat that was digested on the surface, enveloping the
remainder of the meat in the gastric fluid, and giving this fluid access to the
undigested portions."* Many variations were made in other experiments ;
some of which strikingly displayed the effects of thorough mastication, in
aiding both natural and artificial digestion.

666. The attempt was made by Dr. Beaumont, to determine the relative
digestibility of different articles of diet, by observing the length of time re-
quisite for their solution. But, as he himself points out, the rapidity of diges-
tion varies so greatly, according to the quantity eaten, the nature 'and amount
of the previous exercise, the interval since the preceding meal, the state of
health, the condition of the mind, and the nature of the weather, that a much
more extended inquiry would be necessary to arrive at results to be depended
on. Some important inferences of a general character, however, may be
drawn from his inquiries. — It seems to be a general rule, that the flesh of
wild animals is more easy of digestion than that of the domesticated races
which approach them most nearly. This may, perhaps, be partly attributed
to the small quantity of fatty matter that is mixed up with the flesh of the
former, whilst that of the latter is largely pervaded by it. For it appears from
Dr. B.'s experiments, that the presence in the stomach of any substance which
is difficult of digestion, interferes with the solution of food that would other-
wise be soon reduced. It seems that, on the whole, Beef is more speedily
reduced than Mutton, and Mutton sooner than either Veal or Pork. Fowls
are far from possessing the digestibility that is ordinarily imputed to them ;
but Turkey is, of all kinds of flesh except Venison, the most soluble. Dr.
B.'s experiments further show, that bulk is as necessary for healthy digestion,
as the presence of the nutrient principle itself. This fact has been long known
by experience to uncivilized nations. The Kamschatdales, for example, are
in the habit of mixing earth or saw-dust with the train-oil, on which alone
they are frequently reduced to live. The Veddahs or wild hunters of Ceylon,
on the same principle, mingled the pounded fibres of soft and decayed wood
with the honey, on which they feed when meat is not to be had ; and on one
of them being asked the reason of the practice, he replied, " I cannot tell you,
but I know that the belly must be filled." It is further shown by Dr. B.,
that soups and fluid diet are not more readily chymified than solid aliment,
and are not alone fit for the support of the system ; and this, also, is conform-
able to the well-known results of experience ; for a dyspeptic patient will
frequently reject chicken-broth, when he can retain solid food or a richer
soup. Perhaps, as Dr. A. Combe remarks, the little support gained from
fluid diet, is due to the rapid absorption of the watery part of it ; so that the
really nutritious portion is left in too soft and concentrated a state, to excite
the healthy action of the stomach. — Dr. Beaumont also ascertained that
moderate exercise facilitates digestion, though severe and fatiguing exercise

* Experiments 2 and 3 of First Series.
43

506 OF FOOD, AND THE DIGESTIVE PROCESS.

retards it. If even moderate exercise be taken immediately after a full meal,
however, it is probably rather injurious than beneficial ; but if an hour be per-
mitted to elapse, or if the quantity of food taken have been small, it is of de-
cided benefit. The influence of temperature on the process of solution, is
remarkably shown in some of Dr. B.'s experiments. He found that the gas-
tric juice had scarcely any influence on the food submitted to it, when the
bottle was exposed to the cold air, instead of being kept at a temperature of
100°. He observed on one occasion, that the injection of a single gill of
water at 50° into the stomach, sufficed to lower its temperature upwards of
30° ; and that its natural heat was not restored for more than half an hour.
Hence the practice of eating 'ice after dinner, or even of drinking largely of
cold fluids, is very prejudicial to digestion.

667. From the foregoing statements we may conclude, that the process by
which the food is dissolved in the Gastric fluid is of a purely Chemical na-
ture, since it takes place out of the living body as well as in it, — allowance
being made for the difference in its physical condition. That the natural pro-
cess of digestion is imitated, when the food is submitted to the action of the
gastric juice in a vial, not only in regard to the disintegration of its particles,
but as to the change of character which they are made to undergo, is proved
by the fact, that the artificial chyme thus formed exhibits the same changes as
the real chyme, when submitted to the action of the bile (§ 658). The pro-
cess of digestion, however, may be freely conceded to be vital, in so far as it
is dependent upon the agency of a secreted product, which vitality alone (so
far at least as we at present know) can elaborate ; and all for which it is here
contended is, that, when this product is once formed, it has an agency upon
the alimentary matter, which, though not yet fully understood, is conformable,
. in all that is known of its operation, to the ordinary laws of chemistry. Thus,
Digestion is conformable to Chemical solution, — -Jirst, in the assistance which
both derive from the minute division of the solids submitted to it; — secondly,
in the assistance which both derive from the successive addition of small por-
tions of the comminuted solid to the solvent fluid, and from the thorough in-
termixture of the two by continual agitation ; — thirdly, in the limitation of the
quantity of food on which a given amount of gastric juice can operate, which
is precisely the case with chemical solvents ; — -fourthly, in the assistance which
both derive from an elevation of temperature, — the beneficial influence of heat
being only limited, in the case of digestion, by its tendency to produce decom-
position of the gastric fluid ; — -fifthly, in the different action of the same solvent
upon the various solids submitted to it.

668. It may be considered a well-established fact, that diluted acids alone
have no power of chymifying alimentary substances, although capable of
•partially dissolving some of them ; but that their presence in the gastric fluid
is essential to its effectual action. The active agent in the process appears to
be an Organic compound, to which the name of pepsin has been given. The
properties of this have been investigated by Wasmann, who first succeeded in
obtaining it in an isolated state ; his observations were made upon the mucous
membrane of the stomach of the Pig, which greatly resembles that of Man.

a. When this membrane is digested in a large quantity of water at from 85° to 05°, many
other matters are removed from it besides pepsin; but if this water l>e removed, and the
digestion be continued with fresli water in the eold, very little but pepsin is then taken up.
Pepsin appears in be but sparingly soluble in water; when its Dilution is evaporated to dry-
tit-ss, there remains a brown, grayish, -\iscid mass, with the odour of glue, and having the
appearanee of an extract. The solution of this in water is turbid, and still possesses a por-
tion of the characteristic power of pep>in, but greatly reduced. When strong alcohol is added
to a fresh solution of pepsin, the latter is precipitated in white flocks, which maybe collected
on'a filter, and produce a grey compact mass when dried. Pepsin enters into chemical com-

NATURE OF CHYMIFICATION PEPSIN. 507

bination with many acids, forming compounds which still redden litmus paper ; and it is
when thus united with acetic and muriatic acids, that its solvent powers are the greatest.

6. "In regard to the solvent power of pepsin for coagulated albumen, it was observed by
M. Wasmaim that a liquid which contains 17-lO,OOOths of acetate of pepsia, and 6 drops
of hydrochloric acid per ounce, possesses a very sensible solvent power, so that it will dis-
solve a thin slice of coagulated albumen in the course of 6 or 8 hours' digestion. Witli 12
drops of hydrochloric acid per ounce, the white of egg is dissolved in 2 hours. A liquid
which contains ^ gr. of acetate of pepsin, and to which hydrochloric acid and white of egg
are alternately added, so long as the latter dissolves, is capable of faking up 210 grains of
cumulated white of egg at a temper^ure between 95° and 104°. It would appear, from
such experiments, that the hydrochloric acid is the true solvent, and that the action of the
pepsin is limited to that of disposing the white of egg to dissolve in hydrochloric acid. The
acid when alone dissolves white of egg by ebullition, just as it does under the influence of
pepsin; from which it follows that pepsin replaces the effect of a high temperature, which
is not possible in the stomach. The same acid with pepsin dissolved blood, fibrine, meat
and cheese; while the isolated acid dissolved only an insignificant quantity at the same
temperature; but when raised to the boiling point, it dissolved nearly as much, and the part
dissolved appeared to be of the same nature. The epidermis, horn, the elastic tissue (sue!)
as the fibrous membrane of arteries), do not dissolve in a dilute acid containing pepsin. M .
Wasmann has remarked that the pepsin of the stomach of the pig is entirely destitute of the
power to coagulate milk, although the pepsin of the stomach of the calf possesses it in a very
high degree ; from which he is led to suppose, that the power of the latter depends upon a
particular modification of pepsin, or perhaps upon another substance accompanying it, which
ceases to be formed when the young animal is no longer nourished by the milk of its mother."*

669. It is considered by Liebig, however, that Pepsin has no proper ex-
istence as such ; and that it is nothing else than a proteine-compound in a
state of change, — being, when obtained after the method of Wasmann, the
result of the partial decomposition of the membrane of the stomach, which
has been induced in it by exposure to air. This view accords well with the
fact, recently ascertained by MM. Bernard and Barreswill, that the Saliva and
Pancreatic fluid have an equal solvent power when acidulated. In their alka-
line condition, their action appears limited to starchy matters ; of which they
effect the conversion into sugar. In their acid state, they act, like the gastric
fluid, upon azotized matters; and, in common with it, they are destitute 'of
power to act upon starch. — We are further led, by this remarkable fact (the
knowledge of which enables us to harmonize many previous results, which
were apparently discordant), to a better understanding of the nature of the
action of this Organic compound in the Digestive process. Its operation on
starch is precisely that of the substance termed Diastase, which is found in
Plants, and which is the agent employed for the conversion of starch into
sugar, in various processes of the Vegetable economy. In so doing, it acts as
a sort of ferment ; having the power of exciting a change in another substance,
in which it does not itself participate. This appears to be precisely the
nature of its operation upon azotized matters ; in which it produces an in-
cipient change, that so alters their condition, as to dispose them to solution in
hydrochloric and acetic acids, with which they form definite chemical com-
pounds.— The analogy of the action of Pepsin to that of a ferment, is further
shown in the power possessed by a very small quantity of it, to excite the
required change in an almost unlimited amount of alimentary matters; whilst
only a definite quantity of these matters, when thus prepared, can be dissolved
in a limited amount of dilute acid; which is precisely analogous to the pro-
cess of chemical solution. The agency of Pepsin, in preparing them for that
process, resembles that of Heat ; by which it may be replaced, — the dilute
acids alone, at a high temperature, having the power of dissolving -azotized
compounds.

670. We have, in the last place, to consider the changes which are effected

* Graham's Elements of Chemistry, [Am. ed. p. C95.]

508 OF FOOD, AXD THE DIGESTIVE PROCESS.

in the nutritive materials, by the admixture of the biliary and pancreatic secre-
tions ; and to inquire into the form in which they are received into the absorb-
ent vessels. — The substances of the first or saccharine group consist chiefly
of Sugar and Starch. It appears from the late researches of MM. Bouchardat
and Sandras, that Sugar is gradually converted, during its passage along the
alimentary canal, into lactic acid ; and that it is absorbed in this form alone,
unless it have been administered in considerable quantity or for a long period.
The conversion of sugar into lactic acid, appears to be preliminary to the
elimination of that substance by the respiAtory process. The particles of
Starch, as already mentioned, are but very little acted on by the digestive pro-
cess, at least in Man and the Mammalia, unless their envelopes have been
previously ruptured by heat or chemical agents ; but the triturating power of
the gizzard in granivorous Birds, aided by the high temperature and the more
alkaline character of the secretions, enables them to act with more energy upon
amylaceous substances. The products of the digestive action upon starch,
are dextrine and grape-sugar; and this is gradually converted into lactic acid,
in which state it is absorbed. If sugar be introduced into the blood-vessels
unchanged, it is drawn off by the urine ; and its heat-sustaining agency, there-
fore, is not exerted. It is probably to avoid its too rapid introduction that
the conversion of amylaceous into saccharine matter is so slowly effected in
the alimentary canal ; this conversion seems to begin in the mouth, to cease
in the stomach during the operation of the acid solvent, and to recommence
•after the neutralization of the acid by the biliary and pancreatic fluids, — sub-
sequently continuing during nearly the whole of the passage of the alimentary
matter along the intestinal tube. — It is now quite certain, that the substances
of this class may be converted, in the living body, into oleaginous matter. Of
the mode and the situation in which this conversion takes place, nothing
whatever is certainly known ; but a clue to an acquaintance with the former
seems to be given by the recently-discovered fact, that the continued contact
of bile with saccharine matter occasions the conversion of a portion of the
siigar into an adipose compound (§ 835).

671. The substances forming the Oleaginous class do not seem to undergo

o

any change, except minute division of their particles, until the Chyme is min-
gled with bile; which substance acts as a soap, and renders the oily matters
soluble, or at any rate reduces them to a condition in which they can be ab-
sorbed by the lacteals. This, indeed, seems to be the main purpose of that
admixture of the bile with the mass in process of digestion, which experiments
and pathological observation abundantly prove to be requisite for the due per-
formance of that function. Thus, it has been shown by the experiments of
Schwann, that, if the bile-duct be divided, and be made to discharge its con-
tents externally through a fistulous orifice in the walls of the abdomen, instead
of into the intestinal canal, those animals which survive the immediate effects
of the operation, subsequently die from inanition, almost as soon as if they
had been entirely deprived of food. In like manner, if the flow of the biliary
secretion into the intestine be prevented by disease, — such as obstruction of
the gall-duct, — the digestive function is evidently disordered, the peristaltic
action of the intestine is not duly performed, the ftrces are while and clayey;
and there is an obvious insufficiency in the supply of nutriment prepared for
the absorbent vessels. This deficiency seems partly due to the want of power
to absorb the oleaginous particles of the food, which is the result of the non-
intermixture of the bile with the chyme; and partly to the suspension of the
supply of combustible matter, that is afforded by certain constituents of the
bile itself, which are destined, not to be carried out of the system, but to be
ro-absorbcd. — The presence of bile in the stomach has the effect of suspend-

ABSORPTION FROM THE DIGESTIVE CAVITY. 509

ing the solution of the various azotized principles, and in regard to them,
therefore, it is injurious; but it seems, from the observations of Dr. Beaumont,
to be a spontaneous occurrence, whenever the diet has been for a long time,
and in great part, of an oleaginous nature ; and it then appears destined to aid
in the reducing process, which is the proper function of the stomach. It is
suggested by Dr. A. Combe, whether the peculiar digestibility of a piece of
fat bacon, in certain forms of Dyspepsia, may not be due to the abnormal
presence of bile in the stomach. The power of precipitating the proteine-
compounds from their acid solutions, which has been shown, by the recent
experiments of Plainer, to belong to the peculiar principles of bile, fully ex-
plains its injurious effects upon the solvent processes, which normally take
place in the stomach. — In regard to the Albuminous and Gelatinous articles
of food, there is no evidence that any other change is effected in them, than
one of simple solution ; and they appear to be absorbed in the same condition
as that to which they are reduced by the action of the stomach.

CHAPTER XI.

OF ABSORPTION AND SANGUIFICATION.

I. — Absorption from the Digestive Cavity.

672. So long as the Alimentary matter is contained in the digestive cavity,
it is as far from being conducive to the nutrition of the system, as if it were in
contact with the external surface. It is only when absorbed into the vessels,
and carried by the circulating current into the remote portions of the body,
that it becomes capable of being appropriated by its various tissues and organs.
Among the Invertebrata, we find the reception of alimentary matter into the
Circulating system to be entirely accomplished through the medium of the
blood-vessels, which are distributed upon the walls of the digestive cavity.
But in the Vertebrata, we find an additional set of vessels interposed between
the walls of the intestine and the sanguiferous system; for the purpose, as it
would seem, of taking up that portion of the nutritive matter which is not in
a state of perfect solution, and of preparing it for being introduced into the
current of the blood. These are the lacteals, or absorbents of the intestinal
walls. That their special office is to take up the product of the admixture of
the chyme with the biliary and pancreatic fluids, appears from the fact, that
they are not distributed at all upon the walls of the stomach, nor upon those of
the duodenum above the point of entrance of the hepatic and pancreatic ducts;
but that they are copiously distributed upon the walls of the remainder of the
small intestine, and more sparingly upon those of the large. Each lacteal
tube originates in the interior of one of the villous processes of the mucous
membrane lining the intestinal tube. The accompanying figure represents the
appearance offered by the incipient lacteals, in a villus of the jejunum of a
young man, who had been hung soon after taking a full meal of farinaceous
food. The trunk that issues from the villus is formed by the confluence of

43*

510 OF ABSORPTION AND SANGUIFICATION.

Fig. 204. several smaller branches, whose origin it is difficult to

trace ; but it is probable that they form loops by anasto-
mosis with each other, so that there is no proper free
extremity in any case. It is quite certain that the lac-
teals never open by free orifices upon the surface of the
intestine, as was formerly imagined. From the researches
of Mr. J. Goodsir, already referred to (§ 181), it appears
that these loops are imbedded in a mass of cells, which
are the real agents in the selection of the materials that
are destined to be conveyed into the lacteals. When

these cells have distended themselves, by their inherent

power of growth, with the materials which are adapted

One of the intestinal vilLi. r . ' . . , . . r.

with the commencement of to their selecting function, and have reached their full
a lacteal. term of maturity, they appear to yield their contents to

the absorbent vessels, either by bursting or by deli-
quescence.— It is thought by Prof. E. Weber, that the epithelial cells, which
cover the villus, perform a preliminary office; the nutrient matter being first
absorbed and partially prepared by them ; and then being drawn, through the
basement membrane of the villus, into the special absorbent cells which form
part of its substance. This seems the more likely, as we shall hereafter
find that the epithelial cells of the placental tufts appear to perform a like
function.

673. The mill are also furnished with a minute plexus of blood-vessels ;
of which the larger branches may be seen with the naked eye, when they are
distended with blood, or with coloured injection (Figs. 205, 206). The par-
ticular arrangement of the capillaries of which the plexus is formed, varies in
different animals; but in all they seem to be most copiously distributed upon
the surface of the villus. The purpose of these may be partly to afford some
of the materials for the development of the absorbent cells ; and this would
seem probable from the recent experiments of Mr. Fenwick,* which show
that the lacteals will not absorb alimentary matter from any part of the intes-
tinal canal, in which the blood is not circulating. But there can be no reason-
able doubt, that the blood-vessels of the mucous membrane lining the digestive
cavity, and especially those of the villi, perform an important part in the func-
tion of Absorption. This is established by the fact, that soluble substances
introduced into the stomach, and prevented from passing beyond its pyloric
orifice, are absorbed from its walls.

674. In regard to the degree ia which the function of Nutritive Absorp-
tion is performed by the Lacteals, and by the Sanguiferous System, respect-
ively, considerable difference of opinion has prevailed. When the Absorbent
vessels were first discovered, and their functional importance perceived, it
was imagined that the introduction of alimentary fluid into the vascular sys-
tem took place by them alone. A slight knowledge of Comparative Anatomy,
however, might have sufficed to correct this error; since no lacteals exist in
the Invertebrated animals, the function of Absorption being performed by the
Mesenteric, blood-vessels only ; from which it is evident, that these do pos-
sess the power of absorption : and it is scarcely to be supposed that they
should not exercise this power in Vertebrated animals also, since their dis-
position on the walls of the intestinal cavity is evidently favourable to it. On
the other hand, the introduction of a new and distinct system of vessels would
seem to indicate, that they must have some special purpose ; and there can
be no doubt that the absorption of certain kinds of nutritive matter is that
for which they are peculiarly designed. The fluid found in the lacteals is

* Lancet. Jan. and Feb. 1845.

ABSORPTION BY BLOOD-VESSELS OF VILLI.

Fig. 205.
.2 x

511

Vessels of an intestinal vil'.ns
of a Hare, from a dry prepara-
tion by Dolimger : 1, 1, veins
filled with white injection; 2, 2.
arteries injected red. Magnified
about 45 diameters.

A, apex of intestinal vil-
!us from the duodenum of
Human female ; B, a mesh of
the vascular net-work, 1, 1,
filled up with delicate cellu-
lar tissue, 2, magnified about
45 diameters.

almost invariably the same ; being that to which the name chyle has been
applied. It appears from the uniformity of its composition, which forms a
striking contrast with the diversity of the food from which it is obtained, that
the lacteals (or rather the absorbent cells, amongst which they originate) have
in some degree the power of selecting the particles of which it is composed ;
and that, whilst they take up such a proportion of each class of alimentary
materials as will rightly blend with the rest in the nutritious fluid, they reject
not only the remainder, but also (for the most part at least) any other ingre-
dients which may be contained in the fluid of the intestines. Such may be
stated as the general result of the experiments that have been made to de-
termine their function ; though it is unquestionable that extraneous substances,
especially of a saline nature, occasionally find their way into this system of
vessels. This may not improbably be due to a correspondence in the size
and form of the ultimate particles of such substances, with those of the mate-
rials normally absorbed by the lacteals.*

675. On the other hand, the Blood-vessels seem to be less concerned in
nutritive absorption, but take up from the alimentary canal a portion of almost
any fluid matters which it may contain. This seems to have been established
by the carefully-conducted experiments of MM. Tiedemann and Gmelin, who

1 Experiments upon the function of Absorption in Plants, whose radical vessels have a
corresponding power of selection, appear likely to assist in elucidating this interesting subject.
By the experiments of Dr. Daubeny it has been ascertained, that if a plant absorb any par-
ticular saline compound, it can also be made to absorb those which are isomorphous with it,
though it will reject most others. — See Princ. of C4en. and Comp. Phys.,§ 294.

512 OF ABSORPTION AND SANGUIFICATION.

mingled with the food of animals various substances, which, by their colour,
odour, or chemical properties, might be easily detected in the fluids of the
body. After some time the animal was examined ; and the result was, that
unequivocal traces of the substances were not unfrequently detected in the
venous blood and in the urine ; whilst it was only in a very few instances,
that any indication of them could be discovered in the chyle. The colouring
matters employed were various vegetable substances ; such as gamboge, mad-
der, and rhubarb: the odorous substances were camphor, musk, assafoetida,
&c. ; while, in other cases, various saline bodies, such as muriate of barytes,
acetate of lead and of mercury, and some of the prussiates, which might easily
be detected by chemical tests, were mixed with the food. The colouring
matters, for the most part, were carried out of the system, without being re-
ceived either into the veins or lacteals ; the odorous substances were gene-
rally detected in the venous blood and in the urine, but not in the chyle ;
whilst of the saline substances, many were found in the blood and in the
urine, and a very few only in the chyle. A similar conclusion might be
drawn from the numerous instances in which various substances introduced
into the intestines have been detected in the blood, although the thoracic duct
had been tied ; but these results are less satisfactory, because even if there is
no direct communication (as maintained by many) between the lacteals and
the veins in the mesenteric glands, the partitions which separate their respect-
ive contents are evidently so thin, that transudation may readily take place
through them. — It would seem probable, that substances perfectly dissolved
in the fluids of the stomach, are taken into the blood-vessels so copiously dis-
tributed on its walls, by the simple and necessary process of Endosmose ; in
this manner we may account for the fact, that saline substances are for the
most part readily absorbed into the blood ; and there seems reason to believe
that the Albuminous portion of the chyme, together with the Saccharine prin-
ciples or the products of their transformation, may thus be introduced directly
into the circulating current, without passing through the lacteals. — On this
subject there is much need of further information.

2. — Absorption from the Body in general.

676. The Mucous Membrane of the alimentary canal is by no means the
only channel, through which nutritive or other substances may be introduced
into the circulating apparatus. The Lymphatic system is present in all animals
which have a lacteal system ; and the two evidently constitute one set of ves-
sels. The lymphatics, however, instead of commencing on the intestinal
walls, are distributed through the greater part of the body, especially on the
Skin ; their origins cannot be clearly traced ; but they seem in general to form
a plexus in the substance of the tissues, from which the convergent trunks
arise. After passing, like the lacteals, through a series of glandular bodies
(the precise nature of which will be presently considered, § 682), they empty
their contents into the same receptacle with the lacteals ; and the mingled
products of both pass into the Sanguiferous system. — We find in the Skin,
also, a most copious distribution of capillary blood-vessels, the arrangement of
which is by no means unlike that of the blood-vessels of the alimentary canal ;
and its surface is further extended by the elevations that form the sensory
papillae, which are in many points comparable to the intestinal villi, although
their special function is so different. — In the lowest tribes of animals, and in
the earliest condition of the higher, it would se^m as if Absorption by the ex-
ternal surface is almost equally important to the maintenance of life, with
that which takes place through the internal reflexion of it forming the walls
of the Digestive cavity. In the adult condition of the higher animals, how-

ABSORPTION THROUGH THE CUTANEOUS SURFACE. 513

ever, the special function of the latter is so much exalted, that itusually super-
sedes the necessity of any other supply ; and the function of the cutaneous
and pulmonary surfaces may be considered as rather that of exhalation, than
of absorption. But there are peculiar conditions of the system, in which the
imbibition of fluid through these surfaces is performed with great activity,
supplying what would otherwise be a most important deficiency. It may
take place either through the direct application of fluid to the surface, or even
through the medium of the atmosphere, in which a greater or less proportion
of watery vapour is usually dissolved. This absorption occurs most vigour-
ously, when the system has been drained of its fluid, either by an excess of
the excretions, or by a diminution of the regular supply.

677. It may be desirable to adduce some individual cases, which will set
this function in a striking point of view; and those may be first noticed, in
which the absorption took place, through the contact of liquids with the skin.
It is well known that shipwrecked sailors, and others, who are suffering from
thirst, owing to the want of fresh water, find it greatly alleviated, or altogether
relieved, by dipping their clothes into the sea, and putting them on whilst still
wet, or by frequently immersing their own bodies. — Dr. Currie relates the
case of a patient labouring under dysphagia in its most advanced stage; the
introduction of any nutriment, whether solid or fluid into the stomach, having
become perfectly impracticable. Under these melancholy circumstances, an
attempt was made to prolong his existence, by the exhibition of nutritive ene-
mata, and by immersion of the body, night and morning, in a bath of milk and
water. During the continuance of this plan, his weight, which had previously
been rapidly diminishing, remained stationary, although the quantity of the
excretions was increased. How much of the absorption, which must have
been effected to replace the amount of excreted fluid, is to be attributed to the
baths, and how much to the enemata, it is not easy to say; but it is important
to remark that " the thirst, which was troublesome during the first days of the
patient's abstinence, was abated, and, as he declared, removed by the tepid
bath, in which he had the most grateful sensations." " It cannot be doubted,"
Dr. Currie observes, "that the discharge by stool and perspiration exceeded
the weight of the clysters;" and the loss by the urinary excretion, which in-
creased from 24 oz. to 36 oz. under this system, is only to be accounted for
by the cutaneous absorption. — Dr. S. Smith mentions that a man, who had
lost nearly 3 Ibs. by perspiration, during an hour and a quarter's labour in a
very hot atmosphere, regained 8 oz. by immersion in a warm bath at 95°, for
half an hour. — The experiments of Dr. Madden* show that a positive increase
usually takes place in the weight of the body, during immersion in the warm
bath, even though there is at the same time a continual loss of weight by pul-
monary exhalation, and by transudationt from the skin. This increase was,
in some instances, as much as 5 drachms in half an hour ; whilst the loss of
weight during the previous half hour had been 6| drachms: so that, if the
same rate of loss were continued in the bath, the real gain by absorption must
have been nearly an ounce and a half. Why this gain was much less than
in the cases just alluded to, is at once accounted for by the fact that there was
no deficiency, in the latter case, of the fluids naturally present in the body.

678. The quantity of water which may be imbibed from the vapour of the
atmosphere, would exceed belief, were not the facts on which the assertion
rests, beyond all question. Dr. Dill relates the case of a diabetic patient,

' Prize Essay on Cutaneous Absorption, pp. 50 — 63.

f That part of the function of cutaneous transpiration, which consists in simple exhalation ,
is of course completely checked by such immersion ; but that which is the result of an actual
secreting process in the cutaneous glands (CHAP, xv., Sect. S) is increased by heat, even
though this be accompanied with moisture.

514 OF ABSORPTION AND SANGUIFICATION.

who for five weeks passed 24 Ibs. of urine every twenty-four hours ; his in-
gesta during the same period amounted to 22 Ibs. At the commencement of
the disease he weighed 145 Ibs. ; and when he died, 27 Ibs. of loss had been
sustained. The daily excess of the excretions over the ingesta could not have
been less than 4 Ibs. ; making 140 Ibs. for the thirty-five days during which
the complaint lasted. If from this we deduct the amount of diminution which
the weight of the body sustained during the time, we shall still have 113 Ibs.
to be accounted for, which can only have entered the body from the atmo-
sphere.— A case of ovarian dropsy has been recorded, in which it was ob-
served that the patient, during eighteen days, drank 692 oz. or 43 pints of
fluid, and that she discharged by urine and by paracentesis, 1298 oz. or 91
pints, which leaves a balance of 606 oz. or 38 pints, to be similarly accounted
for.* — The following remarkable fact is mentioned by Dr. Watson in his Che-
mical Essays. " A lad at Newmarket, having been almost starved, in order
that he might be reduced to a proper weight for riding a match, was weighed
at 9 A. M., and again at 10 A. M. ; and he was found to have gained nearly 30
oz. in weight in the course of this hour, though he had only drunk half a
glass of wine in the interim." — A parallel instance was related to the Author
by the late Sir G. Hill, then Governor of St. Vincent. A jockey had been
for some time in training for a race, in which that gentleman was much inte-
rested ; and had been reduced to the proper weight. On the morning of the
trial, being much oppressed with thirst, he took one cup of tea ; and shortly
afterwards his weight was found to have increased 6 Ibs. ; so that he was in-
capacitated for riding. — Nearly the whole of the increase in the former case,
and at least three-fourths of it in the latter, must be attributed to cutaneous
absorption ; which function was probably stimulated by the wine that was
taken in the one case, and by the tea in the other.

679. Not only water, but substances dissolved in it, may be thus introduced.
It has been found that, after bathing in infusions of madder, rhubarb, and tur-
meric, the urine was tinged with these substances ; and that a garlic plaster
affected the breath, when every care was taken, by breathing through a tube
connected with the exterior of the apartment, that the odour should not be re-
ceived into the lungs.t Gallic acid has been found in the urine, after the ex-
ternal application of a decoction of a bark containing it; and the soothing influ-
ence in cases of neuralgic pain, of the external application of cherry-laurel
water, is well known. Many saline substances are absorbed by the skin,
when applied to it in solution ; and it is interesting to remark, that, contrary
to what happens in regard to the absorption of these from the alimentary ca-
nal, they are for the most part more readily discoverable in the absorbents
than in the veins. This is probably clue to the fact, that the imbibition of
them is governed entirely by physical laws; in obedience to which, they pass
most readily into the vessels which present the thinnest walls and the largest
surface. In the intestines, the vascular plexus on each villus is far more ex-
tensive than the ramifying lacteal which originates in it; and as the walls of
the veins are thin, there is considerable facility for the entrance of saline and
other substances into the general current of the circulation ; but in the skin,
the lymphatics are distributed much more minutely and extensively than the
veins ; and soluble matters, therefore, enter them in preference to the veins.
The absorbent power of the Lymphatics of the Skin is well shown by the
following experiment. A bandage having been tied by Schreger round the
hind-leg of a Puppy, the limb was kept for twenty-four hours in tepid milk ;

* Madden, loo. oil. — In this case, however, something is to be allowed for the quantity of
•water continued in the solid food invested.

"I" Dunglison's Physiology, [lith. ed., vol. i. p. G47.]

ABSORPTION FROM THE BODY IN GENERAL. 515

at the expiration of this period, the lymphatics were found full of milk, whilst
the veins contained none. In repeating this experiment upon a young man,
no milk could be detected in the blood drawn from a vein. It has been shown
by Muller that, when the posterior extremities of a Frog were kept for two
hours in a solution of prussiate of potass, the salt had freely penetrated the
lymphatics, but had not entered the veins. — It does not follow, however, from
these and similar experiments, that in all tissues the lymphatics absorb more
readily than the veins ; for as the capillary blood-vessels in the lungs are much
more freely exposed to the surface of the air-cells, than are the lymphatics,
we should, on the principles just now stated, expect the former to absorb more
readily. This appears from experiment to be the fact ; for when a solution
of prussiate of potass was injected by Mayer into the lungs, the salt could be
detected in the serum of the blood much sooner than in the lymph, and in
the blood of the left cavities of the heart, before it had reached that of the
right.

680. Our inferences with regard to the ordinary functions of the Lymphatic
system, however, must be rather drawn from the nature of the fluid which it
contains, and from the uses subsequently made of it, than from experiments
such as the preceding. We shall presently see, that there is a close corre-
spondence in composition between the Chyle of the Lacteals, and the Lymph
of the Lymphatics ; the chief difference being the presence in the former, of
a considerable quantity of fatty matter, and of a larger proportion of the as-
similable substances (albumen and fibrine) which are equally characteristic of
both (§ 691). This evident conformity in the nature of the fluid which these
two sets of vessels transmit, joined to the fact of the fluid Lymph, like the
Chyle, being conveyed into the general current of the circulation, just before
the blood is again transmitted to the system at large, almost inevitably leads
to the inference, that the lymph is, like the chyle, a nutritious fluid, and is not
of an excrementitious character, as formerly supposed. On the other hand,
the close resemblance between the contents of the Lymphatics, and diluted
Liquor Sanguinis, seems to indicate that the former are partly derived from
the fluid portion of the Blood, which has transuded through the walls of the
Capillary vessels ; and we shall presently see reason to believe that this
transudation is for the purpose of subjecting certain crude materials, that have
been taken up direct into the blood-vessels, to an elaborating or preparatory
agency, which it seems to be the especial object of the Absorbent system to
exert upon certain of the nutritive components of the circulating fluid.

681. But it seems not improbable that there may be another source for the
contents of the Lymphatics. We have already had to allude, on several oc-
casions, to the disintegration which is continually taking place within the living
body; whether as a result of the limited duration of the life of its component
parts, or as a consequence of the decomposing action of Oxygen. Now the
death of the tissues by no means involves their immediate and complete de-
struction ; and there seems no more reason why an animal should not derive
support from its own dead parts than from the dead body of another indi-
vidual. Whilst, therefore, the matter, which has undergone too complete a
disintegration to be again employed as nutrient material, is carried off by the
excreting processes that portion which is capable of being again assimilated,
may be taken up by the Lymphatic system. If this be the case, we may say,
with Dr. Prout, that " a sort of digestion is carried on in all parts of the body."
It may be stated, then, as a general proposition, that the function of the Ab-
sorbent System is to take up, and to convey into the Circulating apparatus,
such substances as are capable of appropriation to the nutritive process ;
whether these substances be directly furnished by the external world, or be
derived from the disintegration of the organism itself. We have seen that,

516 OF ABSORPTION AND SANGUIFICATION.

in the Lacteals,the selecting power is such, that these vessels are not disposed
to convey into the system any substances but such as are destined for this
purpose ; and that extraneous matters are absorbed in preference by the Me-
senteric Blood-vessels. The case is different, however, with regard to the
Lymphatics ; for there is reason to believe, that they are more disposed than
the veins to the absorption of other soluble matters ; especially when these
are brought into relation with the skin, through which the lymphatic vessels
are very profusely distributed.

a. Since the time of Hunter, who first brought prominently forward the doctrine alluded
to, it has been commonly supposed that the function of the Lymphatics is to remove, by in-
terstitial absorption, the effete matter, •which is destined to be carried out of the system ; and
any undue activity in this process (such as exists in ulceration), or any deficiency in its
energy (such as gives rise to dropsical effusions, and other collections of the same kind),
have been attributed to excess or diminution in the normal operation of the Absorbent Sys-
tem.— From what has been stated, however, it appears that the special function of the
Lymphatics, like that of the Lacteals, is nutritive absorption;* and that the reception of any
other substances into their interior, must be looked upon as resulting simply from the per-
meability of their walls. This statement applies to the not unfrequent occurrence of the
absorption of bile, and other fluids, from the walls of the cavities in which they were col-
lected: with regard to the absorption of pus, however, which has been occasionally noticed
to take place, both from internal collections, and from open ulcers, it may be remarked, that
the lymphatic vessels were not improbably laid open by ulceration ; since in no other way
can be understood the entrance of globules so large as those of pus, into their interior.

b. If this view of the function of the Lymphatics be correct, it follows that we must at-
tribute to the Blood-vessels the absorption of the truly effete particles ; and in this there
would seem no improbability. We know that VenousJ^lood contains the elements of two
important excretions, that of the lungs and that of the bile, in a far higher amount than does
arterial blood ; and we shall hereafter see, that there is a certain portion of the fluid, which
consists of " ill defined animal principles" that seem ready to be thus thrown off.

c. It may be further remarked, that the reciprocal part which Hunter imagined the Ar-

* The Author, at the time of the publication of the First Edition of this work, believed
this view to be altogether novel ; he has since learned, however, that a similar doctrine had
been put forward by Dr. Moultrie, of South Carolina, in the American Journal of the Medi-
cal Sciences, for the year 1S27.

[In the American Journal of the Medical Sciences, for 1827, Dr. James Moultrie pub-
lished an essay on the l; Uses of the Lymph," in which, amongst other things attempted to
be sustained, will be found the following views.

1. The lacteals and lymphatics do not constitute, as they are supposed to do, the absorbent
system of the animal economy ; they do not, as the absorbent theory supposes, remove from
the organs the "cast oft" molecules" of which they are composed, or carry out of the body
the " effete" particles disintegrated by the act of the assimilative function. The one is en-
gaged in the preparation and introduction of chyle, and chyle only into the blood ; the other
in elaborating an organizable product — a recremcntitious secretion destined to unite with it
for objects of a common and nutritious nature. 2. The primary object of the lymph, and
that for which it is made to commingle with the chyle in the thoracic duct, is the vitalization
of the latter fluid. 3. The truly "effete" matter of the body is the carbonaceous element
of the venous blood, to which mny be added the urea or azotic element of the urine. Thau
these, we know of nothing to which that term can be applied. 4. The venous and not tin;
lacteal or lymphatic system, therefore, is the "absorbent system," in any disintegratory or
effete sense of the phrase. 5. Nature, in effecting the elimination of excrementitious mat-
ter from the constituency of the solid or fluid parts, appears to aim at restoring to the physi-
cal universe, the matter temporarily borrowed for subsistence, in a state of elementary sim-
plicity, or an approximation thereto; that is, the carbon as carbon, the azote as a/otc, and
hydrogen and oxygen as hydrogen nnd oxygen. The lungs she uses as one medium of es-
cape; the ki<lncy> as ;i second; and the skin ;is a third, &e. Hence, the ear! ionic acid gas
of respiration; the urea of the kidneys, and the aqueous exhalations of the skin, pulmonary
transpiration and urine.

These doctrines have been regularly taught by Dr. M.. in his course of lectures on physi-
ology, delivered in the Medical College of the State of South Carolina, since the establish-
ment of the College in 1833. They have also been recently enforced in a brochure published
by Dr. M., in which he asserts and vindicates his claim to their paternity. On the Organic
Functions of Animals. By JAMKS MOULTIUE, M.D., etc., Charleston, S. C. 1844. — M. C.]

STRUCTURE OF ABSORBENT GLANDULE.

517

teries and Lymphatics to perform in the function of Nutrition, is quite inconsistent with
what is now known of the nalfcre of that process: for, as will subsequently appear, it en-
tirely consists in a reaction between the tissues and the nutritious fluid, in which the vessels
have no share save as the channels of supply. When these channels are obstructed, or the
supply of new matter is cut off in any other way, the removal of the old by interstitial ab-
sorption becomes evident ; and that this is accomplished at least as much by the veins as by
the lymphatics, appears from the fact that in some tissues, in which it may take place with
rapidity, lymphatics do not exist.

3. — Of the Elaboration of the Nutrient Materials.

682. The alimentary substances, taken up by the Absorbent vessels, seem
very far from being capable of immediate application to the nutrition of the
body; for we find that they are not conveyed by any means directly into the
Circulating current, but that they first traverse a long series of tubes, convo-
luted at intervals into ganglia or knots ;* and that, in the course of this pas-
sage, they undergo considerable changes, which tend to bring the fluid into
closer relationship with the Blood. It seems probable that the materials,
which are directly received into the Blood-vessels, are equally far from being
immediately applicable to the Nutritive processes ; for we find, in connection
with the vascular system, certain bodies having the essential structure of
glands, but destitute of efferent ducts ; which must restore to the circulating
current any substances which they withdraw from it; and which there are
various reasons (as will presently appear) for placing in the same category
with the glandulae of the Absorbent system. — The Absorbent Glandulae, whe-
ther placed upon the Lacteals in the Mesentery, or upon the Lymphatics in
various parts of the body, have the same general structure. They are made
up of convoluted knots of absorbent vessels, the simple cylindrical canals of
which, however, are usually dilated into larger cavities, or cells ; and amongst
these, capillary blood-vessels are minutely distributed. These blood-vessels
have no direct communication with the interior of the absorbents and the
cavities of the glandulae, being separated from them by the membranous walls
of both sets of tubes ; but there can be no doubt that transudation readily
takes place from one set of canals to the other. The epithelium, which
lines the absorbent vessel, undergoes a marked change where the vessel en-
ters the gland ; and becomes more like that of the proper glandular follicles
in its character. Instead of being flat and scale-like, and forming a single
layer in close apposition with the basement-membrane, as it does in the ab-
sorbents previous to their entrance into the gland and after their emergence
from it, we find it composed of numerous layers of spherical nucleated cells,
of which the superficial ones are easily detached, and appear to be identical

Fig. 207.

Fig. 208.

Diagram of a lymphatic gland, showing the
intra-glandular network, and the transition
from the scale-like epithelia of the extra-glan-
dular lymphatics, to the nucleated cells of the
intra-glandular.

Portion of intra-glandular lymphatic,
showing along the lower edge the thick-
ness of the germinal membrane, and upon
it, the thick layer of glandular epithelial
cells.

* In Reptiles, in which there are no glands or ganglia in the Absorbent system, the tubes
are immensely extended in length.
44

518 OF ABSORPTION AND SANGUIFICATION.

with the cells found floating in the Chyle.* Their purpose will be considered
hereafter.

683. To the class of Vascular Glands belong the Spleen, the Thymus
and Thyroid Glands, and the supra-Renal Capsules. With the exception of
the first, they all have their origin (as recently ascertained by Mr. J. Good-
sirt) in involuted portions of the Germinal membrane; and, at an early period
of embryonic life, they are in actual continuity with each other. Their original
identity of function, therefore, cannot be doubted; and the probability of the
inference, which rests on other grounds, that this function is to assimilate or
elaborate the nutrient materials (in the manner in which the cells of the
leaves of Plants prepare their elaborated sap), is strengthened by its exact
conformity with the original function of the Germinal membrane. But there
is no improbability that they may severally have some subsidiary or supple-
mentary function to perform ; varying according to their respective structure,
position, and connections. This seems peculiarly the case in regard to the
Spleen; the origin of which body is not the same with that of the other three.

a. According to the account of Dr. Julian Evans,J whose researches appear to have been
more successful than those of any other Anatomist, the Spleen essentially consists of a fibrous
membrane, which constitutes its exterior envelope, and which sends prolongations in all
directions across its interior, so as to divide it into a number of minute cavities or lacunae
of irregular form. These Splenic lacuna communicate freely with each other, and with
the Splenic vein; and they are lined by a continuation of the lining membrane of the latter,
which is so reflected upon itself, as to leave oval or circular foramina, by which each lacuna
opens into others, or into the splenic vein. The lacunae, whose usual diameter is estimated
by Dr. Evans at from half to one-third of a line, are generally traversed by filaments of
elastic tissue, imbedded in which a small artery and vein may be frequently observed ; over
these filaments, the lining membrane is reflected in folds ; and in this manner each lacuna
is incompletely divided into two or more smaller compartments. There is no direct com-
munication between the splenic artery and the interior of the lacuna- ; but its branches are
distributed through the intercellular parenchyma (which will be presently described); and
the small veins, which collect the blood from the capillaries of the organ, convey it into
these cavities, from which it is conveyed away by the splenic vein. The lacuna? may be
readily injected from the splenic vein with either air or liquid, — provided they are not filled
with coagulated blood; and they are so distensible, that the organ may be made to dilate to
many times its original size, with very little force. This is especially the case in the Spleen
of the Herbivora; for the Spleen of a Sheep, weighing 4 ounces, may be easily made to con-
tain 30 ounces of water. That of Man, however, is less capable of this kind of enlargement.
— According to Dr. Evans, the lacunae of the spleen never contain anything but blood ;§ and
he notices that a frequent condition of the Human Spleen after death, which is sometimes
described as a> morbid appearance, consists in the filling of the lacunas with firmly-coagulated
blood, which gives a granular appearance to the organ.

b. The partitions between the lacunas are formed, not only by the membranes already
mentioned, but by the peculiar parenchyma of the Spleen; which constitutes a larger part
of the organ in Man than in the Herbivorous Mammalia. It presents a half fluid appear-
ance to the eye; but when an attempt is made to tear it, considerable resistance is expe-
rienced in consequence of its being intersected by what appear to be minute fibres. When
a small portion of it is pressed, a liquid is separated; which is that commonly known as the
Liquor Lienis. or Splenic blood; and which is usually described (but erroneously, according
to Dr. E.) as filling the lacunio of the Spleen. This liquid, when diluted with scrum and
examined under the Microscope, is found to contain two kinds of corpuscles, — one M>rt being
apparently identical with ordinary blood-corpuscles — and the other with the globules cha-

* See Mr. J. Goodsir's Anatomical and Pathological Researches, p. 4G.

•f Proceedings of the 1 loyal Society, 18-16.

t Lancet, April C>, 1844.

§ "It dill'ers in no respect from venous blood taken out of any other part of the portal
system. 1 have found it fluid or coagulated, as in other parts of the venous system ; and I
have frequently pulled out from the splenic vein colourless coagula. Occasionally a number
of globules may be distinguished in it, resembling those found in the parenchyma; but in
these cases the organ appears to have suffered injury, and these matters appear to have got
into the cells and vein in consequence." Loc. cit.

STRUCTURE AND FUNCTIONS OF THE SPLEEN. 519

ractcristio of the lymph and abundant in the lymphatic glands. The remaining fibrous
substance consists entirely of capillary blood-vessels and lymphatics, with minute corpuscles,
much smaller than blood-corpuscles, varying in size from about 1-GOOOth to l-7000th of an
inch, of spherical form, and usually corrugated on the surface. These lie in great numbers
in the meshes of the sanguiferous capillaries; and the minute lymphatics are described by
Dr. E. as connected with the splenic corpuscles, and apparently arising from them. — Lying
in the midst of the parenchyma are found a large number of bodies, of about a third of a line
in diameter, which are evidently in close connection with the vascular system : these have
long been known as the Malpighian bodies of the spleen, after the name of their discoverer ;
but since his time, their existence has been denied, or other appearances have been mistaken
for them. According to Dr. E., they in all respects resemble the mesenteric or lymphatic
glands in miniature, — consisting as they do of convoluted masses of blood-vessels and lym-
phatics, united together by elastic tissue, so as to possess considerable firmness: and they
further correspond with them in this, — that the lymph they contain, which was quite trans-
parent in their afferent lymphatics, now becomes somewhat milky, from containing a large
number of Lymph-globules.

684. In regard to the functions of the Spleen, great uncertainty exists. It
appears from the foregoing account of its structure, that it may be regarded
as an organ of duplex character, and probably of double function. The cel-
laled structure maybe considered as a muhilocular reservoir, capable of great
distention, and lined with a continuation of the inner membrane of the vein;
receiving blood, on the one hand, from the veins of the interior of the organ,
and transmitting it onward to the Vena Porue ; and on the other hand, acting
as a reservoir for the venous blood of the abdomen, when, from any cause,
its passage into the Vena Cava is obstructed. The splenic parenchyma, on
the other hand, must be regarded as a complex Lymphatic tissue, essentially
resembling that of the lymphatic glands, but differently arranged. In those
animals in which it predominates, as in Man, the artery is large ; on the other
hand, where the collated structure is most developed, as in the Herbivora, the
Vein is very large, and the artery comparatively small. — Nothing completely
analogous to a Spleen is found in Invertebrated animals ; and from the absence
of the Lymphatic system in them, it is evident that the parenchymatous por-
tion can have no existence as such. Something analogous to the cellated por-
tion of the Spleen, however, exists in the venous system of many Cephalopoda:
and this circumstance is an additional proof of the duplicity of the character
of this remarkable organ.

685. Out of the numberless theories of its operation, which have been at
different times brought forwards, the one which seems best to account for its
cellated structure, is that which regards it as a sort of diverticulum or reser-
voir; which may serve to relieve the Portal Venous system from undue dis-
tention, under a great variety of circumstances. This system is well known
to be destitute of valves ; so that the Splenic vein has free communication
with the whole of it. Hence the Spleen will be a ready diverticulum for the
venous blood, when the secreting action of the Liver is feeble, so that the
Portal circulation receives a partial check (§ 832). That any cause of con-
gestion of the Portal system peculiarly affects the Spleen, has been proved by
experiment ; for after the Portal Vein has been tied, the Spleen of an animal,
which previously weighed only 2 ounces, has been found to weigh a pound
and a quarter, or ten times as much. Now it is evident that congestion of
the Portal system is liable to occur, when the alimentary canal is distended
with food ; and this from two causes, — the pressure on the Intestinal veins,
and the quantity of fluid absorbed by these veins. Hence it may be conceived,
that the Spleen, by affording a reservoir into which the superfluous Venous
blood may be directed, serves an important purpose in preventing congestion
of other organs. From the observations of Mr. Dobson,* it appears that the

* London Med. and Phys. Journal, Oct. 1820.

520 OF ABSORPTION AND SANGUIFICATION.

Spleen has its maximum volume, at the time when the process of chymifica-
tion is at an end, — namely, about five hours after food is taken ; and that it
is small and contains little blood seven hours later, when no food has been
taken in the interval. Hence he inferred, that this organ is the receptacle for
the increased quantity of Blood, which the system acquires from the food, and
which cannot, without danger, be admitted into the blood-vessels generally ;
and that it regains its previous dimensions, after the volume of the circulat-
ing fluid has been reduced by secretion. This view is confirmed by the fact
noticed by several observers, — that the Spleen rapidly increases in bulk after
the ingestion of a large quantity of fluid, which is absorbed rather by the
Veins than by the Lacteals. It has been further stated in support of this
theory, that animals from which the Spleen has been removed, are very lia-
ble to die of apoplexy, if they take a large quantity of food at a time ; but
that, if they eat moderately and frequently, they do not sutler in this manner.
The use of the Spleen as a diverticulum for the internal Venous circulation,
is further borne out by its liability to become enlarged in consequence of in-
termittent fever ; during the cold stage of which, a great quantity of blood is
driven from the surface towards the internal organs ; and it may be easily
imagined that, if there were no such reservoir, the congestions in these would
be much more dangerous than those which actually do occur. The perma-
nent enlargement of the organ is of course, on this idea of its use, a result of
its frequent distention. But besides this safety-valve function, there can be
little doubt that the Spleen performs another, in virtue of the parenchymatous
portion of its structure ; and that this function corresponds with that of the
Absorbent Glands in general. The identity in structure between its Malpi-
ghian bodies and the ordinary Lymphatic glands, is such as clearly points to
this inference ; which is confirmed by the remarkable fact, determined by the
recent experiments of Prof. Mayer, that, after the Spleen has been extirpated,
the lymphatic glands of the neighbourhood increase in size, and cluster toge-
ther as they enlarge, so as to form an organ which at least equals the original
spleen in volume.* This circumstance explains the reason of the almost in-
variable negative result of the extirpation of the Spleen ; for although the
operation has been frequently practised, with the view of determining the
functions of the organ by the symptoms presented by animals after its removal,
no decided change in the ordinary course of their vital phenomena has ever
been observed ; and the health, if at all disturbed for a time, is afterwards re-
gained. Now if the functions of the Spleen, — putting aside the safety-valve
action of its distensible cavities, — be the same with that of the Lymphatic
Glands in general, it is easy to understand, how its loss may be at once com-
pensated by an increased action on their part, and how it may be permanently
replaced by an increased development of some of those bodies. — Thus, then,
we may fairly regard the Spleen as concurring in function with the glands of
the Absorbent system, in the Assimilating process, by which the crude nutri-
tive materials are rendered fit to circulate through the system ; the diiTerence
between them appearing to be chiefly this, — that, whilst the latter operate upon
the nutritive substances taken up by the Lacteals, the Spleen exerts its influ-
ence upon those which have been received into the Veins ; separating them
from the mass of the blood, and delivering them to the lymphatic system to
be further elaborated.

686. The Supra-Renal Capsules seem to correspond with the Spleen in
their general structure, and in their connection with the Lymphatic system ;
whilst, in the arrangement of their component parts, they bear more resem-
blance to the Kidney.

• Medical Times, March 29, 1845.

SUPRA-RENAL CAPSULES. THYMUS GLAND.

521

a. In the Supra-Renal Capsules, as in the Kidneys, there is an obvious difference between
the cortical and the mf'litllnnj substances. The former is of a yellowish colour ; and presents
an appearance, when cut into, as if it were made up of straight parallel libres, arranged side
by side. Of these straight libres, however, a part are branches of arteries, whicb enter this
body at every point of its exterior, from a capillary network covering its surface; and others
are corresponding branches of veins, that receive the blood from these arteries, and convey
it into a venous plexus which forms the centre of the .organ. Between the radiating blood-
vessels, there are found lying, in the cortical substance, numerous parallel cylinders or elongat-
ed cones, formed by closed sacs of basement-membrane, including nuclei and cells in various
stages of development, with fat-cells. — The medullary substance is partly made up of the ve-
nous plexus, dilated into a sort of cavernous texture, together with empty cavities or lacuna,
that seem destitute of a lining membrane, and contain only a thick grayish-white fluid ; and
partly of an intervening parenchyma, consisting of cells in various stages of development.
In the Human adult, there is a great predominance of nuclei, which seem as if they did not
attain their full development; but in Ruminant animals, and in the Human subject in early
life, the cells are more or less developed, and then resemble the ordinary lymph-corpuscles
in size and appearance. The Lymphatics are of large size, like those of the Spleen ; and
probably convey away the matter which has been elaborated by these organs, that it may be
mingled with that which is being taken up and prepared by other parts of the Absorbent
system. The Supra-Renal capsules attain a very large size early in fcetal life, surpassing
the true Kidneys in dimension, up to the tenth or twelfth week: but they afterwards dimi-
nish relatively to the latter, and are evidently subordinate organs during the whole remainder
of life.

It does not seem unlikely that these bodies, like the Spleen, have a double
function ; and that, besides participating in the general actions of the Absorb-
ent glandulse, they may serve as a diverticulum tor the Renal circulation, when
from any cause the secreting function of the Kidneys is retarded or checked,
and the movement of blood through them is stagnated.

687. The Thymus Gland is another body which seems referrible to the
same group ; having all the essential characters of a true gland, save an excre-
tory duct; and its function being evidently connected, during the early period
of life at least, with the elaboration of nutritive matter, which is to be re-
introduced into the circulating current.

a. Its elementary structure may be best understood from the simple form it presents when
it is first capable of being distinguished in the embryo. It then consists of a single tube,
closed at both ends, and filled with granular matter ; and its subsequent development consists

[Fig. 209.

A section of the Thymus gland at the eighth month, showing its anatomy ; from a preparation of
Sir A. Cooper's; 1, the cervical portions of the gland; the independence of the two lateral glands is
well marked; 2, secretory follicles seen upon the surface of the section; these are observed in all
parts of the section ; 3, 3, the pores or openings of the secretory follicles and pouches ; they are seen
covering the whole internal surface of the great central cavity or reservoir. The continuity of the
reservoir in the lower or thoracic portion of the gland with the cervical portion, is seen in the figure.]

44*

522 OF ABSORPTION AND SANGUIFICATION.

in the lateral growth of branching off-shoots from this central tubular axis. In its mature
state, therefore, it consists of an assemblage of glandular follicles, which are surrounded by
a plexus of blood-vessels; and these follicles all communicate with the central reservoir, from
which, however, there is no outlet. The Lymphatics are large, and communicate directly
with the Vena Cava ; but their immediate connection with the cavity of the Thymus body
has not yet been demonstrated. The cavities of the follicles contain a fluid in which a
number of corpuscles are found, giving it a granular appearance. These corpuscles are, for
the most part, in the condition of nuclei; but fully developed cells are found among them, at
the period when the function of this body seems most active. The chemical nature of the
contents at this period, closely resembles that of the ordinary proteine-compounds. — It has
been commonly stated, that the -Thymus attains its greatest development, in relation to the
rest of the body, during the latter part of foetal life ; and it has been considered as an organ
peculiarly connected with the embryonic condition. But this is a mistake; for the greatest
activity in the growth of this organ manifests itself in the Human infant, soon after birth;
and it is then, too, that its functional energy seems the greatest. This rapid state of growth,
however, soon subsides into one of less activity, which merely serves to keep up its propor-
tion to the rest of the body: and its increase usually ceases altogether at the age of about
two years. From that time, during a variable number of years, it remains stationary in
point of size; but, if the individual be adequately nourished, it gradually assumes the cha-
racter of a mass of fat, by the development of the corpuscles of its interior into fat-cells, which
secrete adipose matter from the blood. This change in its function is most remarkable in
hybernating Mammals; in which the development of the organ continues, even in an in-
creasing ratio, until the animal reaches adult age, when it includes a large quantity of fatty
matter. The same is the case, generally speaking, among Reptiles. It is an important fact
in the history of this organ, that it is not to be detected in Fishes; and does not appear to
exist, either in the tadpole state of the Batrachian reptiles, or in the Perennibranchiate group;
so that we may regard it as essentially connected with pulmonic respiration.*

688. Various facts lead to the conclusion, that the function of the Thymus,
at the period of its highest development, is that of elaborating and storing up
nutritive materials, to supply the demand which is peculiarly active during the
early period of extra-uterine life. The elaborating action probably corresponds
with that which is exerted by the glands of the Absorbent system ; and the
product, as in the preceding cases, seems to be conveyed away by the lymph-
atics. The provision of a store of nutritive matter seems a most valuable one,
under the circumstances in which it is met with ; the waste being more rapid
and variable than in adults, and the supply not constant. Thus it has been
noticed that, in over-driven lambs, the thymus soon shrinks remarkably ; but
that it becomes as quickly distended again, during rest and plentiful nourish-
ment. As the demand becomes less energetic, and as the supplies furnished
by other organs become more adequate to meet it, the Thymus diminishes in
size, and no longer performs the same function. It then obviously serves to
provide a store of material, not for the nutrition of the body, but for the re-
spiratory process, when this has to be carried on for long periods — as in hy-
bernating Mammals and in Reptiles — without a fresh supply of food. — It is
possible, that the Thymus gland may further stand in the same relation to the
Lungs, as the Spleen to the Liver, and the Supra-Renal capsules to the Kid-
neys ; that is, as a diverticulum for the blood transmitted through the bron-
chial arteries (which are the nutritive vessels of the Lungs), before the Lungs
acquire their full development in comparison with other organs, or when any
cause subsequently obstructs the circulation through their capillaries.

089. The Thyroid Gland bears a general analogy to the Thymus; but its
vesicles are distinct from each other, and do not communicate with any com-
mon reservoir. They are surrounded, like the vesicles of the true glands,
with a minute capillary plexus; and in the1 fluid they contain, numerous cor-
puscles are found suspended, Avhich appear to be cell-nuclei, in a state of
more or less advanced development. This body is supplied with arteries of
considerable size; and with peculiarly large lymphatics. Though propor-

* See Mr. Simon's admirable Prize Essay on the Thymus Gland.

THYROID GLAND. ASSIMILATING GLANDS IN GENERAL. 523

tionably larger in the foetus than in the adult, it remains of considerable size
during the whole of life. It appears, from the recent inquiries of Mr. Simon,*
that a Thyroid gland, or some organ representing it in place and office, exists
in all Vertebrated animals. It presents its simplest form in the class of Fishes ;
in some of which it appears to consist merely of a plexus of capillary ves-
sels, connected with the origin of the cerebral vessels, and capable, by its dis-
tensibility, of relieving the latter, in case of any obstruction to the proper
movement of blood through them. In the higher forms of this organ, the
glandular structure, — consisting of closed vesicles over which the capillary
plexus is distributed, and of their cellular contents, — is superadded ; and the
organ then appears, like the Spleen, to be destined for two different uses ;
namely, to serve as a diver ticulurfi, to the Cerebral circulation ; and to aid in
the elaboration of nutritive matter, which is taken up by the Absorbent sys-
tem, and which is again poured by it into the general current of the circula-
tion.

690. Thus the Spleen, the Supra-Renal Capsules, the Thymus Gland, and
the Thyroid Gland, all seem to share in the preparation of the nutritive ma-
terials of the blood, along with the ordinary glandulse of the Absorbent system.
In fact, we may regard them all as together constituting an apparatus, which
is precisely analogous to that of the ordinary glands, but of which the element-
ary parts are scattered through the body, instead of being collected into one
compact structure. Thus if we could imagine any tubular gland, such as the
Kidney or the Testis, to be unravelled, and its convoluted tubuli to be spread
through the system, yet all discharging their contents by a common outlet, we
should have no unapt representation of the Lymphatic portion of the Absorb-
ent system. Its function appears to be, to separate the crude Albuminous
matter from the blood, to subject it to an elaborating action performed by the
epithelium-cells lining the tubes, and then to pour forth this elaborated pro-
duct,— not as an excretion to be carried out of the body, — but (in conjunction
with that, which has been newly taken in by the Lacteal portion of the sys-
tem, and which has undergone elaboration by its glandulae), into the blood-
vessels, which are to convey it to the different parts of the body where it is
to be appropriated. The four bodies we have been just considering, appear
to be, so far as their glandular function is concerned, appendages to this sys-
tem. Their uses as diverticula to the circulation through other organs, render
them liable to occasional distention with blood; and it seems determined that
this blood shall not lie useless, but shall be subservient to the action in ques-
tion ; the gland-cells that line the cavities of the organ withdrawing certain
constituents of the blood, to restore them, through the Lymphatic system, in
a state of more complete preparation for the operations of Nutrition. Their
function is very probably vicarious ; that is, the determination of blood is
greatest (through the state of the other organs) at one time to one of these bodies,
and at another time to another. Hence the effects of the loss of any one of
them are not serious ; as the others are enabled in great degree to discharge
its duty.

4. — Composition and Properties of the Chyle and Lymph.

691. The chief chemical difference between the Chyle and the Lymph,
consists in the much smaller proportion of solid matter in the latter, and in the
almost entire absence of fat, which is an important constituent of the former.
This is well shown in the following comparative analyses, performed by Dr.
G. O. Rees, of the fluids obtained from the lacteal and lymphatic vessels of a

* Philosophical Transactions, 1844.

524 OF ABSORPTION AND SANG-UIFICATION.

donkey, previously to their entrance into the thoracic duct: the animal having
had a full meal seven hours before its death.

CHYLE. LYMPH.

Welter 90-237 95-536

Albuminous matter (eoagulable by heat) . . . 3-516 1-200

Fibrinous matter (spontaneously coagulable) . . . 0-370 0-120

Animal extractive matter, soluble in water and alcohol' . 0-332 0-240

Animal extractive matter, soluble in water only . . 1"233 1.319

Fatty matter ......... 3'601 a trace.

Salts; — Alkaline chloride, sulphate and carbonate, with traces of

alkaline phosphate, oxide of iron .... 0-711 0-585

100-000 100-000

The Lymph obtained from the neck of a horse has been recently analyzed by
Nasse, with nearly the same result. He found it to contain 95 per cent, of
•water; and the 5 per cent, of solid matter was chiefly composed of albumen
and fibrine, with watery extractive, — scarcely a trace of fat being to be found.
The proportions of saline matter were found to be remarkably coincident with
those which exist in the serum of the blood; as might be expected from the
fact, that the fluid portion of the lymph must have its origin in that which has
transuded through the blood-vessels : the absolute quantity, however, is rather
less. — A similar analysis of the Chyle of a cat by Nasse, has given results
very closely correspondent with that of Dr. Rees; for the proportion of water
was 90'5 per cent. ; and of the 9'5 parts of solid matter, the albumen, fibrine,
and extractive amounted to more than 5, and the fat to more than 3 parts. —
Dr. Rees has also analyzed the fluid of the Thoracic duct of Man ; and found
it to consist of 90'48 per cent, of water, 7'08 parts of albumen and fibrine,
1'08 parts of aqueous and alcoholic extractive, and 0'92 of fatty matter, with
Q'44 per. cent, of salines. Thus the composition of this fluid would seem to
resemble that of the Lymph, rather than that of the Chyle ; the proportion of
the fatty to that of the albuminous matter being very small. This, however,
might have been very probably due to the circumstance, that the subject from
which the fluid was obtained (an executed criminal) had eaten but little for
some hours before his death.

692. The characters of the Chyle drawn from the larger absorbent trunks,
near their entrance into the Receptaculum Chyli, are very different, however,
from those of the fluid as first absorbed into the Lacteals ; for during its
passage through these vessels, and their ganglia or glands, it undergoes
important alterations, which gradually assimilate it to Blood. The chyle
drawn from the lacteals that traverse the intestinal walls, contains Albumen in
a state of complete solution ; but it is generally destitute of the power of co-
agulation, no Fibrine being present in it. The Salts, also, are completely
dissolved; but the Oily matter presents itself in the form of globules of varia-
ble size.* It is generally supposed, that the milky colour of the chyle is
owing to these; but Mr. Gulliver has recently pointed outt that it is really due
to an immense multitude of far more minute particles, which he describes as
forming the molecular base of the chyle. These molecules are most abundant
in rich, milky, opaque chyle ; and in poorer chyle, which is semi-transparent
or opaline, the particles float thinly or separately in the transparent fluid, and
often exhibit the vivid motions common to the most minute molecules of vari-
ous substances. Such is their minuteness, that, even with the best instru-

* These oily globules are more abundant in the Chyle of Man and of the Carnivora, than
jn that of the Herbivora : their diameter has been observed to vary from l-25,000th to l-2000th
of an inch.

t Dublin Medical Press, Jan. 1, 1840, and Gerber's General Anatomy, Appendix, p. 88.

CHARACTERS AND COMPOSITION OF CHYLE. ' 525

merits, it is impossible to form an exact appreciation either of their form or
their dimensions. They seem, however, to be generally spherical; and their
diameter may be estimated at between 1 -36,000th and 1 -24,000th of an inch.
Their chemical nature is as yet uncertain : they are remarkable for their un-
changeableness, when subjected to the action of numerous re-agents; which
quickly affect the proper Chyle-corpuscles; and they are readily soluble in
Ether, the addition of which causes the whole molecular base instantly to dis-
appear, not a particle of it remaining; whence it may be inferred that they
consist of oily or fatty matter. The milky colour, which the serum of blood
sometimes exhibits, is due to an admixture of this molecular base with the
circulating fluid ; it is most common in young animals that are suckling ; but
it is not uncommon in adults, and is not to be attributed to an absorption of
milk into the chyle, as the physical properties of the two are quite different.
(See § 697, e.)

693. During the passage of the Chyle through the absorbents on the intes-
tinal edge of the Mesentery, towards the Mesenteric Glands, its character
changes in several important particulars. The presence of Fibrine begins to
manifest itself, by the slight coagulability of the fluid when withdrawn from
the vessels ; and while this ingredient increases, the Albumen and the Oil-
globules gradually diminish in amount. The Chyle drawn from the neigh-
bourhood of the mesenteric glands exhibits the Corpuscles regarded as cha-
racteristic of that fluid ; these are peculiarly abundant in the fluid drawn from
the glands themselves ; and they are constantly found in it, through its whole
subsequent course. The Chyle-corpuscles are much larger than the mole-
cules just described, and an examination of their character presents no diffi-
culty. Their diameter varies from 1-71 10th to 1 -2600th of an inch ; the
average being about l-4600th. They are usually minutely granulated on the
surface, seldom exhibiting any nuclei, even when treated with acetic acid ; but
sometimes three or four central particles may be distinguished within them.
— During the passage of the Chyle through the mesenteric glands, a further
increase in the proportion of Fibrine takes place ; and the resemblance of
the fluid to Blood becomes more apparent. The Chyle drawn from the vessels
intermediate between these and the central duct, possesses a pale reddish-
yellow colour; and, when allowed to stand for a time, undergoes a regular
coagulation, separating into clot and serum. The former is a consistent gela-
tinous mass, which, when examined with the microscope, is found to include
the Chyle-corpuscles, each of them being surrounded by a delicate film of
oil: the Fibrine of which it is principally composed, differs remarkably from
that of the blood, in its inferior tendency to putrefaction ; whence it may be
inferred that it has not yet undergone its complete vitalization. The serum
contains the Albumen and Salts in solution, arid a proportion of the Chyle-
corpuscles suspended in it. It is curious, however, that considerable differ-
ences in the perfection of the coagulation, and in its duration, should present
themselves in different experiments. Sometimes the chyle sets into a jelly-
like mass, which, without any separation into coagulum and serum, liquefies
again at the end of half an hour, and remains in this state. This change takes
place in the true coagulum also, if it be kept moist for a sufficient length of
time. The Chyle from the Receptaculum and Thoracic Duct coagulates
quickly, often almost instantaneously; and few or none of the corpuscles re-
main in the serum. — It is to be remembered that the Lacteals are the Lym-
phatics of the intestinal walls and mesentery ; performing that function of
Interstitial Absorption which is elsewhere accomplished by vessels that are
not concerned in the introduction of alimentary substances from without.
During the intervals of digestion, they contain a fluid which is in all respects
conformable to the Lymph of the Lymphatic trunks.

526 OF ABSORPTION AND SANGUIFICATION.

a. The fluid drawn from the Thoracic Duct, and from the Absorbent vessels which empty
their contents into it. is frequently observed to present a decided red tinge, which increases
on exposure to the air. This tinge is due to the presence of true Blood-corpuscles; but
these are somewhat modified in form and size, being a little smaller than the ordinary Blood-
discs, and frequently angular, granulated, or indented at the edges. By Mr. Lane* it is stated
that this intermixture is accidental ; and that it results from the absorption of Blood-particles
into the Lymphatics, at the points where the latter are divided, in making the sections ne-
cessary to expose the centres of the Absorbent system; and he mentions a striking fact in
illustration of his view. He considers that the alteration in the character of the corpuscles
is due to the action of the Chyle on the Blood, since many other fluids will produce analogous
eifects; and he states that, shortly after a flow of chyle into the blood, a large number of such
altered discs may be seen in the circulating fluid. On the other hand, Mr. Gulliver and
several eminent observers, regard these blood-discs as true constituents of the fluid of the
absorbents ; and suppose that they are in process of formation. Reasons have been given,
however, for the belief, that the red Blood-discs are not formed from the Chyle-corpuscles;
so that Mr. Lane's view is probably the correct one. Even if the Blood-discs are not intro-
duced into the Lymphatics during the operation of exposing the Thoracic Duct, it may not
be considered as improbable that, in those animals in which the Lymphatics have several
communications with the veins, they should naturally obtain an entrance in various parts of
the system. Such communications, according to Gerber, decidedly exist in the Horse ; and
it is in the Chyle of that animal, that the rosy tint, and the Blood-corpuscles which occasion
it, have been chiefly observed. — The following table, slightly modified from that of Gerber,
presents in a concise form, a view of the relative proportions of the three chief ingredients
in the Chyle, in different parts of the absorbent system, and thus gives an idea of its advance
in the process of assimilation.

In the afferent or peripheral fFat, in maximum quantity (numerous fat or oil globules).

Lacteals (from the Intes- J Albumen in minimum quantity.

tines to the Mesenteric | Few or no Chyle-corpuscles.

glands). (Fibrine almost entire wanting.

In the efferent or central f Fat, in medium quantity (fewer oil globules).

Lacteals (from the Mesen- j Albumen, in maximum quantity.

teric glands to the Thoracic ] Chyle-corpuscles very numerous, but imperfectly developed.

Duct). [ Fibrine in medium quantity.

(Tat, in minimum quantity (fewer or no oil-globules).

i \ T"I • TV I Albumen, in medium quantity.

in the llioracic Duct. < ,-,, ,. .

I Chyle-corpuscles numerous, and more distinctly cellular.

^ Fibrine in maximum quantity.

694. The aspect of the Lymph greatly differs from that of the Chyle, the
former being nearly transparent, whilst the latter is opaque or opalescent; and
this difference is readily accounted for, when the assistance of the microscope
is sought, by the entire absence from the Lymph of that molecular base
which is so abundant in the Chyle. A considerable number of corpuscles
are generally present in it; and these seem to correspond in all respects with
the white or colourless corpuscles of the Blood (§ 151). Their amount,
however, is extremely variable ; as is also that of the oil-globules, which
sometimes occur, whilst in other instances none can be discovered. Lymph
coagulates like chyle; a colourless clot being formed, which incloses the
greater part of the corpuscles.

695. The fluid drawn from the Thoracic Duct, consisting as it does of an
admixture of Chyle and Lymph, will probably vary in its character and com-
position, according to the predominance of the former, or of the latter, of these
fluids. It may be noticed, however, that the floating corpuscles have a more
distinctly cellular character than have those of the chyle and lymph; and
that they are of larger size, their diameter usually ranging from about 1 -2600th
to l-2900th of an inch. In these particulars, they correspond with the Colour-
less corpuscles of (he Blood ; as also in the change they exhibit on the action
of acetic acid, which brings into view three or four large central particles.
Some observations have been recently made by Bidder, on the amount of

* Cyclopaedia of Anatomy and Physiology, vol. iii. p. 220.

PHYSICAL AND VITAL PROPERTIES OF THE BLOOD. 527

liquid which flows through the Thoracic duct into the venous system; and if
any inference can be fairly drawn from the measurement of the quantity de-
livered in the" course of a few minutes, it would appear that the total amount
thus transmitted in one day is nearly or quite equal to the entire mass of the
blood. At any rate, it so far exceeds the amount of liquid ingested, that we
must believe a large portion of it to be derived from the circulating current, —
having been withdrawn from it for a time, to be again delivered into its stream,
after having undergone the requisite elaboration.

5. — Physical and Vital Properties of the Blood.

696. Having now traced the steps, by which the Blood is elaborated and
prepared for circulation through the body, and having formerly inquired into
the characters of its chief constituents (Chap. HI.), we have now to consider
the fluid as a whole, to study the usual proportions of these constituents, and
the properties which they impart to it. — The Blood, whilst circulating in the
living vessels, may be seen to consist of a transparent, nearly colourless,
liquid, termed Liquor Sanguinis; in which the Red Corpuscles, from which
the Blood of Vertebrated animals derives its peculiar hue, as well as the White
or Colourless corpuscles, are freely suspended and carried along by the cur-
rent.— On the other hand, when the Blood has been drawn from the body,
and is allowed to remain at rest, a spontaneous coagulation takes place, sepa-
rating it into Crassamentum and Serum. The Crassamentum or Clot is
composed of a network of Fibrine, in the meshes of which the Corpuscles,
both red and colourless, are involved, together with a certain amount of serous
fluid. The Serum, which is the same with the Liquor Sanguinis deprived of
its Fibrine, coagulates by heat, and is therefore known to contain Albumen ;
and if it be exposed to a high temperature, sufficient to decompose the animal
matter, a considerable amount of earthy and alkaline Salts remains. — Thus
we have four principal components in the Blood; namely, Fibrine, Albumen,
Corpuscles, and Saline matter. In the circulating blood, they are thus com-
bined : —

Fibrine }

Albumen > In solution, forming Liquor Sanguinis.

Salts )

Corpuscles, — suspended in Liquor Sanguinis.

But in coagulated blood, they are combined as follows: —

i rinc i Crassamentum or Clot.
Corpuscles 3

c > Remaining in solution, forming Serum.

Ill the blood of Man and the higher Vertebrata, the Colourless Corpuscles
usually bear so small a proportion to the Red, that they have until recently
escaped notice. In Reptiles, however, they attract attention, from their
marked difference in size and form, even whilst the blood is moving through
the capillaries; and they are the more easily watched, owing to the compara-
tively small number of the Red Corpuscles in those animals. The blood of
the Invertebrata is usually pale, and contains very few red corpuscles ; indeed
they would seem to be absent altogether in the lower Articulata and Mollusca.
On the other hand, the colourless corpuscles are frequently very numerous,
especially during the periods of most active growth. The blood of these
animals may be likened, therefore, in many respects to the Lymph and Chyle
of the Vertebrata; and the resemblance is the more close, as there is no

528

OF ABSORPTION AND SANGUIFICATION.

distinction among the Invertebrata between the absorbent and sanguiferous
vessels.

697. The proportion of the several components of Blood is subject to con-
siderable variations, within the limits of health. Some of these variations
may be habitual, depending upon the constitution of the individual, his diet,
mode of life, &c.; whilst others are probably referrible to the period at which
the last meal was taken, and the amount of bodily exertion made within a
short time previous to the analysis.

a. The discordance in the results obtained by different experimenters is doubtless owing
in part to the diversity in their methods of analysis;* but even where the same method is
employed, a wide diversity is apparent ; as in the analysis of MM. Becquerel and Rodier.
As there is a tolerably constant difference between the Male and the Female, it will be de-
sirable to class them separately ; and the results of some of the most recent and trustworthy
analyses of each will be brought together for the sake of comparison. — The analyses of M.
Lecanu were made on the blood of two stout and healthy men ; whilst those of MM. Bec-
querel and Rodier give the maximum, minimum, and mean amount, of each ingredient in
the blood of eleven healthy men, between the ages of 21 and 66 years.

Lecanu.

Water

Fibrine

Corpuscles

Albumen

Extractive mat-
ters, Salts, and
loss

Fatty matters .

i.

n.

Mean.

.

. . . 780-2

785-6

779-0

t t

... 2-1

3-6

2-2

es .

. . . 133-0

119-6

141-1

n .

66-3

71-5

69-4

14-6
3-8

13-1
6-6

MM. Eecquerd and Rodier.
Mean. Maxima. Minima.

779-0
2-2
141-1
69-4

800-0
3-5
152-0
73-0

760-0
1-5
131-0
62-0

6-8

8-0

5-0

1-5

3-2

1-0

1000-0 1000-0 1000.0

Simon.

791-9

2-0

114-3

75-6

14-2

2-0
1000-0

Nasse.

798-4

2-3

116-5

74-2

6-6
2-0

1000-0

The following table gives the results of similar analyses on the blood of Females; those
of MM. Becquerel and Rodier being made upon eight healthy subjects between the ages of
22 and 58 years.

Water

Fibrine ....
Corpuscles .

Albumen ....
Extractive matters and Salts
Fatty matters

MM. Becquerel and Rodier.

Mean. Maxima. Minima.

791-1 813-0

2-2 2-5

127-2 137-5

70-5 75-5

7-4 8-5

1-6 2-9

Simon.

1000-0

1000-0

6. Of the Fatty matters of the Blood, a portion seems to correspond with the constituents
of ordinary Fat; another portion seems identical with the Chokstcrine, or Biliary Fat ; whilst
another contains Phosphorus, and seems allied to the fatty acids of Nervous matter (§ 249).

c. Of the nature of the substances classed under the head of Extractive, very little is
known. It has been lately asserted, that a portion of them consists of binoxidc of proteino
(§ 11G, a) ; but as to the actual existence of this substance, there is still much doubt. Under
the genera! designation of extractive are arranged the " ill-defined animal principle*,'1 which
may include various substances in a state of change or disintegration, that are being elimi-
nated from the blood by the processes of Excretion.

d. The Saline constituents of the Blood, obtained by drying and incinerating the -whole
mass, usually amount to between 6 and 7 parts in 1000. More than half their total quan-
tity is composed of the Chlorides of Sodium and Potassium ; and the remainder is made up
of the tribasic Phosphate of Soda, the Phosphates of Lime and Magnesia, Sulphate of Soda,

* Thus the small amount of Salts, in the analysis of Nassc and of MM. Becquerel and
Rodier, as compared with those of MM. Lecanu and Simon, appears due to the fact that the
former express only the free salts, whilst the latter include those which are in combination
with the organic constituents.

USES OF THE SEVERAL CONSTITUENTS OF THE BLOOD. 529

and a little Phosphate and Oxide of Iron. Of these, the chief part are dissolved in the
Serum ; but the Earthy Phosphates, which are insoluble by themselves, are probably com-
bined with the Protein e-compounds (§ 113); and the iron is contained, chiefly or entirely,
in the red corpuscles. — It is difficult to speak with certainty, from the examination of the
ashes of the blood, as to the state of the Saline constituents of the circulating fluid. Thus
the Serum has an alkaline reaction ; and this has been supposed to be due to the presence
of alkaline Carbonates. Moreover the presence of the Lactates of potass and soda has been
usually asserted. On the other hand, the recent analyses of Enderlin, which have been con-
firmed by Liebig, would indicate that the alkaline reaction is entirely due to the presence of
the tribasic Phosphate of soda ; and that no alkaline carbonates or lactates exist in the blood.
This discrepancy seems partly due to the mode of analysis employed; for it has been lately
pointed out by Dr. G. O. Kecs,* that although the ashes of the entire mass of blood do not
effervesce on the addition of an acid, effervescence takes place when acid is added to the
ashes of the serum, showing the existence in it, either of alkaline Carbonates, or of Lactates,
which have been reduced to the state of Carbonates by incineration. — It appears that, when
the entire mass of blood is incinerated, enough phosphoric acid is produced from the phos-
phorized fats, to neutralize the alkaline carbonates, and thus to prevent their presence from
being recognized. There can be no doubt, however, that the tribasic Phosphate of Soda
exists as such in the blood, and contributes to its alkaline reaction ; and it appears to confer
upon the liquid a special power of absorbing Carbonic Acid.

e. Some very interesting observations upon the state of the blood soon after a meal, have
been recently made by Drs. Buchanan and R. D. Thompson. They are confirmatory of the
belief generally entertained, that the milky appearance, sometimes presented by the Serum,
is due to the admixture of Chyle. When a full meal containing oily matter is taken after
a long fast, and a small quantity of blood is drawn previously to the meal and at intervals
subsequently, the Serum, though quite limpid in the blood first drawn, shows an incipient
turbidity about half an hour afterwards^ this turbidity increases for about six hours subse-
quently, after which it usually begins to disappear. The period at which the discoloration
is the greatest, however, and the length of time during which it continues, vary according
to the kind and quality of the food, and the state of the digestive functions. Neither starch,
nor sugar, nor proteine-compounds, alone or combined, occasion this opacity in the chyle ;
but it seems entirely dependent upon an admixture of oleaginous matter with the food.
There are few ordinary meals, however, from which such matter is altogether excluded.
When such milky serum is examined with the Microscope, the opacity is found to be due
to the presence of an immense number of exceedingly minute granules, resembling in ap-
pearance those which form the " molecular base" of the chyle. They seem to be composed
of two chemically-distinct substances; for when the milky serum is agitated with ether, a
part is dissolved, whilst another portion remains suspended ; and this latter is soluble in
caustic potass. The former, therefore, appears to be identical with the "molecular base" of
the Chyle, and to be of an oily or fatty nature ; whilst the latter belongs to the proteine-
compounds. The Crassamentum of such blood often exhibits a pellucid fibrinous crust,
sometimes interspersed with white dots ; and this seems to consist of an imperfectly-assi-
milated proteine-compound, analogous to that found in the serum. The quantity of this varies
according to the amount of the proteine-compounds present in thefood.f — It is evident from
these experiments, that the assimilating process is by no means completed, at the time of
the passage of the Chyle into the Blood ; and it would seem that the return of the trans-
parency of the serum is due to the gradual removal of the superfluous fatty matter through
the respiratory process, whilst the proteine-compound, of which part of the granules are
composed, is gradually reduced to a state of perfect solution.

/. The occasional presence of Sugar, even in healthy blood, when a large quantity of
saccharine matter exists in the food, appears to be now well established. But it seems to
be commonly transformed, either into lactic acid, or into fatty matter, previously to its recep-
tion into the circulating current. This last transformation is partly effected through the
agency of the Bile ; as will be shown hereafter (§ 835).

698. It cannot be doubted that, upon the due admixture in the Blood of all
these elements, the regular performance of its actions is dependent. In regard
to its physical properties merely, it is easily shown that a slight alteration may
produce the most injurious consequences; for a certain degree of viscidity has
been found (by the experiments of Poisseuille) to favour the passage of fluid
through capillary tubes; and thus, if the viscidity of the blood be diminished
by a loss of part of its fibrine, stagnation of the current, and extravasation of a

* On the Analysis of the Blood and Urine, p. 30.
f Medical Gazette, Oct. 10, 1845.
45

530 OF ABSORPTION AND SANGUIFICATION.

portion of the contents of the vessels, will be the result. This has been fully
proved by the numerous experiments of Magendie ; and the fact is one of very
important Pathological applications (§ 707, />). But the vital properties of the
fluid are still more immediately dependent upon the Fibrine it contains ; since,
as we have seen reason to believe, it is the material which is most completely
prepared for organization, and which supplies what is requisite for the nutri-
tion of the larger proportion of the solid tissues of the body. It is, therefore,
continually being withdrawn from the blood by the nutritive operations; and
the demand appears to be supplied, in part by the influx of Fibrine that has
been prepared in the Absorbent system, and in part by the continued trans-
formation of Albumen, which takes place during the circulation of the Blood,
and of which we have seen reason to believe that the Colourless Corpuscles
are the instruments (§§ 153 — 159). — The Albumen of the Blood is the raw
material, at the expense of which not only the Fibrine, but many other sub-
stances, are generated during the nutritive process. All the Albuminous com-
pounds of the Secretions, the Horny matter of the Epidermic tissues, the
Gelatine of the simple Fibrous tissues, and the Haematine of *the Red Cor-
puscles, may be regarded as almost certainly produced by the transformation
of the Albumen of the Blood ; and a continual supply of this from the food
is therefore requisite to preserve the due proportion in the circulating fluid. —
The Red Corpuscles appear to be more connected with the function of Respira-
tion than with that of Nutrition (§ 150); and the stimulating action of Arterial
blood, especially upon the Nervous and Muscular tissues, appears to depend
upon their presence. It is by no means impossible that their peculiar con-
nection with the activity of the latter may be dependent upon an actual
Chemical relation between their contents and the red matter of the Ganglionic
corpuscles (§ 245) ; and that a part of their function may be, to prepare the
substance which is afterwards to be appropriated as a peculiar nutritive prin-
ciple, by the active instruments of Nervous operations. It appears from the
experiments of Dieffenbach on transfusion, that the Red Corpuscles are more
effectual as stimuli to the Heart's action, than is any other constituent of the
blood. The rapidity with which they may be decomposed and reconstituted,
is made remarkably evident by the experiments of Magendie; who found that,
when the Blood of one animal was injected into the veins of another having
discs of very different size and form (care being taken to prevent the coagula-
tion of the Fibrine during the operation), the original Red particles soon dis-
appeared, and were replaced by those characteristic of the species, in whose
veins the fluid was circulating. — The use of the Saline matter is evidently in
part to supply the mineral materials, requisite for the generation of the tissues,
and for the production of the various secretions. It is by the Saline and
Albuminous matters in conjunction, that the specific gravity of the Liquor
Sanguinis is kept up to the point, at which it is equivalent to that of the con-
tents of the Red corpuscles; and it is only in this condition that the latter
present their proper characters. Thus it has been shown by Dr. G. O. Rees,
that when the quantity of water in the Liquor Sanguinis has been reduced by
copious perspirations or othor similar causes, the corpuscles are thin, and very
like those whose contents have exuded by exosmose into a denser liquid
around (§ 1-13). On tho other hand, if the Liquor Sanguinis be diluted by the
withdrawal of blood and the injection of an equivalent quantity of water, the
serum speedily becomes tinged with the colouring matter of the corpuscles;
apparently in consequence of a rupture of some of the cells, by endosmose
from the circumambient liquid, now reduced to a lower specific gravity than
that of their contents. — The Fatty matters of the Blood are evidently derived
from the food, either directly, or by the transformation of its farinaceous in-
gredients ; and they are chiefly appropriated to the maintenance of the coin-

COAGULATION OF THE BLOOD. 531

bustive process. That which may be superfluous, is either deposited in the
cells of Adipose tissue, or it is eliminated by the Liver, the Sebaceous follicles
of the Skin, and (in the nursing female) by the Mammary glands. How the
peculiar Phosphorizcd Fats of the Blood are formed, — whether by the con-
tinuation of the azotized and phosphorized materials with ordinary fat, or
by the metamorphosis of albuminous matter, — cannot be said to be yet de-
termined.

699. When the Blood is drawn from the body, and left to itself, its organic
elements speedily undergo a new arrangement. The Fibrine coagulates, and
separates itself from the fluid in which it was previously dissolved ; and during
its coagulation it attracts the Red particles ; these are included in areolac or
meshes of the Clot, the substance of which has a tendency to assume a fibrous
arrangement (§ 118) ; and they usually group themselves together in columnar
masses, resembling piles of money. The Coagulum or clot becomes dense,
in proportion to the amount of the Fibrine it contains ; and the Albuminous and
Saline matter still dissolved in the water are separated from it, constituting the
Serum. This separation will not occur, however, if the coagulation take
place in a shallow vessel; nor if the amount of Fibrine should be small, or
its vitality low. A homogeneous mass, deficient in firmness, presents itself
under such circumstances; though the solid part of this may pass into a state
of more complete condensation, after the lapse of a certain time. — That the
coagulation is due to the Fibrine, and that the Red particles are merely passive
in the process, appears from several considerations. A microscopical exami-
nation of the Clot shows, that it has the same texture with Fibrine, when
coagulating by itself; the Corpuscles clustering together in the interspaces of
the network, and not being uniformly diffused through the whole mass. Their
Specific Gravity being greater than that of tf*e Fibrine, they are usually most
abundant at the lower part of the clot ; and the upper surface is sometimes
nearly colourless, especially when the coagulation has taken place slowly ; yet
this upper part is much firmer than the under, showing that the Fibrine alone
is the consolidating agent. — This has been proved to demonstration by an
experiment of Miiller's. He placed the blood of a Frog, diluted with water
(or still better with a very thin syrup) on a paper filter, of sufficiently fine
texture to keep back the Corpuscles ; and the Liquor Sanguinis, having passed
through the filter completely unmixed with them, presented a distinct coagu-
lum, although from the diluted state of the fluid, this did not possess much
consistency. Owing to the more minute size of the Blood-discs of warm-
blooded animals, this experiment cannot be so readily performed with their
blood. The sole agency of the Fibrine in coagulation is very easily proved
in another way. If fresh drawn blood be continually stirred with a stick, the
Fribrine will adhere to it in strings during its coagulation ; and the Red parti-
cles will be left suspended in the serum, without the slightest tendency to
coagulate. Moreover, if a solution of any salt, that has the property of re-
tarding the coagulation (such as carbonate of potash or sulphate of soda), be
added to the blood, the Corpuscles will have time to sink to the lower stratum
of the fluid, before the clot is formed ; the greater part of the Coagulum is
then entirely colourless, and is found by the microscope to contain few or no
red particles.

700. That the Coagulation of the Blood is not, as some have supposed, a
proof of its death, but is rather an act of vitality, appears evident from what
has been already stated (§ 118) of the incipient organization which may be
detected even in an ordinary clot ; and still more from the fact that, if the
effusion of Fibrine take place upon a living surface, its coagulation is the first
act of its conversion into solid tissues possessing a high degree of vitality. It
is absurd to suppose that the Blood dies, in order to assume a higher form.

532 OF ABSORPTION AND SANGUIFICATION.

A complete demonstration of the truth of the Hunterian doctrine, that the
Blood might become organized, like plastic exudations of " coagulable lymph,"
has been lately afforded by the researches of Dr. Zvvicky, on the changes
occurring in the clots of blood which form in blood-vessels, above the points
where they have been tied. He has traced the successive stages of the meta-
morphosis of the coagulum into fibre-cellular tissue, and the formation of ves-
sels in its substance ; the whole process taking place exactly as in an inflam-
matory exudation, and the blood-corpuscles exerting no other influence upon
it, than that of slightly retarding it.

701. When the Blood is withdrawn from the body, however, its Coagula-
tion is the last act of its life ; for, if not within the influence of a living sur-
face, it soon passes into decomposition. Instances occasionally present
themselves, in which the Blood does not coagulate after death ; and in most
of these, there has been some sudden and violent shock to the Nervous sys-
tem, which has destroyed the vitality of solids and fluids alike. This is
generally the case in men and animals killed by lightning, or by strong elec-
tric shocks ; and in those poisoned by prussic acid, or whose life has been
destroyed by a blow on the epigastrium. It has also been observed in some
instances of rupture of the heart, or of a large aneurism near it; and a very
interesting phenomenon then not unfrequently presents itself, — the coagulation
of the Blood which has been effused into the pericardium (the effusion having
taken place during the last moments of life), whilst that in the vessels has re-
mained fluid. In several of the instances in which the blood has been found
uncoagulated in the vessels, many hours after death, a portion withdrawn from
the body has clotted; and Dr. Polli asserts that the complete absence of
coagulability is a phenomenon which has no real occurrence. During a long
course of researches on this subject, he has never yet met with an instance,
in which the blood, when left to itself, and duly protected from external
destructive influences, did not coagulate before becoming putrid, lie has
even more than once caused blood to coagulate, which had been taken in a
fluid state from the veins, thirty-six or forty-eight hours after death.* — It ap-
pears that simple arrestment of Nervous influence favours the coagulation of
the blood in the vessels ; clots being found in their trunks, within a few
minutes after the Brain and Spinal marrow have been broken down.

702. The length of time which elapses before Coagulation, and the degree
in which the clot solidifies, vary considerably ; in general, they are in the
inverse proportion to each other. Thus, if a large quantity of blood be with-
drawn from the vessels of an animal at the same time, or within short inter-
vals, the portions that last flow coagulate much more rapidly, but much less
firmly, than those first obtained. In blood drawn during Inflammatory states,
again, the coagulation is usually slow, but the clot is preternaturally firm ; espe-
cially at its upper part, where the Buffy coat (§ 704) or colourless stratum
of Fibrine, gradually contracts, and produces the cup, which is usually re-
garded as indicative of a high degree of Inflammation. Except under the
peculiar circumstances just stated, the Blood withdrawn from the body always
coagulates;! whether it be kept at rest or in motion; whether its temperature
be high or low ; and whether it be excluded from the air, or be admitted to
free contact with the atmosphere. The Coagulation may be accelerated or
retarded, however, by variation in these conditions. Thus, if the blood be
continually agitated in a bottle, its coagulation is delayed, though it will at last

* Rankings Half-Yearly Abstract, vol. ii. p. 337.

f £01 lie diseases may ]>rrli;i[).< \><- an exception ; non-coagulation of the Blood is said to be
characteristic of the Scurvy, but this is erroneous. In very severe forms of Typhus, the sumo
lias been stated to occur.

COAGULATION OF THE BLOOD. BUFFY COAT. 533

take place in shreds or insulated portions ; but that rest is not the cause of its
coagulation (as some have supposed), is proved by the fact that, if a portion
of blood be included between two ligatures in a living vessel, it will remain
fluid for a long time. Again, the coagulation is accelerated by moderate heat,
and retarded by cold; but it is not prevented by even extreme cold; for, if
blood be frozen immediately that it is drawn, it will coagulate on being thawed.
Moreover it is accelerated by exposure to air, but it is not prevented by com-
plete exclusion from it, as is proved by its taking place in a vacuum, or in a
shut sac wilbin the dead body: complete exclusion from the air, however,
retards the change ; as has been shown by causing Blood to flow into a ves-
sel containing oil, which will form an impervious coating on its surface, and
will occasion the coagulation to take place so slowly, that the Red particles
have time to subside, and the upper stratum of the clot is colourless.* A re-
markable case has been put on record by Dr. Polli, in which complete coagu-
lation of the blood did not take place until fifteen days after it had been with-
drawn from the body ; and fifteen days more elapsed before putrefaction
commenced. The upper four-fifths of the clot were colourless; the red cor-
puscles occupying only the lowest fifth. It is additionally remarkable, that
the patient (who was suffering under acute pneumonia) being bled very fre-
quently during the succeeding week, the blood gradually lost its indisposition
to coagulate.t An extrication of Carbonic acid usually takes place to a slight
degree during coagulation ; but this is not a constant occurrence ; and the
process is not prevented, even by agitating Carbonic acid with the Blood.

703. The proportions of Serum and Clot which present themselves after
coagulation, are liable to great variation, independently of the amount of the
several ingredients characteristic of each ; for the Coagulum may include not
only the Fibrine and Red particles, but also a large proportion of the Serum,
entangled as it were in its substance. This is particularly the case when the
coagulation is rapid ; and the clot then expels little or none of it by subse-
quent contraction. On the other hand, if the coagulation be slow, the parti-
cles of Fibrine seem to become more completely aggregated, the coagulum is
denser at first, and its density is greatly increased by subsequent contraction.
When a firm fresh clot is removed from the fluid in which it is immersed, its
concretion is found to continue for 24 or even 48 hours, serum being squeezed
out in drops upon its surface; and in order, therefore, to form a proper esti-
mate of the relative proportions of Crassamentum and Serum, the former
should be cut into slices, and laid upon bibulous paper, that the latter may be
pressed from it as completely as possible. — According to the experiments of
Mr. Thrackrah, Coagulation takes place sooner in metallic vessels than in
those of glass or earthenware, and the quantity of Serum separated is much
less; in one instance, the proportion of Serum to Clot was as 10 to 24?,
when the blood coagulated in a glass vessel ; whilst a portion of the same
Blood, coagulating in a pewter vessel, gave only 10 of Serum to 175 of Clot.
The Specific Gravity of Blood is no measure of its coagulating power; for a
high specific gravity may be due to an excess in the amount of globules,
which form the heaviest part of the blood ; and may be accompanied by a
diminution in the quantity of fibrine, which is the coagulating element.

704. The Crassamentum not unfrequently exhibits, in certain disordered
conditions of the Blood, a layer of Fibrine nearly free from colour; and this is
known as the Buffy Coat. The presence of this has been frequently re-
garded as a sign of the existence of Inflammation, occasioning an undue pre-
dominance of Fibrine; but this idea is far from being correct, since, as will pre-

' Babington in Medico-Chinirgical Transactions, vol. xvi.
f Mr. Paget's Report, in Brit, and For. Med. Rev., xix. p. 252.

45*

534

OF ABSORPTION AND SANGUIFICATION.

Fig. 210.

sently appear (§ 705), it may result from a very opposite condition of the
Blood. A similar colourless layer of Fibrine is always observable, when the
Coagulation of the blood is retarded by the addition of agents that have the
power of delaying it (§ 699) ; and since, in Inflammatory states of the system,
the blood is generally long in coagulating, it has been supposed that the sepa-
ration of the red particles is due to this cause alone. Dr. Alison,* however,
main tains that there must be an absolute tendency to separation between the
two components of the clot, in order to account for the phenomena sometimes
presented by it; and he adduces the two following reasons in support of this
view. " 1. The formation of the Bufly coat, though no doubt favoured or
rendered more complete by slow coagulation, is often observed in cases where
the coagulation is more rapid than usual; and the colouring matter is usually
observed to retire from the surface of the fluid in such cases, before any
coagulation has commenced. 2. The separation of the Fibrine from the
colouring matter in such cases takes place in films of blood, so thin as not to
admit of a stratum of the one being laid above the other; they separate from
each other laterally, and the films acquire a speckled or mottled appearance,
equally characteristic of the state of the blood with the buffy coat itself." —
It appears from the observations of Mr. Wharton Jones, that the red corpus-
cles of Inflammatory Blood have an
unusual attraction for each other, which
occasions their coalescence in piles and
masses; so that by this character, the
state of the Blood may be detected,
from the examination of no more than
a single drop of the fluid. Now if we
consider, in connection with this in-
crease in the mutual attraction of the
Blood-discs, the increase in the mutual
attraction of the particles of Fibrine
(which causes the coagulum of Inflam-
matory blood to be so much firmer and
more decidedly fibrous than that of the
healthy fluid), we have a cause suffi-
cient to explain the phenomena noticed
by Dr. Alison; without tile necessity
of resorting to the idea of an absolute
repulsion being present between the two
constituents. — It is in the Bufly Coat
of Inflammatory Blood, that we see
the clearest indications of organization
ever presented by the circulating fluid.
The fibrous network is frequently extremely distinct; and it commonly in-
i.-ludes a large number of White Corpuscles in its meshes. Sometimes,
indeed, according to the observations of Mr. Addison, it almost entirely con-
sists of these bodies. In its Chemical Composition, the bufly coat of Inflam-
matory blood appears to be peculiar; containing a larger or smaller amount
of the substance, readily soluble in boiling water, which is considered by
Mulder to be the Tritoxide of Proteine (§ 116, «).

705. When the Bull' arises from other causes, however, its appearance is
less characteristic. It appears from the researches of Andral, that the usual
condition of its production is an increase in the quantity of Fibrine in propor-
tion to the Red Corpuscles; and not a simple increase of Fibrine. When the

* Outlines of Physiology, 3d edition, p. 89.

The microscopic appearance of a drop of blood
in the inflammatory condition. The red corpus-
cles lose their circular form and adhere together ;
the white corpuscles remain apart, and are more
abundant than usual.

BUFFY COAT. PATHOLOGICAL CHANGES IN THE BLOOD. 535

Blood contains an excessive quantity of Fibrine. it coagulates slowly; thus
the blood of a patient labouring under Rheumatism coagulates more slowly
than that of one affected with Typhoid fever. The increase may occur in
two ways ; — either by an absolute increase in the Fibrine, the amount of the
corpuscles remaining unchanged, of not being augmented in the same pro-
portion ; — or by a diminution of the Corpuscles, the quantity of Fibrine re-
maining the same, or not diminishing in the same proportion. Hence in
severe Chlorosis, in which the latter condition is strongly developed, the buffy
coat may be as well marked, as in the severest Inflammation. Unless the
composition of the blood be altered in one of these two ways, it is stated by
Andral that the bufly coat is never formed; the influence of circumstances
which favour it, not being sufficient to produce it when acting alone. The
absence of these circumstances may prevent it, however, when it would other-
wise have been formed; thus, when the Blood flows slowly, the buff is not
properly produced; because the slow discharge gives one portion time to
coagulate before another; and only the blood last drawn furnishes the Fibrine
at the upper part of the vessel. Again, in a deep narrow vessel, the bufT will
form much more decidedly than in a broad shallow one ; because the thick-
ness of the Fibrinous crust will be greater.

6

6. — Pathological Changes in the Blood.

706. From the part which the Blood performs in the ordinary processes of
Nutrition, it cannot be doubted that it undergoes important alterations, when
these processes take place in an abnormal manner. These alterations must
be sometimes the causes, and sometimes the effects, of the morbid phenomena,
which constitute what we term the Disease. Thus, when some local cause,
affecting the solid tissues of a certain part of the body, produces Inflammation
in them, their normal relation to the blood is altered ; the consequence is, that
the Blood, in passing through them, undergoes a different set of changes from
those for which it is originally adapted ; and thus its own character under-
goes an alteration, which soon becomes evident throughout the whole mass of
the circulating fluid, and is, in its turn, the cause of morbid phenomena in
remote parts of the system. On the other hand, the strong analogy between
many Constitutional diseases, and the effects of poisonous agents introduced
into the Blood, appears clearly to point to the inference, that these diseases
are due to the action of some morbific matter, which has been directly intro-
duced into the current of the circulating fluid, and which has affected both its
physical and its vital properties.* Here, then, is a wide field for investiga-
tion, of which the surface can scarcely be said to be yet broken up, and
which must yield an abundant harvest to those who shall cultivate it with in-
telligence and zeal. The first and most complete series of connected re-
searches, which have been yet published, on the changes which the blood un-
dergoes in disease, are those of MM. Andral and Gavarret ;t these are confined

: This doctrine has been brought prominently forward, in a paper on Symmetrical Dis-
eases, read by Dr. William Buck! before the Medico-Chirurgical Society, Dec. 16, 1841. The
Author ingeniously proves, that the symmetry of many diseases (such as certain forms of
cutaneous eruptions, rheumatism, &c.) which do not immediately depend upon external
causes, necessarily involves the idea of the conveyance of the morbific agent in the circulating
fluid ; the palsy produced by lead is a very interesting example, in which the agent is known
to be mingled with the blood, and to be deposited in the parts affected, which are generally,
if not always, symmetrical.

I An account of these inquiries will be found in the Provincial Medical and Surgical
Journal for May, June, and July 1841; in the Annales des Sciences Naturelles, Dec. 1840,
and March 1841 ; and in the Ann. de Chimie, torn. Ixxv. They have since been published

536 OF ABSORPTION AND SANGUIFICATION.

to the alterations which take place in the proportions of the Organic elements
of tfie fluid. Another series of researches of great value, and in almost every
point confirmatory of the preceding, has been since made by MM. Becquerel
and Rodier;* and another by Dr. Karl Popp.t Numerous other less systematic
analyses have been made by various Chemists and Pathologists. The follow-
ing outline contains the general results of these. — It is, of course, necessary to
determine, in the first instance, what are the usual or normal proportions; and
the following may be estimated as the ordinary quantity of each element, in
1000 parts of healthy Blood: —

Fibrine from 2 to 3^

Corpuscles 110 ' 150

Solid matter of Serum . . . . " 72 " 85

707. Before entering upon the consideration of the alterations in the Blood,
which are effected by particular morbid states, it is requisite to notice the
results of two extraneous causes, usually operating in disease, which may affect
the proportions of its components. These are, Abstinence from food, and
Loss of Blood, as by Hemorrhage or Venesection. It has been commonly
supposed, that these causes have a tendency to diminish the proportion of all
the solid elements of the blood; but this is not the case; for they affect the
Corpuscles, chiefly or exclusively, the quantity of Fibrine and of the solids of
the Serum remaining nearly the same, unless the abstinence has been pro-
longed, or the loss of blood very considerable. — It is probably to the effects
of abstinence, that we are to attribute the general diminution of the solids of
the blood, which presents itself ii} most acute diseases; thus, on the average
of 120 cases, MM. Becquerel and Rodier found the average Specific Gravity
of defibrinated blood reduced from 1060 (in Men) and 1057'5 (in Women), to
1056 (in Men), and 1055 (in Women). The diminution in the proportion of
Corpuscles was well marked; that of the Albumen was much slighter; there
was on the whole a slight augmentation of Cholesterine and Phosphorized
Fat; and a marked increase in the Phosphates. The increase or diminution
of the Fibrine is entirely dependent (as we shall presently see) on the nature
of the disease. — The influence of Venesection in impoverishing the blood is
well shown in the following table of the mean composition of the fluid, at three
successive Venesections in ten persons : —

First Second Third

Bleeding. Bleeding. Bleeding.
Specific Gravity of defibrinated

Blood 1056 1053 1049-6

Water 793 807-7 823-1

Fibrine 3-5 3-8 3-4

Corpuscles 129-2 11O3 99-2

Albumen .... 65-0 63'7 64-f.
Extractive, free salts, and fatty

matters 9'4 S'5 9-5

Thus we see that repeated venesections render the blood more watery; but
this, chiefly by the diminution they produce in the amount of Corpuscles.
They slightly diminish the albumen and fatty matters; but they exert no per-
ceptible influence on the amount of Fibrine; — a point of the highest practical
importance.

a. The most important fact substantiated hy Andral, is one that had been previously sus-
pected,— the invariable increase in the quantity of Fibrine during acute Inflammatory all'ec-
tions; the increase being strictly proportional to the intensity of the Inflammation, and to the

in a separate form, under (lie title of "Essai d'Hematologie Pathologique.'' [See Transla-
tion by Drs. Meigs and Stillo, Phil. 1844.]

* Gazette Medicalc, 1844, Nos. 47 — 57. -j- Banking's Abstract, vol. iii. p. 306.

PATHOLOGICAL CHANGES IN THE BLOOD. 537

degree of symptomatic Fever accompanying it. "The augmentation of the quantity of
Fibrine is so certain a sign of Inflammation, that, if we find more than 5 parts of fibrine in
101 id, in tin- course of any disease, we may positively affirm that some local inflammation
exists." Several cases are mentioned, in which an increase to 7 or 7^ parts took place,
without any apparent cause; but in which it afterwards proved that severe local inflamma-
tion was present; and thus we are furnished with a pathogribmonic sign of great importance.
The average proportion of Fibrine in Inflammation may be estimated at 7; the minimum
at 5; the maximum at 13'3. The greatest augmentation is seen in Pneumonia and Acute
Rheumatism. It does not appear that in robust athletic persons, the proportion of Fibrine is
greater than in those of feeble constitution ; in the latter it is the Corpuscles that are deficient;
and it is rather from this disproportion, than from an absolute excess of Fibrine, that their
greater liability to Inflammatory affections arises. Diseases which commence at the same
time as the Inflammation, or co-exist with it, do not prevent the characteristic increase of the
Fibrine; thus in Chlorotic females, the proportion rises to 6 or 7, under this influence. The
augmentation is observed at the very outset of the affection; the quantity increases with its
progress; and a decrease shows itself when the disease begins to abate.* When the dis-
ease presents alternations of increase and decline, these are marked by precisely correspond-
ing changes in the quantity of Fibrine. It is a curious fact, that an augmentation is commonly
observable during the advanced stage of Phthisis, in spite of the deterioration which the
blood must then have undergone; this is probably dependent upon the development of local
inflammation around the tubercular deposits. In one of Popp's observations, the proportion
of Fibrine in the blood of a Phthisical patient was not less than 10-7. Some experiments
performed by M. Andral on the blood of pregnant women, seem to lead to the conclusion
that, during the first six months, the Fibrine is below the normal standard; and that it sub-
sequently varies, usually undergoing an augmentation between the sixth and seventh, and
the eighth and ninth months. There is also a diminution in the Corpuscles; and these circum-
stances combined favour the production of the buffy coat (§ 704). These observations are
confirmed by those of MM. Becquerel and Rodier.

b. It appears obvious, from what has been just stated, that the increase in the quantity of
Fibrine is not dependent upon the febrile condition, which is secondary to the local inflamma-
tion, but upon the Inflammation itself. This conclusion is confirmed by the interesting fact
that, in idiopathic Fever, the proportion of Fibrine is diminished, instead of undergoing an
increase. This diminution was constantly observed by Andral in the premonitory stage of
Continued Fever; .in some instances the amount was no more than 1-6 parts in 1000. The
proportion of Corpuscles was found to have usually, but not constantly, undergone an increase ;
as had also that of the solid parts of the Serum. In ordinary Continued Fever, in which
there was no evident complication from local disease, the quantity of Fibrin varied from 4-2
to 2-2; that of the Corpuscles from 185-1 to 103-6 (excluding a case in which their amount
was only 82-5, which was that of a Chlorotic female); that of the solid matter of the Serum,
from 98-7 to 909; and that of the Water from 725-6 to 851-9. Hence the quantity of solid
matter appears to be usually increased ; but the peculiar condition of the disease may proba-
bly be stated to be, an increase in the proportion of the Corpuscles to the Fibrine. When,
however, a local Inflammatory affection de.velopes itself during the course of the Fever, the
amount of Fibrine increases ; but its augmentation seems to be kept down by the febrile
condition. — In Typhoid Fever,f the decrease in the proportion of Fibrine is much more de-
cidedly marked; this does not depend upon abstinence; for it ceases as soon as a favourable
change occurs in the disease, long before the effect of food could show itself. In the various
cases examined by Andral, the blood furnished a maximum of 3'7 of Fibrine, and a minimum
of 0-9 ; in this last case, the Typhoid condition existed in extreme intensity, yet the patient
recovered. The proportion of Corpuscles varies considerably; in an early stage of the disease
it is usually found to be absolutely high ; and it always remains high relatively to the amount
of Fibrine. In Typhoid fever, then, the abnormal condition of the Blood, in regard to the

* By experiments on animals, M. Andral has ascertained that no circumstance of pre-
vious debility or privation prevents this characteristic change. Having ascertained the
amount of Fibrine in the blood of three dogs to be 2-3, 2-2, and 1-6 (the natural range for
these animals), he deprived them, completely or partially, of food. On the fourteenth day,
the proportion of fibrine had risen, in the first to 4-5-: and in the second, to 4: these animals
had no food. In the third dog, which was supplied with a very small quantity of food
daily, the same condition developed itself at a later period ; the blood 011 the fourteenth day
exhibiting only 1-8 parts of fibrine: but on the twenty-second day presenting 3'3 parts — In
all these instances, the elevation in the proportion of Fibrine was coincident with Inflamma-
tory changes in the stomach.

f M. Andral confines this term to the species characterized by ulceration of the mucous
follicles of the intestinal canal.

538 OF ABSORPTION AND SANGUIFICATION.

disproportion between the Corpuscles and the Fibrine, is more strongly marked than in ordi-
nary Continued Fever: yet the usual augmentation of Fibrine will take place, if a local in-
flammation developes itself. — In the Eruptive Fevers, it does not appear that the proportion
between the Fibrine and the Corpuscles undergoes so striking a change, as in ordinary Con-
tinued Fever; but the number of cases examined was too small to admit of decided conclu-
sions. It was evident, however, that the specific Inflammations proper to, and characteristic
of, these Fevers, have not the same effect in occasioning an increase of the Fibrine, as an
intercurrent Inflammation of an extraneous character. — By the experiments of Magendie it
has been ascertained that one of the effects of a diminution in the proportion of Fibrine, is a
tendency to the occurrence of Hemorrhage or of Congestion, either in the parcnchymatous
tissue, or on the surface of membranes: these conditions are well known to be of frequent
'occurrence, as complications of febrile disorders. A marked diminution of Fibrine was
noticed also in many cases of the disorder termed Cerebral Congestion, which commences
with headache, vertigo, and tendency to epistaxis, and not unfrequently passes into corn a
and apoplexy. In Apoplexy, the diminution of Fibrine was still more striking ; and in gene-
ral, there was found to be an increase of the Corpuscles. In one instance, the quantity of
Fibrine on the second day of the attack was found to have fallen to l-9, whilst that of the
Corpuscles had risen to 175'5; but on the third day, when the patient's consciousness began
to return the quantity of Fibrine was 3'5, whilst that of the Corpuscles had fallen to 137 7.
It would seem from the great change in the character of the Blood, which was noticed in
this and in other instances, that the want of due proportion between the Fibrine and the
Corpuscles was the cause, rather than the effect, of the Apoplectic attack.

c. The amount of Red Corpuscles seems to be subject to greater variation within the limits
of ordinary health, than is that of Fibrine. In the condition which is ordinarily termed a
highly sanguineous temperament, or Plethora, it is chiefly the entire mass of the blood that
undergoes an increase; but whatever excess there may be in the proportion of its solid con-
stituents, affects the Corpuscles rather than the Fibrine. Plethoric persons are not more
prone to Inflammation, than are those of weaker constitution ; but they are liable to Conges-
tion, especially of the brain, and to Apoplexy or other Hemorrhage. The effect of Bleeding
in diminishing this tendency is now intelligible; since we know that loss of blood reduces
the proportion of Corpuscles. — On the other hand, in that temperament,* which, when ex-
aggerated, becomes Anaemia, there is a marked diminution of the Corpuscles; this tempera-
ment may lead to two different conditions of the system. In Chlorosis, the Red Corpuscles
are diminished, whilst the Fibrine remains the same; so that the clot, though small, is firm,
and not unfrequently exhibits the buffy coat; in some extreme cases of this disease, the Cor-
puscles have been found as low as 27. The influence of the remedial administration of
Iron, in increasing the quantity of Corpuscles, was rendered extremely perceptible by An-
drei's analyses; in one instance, after iron had been taken for a short time, the proportion
of Corpuscles was found to have risen from.49'7 to 64-3 ; whilst in another, in which it had
been longer continued, it hail risen from 46-6 to 95'7. On the other hand, Bleeding reduced
still lower the proportion of Corpuscles; thus in one instance, their amount was found, on a
second bleeding, to have sunk from G'2'8 to 49. The full proportion of Fibrine in the blood
of Chlorotic patients accounts for the infrequency of Hemorrhage in them ; whilst it also
leads us to perceive that they may be, equally with others, the subjects of acute Inflamma-
tion, which we know to be the fact. A diminution of Corpuscles may also co-e\i.-t with a
diminution in the amount, or in the degree of elaboration, of the Fibrine; and this condition
seems to be characteristic of Scrofula. Andral has noticed a diminution in the proportion of
Corpuscles in other Cachectic states, resulting from the influence of various depressing causes
on the nutritive powers; as in the case of Diabetes Mellitus, in which the patient was much
exhausted; — a case of Aneurismal dilatation of the Heart inducing Dropsy; — and in several
cases of Cachexia Saturnina. — The increase in the proportion of Colourless Corpuscles, in
Inflammatory affections, has been particularly noticed by Popp ; he has found them espe-
cially abundant in Pneumonia and in Phthisis, — in the former of which diseases the Fibrine
is invariably, and in the latter generally, increased.

d. The chief class of cases, in which any marked change has been observed in the
amount of solid matter in the Serum, is that of Albuminuria, or Bright'* disease of the Kid-
ney. The diminished Specific Gravity of the Serum was long ago pointed out by Dr. (.'Imsti-
son; but Andral remarks that this is nut an accurate criterion, since, if there be a diminished
amount of Corpuscles (as is not unfreqnently the case in this disease), the proportion of
water in the whole will be increased, and the specific gravity of the serum thus lowered,
without any alteration in its proper quantity of solid matter. According to Andral, the
diminution in the amount of Albumen in the Serum is exactly proportional to the quantity

* The term lymphatic has been applied to this temperament; by which term was meant
a predominance of lymph in the absorbent vessels.

PATHOLOGICAL CHANGES IN THE BLOOD. 539

contained in the urine. A case is related by him, under this head, which affords an interest-
ing exemplification of the general facts that have been already attained by his investigations.
A woman who had been suffering from Erysipelas of the face, and who had lost blood both
by venesection and by leeches, became the subject of Albuminuria. -The blood drawn at
this time exhibited a considerable diminution in the proportion of Corpuscles, as well as of
Albumen, — a fact which the previous loss of blood fully accounted for. After a short period,
during which she had been allowed a fuller diet, another experimental bleeding exhibited
an increase in the proportion of Corpuscles. Some time afterwards, when the Albumen had
disappeared from the Urine, some more blood was drawn ; and it was then observed that
the Albumen of the Serum had returned to its due proportion, but that the Corpuscles had
again diminished, whilst there was a marked increase in the quantity of Fibrine. This altera-
tion was fully accounted for by the fact, that, in the interval, several Lymphatic ganglia in
the neck had been inflamed and had suppurated; and that the patient had been again placed
on very low diet. "Thus," observes Andral, "we were enabled to give a complete explana-
tion of the remarkable oscillations which were presented, in the proportion of the different
elements of the blood drawn at three different times from the same individual; and thus it
is that, the more extended are our inquiries, the more easy does it become to refer to gene'ral
principles the causes of all those changes in the composition of the blood, which, from the
frequency and rapidity with which they occur, seem at first sight to baffle all rules, and to
take place, as it were, at random. In the midst of this apparent disorder, there is but the
fulfilment of laws ; and in order to obtain these, it is only necessary to strip the phenomena
of their complications, and to reduce them to their simplest form."

708. That the Blood is subject to a great variety of other morbid altera-
tions, which are sometimes the causes, and sometimes the results, of Disease,
cannot be for a moment doubted. But our knowledge of the nature of these
changes is as yet very insufficient. The great amount of attention which is
being directed by Chemical Pathologists to the subject, however, will doubt-
less ere long produce some important results. — Among the most frequent
causes of depravation in the character of this fluid, we must undoubtedly rank
the retention, in the Circulating current, of matters which ought to be re-
moved by the Excreting processes. We shall presently see, that a total
interruption to the excretion of Carbonic Acid by the lungs, will occasion
death in the course of a very few minutes ; and even when only a slight im-
pediment is offered it, so that the quantity of Carbonic Acid always contained
in arterial blood is augmented to but a small degree, a feeling of discomfort
and oppression, increasing with the duration of the interruption, is speedily
produced. The results of the retention of the materials of the Biliary and
Urinary excretions will be hereafter considered (Chap, xv.) ; and at present
it will be only remarked, that such retention is a most fertile source of slight
disorders of the system, that it is largely concerned in producing many severe
diseases, and that if complete it will most certainly and rapidly produce a
fatal result. — The most remarkable cases of depravation of the Blood, by the
introduction of matters from without, are those in which these substances act
as ferments,— exciting such Chemical changes in the constitution of the fluid,
that its whole character is speedily changed, and its vital properties are alto-
gether destroyed. Of such an occurrence, we have characteristic examples in
the severe forms of Typhoid fever, commonly termed malignant; in Plague,
Glanders, Pustule Malignc, and several other diseases; in some of which we
can trace the direct introduction of the poison into the blood, whilst in others
we must infer from the similarity of result) that it has been introduced through
some obscure channel, — probably the lungs. The final symptoms which are
common to all these diseases have been well described by Dr. Williams,*
under the title of Necroemia, or Death by depravation of the blood. " Almost
simultaneously, the heart loses its power, the pulse becomes very weak,
frequent, and unsteady : the vessels lose their tone, especially the capil-
laries of the most vascular organs, and congestions occur to a great amount;

* Principles of Medicine, [Am. Ed. by Dr. Clyiner, p. 373.]

540 OF THE CIRCULATION OF BLOOD.

the brain becomes inactive, and stupor ensues ; the medulla is torpid, and the
powers of respiration and excretion are imperfect: voluntary motion is almost
suspended ; secretions fail ; molecular nutrition ceases ; and at a rate much
more early than in other modes of death, molecular death follows close on
somatic death, — that is, structures die and begin to run into decomposition as
soon as the pulse and breath have ceased ; nay, a partial change of this kind
may even precede the death of the whole body; and parts running into gan-
grene, as in the carbuncle of plague, the sphacelous throat of malignant scarla-
tina, and the sloughy sores of the worst forms of typhus, or the putrid odour
exhaled even before death by the bodies of those who are the victims of simi-
lar pestilential disease, are so many proofs of the early triumph of dead over
vital chemistry." — "The appearance of petechiae and vibices on the external
surface, the occurrence of more extensive hemorrhage in internal parts, the
general fluidity of the blood, and frequently its unusually dark or otherwise
altered aspect, its poisonous properties as exhibited in its deleterious operation
on other animals, and its proneness to pass into decomposition, point out the
Blood as the first seat of disorder; and by the failure of its natural properties
and offices as the vivifier of all structure and function, it is plainly the medium
by which death begins in the body."

CHAPTER XII.

OF THE CIRCULATION OF BLOOD.

1. — Of the Circulation in General.

709. THE Circulation of nutritive fluid through the body has for its object,
on the one part, to convey to every portion of the organism the materials for
its growth and renovation, together with the supply of Oxygen which is re-
quisite for its vital actions, especially those of the Muscular and Nervous
systems ; and at the same time to carry off the particles, which are set free by
the disintegration or waste of the tissues, and which are to be removed from
the body by the Excreting processes. Of these processes, the one most con-
stantly in operation, as well as most necessary for the maintenance of the
purity of the blood, is the extrication of Carbonic acid, through the Respira-
tory organs; and this is made subservient to the introduction of Oxygen into
the system. The extent, therefore, to which a Circulating apparatus is de-
veloped in the Animal kingdom, is partly dependent upon the degree in which
the function of nutritive Absorption is limited to one part of the body; and
partly upon the arrangement of the Excreting surfaces, and especially of the
Respiratory apparatus. Where the Digestive cavity extends itself through
the whole system, so that every part can absorb at once from its parietes,— •
and where the whole external surface is adapted, by its softness and permeability,
to expose the fluids of the body to the aerating medium around, — there is no
necessity for any transmission of fluid from one part to another; and accord-
ingly, in the lowest animals, which are thus formed, no true Circulation exists.
Again, in the Insect tribes, in whose bodies the absorption of fluids can only
take place at fixed points, there is a Circulation, for the purpose of transmit-
ting the absorbed matter to the remote portions of the body; but as every part
of the interior is permeated by air, the second of the above-named purposes

OF THE CIRCULATION IN GENERAL.

541

is already answered ; and the circuit of the blood through the vessels, there-
fore, is not accomplished with the energy and activity which, from the vigor-
ous movements performed by these little beings, might have been supposed
necessary. On the other hand, among the MoUusca, in which the absorption
of fluid and the respiratory action are alike limited, we find the circulating
apparatus almost as extensive, and the movement of blood as vigorous, as it is
in the lower Vertebrata. It is in those animals, in which there is the greatest
activity in the other functions, — which live, in fact, the fastest, — that the Cir-
culation is most energetic ; thus the rapid and energetic movement of the
blood in Birds contrasts most strongly with its slow and feeble propulsion in
Reptiles. The movement may vary considerably, however, in the same ani-
mal at different times, according to its state of repose or activity ; and in dif-
ferent organs of the same animal, according to the energy with which their
functions are being respectively performed.

710. In Man, as in other Vertebrated animals, there is a regular and con-
tinuous movement of the nutritive fluid through the vascular system ; and upon
the maintenance of this, the activity of all parts of the organism is dependent.
The course of the Blood may be likened to the figure 8 ; for there are two
distinct circles of vessels, through which it is transmitted; and the Heart is
placed at the junction of these. The Systemic and Pulmonary circulations
are entirely separate, and might be said to have distinct hearts ; for the left
and right sides of the heart, which are respectively appropriated to these,
have no direct communication with each other (in the perfect adult condition,
at least), and are merely brought together for economy of material. At an
early period of foetal life, as in the permanent state of the Dugong, the heart is
so deeply cleft, from the apex towards the base, as almost to give the idea of
two separate organs. Each system has its own set of Arteries or efferent
vessels, and Veins or afferent trunks; these communicate at their central ex-
tremity by the Heart ; and at their peripheral extremity by the Capillary ves-
sels, which are nothing else than the minutest ramifications of the two systems,
inosculating into a plexus (§ 219).

Fig. 211.

Web of Frog's foot, stretching between two toes, magnified 3 diam. ; showing the blood-vessels, and

their anastomoses : 1,1, veins; 2, 2, 2, arteries.

46

542

OF THE CIRCULATION OF BLOOD.

a. Although the diameters of the branches, at each subdivision, together exceed that of
the trunk, yet there is but little real difference in their size. For, according to a well-known
geometrical law, the areas of circles are as the squares of their diameters ; and, as the calibre
of a tube is estimated by its area, not by its diameter, it follows that, in comparing the size
of a trunk with that of its branches, we are to square the diameter of the former, and com-
pare the result with the sum of the squares of the diameters of the branches. When this is
done, there is found to be a very close correspondence. The following table gives the re-
sult of eight measurements, taken with a view to determine the question. The first three
were taken from the mesenteric artery of a Sheep ; the next three from the aorta and iliac
arteries ; the last two from the Horse.*

TRUNK.

DIAMETER.

I.

9

II.

7.2

III.

3.5

IV.

7.0

V.

17

VI.

10

VII.

4.5

VIII.

8

SQ.UAHE.

81

51.64
12.25

49

289

100

20.25

64

BRANCHES.

DIAMETERS.

7.5+5
6+4
3+2
5+5

10+10+9.5
7+7+2
3.5+3
4+7

SUM OF S4UARES.

81.25

52

13

50
290.25

102
21.25

65

The discrepancy between the two results must be considered extremely small, when it is
stated that the unit, in the above measurements, is no more than one-fortieth of an inch ;
and when it is remembered that any error in the measurement is greatly increased in the
calculation.

b. From Mr. Paget's observations, however, it appears that there is seldom an exact
equality between the area of the trunk and that of its branches, but the area sometimes in-
creases, and sometimes diminishes; — the former being the general rule for the subdivision
of the aorta and its principal branches in the upper extremities; — the latter in the lower.
The following Table shows the relative areas of several arterial trunks, and of the branches
proceeding from them.

TRUNK. BRANCHES.

Arch of Aorta 1 1-055

Innominate. ....... 1 1-147

Common carotid ...... 1 1-013

External carotid 1 1-190

Subclavian ....... 1 1-055

Abdominal Aorta, to last lumbar art. . . 1 1-183

, just before dividing . . 1 -893

Common Iliac 1 -982

External Iliac 1 1-150

711. That the movement of the Blood through the Arterial trunks and the
Capillary tubes is, in Man, and in other warm-blooded animals, chiefly de-
pendent upon the action of the Heart there can be no doubt whatever. It can
be easily shown by experiment, that, if the Arterial current be checked, the
Capillaries will immediately cease almost entirely to deliver the blood into
the veins, and the Venous circulation will be instantaneously arrested. And
it has also been proved, that the usual force of the Heart is sufficient to propel
the blood, not only through the Arterial tubes, but through the Capillaries,
into the Veins; since even a less force will serve to propel warm water through
the vessels of an animal recently dead.t But there are certain "residual phe-
nomena" even in Man, which clearly indicate that this is not the whole truth :
and that forces existing in the Blood-vessels have a considerable influence, in
producing both local and general modifications of the effects of the Heart's
action. There are also indications of the nature of an influence, in which the
blood-vessels do not partake, arising from those changes occurring between
the Blood and the Tissues, that constitue the processes of Nutrition, Secretion,

* Ferneley in Medical Gazette, Dec. 7, 1839.

I See Dr. Williams' Principles of Medicine, p. 143, note.

MOTION OF THE BLOOD IN THE VESSELS. 543

&c. Such, for instance, would appear to be the interpretation of the fact,
that whilst any variations in the action of the Heart affect the whole system
alike, there are many variations in the Circulation, which, heing very limited
in their extent, cannot be attributed to such central disturbances, and must
therefore be dependent on causes purely local. — Of the nature of these in-
fluences, and of the mode of their operation, we shall probably arrive at a
more correct knowledge, if we examine the phenomena of the Circulation in
those beings, in which the moving power is less concentrated than it is in the
higher Animals ; for just as we find in the latter, that the development of
special absorbent vessels does not exclude the function of absorption from
being still performed by the general vascular system (§ 675), so may we here
be led to perceive, that there is a generally-diffused force, to which alone the
Circulation of the nutritious fluid in the lowest organisms is due, and which
is not altogether replaced by the special organ of impulsion, that is developed
in the centre of the system in the higher.

712. The ascent of. the sap in Vegetables is probably to be regarded as due,
in part, to the vis a tergo occasioned by the action of Endosmose at the
roots; and in part, to the demand for fluid, occasioned by the vital processes
taking place in the leaves. For if the stem of the Vine, in which the sap is
rising, be cut across, the sap will continue to flow for some time from the top
of the lower portion ; and its force of ascent may be shown to be very con-
siderable, by tying over the cut surface a piece of bladder, which will be
speedily burst, — or by affixing to it a bent tube, containing a column of mer-
cury, which will be raised to the height of forty inches or more. On the
other hand, the attractive force of the leaves is shown by the fact, that if the
lower end of the upper division be put into water, it will continue to absorb,
as long as the vital actions of the leaves are being performed with vigour;
but, if the branch be carried into a dark room, the exhalation from the leaves
is immediately checked, and absorption is checked also. The influence of
the actions at the periphery of the circulating system, in maintaining the flow
of fluid towards the part, is further shown by the fact, that, if a shoot of an
evergreen species be grafted on a stock of one with deciduous leaves, a con-
tinual and unwonted ascent of sap will be kept up in the latter through the
winter; this being evidently due to the demand occasioned at its summit.
Again, the recommencement of the annual flow of sap in an ordinary tree, has
been found to take place in the first instance, not at its roots, but in the
neighbourhood of the buds; for their expansion, under the influence of the
returning warmth, exhausts the fluid from the vessels of their neighbourhood ;
this, again, occasions a demand from below; and thus the motion is gradually
propagated to the roots. Now it has been experimentally ascertained, that if
a branch of a vine growing in the open air be trained into a hot-house, it may
be made to vegetate during the winter, and to draw up fluid through the
stems and roots, whose condition has not been changed. It is evident, then,
that in Plants, the demand for fluid, in the organs to which it is distributed by
the vascular system, is one of the chief forces by which the supply is obtained.

713. This is still more evidently the case, in regard to the Circulation of
nutritious or elaborated sap, which takes place in the under surface of the
leaves and in the bark. The object of this movement is not to convey the
fluid in a direct line from one point to another (as in the case with the
ascending current), but to supply every part with materials for its growth, or
for the production of its peculiar secretions. Hence the vessels in which it
takes place, form a minutely-anastomosing net-work, instead of consisting ot a
system of straight and distinct tubes. Through this net-work, the latex or
elaborated sap is seen to move, exactly as does the blood through the capil-
lary vessels of animals. The movement takes place, under favourable circum-

544 OF THE CIRCULATION OF BLOOD.

stances, with considerable rapidity ; it is accelerated by heat, and retarded by
cold; and it is subject to all those minor irregularities (such as the cessation
of movement, or change in the direction of the current, in a particular chan-
nel), which are so constantly to be noticed by any one who attentively watches
the capillary circulation of Animals, and which clearly prove the operation of
some causes independent of the heart's action (§ 734). The general direction
of the elaborated sap, through this capillary system, is downwards ; but that
the force of gravity cannot have much to do with the movement, is shown by
the fact that, in dependent branches, it has to ascend towards the stem, which
it will do without interruption from this cause. Moreover it may be noticed
that this circulation takes place most actively, in parts which are undergoing a
rapid developement; and that its energy corresponds with the vitality of the
part. Further; it may be observed to continue for some time in parts that
have been completely detached from the rest; and on which neither vis a
tergo, nor vis a fronte, can have any influence. It is evident, then, that the
force, — whatever be its nature, — by which this continued movement is kept
up, must be developed by the processes to which that movement is subserv-
ient; in other words, that the changes involved in the acts of nutrition and
secretion are the real source of the motor power. The manner in which they
become so, is the next object of our inquiry: and on this subject, some new
views have recently been put forth by Prof. Draper,* which seem to account
well for the phenomena.

a. It is capable of being shown, by experiments on inorganic bodies, that, if two liquids
communicate with each other through a capillary tube, ibr the walls of which they both
have an affinity, and if this affinity is stronger in the one liquid than in the other, a
movement will ensue; the liquid which has the greatest affinity being absorbed most ener-
getically into the tube, ami driving the other before it. The same result occurs when the
fluid is drawn, not into a single tube, but into a net-work of tubes, permeating a solid
structure; ibr if this porous structure be previously saturated with the fluid, for which it has
the less degree of attraction, this will be driven out and replaced by that for which it has
the greater affinity, when the latter is permitted to outer it. Now if, in its passage through
the porous solid, the liquid undergo such a change, that its affinity be diminished, it is ob-
vious that, according to the principle just explained, it must be driven out by a fresh supply
of the original liquid; and lhat thus a continual movement in the same direction would be
produced.

l>. Now this is precisely that which seems to take place in the organized tissue, per-
meated by nutritious fluid. The particles of this fluid, and the solid matter through which
it is distributed, have a certain affinity Ibr each other; which is exercised in the nutritive
changes, to which the fluid becomes subservient during the course of its circulation. Cer-
tain matters are drawn from it. in one part, for the support and increase of the woody tis-
sue; in another part, the secreting cells demand the materials which are requisite for their
growth, — as starch, oil, resin, &c.; and thus in every portion that is traversed by the vessels^
there are certain affinities between the solids and the fluids, which are continually bem-
newly developed by acts of growth, as fast as those which previously existed are satisfied
or neutrali/ed by the changes that have already occurred. Thus in the circulation nf the
elaborated sap, there is a constant attraction of its particles towards the walls of the vessels,
and a continual series nf changes produced in the fluid as the result of that attraction. The
flnni, which has given up to a certain tissue some of its materials, no longer has the same
attraction for that tissue; and it is consequently driven from it by the superior attraction then
possessed by the li-sue for another portion of the fluid, which is ready to undergo the same
changes, to be in its turn rejected for a fresh supply. Thus in a growing part, there is a
coiistantly-rencu-ed attraction for the nutritive fluid, which has not yet traversed it; whilst
on the other hand, there is a diminished attraction lor the fluid, which has yielded up the
nutritive materials required by the particular tissues of the part ; and thus the former is con-
tinually driving the latter beliire it.

c. But the fluid, which is thus icpclled from one part, may still be attracted towards ano-
ther; because that portion of its contents, which the latter requires, may not yet have been
removed from it. And in this manner, it would seem that the flow of sap is maintained

On the Forces which produce the Organization of Plants, Chap. in.

MOTION OF THE BLOOD IN THE VESSELS. 545

through the whole capillary net-work, untili t is altogether exhausted of its nutritive matter.
The source of the movement is thus entirely to be looked for in the changes which take place
in the act of growth; and the influence of heat, cold, and other agents, upon the movement
is exercised through their power of accelerating or retarding those changes.

714. The fluid which thus descends through the stem and roots, seems to
be at last almost entirely exhausted ; a portion of it appears to find its way
into the ascending current, and to be mingled with it ; but all the rest seems
to have been entirely appropriated by the different tissues, through which it
has circulated. Thus there is no need of any general receptacle, into which
it may be collected, and from which it may take a fresh departure; — such as
is afforded by the heart of the higher animals. And as the purpose of this
circulation is only to supply the nutritive materials, and not to convey oxy-
gen,— this element being but little required in the vegetative processes, and
being supplied by other means, — the same energy and rapidity are not re-
quired in it, as need to be provided for in the higher animals.

715. In the lowest Animals, the movement of the circulating fluid seems
as independent of any central organ of impulsion, as it has been shown to be
in Plants. Thus, in the living Sponge, a current of water is continually
flowing through the tubes and channels, by which its substance is traversed,
the fluid being taken in by the small orifices, and ejected in powerful streams
from the large ones; and yet the most attentive examination has not revealed
any mechanical cause for this movement. In some of the compound Polypi-
fera, a similar current may be seen ; and it is curious that, in many species,
its direction undergoes a periodical change ; being reversed at intervals of a
certain number of seconds. In the Star-Fish and Sea-Urchin tribe, a com-
plex circulation of blood takes place, through regular vessels ; and here we
find some indication of a contractile cavity, by the power of which it may be.
in some degree, kept up ; but its feeble pulsations can scarcely be regarded,
as having any great share in the movement of the fluid which passes through
it. — In the Articulated series, there is, with a few exceptions, an absence of
any central organ of impulsion, possessed of power sufficient to carry the
blood through the vascular system, by its contractions alone. In many of the
aquatic worms and larvae, the movement of the blood, and the pulsations of
the dorsal vessel, may be distinctly seen: and the thinness of the walls of the
latter, and the character of its movements, seem clearly to show, that these
can scarcely be regarded as propulsive, but that they merely result from the
variations in the current which passes through it, — the sides flapping together
when there is an outward flow, and bulging out when there is an influx. It
is in these Articulata, in which there is a provision for respiration throughout
the whole structure, as is especially the case in Insects, that the absence of
any central impulsive power is most remarkable. — In the Crustacea, and in
the Mollusca in general, the respiration is aquatic, and is restricted to a par-
ticular organ ; and in these, the heart is found to be more muscular, and the
circulation to be more under its control. It is curious to remark, however,
that, in some of the lower Mollusca, which exhibit a tendency to aggregation
into compound structures, like those of the Polypifera, there is the same want
of definiteness in the course of the circulation, as lias been just stated to exist
in the latter group; — the flow of blood, through their complex apparatus of
nutritive organs, being arrested at regular intervals, and then recommencing
in the reverse direction.

716. Even in Vertebrated animals, we find indications of the same defi-
ciency of central power, over the peripheral circulation. When we look at
the simple, thin-walled heart of Fishes, for example, it seems impossible that,
it should have much power over the current of blood flowing back to it by
the veins ; for of this blood, a considerable portion has to pass through three

46*

546 OF THE CIRCULATION OF BLOOD.

sets of capillaries, between its ejection from the heart, and its return to it. It
is first transmitted through the respiratory capillaries, for the purpose of aera-
tion ; the confluent vessels, which collect the arterial blood from these, ter-
minate in the general systemic trunk or Aorta, in which, as in the veins of
Man, there is an absence of pulsation, and by these, it is distributed to the
systemic capillaries ; and the blood which, after passing through these, re-
turns from the posterior part of the body, and from the viscera, passes through
another set of capillaries, those of the liver and kidneys, before it returns to
the heart. — Even in the warm-blooded Vertebrata, in which the respiratory
circulation is separately performed, the blood which is returned from the in-
testines, passes into a trunk, the Vena Portae, which again subdivides into
capillary ramifications, being transmitted over the plexus of biliary ducts, of
which the liver is chiefly composed ; and thus the Vena Portae, as Hunter
justly observed, should be considered rather in the light of an artery,* re-
sembling as it does the aorta of Fishes. Considering the small amount of
pressure which is exerted by the blood, upon the sides of the vessels that are
formed by the reunion of capillaries, it seems impossible to imagine that the
vis a tergo derived from the impulsive action of the Heart, can be alone suf-
ficient to maintain the portal circulation.

2. — Action of the Heart.

717. The Heart is endowed in an eminent degree with the property of
irritability ; by which is meant, the capability of being easily excited to
movements of contraction alternating with relaxation (§ 574). Thus, after
the Heart has been removed from the body, and has ceased to contract, a
slight irritation will cause it to execute, not one movement only, but a series
of alternate contractions and dilatations, gradually diminishing in vigour until
they cease. The contraction begins in the part irritated, and then extends to
the rest. It appears from Mr. Paget's experiments,! that it is necessary for
the propagation of this irritation, that the parts should be connected by mus-
cular tissue, of which a very narrow isthmus will suffice ; and that the pro-
pagation will not take place, if the connecting isthmus be composed of ten-
don, even though this be a portion of the auriculo-ventricular ring, which has
been supposed by some to be peculiarly efficacious in this conduction. — That
the irritability of the heart is not dependent upon the Cerebro-spinal system,
appears not merely from the manifestation of it, when the organ is altogether
removed from the body, but also from the fact, that if the flood of blood
through the lungs be kept up by artificial respiration, the heart's action will
continue for a lengthened period, even after the Brain and Spinal Cord have
been removed, and when animal life is, therefore, completely extinct. Hence
we see that the Irritability of this organ must be an endowment properly be-
longing to it, and not derived from that portion of the Nervous System. Like
the contractility of other muscles, it can only be sustained for any great length
of time, by a supply of Arterial blood to its own tissue (§ 584). It is much
less speedily lost in cold-blooded animals, however, than in warm-blooded ;
the heart of the Frog, for example, will go on pulsating for many hours after
its removal from the body ; and it is stated by Dr. MilchellJ that the heart of
a Sturgeon, which he had inflated with air, continued to beat, until the auricle

* That it conveys venous blood, is no reason to the contrary; since this is the case with
the pulmonary artery. The character of an artery is derived iroiu the. division of its current
into several divergent streams.

f Brit, and For. Mod. Review, vol. xxi. p. 551.

J American Journal of the Medical Sciences, vol. vii. p. 5S.

ACTION OF THE HEART. 547

had absolutely become so dry, as to rustle during its movements. It has
lately been shown by Mr. Todd, that the irritability of the heart is of long
duration after death in very young animals : which, as long since demonstrated
by Dr. Edwards, agree with the cold-blooded Vertebrata in their power of
sustaining life, for a lengthened period, without oxygen. — It is difficult to ac-
count for the long continuance of the alternate contractions and relaxations of
the muscular parietcs of the heart, after all evident stimuli have ceased to act
upon it; and many theories have been offered on the subject, none of which
afford an adequate explanation. The extraordinary tendency to rhythmical
action, which distinguishes the heart from all other muscles, is shown by the
fact that not only do the entire hearts of cold-blooded animals continue to act,
long after their removal from the body, but even separated portions of them
will contract and relax with great regularity for a long time. Thus the auri-
cles will persist in their rhythmical action, when cut off above the auriculo-
veritricular rings ; and the apex of the heart will do the same, when separated
from the rest of the ventricle. The stimulus of the contact of blood with the
lining membrane of .the heart, to which its regular actions have been com-
monly referred, can have no influence in producing these movements; nor
does it appear that the contact of air can take its place ; since, as Dr. J. Reid
has shown, the rhythmical contractions of the heart of a frog will continue
in vacua. Nor is there any evidence that the flow of blood through the
cavities has the effect of securing the regularity of their successive contrac-
tions in the living body ; for this regularity is equally marked in the contrac-
tions of the excised heart, when perfectly emptied of blood, so long as its
movements continue vigorous. But when its irritability is nearly exhausted,
the usual rhythm is often a good deal disturbed, so that the contractions of
the auricles and ventricles do not regularly alternate with each other ; and one
set frequently ceases before the other.

a. It was formerly supposed, that the movements of the Heart were dependent upon its
connection with the centres of the Cerebro-Spinal nervous system ; and the experiments of
Legallois and others, who found that they were arrested by crushing, or otherwise suddenly
destroying, large portions of these centres, appeared to favour the supposition. But it has
been shown by Dr. Wilson Philip and his successors in the same inquiry, that the whole
Cerebro-Spinal axis might be gradually removed, without any such consequence; which
fact harmonizes perfectly with the "experiments prepared for us by Nature," in the pro-
duction of monsters destitute of these centres, which nevertheless possessed a regularly-
pulsating heart. As already mentioned (§ 416), it is difficult to obtain any distinct evidence,
that the actions of the heart are affected by any ordinary irritation of the Par Vagum ; but
the recent experiments of MM. Weber have shown that its movements may be immediately
arrested, by the transmission of the electric current from a rotating magnet, either through
the Spinal Cord, or through the Vagi nerves divided at their origin. The same irritation,
however, applied to a single one of the Vagi, produced no effect.*

b. It has latterly been the fashion with many, however, to attribute the action of the Heart
to the Sympathetic system ; but of this there is no sufficient evidence. The possibility of
exciting the action of the heart through the Sympathetic nerve (§ 576), shows that this may
have an influence on its movements; whilst the great difficulty with which any evidence
to this effect can be procured, seems a sufficient proof, as in the case of the Muscular coat of
the intestines (§ 388), that this influence cannot be nearly adequate to the constant main-
tenance of a function so energetic. Some have more recently maintained, that the move-
ments are of a strictly reflex nature, and that fliey are effected through the agency of certain
minute ganglia, belonging to the Sympathetic system, and scattered through the substance of
the heart ; — in this way endeavouring to account for the persistence of the motions of the
organ after its complete removal from the body, and under circumstances which suspend all
reflex movements that have their centre in the cerebro-spinal system. But this attempt at
explanation affords no aid in the solution of the cause of the continued rhythmical move-
ments of the organ, or of its separated portions, after the withdrawal of all stimuli that can
be supposed to operate in exciting them ; and the phenomena are just as fully explained by

* Archives d'Anat. Gener. et de Physiol., Janv. 1846.

548 OF THE CIRCULATION OF BLOOD.

attributing them to the independent irritability of the muscular fibre, as by supposing the
nervous system to be concerned in them.

c. It would appear, however, that changes in the Ganglionic nerves, like strong impres-
sions upon the Cerebro-spinal system (§ 580), may have the effect of impeding or even
checking the Heart's action ; for a case has lately been recorded, in which the movements
were occasionally checked for an interval of from 4 to 6 beats, its cessation of action giving
rise to the most fearful sensations of anxiety, and to acute pain passing up to the head from
both sides of the chest. — these symptoms being connected, as it proved on a post-mortem
examination, with the pressure of an enlarged bronchial gland upon the great cardiac nerve.*
It may be surmised, that in many cases of angina pectoris, in which no lesion sufficient to
account for death could be discovered, some affection of the cardiac plexus might have been
traced on a more careful examination.

718. When the Heart is exposed in a living animal, and its movements are
attentively watched, they are seen to follow each other with great regularity.
In an active and vigorous state of the circulation, however, they are so linked
together, that it is not easy to distinguish them into periods. A case has
fallen under the notice of Prof. Cruveilhier, in which the heart was exterior
to the chest, having escaped from it by a perforation in the superior part of
the sternum ; and his observations upon it may be perhaps regarded as more
satisfactory than such as are made after the very severe operation required for
the artificial exposure of the organ ; although they are liable to some excep-
tion, from, the very early age of the subject of them, which had only been
born nine hours. His conclusions will be here adopted ; with such addi-
tional remarks as are suggested by the experimental researches of others,
who have made this question a subject of special attention.! It is universally
admitted, that both Auricles contract, and also dilate simultaneously ; and that
both Ventricles do the same: — also that the systole or contraction of the ven-
tricles corresponds with the projection of blood into the arteries, causing the
pulse ; whilst the diastole or dilatation of the ventricles coincides with the
collapse of the arteries. It is further admitted, that the contraction of the
Ventricles, and that of the Auricles, alternate with one another ; each taking
place (for the most part, at least), during the dilatation of the other. But it
is a question whether there is any interval between them. In the case just
alluded to, the contraction of the Ventricles is stated to have been precisely
synchronous with the dilatation of the Auricles ; and the dilatation of the
Ventricles to have been performed at the same time with the contraction of
the Auricles, no period of repose intervening between the two sets of actions.
It appears, however, from the concurrent testimony of numerous experiment-
ers, that, whilst the contraction of the Ventricle immediately succeeds that of
the Auricle, an interval, which is usually, however, extremely brief, may elapse
between the partial dilatation of the Ventricles and the succeeding systole of
the Auricles. The Ventricular dyastolemzy be distinguished into two stages,
of which the first immediately succeeds its systole, and manifests itself in the
recession of the Heart's apex from the front of the chest; whilst the second
is attended with an enlargement of the heart in all its dimensions, and is
synchronous with the Auricular contraction. It is between these two, that
the interval of repose occurs, where it can be observed. The following
tabular view will, perhaps, make this Account more intelligible ; it is framed
in such a manner as to commence with the Auricular contraction ; but, when
considering the Sounds of the heart, it will be necessary to commence with
the Ventricular systole.

* Muller's Archiv. 1841, heft iii. ; and Brit, and For. Mod. R.-v., Oct. 1S41.
f See also another case, recently observed by M. Monod, in Bullet, d.- 1'Acad. de Mod.,
Fevr. 1843 ; and Edinb. Med. and Surg. Journ., July 1843.

ACTION OF THE HEART. 549

^Auricles. Ventricles.

Contraction. 2d stage of dilatation.

Dilatation. Contraction. — Pulse.

1st stage of dilatation.
Brief interval of Repose.
Contraction. 2d stage of dilatation.

Dilatation. Contraction. — Pulse.

719. The duration of the Contraction of the Ventricles is, according to
Cruveilhier, double that of their Dilatation; and the same holds good of the
Auricles. In the Systole of the Ventricles, their surface becomes rugous ; the
superficial veins swell ; the carneae columnae of the left ventricle are delineated ;
and the curved fibres of the conical termination of the left ventricle, which
alone constitutes the apex of the heart, become more manifest. During their
contraction, every diameter of the Ventricles is lessened ; their shortening is
the most sensible change; but this is owing to the vertical diameter being the
greatest. The lower extremity of the left ventricle, or, in other words, the
apex of the heart, describes a spiral movement from right to left, and from be-
hind forwards. It is to this slow, gradual, and as it were successive spiral
contraction, that the forward movement of the apex of the heart is owing, and
its consequent percussion against the thoracic parietes. The ventricular sys-
tole is not accompanied by a projection of the entire heart forwards (as some
have maintained) ; for it is exclusively the spiral contraction, which determines
the approach of the apex of the heart to the thoracic parietes. The Diastole
of the heart, according to Cruveilhier, has the rapidity and energy of an active
movement: triumphing over pressure exercised upon the organ, so that the
hand closed upon it is opened with violence. This is an observation of great
importance ; but of the cause to which this active dilatation is due, no definite
account can be given. It may partly be explained, perhaps, by the elasticity
of the tissue, interwoven with muscular fibre in the substance of the heart;
and this may be the cause of the first Ventricular dilatation, the second being
produced by the ingress of blood occasioned by the auricular systole. But
the dilatation of the Auricles appears to be much greater than can be accounted
for by any vis a tergo (which, as will hereafter appear, is extremely small in
the venous system), or by the elasticity of its substance ; for it was observed
in this case to be so great, that the right auricle seemed ready to burst, so great
was its distension, and so thin were its walls. Moreover, the large Veins
near the heart contract simultaneously with the auricular Systole, and not with
its Diastole; so that they can have no influence in causing its dilatation. The
Ventricular diastole is accompanied with a projection of the heart downwards;
this motion was at its maximum when the child was placed vertically, and
was very strongly marked.

720. When the ear is applied over the cardiac region, during the natural
movements of the Heart, two successive sounds are heard ; each pair of which
corresponds with one pulsation. The whole interval between one beat of the
the Heart, and the next, may be divided into four parts ; of which the two
first are occupied by what is commonly known as ihejirst sound; the third,
by the second sound ; whilst the fourtli is a period of repose. — The first sound
is dull and prolonged ; it is evidently synchronous with the impulse of the
Heart against the parietes of the chest, and also with the pulse, as felt near
the heart; it must, therefore, be produced during the Ventricular Systole. —
The second sound follows so immediately upon the conclusion of the first,
that it can scarcely be imagined to take place during the auricular systole as
some have supposed, but must be assigned to the period of the first stage of
the Ventricular Diastole. This, indeed, may now be regarded as clearly esta-
blished; for it has been fully demonstrated, that the second sound is due to

550 OF THE CIRCULATION OF BLOOD.

the sudden filling-out of the Semilunar valves of the aorta and pulmonary
artery, with blood ; when the outward current through them has ceased, and
the incipient dilatation of the ventricles occasions a vacuum behind them. If
one of these valves be hooked back by a curved needle against the side of the
artery, so that a reflux of blood is permitted, the sound is entirely suppressed.
The first sound cannot be so readily or satisfactorily accounted for. That it
is partly due to the Impulse of the apex of the Heart, seems proved by the
fact, that, when this impulse is prevented, the sound is much diminished in
intensity ; and also by the circumstance that, when the Ventricles contract
with vigour, the greatest intensity of the sound is over the point of percussion.
But that it is not entirely due to this cause is also evident from the fact, that
a sound may still be heard, when the Heart is contracting out of the body; as
in the case observed by Prof. Cruveilhier. This sound has been attributed,
by some experimenters, to the flapping-back of the auriculo-ventricular valves ;
by others to the muscular contraction of the walls of the ventricles ; by others
again to the rush of blood along the irregular walls of the ventricles, and
through the comparatively narrow orifices of the aorta and pulmonary artery.
This last is probably the most consistent with truth ; as would appear from
the following interesting observations made by Cruveilhier. By applying the
finger to the origin of the pulmonary artery (which is situated in front of the
aorta, and completely conceals it), a perfectly distinct vibratory fremissement
corresponding with the ventricular diastole, was perceived; but no such vibra-
tory thrill could be felt by the finger, when applied to any part of the base of
the ventricles : whence it was evident, that no action takes place in the mitral
and tricuspid valves, which can give rise to the same palpable effects, as those
produced by the semilunar valves. The same was ascertained regarding the
valvular sound, which could be distinctly heard, by laying the finger against
the origin of the pulmonary artery, and applying the ear to it as to a stetho-
scope: whilst nothing of the kind could be perceived in the region of the
auriculo-ventricnlar valves. Hence it seems quite certain, that the natural first
sound cannot be dependent in any way upon the action of the mitral and tri-
cuspid valves. It appeared, on the contrary, that the maximum intensity of
the first sound was in precisely the same situation as the maximum intensity
of the second, — namely, at the origin of the large arteries ; and that it dimin-
ished, as the ear was carried from the base, towards the apex of the heart.
Moreover, the first sound was observed to be of exactly the same character
with the second (the complicating effect of the impulse being here withdrawn) ;
except as to its intensity, which was less, — and its duration, which was greater.
721. Hence, although these observations do not entitle us to deny the par-
ticipation of the muscular contraction, and of the movement of the blood over
the ventricular walls, in the production of the first sound, they establish (if
correct), that the principal cause of it exists at the entrances to the arterial
trunks; and it does not seem that any other reason can be assigned for it, than
the prolonged rush of blood through their orifices, and the throwing back of the
Semilunar valves ; which, in suddenly flapping clown again, produce the second
sound. — That an exaggeration of the first sound, not essentially differing from
it in character, is often produced by disease of the sigmoid valves, which
causes an obstruction of their orifice, has long been known ; and in such
cases, the character of the second sound is also changed. Indeed, M. Cru-
veilhier states it as, in his opinion, an uniform occurrence, that disease of the
Semilunar valves alters both sounds. When this disease is such as to prevent
the valves from effectually closing, a reflux of blood takes place into the ven-
tricle at the time of its diastole; causing a rushing sound, more or less pro-
longed, to be heard in the intervals of the pulse, instead of with it. These
considerations appear to prove almost incontestably, that the cause of the first

ACTION OF THE HEART.

551

sound, and that of the second, are very closely allied ; and this view, which if
correct is of great importance in the explanation of numerous morbid phe-
nomena, harmonizes well with the known effect of a slight obstruction in a
tube, through which fluid is being rapidly forced, in producing a prolonged
sound, very analogous to the first sound of the heart. The following table
may assist the student in connecting the sounds of the Heart with its move-
ments.

Ventricular Systole, and Auricular Diastole. Impulse of apex against

parietes of chest. Pulsation in arteries.
First stage of Ventricular Diastole.
Short repose ; then Auricular Systole, and second stage of Ventricular

Diastole.

722. The course of the circulating fluid through the Heart, and the action
of its different valves, will now be briefly described. The Venous blood,
which is returned by the ascending and descending Vena Cava, enters the
right Auricle during its diastole ; and, when it contracts, is forced between
the Tricuspid valves, into the Ventricle. The reflux of blood into the veins,
during the auricular systole, is prevented by the valves with which they are
furnished ; but these valves are so formed, as not to close accurately, espe-

[Fig. 212.

FIRST SOUND.

SECOND SOUND.
INTERVAL.

The Anatomy of the Heart; 1, the right auricle; 2, the entrance of the superior vena cava; 3, the
entrance of the inferior cava ; 4, the opening of the coronary vein, half closed by the coronary valve j
5, the Eustachian valve ; 6, the fossa ovalis, surrounded by the annults ovalis ; 7, the tuberculum Low-
er! ; 8, the musculi pectinati in the appendix auriculae; 9, the auriculo- ventricular opening; 10, the
cavity of the right ventricle; 11, the tricuspid valve, attached by the chordae tendineae to the carnese
columnar (12); 13, the pulmonary artery, guarded at its commencement by three semilunar valves; 14,
the right pulmonary artery, passing beneath the arch and behind the ascending aorta; 15, the left pulmo-
nary artery, crossing in front of the descending aorta; *, the remains of the ductus arteriosus, acting as
a ligament between the pulmonary artery and arch of the aorta; the arrows mark the course of the
venous blood through the right side of the heart; entering the auricle by the superior and infeiior cava,
it passes through the auriculo- ventricular opening into the ventricle, and thence through the pulmonary
artery to the lungs ; 16, the left auricle ; 17, the openings of the four pulmonary veins ; 18, the auriculo-
ventricular opening ; 19, the left ventricle ; 20, the mitral valve, attached by its chorda? tendinea? to two
large columnar carneaj, which project from the walls of the ventricle; 21, the commencement and course
of the ascending aorta behind the pulmonary artery, marked by an arrow; the entrance of the vessel
is guarded by three semilunar valves ; 22, the arch of the aorta. The comparative thickness of the two
ventricles is shown in the diagram. The course of the arterial blood through the left side of the heart
is marked by arrows. The blood is brought from the lungs by the four pulmonary veins into the left
auricle, and passes through the auriculo-ventricular opening into the left ventricle, whence it is con-
veyed by the aorta to every part of the body.]

552 OF THE CIRCULATION OF BLOOD.

cially, when the tubes are distended ; so that a small amount of reflux usually
takes place, and this is much increased when there is any obstruction to the
pulmonary circulation. Whilst the right Ventricle is contracting upon the
blood that has entered it, the carnese columns?, which contract simultaneously
with its proper walls, put the chordse tendinese upon the stretch; and these
draw the flaps of the Tricuspid valve into the auriculo-ventricular axis. The
blood then getting behind them, and being compressed by the contraction of
the ventricle, forces the flaps together in such a manner as to close the orifice ;
but they do not fall suddenly against each other, as is the case with the semi-
lunar valves, since they are restrained by the r.hordse tendinese ; whence it is,
that no sound is produced by their closure. The blood is expelled by the
ventricular systole into the Pulmonary Artery, which it distends, passing
freely through the Semilunar valves; but as soon as the vis a tergo ceases,
and reflux might take place by the contraction of the arterial walls, the valves
are filled out by the backward tendency of the blood, and completely check
the return of any portion of it into the ventricle. The blood, after having cir-
culated through the lungs, returns as Arterial blood, by the Pulmonary Veins,
to the left Auricle; whence it passes through the mitral valves into the left
Ventricle, and thence into the Aorta, — in the same manner with that on the
other side, as just described.

723. There are, however, some important differences in the structure and
functional actions of the two divisions of the Heart, which should be here
adverted to.

a. The walls of the left Ventricle are considerably thicker than those of the right; and
its force of contraction is much greater. The following are the comparative results of M.
Bizot's recent measurements, taking the average of males from 16 to 89 years.

BASE. MIDDLE. APEX.

Left Ventricle 4g lines 5^ lines 3J lines

Right Ventricle lj| lines 1| lines I3'ff lines

In the female, the average thickness is somewhat less. It will be seen that the point of
greatest thickness in the left Ventricle is near its middle ; while in the right, it is nearer the
base. The thickness of the former goes on increasing during all periods of life, from youth
to advanced age ; whilst thatof the right is nearly stationary. The left Auricle is somewhat
thicker than the right; the average thickness of the former being, according to Bouillaud,
a line and a half; whilst thatof the latter is only a line. In regard to the relative capaci-
ties of the right and left cavities, much difference of opinion has prevailed. The right Au-
ricle is generally allowed to be more capacious than the left ; and the same is commonly
taught of the right Ventricle. So much fallacy may arise, however, from the peculiar condi-
tion of the animal at the moment of death, that this is not easily proved, and is, indeed, by
no means certain.

b. Many eminent Anatomists maintain, that the two cavities are equal. The capacity of
each of the cavities may be estimated, in the full-sized Heart, at about two ounces; that of
the Auricles being probably a little less; and that of the Ventricles a little greater. That
the Ventricles receive more blood from the Auricles, than the latter could transmit to them
by simply emptying themselves once, seems, therefore, probable; and may be accounted for
by the fact already stated, regarding the slight intermission in the Ventricular Diastole, during
which more blood may enter the Auricle from the veins.

c. There is a well-known anatomical difference between the Amiculo- Ventricular valves,
on the two sides, which has given rise to the diversity of name. This seems, from the re-
searchesof Mr. King,* to be connected with an important functional difference. The .Mitral
valve closes much more perfectly than the Tricuspid : and tln> hitter is so constructed, as to
allow of considerable reflux, when the cavities are greatly distended. Many occasional
causes tend to produce an accumulation of blood in the venous system, and in the right side
of the Heart; thus, any obstruction to the pulmonary circulation, cold, compression of the
venous system by muscular action. &c.. are known to favour such a condition. This is a
state of peculiar danger, from the liability which over-distension of the Ventricular cavity
has, to produce a state of muscular paralysis; and in the structure of the Heart itself, there
seems to be a provision against it. For, when the ventricle is thus distended, the Tricuspid

* Guy's Hospital Reports, vol. ii.

ACTION OF THE HEART. 553

valves do not close properly; and a reflux of blood is permitted, not only into the Auricle,
but also (through the imperfect closure of their valves under the same circumstances), into
the large veins. This is proved by the fact, several times observed by Dr. J. Reid, in his
experiments upon Asphyxia, &e., that, when the action of the Right Ventricle had ceased
from over-distension, he could frequently re-excite it, not merely by puncturing its walls, but
by making an opening in the jugular vein. This fact evidently affords an indication of great
importance in the treatment of Asphyxia ; and it explains the reflux of blood, or venous
piilxf, which is frequently observed in cases of pulmonary disease, and which, according to
JVIr. King, always exists, though in a less striking degree.

724. It is not quite certain whether the Ventricles empty themselves com-
pletely at each contraction ; but it seems probable that the blood which they
contain, is not entirely forced into the arteries. The quantity which is pro-
pelled by each Ventricle, at every stroke, may be estimated, therefore, at from
1* oz. to 2 oz. If we adopt the lower of these numbers, we shall find that,
reckoning 75 pulsations of the Heart to a minute, 112 oz., or 7 Ibs., of blood
pass through each ventricle in that time; and, on the higher estimate, 150
oz., or 9 Ibs. 6 oz., would pass through in the same period. Now the whole
quantity of blood contained in the human body, according to the estimate of
Haller (which is considered by Dr. Allen Thomson to be near the truth), is
about one-fifth of the weight of the body, or 28 Ibs. in a person weighing
140 Ibs.* This quantity would pass through the Heart, therefore, in four
minutes, on the lower of the two preceding estimates, or in three minutes on
the higher; and would circulate afresh, fifteen or twenty times in an hour. It
Avould appear, however, that this estimate of the rapidity of the circulation is
very far from the truth; for recent experiments have shown, that substances
introduced into the Venous circulation, may be detected in the remotest parts
of the Arterial circulation, even in animals larger than Man, in less than half
a minute. — The earliest of such experiments were those of Hering,t who en-
deavoured to ascertain the rapidity of the circulation, by introducing Prussiate
of Potash into one part of the system, and drawing blood from another. He
states that he detected this salt, in blood drawn from one of the Jugular veins
of the Horse, within 20 or 30 seconds after it had been introduced into the
other ; in which brief space the blood must have been received by the Heart,
must have been transmitted through the Lungs, have returned to the Heart
again, have been sent through the Carotid artery, and have traversed its ca-
pillaries. From experiments of a similar nature upon other veins, he states
that the salt passed from the Jugular vein into the Saphena in 20 seconds ;
into the Masseteric artery in from 15 to 20 seconds ; into the External Max-
illary artery in from 10 to 25 seconds ; and into the Metatarsal artery in from
20 to 40 seconds. An attempt has been made to invalidate the inference
which seems inevitably to flow from these experiments, in regard to the rate
of the circulation, by attributing the transmission of the salt to the permea-
bility of the animal tissues ;J but it has never been shown, that even Prussiate
of Potash (which is probably more transmissible through this channel than
any other salt), can be carried from one part to another, with a rapidity at all
proportional to this. The only mode in which this property can be con-
ceived materially to facilitate the transmission of the salt through the vascular
system, would be by allowing it to pass through the septum of the auricles,
and thus to make its way from the right to the left side of the heart, without
passing through the pulmonary circulation ; and this it could scarcely do, to
the large amount which is evidently transmitted, in so short a time.

725. The experiments of Hering have been recently fully confirmed by

Valentin's estimate, founded upon different data, closely corresponds with this.
[• Tiedemann's Zeitschrift, vol. iii. p. 85.
j See Dr. Allen Thomson, foe. tit.

47

554 OF THE CIRCULATION OF BLOOD.

those of Mr. Blake;* who varied them by employing different substances,
and took other precautions against sources of fallacy. Ten seconds after
having injected a solution of Nitrate of Baryta into the Jugular vein of ahorse,
he drew blood from the Carotid artery of the opposite side ; after allowing
this to flow for five seconds, he substituted another vessel, which received the
blood that flowed during the five ensuing seconds ; and the blood that flowed
after the twentieth second, by which time the action of the Heart had stopped,
was received into a third vessel. These different specimens were carefully
analyzed. No trace of Baryta could be detected in the blood, which had
escaped from the artery between the tenth and fifteenth second after the in-
jection of the poison ; but in that which was drawn between the fifteenth and
the twentieth second, the salt was found to be present, and in greater abun-
dance than in the blood which had subsequently flowed. Moreover, the
coincidence between the cessation of the Heart's action, and the diffusion of
the salt through the arterial blood, bear a striking correspondence ; and it may
be hence inferred, that the arrestment of its muscular movement is due to the
effect of this agent upon its tissue, when immediately operating upon it,
through the capillaries of the coronary artery. This conclusion is borne out
by a variety of other experiments ; which show that the time of the agency
of other poisons, that suddenly check the Heart's action (which is the espe-
cial property of mineral poisons), nearly coincides, in different animals, with
that which is required to convey them into the Arterial capillaries. And it
seems to derive full confirmation from the fact, that poisons, which act locally
on other parts, give the first indications of their operation, in the same period
after they have been introduced into the Venous circulation. Thus, in the
Horse, the time that is required for the blood to pass from the Jugular vein
into the capillary terminations of the Coronary arteries, is 16 seconds ; as is
shown by the power of Nitrate of Potass to arrest the Heart's action within
that time : and Nitrate of Strychnia, injected into a vein, gave the first mani-
festation of its action on the Spinal Cord, in precisely the same number of
seconds. In the Dog, the Heart's action was arrested by the Nitrate of Potass
in 11 or 12 seconds; and the tetanic convulsions occasioned by Strychnia,
also commenced in 12 seconds. In the Fowl, the former period was 6
seconds, and the latter 63 ; in the Rabbit, the first was 4, and the other 4k
seconds. From these experiments, it seems difficult to resist the conclusion,
that the rapidity of the Circulation is very much underrated, in any estimate
that we found upon the capacity of the Heart, and its number of pulsations in
a given time ; and that some other force, than its contractions, must have a
share in producing the movement of the blood through the vessels.

726. The/ore^ with which the Heart propels the Blood, may be estimated
in two ways; — either by ascertaining the height of the column of that fluid,
which its contractile action will support; — or by causing the blood to act
upon a shorter column of mercury. — The former method was the one adopted
by Hales, who introduced a long pipe into the Carotid artery of a Horse, and
found that the blood would sometimes rise in it to the height of 10 feet. From
parallel experiments upon Sheep, Oxen, Dogs, and other animals, and by
comparing the calibre of their respective vessels with that of the Human aorta,
Hales concluded, that the usual force of the Heart in Man would sustain a
column of blood 7 A feet high, the weight of which would be about 4 Ibs. 6
oz. — The second method is that more recently adopted by Poisseuille ; and
the instrument which ho contrived for carrying it into practice (termed by him
the Htemadynamometer) has been the means of aiding many valuable inqui-
ries on the physiology of the Circulation. The result of his experiments is

» Edinb. Mecl. and Surg. Journal, Oct. 1841.

ACTION OF THE HEART.

555

very nearly the same as that of Hales ; his estimate of the force, with which

ihe blood is propelled into the Aorta, being 4
Ibs. 3 oz. The backward pressure upon the
walls of the Heart, or in other words the
force which they have to overcome in pro-
pelling the blood, is properly estimated, by
multiplying the pressure of blood in the aorta,
into the surface of a plane passing through
the base and apex of the left ventricle ; by
which calculation it is found to be about 13
Ibs.* The pressure appears, from the experi-
ments of Poisseuille, to be very nearly equal
for equal surfaces, throughout the larger arte-
rial branches ; since it diminishes regularly
in proportion to their calibre; in the radial
artery at the wrist, it was estimated by him
at 4 drachms.

727. The number of contractions of the
Heart in a given time, is liable to great varia-
tion, within the limits of ordinary health,
from several causes ; the chief of these are,
diversities of Age, of Sex, of Muscular exer-
tion, of the condition of the Mind, of the state
of the Digestive system, and of the Period of
the day.

a. Putting aside the other causes of uncertainty, the
following table may be regarded as an approximation
to the average frequency of the Pulse, at the several
ages specified in it.

[Fig. 213.

In the fetus in utero
Newly-born infant
During the First year
During the Second year
During the Third year ,
About the Seventh year
Age of Puberty
Manhood .

BEATS PER MINUTE.

. 140 -- 150

. . 130 — 140

. 115—130

. . 100 — 115

. 90 — 100

85—90

80— 85

70—80

50— 65

Htemadynamometer of Poisseuille. A
bent glass tube, filled with mercury in
the lower part, a d e. The horizontal
part 6, is provided with a brass head,
which fits into the artery. A small
quantity of a solution of the carbonate
of soda is interposed between the mer-
cury and the blood, to prevent its coagu-
lation. When the blood presses on the
fluid in the horizontal limb, the rise of
the mercury towards P, measured from
the level to which it has fallen towards
a, gives the pressure under which the
blood moves.]

Old age ....

b. The difference caused by sex is very considerable,
especially in adult age; it appears from the inquiries
of Dr. Guy,"!' mat ^ie pulse of the adult Female ex-
ceeds in frequency the pulse of the adult Male, at the
same mean age, by from 10 to 14 beats in a minute.

c. The effect of muscular exertion in raising the pulse is well known; as is also the fact,
which is one exemplification of it, that the pulse varies considerably with the posture of the
body. The amount of this variation has been made the subject of extensive inquiry by Dr.
Guy ; and the following are his results. In 100 healthy Males, of the mean age of 27 years,
in a state of rest, the average frequency of the pulse was, when standing, 79, — when sitting,
70, — and when lying, 67 per minute. Several exceptions occurred, however, to the general
law; and when these were excluded, the average numbers were, — standing, 81, — sitting,
71, — and lying, 66; so that the difference between standing and sitting was 10 beats, or
1— 8th of the whole; the difference between sitting and lying was 5 beats, or 1— 13th of the
whole; and the difference between standing and lying was 15 beats, or l-5th of the whole.
In 50 healthy Females, of the same mean age, the average pulse, when standing, was 89, —

* The extreme latitude of the estimates which have been made of this force, has been n.
subject of not undeserved ridicule. Borelli imagined it to be 180,000 Ibs.; whilst by Keill it
was supposed to be no more than from 5 to 8 ounces.

f Guy's Hospital Reports, vol. iii. p. 312.

556 OF THE CIRCULATION OF BLOOD.

when sitting, 81, — and when lying, 80. When the exceptions (which were more numerous
in proportion than in males) were excluded, the averages were, standing, 91, — sitting, 84, —
lying, 79; the difference between standing and sitting was thus 7 beats, or l-13th of the
whole; that between sitting and lying was 4, or l-21st of the whole; and that between
standing and lying was 11, or l-8th of the whole. In both sexes, the effect produced by
change of posture increases with the usual frequency of the pulse; whilst the exceptions to
the general rule are more numerous, as the pulse is less frequent. The variation is tem-
porarily increased by the muscular effort, involved in the absolute change of the posture ;
and it is only by the use of a revolving board, by which the position of the body can be
altered, without any exertion on the part of the subject of the observation, that correct results
can be obtained. That the difference between standing and sitting should be greater than
that between sitting and lying, is just what we should expect; when we compare the^
amount of muscular effort required in the maintenance of the two former positions respect-
ively.

d. The Pulse is well known to be much accelerated by Mental excitement, especially by
that of the Emotions ; it is also quicker during Digestion ; but on neither of these points can
any exact numerical statement be given.

e. The diurnal variation of the pulse, however, has been made the subject of observation,
by Dr. Guy ;* and, as the results of his inquiries have much interest, although (from having
been made only on his own person) they may ultimately require some modification, they
will be here stated. '• 1. The pulse of a healthy male in a state of rest, unexcited either by
food or exercise, is most frequent in the morning, and gradually diminishes as the day ad-
vances. , 2r The pulse diminishes in frequency more rapidly in the evening, than in the
morni&g. .3. The diminution in the frequency of the pulse (after excitement) is more regu-
lar and progressive in the evening than in the morning. 4. The effect of food is greater
and more lasting in the morning, than in the evening ; and in some instances, the same food,
•which in the morning produces an effect considerable both in amount and duration, has no
effect whatever in the evening." It may be hoped that, ere long, this interesting and im-
portant subject will receive further elucidation.

[/. Dr. Valleix has recently published a series of interesting observations on the fre-
quency of the pulse in newly-born infants, and in children aged from seven months to six
years. He obtained the following results: 1. At birth the pulse is less frequent than at six
months; the number of beats in a minute may be stated with considerable exactness to be
between 90 and 100. 2. Increase of temperature, even in the slightest degree, invariably
produces a notable acceleration of the pulse. The exact ratio between the degree of eleva-
tion of temperature and the increase in the frequency of the pulse, is not yet accurately
ascertained. 3. Although the observations of Dr. Valleix show a progressive diurnal diminu-
tion in the frequency of the pulse, still, he thinks, it would be premature to conclude that
these facts support those of Dr. Guy. Dr. Valleix examined his patients in the morning
after they had been eating, and to this fact, he thinks, should be attributed the acceleration
of the pulse in the early part of the day, and its subsequent diminution towards evening.
4. The slightest muscular effort in children is sufficient to augment considerably the number
of pulsations. The same is true of any moral emotion. 5. The influence of sex on the
pulse is very marked in young children. The pulse is much more frequent in young girls
than in boys of the same age. 6. During sleep there is a decided diminution in the number
of beats. 7. Between 7 and 27 months there is no sensible change in the frequency of the
pulse. Its mean may be stated at 120 beats in the minute, without distinction of sex. If
sex be considered, it would be 121 for males and 128 for females. These numbers express
the frequency of the pulse at this age under ordinary circumstances, but if a state of perfect
cairn is supposed, the numbers would be 119 for the males, and 124 for females. 8. After
some observations, not very numerous, however, the pulse would appear to range a little
above 100 till six years of age. 9. The mean number of inspirations in a minute in chil-
dren aged from 7 months to two years and a half, is between 30 and 32, and is to number
of pulsations : : 1 : 4. — M. C.]

3. — Movement of the Blood in the Arteries and Capillaries.

728. We have next to consider the influence of the Arterial tubes on the
flow of Blood through them. This influence is exerted by the middle or
tibrous coat, which alone is possessed of contractile properties. We find in
this coat, a layer of annular fibres, possessing no small resemblance to that
of which the muscular coat of the alimentary canal is composed. On the out-

* Op. cit., vol. iv. p. 69.

MOTION OF THE BLOOD IN THE ARTERIES. 557

side of this, is a layer of yellow elastic tissue, which is much thicker in the
larger arteries, in proportion to their size, than in the smaller. To this last
tissue is due the simple elasticity of the arterial walls, which is a physical
property that persists after death, until a serious change takes place in their
composition : whilst to the one first mentioned, we are to attribute the property
which they unquestionably possess — in common with proper muscular tissue,
— of contracting on the application of a stimulus, so long as their vitality re-
mains. These two endowments exist, in various proportional degrees, in the
different parts of the Arterial system. Thus it was justly remarked by Hun-
ter, that elasticity, being the property by which the interrupted force of the
Heart is made equable and continuous, is most seen in the large vessels more
immediately connected with that organ. On the other hand, the contractility
is most observable in the smaller vessels, where it is more required for regu-
lating the flow of blood towards particular organs.

729. It is easily shown that the action of the Elasticity of the Arterial
tubes, is one of a purely physical character; and that its purpose is to con-
vert the intermitting impulses, which the fluid receives from the heart, into a
continuous current. The former are very evident in the larger trunks; but
they diminish with the subdivision of these, until they entirely disappear in
the capillaries, in which the stream is usually equable or nearly so. AVe may
imagine a powerful forcing-pump injecting water, by successive strokes, into
a system of tubes with unyielding walls ; — the flow of fluid at the farther ex-
tremities of these tubes, would be as much interrupted as its entrance into
them. But if an air-vessel (like that of a fire-engine) were placed at their
commencement, the flow Avould be in a great degree equalized; since a part
of the force of each stroke would be spent upon the compression of the air
included in it; and this force would be restored by the elasticity of the air
during the interval, which would propel the stream, until directly renewed by
the next impulse. A much closer imitation of the natural apparatus would
be afforded, by a pipe which had elastic walls of its own ; if water were
forced by a syringe into a long tube of caoutchouc, for example, the stream
would be equalized before it had proceeded far. This effect is found to be
accomplished, at any point of the Arterial circulation, in a degree proportionate
to its distance from the Heart; and it is another effect of the same cause, that
the pressure of the blood upon the wall of the arteries (as shown by the ex-
periments of Poisseuille) is nearly the same all over the system. It is to the
distension of the arterial tubes, both in their length and calibre, that their
pulsation is due. Their elongation is the more considerable of the two effects ;
and it causes the artery to be lifted from its seat and to become curved. The
transverse dilatation has been denied by some physiologists ; but it has been
recently proved to take place, by an ingenious experiment of Poisseuille's.
The increase of capacity, however, is not more than l-10th ; so that the in-
crease of diameter will not be so much as l-20th, — a quantity scarcely per-
ceptible to ordinary measurement. The transmission of the pulse-wave
through the whole system is not instantaneous, but takes place in an appre-
ciable time. The pulsation of the large arteries near the Heart, is synchron-
ous with the Ventricular systole ; but that of other arteries is somewhat later,
— the difference varying with their distance, and amounting in some instances
to between l-6th and l-7th of a second.

730. It has been denied by many Physiologists, that the middle coat of the
Arteries possesses any property which can be likened to Muscular Contrac-
tility; and it will therefore be desirable to enter somewhat in detail into the
question. That it cannot be readily stimulated to contraction, through the
medium of its nerves, is universally admitted ; but the same is the case in
regard to the Muscular coat of the alimentary canal, which contracts most

47*

558 OF THE CIRCULATION OF BLOOD.

vigorously on the direct application of stimuli to itself; and Valentin and
others have recently succeeded in producing evident contractions in the Aorta,
by irritation of the Sympathetic nerve, and of certain roots of the Spinal
nerves. Further, although many experiments have failed in producing con-
tractions of this tissue, by stimuli directly applied to itself, yet others have
distinctly witnessed them; and, in any question of this kind, the positive
evidence must be held to outweigh the negative. Thus Verschuir states, that
he has seen arteries contract, when stimulated by the mineral acids, by elec-
tricity, and by the application of the point of a scalpel. Dr. Thomson also
saw them contract, on the application of ammonia, and when punctured with
the point of a fine needle, in the living body. It has been ascertained by the
direct and careful experiments of Poisseuille, that, when the artery is dilated
by the blood injected into it from the heart, it reacts with a force superior to
the impressing impulse ; and he has also shown that, if a portion of an artery
from an animal recently dead (in which the vital contractility seems to be
preserved), and one from an animal that has been dead some days (in which
nothing but the elasticity remains), be distended with an equal force, the for-
mer becomes much more contracted than the latter, after the distending force
is removed.

731. Several experiments also indicate the existence of that power of slow
contraction in the arteries, which has been distinguished by the appellation
Tonicity ; but which does not seem anything else than a particular manifesta-
tion of the general property of vital contractility, and is certainly of a nature
quite distinct from ordinary elasticity. Thus, when a ligature is placed upon
an artery in a living animal, the part of the artery beyond the ligature becomes
gradually smaller, and is emptied to a certain degree, if not completely, of the
blood it contained. Again, when part of an artery in a living animal is isolated
by means of two ligatures, and is punctured, the blood issues from the orifice,
and the inclosed portion of the artery is almost completely emptied of its
contents. The exposure of arteries to the air was found by Hunter to occa-
sion their contraction, to such an extent, that obliteration of their tube was
the result ; and this statement has been subsequently confirmed. Further,
every Surgeon knows, that the contraction of divided arteries is an efficient
means of the arrest of hemorrhage from them, especially when they are of
small calibre ; so that, in the case of the temporal artery, for example, the
complete division of the tube is often the readiest means of checking the flow
of blood from it, when it has been once wounded. This contraction is much
greater than could be accounted for by the simple elasticity of the tissue ; and
is more decided in small, than in large vessels. The empty condition of the
arteries, generally found within a short time after death, seems to be in part
due to the same cause ; since their calibre is usually much diminished, and is
sometimes completely obliterated. A remarkable example of the same slow
contraction, is that which takes place in the end of the upper portion of an
arterial trunk, when the passage of blood through it is interrupted by a liga-
ture ; for the current of blood then passes oft* by the nearest large lateral
branch ; and the tube of the artery shrivels, and soon becomes impervious,
from the point at which the ligature is applied, back to the origin of that
branch. This last fact is important, as proving how little influence the vis d
tergo possesses over the calibre of arterial tubes ; since, without any interrup-
tion to the pressure of blood occasioned by it, the tube becomes impervious. —
It is to the moderate action of the Tonicity of arteries, that their contraction
upon the stream of blood passing through them (which serves to keep the
tubes always full) is due. If the tonicity be excessive, the pulse is hard and
wiry ; but if it he deficient, the pulse is very compressible, though bounding,
and the flow of blood through the arteries is retarded. Dr. Williams has

MOTION OF THE BLOOD IN THE ARTERIES. 559

performed some ingenious experiments, which prove that the force required,
to propel fluid through a tube, whose sides are yielding, is very much greater
than that which will carry it through a tube of even smaller size, with rigid
parietes; consequently, a loss of tonicity in the blood-vessels retards the flow
of blood through them ; whilst an increase hastens it. The Tonicity of the
arteries differs from their ordinary Contractility, in being augmented by cold,
and diminished by warmth. Hence cold and heat are two most valuable
remedial agents, when this property is deficient or in excess.

732. It is still to be inquired, in what manner the Contractility of the Arte-
ries is to be regarded as influencing the flow of Blood through them. It is at
once evident, that any general contraction of the arterial tubes would have
rather the effect of opposing, than of assisting the flow ; but if the fibrous
coat of the Arteries is in some degree disposed to the alternate contraction and
relaxation, which are so remarkable in the Heart, they may exert a force which
shall be supplementary to that of the Heart's impulse, — relaxing to receive
the blood from it, and contracting upon their contents, with a power superior
to that by which they were distended. It is difficult to say whether or not
this be the case ; though there would certainly appear some evidence in favour
of the supposition. The loss of the Heart's power over the currents of blood,
in proportion to their degree of subdivision, occasioned by the increased fric-
tion to which they will be subjected, would seem to require some compensat-
ing power, in order that the perfect equality of pressure may be obtained
which has been spoken of as existing in all parts of the arterial system. In
no other way than this can the fibrous coat of the Arteries be regarded as
having any propulsive power over their contents ; except by a peristaltic or
vermicular movement, resembling that which takes place in the alimentary
canal ; and of such there is no evidence whatever. — A very important use
may be assigned to this muscular coat, which has been generally overlooked
by Physiologists, — that of regulating the diameter of the tubes, in accord-
ance with the quantity of blood to be conducted through them to any part ;
which will depend upon its peculiar circumstances at the time. Such local
changes are continually to be observed, in the various phases of normal life,
as well as in diseased states ; and they will be found to be constantly in har-
mony with the particular condition of the processes of Nutrition, Secretion,
&c., to which the Capillary circulation ministers. Of this kind are the en-
largement of the trunks of the Uterine and Mammary arteries, at the epochs
of pregnancy and lactation ; — the enlargement and strongly-increased pulsa-
tion of the Radial artery, when there is any active inflammation in the thumb ;
— the enormous diameter which the Spermatic artery will attain, when the
testicle is greatly increased in size by diseased action; and many other simi-
lar phenomena. In such cases, it cannot be the action of the Heart that in-
creases the calibre of the vessels ; since this is commonly unaltered, and is
itself unable, as we have just seen, even to maintain their permeability. It
must, therefore, be by a power inherent in themselves, that their dilatation is
effected. The minute distribution of the Sympathetic nerve upon the walls
of the arteries, — the known power which this has of producing contractions,
alike in their fibrous coat, and in the muscular tunic of the intestinal canal, —
and various phenomena, which indicate the power of certain states of mind
over the dimensions of the arteries, in particular parts of the body at least, —
render it highly probable that the calibre of the arteries is regulated in no in-
considerable degree through its intervention.* The permanent dilatation,
however, which is seen in the arteries supplying parts that are undergoing

" For Anatomical evidence to this effect, see Henle on the Contractility of the Blood-
vessels, in Casper's Wochenschrift, May 1840, and Brit, and For. Med. Rev., vol. x. p. 551.

560 OF THE CIRCULATION OF BLOOD.

enlargement, must be due, not to simple dilatation merely, but to increased
nutrition ; since we find that their walls are thickened as well as extended.
And, on the other side, when slow contraction occurs in these tubes, as a
consequence of disease, it must be in part occasioned by atrophy; since
their nutrition is so much diminished, that in time they almost entirely disap-
pear,— a portion of a large artery occasionally shriveling into a ligamentous
band.

733. We now come to the last head of the inquiry into the powers which
convey the blood through the capillary system ; — that, namely, which con-
cerns the agencies existing in the Capillaries themselves. Many discussions
on this subject may be found in Physiological writings ; and it has so imme-
diate a bearing on one of the most important questions in Pathology, — the
nature of Inflammation, — that it deserves the fullest attention. The chief
question in debate, is the degree in which the Capillary circulation is influ-
enced by any other agency than the contractile power of the Heart and Arte-
rial system ; — some Physiologists maintaining that this alone is sufficient
to account for all the phenomena of the Capillary circulation ; — and others
asserting that it is necessary to admit some supplementary force, which may
be exerted either to assist, retard, or regulate the flow of blood from the Arte-
ries into the Veins. We shall first consider what evidence there is of the
existence of any such force ; and, when led to an affirmative conclusion, we
shall examine into its nature. — No physiological fact is more clearly proved
than the existence, in the lower classes of Animals, as well as in Plants, of
some power independent of a vis u tergo, by which the circulating fluid is
caused to move through their vessels (§§ 712 — 716). This power seems to
originate in themselves, and to be closely connected with the state of the
Nutritive and Secreting processes : since anything which stimulates these to
increased energy, accelerates the circulation : whilst any check to them occa-
sions a corresponding stagnation. It may be convenient to designate this
motor force by the name of capillary power; it being clearly understood,
however, that no mechanical propulsion is thence implied. On ascending the
Animal scale, we find the power which, in the lower organisms, is diffused
through the whole system, gradually concentrated in a single part'; a new
force, that of the Heart, being brought into operation, and the Circulation
placed, in a greater or less degree, under its control. Still there is evidence,
that the movement of blood through the capillaries is not entirely due to this ;
since it may continue after the cessation of the Heart's action, — may itself
cease in particular organs when the Heart is still acting vigorously,*— and is
constantly being affected in amount and rapidity, by causes originating in the
part itself, and in no way affecting the Heart. The chief proofs of these
statements will now be adverted to.

734. When the flow of blood through the Capillaries of a transparent part,
such as the web of a Frog's foot, is observed with the Microscope, it appears
at first to take place with great evenness and regularity. But on watching the
movement for some time, various changes may be observed, which cannot be
attributed to the Heart's influence, and which show that a certain regulating
or distributive power exists in the walls of the capillaries, or in the tissues
which they traverse. Some of these changes, involving variations in ihesize
of the Capillary tubes, have been already referred to (§ 219). Others, how-
ever, are manifested in great and sudden alterations in the velocity of the cur-
rent ; which cause a marked difference in the rates of the movement of the
blood through the several parts of the area under observation. Sometimes
this variation extends even to the entire reversion, for a time, of the direction
of the movement, in certain of the transverse or communicating branches ; the
flow always taking place, of course, from the stronger towards the weaker cur-

MOTION OF THE BLOOD IN THE ARTERIES. 561

rent. Not unfrequently an entire stagnation of the current, in some particular
tube, precedes this reversal of its direction. Irregularities of this kind, how-
ever, are more frequent when the Heart's action is partially interrupted ; as
it usually is by the pressure, to which the Tadpole or other animal must be
subjected, in order to allow microscopic observations to be made upon its cir-
culation. Under such circumstances, the varieties in the capillary circulation,
induced by causes purely local, become very conspicuous ; for when the
whole current has nearly stagnated, and a fresh impulse from the heart re-
news it, the movement is not by any means uniform (as it might have been
expected to be) through the whole plexus supplied by one arterial trunk, but
is much greater in some of the tubes than it is in others ; the variation being
in no degree connected with their size, and being very different at short in-
tervals.

735. The movement of the blood in the Capillaries of cold-blooded ani-
mals, after complete excision of the Heart, has been repeatedly witnessed.
In warm-blooded animals, this cannot be satisfactorily established by experi-
ment, since the shock occasioned by so severe an operation much sooner de-
stroys the general vitality of the system ; but it may be proved in other ways
to take place. After most kinds of natural death, the arterial system is
found, subsequently to the lapse of a few hours, almost or completely emptied
of blood ; this is partly, no doubt, the effect of the tonic contraction of the
tubes themselves ; but the emptying is commonly more complete than could be
thus accounted for, and must, therefore, be partly due to the continuance of
the capillary circulation. Moreover, when death has taken place suddenly
from some cause (as, for instance, a violent electric shock), that destroys the
vitality of the whole system at once, the arterial tubes are found to contain
their due proportion of blood. Further, it has been well ascertained that a
real process of secretion not unfrequently continues after general or somatic
death ; urine has been poured out by the ureters, sweat excluded from the
skin, and other peculiar secretions formed by their glands; and these changes
could not have taken place unless the capillary circulation were still continu-
ing. In the early embryonic condition of the highest animals, the movement
of blood seems to be unquestionably due to some diffused power, independent
of any central impulsion ; for it may be seen to commence in the Vascular
Area, before the development of the Heart. The first movement is towards
instead of from, the centre ; and even for some time after the circulation is
fairly established, the walls of the Heart consist merely of cells loosely at-
tached together, and can hardly be supposed to have any great contractile
power.

736. The last of these facts may be said not to have any direct bearing on
the question, whether the Capillary power has any existence in the adult con-
dition ; but the phenomena occasionally presented by the Foetus, at a later
stage, appear decisive. Cases are of no very unfrequent occurrence, in which
the heart is absent during the whole of embryonic life, and yet the greater part
of the organs are well developed. In most or all of these cases, however, a
perfect twin foetus exists ; of which the placenta is in some degree united with
that of the imperfect one ; and it has been customary to attribute the circula-
tion in the latter, to the influence of the heart of the former, propagated
through the placental vessels. This supposition has not been disproved
(however improbable it might seem) until recently; when a case of this
kind occurred, which was submitted to the most careful examination by an
accomplished anatomist ;* and this decisive result was obtained, that it seemed

* See Dr. Houston in the Dublin Medical Journal, 1837. An attempt has been recently
made by Dr. M. Hall (Edinb. Monthly Journal, 1843) to disprove Dr. Houston's inferences;

562 OF THE CIRCULATION OF BLOOD.

impossible for the heart of the twin fetus to have occasioned the movement
of blood in the imperfect one; and that some cause present in the latter, must
have been sufficient for the propulsion of blood through its vessels. It was
a very curious anomaly in this case, that the usual functions of the Arteries
and Veins must have been reversed; for the Vena Cava, receiving its blood
from the Umbilical Vein nearly as usual, had no communication with the
Arterial system (the Heart being absent), except through the Systemic Capil-
laries ; to which, therefore, the blood must have next proceeded, returning to
the placenta by the Umbilical Artery. This view of the course of the blood
was confirmed by the fact, that the veins were everywhere destitute of valves.
— It is evident, that a single case of this kind, if unequivocally demonstrated,
furnishes all the proof that can be needed, of the existence, even in the high-
est animals, of a capillary power; which, though usually subordinate to the
Heart's action, is sufficiently strong to maintain the circulation by itself, when
the power of the central organ is diminished. In this, as in many other cases,
we may observe a remarkable power in the living system, to adapt itself to
exigencies. In the acardiac F(etus, the capillary power supplies the place
of the Heart, up to the period of birth ; after which, of course, the circula-
tion ceases, for want of due aeration of the blood. It has occasionally been
noticed, that a gradual degeneration in the structure of the Heart has taken
place during life, to such an extent that scarcely any muscular tissue could at
last be detected in it ; without any such interruption to the circulation, as
must have been anticipated, if it furnished the sole impelling force.

737. Further, it is a general principle, unquestioned by any Physiologist,
and embodied in the ancient aphorism Ubi stimulus, ibi jluxiis, that, when
there is any local excitement to the processes of Nutrition, Secretion, &c., a
determination of blood towards the part speedily takes place, and the motion
of blood through it is increased in rapidity; and although it might be urged,
that this increased determination may not be the effect, but the cause, of the
increased local action, such an opinion could not be sustained, without many
inconsistencies with positive facts. For it is known that such local determi-
nations may take place, not only as a part of the regular phenomena of growth
and development (as in the case of the entire genital system at the time of
puberty and of periodical heat, the uterus after conception, and the mammee
after parturition), but also as a consequence of a strictly local cause. Thus,
the student is well aware that, after several hours' close application, there is
commonly an increased determination of blood to the brain, causing a sense
of oppression, a feeling of heat, and frequently a diminished action in other
parts; and, again, when the capillary circulation is being examined under the
microscope, it is seen to be quickened by moderate stimuli, and equally re-
tarded by depressing agents. All these facts harmonize completely with the
phenomena, which are yet more striking in the lower classes of organized
beings, and which are evidently the results of the same laws.

738. It is equally capable of proof, on the other hand, that an influence
generated in the Capillaries may afford a complete check to the circulation
in the part ; even when the Heart's action is unimpaired, and no mechanical
impediment exists to the transmission of blood. Thus, cases of spontaneous
gangrene of the lower extremities are of no unfrequent occurrence, in which
the death of the solid tissues is clearly connected with a local decline of the
circulation ; and in which it has been shown, by examination of the limb after
its removal, that both the larger tubes and the capillaries were completely

but a most satisfactory reply has been made by Dr. Houston, at the Meeting of the British
Association, August IS-l.'i, and piibli>licd in the Dublin Journal, Jan. 1844. See also Edinb.
Med. and Surg. Joiirn. July 1S44.

MOTION OF THE BLOOD IN THE CAPILLARIES. 503

pervious ; so that the cessation of the flow of blood could not be attributed to
any impediment, except that arising from the cessation of some power which
exists in the capillaries, and which is necessary for the maintenance of the
current through them. The influence of the prolonged application of Cold
to a part, may be quoted in support of the same general proposition ; for, al-
though the calibre of the vessels may be diminished by this agent, yet their
contraction is not sufficient to account for that complete cessation of the flow
of blood through them which is well known to occur, and to terminate in the
loss of their vitality. The most remarkable evidence on this point, however,
is derived from the phenomena of Asphyxia, which will be more fully ex-
plained in the succeeding Chapter. At present it may be stated as a fact,
which has now been very satisfactorily ascertained, that, if admission of air
into the lungs be prevented, the circulation through them will be brought to a
stand, as soon as the air which they contain has been to a great degree de-
prived of its oxygen, or rather has become loaded with carbonic acid; and
this stagnation will, of course, be communicated to all the rest of the system.
Yet, if it have not continued sufficiently long, to cause the loss of vitality in
the nervous centres, the movement may be renewed by the admission of air
into the lungs. Now, although it has been asserted that the stagnation is due
to a mechanical impediment, resulting from the contracted state of the lungs in
such cases, this has been clearly proved not to be the fact, by causing animals
to breathe a gas destitute of oxygen, so as to produce Asphyxia in a different
manner; the same stagnation results as in the other case.

739. If the phenomena which have been here brought together, be con-
sidered as establishing the existence, in all classes of beings possessing a cir-
culating apparatus, of a Capillary power, which affords a necessary condition
for the movement of the nutritious fluid, through those parts in which it comes
into more immediate relation with the solids, — the question still remains
open, as to its nature. That the Capillaries possess a contractile power, far
higher in degree than that of the large Arteries, and more easily excited than
that of the smaller, appears scarcely to admit of doubt; though to what it is
due, may be reasonably questioned. It has been recently asserted by
Schwann, that they possess the same kind of fibrous tissue in their walls, as
do the large vessels: and this cannot be regarded as improbable. It is not
possible, however, that their contractility could have any influence in aiding
the continuous motion of blood through them ; unless it were exercised in a
very different manner from that of which observation affords us evidence.
For, when we are microscopically examining the Capillary circulation of any
part, it is at once seen, that the vessels present no obvious movement ; and
that the stream, now rendered continuous by the elasticity of the arteries,
passes through them, as through unelastic tubes. The only method, in which
the contractility of the Capillaries could produce a regular influence on the
current of blood, would be an alternate contraction and dilatation, or a peri-
staltic movement; and of neither of these can the least traces be discerned.
Hence we should altogether dismiss from our minds the idea of any 'mechani-
cal assistance, afforded by the action of the Capillaries, to the movement of
the blood. That the contractile coat of the Capillaries has for its office, to
regulate the calibre of the vessels, can scarcely be doubted ; but any general
permanent contraction would only occasion an obstacle to the circulation, —
as is shown by the effects of stimulating injections, which, if thrown into the
vessels before their vitality has been lost, will not pass through the capillaries.
It would appear, therefore, to be through their action on this coat, that local
stimuli occasion a contraction of the capillaries ; their effect, however, is dif-
ferent from what might have been anticipated ; for, instead of the capillary
circulation being retarded, it is accelerated, at least until an abnormal condition

564 OF THE CIRCULATION OF BLOOD.

results from their continued operation. Here, again, is another evidence, that
something different from mechanical power must be the agent, that operates
in all the foregoing cases.

740. It appears, from the preceding facts, that the conditions, under which
the power in question uniformly operates, may be thus simply and definitely
expressed: — Whilst the injection of blood into the Capillary vessels of every
part of the system, is due to the action of the Heart, its rate of passage
through those vessels is greatly modified by the degree of activity in the pro-
cesses, to which it should normally be subservient in them ; — the current
being rendered more rapid by an increase in their activity, and being stagnated
by their depression or total cessation. — Thus it seems that " the capillaries
possess a distributive power over the blood, regulating the local circulation,
independently of the central organ, in obedience to the necessities of each
part." If this be true, it is evident that the dilatation or contraction of the
Capillaries will only have a secondary influence on the movement of the blood
through them. The former condition is usually an indication of diminished
vital energy ; and when it is observed, it is almost invariably accompanied by
a retardation or partial stagnation of the current; on the other hand, the ap-
plication of a moderate stimulus, which excites the contractility, accelerates
for a time the motion of the blood, by rendering more energetic that reaction
between the fluids and the surrounding tissues, which is the condition that
really has the most influence over the current. — That alterations in the chemi-
cal state of the blood (involving, of course, important changes in its vital pro-
perties) are capable of exercising a most important effect on the Capillary cir-
culation, is shown, not merely by the stagnation of the Pulmonary Circulation
in Asphyxia (§ 780), but by the curious fact ascertained by Dr. J. Reid, — that
the blood, when imperfectly arterialized, is retarded in the systemic capilla-
ries, causing an increased pressure on the walls of the arteries. He found that,
when the ingress of air through the trachea of a Dog was prevented, and the
Asphyxia was proceeding to the stage of insensibility, — the attemps at inspi-
ration being few and laboured, and the blood in an exposed artery being quite
venous in its character, — the pressure upon the Arterial walls, as indicated by
the haemadynamometer applied to the Femoral artery, was much greater than
usual. Upon applying a similar test to a Vein, however, it was found that
the pressure was proportionally diminished; whence it became apparent, that
there was an unusual obstruction to the passage of venous blood through the
systemic capillaries. After this period, however, the mercury in the ha?ma-
dynamometer applied to the artery began to fall steadily, and at last rapidly,
in consequence of the diminished force of the heart, and the retardation of the
blood in the pulmonic capillaries; but, if atmospheric air was admitted, the
mercury rose very speedily, showing that the renewal of the proper chemical
state of the blood, restored the condition necessary for its circulation through
the Capillaries.

741. The principles already noticed (§ 713) as put forth by Prof. Draper,
seem fully adequate to explain these phenomena.

a. The arterial blood, — containing oxygon with which it is ready to part, and being pre-
pared 1d receive in exchange the carbonic acid which the tissues set free. — must obviously
have a greater alliniiy li>r the tissues, than venous Mood; in which both these changes have
already been eliccled. Consequently upon mere physical principles, the arterial Mood which
enters the .»y.->temic Capillaries on one side, must drive before it, and expel on the other side
of the net-work, the blood which has become venous whilst traversing it. But if the blood
which enters the Capillaries have no such affinity, no such motor power can be developed.

/). On the other hand, in the Capillaries of the lungs the opposite allinities prevail. The
venous Mood and the air in the pulmonary cells have a mutual attraction, which is satisfied
by the exchange of oxygen and carbonic acid that takes place through the walls of the capil-
laries; and when the blood has become arterialized, it no longer has any attraction for the

MOTION OF THE BLOOD IN THE CAPILLARIES. 565

air. Upon the very same principle, therefore, the venous blood will drive the arterial before
it, in the pulmonary capillaries, whilst respiration is properly going on: but if the supply of
oxygen be interrupted, so that the blood is no longer aerated, no change in the affinities takes
place whilst it traverses the capillary net-work; the blood continuing venous, still retains its
need of a change, and its attraction for the walls of the capillaries; and its egress into the
pulmonary veins is thus resisted, rather than aided, by the force generated in the lungs.

c. The change in the condition of the blood, in regard to the relative proportions of its
oxygen and carbonic acid, is the only one to which the Pulmonary Circulation is subservient;
but in the Systemic Circulation, the changes are of a much more complex nature ; — every
distinct organ attracting to itself the peculiar substances which it requires as the materials
of its own nutrition ; and the nature of the affinities thus generated being consequently differ-
ent in each case. But the same law holds good in all instances. Thus the blood conveyed
to the liver by the portal vein, contains the materials at the expense of which the bile-secret-
ing cells are developed; consequently the tissue of the liver, which is principally made up
of these cells, possesses a certain degree of affinity or attraction for blood containing these
materials; and this is diminished, so soon as they have been drawn from it into the cells
around. Consequently the blood of the portal vein will drive before it, into the hepatic vein,
the blood which has traversed the capillaries of the portal system, and which has given up,
in doing so, the elements of bile to the solid tissues of the liver. — The same principle holds
good in every other case.

742. It can be scarcely doubted, that it is by some influence exercised over
the molecular actions, to which the Blood is subject in the Capillaries, that
the Nervous system can operate on the functions of Nutrition, Secretion, &c.,
in the manner already alluded to (Chap, vn.) ; and this influence may be not
improperly termed vital, if by so designating it we merely imply that its
nature and mode of operation are unknown, but that it is closely connected
with those actions which are altogether peculiar to living beings. The follow-
ing experiment, made by Dr. Wilson Philip, exhibits in a convincing manner
the possibility of such an influence. " The web of one of the hind legs of a
frog was brought before the microscope; and while Dr. Hastings observed the
circulation, which was vigorous, the brain was crushed by the blow of a ham-
mer. The vessels of the web instantly lost their power, the circulation ceas-
ing; an effect which cannot arise, as we have seen, from the ceasing of the
action of the heart. [Dr. P. here refers to experiments, by which it was ascer-
tained, that the circulation in the capillary vessels of the frog will continue for
several minutes, after the interruption of the heart's action.] In a short time
the blood again began to move, but with less force. This experiment was
repeated, with the same result. If the brain is not completely crushed, although
the animal is killed, the blow, instead of destroying the circulation, increases
its rapidity."* We are not hence to conclude, however, that the Nervous
system supplies any influence, which is essential to the. continuance of the
Circulation ; since it is only by such sudden and severe injuries to the nervous
centres, as instantaneously destroy the vitality of the whole system (§ 735),
that the movement of the blood is arrested. The experiments of Muller and
others satisfactorily prove, that mere action of the Nerves does not produce
any direct effect upon the Capillary circulation; and this corresponds with the
well-known fact, that the Nutritive processes may continue as usual, after this
action has been suspended. All the facts, which bear upon the question of
the connection between Nervous agency and the forces maintaining the
Capillary Circulation, have an equal relation to the functions of Nutrition and
Secretion in general; and as already shown, the Nervous System also influ-
ences these, by the control it exerts over the diameter of the blood-vessels
(§ 730).

* Experimental Inquiry into the Laws of the Vital Functions. 4th edition, p. 52.
48

566 OF THE CIRCULATION OF BLOOD.

4. — Of the Venous Circulation.

743. The Venous system takes its origin in the small trunks that are
formed by the re-union of the Capillaries ; and it returns the blood from these
to the Heart. The structure of the Veins is essentially the same with that of
the Arteries ; but the fibrous tissue, of which their middle coat is made up,
bears more resemblance to the areolar tissue of the skin, than it does either
to muscular fibre, or to the true elastic tissue. The Elasticity of the Veins,
however, is shown by the jet of blood, which at first spouts out in ordinary
venesection; when, by means of the ligature, a distension has been occasioned
in the tubes below it. A slight Contractility on the application of stimuli,
and on irritation of the Sympathetic nervous fibres, has been observed ; but
this is not so decided as in the Arteries. The whole capacity of the Venous
system is considerably greater than that of the Arterial ; the former is usually
estimated to contain from 2 or 3 times as much blood as the latter, in the
ordinary condition of the circulation ; and when we consider the great pro-
portion, which the Veins in almost every part of the body bear to the arteries,
we shall scarcely regard even the larger of these ratios as exaggerated. Of
course the rapidity of the movement of the blood in the two systems, will
bear an inverse ratio to their respective capacities ; thus if, in a given length,
the Veins contain three times as much blood as the Arteries, the fluid will
move with only one-third of the velocity. Even at their origins in the
Capillary plexus, the Veins are larger than the Arteries which terminate in
the same plexus ; so that, wherever the arterial and venous net-works form
distinct strata, they are readily distinguished from each other. The Veins
are remarkable for the number of valves which they contain, formed of dupli-
catures or loose folds of the internal tunic, between the component lamina? of
which, contractile fibres are interposed ; and also for the dilatations behind
these, which, when distended, give them a varicose appearance. The valves
are single in the small veins, the free edge of the flap closing against the
opposite wall of the vein ; in the larger trunks they are double ; and in a
few instances they are composed of three flaps. The object of these valves
is evidently to prevent the reflux of blood; and we shall presently see that
they are of important use in assisting in the maintenance of the venous circu-
lation. They are most numerous in those Veins which run among parts
afl'ected by muscular movement ; and they are not found in the veins of the
lungs of the abdominal viscera or of the brain.

744. The movement of the blood through the Veins is, without doubt,
chiefly effected by the vis d tergo or propulsive force ; which results from
the action of the Heart and Arteries, and from the additional power generated
in the Capillary vessels. This is shown by the immediate arrestment of it,
which takes place when these forces are suspended. There are some con-
current causes, however, which are supposed by some to have much influence
upon it, and of which the consideration must not be neglected.

a. One of these is the suction-power attributed to the Heart; acting as a vis a fronte, in
drawing the blood towards it. It is very doubtful how far the Auricles have Mich a power
of active dilatation, a.s that which would be required for this purpose; and no sufficient
evidence has been given, that the current of blond at any distance from the Heart is affected
by it. Indeed, lor a rra.-on if) be presently stated, this may be regarded as impo.-sible.

b. Another important agency has been loimd by sonic Physiologists in the luspiratory
movement; this is supposed to draw the blood of the Veins into the chest, in order to sup-
ply the vacuum which is created there, at the moment of the descent of tho Diaphragm.
That the movement in question has some influence on the flow of Venous blood into the
chest, is evident from the occurrence of the respiratory pulse, long ago described by Halter ;
which may be seen in the veins of the neck and shoulder in thin persons, ami in those
especially who are suffering from pulmonary diseases. During Inspiration, the Veins are

VENOUS CIRCULATION. 567

seen to be partially emptied ; whilst during Expiration they become turgid, partly in con-
sequence of the accumulation from behind, and of the check in front ; and partly (it may
bo) in some cases, through an absolute reflux from the veins within the chest (§ 723, c).
The fact that, in the immediate neighbourhood of the chest, the flow of blood towards the
heart is aided by Inspiration and impeded by Expiration, is further proved by Sir D. Barry's
experiment, which consisted in introducing one extremity of a tube into the Jugular vein of
a Horse, and the other into water, which exhibited an alternate elevation and depression
with inspiration and expiration ; this has been repeated and confirmed by several Physiolo-
gists. On the other hand, the expiratory movement, while it directly causes accumulation
in the Veins, will assist the Heart in propelling the blood into the Arteries; and by the com-
bined action of these two causes are produced, among other effects, the rising and sinking of
the Brain, synchronously with expiration and inspiration, which are observed when a por-
tion of the cranium is removed. Several considerations, however, agree in pointing to the
conclusion, that no great efficacy can be rightly attributed to the Respiratory movements, as
exerting any general influence over the Venous circulation. The Pulmonary circulation,
being entirely within the chest, cannot be affected by variations in atmospheric pressure ;
and it may be further remarked, that the whole mechanism of respiration is so different in
Birds, from that which exists in Mammalia, that no vacuum can ever be said to exist in
their chests, although the venous circulation is performed as actively as usual. The Venous
circulation of the fcetus, also, is independent of any such agency. Again, it has been sho\vn
experimentally by Dr. Arnott and others, that no suction-power exerted at the farther end
of a long tube, whose walls are so deficient in firmness as are those of the Veins, can oc-
casion any acceleration in a current of fluid transmitted through it; for the effect of the
suction is destroyed, at no great distance from the point at which it is applied, by the flap-
ping together of the sides of the vessel.

c. One of the most powerful of the general causes which influence the Venous circula-
tion, is doubtless the frequently-recurring action of the Muscles upon their trunks. In every
instance that Muscular movement takes place, a portion of the Veins of the part will undergo
compression ; and as the blood is prevented, by the valves in the veins, from being driven
back into the small vessels, it is necessarily forced on towards the Heart. As each set. of
muscles is relaxed, the Veins compressed by it fill out again, — to be again compressed by
the renewal of the force. That the general Muscular movement is an important agent in
maintaining the Circulation, at a point above that, at which it would be kept by the action
of the Heart and Capillaries alone, appears from several considerations. The pulsations
are diminished in frequency by rest, accelerated by exertion, and very much quickened by
violent effort. In all kinds of exercise, and in almost every sort of effort, there is that
alternate contraction and relaxation of particular groups of Muscles, which has been just
mentioned, as effecting the flow of blood through the Veins; and there can be little doubt,
that the increased rapidity of the return of blood through them, is of itself a sufficient cause
for the accelerated movements of the Heart. When a large number of Muscles are put in
action after repose, as is the case when we rise up from a recumbent or a sitting posture,
the blood is driven to the Heart with a very strong impetus ; and if that organ should be
diseased, it may arrive there in a quantity larger than can be disposed of; so that sudden
death may be the result. Hence the necessity for the avoidance of all sudden and violent
movements, on the part of those who labour under either a functional or structural disease of
the centre of the circulation.

745. The Venous circulation is much more liable than the Arterial, to be
influenced by the force of Gravity ; and this influence is particularly notice-
able, when the tonicity of the vessels is deficient.

a. The following experiments performed by Dr. Williams, to elucidate the influence of
deficient firmness in the walls of the vessels, and of gravitation, over the movement of fluids
through tubes, throw great light on the causes of Venous Congestion. — A tube with two
equal arms having been fitted to a syringe, a brass tube two feet long, having several right
angles in its course, was adapted to one of them, whilst to the other was tied a portion of a
rabbit s intestine four feet long, and of calibre double that of the brass tube, this being
arranged in curves and coils, but without angles and crossings. When the two tubes were
raised to the same height, the small metal tube discharged from two to five times the quan-
tity of water discharged in a given time by the larger but membranous tube; the difference
being greatest, when the strokes of the piston were most forcible and sudden, by which the
intestine was much dilated at its syringe end, but conveyed very little more water. When
the discharging ends were raised a few inches higher, the difference increased considerably,
the amount of fluid discharged by the gut being much diminished ; and when the ends were
raised to the height of eight or ten inches, the gut ceased to discharge, each stroke only
moving the column of water in it, and this subsiding again, without rising high enough to

568 OF THE CIRCULATION OF BLOOD.

overflow. When the force of the stroke increased, the part of the intestine nearest the
syringe burst.

b. From these experiments it is easy to understand, how any deficiency of tone in the
Venous System will tend to prevent the ascent of the blood from the depending parts of the
body, and will consequently occasion an increased pressure on the walls of the vessels, and
an augmentation in the quantity of blood they contain. All these conditions are peculiarly
favourable to the escape of the watery part of the blood from the small vessels; and this
may either infiltrate into the areolar tissue, or it may be poured into some neighbouring
serous cavity, producing dropsy. Thus it happens, that such effusions may often be traced
to that state of deficient vigour of the system, which peculiarly manifests itself in want of
tone of the blood-vessels ; and that it is relieved by remedies which restore this. In many
young females of leuco-phlegmatic temperament, for example, there is a tendency to swell-
ing of the feet, by cedematpus effusion into the areolar tissue, in consequence of the depend-
ing position of the limbs; the cedema disappears during the night, but returns during the clay,
and is at its maximum in the evening. And the congestion which frequently manifests
itself in the posterior parts of the body, towards the close of exhausting diseases, in which
the patient has lain much upon his back, is attributable to a similar cause; of such conges-
tion, effusions into the various serous cavities are frequent results ; and such effusions, taking
place during the last hours of life, are often erroneously regarded as the cause of death. To
the same cause we are to attribute the varicose state of the veins of the leg, which is so
common amongst persons of relaxed fibre, and especially in those whose habits require
them to be much in the erect posture ; and this distension occasionally proceeds to complete
rupture, the causes of which are fully elucidated by the experiments just cited.

5. — Peculiarities of the Circulation in different Parts.

746. In several portions of the Human body, there are certain varieties in
the distribution and in the functional actions of the Blood-Vessels, which
should not be omitted in a general account of the Circulation. Of these, we
have in the first place to notice the apparatus for the Pulmonary circulation ;
the chief peculiarity of which is, that venous blood is sent from the heart,
through a tube which is Arterial in its structure, whilst arterial blood is re-
turned to the heart, through a vessel whose entire character is that of a Vein.
The movement of the blood through these is considerably affected by the
physical state of the Lungs themselves ; being retarded by any causes, which
can occasion pressure on the vessels (such as over-distension of the cells with
air, obstruction of their cavity by solid or fluid depositions, or by foreign sub-
stances injected into them, &c.); and proceeding with the greatest energy and
regularity, when the respiratory movements are freely performed. — The Por-
tal circulation, again, is peculiar, in being a kind of offset from the general or
systemic circulation; and also in being destitute of valves; and it may be
surmised with much probability, that the purpose of their absence is, to allow
of an unusually free passage of blood from one part of that system to another,
during the very varying conditions to which it is Subjected (§ 685).

"747. Another very important modification of the Circulating system, is that
which presents itself within the Cranium. From the circumstance of the
cranium being a closed cavity, which must be always filled with the same
total amount of contents, the flow of blood through its vessels is attended with
some peculiarities. The pressure of the atmosphere is here exerted, rather
to keep the blood in the head, than to force it out; and it might accordingly
be inferred that, whilst the quantity of cerebral matter remains the same, the
amount of blood in the cranial vessels must also be invariable. This infer-
ence appeared to derive support from the experiments of Dr. Kellie.* On
bleeding animals to death, he found that, whilst the remainder of the body was
completely exsanguine, the usual quantity of blood remained in the arteries
and veins of the cranium ; but that, if an opening was made in the skull, these
vessels were then as completely emptied as the rest. It is not to be hence

* Edinburgh Medico-Chirurgical Transactions, vol. i.

PECULIARITIES OF CIRCULATION. 569

inferred, however, that the absolute quantity of blood within the cranium is
not subject to variation; and that in the states of inflammation, congestion, or
other morbid affections, there is only a disturbance of the usual balance of
the arterial and venous circulation. The fact in all probability is rather, that,
the softness of the Cerebral tissue, and its varying functional activity, render
it peculiarly liable to undergo alterations in bulk ; and that the amount of the
cerebro-spinal fluid varies considerably at different times (§ 476) ; so that the
quantity of blood may thus, even in the healthy condition, be continually
changing. Moreover, in disordered states of the circulation, the quantity of
blood in the vessels of the cranium may be for a time diminished by a sudden
extravasation, either of blood or serum, into the cerebral substance; and the
amount of interior pressure upon the walls of the vessels may also be con-
siderably altered, even when there is no difference in the quantity of fluid
contained in them.*

748. The Erectile tissues constitute another curious modification of the
ordinary vascular apparatus. The chief of these are the Corpora Cavernosa
in the penis of the male, and in the clitoris of the female ; the collection of
similar tissues round the vagina, and in the nymphae, of the female ; and the
nipple in both sexes. In all these situations, erection may be produced by
local irritation ; or it may take place as a result of certain emotional conditions
of the mind ; the influence of which is probably transmitted through the
Sympathetic nerve, as it may be experienced even in cases of paraplegia.
The erectile tissue appears essentially to consist of a plexus of varicose Veins,
inclosed in a fibrous envelope. According to Gerber,t this plexus is traversed
by numerous contractile fibres, which are analogous to those that form the
dartos ; and to the contraction of these is probably to be attributed that ob-
struction to the return of blood by the Veins, which is the occasion of the
turgescence. The proximate cause of the erection of the Penis, has been
stated by some to be the action of the Ischio-Cavernosi muscles ; and by others
it has been attributed to the compression of the Vena dorsalis penis against
the Symphysis pubis. But it is obvious that nothing analogous to this can
apply to the other erectile organs, especially to the Nipple. In the Penis,
according to Miiller, there are two sets of arteries ; of which one, destined for
the nutrition of the tissues, communicates with the veins in the usual way,
through a capillary net-work ; whilst the others pass off as large branches, and
penetrate the cavernous substance in a helicine manner, communicating ab-
ruptly with the venous cells. It would seem not improbable, that these last
are not ordinarily pervious to blood ; but that the same change in the contrac-
tile fibres, which impedes the return of the blood by the veins, may also
permit it to enter more freely from the helicine arteries. This double com-
munication, however, is denied by Valentin, who gives a different explanation
of the appearances described by Miiller. — The arteries are protected in such
a manner, that, even when the veins are most compressed, and the erection
most complete, they are still quite pervious.

The results of the more recent experiments of Dr. G. Burrows (Med. Gaz., April and
May, 1843) fully confirm the views stated above.
| General Anatomy, p. 298.

48*

570 OF RESPIRATION.

CHAPTER XIII.

OF RESPIRATION.

1. — Nature of the Function: and Provisions for its Performance.

749. IT is obvious that the Nutritive fluid, in its circulation through the
capillaries of the system, must undergo great alterations, both in its physical
constitution, and its vital properties. It gives up to the tissues with which it
is brought into contact, some of its most important elements ; and, at the same
time, it is made the vehicle of the removal, from these tissues, of ingredients
which are no longer in the state of combination, that fits them for their offices
in the Animal Economy. To separate these ingredients from the general cur-
rent of the circulation, and to carry them out of the system, is the great object
of the Excretory organs ; and it is very evident that the importance of the
respective functions of these will vary with the amount of the ingredient
which they have to separate, and with the deleterious influence which its re-
tention would exert on the welfare of the system at large. Of all these injuri-
ous ingredients, Carbonic Acid is without doubt the one most abundantly
introduced into the nutritive fluid; and it is also most deleterious in its effects
on the system, if allowed to accumulate. — We find, accordingly, that the pro-
vision for the removal of Carbonic Acid from the Blood, is one of peculiar
extent and importance, especially in the higher forms of Animals ; and further,
that instead of being effected by an operation peculiarly vital (like other acts
of Excretion), its performance is secured by being made to depend upon simple
physical laws, and is not nearly so susceptible of derangement from disorder
of other processes, as it would be if its conditions were less simple. All that
is requisite for it, as we shall presently see, is the exposure of the Blood to
the influence of the Atmospheric air, or of Air dissolved in water, through the
medium of a membrane that shall permit the diffusion of gases; and an inter-
change then takes place between the gaseous matters on the two sides, — Car-
bonic acid being exhaled from the Blood, and being replaced by Oxygen.
Thus the extrication of Carbonic acid is effected in a manner, that renders it
subservient to the introduction of the element which is required for all the
most active manifestations of vital power; and it is in these two processes
conjointly, not in either alone, that the function of Respiration essentially con-
sists.— We shall now inquire into the sources from which Carbonic acid is
produced in the living body; and the causes of the demand for Oxygen.

7f)0. All organized bodies, as already explained, are liable to continual
dec-ay, even whilst they are most actively engaged in performing the actions
of Life ; and one of the chief products of that decay is Carbonic Acid. A
large quantity of this gas is set free, during the decomposition of almost every
kind of organized matter; the Carbon of the substance being united with the
oxygen supplied by the air. Hence we find, that the formation and liberation
of carbonic Acid go on with great rapidity after death, both in the Plant and
in the Animal ; and that they take plaae, also, to a very great extent, in the
period that often precedes the death oFtlie body, during which a general de-
composition of the tissues is occurring. Thus in Plants, as soon as they
become unhealthy, the extrication of carbon in the form of carbonic acid takes

SOURCES OF CARBONIC ACID. 571

place in greater amount than its fixation from the carbonic acid of the atmo-
sphere ; and the same change normally occurs during the period that immedi-
ately precedes the annual fall of the leaves, their tissue being no longer able
to perform its proper functions, and giving rise, by its incipient decay, to a
large increase in the quantity of carbonic acid set free. The same thing
happens in the Animal body, during the progress of many diseases which are
attended with an unusual tendency to decomposition in the solids and fluids,
— such as eruptive fevers ; — the quantity of carbonic acid set free in Respira-
tion is greatly increased, although the body remains completely at rest ; and
notwithstanding this, the blood frequently exhibits a very dark hue, indicating
that it has not been freed from the unusual amount of that substance which
it has received from the tissues. — Hence the first object of the Respiratory
process, which is common to all forms of organized being, is to extricate from
the body the carbonic acid, which is one of the products of the continual de«-
composition of its tissues. The softness of many of the tissues of Animals,
and the large quantity of fluid contained in their bodies, render them more
prone than Plants to this kind of decomposition; and in warm-blooded animals,
the high temperature at which the fabric is usually maintained, adds con-
siderably to the degree of this tendency, so that the waste of their tissues,
from this cause alone, is as much greater than that of cold-blooded animals,
as the latter is than that of Plants. But when the temperature of the Reptile
is raised by external heat to the level of that of the Mammal, its need for
respiration increases, owing to the augmented waste of its tissues. When, on
the other hand, the warm-blooded Mammal is reduced, in the state of hyber-
nation, to the level of the cold-blooded Reptile, the waste of its tissues dimin-
ishes to such an extent, as to require but a very small exertion of the respira-
tory process to get rid of the carbonic acid, which is one of its chief products.
And in those animals which are capable of retaining their vitality, when they
are frozen, or when their tissues are completely dried up, the decomposition
is for the time entirely suspended, and consequently there is no carbonic acid
to be set free.

751. But another source«of Carbonic acid to be set free by the Respiratory
process, and one which is peculiar to animals, consists in the rapid changes
which take place in the Muscular and Nervous tissues, during the period of
their activity. It has been already shown (§ 586), that there is strong reason
to believe the waste or decomposition of the muscular tissue to be in exact
proportion to the degree in which it is exerted; every development of muscu-
lar force being accompanied by a change in the condition of a certain amount
of tissue. In order that this change may take place, the presence of Oxygen
is essential ; and one of the products of the union of oxygen with the elements
of muscular fibre is carbonic acid. The same may probably be said of the
Nervous tissue (§ 292). Hence it may be stated as a general principle, that
the peculiar waste of the Muscular and Nervous substances, which is a con-
dition of their functional activity, and which is altogether distinct from the
general slow decay that is common to these tissues with others, is another
source of the carbonic acid which is set free from the animal body ; and that
the amount thus generated will consequently depend upon the degree in which
these tissues are exercised. In animals which are chiefly made up of the
organs of vegetative life, in whose bodies the nervous and muscular tissues
form but a very small part, and in whose tranquil plant-like existence there is
but very little demand upon the exercise of these structures, the quantity of
carbonic acid thus liberated will b^jhctremely small. On the other hand, in
animals, whose bodies are chiefly composed of muscle, and whose life is an
almost ceaseless round of exertion, the quantity of carbonic acid thus liberated
is very considerable.

572 OF RESPIRATION.

752. Besides these sources of Carbonic acid, which are common to all
Animals, there is another, which appears to be peculiar to the two highest
classes, Birds and Mammals. These are capable of maintaining a constantly
elevated temperature, so long as they are supplied with a proper amount of
appropriate food; and their power of doing so appears to depend upon the
direct combination of certain elements of the food, with the oxygen of the air,
by a process analogous to combustion ; these elements having been introduced
into the blood for that purpose, but not having formed a part of any of the
solid tissues of the body, unless they have been deposited in the form of fat.
The nature of these substances has been already noticed (§ 641). It is quite
clear that they cannot be applied in their original form, to the nutrition of the
tissues that originate in proteine compounds; and it is tolerably certain that,
in the ordinary condition of the body, they undergo no such conversion, as
would adapt them to that purpose. The Liver seems to afford a channel, by
which some of the fatty matters are drawn off from the blood; but even these
seem, in part at least, to be reabsorbed (§ 671), and to be thrown off by the
respiratory process.

753. The quantity of carbonic acid, that is generated directly from the
elements of the food, seems to vary considerably in different animals, and in
different states of the same individual. In the Carnivorous tribes, which spend
the greater part of their time in a state of activity, it is probable that the quan-
tity which is generated by the waste or metamorphosis of the tissues is suffi-
cient for the maintenance of the required temperature, — and that little or none
of the carbonic acid set free in respiration is derived from the direct combus-
tion of the materials of the food. But in Herbivorous animals of comparatively
inert habits, the amount of metamorphosis of the tissues is far from being suf-
ficient; and a large part of the food, consisting as it does of substances that
cannot be applied to the nutrition of the tissues, is made to enter into direct
combination with the oxygen of the air, and thus to compensate for the de-
ficiency. In Man and other animals, which can sustain considerable variations
of climate, and can adapt themselves to a great diversity of habits, the quantity
of carbonic acid formed by the direct combination*of the elements of the food
with the oxygen of the air, will differ extremely under different circumstances.
It will serve as the complement of that which is formed in other ways; so
that it will diminish with the increase, and will increase with the diminution
of muscular activity. On the other hand it will vary, in accordance with the
external temperature; increasing with its diminution, as more heat must then
be generated; and diminishing with its increase. — In all cases, if a sufficient
supply of food be not furnished, the store of fat is drawn upon: and if this be
exhausted, the animal dies of cold (§ 896).

754. To recapitulate, then, the sources of Carbonic Acid in the animal body
are threefold. — i. The continual decay of the tissues; which is common to
all organized bodies; which is diminished by cold and dryness, and increased
by warmth and moisture; which takes place with increased rapidity at the
approach of death, whether this affect the body at large, or only an individual
part; and which goes on unchecked when the actions of nutrition have ceased
altogether. — n. The Metamorphosis, which is peculiar to the Nervous and
Muscular tissues ; which is the very condition of their activity, and which
therefore bears a direct relation to the degree in which they are exerted. — in.
The direct conversion of the carbon of the food into carbonic acid; which is
peculiar to warm-blooded animals ; and which seems to vary in quantity, in
accordance with the amount of heat to be generated. — We shall now examine
into the manner in which this compound is set free, in the principal groups of
the Animal kingdom.

755. Notwithstanding their diversity in external form, the organs of Re-

GENERAL STRUCTURE OF THE RESPIRATORY ORGANS. 573

spiration are always formed upon the same general plan; being essentially
composed of a membranous prolongation of the external surface, adapted, by
its vascularity and permeability, to bring the blood into close relation with the
surrounding medium. But as this medium may be either air or water, we
find two principal forms of the apparatus; one of them adapted for each kind
of respiration. In aquatic animals, the membrane is usually prolonged ex-
ternally into tufts or fringes, which are so arranged as to expose the greatest
amount of surface to the water ; each filament of which these are composed,
includes an afferent and efferent capillary vessel; and it is whilst the fluid is
passing through them, that its aeration is accomplished. The collection of
tufts or fringes constitutes what are known as gills ;
and though their arrangement varies considerably, their Fig. 214.

essential character is but little different, throughout the
classes of animals that possess them. On the other
hand, in air-breathing Animals, the aerating surface
is reflected inwardly, forming passages or chambers
into which the air is received, and on the walls of
which the blood is distributed in a minute capillary
net-work. Such a conformation is found even among
some of the lower Articulata, which have a series of
air-sacs disposed along each side of the body, one for
every segment. In Insects we find, instead of the
sacs, a system of prolonged tubes, ramifying through
the body, and carrying air into its minutest por-
tions. Even in SOlTie MollllSCa, Such as the Snail One of the arborescent pro-
• ,i_ , • , f-^ -i /• j • • cesses, forming the pills of

and other terrestrial Gasteropods, we find a provision Doris '3ohn^ separated
for aerial respiration ; a large cavity being formed in and enlarged.
the back, communicating with the air, and having a

beautifully-reticulated plexus of blood-vessels on its walls. In none of
the Invertebrata, however, does ihe respiratory apparatus communicate with
the mouth; which is an organ solely appropriated, in them, to the ingestion
of food. In the Mollusca, indeed, the channel through which the water,
that has passed over the aerating surface, leaves the chamber (formed by
a fold of the mantle or general envelope) which contains the gills, is the
same as that through which the excrementitious matter is discharged from
the intestine ; and the gills themselves are very commonly situated in the
neighbourhood of the anal orifice. This fact is interesting in regard to the
character of the temporary respiratory apparatus of the Human embryo. In
Fishes and the larva? of Batrachia, which are the highest animals that breathe
by gills, these organs are so disposed in connecting with the cavity of the
mouth, that fresh currents of water are continually being forced over them by
its muscles ; and thus the energy of their action is greatly increased. More-
over the whole blood, which is propelled from the heart, proceeds first to the
respiratory organs ; instead of passing through them on its return from the
systemic circulation, as in most of the aquatic Invertebrata. Still, as the
quantity of oxygen which the blood can obtain in this manner is very small,
being limited to that contained in the atmospheric air dissolved in the water,
the amount of aeration must be considered as low.

756. In the lowest Vertebrata that possess anything like a pulmonary cavity,
this has a structure as simple as that of the air-sac of the Snail. This is the
case in many Fishes, where it is known as the air-bladder ; it is frequently
single in this class, and communicates with the intestinal canal near the sto-
mach, or is altogether destitute of outlet. In others, however, it is double,
and its duct opens into the oesophagus near the mouth ; so that its analogy to
the lungs of higher animals is very evident. The Batrachia begin life as

574

OF RESPIRATION.

Fishes, breathing by gills during their tadpole state ; but at the time that the
legs are developed and the tail has decreased, the pulmonary organs also are
evolved, and the course of the blood is altered, so that it is no longer trans-
mitted through the gills, which speedily shrivel and disappear (§ 31). There
are some species, however, whose metamorphosis is checked, so that in their
permanent condition both lungs and gills are present ; but the former are then
present in a very rudimentary form, not being more developed than the air-
sacs of many Fishes. The lungs of Reptiles are, for the most part, simple
sacs ; into which the bronchial tubes open freely ; and on the walls of which,
the pulmonary vessels are distributed. The extent of surface is considerably
increased, however, by the formation of a number of little pits or sacculi on
the inner wall of the cavity, especially at its tipper part ; and between these,
we observe a sort of cartilaginous frame-work, which is continuous with the
cartilage of the bronchus on either side. The Turtles and their allies are the
only Reptiles, in which the cavity of the lung is itself divided by membranous
partitions ; and thus it happens that, excepting in these, the net-work of pul-
monary capillaries, in the class of Reptiles, is exposed only on one side to
the influence of the air. The general distribution of these vessels is shown
in the accompanying figures. It will be seen that the trunk of the pulmonary
artery runs along one side of the sac, and that of the pulmonary vein along
the other (Fig. 215) ; and that numerous branches arise from the former,
which subdivide into capillaries that ramify over the whole surface, and then
reunite into small veins which terminate in the latter. The islets of paren-
chyma left between the capillary vessels, are seen to be much smaller than
those which are usually to be observed in the systemic circulation (Figs.
216, 217); so that the membrane is more copiously traversed by vessels, than

Fig. 215.

[Fig. 216.

Lung of Triton cristatxs, magnified
about 3 diameters ; a, pulmonary artery;
b, pulmonary vein.

Portion of the Inner of the same animal,
more highly magnified ; the vessels, finely-
injected with size and vermilion, form a
net-work so minute, that the parenchyma is
only seen in small islets in its interstices.

GENERAL STRUCTURE OF THE RESPIRATORY ORGANS.

575

any other that is known. The walls of the capillaries, moreover, are much
less distinct than those of the systemic circulation. These two conditions
are obviously favourable to the exposure of the largest possible quantity of
blood to the influence of the air ; but as the surface is not an extensive one,
the amount which can be thus exposed at any one time is very limited ; and
the pulmonary artery is in fact one of the smaller branches of the aorta, which
conveys a mixed fluid to the system at large. •

Fig. 217.

Portion of the lung of a living Triton, as seen under the microscope with the power of 150 diam. ; a,
b, pulmonary vein, receiving blood from the large trunk c, and a smaller vessel d.

757. In the warm-blooded Vertebrata, which have a complete double cir-
culation,— namely, Birds and Mammalia, — a much larger extent of surface is
provided for the aeration of the blood ; the whole current of which is trans-
mitted to the lungs, before circulating again through the system. This in-
crease is provided in Birds, partly by the greater extension of surface in the
lungs themselves, — these cavities being subdivided by partitions into numerous
smaller chambers, each having pitted walls, and resembling the entire lung of
a Reptile ; — and partly by the addition of a number of large air-sacs, which
are disposed in various parts of the body, and even in the interior of the long
bones. Hence it happens, that the amount of Respiration is greater in this
class than in any other ; although the form of the apparatus is not nearly so
concentrated as in the Mammalia ; nor is the mechanism of the chest so well
adapted to a constant exchange of the air contained in its cavities (§ 37). In
Mammalia the lungs are proportionally smaller ; and the whole respiratory

576

OF RESPIRATION.

apparatus is restricted to the thorax: but the minute subdivision of their cavity,
and the mechanism by which a continual interchange of air is provided for,
render them very efficient for their designed purpose. — The following, accord-
ing to the latest researches, especially those of Mr. Rainey,* appears to be
the nature of the ultimate structure of the lungs in Man and the Mammalia
in general. The bronchial tubes divide and subdivide, like the branches of a
tree, still retaining their ordinary characters, until they are no more than from
l-50th to l-30th of an inch in diameter ; and in these the longitudinal and
. annular fibres, together with the ciliated epithelium, come to an abrupt ter-
mination. Beyond this boundary, the tubular form of the air-passages con-
tinued from the bronchi is retained for some distance ; but it is gradually
changed by the irregular branching of the passages, and by the increase of
the number of apertures in their walls, which lead to the air-cells. Thus, at
last, each minute division of the air-passages becomes quite' irregular in form ;
air-cells opening into every part of it, and almost constituting its walls ; until
it terminates, almost without dilatation, in an air-cell. This terminal portion
of the air-passage, with its surrounding cluster of air-cells, may be regarded
as forming a sort of lobule, and as representing the entire lung of a Frog or

[Fig. 218.

The Larynx, Trachea and Bronchine, deprived of their fibrous covering, and with the outline of the
Lungs ; 1, 1, outline of the upper lobes of the lungs ; 2, outline of the middle lobe of the right lung ; 3, 3,
outline of the inferior lobes of both lungs ; 4, outline of the ninth dorsal vertebra, showing its relation to
the lungs and the vertebral column ; 5, thyroid cartilage ; 6, cricoid cartilage ; 7, trachea; S, right bron-
chus ; 9, left bronchus ; 10, crico-thyroid ligament; 11, 12, rings of the trachea; 13, first ring of the tra-
chea; 14, last ring of the trachea, which is corset-shaped; 15, 16, a complete bronchial cartilaginous
ring; 17, one which is bifurcated ; 19, double bifurcated bronchial rings; 19. 19, smaller bronchial rings;
20, depressions for the course of the large blood-vessels.]

* Medico-Chirurgical Transactions, vol. xxviii.

STRUCTURE AND DEVELOPMENT OF HUMAN LUNG.

[Fig. 219.

577

A view of the Bronchise and Blood-Vessels of the Lungs as shown by dissection, as well as the rela-
tive position of the Lungs to the Heart ; 1, end of the left auricle of the heart ; 2. the right auricle ; 3,
the left ventricle with its vessels; 4, the right ventricle with its vessels; 5, the pulmonary artery ; 6,
arch of the aorta ; 7, superior vena cava ; S, arteria innominata ; 9, left primitive carotid artery ; 10, left
subclavian artery ; 11, the trachea ; 12, the larynx ; 13, upper lobe of the right lung ; 14, upper lobe of the
left lung ; 15, trunk of the right pulmonary artery ; 16, lower lobes of the lungs. The distribution of the
bronchia and of the arteries and veins, as well as some of the air-cells of the lungs, is also shown in
this dissection.]

other Reptile ; the whole lung of the Mammal being made up of a multitude
of such lobules, which are almost exact repetitions of each other. There is,
however, this difference ; — that the air-cells in the lung of the Reptile are mere
sacculated depressions in the walls of the cavity, opening very freely into it ;
— whilst the air-cells of each lobule of the lung of the Mammal are arranged
around the central passage in such numbers, that the outer ones can only
communicate with this passage through the medium of those which are nearer
the middle of the cluster. Those cells which communicate directly with the
bronchial tubes and intercellular passages, open into them by large circular
apertures ; and they are themselves similarly opened into by other cells, which
again communicate with others beyond them ; so that each of the openings
in the air-passage leads to a series of air-cells, extending from it to the surface
of the lobule. These cells have also lateral communications with each other.
The walls of the air-cells are formed, of a very thin and transparent mem-
brane, which is folded sharply at the orifices of communication, so as to
form a very definite border to them; and the capillary plexus is so placed
between the two layers, which form the walls of two adjacent air-cells, as to
expose one of its surfaces each ; by which provision, the full influence of the
air upon it is secured.
49

578 OF RESPIRATION.

«. It appears from the researches of M. Bourgery,* that the development of the air-cells
continues in the human subject up to the age of thirty, at which time the capacity for re-
spiration is the greatest ; it subsequently decreases, especially in persons who suffer from
rough, — the violence of which expiratory effort frequently causes rupture of the air-cells,
and thus gradually produces that emphysematous state of the lungs, which is so common in
elderly persons. The power of increasing the volume of air taken in, by a forced inspira-
tion, is much less in the old person than in the child, though the average amount of air in-
spired may be the same; hence the young person possesses a greater capacity of respiration,
as it were, in reserve ; whilst the old man has little, and is, therefore, unfit for great exer-
tion.

b. The Lungs are developed, in the first instance, as diverticula from the cesophageal tube.
In the Chick, about the fourth day, a little sacculus is described as shooting forth at its pos-
terior and inferior part; and this soon subdivides at its lower part into two; at the same
time becoming more separated from the tube, by a constriction around the neck, which soon
elongates so as to form the trachea. On the fifth or sixth day, the lung of one side is com-
pletely distinct from that of the other, and each

Fif. 220. *s atla°hed to the common pedicle by a pecu-

liar branch, the future bronchus. The upper
portion has much thicker walls than the lower;
and these appear to contain a large quantity
of vesicular parenchyma, in which the rami-
fications of the bronchial tubes subsequently
extend themselves. About the tenth or ele-
venth day of incubation, these ramifications
possess nearly their permanent character and
situation. The first trace of the Glottis ap-
First appearance of the lungs: a, in a Fowl at pears about the fifth day; it is then a mere
four days ; 6, in a Fowl at six days ; c, termina- slit in the walls of the oesophagus, resembling
tion of bronchus in a very young Pig. that by which the ductus pneumaticus of some

Fishes, opens into the alimentary canal. The

formation of the cartilaginous rings of the trachea does not commence until after the twelfth
day, when they first appear as transverse stria? on the median line of the front only ; they
gradually become solid, and extend themselves on either side, until they nearly meet at last
on the median line on the back or vertebral side of the tube.

c. The history of the process in the Human embryo, appears to be very nearly the same.
The first appearance of the Lungs takes place about the sixth week, at which time they are
simple vesicular prolongations of the cesophageal membrane. Their surface, however, soon
becomes studded with numerous little wart-like projections; and these are caused by the
formation of corresponding enlargements of their cavity. These enlargements soon become
prolonged, and develope corresponding bud-like enlargements from their sides; and in this
manner, the form of the organs is gradually changed, a progressive increase in their bulk
taking place from above downwards, in consequence of the extension of the bronchial ra-
mifications from the single tube at the apex. At the same time, however, a corresponding
increase in the amount of the parenchymatous tissue of the lung is taking place ; for this is
deposited in all the interstices between the bronchial ramifications, and might be compared
with the soil filling up the spaces amongst the roots of a tree. It is in this parenchyma that
the pulmonary vessels are distributed ; and the portion of it which extends beyond the ter-
minations of the bronchial tubes, seems to act as the nidus for their further extension. It
can be easily shown that, up to a late period of the development of the lungs, the dilated
terminations of the bronchi constitute the only air-cells (Fig. 220, c) : but, as already men-
tioned, the parenchyma subM.-qucntly has additional cavities formed within it. — It is a fact
of some intercut, as an example of the tendency of certain diseased conditions to produce a
r-'turn to forms which are natural to the fretal organism, or which present themselves in other
animals, — that up to a late period in the development of the Human embryo, the lungs do
not nearly fill the cavity of the chest, and the pleura of each side contains a good deal of
serous fluid.

758. The network of vessels on the walls of the air-cells is so minute, that
the diameter of the meshes is scarcely so great as that of the capillary ves-
sels which inclose them. According to Mr. Addison, the capillaries in the
lung of a Toad admit, in iheir natural state, no more than one, or at most two
rows of blood-corpuscles ; and the islets of tissue between them are compa-

* Archives Generates de Medecine, Mars 1843.

STRUCTURE AND DEVELOPMENT OF HUMAN LUNG.

579

Arrangement of the Capillaries of the air-cells of
Ihe Human Lung.

ratively large ; whilst, if the lung FiS- 221.

be congested or inflamed, five or
six rows of corpuscles are seen in
the vessels ; and the islets of tissue
are almost entirely obliterated. —
The diameter of the Human air-
cells is about twenty times greater
than that of the capillaries which
are distributed upon their parietes ;
varying (according to the measure-
ment of Weber) from the 1 -200th
to the l-70th of an inch. It has
been calculated by M.Rochoux, that
as many as 17,790 air-cells are
grouped around each terminal bron-
chus ; and that their total number
amounts to no less than 600 mil-
lions.

759. The fibrous coat of the bronchial tubes possesses a considerable amount
of contractility, which can scarcely be regarded as otherwise than muscular.
From the experiments of Dr. C. B. Williams,* it appears that all the air-
tubes are endowed with a considerable amount of contractility, which may
be excited by electrical, chemical, or mechanical stimuli, applied to them-
selves ; but this is not so readily excitable through their nerves, although the
experiments of Volkmann and Longet have clearly shown the possibility of
thus calling it into action (§ 410). This contractility resembles that of the
intestines or arteries, more than that of the voluntary muscles or heart; the
contraction and relaxation being more gradual than that of the latter, though
less tardy than that of the former. It is chiefly manifested in the smaller
bronchial tubes ; since, in the trachea and the larger bronchi, the cartilaginous
rings prevent any decided diminution in the calibre of the tube. Wedemeyer
did not succeed in producing any distinct contraction of the fibres of the tra-
chea and larger bronchi ; but he states that tubes of less than a line in dia-
meter could be perceived to contract gradually under the stimulus of galva-
nism, until their cavity was nearly obliterated. It is remarked by Dr. Williams,
that the contractility of the bronchial muscles is soon exhausted by the action
of a stimulus ; but that it may in some degree be restored by rest, even when
the lung is removed from the body. When the stimulation is long continued,
however, as by intense irritation of the mucous membrane during life, the
contractile tissue passes into a state which resembles that of the tonic con-
traction of muscular fibre (§ 593). The contractility is greatly affected by
the mode of death, and is remarkably diminished by the action of vegetable
narcotics, particularly stramonium and belladonna ; whilst itseems to be scarcely
at all affected by hydrocyanic acid. — These facts are very important, as
throwing light upon certain diseased conditions. It has long been suspected,
that the dyspnoea of Spasmodic Asthma depends upon a constricted state of
the smaller bronchial tubes, excited through the nervous system, frequently
by a stimulating cause at some distance ; and there can now be little doubt
that this is the case. The peculiar influence of stramonium and belladonna,
in diminishing the contractility of these fibres, harmonizes remarkably with
the well-known fact of the relief frequently afforded by them in this distress-
ing malady.

760. The Lungs themselves are to be regarded :>* quite passive in the

Athenceum Report of the Meeting of the British Association, 1S40, p. 802.

580 OF RESPIRATION.

movements of respiration ; the renewal of their contained air being accom-
plished by the action of the muscles external to the thorax, or partly forming
its parietes. The lung completely fills the cavity of the pleura, in the healthy
state at least; so that, when this is enlarged, a vacuum is produced, which
can only be filled by a corresponding enlargement of the lung ; and to pro-
duce this, the air rushes down the trachea, and passes to the remotest air-cells.

a. The distension of the whole tissue of the lung, which is effected in this manner, is
much more complete than that, which could be occasioned by simple insufflation from the
trachea ; — a fact of which it has been proposed to take advantage in juridical inquiries in
regard to suspected cases of Infanticide, where the lungs are found to float, and the defence
is set up that the child was still-born, and that air was blown into the chest for the purpose
of resuscitating it. It has been ascertained by the experiments of Mr. Jennings,* that if a
piece of lung, which has been filled with air by insufflation, be exposed to great pressure,
the air may be expelled from it sufficiently to cause it to sink in water; but that no pressure
can produce the same effect upon that which has been filled by a natural inspiratory effort.
It is a serious objection to the use of this test of juridical investigations, however, that the
early inspiratory efforts of the infant are often so feeble, as to produce but a very imperfect
dilatation of the air-cells; so that the lung of an infant which has naturally inspired cannot,
by such moans, be distinguished from one that has been artificially inflated. The fact ascer-
tained by Mr. J., however, is one of much physiological interest. — Owing to the freedom
with which the air enters the lungs, when there is no abnormal obstruction, the external
surface is always in contact with the walls of the chest, so that the pulmonary and costal
pleurae glide over one another with every inspiration and expiration. The smooth and
moistened character of their surface prevents the movement from producing any sound; but
it becomes evident when the friction is increased, either by the dryness that is commonly
one of the early changes produced by inflammation, or by the rough deposit that subsequently
appears.

b. The complete dependence of the expansion of the Lungs upon the production of a
vacuum in the chest, is well shown by the effect of admission of air into the pleural cavity.
When an aperture is made on either side, so that the air rushes in at each inspiratory
movement, the expansion of the lung on that side is diminished, or entirely prevented, in
proportion to the size of tjie aperture. If air can enter through it more readily than through
the trachea, an entire collapse of the lung takes place; and by making such an aperture on
each side, complete asphyxia is produced. But if it be too small to admit the very ready
passage of air, the vacuum produced by the inspiratory movement is more easily filled by the
distension of the lungs, than by the rush of air into the pleural cavity ; so that a sufficient
amount of change takes place for the maintenance of life. This is frequently observed in
the case of penetrating wounds of the thorax, in the surgical treatment of which, it is of
jjreat importance to close the aperture as completely as possible ; when this has been accom-
plished, the air that had found its way into the cavity is soon absorbed, and the lung re-
sumes its fall play. When one lung is obstructed by tubercular deposit, or is prevented in
any other way from rightly discharging its function, an opening that freely admits air into
the pleural cavity of the other side, is necessarily attended with an immediately fatal result;
and in this manner it not unfrequently happens, that chronic pulmonary diseases suddenly
terminate in Asphyxia, a communication being opened by ulceration between a bronchial
tube and the cavity of the thorax.

761. The dilatation of the chest during Inspiration, is chiefly accomplished
by the contraction of the Diaphragm, which, from the high arch that it pre-
viously formed, becomes nearly plane; in this change of figure, it presses on
the abdominal viscera, so as to cause them to protrude, which they are ena-
bled to do by the relaxation of the abdominal muscles. In ordinary tranquil
breathing, the action of the diaphragm is alone nearly sufficient to produce
the necessary exchange of air; but, when a full inspiration is required, the
cavity of the chest is dilated laterally, as well as infcriorly. This is accom-
plished by the Intercostal muscles, the Scaleni, Serruti, and others ; which,
by elevating the ribs, bring them and their cartilages more nearly into the
same direction, and thus separate them more widely from the median line.
Expiration is chiefly effected by the contraction of the abdominal muscles,
which at the same time force up the diaphragm by their pressure on the vis-

* Transactions of the Provincial Medical and Surgical Association, vol. ii.

ACTION OF THE LUNGS IN RESPIRATION. 581

cera, and depress the ribs; in the latter movement they are aided by the
Longissimus Dorsi, Sacrolumbalis, &c., and also by the elasticity of the car-
tilages of the ribs, with that of the air-cells and air-tubes themselves.

762. It is difficult to form an estimate by observations on one's self, of the
usual number and degree of the respiratory movements; since the direction of
the attention to them is certain to increase their frequency and amount. In
general it may be stated, that from 14 to 18 alternations usually occur in a
minute; of these the ordinary inspirations involve but little movement of the
thorax ; but a greater exertion is made at about every fifth recurrence. The
average numerical proportion of the respiratory movements, to the pulsations
of the heart, is about 1 to 5 or 4£ ; and when this proportion is widely de-
parted from, there is reason to suspect some obstruction to the aeration of the
blood, or some disorder of the nervous system. Thus in Pneumonia, in which
a greater or less amount of the lung is unfit for its office, the number of respira-
tions increases in a more rapid proportion than the acceleration of the pulse;
so that the ratio becomes as 1 to 3, or even 1 to 2, in accordance with the de-
gree of engorgement.* In Hysterical patients, however, a similar increase,
or even a greater one, may take place without any serious cause; thus Dr.
Elliotsont mentions a case, in which the respiratory movements of a young
female, through nervous affection, were 98 or even 106, whilst the pulse was
104. On the other hand, the respirations in certain typhoid conditions and
in narcotic poisoning become abnormally slow, owing to the torpid condition of
the nervous centres, the proportion being 1 to 6, or even 1 to 8 ; and in such
cases, the lungs not unfrequently become cedematous, from the cause formerly
mentioned (§ 411).

763. The amount, also, of the Respiratory Movements is affected by vari-
ous morbid conditions ; thus when dislocation of the spine takes place above
the origin of the intercostal nerves, but below that of the phrenic, so that the
former are paralyzed, the respiratory movement is confined to the diaphragm ;
and as this is insufficient, serum is effused into the lungs, and a slow Asphyxia
supervenes, which usually proves fatal in from three to seven days. Even
where the muscles and nerves are all capable of action, the full performance
of the inspiratory movements is prevented, by the solidification or engorge-
ment of any part of the lung, which interferes with its free distension; or by
adhesions between the pleural surfaces, which offer a still more direct impedi-
ment. When these adhesions are of long standing, they are commonly stretched
into bands, by the continual tension to which they are subjected. If the
impeding cause affect both sides, the movements of both will be alike inter-
fered with; but if one side only is affected, its movements will be diminished,
whilst those of the other remain natural ; and the physician hence frequently
derives an indication of great value, in regard to the degree in which the lung
is incapable of performing its functions. It is to be remembered, however,
that the action both of the diaphragm and of the elevators of the ribs may be
prevented, by pain either in the muscles themselves or in the parts which they
move ; thus the descent of the diaphragm is checked by inflammation of the
abdominal viscera or of the peritoneum ; and that of the intercostals by rheu-
matism, pleuritis, pericarditis, or other painful disorders of the parts forming
the parietes of the thorax (§ 431).

764. The capacity of the Lungs for air varies considerably in different in-
dividuals ; and as the most complete expiration does not by any means empty

* See a Paper by Dr. Hooker, on the Relation between the Respiratory and Circulating
Functions, in the Boston (N. E.) Medical and Surgical Journal ; an abstract of which will be
found in British and Foreign Medical Review, vol. vi. p. 263.

f Physiology, p. 215. note.

49*

582 OF RESPIRATION.

them, it is not possible to ascertain it with accuracy. But the amount which
can be expelled by a forcible expiration, after a full inspiration, may be taken
as a measure of the comparative " capacity of respiration" in different indi-
viduals ; and the researches of Mr. Hutchinson have shown that, in the state
of health, this bears a very constant proportion to the height. Thus he found
that the average capacity of men of 5 ft. 7 in. is about 224 cubic inches, whilst
that of men of 5 ft. 2 in. is about 173 cubic inches, and that of men of 6 feet,
about 255 cubic inches. The size of the chest affords no good indication of
the capacity of expiration. The results of such examinations are so nearly
uniform, that disease may be suspected in any man, who cannot blow out
nearly so many cubic inches as the average of those of the same height ; the
only exceptions among healthy subjects, being in the case of fat men, whose
capacity is always low. — It is obvious from these facts, that the amount of air
ordinarily respired will vary greatly in different individuals ; and this is doubt-
less one source of the discrepancy of the results of the various experiments,
which have been made to determine this point. Some of the most recent ex-
periments on the subject are those of Mr. Coathupe,* in which the Author has
much reason to feel confidence. According to his estimate, about 266^ cubic
feet, or 460,224 cubic inches of air, pass through the lungs of a middle-sized
man in 24 hours; reckoning the average number of inspirations at 16 per
minute, this would give 20 cubic inches as the amount inhaled at each.

2. — Effects of Respiration on the JLir.

765. We naturally pass from the foregoing inquiries, to those that relate to
the alterations in the Air, which are effected by Respiration. These mainly
consist in the removal of a portion of the Oxygen, and the substitution of a
quantity of Carbonic Acid, rather less in bulk than the Oxygen which has
disappeared. The proportion of the air thus changed appears to vary accord-
ing to the frequency of the respirations. Thus Vierordt found that, if he only
respired six times in a minute, the quantity of Carbonic acid was 5'5 per
cent, of the whole air exhaled ; with twelve respirations, it was 4*2 ; with
twenty-foiir, it was 3'3; \viihforty-eight, it was 3'0 ; and with ninety-six, it
was 2'6 per cent. In some of the experiments of Messrs. Allen and Pepys,
it was as much as 8 per cent. Probably about 4 per cent, may be taken as
the average, at the ordinary rate of respiration. — It appears, however, from the
researches of the last-named experimenters, that if the air be already charged
in some degree with Carbonic acid, the quantity exhaled is much less ; for
when 300 cubic inches of air were respired for three minutes, only 28 £ cubic
inches (9i per cent.) of Carbonic acid were found in it; although the previous
rate of its production, when fresh air was taken in at every respiration, was
32 cubic inches in a minute. Knowing, then, the necessity of a free excre-
tion of carbonic acid, we are led by this fact to perceive the high importance
of ventilation; for it is not sufficient for health, that a room should contain the
quantity of air requisite for the support of its inhabitants during a given time;
since after they have remained in it but a part of that time, the quantity of
carbonic acid which its atmosphere will contain, will be large enough to inter-
fere greatly with the due aeration of their blood, and will thus cause oppres-
sion of the brain and the other morbid affections that result from the accumu-
lation of carbonic acid in the circulating fluid. — On the other hand, it has been
ascertained by the recent experiments of Dr. Bosvvell Reid that, if the carbonic
acid be removed as fast as it is formed, an animal may remain in a limited
quantity of air, without much inconvenience, until nearly the whole of its

* Athcnoeum Report of Meeting of die British Association, 1839; p. 707.

EXCHANGE OF OXYGEN AND CARBONIC ACID. 583

oxygen is exhausted ; — thus showing that the respirability of air does not de-
pend so much upon the proportion of oxygen it contains, as upon its freedom
from contamination with carbonic acid or other poisonous gases.

760. The reaction which thus takes place between the Air and the Blood,
is easily explained upon physical principles. If the Blood come to the Lungs
charged with Carbonic acid, and is exposed in their cells to the influence of
atmospheric air, which is a mixture of Oxygen and Nitrogen, an endosmose
and exosmose of gases will take place, according to certain fixed laws.* The
Carbonic acid of the blood will pass out, to be replaced by Oxygen and Ni-
trogen ; and the quantity of the former which enters will be much greater than
that of the latter, on account of the superior facility with which oxygen passes
through porous membranes. If the venous blood also contain Nitrogen as
well as carbonic acid, this also will pass out, to be replaced by the Oxygen of
the air. Thus, there will be a continual Exosmose of Carbonic acid and Ni-
trogen, and a continual Endosmose of Oxygen and Nitrogen. The exhalation
and absorption of Nitrogen appear usually to balance each other; so that the
amount of this gas in the respired air undergoes little or no change. But the
case is different in regard to the exchange of Carbonic acid and Oxygen.
According to the law of mutual diffusion of gases, the volume of Oxygen that
ffs taken in, should exceed that of the Carbonic acid which passes out, in the
proportion of 1174 to 1000. This calculation, deduced from the relative
densities of the two gases, corresponds so closely with the actual results of
experiments upon the respiration of Man, that the interchange may be regarded
as always taking place in accordance with the law of mutual diffusion ; so
that, from the amount of Carbonic acid exhaled, the quantity of Oxygen ab-
sorbed may be readily calculated.! Now as Carbonic acid contains its own
bulk of Oxygen, it follows that the amount of Oxygen absorbed exceeds that
which is given off, by 174 parts in every 1000 ; so that a quantity of oxygen,
equal to more than one-sixth of that which is converted into Carbonic acid, is
employed in the system for other purposes. It appears probable that a part
of this additional Oxygen is made to combine with Hydrogen furnished by the
food or by the disintegration of the tissues ; and that the water thus generated
forms part of that exhaled from the lungs; whilst another part will be applied
to the oxidation of the Sulphur and Phosphorus, which are taken in as such
in the food, and which, after forming part of the solid tissues, are excreted in
the condition of Sulphuric and Phosphoric acids, — chiefly through the kidneys.

767. The absolute quantity of Carbonic Acid exhaled from the Lungs is
liable to variation from so many sources, that no fixed standard can be
assigned for it. The mean of a great number of observations, however,
made in different modes, and under different circumstances, would give about
160 grains of Carbon per hour as the amount set free by a well-grown adult
man, under ordinary circumstances. Taking this as the average of the
twenty-four hours, the total quantity of Carbon thus daily expired from the
Lungs would be 3840 grains, or 8 oz. Troy. The chief causes of variation
are, — the Temperature of the surrounding medium, Age, Sex, Development
of the body, state of .Health or Disease, Muscular Exertion or Repose, Sleep
or Watchfulness, Period of the Day, and state of the Digestive process.
These will now be considered in detail.

a. Temperature of surrounding Medium. — The amount of Carbonic Acid exhaled by
warm-blooded animals is greatly increased by external Cold, and diminished by Heat ; as is
shown by the following results of comparative experiments upon the quantity set free by
the same animals, at low, medium, and high temperatures, in periods of an hour (Letellier).

See Principles of General and Comparative Physiology, §§ 437 — 9.
t Valentin's Lehrbuch der Physiologic, vol. i., pp. 507-580.

584

OF RESPIRATION.

A Canary -
A Turtle-Dove
Two Mice -
A Guinea-Pig

Temp, about 32°.
Grammes.
0-325
0-974
0-531
3-006

Temp. 59°— 68°. Temp. 86°— 106°.
Grammes. Grammes.

0-250 0-129

0-684 0-336

0'498 0-268

2-080 1-453

From this table it appears that the quantity of carbonic acid exhaled by Mammals between
86° and 106° is less than half that set free near the freezing-point; whilst that which is
exhaled between 59° and 68° is but little more than two-thirds of the same amount. The
diminution occasioned by heat is still more remarkable in Birds; which exhaled at the
highest temperature scarcely more than one-third of that set free at the lowest. The ob-
servations of Vierordt upon himself show that the same is true of the Human subject ; a
difference of 10° Fahr., according to him, producing a variation of rather more than two
cubic inches in the amount of Carbonic Acid hourly expired.

b. Jlge. — The amount of Carbonic Acid exhaled increases in both sexes up to about the
thirtieth year; it remains stationary until about the forty-fifth ; and then diminishes. The
following are the comparative results of experiments upon males of different ages, and of a
moderate degree of muscular development (Andral and Gavarret).

Age.

8 years
12 " •
14 "
20 "
26 "

Carbon exhaled
per hour.
77-0 grains

- 113-9 "

- 126-2 "

- 166-3 "

- 169-4 "

Age.
37 years

48 "
59 "
68 "
76 "

Carbon exhaled

per hour.
164-7 grains.

- 161-7 "

- 154-0 "

- 147-8 "

92-4 "

c. Sex. — At all ages beyond eight years, the exhalation is greater in Males than in Fe-
males. Nearly the same proportionate increase takes place, however, in females, up to the
time of puberty; when the quantity abruptly ceases to increase, and remains stationary so
long as they continue to menstruate. When, however, menstruation has ceased, the exhala-
tion of carbonic acid begins again to augment; and then again diminishes, with the advance
of years, as in men. Should menstruation temporarily cease at any time, the exhalation of
carbonic acid immediately undergoes an increase, precisely as at the final cessation of the
function. And during pregnancy, the exhalation increases in like manner. The following
table of the comparative respiration of females at different ages, will serve at the same
time for comparison with the preceding, so as to exhibit the general difference between the
two sexes, at ages nearly corresponding ; and also to indicate the peculiar modifications
induced by the operations of the genital system (Andral and Gavarret).

jlfter Cessation of Catamenia.

Carbon exhaled

Age.

38 years -
49 "
52 "
56 "
66 "

per hour.
120-3 grains.
113-9 "
115-5 "
119-3 "
104-7 "
101-4 "
92-4 "

Carbon exhaled
Age. per hour.

10 years - - 92 '4 grains
13 " - 97-0 "

During Menstrual life.
15^ years - - 97-0 grains.
26 " - - 97-0 "
32 " - - 95-4 "
45 " - - 95-4 " 76

During Pregnancy. 82

22 years - - 129-3 grains.
32 " - 126-7 "

42 " - 120-3 "

d. Development of the Body. — The more robust the individual, cetteris paribtt?, the more
Carbonic Acid is exhaled ; and the variation is much more influejiced by the development
of the muscular system, than by the height, or weight, capacity of the chest, &c. Thus, a
very strong man of twenty-six years of age exhaled at the rate of 217-1 grains per hour;
when a man of moderate muscular power set free but 169-4 grains in the same time. An-
other robust man of sixty years of age exhaled at the rate of 209-4 per hour; another of
similar constitution, and sixty-three years of age, at the rate of 190-9 grains per hour ; and
an old man of 92 years, who still preserved an uncommon degree of energy, and who in
his younger days had boasted of extraordinary muscular powers, exhaled at the rate of 135-5
grains per hour. So also, a remarkably vigorous young woman of nineteen years exhaled
at the rate of 107-8 grains per hour ; another of twenty-two years, rather less powerful, at
the rate of 103-1 grains; and a strong woman of forty-four years (who had ceased to men-
struate) 152-4 grains. — On the other hand, a slender man of forty-five years, in the enjoy-

AMOUNT OF CARBONIC ACID EXHALED. 585

ment of good health, only exhaled at the rate of 132'4 grains per hour (Andral and Ga-
varret).

e. State of Health or Disease. — Upon this very important cause of variation, few accurate
researches have yet been made. The per cent age of carbonic acid in the expired air has
been found to be unusually great in the Exanthemata, and in chronic skiu diseases (Mac-
gregor) ; and it has been stated to be diminished in typhus (Malcolm). — Thus, the average
proportion in health being about 3'96 per cent. (Prout), it has been seen at 8 per cent, in
confluent small-pox, at 5 percent, in measles, and at 7-2 per cent, in a severe case of icthyosis
which terminated fatally; whilst in Typhus the per centage has been found to range from
1'IS to 2'50. But these statements do not indicate the total quantity exhaled in each case. —
The remarkable increase of the exhalation in cases of Chlorosis, has been already noticed;
in four cases recorded by Hannover, the hourly expiration was 123-6, 118-6, 116-9, and 106-3
grains, — the absolute quantity diminishing as the respirations increased in rapidity. — In chronic
diseases of the respiratory organs, as might be anticipated, the amount of Carbonic acid ex-
haled undergoes a sensible diminution (Nysten and Hannover). — Further researches are
much needed on this subject; but, for obvious reasons, they cannot be readily made in severe
forms of disease.

f. Muscular Exertion or Repose. — The effect of bodily exercise, in moderation, is to produce
a considerable increase in fhe amount of carbonic acid exhaled, both during its continuance,
and for some little time subsequently to its cessation. According to the observations of Vie-
rordt, the increase amounts to one-third of the quantity exhaled during rest; and it lasts for
more than an hour afterwards, being manifested in the greater quantity of air respired, and
in the larger per centage of carbonic acid contained in it. If the exercise be prolonged,
however, so as to occasion fatigue, it is succeeded by a diminished exhalation. — The connec-
tion between muscular exertion and the exhalation of carbonic acid, is most remarkably
shown in Insects; in which animals we may witness the rapid transition betvveen the op-
posite conditions of extreme muscular exertion, and tranquil repose; and in which the effects
of these upon the respiratory process are not masked by that exhalation of carbonic acid,
which is required in warm-blooded animals simply for the maintenance of a fixed tempera-
ture. Thus a Humble-Bee has been found to produce one-third of a cubic inch of carbonic
acid, in the course of a single hour, during which its whole body was in a state of constant
movement, from the excitement resulting from its capture; and yet, during the whole twenty-
four hours of the succeeding day, -which it passed in a state of comparative rest, the quantity
of carbonic acid generated by it was absolutely less.

g. Sleep 07- Watchfulness. — The amount of carbonic acid exhaled during sleep is considera-
bly less than that set free in the waking state. This is particularly shown by the experi-
ments of Scharling; who confined the subjects of them in an air-tight chamber, within
which they could sleep, take their meals, &c. Thus in one case, the hourly exhalation sank
from 160 to 100, in another from 194-7 to 122-3, and in another from 99 to 75-1. The cause
of this result is partly to be sought in the cessation of all muscular exertion (save that con-
cerned in the maintenance of the respiration) ; and partly in the diminution in the dissipa-
tion of the heat of the body itself.

h. State of the Digestive Process. — It is well established, that the exhalation of carbonic acid
is greatly increased by eating, and that it is diminished by fasting. Thus Prof. Scharling
states the hourly exhalation to have increased in one instance from 145 to 190, after break-
fast and a walk; in another from 140 to 177 after breakfast alone; and in another from 111'9
to 188-9, after dinner. It is remarkable that alcoholic drinks have a tendency to diminish the
exhalation of carbonic acid, especially when taken into an empty stomach; and strong tea is
said to have the same effect (Prout, Vierordt). — The quantity is also increased by exhilarating
emotions, and decreased by depressing affections of the mind (Prout).

t. Period of the Day. — Independently of these variations, which have their source in the
condition of the individual, there appears to be a slight tendency to increase in the quantity
of carbonic acid exhaled during the early part of the day, and a steady decrease during the
afternoon; so that, in the evening the quantity is decidedly less than in the morning. It is
very difficult to separate the effects of this influence, however, from those of the causes pre-
viously adverted to.

768. The aeration of the blood may take place, not only by means of the
Lungs, but also through the medium of the Cutaneous surface. In some of
the lower tribes of animals, indeed, this is a very important part of their
respiratory process : and even in some Vertebrata, the cutaneous respiration
is capable of supporting life for a considerable time. This is especially the
case in the Batrachia, whose skin is soft, thin, and moist ; and the effect is
here the greater, since the blood which circulates through the system is, from

586 OF RESPIRATION.

the small proportion of it that has passed through the lungs, very imperfectly
arterialized. By the experiments of Bischoff it was ascertained that, even
after the lungs of a Frog had been removed, a quarter of a cubic inch of car-
bonic acid was exhaled from the skin, during eight hours. Experiments which
have been made on the Human subject leave no room for doubt, that a similar
process is effected through the medium of his general surface ; for, when a
limb has been inclosed for some hours in an air-tight vessel containing atmo-
spheric air freed from carbonic acid, a sensible amount of this gas has been
found to be generated. Moreover, it has been observed not unfrequently, that
the livid tint of the skin which supervenes in Asphyxia, owing to the non-
arterialization of the blood in the lungs, has given place after death to the
fresh hue of health, owing to the reddening of the blood in the cutaneous
capillaries by the action of the atmosphere upon them. We have no means
of ascertaining the usual amount of carbonic acid excreted through the Skin,
except by determining the whole quantity disengaged from the body, and sub-
tracting the portion exhaled from the lungs ; and no sufficiently precise experi-
ments upon this subject have yet been made. The only way to separate the
results of the pulmonary and cutaneous exhalation of carbonic acid, would be
to confine the body in a close chamber, into which the product of the cutaneous
respiration might freely pass ; whilst the pulmonary respiration during the
same period should be measured by a distinct apparatus. It is not improbable
that, in cases of obstruction to the due action of the lungs, the exhalation of
carbonic acid through the skin may undergo a considerable increase; for we
find a similar disposition to vicarious action in other parts of the excreting
apparatus. Moreover, there is evidence, that the interchange of gases between
the air and the blood, through the skin, has an important share in keeping up
the temperature of the body (Chap, xvi., Sect. 2) ; and we find the tempera-
ture of the surface much elevated in many cases of pneumonia, phthisis, &c.,
in which the lungs seem to perform their function very insufficiently.

3. — Effects of Respiration on the Blood.

769. That an important change is effected in the character of the Blood, by
exposure to Atmospheric air in the lungs, has been known, from the time
when it was first ascertained that it is regularly transmitted to those organs.
The most obvious part of this change is the alteration in its colour, from the
dark purple of the venous fluid, to the rich crimson of the arterial. But this
alteration is only the index of changes far more important, which occur in its
chemical constitution. Respecting the nature of these changes, there has
been, as formerly stated, much difference of opinion ; some maintaining that
the carbonic acid exhaled is formed in the lungs ; and others, that it is con-
tained in the venous blood, and is truly excreted from it. The latter opinion,
which was long since brought forward by La Grange and Hassenfratz, has
recently obtained such full confirmation, from the experiments of Spallanzani,
Edwards, Miiller, Bischoff, Magnus, and others, as to have a full claim for
adoption as a physiological truth. These experiments are of two kinds ; first,
those which show that an exhalation of carbonic acid may continue for a long
time, when the animal is breathing an atmosphere in which no oxygen exists ;
and, secondly, those which prove that much more carbonic acid exists in an
uncombined state in venous blood than in arterial, whilst more oxygen exists
in a similar condition in arterial blood than in venous. The results of these
will now be briefly stated. — It was shown by Spallanzani, that Snails might
be kept for a long period in Hydrogen, without apparent injury to them; and
that during this period they disengaged a considerable amount of Carbonic
acid. Dr. Edwards subsequently ascertained that, when Frogs were kept in

EFFECTS OF RESPIRATION ON THE BLOOD. 587

hydrogen for several hours, the quantity of carbonic acid exhaled was fully as
great as it would have been in atmospheric air, or even greater ; this latter fact,
if correct, may be accounted for, by the superior displacing power, which (on
the laws of the diffusion of gases) hydrogen possesses for carbonic acid.
Collard de Martigny repeated this experiment in nitrogen, with the same re-
sults. In both sets of experiments, the precaution was used of compressing
the flanks of the animal, previously to immersing it in the gas, so as to expel
from the lungs whatever mixture of oxygen they might contain. These ex-
periments have been since repeated by Miiller and Bergemann, who took the
additional precaution of removing, by means of the air-pump, all the atmo-
spheric air that the lungs of the frog might previously contain, together with the
carbonic acid that might exist in the alimentary canal. They found in one of
their experiments, that the quantity of carbonic acid exhaled in hydrogen was
nearly a cubic inch in 6| hours ; and in another, that nearly the same amount
was given off in nitrogen ; but this required rather a longer period. It appears
from the table of their results,* that the amount was not ordinarily greater in
the experiments which were prolonged for twelve or fourteen hours, than in
those which were terminated in half the time ; hence it may be inferred, that the
quantity which the blood is itself capable of disengaging is limited, and that
the absorption of oxygen is necessary to enable carbon to be set free from the
tissues. — It is impossible, however, for an adult Bird or Mammal to sustain
life for any considerable time, in an atmosphere deprived of oxygen; since the
greatly-increased rapidity and energy of all their vital operations, necessitate
a much more constant supply of this vivifying agent, than is needed by the
inferior tribes; and, as we shall presently see, the capillary action necessary
for the passage of the blood through the lungs will not take place without it.
But Dr. Edwards has shown, that young Mammalia can sustain life in an
atmosphere of hydrogen or nitrogen, fora sufficient length of time to exhale a
sensible amount of carbonic acid ; so that the character of the process is clearly
proved to be the same in them, as in Reptiles and Invertebrata.

770. That the changes which Venous Blood undergoes in the lungs, are to
be explained upon principles of a purely chemical and physical nature, is evi-
dent from the fact, that the same changes will take place when it is exposed
to the air out of the body, even through the medium of a thick membrane, such
as a bladder. Such changes, however, only affect the surface of the fluid; but
this is exactly what we should expect, since the air has no access to the part
beneath. The Blood, whilst circulating through the capillaries of the Lungs,
is divided into an innumerable multitude of minute streamlets, each so small
as to admit but a single layer of its corpuscles ; and in these, therefore, the
surface which is placed in contact with the air is so enormously extended, as
to be almost beyond calculation. Hence, then, we can at once understand
how such a change may be instantaneously effected in it, as would occupy
several hours, when the blood is less advantageously exposed to the influence
of oxygen. — In studying the nature of these alterations, it is very necessary
to ascertain whether Oxygen and Carbonic Acid exist in a free state in the
Blood; and to what extent their proportions differ in Venous and Arterial
blood. The late researches of Professor Magnus have shown that Blood
possesses a very remarkable absorbing power for these gases, especially for
Carbonic acid. By freely exposing it to the latter gas, it was found that it
could take up as much as 1* times its bulk; and that after all its Oxygen and
Nitrogen had been thus displaced, it could still absorb as much as 16 per
cent, of its volume of Oxygen, and 6'3 of Nitrogen, on being exposed to those
gases respectively. The usual quantity of Oxygen present in arterial blood

* Miiller's Physiology, p. 341.

588 OF RESPIRATION.

is, according to the experiments of Magnus, about 10 per cent.; but while
passing through the systemic capillaries, this is diminished about one-half, so
that Venous blood does not contain more than 5 per cent, of its volume of
Oxygen. On the other hand, the Carbonic acid of Arterial blood is about 20
per cent, of its volume ; and this proportion is increased in Venous blood to
nearly 25 per cent. The amount of Nitrogen varies considerably, being some-
times as little as 1'7 per cent, of the volume of the blood, and sometimes
nearly double that proportion ; it does not appear to differ, according to any
constant law, in arterial and venous blood.*

771. There can be little doubt, then, that the changes which the function
of Respiration effects in the Blood have reference in great part to the relative
proportions of the different gases, which it holds in solution. And although
it might appear that the change of colour, which the Red Corpuscles undergo,
is a proof of a change of composition in the Haematine which they contain,
yet such a supposition is not borne out by experiment ; for no difference of
composition has been detected, between the Hsematine of Venous and that of
Arterial blood ; and it appears from the researches of Peligot on the action of
the protoxide of nitrogen upon solutions of the salts of the protoxide of iron,
that liquids may have their colour changed by the absorption of gases, which
form no chemical union with them. — There seems reason to conclude, how-
ever, from the statements formerly quoted (§ 115) in regard to the difference
between the Fibrine of Venous and that of Arterial blood, that Oxygen derived
from the inspired air enters into actual combination with this element ; and
the same may very probably be true of other constituents of the blood: — so
that we are to regard the influence of Respiration as partly exerted in modify-
ing the proportions of the gases dissolved in the blood, substituting Oxygen
for a portion of its Carbonic Acid; and partly in enabling the ingredients of
the liquid to enter into new combinations with the Oxygen of the air. For
the reasons formerly stated (§ 150) it appears probable that, whether or not
their Haematine be chemically affected by the change, the Red Corpuscles are
the chief carriers of the two gases to be interchanged, between the pulmonary
and systemic capillaries.

772. Although the alteration in the relative proportions of Oxygen and Car-
bonic acid which it contains, is doubtless the essential change effected in the
Blood by the Respiratory process, the alteration in its colour is the most ob-
vious; and this is, under ordinary circumstances, an indication that the other
change has taken place. Thus, if Arterial blood be exposed, out of the body,
to carbonic acid, it will acquire the dark hue of venous blood; and Venous
blood exposed to it becomes darker still. On the other hand, if Venous
blood be exposed to Oxygen, it acquires the Arterial hue. The presence of a
certain amount of saline matter appears, from the experiments of Dr. Stevens
and others, to be a condition necessary for the due influence of oxygen upon
the colour of the blood; since, if it be deficient, the contact of oxygen will not
produce its usual effect. On the other hand, the addition of saline matter
(especially nitre) will occasion a decided change of hue in venous blood, with-
out any extrication of carbonic acid or absorption of oxygen.

* For the latest researches of Prof. Magnus, which have had their origin in the objections
of M. Gay Lussac to those previously published by him, see the Annalen der Physik und
Chemie, vol. Ixvi., p. 177, and an Abstract in the Philosophical Magazine, Dec. 1845, Suppl.
In these researches, far greater success was obtained in removing the gases from the blood,
than in any previous experiments; and the account of their proportions, therefore, is more
satisfactory. It is extremely diflicuk to avoid all sources of error, in such researches; but
the constancy of the results obtained by Magnus indicates that we may place much confidence
in them.

ABSORPTION THROUGH THE LUNGS. 5t>9

a. It li:is recently been attempted, by Mulder and others, to account for the change of hue
under the influence of carbonic acid, oxygen, and saline matter, by a change of form in the
red corpuscles ; which are supposed to be bi-concave and reflecting in bright coloured blood,
and bi-ennvex and refracting in blood presenting the venous tint. But the supposition is not
borne out by minute and careful observations on the forms of the corpuscles, nor by varied
experiments on the effects of re-agents. As Dr. G. 0. Rees has shown, the blood-corpuscles
maybe changed in form, without any consequent change of colour; whilst, on the other
hand, the blood is reddened by saline solutions, whether they produce endosmose or exos-
mose in the red corpuscles, thus either filling or emptying them, and rendering them either
bi-convex or bi-concave.

773. Exhalation and Absorption by the Lungs. — The alteration in the
proportions of its usual gaseous ingredients, is by no means the only change
which the Blood undergoes in the Lungs. It parts also, with a considerable
amount of water, in the form of vapour; this usually contains a certain pro-
portion of animal matter; and it is sometimes charged with volatile substances,
which have been elsewhere introduced into the blood, or which have been
formed during its assimilation. It may also absorb from the atmosphere vola-
tile matter diffused through it. Both these changes are probably to be ex-
plained upon simple physical principles ; being dependent on the exposure of
the blood to the atmosphere, over a very extensive surface, and through a
membrane of great permeability. Of the fluid ordinarily exhaled with the
breath, a part doubtless proceeds from the moist lining of the nostrils, fauces,
&c. ; but it is indisputable that the greater proportion of it comes from the
lungs, since, when the respiration is entirely performed through a canula intro-
duced into the trachea, the amount of watery vapour which the breath contains,
is still very considerable. The quantity which thus passes off is by no means
trifling; probably between 16 and 20 ounces in the twenty-four hours. It is
not so liable to variation under the influence of temperature, the movement of
the surrounding air, and other similar causes, as is the cutaneous transpira-
tion ; for air, which has found its way into the air-cells of the lungs, is,
under almost all circumstances, nearly the same in regard to such conditions,
and becomes charged with that amount of watery vapour which saturates it at
the temperature of the body. It is considered by Dr. Prout, that the principal
source of this vapour is not the blood properly so called, but the chyle and
lymph which have just been introduced into it from the thoracic duct; a loss
of a portion of their fluid being required, to give them sufficient concentration.
A process very analogous takes place in Plants; for a very large proportion of
the water taken up in the crude sap, is parted with in the leaves. But it is
probable that a part, at least, of the water thrown off by the lungs is generated
by the union of Oxygen and Hydrogen during the course of the Circulation..

774. The fluid thrown off from the Lungs is not pure water. It holds in
solution, as might have been expected, a considerable amount of carbonic acid,
and also some animal matter; the exact nature of the latter, which, according
to Collard de Martigny, constitutes about 3 parts in 1000, has not been ascer-
tained. If the fluid be kept in a closed vessel, and be exposed to an elevated
temperature, a very evident putrid odour is exhaled by it. Every one knows
that the breath itself has, occasionally in some persons, and constantly in
others, a fetid taint; when this does not proceed from carious teeth, ulcerations
in the air-passages, disease in the lungs, or other similar causes, it must result
from the excretion of the odorous matter, in combination with watery vapour,
from the pulmonary surface. That this is the true account of it seems evident,
from the analogous phenomenon of the excretion of turpentine, camphor, alco-
hol, and other odorous substances, which have been introduced into the venous
system, either by natural absorption, or by direct injection; and also from the
suddenness with which it manifests itself, when the digestive apparatus is
slightly disordered.

50

590 OF RESPIRATION.

775. The Lungs are capable, under peculiar circumstances, of absorbing
fluid from the atmosphere. Thus Dr. Madden* has shown that, if the vapour
of hot water be inhaled for some time together, the loss by exhalation is found
to be so much less than usual, as to indicate that the cutaneous transpiration
is partly counterbalanced by pulmonary absorption; the pulmonary exhalation
being at the same time entirely checked. It is probable that, if the quantity
of fluid in the blood had been previously diminished by excessive sweating,
or by other copious fluid secretions, the pulmonary absorption would have
been much greater. Still in the cases formerly mentioned (§ 678), in which
a large increase in weight could only be accounted for on the supposition of
absorption of water from the atmosphere, it seems probable that the cutaneous
surface was chiefly concerned: for it can only be when the air introduced into
the lungs is saturated with watery vapour, that the usual exhalation will be
checked, or that any absorption can take place.

776. That absorption of other volatile matters diffused through the air is,
however, continually taking place by the lungs, is easily demonstrated. A
familiar example, is the effect of the inhalation of the vapour of Turpentine
upon the urinary excretion. It can only be in this manner that those gases
act upon the system, which have a noxious or poisonous effect, when min-
gled in small quantities in the atmosphere. Of these, Sulphuretted Hydrogen
is one of the most powerful in its action ; for it has been found that air im-
pregnated with l-1500th part of it, will kill a bird in a very short time ; and
that a quantity but little more than double, namely l-800th part, will soon kill
a dog. This gas is exhaled in large quantities from many forms of decom-
posing animal and vegetable matter ; and it has recently been shown (by Pro-
fessor Daniell) to be absorbed by the water of the estuaries of those African
rivers, whose mouths are regarded as among the most pestilential spots upon
the surface of the globe.— Carburetted hydrogen is another gas whose effects
are similar ; but a larger proportion is required to destroy life. — Carbonic
acid gas, also, appears to be absorbed by the lungs, when a large proportion
of it is contained in the atmosphere. The accumulation of this gas in the
blood, when the respired air is charged with it even to a moderate amount,
might be attributed to the impediments thus offered to its ordinary exhalation :
but the following experiment appears to prove, that it may be actually absorbed
into the blood ; and that it will thus exert a real poisonous influence, and not
merely produce an asphyxiating effect. It was found by Rolando, that the
air-tube of one lung of the land-tortoise may be tied, without apparently
doing any material injury to the animal, as the respiration performed by the
other is sufficient to maintain life for sometime ; but, having contrived to make
a tortoise inhale carbonic acid by one lung, whilst it breathed air by the other,
he found that the animal died in a few hours.t — Cyanogen is another gas
which has an actively-poisonous influence upon animals, when absorbed into
the lungs ; its agency, also, is of a narcotic character.

777. It is singular that the effects of the respiration of pure Oxygen should
not be dissimilar. At first, the rapidity of the pulse and the number of the
respirations are increased, and the animal appears to sufler little or no incon-
venience for an hour; but symptoms of coma then gradually develop them-
selves, and death ensues in six, ten, or twelve hours. If the animals are

* Prize Essay on Cutaneous Absorption, p. 55.

•f" The fat;il result of breathing the fumes of charcoal is, therefore, not simple asphyxia,
such as would result from breathing hydrogen or nitrogen. Other volatile products are set
free in the combustion of charcoal, besides carbonic acid. Mr. Coathupe (loc. cit.) states
these to be Carbonate, Muriate and Sulphate of Ammonia, Carbonic Oxide, Oxygen, Nitro-
gen, Watery vapour, ami Empyreumatic Oil: to these Sulphurous acid may appear to be
properly added.

EFFECTS OF SUSPENSION OF RESPIRATION. 591

removed into the air before the insensibility is considerable, they then quickly
recover. When the body is examined, the heart is seen beating strongly
while the diaphragm is motionless ; the \vhole blood in the veins, as well as
in the arteries, is of a bright scarlet colour; and several of the membranous
surfaces have the same tint. The blood is observed to coagulate with re-
markable rapidity ; and it is to the alteration in its properties, occasioned by
the hyper-arterialization, and indicated by this condition, that we are proba-
bly to attribute the fatal result. There can be no doubt that in this instance
an undue amount of oxygen is absorbed ; and it does not seem unlikely that
one cause of the fatal result, is a stagnation of the blood in the systemic capil-
laries, consequent upon the want of sufficient change in its condition. — When
Nitrogen or Hydrogen is breathed, for any length of time, death results from
the deprivation of Oxygen, rather than from any deleterious influence which
these gases themselves exert. — Death is also caused by the inhalation of
several gases of an irritant character, such as Sulphurous, Nitrous, and Muria-
tic acids : but it is doubtful how far they are absorbed ; or how far their
injurious effects are due to the abnormal action, which they excite in the
lining membrane of the air-cells and tubes. — It cannot be doubted, that mias-
mata and other morbific agents diffused through the atmosphere, are more
readily introduced into the system through the pulmonary surface than by
any other ; and our aim should therefore be directed to the discovery of some
counteracting agents, Avhich can be introduced in the same manner. The
pulmonary surface affords a channel for the introduction of certain medicines
that can be raised in vapour, when it is desired to affect the system with them
speedily and powerfully ; such are iodine, mercury, tobacco, stramonium, &c.

4. — Effects of Suspension of Respiration.

778. We have now to consider the results of the cessation of the Respira-
tory function, and the consequent retention of carbonic acid in the blood. If
this be sufficiently prolonged, a condition ensues, to which the name of
Asphyxia has been given ; the essential character of which is the cessation
of muscular movement, and shortly afterwards of the circulation ; with an
accumulation of blood in the venous system. The time which is necessary
for life to be destroyed by asphyxia varies much, not only in different animals,
but in different states of the same. Thus Warm-blooded animals are much
sooner asphyxiated than Reptiles or Invertebrata ; on the other hand, a hyber-
nating Mammal supports life for many months, with a respiration sufficiently
low to produce speedy asphyxia if it were in a state of activity. And among
Mammalia and Birds, there are many species which are adapted, by peculiari-
ties of conformation, to sustain a deprivation of air for much more than the
average period.* Excluding these, it may be stated as a general fact, that, if
a warm-blooded animal in a state of activity be deprived of respiratory power,
its muscular movements (with the exception of the contraction of the heart)
will cease within five minutes, often within three ; and that the circulation
generally fails within ten minutes. Many persons, however, are capable of
sustaining a deprivation of air for three, four, or even five minutes, without
insensibility or any other injury ; but this power, which seems possessed to

Thus, the Cetacea contain far more blood in their vessels, than do any other Mamma-
lia ; and these vessels are so arranged that both arteries and veins are in connection with
large reservoirs or diverticula. The reservoirs belonging to the former are usually full ; but
when the Whale remains long under water, the blood which they contain is gradually in-
troduced into the circulation, and, after becoming venous, accumulates in the reservoirs con-
nected with the venous system. By means of this provision, the Whale can remain under
water for more than an hour.

592 OF RESPIRATION.

the greatest degree by the divers of Ceylon, can only be acquired by habit.
The period during which remedial means may be successful in restoring the
activity of the vital and animal functions, is not, however, restricted to this.
Cases are not unfrequent, of the revival of drowned persons after a submer-
sion of half an hour; and more than one has been credibly recorded, in which
above three-quarters of an hour had elapsed. It is not improbable, however,
that in some of these cases a state of Syncope had come on at the moment
of immersion, through the influence of fear or other mental emotion, concus-
sion of the brain, &c. ; so that, when the circulation was thus enfeebled, the
deprivation of air would not have the same injurious effect, as when this
function was in full activity. The case would then closely resemble that of
a hybernating animal ; for in both instances the being might be said to live
very slowly, and would therefore not require the usual amount of vital stimuli.
The condition of the still-born infant is in some respects the same ; and re-
animation has been successfully attempted, when nearly half an hour had
intervened between birth and the employment of resuscitating means, and when
probably a much longer time had elapsed from the period of the suspension
of the circulation.

779. It has now been sufficiently proved, both by experiment and by pa-
thological observation, that the first effect of the non-arterialization of the
blood in the lungs, is the retardation of the fluid in their capillaries (§ 738) ;
of which the accumulation in the venous system, and the deficient supply to
the arterial, are the necessary consequences. It is some time, however, be-
fore a complete stagnation takes place from this cause: since, as long as the
proportion of oxygen which remains in the air in the lungs is considerable,
and that of the carbonic acid is small, so long will some imperfectly-arte-
rialized blood find its way back to the heart, and be transmitted to the system.
This blood will have a depressing influence upon the functions of the brain
and of the muscular system ; which influence is aided by the diminution that
gradually takes place, in the quantity of blood propelled through the aorta ;
and the actions of the respiratory muscles and of the heart will therefore
soon become enfeebled. The cessation of the heart's contraction is due to
two distinct causes, acting on the two sides ; for on the right side it is the
result of the over-distension of the walls of the ventricle, owing to the accu-
mulation of venous blood ; and on the left to deficiency of the stimulus ne-
cessary to excite the movement. The property of contractility is not finally
lost, nearly as soon as the movements cease; for the action of the right ven-
tricle may be renewed, for some time after it has ceased, by withdrawing a
portion of its contents, — either through the pulmonary artery, their natural
channel, — or, more directly, by an opening made in its own parietes, in the
auricle, or in the jugular vein ( § 723, c). On the other hand, the left ventricle
may be again set in action, by renewing its appropriate stimulus of arterial
blood. Hence, if the stoppage of the circulation have not been of too long
continuance, it may be renewed by artifical respiration : for the replacement
of the carbonic acid by oxygen in the air-cells of the lungs, restores the cir-
culation through the pulmonary capillaries ; and thus at the same time relieves
the distension of the right ventricle and conveys to the left the due stimulus to
its actions.

780. Of the mode in which the pulmonary circulation is stagnated by the
want of oxygen, and renewed by its ingress into the lungs, no other explana-
tion can be given, than that which has been heretofore offered of the capillary
circulation in general; — namely, that the performance of the normal reaction
between the blood and the surrounding medium (whether this be air, water,
or solid organized tissue) is a condition necessary to the regular movement

GENERAL VIEW OF THE PROCESS OF NUTRITION. 593

of the blood through the extreme vessels.* This view has recently obtained
additional support from the experiments of Dr. J. Reid on the Respiration of
Azote.t He found that, when the ordinary respiration of an animal is inter-
rupted, and the Asphyxia is proceeding to the stage of insensibility, the first
effect upon the arterial system is an increased distension (as indicated by the
hsemadynamometer), even although the blood is at that time nearly venous in
its character ; this indicates that the fluid, now so perverted, is unable to pass
with facility through the systemic capillaries, in consequence of its not being
in a state fit for the performance of its normal actions. As the stagnation in
the pulmonary capillaries becomes more complete, however, less and less
blood is returned from the lungs to the heart; and, the systemic arteries
being gradually unloaded without being refilled, the pressure of the blood
upon their walls diminishes, and is at last no longer experienced. Its dimi-
nution is not arrested by causing the animal to breathe nitrogen, although the
respiratory movements are renewed, — thus proving that the stagnation of the
blood in the capillaries of the lungs is not due (as some have supposed) to a
mechanical impediment: but the pressure is immediately increased by the
admission of atmospheric air, which occasions the renewal of the pulmonary
circulation, and the consequent increase in the supply of aerated blood to the
systemic arteries. — It has been shown by Mr. Wharton Jones,J that the ca-
pillary circulation in a frog's foot is retarded or even checked, by the direc-
tion of a stream of carbonic acid gas against the membrane ; and he attributes
this stagnation to the disposition thus produced in the red corpuscles, to ag-
gregate together and to adhere to the walls of the vessel, so as to choke up
its calibre.

CHAPTER XIV.

OF NUTRITION.

1. — General Considerations. — Selective Power of Individual Parts.

781. THE function of Nutrition, considered in the widest acceptation of the
term, includes the whole series of processes, by which the fluid alimentary
materials, — prepared by the Digestive process, introduced into the system by
Absorption, and carried into its penetralia by the Circulation, — are converted
into Organized tissue ; by which conversion it is caused to manifest a set of
properties altogether new, which, being neither Physical nor Chemical, are
termed Vital. Thus Albumen, which is a perfectly dead or inert substance,
and of which the distinguishing properties are entirely attributable to its pecu-
liar composition, is transformed by the Nutritive process into Muscular Fibre,
possessed of the remarkable Vital property of Contractility. — But this process
of conversion commences in the nutritive materials whilst they are still in a
fluid condition, and are moving through the vessels ; for we have seen that, at
this stage of the operation, the unorganizable Albumen is transformed into

' For a fuller discussion of the Pathology of Asphyxia, see the Author's essay on the sub-
ject in the Library of Practical Medicine, vol. iii.
t Edinb. Med. and Surg. Journal, April 1841.
j British and Foreign Medical Review, vol. xiv., p. 600.

50*

594 OF NUTRITION.

Fibrine, — a substance which possesses a tendency to spontaneous organization,
and which must be regarded as endowed with Vital properties. It is convenient
to speak of it, therefore, under a distinct designation ; and the term Assimilation
has been applied to it. In its more restricted sense, the term Nutrition is
applied to the growth of the various tissues of the body, at the expense of the
materials prepared by the Assimilating process, and supplied by the Circu-
lating current.

782. It appears evident, from what has been formerly stated (Chap, in.),
that the process of Nutrition mainly consists in the growth of the individual
cells composing the fabric; and that these derive their support from the
organic compounds with which they are supplied by the blood, just as the
cells composing the simplest Plants derive theirs from the inorganic elements
which surround them. And as different species of the latter select and com-
bine these in such modes and proportions as to give rise to organisms of
very diversified forms and properties, so is it easily intelligible that the dif-
ferent parts of the fabric of the highest Animals should exercise a similar
selective power, in regard to the materials with which the blood supplies
them. The structure composing every separate portion of the body has
(what may be termed) an elective affinity for some particular constituents of
the blood ; causing it to abstract from that fluid, and to convert into its own
substance, certain of its elements. The property by which the cells of the
Animal or Vegetable structure are enabled to perform it, is one of which we
are not likely soon to know more. It will probably long remain an ultimate
fact in Physiology, that cells have the power of growing from germs, of under-
going certain transformations, and of producing germs that will develope other
cells similar to themselves ; — just as it is an ultimate fact in Physics, that
masses of matter attract each other; or in Chemistry, that the molecules of
different substances have a tendency to unite, so as to form a compound dif-
ferent from either of the elements. It is of such ultimate facts as these, that
the science of Vitality essentially consists : since the Physical and Chemical
phenomena which occur in living bodies, are not strictly removable from the
laws of Inorganic Nature. The conditions under which this appropriating
power operates, however, are freely open to our investigation ; and it is a
great step in the progress of the inquiry, to become aware that these are so
closely conformable, throughout the organized world, as they have been
shown to be. It may be stated, as a general fact, that in assimilating, or con-
verting into its own substance, matter which was previously unable to exhibit
any of the manifestations of life, every cell thereby participates in the process
of organization and vitalization; for, by the new circumstances in which the
matter is placed, its properties undergo a change, — or, to speak more correctly,
properties which were previously dormant are caused to manifest themselves.
No matter, that is not in a state of Organization, can exhibit those properties,
which, from their being peculiar to living bodies, and altogether different from
Physical and Chemical, are termed Vital; and it may also be asserted that
no matter, which exhibits perfect organization, is destitute of the peculiar
vital properties belonging to its kind of structure.* As a corollary to this
general fact, it may be stated, that no organism can be produced by any
fortuitous combination of inorganic matter; since, even for the generation of
the simplest cell, there is required a cell previously existing, to furnish the
germ.

* Fora fuller consideration of this question, and the grounds upon which this view is
supported, the reader is referred to the Article Life in the Cyclopedia of Anatomy and Phy-
siology; and to the Chapter on the ''Nature and Causes of Vital Actions," in his 1'riuciples of
General and Comparative Physiology.

SELECTIVE POWER OF INDIVIDUAL PARTS. 595

783. We have seen that, in some cases, the germs are prepared by pre-
viously-existing cells of the same kind; thus the Red and colourless corpuscles
of the Blood, the Cartilage-cells, the cells of Vesicular Nervous matter, and
those of many other tissues, appear to be the offspring of parents exactly
similar to themselves. In other cases, however, the germs seem to be fur-
nished by certain " nutritive centres," which appear to be constantly engaged
in the preparation of them, deriving their materials from the blood.* Thus
the Epidermic and Epithelial cells are produced, not from preceding cells of
a similar character (for these are thrown off without performing any such
reproductive act), but from germs derived from the basement or primary mem-
brane beneath; and, in like manner, the minute cells, of which the ultimate

Jibrillse of Muscle are composed, appear to originate in nuclei or germinal
centres, belonging to the tubular Myolemma. But even these germinal centres
may probably be considered as nothing else than the nullei of certain parent-
cells, which, instead of producing their like, give origin to a new generation
having different properties. Thus, the basement or primary-membrane has
been already stated (§ 135) to exhibit not unfrequently the indications of a
cellular constitution ; the germinal centres which it contains being the nuclei
of its component cells : and its character is particularly well seen where it is
inverted so as to form secreting follicles ; for, as we have seen (§ 174), each
of these follicles may be regarded as a single parent-cell, which opens at the
extremity farthest from the nucleus, and continues to discharge from its orifice
successive generations of cells, having their origin in its nucleus, which thus
acts as a permanent " germinal centre." And in like manner, the germinal
centres of Muscular Fibre may be regarded as the nuclei of the cells, of which
it was originally composed.

784. The Selecting power, which is possessed by the germs of each kind
of tissue, and which enables them to draw from the Blood the materials which
they severally require for their development, manifests itself also in the mode
in wKich substances, that are abnormally present in the Blood, affect the con-
dition and development of the solid tissues. Thus we find that the presence
of a certain quantity of Arsenic in the Blood, will produce a state of irritation
of all the Mucous membranes in the body. The continued introduction of
Lead into the circulating system, occasions a modification in the nutrition of
the extensor muscles of the forearm, producing the form of partial paralysis
commonly termed wrist-drop; and the existence of this modification is shown
by the fact (disclosed by Chemical analysis) of the actual presence of lead in
the palsied muscles. — Here we have to remark the Symmetrical nature of the
affection, consequent upon the occurrence of the same disorder in the corre-
sponding parts of the two sides of the body; for these muscles appear to have
the same kind of tendency to attract Lead from the circulating current, in a
degree that is equal on the two sides, as they have to draw from the blood
the materials of their regular growth, and to develops themselves in an exactly
similar manner. In like manner, the cutaneous eruptions, which are occa-
sionally produced by the internal exhibition of iodide of potassium, are found
to be almost precisely symmetrical; the presence of the medicine in the blood
being the occasion of a disordered nutrition of certain parts of the skin; and
the selecting power of particular spots being evinced by the exact correspond-
ence of the parts affected on the two sides.

785. The same appears to be the case with regard to substances, whose
presence in the blood is rather the result of a disordered condition of the
digestive and assimilating processes, than of their direct introduction from
without. Thus in Lepra and Psoriasis, — chronic diseases of the Skin, which

* See Gooclsir's Anatomical and Pathological Observations, Chap. I.

596 OF NUTRITION.

seem to have their origin in a disordered state of the Blood, rather than in the
solid tissues affected, — we find a remarkable tendency to the repetition of the
patches, on the two sides of the body, or on the corresponding parts of the
limbs; and this we must attribute to the peculiar attraction subsisting between
the solid tissues of those parts, and the morbid matter circulating through
them. — So in those chronic forms of Gout and Rheumatism, which modify
the nutrition of the joints, producing a deposit of "chalk stones," or perma-
nent distortion and stiffening from an alteration of the tissues, of the joint, we
almost invariably find the corresponding joints of the two sides affected. —
The chief exceptions to the general principle, that the presence of morbid or
extraneous matters in the blood affects all parts alike, are found to occur
where there is much febrile disturbance, or where local causes produce a
peculiar tendency to disorder of a single part. The nearer the approach
presented by the mofbid process, in point of rate and character, to the ordi-
nary nutritive operations of the part, the more does it tend to approach these,
in the symmetry with which it developes itself.*

2. — Varying Activity of the Nutritive Processes. — Reparalive Operations.

786. Without any change in the character of the Nutritive processes, there
may be considerable variations in their degree of activity ; and this, either as
regards the entire organism, or individual parts, though most commonly the
latter. These variations maybe so considerable as to constitute Disease;
though there are some which take place as part of the regular series of Phy-
siological phenomena. Thus, the Nutritive processes should have a degree
of activity more than sufficient to supply the Waste of the body during the
whole period of infancy, childhood and adolescence, until, in fact, its full
dimensions are obtained ; whilst, on the other hand, they are usually less
rapid than the disintegrating processes in old age, so that the bulk of the body
diminishes. Now as the Waste of the body, so far from being more rapid in
old age than in childhood, is much less so, it follows that the difference in
the activity of the Nutritive processes in these two states must be very con-
siderable ; and this is manifested, not only in the greater demand for food
which exists in the child (relatively to the bulk of its body), but also in the
greater quickness and facility with which injuries are repaired. Local varia-
tions may also occur, as part of the regular train of vital actions in the adult;
thus we perceive an enormous increase in the amount of tissue contained in
the Uterus and Mammary glands during pregnancy, and a decrease in the
bulk of the Thymus gland after the period of infancy. Now in these cases
we see, that increased Nutrition is invariably connected with increased Func-
tional activity; and diminished nutrition with diminished functional activity:
and this we shall find to be the constant rule, in regard also to those variations
which must be considered as abnormal.

787. Increased Nutrition, or Hypertrophy, is never known to affect the
whole body, to a degree sufficient to constitute disease. It cannot be pro-
duced as a consequence of the ingestion of an undue supply of food : for this
does not increase the formative activity of the tissues, but merely renders the
blood richer in nutritive materials; a part of which the excreting organs are
called on to be continually removing, without its being rendered subservient to
the wants of the body (§ 819); whilst another part may be employed in the
nutrition of one particular tissue, the Adipose, which has a tendency to in-
crease with the superfluity of non-azotized food, provided that the requi-

* See Dr. W. Budd's valuable paper on the "Symmetry of Disease," in vol. xxv. of the
Medico-Chirurgical Transactions.

VARYING ACTIVITY OF THE NUTRITIVE PROCESSES. 597

site amount of cellular tissue be generated to hold the fatty matter (§ 184).
But examples of Hypertrophy of particular tissues or organs are very com-
mon. Thus any particular set of Muscles, which is subjected to frequent and
energetic use, acquires a great increase in bulk ; as we see in the arms of a
Blacksmith or Waterman, the legs of an Opera-dancer, &c. The hypertrophy
of these muscles is a consequence of their increased functional activity ; which,
being produced by an exertion of the will, and unaccompanied with any in-
jurious effects on the system, can scarcely be regarded as morbid. But there
are many instances, in which the involuntary muscles acquire a greatly-
increased strength,, in consequence of an obstruction to their action, which
results from disease. Thus we see the right ventricle of the Heart become
hyperlrophied (and dilated at the same time), where chronic pulmonary dis-
ease produces a difficulty in the propulsion of the blood through the vessels
of the lungs; the muscular fibres of the Bladder become enormously hyper-
trophied, when stricture, diseased prostate, or other causes produce a demand
for increased expulsive force on the part of that organ ; and those of the
Stomach also become so, in cases of stricture of the pylorus. As an instance
of hypertrophy of a Secreting organ in consequence of an undue excitement
of its function, we may notice the enlargement which usually takes place in
the Kidney, when its fellow is incapacitated by disease. And the Nervous
system presents us with a very remarkable case of hypertrophy of a part,
resulting from over-excitement of its function; for if young persons, who
naturally show precocity of intellect, are encouraged rather than checked in
the use of their brain, the increased nutrition of the organ (which grows faster
than its bony case) occasions pressure upon its vessels, it becomes indurated
and inactive, and fatuity and coma are the result.

788. Local hypertrophy may be induced also by local congestions ; but in
such cases it will usually be found, that the form of tissue produced is of the
lowest kind, unless the functional activity of the part be increased by the
congestion. Thus, when disease of the Heart produces long-continued con-
gestion of the Lungs, Liver, Spleen, &c., the bulk of these organs increases;
but chiefly by the production of an additional amount of interstitial Areolar
tissue, which may result (as we have seen) from the simple consolidation of
Fibrine ; and partly also (in the case of the spleen especially) by the gorging
of their distensible veins with blood. — One of the least explicable cases of
Hypertrophy, is that which takes place in the Thyroid gland, causing Bron-
chocele. So little is known of the normal office of this organ, that it cannot
be determined, whether its increased size be due to an increased activity of
its functional operations, or to an unusual formative activity in its tissue,
depending on some hidden cause. The connection of this disorder with
causes which affect the whole constitution rather than individual parts, would
seem to indicate the former.

789. When the Waste of the Tissues is more rapid than their replacement
by Nutrition, Atrophy is said to take place ; and this may affect either the
whole body, or individual parts. General Atrophy, Marasmus, or emaciation,
may result from an insufficient supply of plastic matter, from want of forma-
tive power in the tissues themselves, or from their too rapid disintegration.
The insufficiency of the supply of nutritive matter may depend either on de-
ficiency in the azotized substances ingested as food, or on imperfect perform-
ance of those processes by which they are converted into the plastic ele-
ment,— Fibrine. Hence, even when there is an ample supply of food,
atrophy may take place to a very severe extent, in consequence of disordered
digestion, or a want of vital power in the fibrine-elaborating cells. Again, we
have reason to believe that the formative power in the tissues themselves may
be diminished, so as to check the process of Nutrition, even when the plastic

598 OF NUTRITION.

material is supplied ; thus there seems to be a complete stoppage of this action
in Fever, and a diminution of it in that irritable state of the system, which
results from excessive and prolonged bodily exertion or anxiety of mind, es-*
pecially when accompanied by want of sleep. It is difficult to separate this
cause, however, from mal-assimilation on the one hand, or from too rapid
decay of the tissues on the other : for we know that, in such states, there is a
tendency to imperfect elaboration of the Fibrinous element, and at the same
time an unusually rapid disintegration, as manifested by the increased amount
of Urea in the urine. The influence of excessive waste in causing Atrophy
of the body, is well shown in the cases of Diabetes mellitus and colliquative
Diarrhoea ; in both these, the increase and depravation of the secretions are
undoubtedly to be regarded as the effects, and not the causes, of the textural
changes with which they are associated. Colliquative Diarrhoea is a constant
occurrence on the last day or two of life, in animals reduced by Starvation ;
and is accompanied by that foetid odour of the body, which indicates that
decomposition is already going on throughout the system. The same thing
occurs as the ordinary termination to many diseases of exhaustion ; in which
Inanition is unquestionably the immediate cause of death.

790. Partial Atrophy may occur in consequence of disuse of the organ
affected, occasioning inactivity in its formative processes; or as a result of a
deficiency of nutriment, occasioned by an obstruction to the circulation. Of
the operation of the former cause, we have many examples in the ordinary
processes of the economy. Thus the Uterus is atrophied, relatively to its
previous condition, as soon as parturition has taken place ; and the Mammary
glands, when lactation has been discontinued. It is probably in part to this
cause, and in part to the diversion of the blood into other channels, that we
are to attribute the atrophy of many parts, as the development of the system
advances, which at an earlier period were of large comparative size, — such as
the Corpora Wolffiana, the Suprarenal capsules, and the Thymus gland.
Many instances might be adverted to, of the influence of suspension of func-
tional activity, as a result of disease or injury, in producing local atrophy.
One of the most common cases, is' the atrophy of Muscles which is conse-
quent upon their disuse. This disuse will produce the same effect, whether
it be occasioned by paralysis, which prevents the nervous centres from excit-
ing the muscles to contraction; or by anchylosis, which interposes a mechani-
cal impediment to their use ; or by fractures or other accidents, the reparation
of which requires the limb to be kept at rest. Or even if, without having
suffered from any injury, a limb be fixed during some time in one posture, its
muscles will become atrophied, as is seen in the case of the Indian Fakirs.
(See § 588). Similar facts may be adduced, in regard to Atrophy of Nerves,
from interruption of their normal function. Thus when the Cornea has been
rendered so opaque by accident or disease, that no light can penetrate to the
interior of the eye, the Retina and the Optic nerve lose, after a time, their
characteristic structure ; so that scarcely a trace of the peculiar globules of the
former, or of the nerve-tubes of the latter, can be found in them. These and
similar facts are readily understood, when connected by the general principle
formerly laid down, — that every proper vital operation involves an act of
nutrition ; in such a manner that, whilst the vital properties of any part are
dependent upon its due nutrition, the amount of its nutrition will in return
depend upon the degree in which these properties are exercised.

791. Partial Atrophy may depend, however, upon causes of a purely me-
chanical nature; such, for example, as produce an interruption of the current
of Blood through the part. This may result from changes in the Arteries
supplying it; such as ossification, or other forms of obstruction. Or it may
be consequent upon disease in the part itself ; as when the deposits produced

VARYING ACTIVITY OF THE NUTRITIVE PROCESSES. 5S9

by Inflammation tend to contract, and thus to press upon the vascular struc-
ture, which frequently happens in the lungs, liver, and kidneys ; or when the
inflammation occurs in the vessels themselves, causing adhesion of their walls,
and obliteration of their tubes ; or when a new growth absorbs into itself all
the nutritive materials which the Blood supplies.*

792. The nutritive operations take place, with extraordinary energy and
rapidity, in the process of Reparation ; by which losses of substance, occa-
sioned by injury or disease, are made good. In its most perfect form, this
process is exactly analogous to that of \\\& first development of the correspond-
ing parts ; and its results are as complete in the one case as in the other. In
fact, among the lowest tribes of Animals, we find these two conditions
blended, as it were, together; for the process of reparation may be carried in
them to such an extent, as to regenerate the whole organism from a very small
portion of it. In the Hydra, or Fresh-water Polype, there would seem to be
scarcely any limit to this power; for, if the body of the animal be minced
into the smallest possible fragments, every one of these can produce a new
and perfect being. In this manner no less than forty have been artificially
generated from a single individual. — In ascending the Animal scale, we find
this reparative power less conspicuous, because exercised with regard to
smaller parts only of the body ; but the greater complexity of the changes
involved in the process, renders it in reality not less considerable than in the
lower classes. Thus, the restoration of a Bone destroyed by Necrosis is a
much more extraordinary operation, than the growth of an entire Polype from
a single fragment; since it involves a far greater amount and variety of
actions. Numerous and well-authenticated instances are on record, of the
reunion of parts that had been entirely separated from the body, and of the
restoration of all their vital properties : and this could only take place, through
the perfect reproduction of a large number of very different structures. The
reappearance of Fungous growths, whose organization is of a low character,
is a fact with which every surgeon is familiar ; and cases occasionally, though
rarely, present themselves, in which reproduction of a whole member takes
place even in the Human subject.!

793. It is the general opinion among British surgeons (founded upon what
they believe, but erroneously, to have been the doctrine of Hunter), that In-
flammation is essential to the process of Reparation. There is no doubt that,
as usually conducted, the healing of wounds is attended by a greater or less
degree of Inflammation ; but it does not thence follow that this morbid con-
dition is essential to the renewal of the healthy state ; and in fact it can be
shown that, in the majority of cases, the Inflammation is injurious rather than
beneficial. The following important conclusions are drawn by Dr. Macart-
ney:]: from a very philosophical comparative survey of the operations of Re-
paration and Inflammation, as performed in the different classes of animals :
— " That the powers of Reparation and Reproduction are in proportion to the
indisposition or incapacity for Inflammation ; — that Inflammation is so far
from being necessary to the Reparation of parts, that, in proportion as it exists,
the latter is impeded, retarded, or prevented; — that, when Inflammation does
not exist, the Reparative power is equal to the original tendency to produce
and maintain organic form and structure ; — and that it then becomes a natural
function, like the growth of the individual, or the reproduction of the species."
794. Guided chiefly by Dr. Macartney's views, which have derived im-

* See on this subject Dr. Williams' Elements of Medicine, chap. iv. ; to which the Author
is partly indebted for the preceding paragraphs.

f See, on the whole of the subject of the comparative powers of Reparation in the Ani-
mal series, the Author's Principles of Gen. and Comp. Physiol. §§ 586, 587.

J Treatise on Inflammation, p. 7.

600 OF NUTRITION.

portant confirmation from recent observations, we shall treat of the reparative
processes under three distinct heads : — First, the adhesion of the sides of a
wound by a medium of coagulable lymph, or of a clot of blood. Second,
reparation without any medium of lymph or granulations, the cavity of the
wound being filled by a natural process of growth from its walls. Third,
reparation by means of a new, vascular, and organized substance, termed
Granulations. — The first of these modes of Reparation, is that which is ordi-
narily termed union by the first intention; of this kind of adhesion, the heal-
ing of the incision made in venesection, which usually takes place almost
without consciousness on the part of the patient, and with scarcely any In-
flammation, is a characteristic example: the white line of cicatrix which is
left, marks the formation of new substance; and is the result of the want of
that perfect approximation of the lips of the wound, which may frequently be
obtained in parts, where pressure can be more firmly applied, and where the
space to be filled up is proportionably thinner. This mode of union is ordi-
narily considered by British Surgeons to be the result of an adhesive inflam-
mation. In so regarding it, they conceive that they are following out the
views of Hunter ; but he expressly states that wounds may heal without any
pain or constitutional disturbance, the reunion proceeding "as if nothing had
happened ;" so that he in effect admits, that reparation of this kind may take
place without Inflammation. It is well known that if a slight wound, which
is thus healing, be provoked to an increased degree of Inflammation, its pro-
gress is interrupted ; and all the means which the Surgeon employs to pro-
mote union, are such as tend to prevent the accession of this state. The
doctrine that the effusion of Lymph for the Reparation of the tissues, is not
to be regarded as necessarily a result of the Inflammatory process, is not so
novel as its opponents have regarded it; since it has been maintained by many
eminent observers, even from the earliest times. The only case in which
the occurrence of Inflammation can be regarded as salutary, is that in which
there is a deficiency of Fibrine in the blood, causing a deficient organiza-
bility of the lymph. It has been seen that the amount of Fibrine is rapidly
increased by inflammation; and the Surgeon well knows that a wound with
pale flabby edges, in a depressed state of the system, will not heal, until some
degree of Inflammation has commenced.

795. When the Liquor Sanguinis of the Blood, known as Coagulable
Lymph, is effused between the two edges of a wound, or upon the surface of
a membrane lining a closed sac, the following appears to be the history of its
organization. The new matter, which is poured out in a fluid state, and
which seems to have been subjected to the peculiar influence of the Colour-
less Corpuscles that rapidly collect in large numbers at the injured spot, un-
dergoes a Coagulation resembling that of Blood; the Serum, being set free
by the concretion of the Fibrine, is absorbed; and the fibrinous coagnlum
speedily attains an almost membranous density. If examined with a Micro-
scope at the commencement of the process of organization, it is seen to con-
tain a large number of cells, which sometimes closely resemble the Colourless
Corpuscles of the Blood; and in other instances (especially where there has
been active Inflammation) present greater similarity to Pus-corpuscles; these
cells, which are known as exudation-corpuscles, probably originate in granules
set free from the Colourless Corpuscles of the circulating blood, and exuded
with the Liquor Sanguinis. In a short time, these corpuscles present the
appearance of regular cells, disposed in layers, and adhering together by an
intermediate unorganized substance ; bearing, in fact, a strong resemblance to
the cells of tesselated epithelium. Some hours later, the mass exhibits an
evidently-fibrous character ; which is probably due to the further elaboration
of the plastic material, by the cells just mentioned. Between the fibres, a

REPARATIVE PROCESSES. 601

considerable amount of unorganized substance yet remains; and they maybe
readily separated, or torn in any direction. A vascular rete next makes its
appearance, in connection with the vessels of the subjacent surface; the first
appearance of this network is in the form of transparent arborescent streaks,
which push out extensions on all sides ; these encounter one another, and
form a complete series of capillary reticulations, the distribution of which very
nearly resembles that which has been seen in the villi of the intestines (Fig.
204). — From the observations of Mr. Travers* it appears, that isolated glob-
ules enter these capillary tubes, and perform an oscillatory motion in them
for some hours, before any series of them passes into it; so that we cannot
regard the new channel as burrowed out by a string or file of red corpuscles,
pushed out from the nearest capillary by vis « tergo, as some have maintained.
And he has further established two important facts, in the history of the Re-
paration of Tissues, which correspond with the observation just cited: — 1.
That the Liquor Sanguinis first effused is not sufficiently organizable to be-
ccfme an entirely new and permanent tissue; although adequate both to afford
nutrition to the old, and to form a new tissue of temporary character : — and,
2. That the generation of the new tissues is preceded by the collection of a
large number of white corpuscles, in a nearly stationary condition, in the
blood-vessels immediately subjacent ; and by the appearance of a large number
of similar cells in the newly-forming tissue ; the two together constituting
what Mr. T. has aptly called " the new lymph-bed of organization." The
views formerly advanced (§§ 154-159) respecting the function of the Colour-
less Corpuscles, are thus strikingly confirmed. — This process of Reparation
appears to be conformable, in all essential particulars, with that which has
been observed in the first Development of new parts, — such as the toes of the
larva of the Water-Ne\vt.

796. Although many 'have doubted whetber effusions of Shod could thus
become organized, there seems no valid reason to think that its Fibrine would
comport itself in any other way, when Red particles are included in its coa-
gulum, than when they are absent. That large masses of extravasated Blood
should exhibit little or no tendency to organization, will not be considered
surprising ; when it is remembered that only their surface can be in that re-
lation with a living membrane, which has been stated to be essential to the
further vitalization of the effused Fibrine (§ 119). It has been proved in many
instances, however, that Coagula of Blood completely inclosed within the body
possess an incipient vascularity, being capable of injection from the surface
beneath (§ 700) ;t and there is no valid reason to deny that the thin layer of
Blood which remains between the lips of an incised wound, when these are
closely brought together, is the medium of their reunion. It is unquestionable,
however, that the Fibrine of an ordinary Blood-clot is less highly-elaborated,
and consequently less susceptible of organization, than that of the Liquor
Sanguinis, which is poured forth after an injury, and which has been subjected
to the local action that is its immediate result.

797. To the second mode of Reparation, attention has recently been strongly
directed by Dr. Macartney ; and as this, too, is a strictly Physiological action,
and is one which the Surgeon should aim at producing, it will be here dis-
cussed somewhat in detail. The Surgeon has, until recently, regarded the
processes of Granulation and Suppuration, which are attended with much
local Inflammation, and with a considerable amount of Constitutional disturb-
ance when the surface is large, as the only means by which an open wound

* Physiology of Inflammation and the Healing Process.

•j" For well-established cases of this sort, see communications by Mr. Dalrymple in the
Medico- Chirurgical Transactions, vol. xxiii.; and in Lancet, March 23, 1844.
51

602 OF NUTRITION.

•

can be filled up. Occasional instances, however, have not been wanting, in
which large open wounds have closed up under the dry clot of blood, by which
they were at first covered over, without any suppuration, or other symptom
of inflammation ; and in these it has been found, that the new surface much
more nearly resembles the ordinary one, than does the Cicatrix which follows
granulation. To Dr. Macartney, however, is due the merit of explaining the
rationale of this action ; which is precisely analogous to that which is con-
cerned in the ordinary processes of growth, and to that reproduction of whole
parts which takes place in the lower animals without Inflammation. It is
termed by him the modelling process ; and he remarks as characteristic of it
that, when it goes on perfectly, and without Inflammation, the patients are so
completely free from uneasy sensations, as only to be aware of the extent of the
injury by their own examination. In this process, the surfaces of the wound
do not unite by vascular connection, even when they lie in contact; nor is the
space between them filled up with coagulable lymph ; but they are smooth
and red, moistened with a fluid, and presenting the appearance of one of fhe
natural mucous membranes. " It might be anticipated that, as this mode of
reparation bears so strong a resemblance to the natural formation and develop-
ment of parts, it is the slowest mode ; but this is of little account, when com-
pared with its great advantages in being unattended with pain, inflammation,
and constitutional sympathy, and leaving behind it the best description of
cicatrix." In the case of large burns on the trunk in children, the difference
between the two modes of Reparation will frequently be that of life and death;
for it often happens that the patient sinks under the great constitutional dis-
turbance occasioned by a large Suppurating surface, although he has survived
the immediate shock of the injury.

798. The most effectual means of promoting this kind of Reparative pro-
cess, and of preventing the interference of Inflammation, vary according to
the nature of the injury. The exclusion of air from the surface, and the
regulation of the temperature, appear the two points of chief importance. By
Dr. Macartney, the constant application of moisture is also insisted on.* He
states that the immediate effects of injuries, especially of such as act severely
upon the sentient extremities of the nerves, are best abated by the action of
"steam at a high but comfortable temperature, the influence of which is
gently stimulant, and at the same time extremely soothing. After the pain
and sense of injury have passed away, the steam, at a lower temperature,
may be continued; and, according to Dr. M., no local application can com-
pete with this, when the Inflammation is of an active character. For subse-
quently restraining this, however, so as to promote the simple Reparative
process. Water-dressing will, he considers, answer sufficiently well; its prin-
cipal object being the constant production of a moderate degree of Cold,
which diminishes, whilst it does not extinguish, sensibility and vascular
action, and allows the Reparative process to be carried on as in the inferior
tribes of animals. The reduction of the heat in an extreme degree, as by
the application of ice or iced water, is not here called for, and would be
positively injurious; since it not only renders the existence of Inflammation
in the part impossible, but, being a direct sedative to all vital actions, suspends
also the process of restoration. The efficacy of Water-dressing in injuries
of the severest character, and in those which are most likely to be attended
with violent Inflammation (especially wounds of the large joints) has now
been established beyond all question; and its employment is continually
becoming more general.t — Other plans have been proposed, however, which

Treatise on Inflammation, p. 178.

j- See an acoount of the results of this treatment by Dr. Gilchrist, in Brit, and For. Med.
Rev., July 1846, p. 242.

ORIGIN OF THE SOLID TISSUES. 603

seem in particular cases to be equally effectual. To Dr. Greenhow, of New-
castle, for instance, it was accidentally suggested, a few years since,* to cover
the surface of recent burns with a liquefied resinous ointment; and he states
that in this manner Suppuration may be prevented, even where large sloughs
are formed; the hollow being gradually filled up by new tissue, which is so
like that which has been destroyed, that no change in the surface manifests
itself, and none of that contraction, which ordinarily occurs even under the
best management, subsequently takes place. A plan has, moreover, been
proposed for preventing suppuration, and promoting reparation by the model-
ling process, which consists in the application of ivarm dry air to the wounded
surface. The experiments made on this have not been entirely satisfactory,
but they seem to show that, though the process of healing is much slower
under treatment of this kind, it is attended with less constitutional disturb-
ance than is unavoidable in the ordinary method; and it may, therefore, be
advantageously put in practice in those cases in which the condition of the
patient requires every precaution against such an additional burthen, — as after
amputation in a strumous subject. But of the superiority of this treatment
to the water-dressing, no evidence has yet been adduced.

799. The third method of Reparation, — that by Granulation — appears to
be a means employed by Nature for the purpose, under the unfavourable cir-
cumstances of Irritation or a continuance of Inflammation; proving that parts
previously in a healthy state, are disposed to heal, in despite of many impe-
diments thrown in their way. The Granulation-structure is a special one,
formed for a temporary purpose. It is endowed with higher vascularity and
a more rapid power of growth, than is possessed by any modification of
ordinary tissue; but it is very easily destroyed by injury, or by a higher
degree of inflammation. The existence of Granulations has been supposed
to be necessary to fill up deficiencies; this, however, is not altogether true;
as we occasionally find very considerable vacancies filled with lymph, which
gradually becomes organized, without being converted into granulations; and
the void may be also supplied by the process of natural growth just described.
Moreover, it is only in the beginning that granulations take the place of the
natural structure; for the approximation of the edges of a wound filled with
them, requires that they should be removed by interstitial absorption; so that
wounds healed by this process do not exhibit any remains of the new me-
dium. This approximation somewhat resembles that which occurs in open
wounds that have never inflamed, being the result of the natural processes of
growth; and it does not take place until the Inflammation has in great degree
subsided : but it differs from the modelling processes in this, — that, as the wound
is occupied by granulations, its closure takes place prematurely, as it were ;
so that, when the granulations are subsequently absorbed altogether, a con-
tracted cicatrix is the result. — It will be presently seen that the formation of
the Granulation-structure is intimately connected with the elaboration of Pus ;
and this process, accompanied as it is with such great constitutional disturb-
ance, and involving such a loss of nutritious material, cannot but be regarded
as an action to be altogether avoided, if possible.

800. We shall now consider, more in detail, the nature of the process of
Granulation, and of the Suppuration which usually accompanies it. Its com-
mencement is exactly conformable to the first stage of ordinary reunion by the
first intention ; for Liquor Sanguinis is thrown out, in which Exudation-cor-
puscles present themselves in large numbers. According to Gerber, the trans-
formation of these into a sort of imperfect Epithelium may be seen to take
place within half an hour. New layers are in the mean time developed ; and

* Medical Gazette, Oct. 13, 1838.

604 OF NUTRITION.

the most superficial of the Exudation-corpuscles, which are exposed to the
contact of air, change their character (in the mode to be presently described,
§ 805), and become Pus-Globules ; whilst those in close contact with the sub-
jacent surface take a share in the process of reparation. A new layer of
exudation-corpuscles is next deposited over this : of which the outer portion
degenerates as before into pus-globules, whilst the inner part gives origin to
a kind of areolar tissue, forming Granulations. These Granulations are them-
selves extremely vascular ; and, as recently shown by Mr. Liston,* the ves-
sels of the subjacent tissue are much enlarged, and assume a varicose charac-
ter. The bright red colour of the Granulations, however, does not depend
on their vascularity alone ; for 'the cells themselves, especially those most
recently evolved, are of nearly as deep a colour as the blood-globules ; and
the superficial bleeding which follows even the slightest touch of the granu-
lating surface, does not proceed from blood shed from the newly-formed vessels
only ; for the red fluid shed in this manner contains, besides blood-discs,
newly-developed red cells, ruddy cytoblasts, pale granules and reddish serum.
It is a common property of animal cytoblasts, that they present a red colour
on their first formation, when in contact with oxygen ; but this hue they
lose again, whether they advance to perfect development and become integral
parts of a living tissue, or die and degenerate.

801. The process of Granulation and Suppuration appears to differ from
that of simple Reparation (the modelling process of Dr. Macartney) in this,
— that a large part of the Exudation-corpuscles deposited on the wounded
surface degenerate into Pus in the former case, whilst none are thus wasted
in the latter ; — but that the existence of Inflammation occasions a more co-
pious supply of Fibrine in the former case, and increases its tendency to be-
come organized ; the filling-up of a wound with Granulations being thus a
much more rapid process than that renewal of the completely-formed Tissues,
•which may take place in the absence of Inflammation. The imperfect cha-
racter of the Granulation-structure is shown, by the almost complete disap-
pearance of it after the wound has closed over. The portion of it in immediate
contact with the subjacent tissue, however, 'appears to undergo a higher organi-
zation ; for it becomes the medium by which the Cicatrix is made to adhere
to the bottom of the wound. It is very liable to undergo changes which
end in its disintegration ; as is evident from the known tendency to re-open-
ing, in wounds that have been closed in this manner.

3. — Abnormal Forms of the Nutritive Process.

802. Under the preceding head, we have considered the chief variations
in the degree of activity, that are witnessed in the ordinary or normal condi-
tions of the Nutritive process, — that is, those conditions in which the pro-
ducts are adapted, by their similarity of character, to replace those which
have been removed by disintegration. But we have now to consider those
forms of this process, — in which the products are abnormal, — being different
from the tissues they ought to replace. We shall confine ourselves to a brief
examination of the two most important of these states ; — that which is termed
Inflammation ; — and that which gives rise to Tubercular deposit. The
former results from an excess of the plastic element in the blood ; the latter
from a depraved condition of it, whereby its plasticity is impaired or destroy-
ed.— Notwithstanding all the attention which has been given to the state of
the vessels in Inflammation, a careful consideration of its phenomena, with the
light which recent investigations have thrown upon these, leads us to attach

* Medicc-Chirurgical Transattions, vol. xxiii.

ABNORMAL FORMS OF THE NUTRITIVE PROCESS. 605

comparatively little importance to this, and to seek for the essential character of
the process elsewhere. The researches of Addison, Williams, Barry, Gulli-
ver, Andral, and others, all seem to point to the following conclusions: — 1.
That there is a peculiar afflux or determination of the White Corpuscles of
the Blood towards the inflamed part. 2. That the total amount of these cor-
puscles in the circulating blood undergoes a great increase. 3. That the
quantity of Fibrine in the Blood augments, in proportion to the extent and
intensity of the Inflammation ; and this, even when it was previously, from
the influence of some other morbid condition, below the usual standard.
With its quantity, its plasticity, or tendency to organization, also increases in
a healthy subject. — Now when these facts are compared together, and are
connected with those formerly adduced, in regard to the probable function
of the W^hite Corpuscles of the blood, they lead almost irresistibly to. the con-
clusion, that the process of Inflammation essentially consists in an undue
stagnation of these corpuscles in the vessels of the part, an excessive multi-
plication of them by the ordinary process of generation, and a consequent
over production of Fibrine. By these changes, and by the results which fol-
low them, Inflammation may be distinguished from the various forms of Hy-
peraemia and Congestion. To the results, then, we shall next direct our at-
tention.

803. It may be inferred from various phenomena, that whilst the forma-
tive power of the Blood is increased in Inflammation, that of the Tissues is
diminished. Certainly this is the case in regard to the system at large, when
febrile irritation has been established; for, notwithstanding the increased Plas-
ticity of the Blood, we see the body wasting, instead of increasing in vigour.
And it may be inferred also, in regard to the tissues of the part affected,
from the tendency to Atrophy and Disintegration which they exhibit ; and
which is greater (leading even to the death of whole parts) in proportion as
the inflammation is more intense, and as the tendency to the deposit of new
products is the more decided. That a Stagnation of Blood takes place in
the vessels of the inflamed part, is another general fact, which throws some
light upon the nature of the process ; for this stagnation is obviously favour-
able to the transudation of the fluid Plasma of the blood, through the walls
of the vessels, into the surrounding tissue, or upon a neighbouring surface.
This deposition of the Fibrinous element, possessing a high degree of plasti-
city, and capable of spontaneously passing into simple forms of tissue (which
may be gradually replaced by higher forms, when penetrated by vessels from
the surrounding parts), may be regarded as the first characteristic result of
Inflammation. It is by the deposition, and subsequent organization, of plas-
tic matter in the substance of organs, that their tissues become consolidated ;
and by its deposition and subsequent organization upon their free surfaces,
that false membranes and adhesions are formed. It appears probable, from
the recent inquiries of Mr. Robinson,* that this deposition may be attributed
to physical causes. It is well known, that simple Congestion will occasion
transudation of the serous portion of the Blood ; and if the return of the
Blood by the veins of a part be completely prevented, a greater or less pro-
portion of fibrine also may be poured forth. Now when the quantity of Fi-
brine in the blood is greatly augmented, and the firmness of the walls of the
vessels in the inflamed part is diminished by the alterations taking place in
their tissue, it is easy to understand that the disposition to the effusion of Fi-
brine will be much increased. Sometimes the Fibrine is diluted with a large
quantity of Serum ; and is poured into a cavity (as that of a serous sac) in
the form of a liquid, which afterwards separates into clot and serum.

* Medico-Chirurgical Transactions, vol. xxvi. p. 51.
51*

606 OF NUTRITION.

804. Should the Inflammation increase in intensity, a complete stagnation
of blood in the tissue most affected, or even in an entire organ, will be the
result; and this will occasion its death. If a large part be thus entirely de-
stroyed at once, the process is termed Gangrene; and it separates from the
living part, at a line where the Inflammation is less intense, and where there
is a deposit of Fibrine, which serves the important purpose of closing the
mouths of the blood-vessels that are laid open by the process. .If the destruc-
tion of tissue, however, be interstitial, the dead parts are not thus thrown off,
but are taken up by the absorbent process ; and thus the cavity of an Abscess,
or of an Ulcer is formed. This cavity is usually bounded by tissue, that has
been consolidated by the effusion of Fibrine ; — a fact readily accounted for on
the principles just stated. For the death and removal of tissue take place,
where the Inflammation has been most intense and the stagnation most com-
plete, which is in the centre of the inflamed spot; and the fibrinous effusion,
the result of moderate inflammation, is poured into the surrounding tissue.
The elements of Liquor Sanguinis are poured into the central, as well as the
peripheral, portion of the inflamed tissue; but they assume a different form —
that of Pus. It would appear as if the influence of the surrounding death and
decay produces a degradation of their character; so that they become entirely
aplastic or unorganizable, although immediately derived from Blood highly
charged with Fibrine.

805. Between Coagulable Lymph and Purulent effusions, there are many
degrees of transition ; the very same deposit being frequently organizable at
one part, — presenting the character of a tough fibrous membrane, interspersed
with corpuscles, — whilst it is friable in another, from want of complete fibril-
lation in the fluid portion of the effusion, — and is entirely destitute of tenacity
in a third portion, especially the superficial part, or free surface, of the deposit.
When examined by the Microscope, Pus is found to be characterized by the
presence of a number of cells of a peculiar, aspect, having a very tuberculated
or mulberry surface ; these are seen floating in a fluid, termed liquor puris,
which is of an albuminous or low fibrinous character, being entirely destitute
of organizability. Now the production of Pus in an inflamed part, or in other
words, the act of Suppuration, may be due to one of three causes, viz. — the
intensity of the inflammation; the presence of air. which becomes a source of
irritation ; and a previously vitiated state of the blood. Various attempts
have been made to show that the Pus-globule is a degenerated red or white
corpuscle of the Blood ; it seems more probable, however, that it does not
escape from the vessels as a complete cell, but as a cell-germ, which may
have had its origin in a white corpuscle of the blood ; and which, under
favourable circumstances, might have produced an Exudation-corpuscle (§ 800).
At any rate, it must be regarded as a degenerated form of cell ; and the liquor
/no-is must be considered as analogous to the plasma of the Blood in a de-
generated state.

806. In what manner the Inflammatory process determines the formation
of the Pus-cell, and the consequent degradation of the product, we are at
present unable to state ; but that the degree of irritation in the part has an
influence upon it, is evident from the effects of the contact of air upon inflamed
.surfaces, causing those elements to take the form of Pus, which would other-
wise have been thrown out as a plastic deposit. This circumstance would
seem to indicate, beyond all doubt, that the Exudation and Pus-corpuscles,
the plastic Lymph and the aplastic Liquor puris have the same origin; but
that their character is determined by local circumstances. There is great
reason to believe, that when Pus is introduced into the Blood, it may induce
such a change in the character of the fluid, as speedily to impair its vital pro-
perties ; so that the Pus-corpuscles will rapidly propagate themselves in the

ABNORMAL FORMS OF THE NUTRITIVE PROCESS. 607

Blood, and the plasticity of the Liquor Sanguinis will be diminished. In this
manner the whole system will be seriously affected, and there will be a tend-
ency to deposits of Pus in various organs — especially in those which, like the
Lungs and Liver, serve as emunctories to the system — without any previous
inflammatory changes in these parts. It has been ascertained by Mr. Addi-
son, that if a drop of Pus be treated with Liquor Potassse, it entirely loses its
opaque character, and becomes clear and transparent, like Mucus, — with whose
tenacity and elasticity also it becomes endowed. If it be then treated with
acetic acid, it recovers somewhat of its former opacity ; and, when pressed
into a thin film, exhibits a distinct fibrillation.

807. In persons of that peculiar constitution, which is termed Scrofulous
or St ruinous, we find an imperfectly-organizable or Caco-plastic deposit, or
even an altogether aplastic product, known by the designation of Tubercular
matter, frequently taking the place of the normal elements of Tissue ; both
in the ordinary process of Nutrition, and still more when Inflammation is set
up. From an examination of the Blood of Tuberculous subjects it appears,
that the Fibrinous element is not deficient in amount, but that it is not duly
elaborated ; so that the coagulum is loose, and the red corpuscles are found
to bear an abnormally low proportion to it. We can understand, therefore,
that such a constant deficiency in Plasticity must affect the ordinary nutritive
process ; and that there will be a liability to the deposit of cacoplastic pro-
ducts, without Inflammation, instead of the normal elements of tissue. Such
appears to be the history of the formation of Tubercles in the lungs and other
organs, when it occurs as a kind of metamorphosis of the ordinary Nutritive
process ; and in this manner it may proceed insidiously for a long period, so
that a large part of the tissue of the lungs shall be replaced by an amorphous
deposit, without any other ostensible sign than an increasing difficulty of
respiration. It is in the different forms of Tubercular deposit, that we see
the gradation most strikingly displayed between the plastic and the aplastic
formations. In the semi-transparent, miliary, gray, and tough yellow forms
of Tubercle, we find traces of organization in the form of cells and fibres,
more or less obvious ; these being sometimes almost as perfectly formed as
those of Plastic Lymph, at least on the superficial part of the deposit, which
is in immediate relation with the living structures around ; and sometimes so
degenerated, as scarcely to be distinguishable. In no instances do such de-
posits ever undergo further organization; and therefore they must be regarded
as caco-plastic. But in the opaque, crude, or yellow Tubercle, we do not
find even these traces of definite structure ; for the matter of which it con-
sists is altogether granular, more resembling that which we find in an albu-
minous coagulum. The larger the proportion of this kind of matter in a
tubercular deposit, the more is it prone to soften, whilst the semi-organized
tubercle has more tendency to contraction. This is entirely aplastic.

808. Now although Tubercular matter may be slowly and insidiously de-
posited, by a kind of degradation of the ordinary Nutritive process, yet it can-
not be doubted that Inflammation has a great tendency to favour it ; so that a
larger quantity may be produced in the lungs, after a Pneumonia has existed
for a day or two, than it would have required years to generate in the pre-
vious mode. But the character of the deposit still remains the same ; and its
relation to the plastic element of the blood is shown by the interesting fact, of
no unfrequent occurrence, — that, in a Pneumonia affecting a Tuberculous
subject, Plastic Lymph is thrown out in one part, whilst Tubercular matter is
deposited in another. Now Inflammation, producing a rapid deposition of
Tubercular matter, is peculiarly liable to arise in organs, which have been
previously affected with chronic Tubercular deposits, by an impairment of
the process of textural Nutrition ; for these deposits, acting like foreign bodies,

608 OF NUTRITION.

may of themselves become sources of irritation ; and the perversion of the
structure and functions of the part renders it peculiarly susceptible of the
influence of external morbific causes. — These views, at which several recent
Physiologists and Pathologists have arrived on independent grounds, seem to
reconcile or supersede all the discordant opinions which have been upheld at
different times regarding the nature of Tubercle ; and lead to the soundest
views with respect to the treatment of the Diathesis.

809. We frequently meet with abnormal growths of a Fatty, Cartilaginous,
Fibrous, or even Bony structure ; which result from the development of these
tissues in unusual situations, and appear to originate in some perverted action
of the parts themselves. — But there is another remarkable form of disordered
Nutrition, which is concerned in producing what have been termed hetero-
logous growths, — that is, masses of tissue, differing in character from any
which is normally present in the body. Most of these are included under
the general designation of Cancerous or Fungous structures ; and it has been
shown by Miiller and others, that the new growth consists of a mass of cells;
which, like the Vegetable Fungi, develope themselves with great rapidity ; and
which destroy the surrounding tissues by their pressure, as well as by ab-
stracting from the Blood the nourishment which was destined for them.
These parasitic masses have a completely independent power of growth and
reproduction ; and it seems difficult to refuse them the character of distinct
existences. They can be propagated by inoculation, which conveys into the
tissues of the animal operated on, the germs of the peculiar cells that consti-
tute the morbid growth ; and these soon develope themselves into a new
mass. It seems to be by the diffusion of the germs produced in one part,
through the whole fabric, by the circulating current, that the tendency to re-
appearance (which is one great feature in the malignant character of these
diseases) is occasioned. Yet there is no evidence, that the first production
of a Cancerous growth is due to germs introduced from without ; in fact, as
it appears to the Author, the history of its origin, as well as the analogy of
similar cases, makes it far more probable, that the Cancer-cell is but an abnor-
mal form of the ordinary tissue-cells of the body, — being, in fact, a cell which
possesses to an unusual degree the power of reproduction, instead of under-
going those transformations by which it would be converted into other
kinds of tissue.

a. Several instances have been recently published, of the occurrence of Vegetable organ-
isms as parasites upon the Animal body. That in some of these a true Plant, possessing a
regular apparatus of nutrition and reproduction, has arisen from a germ introduced from
without, there can be little question ; but in other instances (as in the case of the crusts of
Porrigo favosd), it has been assumed that the organization is Vegetable, merely because it
consists of a mass of cells capable of extending themselves by the ordinary process of mul-
tiplication. But it must be remembered, that the cellular organization is common to Ani-
mals as well as to Plants ; being the only form that manifests itself at an early period of
development in either kingdom, and remaining throughout life in those parts which have
not undergone a metamorphosis for special purposes. Hence to speak of Porrigo favosa, or
any similar disease, as produced by the growth of a Plant within the Animal body, appears
to the Author a very arbitrary assumption ; the simple fact being, in regard to this and many
other structures of a low type, that they present the simplest or most general kind of organ-
ization. Their nature must be decided by their Chemical constitution ; and this, in the case
of the Porrigo favosa, appears to be unquestionably Animal.

b. There seems a strong probability in the idea, that the propagation of many diseases by
inoculation, essentially consists in the transplanting of cell-germs from the body of one ani-
mal to that of another. Thus the Vaccine Vesicle appears to be made up of an aggregation
of distinct cells, to which we may very fairly attribute anorigin of this kind. But this seems
rather true of diseases which manifest themselves by a local development of cellular struc-
tures,— such as Cancer and Cow-pox, — than of such as Hydrophobia, Plague, Poisoning by
Serpents, &c., in which the symptoms are referrible, more or less clearly, to an alteration in
the character of the Blood, by the introduction of a substance acting as a ferment (§ 70S).

VARYING DURATION OF CELL-LIFE. 609

4.— Varying duration of different parts of the Organism.

810. From the foregoing details the obvious inference results, — that each
part of the organism has an individual Life of its own, whilst contributing to
uphold the general Life of the entire being. This Life, or state of Vital
Action, depends upon the due performance of the functions of all the subordi-
nate parts, which are closely connected together. The lowest classes of or-
ganized beings are made up of repetitions of the same elements ; and each
part, therefore, can perform its functions in great degree independently of the
rest. But, in ascending the scale, we find that the lives of the individual parts
become gradually merged (so to speak) in the general life of the structure ;
for these parts gradually become more and more different in function, and
therefore more and more dependent on each other for their means of support ;
so that the activity of all is necessary for the maintenance of any one.

811. The doctrine of Development from Cells gives us a clearer idea of the
nature of the continual process of decay and renewal, which take place in the
Animal body. Every Cell has, to a certain degree, an individual life of its
own. This individuality is much more decided in the lower forms of organ-
ized being, where each cell can maintain an independent existence, than it is
in the higher, in whose fabric a- large number having different functions are
united into one structure, the combined activity of the whole of which is
necessary to the life of any one. But, even in the highest, it is evident that
each cell will possess a certain duration of its own ; and that, from its first
period of development, all the changes which it undergoes are governed by
laws peculiar to it. In the various parts of the Vegetable, as in those of the
Animal, we find a great difference in the duration of the existence of the cells
composing them. These differences may be reduced to five heads.

i. Cells may be generated, Avhich have a very transient existence, and
which disappear again, without undergoing any transformation. This may be
seen in the Vegetable ovule, and in the Germinal Vesicle of the Animal Ovum ;
as well as in many other parts. Thus we have Absorbent Cells (§ 181),
Secreting Cells (§ 179), and probably Assimilating or Fibrine-elaborating
Cells (§ 154) ; all of which originate in pre-existing germs, attain their full
development (in the course of which they perform their allotted function),
and then disappear by rupture or liquefaction. In such instances it is obvious
that, from their first origin, the cells are subject to a law of limited duration,
and that their death and decay are as much the result of their inherent consti-
tution, as are those of each entire Animal or Vegetable organism.

n. The contrary extreme to this may be found in those Cells, of which the
function, instead of being transient, is to be indefinitely prolonged; such are
those of which the organs of mechanical support are usually formed. Here
the cell, instead of changing its form, or of giving origin to new cells within
itself, becomes the subject of an internal deposit of hard matter, which lines
its walls, and cuts it off, more or less completely, from the general course of
Vital Action. AVhen this is the case, and the hard matter is not itself liable
to decomposition, the duration of the cell-walls, which are protected by their
peculiar aggregation from exposure to decomposing agents, may undergo little
or no change for an almost indefinite period. Thus the heart-wood of Plants,
the Bones of Animals, and still more their Hair, Hoofs, Horns, &c., may re-
main unaltered through a long series of years. Of some of these parts it can
scarcely be said that they are less alive, when removed from the organism to
which they belonged, than when included in it. In the heart-wood of a Plant,
for example, no vital change takes place, from the time that the woody tubes
and cells are once consolidated by internal deposition ; it may decay, whilst

610 OF NUTRITION.

still firming part of the stem, without interfering with the nutritive operations
of the tree ; and if we could possibly remove it entirely, without doing injury
by the operation to the rest of the structure, its absence would be productive
of no other evil consequences than those which would necessarily result
from the withdrawal of the mechanical support afforded by it. The same
may be said of the Epidermic Appendages of Animals, and of the External
Skeletons of many Invertebrata ; which remain equally unchanged from the
time of their first formation. — Now as long as these structures hold together,
it is evident that the organized part of them must have undergone little change
from the condition in which it existed in the living fabric ; and that their
death takes place, in reality, only when the structures decay, — this decay
being, in fact, the consequence of it. The law of existence of such cells,
therefore, is that of indefinitely-prolonged duration; this law must have been
impressed upon them from their origin; and the power by which their walls
secrete and deposit the consolidating materials, appears to be the chief means
of keeping it in operation.

in. In all the higher forms of Animal structure, the Cells originally com-
posing it are only the means of generating tissues of other kinds, in which
the Cellular character is less obvious. Thus the Muscular and Nervous tis-
sues have their origin in cells, which at first appear in no respect different
from others, but which subsequently undergo a peculiar metamorphosis, and
themselves no longer exist as such. Upon all these primordial cells, there-
fore, a law of transformation is impressed, from the time of their first pro-
duction. In their original aspect, -they cannot be distinguished from the cells
which are not destined to undergo any such metamorphosis; but, just as the
first cell of the embryo, from which Man is produced, must have some real
though not apparent difference from that in which the Polype originates, so
must the cell which is afterwards developed into Muscular Fibre, be inherently
different from that which is subsequently converted into Nervous tissue.

iv. The tissues, thus formed by the transforming processes to which certain
Cells are subject, are evidently governed by the same laws of Nutrition as
those which regulate ordinary Cell-growth; these are modified in their action,
however, by the conditions in which they are placed, in regard to the activity
of the function which the Tissue is called upon to perform. In all instances,
however, these Tissues have a limited period of existence. They are gene-
rated, they grow from the alimentary materials with which they are supplied,
they arrive at maturity, they 'decline, they die, and they decay ; just as do the
isolated vesicles constituting the humblest forms of vegetation. For all of
them there is an appointed duration of life, just as there is for the entire Man.
— Now on this view we can explain many physiological phenomena, which
cannot otherwise be very satisfactorily accounted for. It is owing to the con-
tinual death and decay of its component cells, that the process of decomposition
goes on with such constancy and uniformity in the living body; whilst, on the
other hand, it is by the continual reproduction of new cells, in the place of
those which have disappeared, that the normal organization is maintained.
The limited duration of the life of the cells composing the various tissues is
further made evident, by the rapid disappearance of the normal organization,
and by the loss of the functional power of those tissues, when the cessation
of their activity prevents the development of the new cells, by which alone
their character can be maintained. Of the change of structure and loss of
power which result from disuse and consequent want of nutrition in Muscular
and Nervous tissues, instances have already been given (§§ 588 and 790).
The ordinary processes of Decomposition and Interstitial Absorption are pro-
bably less rapid than usual under such circumstances ; so that the length of
time required for the disappearance of the characteristic structure, and the

VARYING DURATION OF DIFFERENT PARTS. Oil

consequent loss of functional power, affords us some idea of the limit to the
duration of the life of the tissue. It may be stated, then, as a general pro-
position, that the interstitial change, which the whole structure of the body is
continually undergoing, in its normal or physiological condition, is due to the
regularly-occurring death and reproduction of its component cells, of which
every one has its own limit of duration. We uniformly find that those
Tissues, in which the most active vital changes are going on (such as the
Nervous and Muscular), are those in which the duration of the individual
component portions is the least; as is shown by the rapidity of the changes
of removal and reposition, which are continually taking place in them. The
converse holds good also. Further it may be remarked, — and this is a matter
of much practical importance, — that anything which increases the functional
activity of any particular tissue, thus causing it to live faster, diminishes the
duration of its life ; as is shown in the increased rapidity of disintegration,
which results from the continued exercise of the Muscular and Nervous
systems.

v. There is yet another phase, under which Cellular life presents itself as
a natural condition in the lower organisms, and in the early condition of the
higher; but which constitutes a morbid state in the adult condition of the
latter. This is when cells reproduce themselves with extreme rapidity, —
neither the primary nor secondary cells undergoing any further transforma-
tion,— and the duration of each individual being limited by the development
of its progeny within it, causing its own distension and final rupture or dis-
appearance. The growth of the lower Fungi offers a striking example of this
in the Vegetable kingdom ; and the early processes of development in the
Ovum of the highest Animals, exhibit the same character. Every cell, as it
is generated, proceeds at once to the work of multiplication, for which it
seems specially destined; and thus it is subject from the first to the law of
Reproduction. It is this which distinguishes the Fungoid diseases ; which
derive the character designated by the Surgeon as malignancy, simply from
their tendency to propagation, and his want of power to control it. It seems
probable that many other changes of structure are due to a corresponding
cause.

812. The duration of the existence of the individual Cells in corresponding
parts, is further subject to variation, in accordance with the period of life of
the entire organism. Thus all the tissues, even those most consolidated, are
undergoing continual changes in the young animal, in which the processes of
decay and renewal go on much faster than in the adult ; and in the adult, than
in the aged person. Even the cells of the Bony structure, which in the adult
are almost permanent, and in the aged person are subject to extremely little
change, are liable in the infant to an early decomposition ; their places being
filled up by others, of which the form adapts itself to the growth of the struc-
ture. This may be partly accounted for by the imperfect degree, in which,
so long as the entire organism is undergoing rapid increase, the normal struc-
ture is developed in any one portion of it; for the degree of consolidation
being less, the tendency to decay will naturally be greater. But this explana-
tion is not in itself sufficient ; and we must be content for the present to
regard it as a general law (which may ultimately prove to be but a result of
some more general principle) that the duration of the existence of individual
cells increases, cseteris paribus, with the advance of life. At the same time,
their functional activity diminishes. They may be said to live more slowly.
The dull perceptions, and slow and feeble movements, of the aged man, form
a striking contrast with the acute sensibility, and the rapid and vigorous mus-
cular actions, of the child; and the same change may be noticed in the organic
functions. Hence it may be stated as a general law, that the vital activity of

612 OF NUTRITION.

the Cells (and of the tissues produced by their transformation) diminishes in
proportion to the prolongation of the general life of the system ; and this law
exactly corresponds with what has just been observed, as to the comparison
of the tissues of different kinds, which are present in the same body.

5. — Of Death, or Cessation of Nutrition.

813. It is a necessary consequence of that intimate mutual dependence of
the several operations, which is characteristic of the higher organisms, that
the interruption of the function of any one important part is followed by the
Death of the whole structure; because it interferes with the elaboration, cir-
culation, or depuration of that nutritive fluid, which supplies the pabulum for
the growth and reproduction of each portion of the system. Cut the lives
of individual parts may be prolonged for a greater or less duration, after the
suspension of the regular series of their combined operations ; hence it is
that Molecular Death is not always an immediate result of Somatic Death. —
But, on the other hand, if the function of the part have no immediate relation
to the indispensable actions just alluded to, it may cease without affecting
them ; so that Molecular death may take place to a considerable extent (as in
entire limbs, or in the muscles and integuments of the head and trunk) with-
out Somatic death necessarily resulting.

814. The permanent and complete cessation of the Circulating current, is
that which essentially constitutes Somatic Death; and this may be traced to
several distinct causes. — In the first place, it may be due to failure in the pro-
pulsive power of the Heart, which constitutes Syncope; and this may result
from a variety of causes, which cannot be here particularized. — Secondly, it
may be occasioned by an obstruction to the flow of blood through the capil-
laries of the lungs, constituting Asphyxia; and this, as we have seen, may
be consequent upon disordered states of the lungs themselves, or upon sus-
pension of the respiratory movements, through afl'ections of the Nervous
centres. It is in this mode that most fatal disorders of the Nervous System
produce death ; except when a sudden and violent impression (as from con-
cussion of the brain, or a blow on the epigastrium) occasions a cessation of
the heart's power. Thus in Apoplexy, Narcotic Poisoning, &c., death results
from the paralyzed condition of the Medulla Oblongata ; whilst in the con-
vulsive diseases, the fatal result ensues upon a spasmodic fixation of the
respiratory muscles. — Thirdly, Somatic death may be occasioned by a dis-
ordered condition of the Blood itself, which at the same time weakens the
power of the Heart, impairs the activity of the Nervous system, and prevents
the performance of those changes in the systemic capillaries, which afford a
powerful auxiliary to the circulation. This is Death by Necrsemia. — Fourthly,
Somatic death may result directly from the agency of Cold, which stagnates
all the vital operations of the system. Where the cooling is due to the agency
of an extremely low external temperature, which acts rirst upon the super-
ficial parts, there is reason to think that the congestion of the internal vessels
thereby induced, occasions a torpid condition of the nervous centres, and that
the cessation of the Circulation is immediately due to Asphyxia. But when
the cooling is gradual, and the loss of heat is nearly equally rapid throughout,
it is obvious that the stagnation will be universal, and that no cessation of
activity in any one part is the occasion of the stagnation in the functions of
the remainder. It is in this manner that death results from Starvation; and
not by the weakening of the heart's action, as commonly supposed. The
proofs of this will be stated hereafter (§ 896).

815. That Molecular death should speedily follow Somatic death, is not
surprising; when it is borne in mind how constant is the dependence of all

OF DEATH, OR CESSATION OF NUTRITION. 613

those functional operations, in which vital activity consists, upon the due
supply of the circulating fluid. And as a general rule we find, that the more
active the changes which normally take place in any tissue during life, the
more speedily is its complete loss of activity, or Death, when the requisite
conditions of its vital action are no longer supplied to it. We may observe
that, in Cold-blooded animals, the supervention of Molecular upon Somatic
death is much less speedy than it is in Birds and Mammals. This seems
clue to two causes. In the first place, the tissues of the former, being at all
times possessed of a lower degree of vital activity than those of the latter,
are disposed to retain it for a longer time; according to the principle already
laid down. And, secondly, as the maintenance of a high temperature is an
essential condition of the vital activity of the tissues of warm-blooded ani-
mals, the rapid cooling of the body after Somatic death is calculated to extin-
guish it speedily; and that this cause has a real operation, is evinced by the
influence of artificial warmth in sustaining the vital properties of separated
parts. — The rapidity with which Molecular death follows the cessation of the
general circulation, will be influenced by a variety of causes ; but especially
by the degree in which the condition of the solids and fluids of the body has
been impaired by the mode of death. Thus in Necraemia, and in death by
gradual cooling, Molecular and Somatic death may be said to be simultane-
ous; and the same appears to be true of death by sudden and violent impres-
sions on the Nervous System. But in many cases of death by causes, which
suddenly operate in producing Syncope or Asphyxia, the tissues and blood
having been previously in a healthy condition, Molecular death may be long
postponed. We cannot be quite certain that it has supervened, until signs of
actual decomposition present themselves.

816. When Molecular death takes place in an isolated part, it must result
from some condition peculiar to that part, and not primarily affecting the
body in general. Thus we may have Gangrene or Mortification of a limb as
a direct result of the application of severe cold, or of an agent capable of
producing chemical changes in its substance, or of violent contusions occa-
sioning mechanical injury; or, again, from an interruption to the current of
nutritive fluid; or, further, from some ill-understood stagnation of the nutri-
tive process, which manifests itself in the spontaneous death of the tissues
without any assignable cause, as in some cases of Senile Gangrene. Some-
times we are enabled to trace this stagnation to some disordered condition of
the circulating fluid; as in the Gangrene resulting from the continued use of
the Ergot of Rye or Wheat; but we can give no other account of the almost
invariable commencement of such gangrene in the extremities, than we can
of the selection of Lead, introduced into the blood, by the extensors of the
fore-arm. — When Mortification or Molecular Death is once established in any
part, it tends to spread, both to contiguous and to distant portions of the body.
— Thus we have continually to witness the extension of Gangrene of the
lower extremities, resulting from severe injury or from the use of the Ergot,
from the small part first affected, until the whole limb is involved; and this
extension is easily accounted for by our knowledge of the tendency of organic
substances in the act of decomposition, to produce a similar change in other
organic substances subjected to their influence. And the propagation of the
Gangrenous tendency to other parts, is obviously due to the perversion of the
qualities of the Blood, which results from a similar cause. It is not, how-
ever, until some organ is affected, whose action is essential to the due main-
tenance of the Vegetative functions, that Molecular death becomes a cause of
Somatic death ; and very extensive ravages may thus take place without the
extinction of the sufferer's life.
52

614 OF SECRETION.

CHAPTER XV.

OF SECRETION.

1. — Of Secretion in General.

817. The literal meaning of the term Secretion is separation; and this is
nearly its true acceptation in Physiology. We have seen that the JNutritive
materials, which are received into the living body, are combined in a certain
proportion in the circulating fluid; and that they are carried in its current to
every part of the structure. Of the elements of the Blood, some are being
continually separated from it, to be introduced into the solid textures, of which
they become constituents ; forming, as it were, the organized frame-work, in
the interstices of which various other matters (also separated from the blood)
are deposited in an inorganic condition. This separation, the object of which
is to build up a living fabric, has been already considered under the head of
Nutrition; but it may be here remarked, that the deposition of Calcareous
matter in the Bones and Teeth, of Chondrine and Gelatine in the Bones and
Cartilages, and of Horny matter in the cells of the Epithelium and its ap-
pendages (Hair, Nails, Hoofs, &c.), is accomplished by a process analogous
in all respects to that concerned in the separation of those other products
which are ordinarily considered as Secretions. The same may be said of the
Serous fluid, which distends the interspaces of Areolar tissue, the Oily matter
contained in the Fat-cells, the Albuminous fluid of the Humours of the Eye,
and other analogous constituents of the living fabric.

818. But we have chiefly to consider under the present head, the nature
and origin of those products which are continually being cast forth from the
living body ; the amount of which is usually equal, in the adult animal, to
that of the solids and fluids ingested, after allowance has been made for the
portion rejected, in the form of faeces, as indigestible. The experiments of
Dr. Dalton* on his own person, give the following as the proportional quan-
tities discharged through the principal channels of excretion. The mean
quantity of solid and liquid Aliment taken into the system daily (during 14
days in spring) being 91 oz., or about 5| Ibs., the average amount of Faeces
(including part of the solid matter of the bile) was 5 oz. ; the average amount
of Urine was 48^ oz. daily; and, as the total weight of the body remained
the same, the quantity of fluid and solid matter excreted by the Skin and the
Lungs must, have been 37.i oz. At other periods of the year, a variation was
observed ; especially in the relative amount of fluid passing off by the Urine,
and by Cutaneous exhalation.

819. It can scarcely be questioned, that the chief source of the Excretions
is to be found in the continued Decomposition of the various tissues of the
body, which has been several times alluded to (§§ 275 and 811); and it is pro-
bable, from considerations heretofore adduced, that they are derived, not so
much from the fluid returned into the blood by the Lymphatics (as formerly
supposed), as from the Blood itself (§ 680). It has been pointed out by Lie-
big, that there is a remarkable correspondence between the elements of the
Blood, and those of the Bile and Urine taken together ; so that the Tissues,

* Edinburgh New Philosophical Journal, 1832, 1833.

OF SECRETION IN GENERAL. 615

which are all formed from the nutritive fluid, may be regarded as resolving
themselves, by their ultimate decomposition, into these two excretions.
Moreover, the Blood, during its circulation, gives up one portion of its con-
stituents in one part of the body — another at a different situation, — and so on.
Thus, the elaboration of Gelatine, which is deposited so largely in the solid
tissues, must occasion a considerable alteration in the blood: since, in its pro-
duction from Albumen, a certain residuum must be left (§ 141, b, c). This
residuum is probably another important source of the products of Excretion.
The same may be remarked in regard to the Nutrition of the Nervous Sys-
tem (§ 249). In several other instances, peculiarities of action in different
parts will deprive the Blood that passes through them, of its due proportion
of certain of its constituents ; these are partly restored by its admixture in
the Heart, with the Blood that has returned from other parts ; but still a gene-
ral alteration in the character of the Blood is the result of its Circulation ; and
for this alteration, it is the province of the Excretory function to compensate.
A striking illustration may be found, in the change of the colour, and of the
proportional amount of free Oxygen and Carbonic Acid, which takes place
in the Systemic capillaries, and which is reversed in the passage of the Blood
through the Lungs (§ 766). — Moreover it appears that two, at least, of the
Excreting organs have for their function to prevent the accumulation, in the
Blood, of matters which have been taken in as food, but for which there is
no demand in the economy. Thus the Liver appears to be the peculiar
channel for the elimination of superfluous non-azotized matter (§ 833) ; and
the Kidney of these a~otize.il compounds, which cannot be worked up '(so
to speak) into tissue (§ 842). Particular sources for the respective contents
of other Excretions will be pointed out, when they are considered in detail.

820. A distinction has already been drawn (§ 278) between the proper
Excretions, the retention of which in the Blood would be positively injurious,
and those Secretions which are destined for particular purposes within the
system, and the cessation of which has no immediate influence on any but the
function to which they are destined. This distinction is one of great import-
ance, especially when it is considered with reference to the Chemical Elements,
that are found in the two classes of fluids respectively. The solid matter dis-
solved in those of the latter class, is little else than a portion of the constitu-
ents of the Blood, either pure, or but slightly altered ; thus, in the Lachrymal
fluid, the Saliva, the Pancreatic juice, the Serous fluid of areolar tissue and
of serous and synovial membranes, we find little else than Albuminous and
Saline matter, derived at once from the blood. The Caseine, which is the
most characteristic ingredient of Milk (§ 854 b), is but a slightly-altered form
of Albumen; and some curious evidence has recently been obtained, that this
alteration commences in the Blood, and goes on during pregnancy as a pre-
paration for lactation.* On the other hand, the characteristic ingredients of the
Excretions are very different in character from the normal elements of the
Blood. They are all of them completely unorganizable; and they possess,
for the most part, a simple atomic constitution. Some of them also, have a
tendency to assume a crystalline form ; which is considered by Dr. Prout to
indicate their unfitness to enter into the composition of organized tissues.
With regard to some of the chief of these, there is sufficient evidence of their
existence, in small quantity, in the circulating Blood; but it is also clear, that
they exist there as products of decomposition, and that they are destined to
be separated from it as speedily as possible. If their separation be prevented,
they accumulate, and communicate to the circulating fluid a positively delete-
rious character. Of this, we have already seen a striking example in the

* See Dr. G. Bird, in Guy's Hospital Reports, vol. v.

616 OF SECRETION.

case of Asphyxia (§ 779) ; and the history of the other two principal Excre-
tions, the Bile and Urine, will furnish evidence to the same effect. — As a
general fact, then, it may be stated, that the materials of the Secretions pre-
exist in the Blood, in a state nearly resembling that in which they are thrown
oft' by the secreting organs: but that the materials of those secretions, which
are only destined to perform some particular function in the economy, are
derived from the substances which are appropriated to its general purposes ;
whilst those of the excretions are the result of the changes that have taken
place in the system, and cannot be retained in it without injury.

821. Of the reason why certain compounds forming part of the circulating
Blood, are separated from it by one organ, and others by a different one, no
other account can be given, than that which refers them to the special endow-
ments of the cells, which are the real instruments of the process. When the
ultimate structure of Glands is considered, it is found to be neither more nor
less than a vascular membrane, covered with epithelium-cells, and made up
into various forms for convenience of packing. Of such a membrane, in its
most expanded state, that which composes the walls of the Serous cavities, or
of the Synovial capsules, affords a good example. Of Mucous membrane
(§ 178), the structure is in some instances almost equally simple ; but in gene-
ral the secreting surface is extended, by the inversion of the membrane, into
a large number of little open sacs or follicles (Fig. 45), which are lined with
epithelium-cells, and copiously supplied with blood-vessels, and which are
equally concerned with the external superficies, in the elaboration of the pro-
tective secretion that covers these membranes. In the most complex form of
gland, we find nothing- but a very obvious modification of this structure.
Either the sacs are prolonged into coeca or blind tubes, as is the case in the
Human Kidney or Testis ; or they are .very greatly multiplied, and are clus-
tered together (just like currants upon a stalk) upon efferent ducts common to
several of them, as is seen in the Parotid. Now, that the particular modifica-
tion of structure, which the Gland may present, has no essential connection
with the character of the Secretion it is destined to form, is evident from this
circumstance, — that almost ever^ gland may be found under a variety of forms,
in different parts of the Animal series. The Secreting system, like every
other, is far simpler in the lower classes of Animals than in the higher; the
number of effete compounds, to be excreted from the circulating fluid, is much
smaller; and the variety of purposes, for which special secretions are required,
is much less. Hence, for almost every Gland, there is a part of the Animal
scale below which it does not exist ; and when it mal>es its first appearance,
it almost invariably presents a character nearly as simple, as that of the least
complex glanular structures in the higher animals. Thus the Pancreas in
Fishes (Fig. 257), the Mammary Gland in the Ornithorhyncus (Fig. 222), the

Salivary glands in the Echinodermata,

Fig. 222. and the Urinary organs of Insects, are

nothing more than follicles more or less
extended, and having separate orifices.
Again, in Insects, we find that all the
glands, — the Liver and Salivary glands,
as well as the Kidneys and Testes,
— have the form of prolonged tubes ;
whilst in Mollusca, all the secret-
Mammary Gland of Ornithorhyncus. ing organs, — the Urinary and Genital,

as well as the Biliary and Salivary, —

consist of multiplied vesicles connected with a ramifying duct. Moreover, it
is a well-ascertained fact that, even in the highest organisms, the functions of
Glandular structures (especially of those concerned in Excretion) are to a

OF SECRETION IN GENERAL. 617

certain degree vicarious with each other ; so that, when the secretion from one
of them is checked, the system makes an effort to throw off, by another chan-
nel, the injurious products that would otherwise accumulate in the Blood.
What is the nature of the change in any secreting organ, that causes it thus to
take upon itself a new function, is a question upon which we can at present
only speculate ; we have no more certain knowledge of it, than we have of
the cause which occasions their normal actions.

822. It has been recently proved, beyond all reasonable doubt, that in all
secreting organs, the Cells which cover the membranous surfaces, and line the
follicles and tubes, constitute the really operative part. The simplest condi-
tion of a Secreting Cell, in the Animal Body, is that in which it exists in Adi-
pose tissue ; every cell of which possesses the power of secreting or separat-
ing Fatty matter from the Blood. In this case, the secreted product remains
stored up in the cavity of the cell, as it usually does in the Cellular tissue of
Plants ; — not being poured forth, as it generally is elsewhere, by the subse-
quent bursting or liquefaction of the cell. But when the Secreting Cells are
disposed on the surface of a membrane, instead of being aggregated in a mass,
it is obvious that, if they burst or dissolve away, their contents will be poured
into the cavity bounded by that membrane ; and this is the case in the ordinary
Secreting processes. Thus the Mucus, which covers the surface of the Mu-
cous membranes, and which is being continually renewed, is the product of
the elaboration performed by the Epithelium-cells, which cover their free sur-
faces, and line their follicles. These cells are being continually cast off, and
replaced by a fresh growth, which has its origin in germs supplied by the
subjacent membrane ; and thus it is by the act of Cell-growth, that the Secret-
ing process is accomplished. For just as the cells at the extremities of the
Intestinal Villi select, from the contents of the alimentary tube, the nutritious
portion which is to be introduced into the absorbent vessels, — so do the cells
of the Secreting Tubuli or Follicles select from the Blood those effete particles
which it is their peculiar province to assimilate, and then discharge them into
the canals by which they will be carried out of the system.* Hence, as Mr.
Goodsir justly remarks, " there are not, as has been hitherto supposed, two
vital processes going on at the same time, viz., growth and secretion; but
only one, viz., growth. The only difference between this kind of growth,
and that which occurs in other organs is, that a portion of the product is, from
the anatomical condition of the part, thrown out of the system."

823. From the study of the changes which take place in the Glandular
organs, during their first development and their continued activity, Mr. Good-
sir has arrived at the conclusion, that the follicles may be considered as pa-
rent-cells ; and that the secreting cells in their interior may be regarded as a
second generation, developed from the nuclei or germinal spots on the walls
of the first. Now the successive production and development of the latter,
in which the process of secretion essentially consists, may take place on two
different plans.

a. In one class of Glands, the parent-cell, having begun to clevelope new cells in its inte-
rior, gives way at one point, and bursts into the excretory duct, so as to become an open fol-
licle, instead of a closed cell; its contained or secondary cells, in the progress of their own
growth, draw into themselves the matters to be eliminated from the blood, and, having at-
tained their full term of life, burst or liquefy, so as to discharge their contents into the cavity
of the follicle, whence they pass by its open orifice into the excretory duct; and a continual
new production of secondary cells takes place from the germinal spot or nucleus at the ex-
tremity of the follicle, which is here a permanent structure. In this form of gland, we may
frequently observe the secreting cells existing in various stages of development, within a

* We shall hereafter meet with an instance (§ 829) in which, from the position of the
cells secreting it, Adipose matter is discharged from the body as an Excretion.

52*

618 OF SECRETION.

single follicle ; their size increasing, and the character of their contents becoming more dis-
tinct, in proportion to their distance from the germinal spot (which is at the blind termina-
tion of the follicle), and their consequent proximity to the outlet (Fig. 41). In some varieties
of such glands, however, especially when the follicles are extended into prolonged tubes, the
production of new cells does not take place from a single germinal spot at the extremity of
the follicle, but from a number of points scattered through its entire length.

b. In the second type of Glandular structures, the parent-cell does not remain as a perma-
nent follicle; but, having come to maturity, and formed a connection with the excretory
duct, it discharges its entire contents into the latter, and then shrivels up and disappears, to
be replaced by newly-developed follicles. In each parent-cell of a gland formed upon this
type, we shall find all its secondary or secreting cells at nearly the same grade of develop-
ment ; but the several parent-cells, of which the parenchyma of the gland is composed, are
in very different stages of growth at any one period — some having discharged their contents,
and being in progress of disappearance, whilst others are just arriving at maturity, and con-
necting themselves with the excretory duct ; others exhibiting an earlier degree of develop-
ment in the secondary cells ; others presenting the latter in their incipient condition ; whilst
others are themselves just starting into existence, and as yet exhibit no traces of the second
generation, which they are destined subsequently to develope.

c. The former of these seems to be the usual type of the ordinary glands ; the latter is
chiefly, if not entirely, to be met with among the Spermatic Glands.*

824. It is important to bear in mind, that an essential difference exists be-
tween the vital power concerned in the true Secreting process, and the phy-
sical property which occasions fluid Exhalation or Transudation. This dif-
ference is precisely the same as that which exists between the vital act of
Selective Absorption, and the physical operation of Endosmose or Imbibition.
By Imbibition and Transudation, certain fluids may pass through organic
membranes, in the dead as well as in the living body ; and this passage de-
pends merely upon the physical condition of the part, in regard to the amount
and the nature of the fluid it contains, and the permeability of its tissues.
Not only does water thus transude, but various substances that are held in
complete solution in it, especially albumen and saline matter: it is in this
manner that the Blood absorbs fluids from the digestive cavity (§ 675), and
pours out the serous fluid which occupies the interspaces of the areolar tissue
and the serous cavities. The transudation of the watery portion of the blood
is much increased by any impediment to its flow through the vessels, as in
Congestion and Inflammation; and also by any causes that produce a dimi-
nished resistance in their walls. — We shall hereafter see, in examining the
Physiology of the Urinary secretion, a very striking example of the contrast
between physical Transudation and vital Secretion (§ 840).

2. — The Liver. — Secretion of Bile.

825. The Liver is probably more universally found, throughout the Ani-
mal scale, than any other gland. Its form varies so greatly, however, in dif-
ferent tribes, that, without a knowledge of its essential structure, we should be
disposed to question whether any identity of character exists amongst the
several organs which we include under this designation.

a. In the higher polypes, for example, we find it to consist of a number of distinct folli-
cles, lodged within the walls of the stomach, and pouring their secretion into its cavity by
as many separate orifices; and it is more by the peculiar character of their secretion, than
by any other distinction, that these follicles are recognized us Hepatic. — In the lower Articu-
lata, a very similar conformation is met with ; but in the higher classes of this series, such
as Insects, the follicles are prolonged into tubes of considerable extent. It is very curious
to observe, in animals of such complex structure, that a few long tubes, closed at one end,
and opening at the other into the alimentary canal, are all which they have to represent a
Liver ; but the wonder is readily accounted for by keeping in view the extremely active

See Goodsir's Anatomical and Pathological Researches, Chap. v.

THE LIVER SECRETION OF BILE.

619

Respiration of these beings, which renders unnecessary any other complex apparatus for ela-
borating carbon from the system.

b. On the other hand, among the Mollusca, the Liver attains a much greater development.
Instead of the follicles being prolonged into tubes (which is the usual form of the glandular
system in Insects), they are very much increased in number, and arranged on the sides of
canals or efferent ducts, which either separately pour their fluid into the intestine, or partially
unite with each other before doing-so. The Liver thus acquires a lobulated character, each
lobe consisting of a duct with its branching follicles; and the whole organ forms a consider-
able proportion of the mass of the viscera, and is evidently of great importance in the
economy of the animal. — It is interesting to compare this complex structure with the very
simple condition presented by the Liver in insects ; and, when we keep in view the relative
amount of Respiration in the two groups of animals, we are at once struck with the fact,
that the development of the Liver bears an inverse proportion to the opportunity afforded
by the Respiratory organs for the aeration of the blood ; it being peculiarly extended, when
these, either from their small size, or from their employment in an aquatic medium, cannot
perform their function with great activity. This conclusion is confirmed in an interesting
manner by the fact, that the Crustacea, which have the general organization of Insects, but
which inhabit the water and breathe by gills instead of by a complex system of air-tubes,

Fig. 223.

Fig. 224.

VAJ

Lobule of Liver of Squilla Mantis ; exterior.

Lobule of Liver of Squilla Mantis cut open.

possess a Liver corresponding in form and in degree of development with that of the
Mollusca.

c. In the Vertebrated Sub-kingdom, we may trace the operation of the same principle ;
but the internal structure of the Liver, in the adult condition at least, is less easily demon-
strated, than it is in the lower classes; owing to its increased complexity of structure, and
the closer union between its different parts. In Fishes and Reptiles, the Liver is of consider-
able size, and seems to perform a very important part in the decarbonization of the blood :
its form is adapted to that of the cavity in which it is lodged, sometimes one lobe only being
developed. In Birds, on the other hand, whose respiration is so much more active, it is much
smaller, but is placed on the median line, in conformity with the general symmetry of their
internal as well as external organs (§ 40). In Mammalia, also, it is comparatively small ;
but, though reduced in proportional size, it is at the same time much more compact and
firm than in the lower Vertebrata.

d. The Liver of Man is much less developed than that of many other Mammalia ; and
presents, as rudimentary indications, certain organs which are elsewhere fully developed.
The whole mass, which we are accustomed to describe as consisting of a right and left lobe,
does in reality form but one (there being no real division between its two portions), which
must be regarded as the Central lobe ; the Lobulus Spigelii is the rudiment of a second or
right lobe, and the Lobulus Caudatus is a Lobule developed from it. In the Carnivora and
Rodentia, which present the most complex form of Liver that we meet with among Mam-
malia, there are five distinct parts ; — a central or principal lobe, corresponding with the
principal part of the liver of Man; a right lateral lobe with a lobular appendage, correspond-
ing to the Lobulus Spigelii and Lobulus Caudatus ; and a similar lobe and lobule on the left
side.

e. The Gall-bladder is an appendage to the Liver, of which we find no traces in the
Invertebrata. It may be regarded as simply a dilatation of the efferent duct, more or less
prolonged from it, adapted to store up the hepatic-secretion against the time when it may be
required. In Fishes it frequently, but by no means constantly, presents itself; in Reptiles,
on the other hand, it invariably exists. In Birds it is occasionally absent, even in species

620

OF SECRETION.

[Fig. 225.

23,

kY.

:'\\\\\\»vii9
,\ AMfBil,

13

4- 32

The inferior or concave surface of the Liver, showing its subdivisions into lobes ; 1, centre of the right
lobe ; 2, centre of the left lobe ; 3, its anterior, inferior or thin margin ; 4, its posterior, thick or diaphragm-
atic portion ; 5, the right extremity ; 6, the left extremity ; 7, the notch in the anterior margin ; 8, the
umbilical or longitudinal fissure ; 9, the round ligament or remains of the umbilical vein ; 10, the portion
of the suspensory ligament in connection with the round ligament; 11, pons hepatis, or band of liver
across the umbilical fissure; 12, posterior end of longitudinal fissure ; 13, 14, attachment of the obliterated
ductus venosus to the ascending vena cava; 15, transverse fissure ; 16, section of the hepatic duct; 17,
hepatic artery; 18, its branches; 19, venaportarum ; 20, its sinus, or division into right and left branches;
21, fibrous remains of the duclus venosus; 22, gall-bladder : 23, its neck; 24, lobulus quartus; 25, lobulus
spigelii; 26, lobulus caudatus ; 27, inferior vena cava ; 28, curvature of liver to fit the ascending colon;
29, depression to fit the right kidney ; 30, upper portion of its right concave surface over the renal cap-
sule ; 31, portion of liver uncovered by the peritoneum; 32, inferior edge of the coronary ligament in the
liver; 33, depression made by the vertebral column.]

closely allied to others that possess it. and without any marked difference in the food, habits,
&c. of the two. In Mammalia, again, it is frequently absent, especially among herbivorous
animals; sometimes, on the other hand, two are present, a second or accessory gall-bladder

being formed upon the Ductus com-

FFig 226 munis choledochus, which else-

2 where not unfrequently presents a

dilatation in the same situation. In
the first Giraffe dissected by Mr.
Owen, no gall-bladder was found ;
in the second there were two.

/. In the Human species the gall-
bladder is rarely absent, except in
cases of malformation depending
upon general arrest of development,
in which several organs are in-
volved. The Excretory Ducts of
the Liver and Gall-bladder have
three coats, — an internal or mucous,
a middle or fibrous, and an external
or arcolar. The internal coat is con-
tinuous with the Mucous membrane
of the intestinal tube, into which it
opens; and the whole glandular
structure may indeed be considered
as a complex prolongation of this,
copiously supplied with blood-ves-
sels, and packed into the smallest
possible compass. The middle or
Shows the three coats of the Gall-Bladder separated from fibrous coat bears a considerable
each other ; 1, the external or peritoneal coat; 2, the cellular resemblance in aspect to that of the
coat with its vessels injected; 3, the mucous coat covered Arteries; in its properties, however,
with wrinkles; 4, 4, valves formed by this coat in the neck of it is still more nearly allied to true
the gall-bladder; 5,5, orifices of the mucous follicles at this muscle, being capable of exhibiting
point.] contraction on the application of

THE LIVER SECRETION OF BILE.

621

stimuli to the Sympathetic nerves FFiK. 227.

supplying it ; and in some instances

of obstruction, it has presented an

appearance very closely resembling

that of the muscular coat of the

alimi'ntary canal.* Dr. Davy has

pointed out, that the mucous coat of

the Ductus communis is disposed in

valve-like folds; in such a manner,

as to prevent the reflux of the bile,

or of the contents of the intestine.

826. The Liver may be re-
garded as essentially Consist- A vieW °f the Ga"-Bladder distended with air, and with its
c r ii • vessels injected; 1, cystic artery ; 2, the branches of it which

ing of a mass of cells, in con- supply the peritoneal coat of the liver . 3? the branch of the

nection With the ramifications hepalic artery which goes to the gall-bladder; 4, the lymphatics

of the Hepatic Duct : and these Of the gall-bladder.]
are in close relation with the

ramifications of the Portal Vein and Hepatic Artery, that serve to con-
vey blood to the minutest parts of this organ ; and with those of the
Hepatic Vein, which return it to the heart, after it has been subservient to
the Nutrition of the structure and to the elaboration of the Secretion. Be-
sides these, the Liver contains Lymphatics and Nerves ; the latter are chiefly
derived from the Sympathetic system, and are distributed on the walls of the
vessels and ducts. These various portions of the structure are connected
together by a fibrous tissue, to which the name of Glisson's Capsule has been
given. For our present knowledge of their ultimate arrangement, we are
almost entirely indebted to Mr. Kiernan,t whose account of them will be here
followed, — his researches having been confirmed, in all essential particulars,
by other Anatomists.

a. When a Liver is closely examined with the naked eye, it is seen to be made up of a
great number of small granular bodies, about the size of a millet seed, of an irregular form,
and presenting a number of rounded projecting

processes upon their surfaces. These are com-
monly termed lobules, although by some Anatomists
they are spoken of as acini. When divided longi-
tudinally, they have a somewhat foliated appear-
ance (Fig. 229), arising from the distribution of
the Hepatic Vein ; which, passing into the centre
of each division, is termed the in/ra-lobular vein.
The exterior of each Lobule is covered by a pro-
cess of the capsule of Glisson ; which is very dense
in the Pig and other animals ; but which is so thin
as to be almost undistiiiguishable in the Human
liver. Its substance is composed of the minute
ramifications of the before-mentioned vessels, arranged in the manner presently to be de-
scribed; the spaces between which are filled up with a parenchyma, composed of nucleated
cells, like those shown in Fig. 232. The structure of each lobule, then, gives us the essential
characters of the whole gland.

b. The Lobules, when transversely divided, are usually found to present somewhat of a
pentagonal or a hexagonal shape ; the angles being generally somewhat rounded, so as to
form a series of passages, or inter-\6bu\a.r spaces : in these lie the branches of the Vena Portae,
and of the Hepatic Artery and Duct, from which are derived the plexuses that compose the
lobules. Each Lobule, when examined with the microscope, is found to be apparently com-
posed of numerous minute bodies of yellowish colour, and of various forms, connected to-
gether by vessels ,• to these the name of acini was given by Malpighi; and to these, if they
deserve a name, it ought to be restricted. They will be presently shown, however, to be
nothing else than the irregular islets, left between the meshes of the plexus formed by the
ultimate ramifications of the Portal Vein. The Vena Portse, it will be recollected, is formed

[Fig. 228.

1, Nucleated cells composing the parenchy-
ma of the gland; 2, lobules of human liver
with ramifications of the hepatic vein.]

In the Horse and Dog this coat is clearly muscular.
Philosophical Transactions, 1833.

622

OF SECRETION.

by the convergence of the veins, which return the blood from the chylopoietic viscera ; and
there is reason to believe that it also receives the blood, which is conveyed to the Liver for

Fig. 229.

Connection of the lobules of the liver with
the hepatic vein; 1, a trunk of the vein; 2, 2,
lobules depending from its branches, like
leaves on a tree; the centre of each being
occupied by a venous twig,— the Intra-lobu-
lar Vein.

Horizontal section of three superficial lobule?,
showing the two principal systems of Blood-Ves-
sels ; 1, 1, in«ra-lobular veins, proceeding from the
Hepatic veins; 2, 2, inter-lobular plexus, formed
by branches of the Portal veins.

Fig. 231.

the purposes of Nutrition, by the Hepatic Artery. As it is an afferent, not an efferent ves-
sel, it has a strong claim to the character of an Artery; even although it conveys Venous
blood. Like an artery, it gradually subdivides into smaller and yet smaller branches; and
at last forms a plexus of vessels, which lie in the inter-lobular spaces, and spread with the
freest inosculation, throughout the entire Liver. To these vessels, the name of infcr-lobular
Veins is given by Mr. Kieruan. They ramify in the capsules of the lobules, covering with
their ramifications the whole external surface of these ; and then enter their substance.
When they enter the Lobules, they are termed lobular veins ; and the plexus formed by their
convergence, from the circumference of each lobule towards its centre (where their ultimate
ramifications terminate in those of the intra-lobular or hepatic vein), is designated as the
Lobular Venous plexus. In the islets of this plexus (the acini of Malpighi) the ramifications
of the hepatic duct are distributed in the manner next to be described.

c. The Hepatic duct forms, by its subdivision and ramification, an Interlobular plexus of a
very similar character; but the anastomosis between the branches going to the different lobules

is less intimate than that of the inter-
lobular veins, and cannot be directly
demonstrated ; although Mr. Kiernan
thinks that his experiments leave but
little doubt of its existence, — a com-
munication (which cannot be seen to be
established by any nearer channel) be-
ing proved to exist between the right
and left primary subdivisions of the
duct. The Intorlobular Ducts ramify
upon the capsular surface of the lobules,
with the branches of the Portal Vein
and Hepatic Artery ; they then enter its
substance, and subdivide into minute
branches, which anastomose with each
other, and form a reticulated plexus,
Horizontal section of two superficial Lobules, show- termed by Mr. K., the Lobular Biliary
ing the interlobular plexus of biliary ducts; 1, 1, intra- plexus. This plexus constitutes the prin-
lobular veins ; 2, 2, trunks of biliary ducts, proceeding cijml part of the substance of the lobule ;
from the plexus which traverses the lobules ; 3, inter- and when seen through the meshes of
lobular tissue ; 4, parenchyma of the lobules. the Portal plexus, gives rise to the ap-

THE LIVER SECRETION OF BILE. 623

pearance of ccecal terminations of ducts. The ultimate terminations of these ducts have
not, however, been traced in the adult Liver of any of the higher animals, although they are
sufficiently evident in the embryonic condition. From the analogy of other organs, there
would seem good reason to believe, that the ultimate ramifications of the hepatic ducts
anastomose freely together, and that they form a network, in which their terminations are
lost, as it were, without forming true cceca. This view of the matter finds confirmation in
the curious fact pointed out by Mr. Kiernan, that, in the left lateral ligament, the essential
parts of a lobe are found in the simplest form and arrangement. From the edge of the liver
next to the ligament, numerous Ducts emerge, which ramify between the two layers of peri-
toneum of which the ligament is composed. They are accompanied by branches of the Portal
and Hepatic Veins, and of the Hepatic Artery; which also ramify in this ligament, especially
around the parietes of the ducts. These Ducts, of which some are occasionally of considera-
ble size, divide, subdivide, and anastomose with each other; and the meshes formed by the
network of larger or excreting Ducts, are occupied by minute plexuses of their ultimate
ramifications or secreting Ducts.

d. The Hepatic Artery sends branches to every part of the Liver, supplying the walls of
the Portal and Hepatic Veins, and of the Hepatic Ducts, as well as Glisson's capsule. The
principal distribution of its branches, however, is to the Lobules, which they reach, in the
same manner with the Portal vessels and Biliary Ducts, by spreading themselves through the
interlobular spaces. There they ramify upon the interlobular ducts, and upon the capsular
surface of the lobules, which they then penetrate; their minuteness prevents their distribu-
tion within the lobules from being clearly demonstrable ; but, as they enter along with the
biliary ducts, there can be little doubt that, here as elsewhere, they are principally distributed
upon the walls of these. As to the ultimate termination of the capillaries of the Hepatic
Artery, — whether they enter the Portal plexus, or the Hepatic Vein, — there is a difference
of opinion amongst anatomists ; the former view being upheld by Kiernan, the latter by
Miiller. The question is a very interesting one in a physiological point of view; since, if
the former account be the true one, the Blood which is brought to the Liver by the Hepatic
Artery becomes subservient to the secretion of Bile, only by passing into the Portal plexus;
whilst, if the latter be the correct statement, either the arterial Blood is not at all subservient
to the formation of Bile, or the secretion can be elaborated from the arterial capillaries. The
experiments of Mr. Kiernan have satisfactorily proved, that the Intralobular or Hepatic Veins
cannot be filled by injection from the Hepatic Artery, though they maybe readily filled from
the Portal plexus; whilst, on the other hand, there is reason to believe, that a very fine in-
jection into the Hepatic arteries, will find its way into the Portal plexus.* It is certain that
all the branches of the Hepatic artery, of which the termination can be ascertained, end in
the Vena Portse; a free capillary communication existing between their two systems of
branches, on the walls of the larger blood-vessels and ducts. According to Miiller, there is
an ultimate plexus of capillary vessels, with which all the three systems freely communicate ;
but for this idea there is no adequate foundation; and it is inconsistent with the fact just stated,
that injection into the Hepatic Artery does not return by the Hepatic vein. And the views
of Mr. Kiernan have lately received important confirmation from the researches of Mr.
Bowman on the circulation in the Kidney (§ 841).

e. It now only remains to describe the Hepatic Veins, the branches of which occupy the
interior of the Lobules, and are termed intra-lobular veins (1, 1, Figs. 230 and 231). On
making a transverse section of a lobule, it is seen that the central vessel is formed by the
convergence of from four to six or eight minute venules, which arise from, the processes
upon the surface of the lobule. In the superficial lobules, (by which term are designated
those lobules which lie upon the exterior of the glandular substance, not only upon the sur-
face of the Liver, but also against the walls of the larger vessels, ducts, &c.,) the Intralobular
Veins commence directly from their surface; and the minute veriules of which each is com-
posed may be seen in an ordinary injection, converging from the circumference towards
the centre, as in the transverse section of other lobules. The Intralobular Veins terminate in
the larger trunks, which pass along tne bases of the lobules, collecting from them their
venous blood; these are called by Mr. Kiernan sublobular veins. The main trunk of the
Hepatic Vein terminates in the ascending Vena Cava.

/. In regard to the mode in which the nucleated Cells, that are the real agents in the
Secreting process, are arranged in the Liver of Man and the higher animals, there is much
uncertainty; owing especially to our want of acquaintance with the mode in which
the Hepatic Ducts terminate. They would seem to form the greatest part of the Paren-
chyma, which fills up the interstices between the reticulations of the Blood-vessels
and Ducts ; but it is obvious, from their functional operation, that they must have a more

This is stated to have been the case in the injections of Lieberkiihn, although Mr. Kier-
nan has not succeeded in effecting it.

624

OF SECRETION.

Fig. 232.

Glandular cells of
Liver; a, nucleus ; b,
nucleolus (?); c, adi-
pose particles.

Fig. 233.

close relation to the latter than to the former. Their diameter
is usually from l-l500th to l-2000th of an inch; and they are conse-
quently easily recognized, whenever a portion of the substance of
the Liver is torn up and examined with the higher powers of the
Microscope. Their shape is usually spheroidal. They have a distinct
biliary tinge ; and contain a granular amorphous matter, with a few
small adipose globules.

g. In regard to the Embryonic Development of the Human Liver,
a considerable part of our information must necessarily be derived
from the study of that of other animals ; and this not so much from
Mammalia, as from Birds ; since the development of this organ com-
mences so early in the former, its phases are so rapidly hurried
through, and its evolution is so soon completed, that the process cannot
be continuously watched. — In the Chick, the rudiments of the Liver are found at the commence-
ment of the third day of incubation, in the
form of two crecal pouches, which are pro-
longed from the Intestinal tube ; these carry
before them a fold of the vascular layer, from
which the blood-vessels subsequently origin-
ate ; and they soon begin to ramify in this,
sending oft" branches, of which the coecal ex-
tremities are still evident. At the end of the
fourth day, the tubuli and their ramifications
have attained a considerable size ; arid they
approach each other and coalesce at the base,
entering the intestine by an orifice common
to the two. In this process, it is easy to re-
cognize the analogy to the succession of
forms, which we encounter in ascending the
animal scale. The size and density of the
organ are gradually increased; but it is not
until several days afterwards, that the gall-
bladder is developed. — In the Human Em-
bryo, the formation of the Liver begins at

Origin of the Liver from the intestinal wall, in
the embryo of the Fowl, on the fourth day of incu-
bation ;- a, heart ; 6, intestines ; c, everted portion
giving origin to the liver; d, livery e, portion of
yolk-bag.

about the third week of intra-uterine existence ; the organ is from the first of very large
size, when compared with that of the body; and between the third and the fifth week, it is
one-half the weight of the entire embryo. It is at that period divided into several lobes.
By the third lunar month, the liver extends nearly to the pelvis, and almost fills the abdo-
men ; the right side now begins to gain upon the left ; the gall-bladder begins to appear at
this time. The subsequent changes chiefly consist in the consolidation of the viscus, and the
diminution of its proportional size. Up to the period of birth, however, the bulk of the
Liver, relatively to that of the entire body, is much greater than in the adult; the proportion
being as 1 to 18 or 20 in the new-born child, whilst it is about 1 to 36 in the adult: and
the difference between the right and left sides is still inconsiderable. During the first year of
extra-uterine life, however, a great change takes place; the right lobe increases a little or re-
mains stationary, whilst the left lobe undergoes an absolute diminution, being reduced nearly
one-half; and as, during the same period, the bulk of the rest of the body has been rapidly
increasing, the proportion is much more reduced during that period, than in any subsequent
one of the same length. According to Meckel, the liver of the newly-torn infant weighs
one-fourth heavier than that of a child of eight or ten months old ; and as the weight of the
whole body is more than doubled, during the same time, it is obvious that the change in the
proportion of the two must be principally effected at this epoch.

827. The knowledge of the distribution of the Biliary ducts, and of the two
chief systems of Blood-vessels, in the Lobules of the Liver, has enabled Mr.
Kiernan to give a most satisfactory explanation of appearances, by which
Pathological anatomists had been previously much perplexed. When the
Liver is in a state of Anaemia (which rarely happens as a natural condition,
although it may be induced by bleeding an animal to death), the whole sub-
stance of the lobules is pale, as represented in Fig. 234. In general, how-
ever, the Liver is more or less congested at the moment of death; and this
congestion may manifest itself in several ways. The whole substance may
be congested; in which case the lobules present a nearly uniform dark colour
throughout their substance, their centres being usually more deeply-coloured

SECRETION OF BILE.

625

Fig. 234.

Fig. 235.

"•",3

1, angular lobules in a state of Anosmia, as
they appear on the external surface of the liver ;
2, interlobular spaces ; 3, interlobular fissures ;
4, interlobular veins, occupying the centres of
the lobules; 5, smaller veins, terminating in the
central veins.

1, rounded lobules in first stage of Hepatic Ve-
nous congestion, as they appear on the surface
of the liver; 2, interlobular spaces and fissures.

than the margins. An appearance more frequently offered after death, how-
ever, is that represented at Fig. 235, and termed by Mr. Kiernan the first stage
of Hepatic Venous congestion. In this, the isolated centres of the Lobules alone
present the colour of sanguineous congestion; and the surrounding substance
varies from a yellowish-white, yellow, or greenish colour, according to the
quantity and quality of the Bile which it contains'. This accumulation of the
blood in the Hepatic Veins, and the emptiness of the Portal plexus, seem due
to the continuance of capillary action after the general circulation has ceased;
— a circumstance to which we find an exact parallel, in the emptiness of the
systemic arteries, and the fulness of the veins, after most kinds of death. In
the second stage of Hepatic Venous congestion, the accumulation of blood is
found not only in the Intralobular Veins, but even in parts of the Portal or
Lobular Venous plexus. The parts which are freest from it are those sur-

Fis?. 236.

A, lobules in the second stage of Hepatic Venous
•congestion ; B, and c, interlobular spaces ; i>, con-
gested intralobular veins; E, congested patches,
extending to the circumference of the lobules ;
F, non-congested portions of lobules.

53

A, lobules as they appear on the surface in a
state of Portal Venous congestion ; B, interlo -
bular spaces and fissures ; c, intralobular hepatic
veins, containing no blood j D, the central por-
tions in a state of anaemia; E, the marginal por-
tions in a congested state.

626 OF SECRETION.

rounding the interlobular spaces ; so that the non-congested substance here
appears in the form of circular or irregular patches, in the midst of which the
spaces and fissures are seen (Fig. 236).* Although the Portal as well as the
Hepatic venous system is thus involved in this form of congestion, yet, as
the obstruction evidently originates in the latter, the term given by Mr. Kier-
nan is still applicable ; and it is important to distinguish this appearance from
that next to be described. The second stage of Hepatic venous congestion very
commonly attends disease of the heart, and other disorders in which there is
an impediment to the venous circulation; and in combination with accumu-
lation in the biliary ducts, it gives rise to those various appearances, which
are known under the name of dram-drinkers' or nutmeg liver. The other
form of partial congestion arises from an accumulation of blood in the Portal
veins, with a reverse condition of the Hepatic or intralobular veins ; in this
condition, which Mr. K. designates as portal venous congestion, the marginal
portions of the lobules are of deeper colour than usual, and form a continuous
network, the isolated spaces between which are occupied by the non-congested
portions (Fig. 237). This is a very rare occurrence ; having been seen by Mr.
K. in children only. — These differences fully explain the diversity of the state-
ments of different anatomists, as to the relative position of the so-called red
and yellow substances ; for it now appears, that the red substance is the con-
gested portion of the lobules, which may be either interior or exterior, or
irregularly disposed ; whilst the yelloiu is the non-congested part, in which
the Biliary plexus shows itself more or less distinctly.

828. Another very interesting form of Pathological change in the aspect of
the Liver, which the knowledge of the structure of the Lobules enables us to
comprehend, is that to which the name of Cirrhosis has been given. This
has been erroneously attributed to the presence of a new deposit, analogous to
that of Tubercular matter ; but it is really due to Atrophy and partial Con-
gestion in the Liver itself. It is described by Laennec as usually presenting
itself in small masses, varying in size from a cherry-stone to a millet-seed,
and scattered through the substance of the Liver. When these are minute,
and closely set, they impart what appears at first to be a uniform brownish-
yellow tint to the divided surface of the Liver; but when the tissue is more
attentively examined, their separation becomes evident. These small masses
are not distinct lobules in a variable state of hypertrophy (as supposed by
Cruveilhier) ; but small uncongested patches, composed of parts of several
adjoining lobules, and having one or more interlobular spaces for a centre ;
and the biliary plexuses of these, being filled with bile, give them their yellow
colour. On the other hand, there is an atrophy, more or less complete, of
the portions of the substance of the liver intervening between them ; so that
the bulk of the whole organ is much diminished, very commonly to one-half,
and sometimes to one-third, of its original size.

829. The application of the Microscope to the Hepatic Cells, in various states
of disease, has afforded many facts of great interest. The fatly fiver, which
is often found in the bodies of persons who have died from diseases obstructing
the pulmonary circulation, has been shown by Mr. Bowmant to depend
upon the presence of a large quantity of fatty matter in the interior of the
cells ; which frequently appear as if gorged with it. This would seem to
be occasioned by the want of elimination of the fatty matter through the
respiratory process ; and the consequent accumulation of it in the Blood, by

* This very common aspect of the Liver, which presents numerous modifications, has been
a source of givat |>rr|>lr\iiy in those who have studied the minute anatomy of this organ, and
has even led Anatomists of the highest eminence into serious errors. See Cyclop, of Anat.
and Physiol., vol. iii. pp. 185, ISO.

I Medical Gazette, January 1S42.

SECRETION OF BILE. 627

which the burden of separating it is thrown upon the Liver. — Dr. Williams*
mentions, that, in a case of obstruction of the ductus
choledochus by malignant disease, — which occasioned com- Fig. 238.
plete interruption to the passage of bile, and consequent
jaundice, — scarcely an entire nucleated cell could be dis-
covered by attentive examination of a large part of the organ.
Nothing more than minute free particles of fat, and free float-

^o-1 -"' ' •*'' '''-n

ing amorphous granular matter, could be detected. He further
states that, in a case of fever, the hepatic cells were found to Hepatic Ceils
be almost entirely destitute of fatty particles; and that in gorged with Fat:
what is known as "granular liver," the granules (which have ciens-°6 'adipose
much the appearance of tubercles) consist of cells, which globules.'
strongly resemble the ordinary cells of the parenchyma of the
Liver in every respect, except that they are almost or completely destitute of
yellow contents. Similar observations have been also recorded by Dr. G.
Budd. — In two cases of jaundice examined by Mr. Gulliver, the hepatic cells
were gorged with biliary matter; some of them to such an extent, that they
had become nearly opaque. Perhaps if this condition had continued, these
cells would have been all ruptured, and the state of the organ would have
resembled that described by Dr. Williams.

830. Previously to birth, the Liver is the only decarbonizing organ in the
system, the Lungs being at that time inert; but as soon as the latter come
into play, they separate from the Venous blood a large proportion of the car-
bon with which it is charged, and less blood is transmitted to the Liver for
this purpose. The diminution in the quantity of the Blood circulating through
this organ, is extremely rapid; and it is usually very evident within a short
time after birth, in the comparative paleness of the substance of the gland. It
has been proposed to give this fact a practical bearing, in those judicial in-
quiries which are directed to the determination of the question, whether or
not an Infant has respired after birth ; it having been conceived, that the
diversion of the current of the Blood from the Liver to the Lungs, consequent
upon the first inspiration, would be sufficient to make a certain difference in
their relative weights, if that inspiration had taken place. More careful and
extended observatipns, however, have satisfactorily proved that, although an
increase in the weight of the Lungs, and a diminution of that of the Liver, are
generally found to exist after respiration has been fully established, they are
not by any means constantly produced when the inspirations have been feeble,
as they frequently are for some hours or days after birth ; whilst, on the other
hand, it is not uncommon to meet, in infants that have not breathed, with Lungs
as heavy, and Livers as light, as in the average of those which have respired.t

831. We have now to consider the conditions, under which the secretion
of Bile takes place ; and one of the most important of these, is the character
of the Blood with which the organ is supplied. We have seen that there is
anatomical reason for the belief, that the blood supplied by the Hepatic Artery
is not directly concerned in the Secretion ; but that it first serves for the
Nutrition of the organ, and then, passing into the Portal system (in the same
manner as does the blood of the mesenteric and other arteries), forms part of
the mass of Venous Blood, from which the secreting cells elaborate their pro-
duct. This view is borne out by the results of Experiment, and of Patholo-
gical observation. Thus, if the Vena Portse be tied, the secretion of bile still
continues, though in diminished quantity; and several cases are on record, in
which, through a malformation, the Vena Portae terminated in the Vena Cava

* Guy's Hospital Reports, 1843.

t See Dr. Guy, in Edinb. Med. and Surg. Journal, vols. Ivi. and Ivii.

628 OF SECRETION.

without ramifying through the liver, and in which secretion of Bile took
place, — evidently from the blood of the Hepatic Artery, which had become
venous by circulating through the substance of the Liver ; and this blood
appears* to have passed into the ramifications of the Umbilical Vein, which
formed a plexus in the lobules, exactly resembling the ordinary portal plexus.
It must be remembered, however, that in all 'these instances, the arterial
Blood will become abnormally charged with the elements of Bile ; since the
blood of the chylopoietic viscera, from which it ought to have been separated,
returns to the heart without undergoing any such purification : and the secre-
tion of Bile from the blood supplied by the Hepatic Artery under such circum-
stances cannot, therefore, be considered as proving that the arterial blood is
ordinarily concerned in the secretion to the same degree.

832. That the proximate elements of the Bile accumulate in the Blood,
when from any cause the secretion is suspended, is a fact now well ascer-
tained; and this satisfactorily accounts for the disturbance of the other func-
tions, especially those of the Nervous system, which then ensues. When
the suppression is complete, the patient suddenly becomes jaundiced, the
powers of that system are speedily lowered (almost as by a narcotic poison),
and death rapidly supervenes.t When the secretion is diminished, but not
suspended, the same symptoms present themselves in a less aggravated form.
It is probable that much of the disorder in the functions of the Brain, which
so constantly accompanies deranged action of the Digestive system, is due to
the less severe operation of the same cause, — the partial retention within the
Blood, of certain constituents of the Bile, which should have been eliminated
from the circulating fluid. In such a condition, we derive great benefit from
the use of mercurial medicines ; which, by stimulating the Liver to increased
action, cause the removal of the morbific agent from the blood. Deficient
secretion of the Liver may be recognized as the cause of this and of other
diseases, by the paleness of the alvine evacuations, the diffused yellowness of
the surface of the body, the yellowish-brown fur upon the tongue, and the
congestion of the portal system ; this last results from the same cause, as that
which stagnates the blood in the Lungs when there is deficient Respiration
(§ 738), and frequently occasions Ascites, and other disorders of the contents
of the abdomen. An abnormal accumulation of the elements of the Bile in
the Blood, is habitual in some persons; and it produces a degree of indisposi-
tion to bodily or mental exertion, which it is difficult to counteract. It may
often be recognized by the accumulation of dark mucus having distinctly the
taste of bile, on the surface of the tongue, especially during the night; this
secretion being apparently eliminated by the mucous membrane of the tongue,
when the function of the liver is not duly performed.

833. Much discussion has taken place among Chemists, in regard to the
proximate principles of the Biliary secretion ; a large number of analyses hav-
ing been made, amongst the results of which there is great want of conformity.
The discrepancies principally arise from this source, — that the secretion is
acted on with great facility by chemical reagents ; so that many of the com-
ponent parts which have been enumerated, are not true educts ; but are pro-
ducts of the operations, to which the fluid has been subjected. The propor-
tion of solid' matter is usually from 0 to 12 per cent.; and nearly the whole of
this consists of substances peculiar to Bile.

a. The following,' are the general results of the analyses made hy Berzelius, of Human
Bile, and of that uf the Ox: —

* This, at least, was found to be the case, in the only instance in which the liver was
examined with sutiiririit care.

f See Dr. Alison in Edinburgh Medical and Surgical Journal, vol. xliv. p 287.

SECRETION OF BILE. 629

MAX. Ox.

Water ....... 90-44 92-84

Biliary matter ...... 8'00 5'00

.Mucus ....... -30 -23

Alkali (in combination with fatty acids) . . '41

Chloride of sodium, and extractive . . . '74 1'50

Phosphates and sulphates of soda and lime . . -11 '43

10OOO 100-00

In the Biliary matter, we are to distinguish at least three distinct substances ; Cholesterine,
Bilic acid, and Colouring matter. — In healthy bile, the proportion of Cholesterine appears to
be very small ; but in many disordered states of the secretion, and especially in disease of
the Gall-bladder, this substance is present in much larger amount; and it usually forms the
principal, if not the sole, ingredient in biliary concretions. It is a white crystallizable fatty
matter, somewhat resembling Spermaceti ; free from taste and odour ; not. soluble in water,
but dissolving freely in alcohol, from which it is deposited on cooling in pearly scales. It
is almost entirely composed of Carbon and Hydrogen ; its constitution being 36 Carbon, 32
Hydrogen, 1 Oxygen. It may be obtained by a chemical process of no great complexity,
from the Serum of the Blood ; and it is not unfrequently deposited as a result of diseased ac-
tion in other parts of the body, especially in the fluids of local Dropsies, as hydrocele, ovarian
dropsy. &c.

b. The principal constituent of Bile is a compound of soda with a peculiar organic body;
which is now generally regarded in the light of a fatty acid, and named Bilic acid. Accord-
ing to Plainer, this bilic acid and the bibilate of soda may be obtained in a pure crystalline
state from fresh bile; a yellowish-brown syrup being left, which seems principally to consist
of colouring matter diffused through the water. No analysis has yet been made of bilic acid
thus purified; that of Dr. Kemp, made upon an impure bilic acid, gives as its ultimate com-
position 48 Carbon, 42 Hydrogen, 13 Oxygen, and 1 Nitrogen. This is the substance described
by different Chemists (doubtless under various modifications, according to the process used
to obtain it), as Choleic acid, Bilin, Picromel, &c. It is very readily altered by reagents, espe-
cially by acids; and a great variety of products may be formed by its decomposition. Some
of these appear to present themselves in the living body, as results of disordered conditions
of the secreting process.

c. The colouring matter of the bile is now termed Biliverdin. That of the Ox contains no
azote; and appears to be identical with the Chlorophyl of plants. That of Man, however,
contains about 7 per cent, of Azote, with 68 parts of Carbon, 7^ of Hydrogen, and 17| of
Oxygen; and it cannot be derived so directly from the food. When exposed to the air, it
becomes of a deep green absorbing oxygen ; and the same change is produced by nitric acid,
— the liquor soon passing, however, to a red hue. This frequently takes place within the
body, in cases of Jaundice ; but more especially in the urine. Though the colouring matter
is usually present but in small quantity during health, it sometimes accumulates in disease,
so as to produce solid masses, which include little else.

834. The amount of the secretion of Bile appears to bear some proportion
to that of the Food digested. That its formation is continually going on to a
certain degree appears unquestionable ; but that its quantity is greatly increased
during the' solution of food in the stomach, appears also to be well established.
In those animals which are most constantly ingesting food, we find no Gall-
bladder : for in them, the Bile may be poured into the Intestine as fast as it is
formed. In those which only take food occasionally, on the other hand, and
which are provided with a Gall-bladder, the Bile, when not required in the
Intestine, flows back into that reservoir. This reflex would appear due to the
valve-like termination of the Ductus Choledochus in the walls of the Intestine;
by which a certain resistance is offered to the entrance of the fluid, unless it
be propelled by some decided force. The flow of Bile into the Intestinal tube,
when its action is needed there, is commonly imputed to the pressure of the
distended Duodenum against the Gall-bladder; it may be doubted, however,
whether the contractile power of the Duct itself does not afford important aid
in the process; and it is easy to understand, from the known influence of the
Sympathetic system of nerves upon it (§ 825, /), that peristaltic movements
may be thus excited at the time when they are needed. — It is an interesting
fact, proving how completely the passage of Bile into the Intestine is depend-

53*

630 OF SECRETION.

ent upon the presence of aliment in the latter, that the Gall-bladder is almost
invariably found turgid in persons who have died of starvation; the secretion
formed at the ordinary slow rate having gradually accumulated, for want of
demand. This fact is important in juridical inquiries.

835. The Bile, as already shown (§ 660), has an important operation to
effect in the Digestive process ; — that of reducing the oily matter of the food
to a state in which it may be taken up by the Absorbent vessels. This it
effects by means of its soapy character ; which, notwithstanding the doubts
of Chemists, seems to be proved by familiar facts. Thus, Ox-Gall is com-
monly employed to remove grease spots ; and the bile of the Sea-Wolf (Jlnar-
rhicas lupus] is ordinarily used as soap by the Icelanders. Moreover, the
small quantity of Cholesterine contained in healthy Bile, is certainly in a state
of complete solution ; the biliary soap having the same action upon it, as
upon the oleaginous constituents of the chyme. — From the recent experiments
of H. Meckel, however, it appears that the Bile may perform another very
important office, — the transformation of sugar into fatty matter. He found
that, when bile was mingled with grape-sugar, and allowed to remain in con-
tact with it for some time, a much larger quantity of fatty matter existed in
the mixture, than could have been present in the bile ; and that the transfor-
mation is much aided by heat. Thus, the amount of fat, contained in an equal
amount of the bile employed, having been ascertained from parallel experi-
ments to be from '48 to '54 grammes, the amount obtained from the mixture
of bile and grape-sugar, after five hours' exposure to the warmth of an incu-
bating machine, was "87 grammes ; and after twenty-four hours' exposure, 1*84
grammes.* It seems probable that this transformation may take place in the
Liver itself; for in animals fed upon grape-sugar, this substance has been de-
tected in the blood of the portal vein, but not in that of the hepatic vein. It
will take effect, not merely upon the Sugar introduced as such in the food,
but also upon the amylaceous substances, which have been converted into
sugar by the action of the Salivary and Pancreatic fluids (§ 670).

836. There can be no doubt, however, that the Bile is partly an excremen-
titious fluid ; a portion of it being destined to be at once carried out of the
system, by the intestinal canal, although another portion is destined to be re-
absorbed, for the purpose (as it would seem) of being ultimately carried off
by the respiratory process. The former part probably includes the whole of
the colouring matter ; the presence of which in the faeces is sufficiently ob-
vious. The latter seems usually to comprise the fatty or soapy portion ; no
distinct indications of which can be generally found in the faeces, unless they
have rapidly passed through the alimentary canal (§ 662). But in particular
states of the system, the faeces may contain a very large quantity of bile ; the
presence of which almost unchanged, may be recognized in the evacuations
in bilious diarrhoea, and in the stools which follow mercurial purgatives.
Hence the Bile may be a completely excrementitious product ; and the idea
of the action of the Liver, as one of the great purifiers of the body from the
results of its decay, is not at all invalidated by the observation, that a large
part of its secretion is ordinarily destined for immediate re-absorption. The
composition of the secretion clearly indicates, that it is especially intended to
eliminate from the blood its superfluous Hydro-Carbon, — whether this have
been absorbed as such from the aliment, or have been taken up by the Blood
as effete matter, during the course of the circulation.

a. If more non-azoti/ed food be taken into the system, than can be got rid of by the
Respiratory process, and if there be not a sulliciently rapid production of Adipose tissue to
admit of its being deposited as Fat, it would accumulate in the Blood, unless separated by

Mr. Pagi-l's Report, in Brit, and For. Med. Rev., July 1S4G, p. 201.

SECRETION OF BILE. 631

the Liver. If too much work be thrown upon this organ, its function becomes disordered,
from its inability to separate from the Blood, all that it should draw off: the injurious sub-
stances accumulate in the Blood, therefore, producing various symptoms that are known un-
der the general term of bilious. This is particularly liable to happen in warm climates, in
consequence of the diminished excretion through the Lungs,— occasioned by the warmth of
the surrounding air, and the small quantity of exercise usually taken. To remove these
symptoms, medicines are required, which shall stimulate the liver to increased action. The
constant use of such, however,*has a very pernicious effect upon the constitution ; and care-
ful attention to the regulation of the diet, — especially the avoidance of a superfluity of oily
or farinaceous matter, — together with the employment of an increased amount of exercise,
will probably answer the same end in a much better manner.

Besides the source of Biliary matter already pointed out in the decompo-
sition of the Fibrinous tissues (§ 819), it seems probable that there is another
very important one in the continual waste of Nervous matter, which more
nearly approaches Bile in composition (§ 249); especially if, as asserted by
Fremy, the peculiar acids of the Brain may be detected in the Liver. In
cases of slow Asphyxia, the amount of the Biliary secretion is much increased;
as might be expected, from what has just been stated of its purpose.

837. It would not seem improbable, that the Liver acts towards the ab-
sorbed matters which enter the blood by the Mesenteric Veins, the same part
which the Lungs perform for those which are introduced through the Lymph-
atic system ; namely, the affording an opportunity for the excretion of super-
fluous or injurious substances contained in the absorbed fluid, before it
enters the general current of the Circulation. There is every reason to be-
lieve, that the conversion of Chyle into Blood is a slow process, requiring the
prolonged influence of the latter fluid upon the former; during this influence
many chemical changes take place, which are almost certain to be attended
with an extrication of Carbon and Hydrogen, these being the ingredients of
which the Chyle contains most when compared with blood ; and for the extrica-
tion of these, the Lungs and Liver afford ready means. Hence we see why the
Lacteal system should terminate in a Venous trunk near the Heart, so that the
fluid discharged by it will proceed at once to the Lungs ; and why the Liver,
wherever it has a distinct circulation, should receive the blood from the walls
of the Intestines. Among the Mollusca, in which the chyle is absorbed by
the mesenteric veins, (there being no separate lacteal system,) these veins, in-
stead of returning to the heart through the liver, terminate in the branchial
vessels ; and the process of depuration is effected by the gills. Their liver
is supplied only by the hepatic artery.

a. This view derives interesting confirmation from the experiments of Cruveilhier, on
the artificial production of purulent deposits by injection of Mercury into the veins. He found
that, when the mercury was introduced into any part of the general venous system, abscesses
in the Lungs were induced ; each inclosing a globule, the irritation occasioned by which
was the cause of the purulent deposit. When the mercury was introduced into one of the
Intestinal veins, on the other hand, similar purulent deposits occurred in the Liver. It is
well known that abscesses in the Lungs and Liver are very common sequelse of wounds of
the head, and of surgical operations, especially those involving bones; and there seems good
reason to believe, that in such cases Pus (or some of its elements, which may act the part of
a. ferment in exciting suppuration elsewhere), is actually carried along with the current of blood
in the Lungs and Liver; and that, like the globules of mercury, not being susceptible of elimi-
nation by these two great emunctories, it acts as a disturbing cause, and occasions disease of
their tissue. The fact that a considerable amount of Copper may be detected in the substance
of the Liver, after the prolonged introduction of its salts into the system, seems to add weight
to this view of its function. It is yet to be ascertained, however, why some substances should
be arrested in this organ, whilst others are allowed to pass.

632

OF SECRETION.

3. — The Kidneys — Secretion of Urine.

838. The Kidneys cannot be regarded as inferior in importance to the
Liver, when considered merely as excreting organs ; but their function only
consists in separating from the blood certain effete substances, which are to
be thrown off from it; and has no direct connection* with any of the nutritive
operations, concerned in the introduction of aliment into the system. Organs
destined to the elaboration of a Urinary secretion may be traced very low
down in the Animal scale. Among many of the Mollusca we find a small
sac, filled with a semi-fluid secretion which has been shown to contain uric
acid, opening into the intestine, near its anal orifice. In Insects, we often
meet with prolonged tubes, resembling the biliary vessels in form, but termi-
nating in a lower part of the intestinal tube ; in some species these are dilated
near their extremity into a receptacle for their secretion, or a urinary bladder.
Throughout the Vertebrated classes, they exist in a still more evident form.
They are uniformly composed of a congeries of prolonged tubes, subdividing
and ramifying more or less ; which spring from the ureter or efferent duct,
and terminate either in blind extremities, or in a plexus formed by their inos-
culation. There are considerable variations in the arrangement of these tubes,
however, in different tribes of animals. In Fishes, the Kidneys very com-
monly extend the whole length of the abdomen ; and they consist of tufts of
uniform-sized tubules, which shoot out transversely at intervals from the long
ureter. These tubes frequently divide* into pairs, but without any great alte-
ration in their diameter. They appear to terminate in crecal extremities, with-
out any inosculation; the number of bifurcations, and the degree of convolu-

[Fig. 239.

[Fig. 240.

17

13

A view of the Right Kidney with its Renal
Capsule ; 1, anterior face of the kidney ; 2, exter-
nal or convex edge ; 3, its internal edge ; 4, hilum
renale ; 5, inferior extremity of the kidney; G, pel-
vis of the ureter ; 7, ureter ; 8, 9, superior and in-
ferior branches of the emulgent artery ; 10, 11, 12,
the three branches of the emulgent vein ; 13, an-
terior face of the renal capsule ; 14, its superior
edge; 15, its external edge; 16, its internal ex-
tremity; 17, the fissure on the anterior face of the
capsule.]

A section of the Kidney, surmounted by the
Supra-Renal Capsule ; 1, the supra-renal cap-
sule ; 2, the vascular portion ; 3, 3, its tubular
portion, consisting- of cones; 4, 4, two of the
calices receiving the apex of their correspond-
ing cones ; 5, 5, 5, the three infundibula ; G, the
pelvis; 7, the ureter.]

THE KIDNEYS SECRETION OF URINE.

[Fig. 241.

633

13 1

Represents the half of a Kidney di-
vided vertically, and with its arteries
injected ; the matter has also passed
into the excretory ducts; 1, 2, branches
of the emulgent artery ; 3, 3, hilum re-
nale ; 4, 4, cortical substance, as essen-
tially formed by the capillary termina-
tions of the vessels of the kidney ; 5,
medullary or tubular portion.]

A view of half a Kidney divided vertically from its con-
vex to its concave edge ; one of its extremities is perfect;
1, 1, the lobes which form the kidney ; 2, 2, the lines of se-
paration of these lobes; 3, the cortical substance; 4, 5. the
pyramids of Malpighi ; 6, the hilum renale split up and
cleared of its vessels ; 7, 7, points to the tubes of Bellini ;
8, one of the papillae ; 9, 10, two other papillte, uncut, but
Jeprivedof the calices that surrounded them; 11, one of the
foveolae in the papilla; 12,12, the vascular circle sur-
rounding the papillce ; 13, circumference of the tubular
portion ; 14, external surface of the kidney ; 15, the por-
tion of its external surface on a line with its fissure.]

tion, vary greatly in different species. The uriniferous tubes are connected
together by a very loose areolar web. — The structure of the gland in Reptiles
appears to be essentially the same ; its form, however, varies considerably
in the different tribes, being greatly prolonged in the Serpents, and abbreviated
in the Tortoises. In the Crocodile, the distinction between the cortical and
medullary portion begins to show itself; the tubes being nearly straight where
they issue from the ureter, and being convoluted near the surface only of the
lobes. The Corpora Malpighiana (§ 839, 6), however, where they exist in this
class, are scattered through the whole substance ; not being confined, as in
higher animals, to the cortical portion. — In Birds, the urinary tubes, forming
the several clusters, are more closely united together; they frequently ramify
to a considerable degree. — In the Mammalia, as in Man, there is an evident
distinction between the straight and the convoluted portions of the system of
tubes ; the former character is seen in the medullary substance ; the latter in
the cortical. In nearly all below the Mammalia, the kidneys present exter-
nally a lobulated aspect ; resulting from the want of union between the differ-
ent bundles of tubes, which arise from separate parts of the ureter. In the
kidney of the Mammalia, however, the ureter dilates into a capacious recep-
tacle, towards which the several bundles of uriniferous tubes converge, so
that they open into it in close proximity with each other; and the lobules
formed by these bundles are so closely brought together, that no appearance
of a division presents itself, until a section of the gland is made. Among
some Mammalia, however, the lower form is still retained ; and it is presented
in the Human species also, at an early period of its foetal development.

839. The following is an account of the structure of the Kidney, according
to the most recent investigations.* •

* See Bowman in Philosophical Transactions, 1842; also Gerlach, in Miiller's Archiv.,
Heft 4, 1845, and in Banking's Abstract, vol. iii. p. 307.

634

OF SECRETION.

a. The distinction between the cortical and medullary parts of the Kidney essentially con-
sists in this, — that the former is by far the most vascular, and the plexus formed by the
tubuli uriniferi seems to come into the closest relation with that of the sanguiferous capil-
laries, so that it is probably the seat of the greater part of the process of secretion ; whilst
the latter is principally composed of tubes, passing in 'a straight line from the former towards
their point of entrance into the ureter. In this respect there is a considerable analogy of
structure and comparative function, between the two parts of the kidney and the two parts
of the brain. The adjoined figure represents the appearances presented by a portion of an

• • Fig. 244.

Portion of the Kidney of a new-born infant; A, natural
size; 1, 1, corpora Malpighiana, as dispersed points in the
cortical substance ; 2, 2, papilla ; B, a smaller part magni-
fied ; 1, 1, corpora Malpighiana ; 2, 2, tubuli uriniferi.

Portion of one of the tubuli uriniferi,
from the kidney of an adult; showing
its tesselated epithelium. Magnified
250 diameters.

injected kidney, as seen by the naked eye, and under a low magnifying power. The tubuli
uriniferi, in passing outwards from the calices, increase in number by divarication, to a con-
siderable extent, as shown in Fig. 246 ; but their diameter remains the same. When they
arrive in the cortical substance, their previously straight direction is departed from, and they
become much convoluted. The closeness of the texture formed by their interlacement with
the blood-vessels, renders it difficult to obtain a clear view of their mode of termination.
They seem to inosculate with each other, forming a plexus, with a free extremity, or more
probably a loop, here and there (Fig. 24G) ; the number of these free extremities, however,
does not appear to be nearly equal to that of the uriniferous tubes themselves.

b. Scattered through the plexus formed by the blood-vessels and uriniferous tubes, a num-
ber of little dark points may be seen with the naked eye, to which the designation of Cor-
pora Malpighiana has been given, after the name of their discoverer. Each one of these,
when examined with a high magnifying power, is found to consist of a mass of minute
blood-vessels (Fig. 246, 7) ; somewhat resembling those convoluted masses of Absorbents,
termed Lymphatic Glands. Each of these is included in an offshoot from one of the tubuli
uriniferi, which swells into a flask-like dilatation to receive it (Fig. 247) ; and every tube
may have several such lateral offshoots. The Epithelium which elsewhere lines the tube
(whose usual character is shown in Fig. 244) is altered in appearance, where the tube is
continuous with this capsular dilatation (Fig. 247, 2') ; being there more transparent, and
furnished with cilia (as shown at 2"), which in the Frog may be seen, for many hours after
death, in very active motion, directing a current down the tube. Further within the capsule,
the Epithelium is excessively delicate; but it may be clearly seen to cover the convoluied
knot of vessels, which constitutes the Malpighian body.* — The Renal Artery, on entering
the Kidney, divides itself into minute twigs, which are the afferent vessels of the Malpighian
tufts (Fig. 248, a/). After it has pierced the capsule, the twig dilates; and suddenly divides
and subdivides itself into several minute branches, terminating in convoluted capillaries,
which are collected in the form of a ball (m. in) ; and from the interior of the ball, the soli-
tary efferent vessel, ef, arises, which passes out of the capsule by the side of the single affe-
rent vessel. This ball seems to lie loose and bare in the capsule, being attached to it only
by its afferent and efferent vessels (Fig. 248, w); but it appears in reality to be enveloped
in a reflexion of the membrane that forms the cnpsule; find from this are probably generated
the epithelium-cells, by which itis covered. The efferent vessels, on leaving the Malpighian
todies, separately enter the plexus of capillaries, p, surrounding the tubuli uriniferi, st, and
supply that plexus with blood: from this plexus the Renal vein arises. — In Mr. Bowman's

* On this point, which is one of difference between Mr. Bowman and Dr. Gerlach, the
Author's own observations lead him unhesitatingly to concur with the latter.

SECRETION OF URINE.

635

:o

A section of one of the Pyramids of Malpighi, and of its corresponding cortical substance, as seen
under the microscope ; 1, portion of the surface of the kidney ; 2, from this figure up to 1, is the cortical
substance of the kidney : 3, from 2 to this number is the tubular portion ; 4, the foveola j 5, 6, arteries
and veins ramifying through the kidney ; 7, arteries to the acina of the kidney ; 8, capillary extremities
of veins anastomosing with corresponding arterioles; 9, tortuous extremities of the arteries directed
into the interior of the gland ; 10, bases of the cones of the cortical and pyramidal substance of the kid-
ney ; from 10 to 4 is a collection of these cones ; 11 , the envelop of the cortical layer ; 12, prolongations
of the tubular portion ; 13, tortuous tubes, or those of Ferrien ; 14, straight tubes, or those of Bellini ; 15,
vessels which wind between them ; 16, course of the uriniferous lubes in the tubular portion ; 17, the
matter between these tubes j 18, bifurcation of the straight tubes ; 19, sections of these tubes ; 20, their
orifices.]

opinion, all the free extremities of the tubuli uriniferi thus include Corpora Malpighiana ;
and the appearance of coecal terminations, such as those represented at a and c, Fig. 246, he
regards as an optical illusion, caused by a change in the direction of the tubuli, which occa-
sions them to dip away suddenly from the observer.

636

OF SECRETION.

Fig. 246.

z-.

A small portion of the Kidney, magnified about 60 times; 1, supposed ccecal extremity "of a tubulu*
uriniferus ; 3, 3, recurrent loops of tubuli ; 5, 5, bifurcations of tubuli ; 4, 5, 6, tubuli converging towards
the papilla ; 7, 7, 7, Corpora Malpighiana, seen to consist of plexuses of blood-vessels, connected with a
capillary net-work ; 8, arterial trunk.

c. The Embryological Development of the Urinary organs in Vertebrated animals is a
subject of peculiar interest; owing to the correspondence which may be traced between the
transitory forms they present in the higher classes, and their permanent condition in the
lower. In this respect there is an evident analogy with the Respiratory system. The first

THE KIDNEYS SECRETION OF URINE.

637

appearance of anything resembling a Urinary apparatus in the Chick, is seen on the second
half of the third day. The form at the time presented by it is that of a long canal, extend-
ing on each side of the Spinal Column, from the region of the heart, towards the Allantois ;
and the sides of this present a series of elevations and depressions, indicative of the com-
mencing development of caeca. On the fourth day, the Corpora Wofffiana, as they then are
termed, are distinctly recognized, as composed of a series of ccecal appendages, which are
attached along the whole course of the first-mentioned canal, opening into its outer side. On
the fifth day these appendages are convoluted ; and the body which they form acquires
increased breadth and thickness. They evidently then possess a secreting function ; and the
fluid which they separate is poured by the long straight canal into the cloaca. Between
their component shut sacs, numbers of small points appear, which consist of little clusters
of convoluted vessels, exactly analogous to the Corpora Malpighiana of the kidney. — The

Fig. 247.

Fig. 248.

Fig. 249.

Uriniferous Tube, Malpighian
Tuft, and Capsule, from Kidney
of Frog: a, cavity of the tube;
fc, epithelium of the tube; &',
ciliated epithelium of the neck
of the capsule; b", detached
epithelium scale ;' c, basement
membrane of tube ; c', basement
membrane of capsule. Magnified
about 320 diam.

Distribution of the Renal ves-
sels ; from Kidney of Horse ; a,
branch of Renal artery ; of,
afferent vessel ; m, m, Malpig-
hian tufts ; ef, ef, efferent ves-
sels ; p, vascular plexus sur-
rounding the tubes ; st, straight
tube ; ct, convoluted tube. Mag-
nified about 30 diam.

Corpora Wolffiana, with kid-
ney and lestes, from embryo of
Bird; 1, kidney; 2, 2, ureters; 3,
corpus Wolffianum ; 4, its ex-
cretory duct; 5, 5, testicles; at
the summit are seen the supra-
renal capsules.

Corpora Wolmana, however, have only a temporary existence in the higher Vertebrata ;
although it seems that, in Fishes, they constitute the permanent kidney.* The development
of the true Kidneys commences in the Chick about the fifth day. They are seen on the
sixth, as lobulated grayish masses, which sprout from the outer edges of the Wolffian bodies ;
and they gradually increase, the temporary organs diminishing in the same proportion. The
sexual organs, as will be hereafter explained (§ 866, 6), also originate in the Wolffian bodies;
and at the end of fetal life, the only vestige of the latter is to be found as a shrunk rudi-
ment situated near the testes of the male. — The progress of development in the Human
embryo seems closely conformable to the foregoing account. The Wolffian bodies begin to
appear towards the end of the first month ; and it is in the course of the seventh week,
that the true Kidneys first present themselves. From the beginning of the third month the
diminution in the sizeof the Wolffian bodies goes onparipassu with the increase of the Kidneys;
and at the time of birth scarcely any traces of them can be found. At the end of the third

54

* See Principles of General and Comparative Physiology, § 659.

638 OF SECRETION.

month, the kidneys consist of seven or eight lobes, the future pyramids; their excretory
ducts still terminate in the same canal, •which receives those of the Wolffian bodies and of
the sexual organs; and this opens, with the rectum, into a sort of cloaca, or sinus urogeni-
talis, analogous to that which is permanent in the oviparous Vertebrata. The Kidneys are
at this time covered by the Supra-Renal Capsules, which are very large ; about the sixth,
month, however, these have decreased, whilst the kidneys have increased, so that their pro-
portional weight is as 1 to 4£. At birth the weight of the Kidneys is about three times
that of the Supra-Renal Capsules; and they bear to the whole body the proportion of 1 to
80; in the adult, however, they are no more than 1 to 240. The Corpora Wolftiana are,
when at their greatest development, the most vascular parts of the body next to the liver;
four or five branches from the aorta are distributed to each, and two veins are returned from
each to the vena cava. The upper veins and their corresponding arteries are converted
into the Renal or einulgent vessels; and the lower into Spermatic vessels. The tabulated
appearance of the kidney gradually disappears ; partly in consequence of the condensation
of the areolar tissue, which connects the different parts; and partly through the develop-
ment of additional tubuli.inthe interstices. The Urinary Bladder is formed quite inde-
pendently of the secreting apparatus, being a part of the allantois, which is first developed
as a large coscum or diverticulum from the lower extremity of the alimentary canal (Chap,
xvii.). The part of the tube below this forms the Cloaca, or common termination of the
intestinal and vesical apparatus. The sides of this cloaca, however, gradually approach
one another, so as to form a transverse partition, which separates the Rectum from the
Genito-urinary canal ; and the urethra of the female is afterwards separated from the Vagina
by a similar process.

840. The researches of Mr. Bowman on the structure of the Malpighian
bodies, and on the vascular apparatus of the Kidney, have thrown great light
upon the mode in which the Urinary secretion is elaborated. One of the
most remarkable circumstances attending this excretion, in the Mammalia
particularly, is the large but variable quantity of water, which is thus got rid
of, — the amount of which bears no constant proportion to that of the solid
matter dissolved in it. The Kidneys, in fact, seem to form a kind of regu-
lating valve, by which the quantity of water in the system is kept to its proper
amount. The Exhalation from the Skin, which is the other principal means
of removing the superfluous liquid from the blood, is liable to great variations,
from the temperature of the air around (§ 870) : hence, if there were not some
other means of adjusting the quantity of fluid in the Blood-vessels, it would
be liable to continual and very injurious variation. This important function
is performed by the Kidneys ; which allow such a quantity of water to pass
into the urinary tubes, as may keep the pressure within the vessels nearly at
a uniform standard. The quantity of water which is passed off by the kid-
neys, therefore, will depend in part upon that exhaled by the Skin; being
greatest when this is least, and vice versa: but the quantity of solid matter to
be conveyed away in the secretion has little to do with this ; being dependent
upon the amount of waste in the system, and upon the quantity of surplus
azotized aliment which has to be discharged through the channel. — The Kid-
ney contains two very distinct provisions for these purposes. The cells lining
the Tubuli Uriniferi are probably here, as elsewhere, the instruments by which
the solid matter of the secretion is elaborated ; whilst it can scarcely be doubted
that the office of the Corpora Malpighiana is to allow the transudation of the
superfluous fluid through the thin-walled and naked capillaries of which they
are composed. " It would, indeed," Mr. Bowman remarks, " be difficult to
conceive a disposition of parts more calculated to favour the escape of water
from the blood, than that of the Malpighian body. A large artery breaks up
in a very direct manner into a number of minute branches; each of which
suddenly opens into an assemblage of vessels of far greater aggregate capacity
than itself, and from which there is but one narrow exit. Hence must arise
a very abrupt retardation in the velocity of the current of blood. The vessels
in which this delay occurs are uncovered by any structure. They lie bare in
a cell, from which there is but one outlet, the orifice of the tube. This orifice

THE KIDNEYS SECRETION OF URINE. 639

is encircled by cilia, in active motion, directing a current towards the tube.
These exquisite organs must not only serve to carry forward the fluid which
is already in the cell, and in which the vascular tuft is bathed; but must tend
to remove pressure from the free surface of the vessels, -and so to encourage
the escape of their more fluid contents."

841. There is a striking analogy between the mode in which the Tubuli
Uriniferi are supplied with Blood, for the purpose of elaborating their secre-
tion, and the plan on which the Hepatic circulation is carried on. The
secretion of the Liver is formed from blood conveyed to it by one large vessel,
the Vena Portse, which has collected it from the Venous capillaries of the
chylopoietic viscera, and which subdivides again to distribute it through the
liver. The secretion of the Kidney, in like manner, is elaborated from blood
which has already passed through one set of capillary vessels, — those of the
Malpighian tufts; this blood is collected and conveyed to the proper secreting
surface, not by one large trunk (which would have been a very inconvenient
arrangement), but by a multitude of small ones, — the efferent vessels of the
Malpighian bodies, which may be regarded as collectively representing the
Vena Portae, since they convey the blood from the systemic to the secreting
capillaries. Hence the Kidney may be said to have a portal system within
itself. — This ingenious view of Mr. Bowman's finds support from the fact,
that in Reptiles (in which, as in Fishes, the Portal trunk receives the blood
from the whole posterior part of the body, and supplies the Kidneys as well
as the Liver), the efferent vessels of the Malpighian bodies — which receive
their blood, as elsewhere, from the Renal Artery — unite with the branches
of the Portal vein, to form the secreting plexus around the Tubuli Uriniferi.
Here, therefore, the blood of the secreting plexus has a double source ; the
vessels which supply it receiving their blood in part from the capillaries of the
organ itself, and in part from those of viscera external to it; just as, in the
Liver, the secreting plexus is supplied in part by the blood conveyed from the
chylopoietic viscera through the Vena Portse, and in part by the nutritive
capillaries of the organ itself, which receive their blood from the Hepatic
Artery.

842. The nature and purposes of the Urinary secretion, and the alterations
which it is liable to undergo in various conditions of the system, are much
better understood than are those of the Bile ; this is owing, in great part, to
the circumstance, that it may be readily collected in a state of purity ; and
that its ingredients are of such a nature, as to be easily and definitely sepa-
rated from each other by simple chemical means. There can be no doubt
that the chief purpose of this excretion, is to remove from the system the effete
azotized matters which the blood takes up in the course of the circulation, or
which may have been produced by changes occurring in itself. This is evi-
dent from the large proportion of Nitrogen which is contained in the solid
matter dissolved in it ; and from the crystalline form presented by this solid
matter when separated, — a form which indicates that its state of combination
is such, as to prevent it from conducing to the nutrition of the system. The
injurious effects of the retention in the Blood, of the components of the Uri-
nary secretion, are fully demonstrated by the results of its cessation ; whether
this be' made to take place experimentally (as by tying the renal artery), or be
the consequence of a disordered condition of the kidney. Symptoms of great
disorder of the nervous centres, analogous to those produced by many narcotic
poisons, soon exhibit themselves ; and the patient dies comatose, if the secre-
tion be not restored. In such cases, Urea (the characteristic ingredient of the
urine) is found to have accumulated in the Blood ; and it may even be detected
by the smell, in the fluid effused into the Ventricles of the Brain. The con-
clusion which may be drawn from this circumstance, regarding the pre-exist-

640

OF SECRETION.

ence of the components of the secretion in the Blood, is strengthened by the
fact that, even in the healthy state, Urea may be detected in the blood ; it only
exists there normally, however, in very small quantity; but, when there is
any impediment to its excretion, it goes on accumulating, and produces conse-
quences more or less serious in proportion to its amount. It is not improba-
ble that, as in the case of the retention of Bile in the Blood (§ 832), many of
the minor as well as of the severer forms of sympathetic disturbance, connected
with disordered secretion from the Kidney, are due to the directly poisonous
operation of the elements of the Urine, upon the several organs whose func-
tion is disturbed ; and that many complaints, in which no such agency has
been until recently suspected, — especially Convulsive affections arising from
a disordered action of the Nervous centres, — are due to the insufficient elimi-
nation of Urea from the Blood.

843. In order to form a correct opinion of the state of the Urinary secretion
in morbid conditions of the system, it is desirable to be acquainted with every
leading particular regarding its healthy characters. — The average Quantity,
during 24 hours, has been variously estimated: it differs, of course, with the
amount of fluid ingested, and it is influenced also by the external temperature,
— a much smaller amount of the superfluous fluid of the body being set free
from the skin in winter than in summer, and a larger proportion being carried
off by the kidneys. Probably we shall be pretty near the truth, in estimating
the amount at from about 30 oz. in summer, to 40 oz. in winter, for a person
who does not drink more than the simple wants of nature require. — The
Specific Gravity comes to be a very important character, in various morbid
conditions of the urine : and it is therefore desirable to estimate it correctly.
This also is, of course, liable to the same causes of variation ; since, when
the same amount of solid matter is dissolved in a larger or smaller quantity of
Avater, the specific gravity will be proportionally lower or higher. The
average, according to Dr. Prout, in a healthy person, taking the whole year
round, is about 1020; the standard rising in summer (on account of the greater
discharge of fluid by perspiration) to 1025 ; and being lowered in winter to
1015. Simon, however, states the average specific gravity at no more than
1012. It will depend, in each individual case, upon the amount of fluid habitu-
ally ingested, as compared with that dissipated by cutaneous exhalation ; and
it will also vary with the period that has elapsed since the last introduction of
liquid into the stomach. From these and other causes, the proportion of solid
matter in 1000 parts of Urine may vary from 20 to 70. The following table
expresses the relative amounts of the different components, in every 100 parts
of this solid matter ; according to the analyses of different Chemists.

Urea .....

Uric Acid .....
Extractive matter, Ammonia-salts, )
and Chloride of sodium jj

Alkaline Sulphates
Alkaline Phosphates
Phosphates of Lime and Magnesia

Berzelius.
. 45-10
1-50

. 36-30

. 10-30

, 6-88

1-50

Lehmann.
49-68
1-61

Simon.

33-80

1-40

28-95 42-60

11-58
5-96
1-97

8-14
6-50

1-59

Marchand.
48-01
1-59

32-49

10-18
4-57
1-S1

We shall presently find the causes of some of these variations in the nature
of the ingesta, and in the amount of exercise taken by the individual. — The
Urine in health usually exhibits an acid reaction; this depends, however,
upon certain conditions furnished by the aliment; and may be altered (as will
presently appear) by a change in the ingesta.

844. The. most important of the above ingredients (constituting from one-
third to one-half of the whole solid matters of the Urine) is evidently that
which, from its being the principal cause of the characteristic properties of the

SECRETION OF URIXE.

641

secretion, is termed Urea. This maybe readily separated from Urine, in the
form of transparent colourless crystals ; which have a faint and peculiar, but
not urinous odour: and, as already mentioned, it is distinctly traceable in the
Blood, where it rapidly accumulates, if its continual elimination be in any way
interfered with. It is very soluble in water, and combines with acids without
neutralizing them. In its chemical composition, it is identical with cyanate
of ammonia ; this composition being 2 Carbon, 4 Hydrogen, 2 Nitrogen, and
2 Oxygen, — a formula much more simple than that of almost any other
organic substance. The amount of Urea excreted in twenty-four hours has
been made the subject of examination by Lecanu;* and the following are his
results, as deduced from a series of 120 analyses : —

Minimum.

Wean.

Maximum.

357-51 grs.
153-25

433-13 grs.
295-15

510-36 grs
437-06

61-08

126-22

295-15

161-78
57-28

207-99
69-55

254-20

81-83

By men .......

By women

By old men (84 to 86 years)

By children of eight years

By children of four years ....

It is very interesting to perceive, in this table, how large an amount of Urea
is excreted by children ; and how small a quantity, in proportion to their bulk,
by old men. This corresponds precisely with the rapidity of interstitial
change at different periods of life. (See § 812.) Moreover, as this continual
disintegration is very much accelerated by increased vital activity of the Tis-
sues, the amount of Urea undergoes a like augmentation ; so that — other cir-
cumstances being equal — the amount of Urea excreted may fairly serve as a
measure of the waste of the tissues, and consequently of the degree in which
they have been exercised. This will be especially the case in regard to the
Muscular Tissue ; which constitutes so large a part of the fabric. In some
experiments recently made on the influence of various causes upon the con-
stitution of Urine, Dr. Lehmann found that, by the substitution of violent for
moderate exercise, the quantity of Urea was raised from 32k to 45^ parts;
and Simon found that, by two hours' violent exercise, the proportion of the
urea in the urine passed half an hour subsequently was double that contained
in the morning urine. If such increased tvaste be not compensated by in-
creased nutrition, a diminution in the bulk of the body is the necessary con-
sequence.

845. The next important ingredient, Uric or Lithic Acid, exists much
more largely in the Urine of the lower Vertebrata, than in that of Mammalia ;
thus the nearly solid urinary excretion of Serpents, and the semi-fluid urine
of Birds, is almost entirely composed of this acid, in combination with Am-
monia. Its presence has not yet been detected in healthy blood; but when
it is imperfectly eliminated, we are assured of its accumulation in the circu-
lating fluid, by its deposition, in combination with Soda, in the neighbourhood
of the joints, — forming Gouty concretions, or Chalk-stones. Pure Lithic acid
crystallizes in fine scales of a brilliant white colour, and silky lustre ; it is
tasteless and inodorous, and is so sparingly soluble in water, that at least
10,000 times its own weight is required to dissolve it. As it exists in a state
of perfect solution in healthy Urine, it must be in combination with some
base; and that this is the case, is at once proved by the fact, that it is precipi-
tated immediately on the addition of a small quantity of any acid, even the
Carbonic. It is generally believed, that the base is Ammonia ; but it has
recently been affirmed by Liebig,t that the Uric acid (with the Hippuric) is
held in solution by the Phosphate of Soda, — which, from being bibasic or
alkaline, is rendered acid, by yielding up a part of its soda to these organic

* Journal de Pharmacie, torn. xxv.

54*

f Lancet, June 8, 1844.

642 OF SECRETION.

acids, which are thereby rendered soluble. It is in this manner that he partly
explains the usually acid reaction of healthy urine ; the other causes of which
will be presently noticed. — If there be an undue proportion of Lithic acid in
the urine, it will be precipitated on cooling ; because it is less soluble in a
cold than in a warm solution of phosphate of soda ; and the same result will
happen, if there be a predominance of other acids in the urine, which will
seize upon its base, as soon as its own affinity for it is diminished by the
lowering of its temperature. By Dr. Prout it is believed that Lactic acid, ex-
isting in the Blood or in the Urine in excess, is an ordinary source of this
deposit; but the presence of this acid is altogether denied by Liebig (§ 846).
— The composition of Lithic Acid is as follows: — 10 Carbon, 4 Hydrogen,
4 Nitrogen, 6 Oxygen. The amount of it usually excreted in the Urine of
Man is but very small; it is occasionally, however, considerably increased;
but the circumstances under which this increase takes place have not yet been
exactly determined.

a. Uric acid is replaced in the Herbivorous animals by the Hippuric ; the composition and
properties of which are very different from those presented by that substance. When pure,
it forms long transparent four-sided prisms; it is soluble in 400 parts of cold water, and dis-
so.lves readily at a boiling heat; and it has a strong acid reaction, and bitterish taste. Its
formula is 18 Carbon, 8 Hydrogen, 1 Nitrogen, and 5 Oxygen, with 1 equiv. of Water. It
has very curious relations with Benzoic acid ; which it yields, together with Benzoate of
Ammonia, when acted upon by a high temperature, or during the putrefaction of the urine
of which it forms a part. According to Liebig, the Hippuric acid in the urine of the Horse
and Ox is replaced by Benzoic acid, when the animal is subjected to hard labour. — It appears
from his recent experiments,* that we are to regard Hippuric acid as a normal element of
Human urine; for he has detected Benzoic acid among the products of its putrefaction; and
as we know that the latter does not exist in the Urine of Man, and as there is no other sub-
stance at the expense of which it can be formed during the putrefactive process, we can
scarcely hesitate to admit that such must be the case. It is a very curious fact, that the intro-
duction of Benzoic acid into the system causes a large increase in the amount of Hippuric
acid in the Urine; and if this be formed at the expense of the elements, which would other-
wise have produced Uric acid, an easy method is pointed out for the elimination of the latter
substance from the blood, when it has accumulated there, — the salts of Hippuric acid being
so much more soluble than those of the Uric. According to Keller,f whose experiments
were made upon himself, both Urea and Uric acid existed in normal quantity in his urine,
though a large quantity of Hippuric acid was being excreted ; whilst Mr. Alexander Ure
states,J that he has succeeded, by the administration of Benzoic acid, in preventing the de-
position of Gouty concretions, and even in removing them when they had been formed.

b. Many remarkable changes are effected in Lithic acid, by the operation of other chemi-
cal agents; and these changes are very important, in their bearing on pathological conditions
of the Urine. When Uric acid is subjected to the action of Oxygen, it is first resolved into
Urea and a compound termed Jllloxan. Now thisAlloxan, when acted on by a new supply
of Oxygen, is resolved into Urea and Oxalic acid; or, with a still further amount of Oxygen,
into Urea and Carbonic acid : — a i'act, which has a very important bearing on the production
of Calculi composed of Uric and Oxalic acids, and which explains the remarkable alterna-
tions which are often observed in the layers of these concretions. It is affirmed by Liebig,
that the calculi which are composed of Urate of Ammonia, or of Oxalate of Lime, occur in
persons, in whom, from want of exercise, or from other causes, the quantity of Oxygen intro-
duced into the system is beneath what it ought to be. When patients suffering under Uric
sirid Calculi take more exercise, the Urates are replaced by Oxalates, in consequence of the
larger amount of Oxygen introduced into the system; and if the oxygenation could be carried
still further, the latter would cease to be deposited, their elements passing off in the form of
Urea and Carbonic acid. These views are borne out by the results of Lehmann's experi-
ments upon himself; for he found that the violent exercise, which raised the proportion of
Urea in the urine by. more than one-third (§ 844) brought down the amount of Uric acid^
from 1-18 to -042, or nearly one-half.

c. Another change is that which gives rise to the peculiar compound termed JlUantoin;
which naturally exists in the fluid of the Allantois of the fotal calf. This may be formed
artificially by boiling Uric acid with peroxide of lead ; from which process there result an

* Loc. cit. f Liebig's Animal Chemistry, p. 327.

J Medico-Chirurgical Transactions, vol. xxiv.

SECRETION OF URINE. 643

Oxalatc of the protoxide of lead, Urea and Allantoin ; the composition of which last substance
is very dillcrent from that of urea or uric acid, being 8 Carbon, 5 Hydrogen, 4 Nitrogen, and
5 Oxygen.

d. By the operation of Nitric Acid upon Uric acid, several new products are generated,
some of which are of much practical interest. To one of these the name of Murexid has
been given, on account of its reddish purple colour (resembling that of the Tyrian dye which
was obtained from a species of Murex) ; this is a crystalline subslance, sparingly soluble in
cold water, but copiously soluble in warm, imparting to it its vivid colour. By Dr. Prout it
was long since described as consisting of a peculiar acid, the Purpuric, in combination with
Ammonia ; this view of its composition is not generally received by German Chemists ; but
it has lately been supported by Fritzche, who has shown the real existence of the acid, by
obtaining Purpurates of other bases. This substance is one source of the colours of the
pink and lateritious sediments which so often present themselves in the Urine ; these hues
partly depend, however, on the influence of nitric acid upon the peculiar Colouring princi-
ples of the urine, the nature of which principles is not yet fully understood.

846. It was supposed until recently, that Lactic acid is a normal constitu-
ent of Human Urine. It appears to have been demonstrated by the experi-
ments of Liebig, however, that this is not the case ; and that another organic
substance, which forms a crystalline compound with zinc, very similar to the
lactate, has been mistaken for it. The composition of this substance, which
usually forms about one part in 200 of Urine, has been recently determined
to be 8 Carbon, 8 Hydrogen, 3 Nitrogen, and 3 Oxygen. It thus differs from
Lactic acid in containing Nitrogen ; as well as in proportion of its other com-
ponents.

847. It has been shown (§ 843). that the Urine contains a considerable
amount of Saline matter; the excretion of which from the system appears to
be one of the principal offices of the Kidney. Various saline compounds,
and the bases of others, are being continually introduced with the food (§ 648) ;
and these, after performing their part in the organism, must be eliminated from
the circulating fluid, in order to prevent injurious accumulation. Of these
we shall now examine the chief sources. — The mode in which the Muriates
find their way into the Urine is easily understood. Of the Common Salt in-
gested, a considerable part is decomposed into Muriatic Acid and Soda ; the
former being found uncombined in the Gastric juice ; and the latter in the Bile.
By the mixture of the Bile with the Chyme, a re-union of these two consti-
tuents takes place ; and Salt is again formed, which is received into the Cir-
culation that it may be eliminated (its part in the economy having been now per-
formed) by the Kidney. — The quantity of the Sulphates present in the Urine,
appears to have no relation with that of the amount of Sulphuric acid ingested ;
for it much surpasses what could be thus accounted for, — being often consi-
derable, when no Sulphate whatever can be detected in the food. But most
of the azotized compounds employed as food have Sulphur in combination
with them ; and there can be no doubt, that this undergoes oxidation within
the system, and thus generates Sulphuric acid, which unites with any free
or weakly-combined bases it may meet with, to form the Sulphates present in
the Urine. — The Phosphates are probably derived in part from the Phos-
phates taken in with the food, and in part from the free Phosphorus, which
its elements contain. Of the latter, great use is made in the production of
Nervous matter (§ 249) ; the continual waste of which must set it free again.
When thus set free, there is obviously no channel for its elimination, save by
its conversion into Phosphoric acid, and its union with an alkaline base.*
That this is really the case, would appear from the fact noticed by Dr. Prout,
and confirmed by many others, — that mental or bodily labour which involves

* This circumstance has been entirely overlooked by Liebig, in his late discussion (foe.
a/.) of the Constitution of the Urine ; the Phosphates being regarded by him as having their
sole origin in the Phosphates of the ingesta.

644 OF SECRETION.

much waste of the Nervous System, is followed by an increase in the quan-
tity of the alkaline Phosphates in the Urine (§ 295). This increase cannot
proceed from the waste of the Muscular system ; for this would set free
Phosphate of Lime, which chiefly passes off by the fasces.

848. The alkaline or acid reaction of the Urine, therefore, will not only
depend upon the quantity of alkaline Phosphates converted into acid Phos-
phates by the Uric and Hippuric acids (§ 845) ; but also upon the amount of
the bases in the ingesta, compared with that of the permanent Acids intro-
duced into the system or generated within it. The Urine of animals which
live chiefly or entirely upon Vegetable food, is almost invariably alkaline;
because this food contains a large quantity of alkaline bases, in combination
with Citric, Tartaric, Oxalic, and other acids, which are decomposed within
the system ; and the amount of Sulphuric and Phosphoric acids produced is
not sufficient to neutralize them. On the other hand, the food of Carnivo-
rous animals contains no free or weakly-combined bases ; and as its Sulphur
and Phosphorus, when oxidized in the system, produce a considerable quan-
tity of free acids, which share the bases with the Muriatic acid already there,
the Urine must necessarily have an acid reaction. The character of the
Urine of Man, in this respect, is considered by Liebig to depend entirely upon
that of the food ingested.

a. Proceeding upon his determination that no Lactic acid is ever present in the Urine, he
remarks : " The acid, neutral, or alkaline reaction of Urine of healthy individuals, does not
depend on any difference in the processes of digestion, respiration, or secretion, in the va-
rious classes of animals, but upon the constitution of the aliments, and upon the alkaline
bases which enter the organism through the medium of these aliments. If the amount of
these bases is sufficiently large to neutralize the acids formed in the organism, or supplied
by the aliments, the urine is neutral ; whilst it manifests an alkaline reaction, when the
amount of alkaline bases thus supplied to the organism is more than sufficient to neu-
tralize the acids; but in all these cases, the urine accords with the nature of the aliments
taken." The varying amount of Uric Acid, — which, on Prof. Liebig's own showing, is very
much influenced by the respiration, — is altogether left out of consideration in this sweeping

generalization.

849. The amount of Azotized matter in the Urine, also, is greatly influ-
enced by the nature of the food ingested, whilst the constitution of the Ani-
mal frame remains nearly the same ; hence it appears, that a certain portion
of it must be derived from the unassimilated materials which have been taken
into the blood, and which, being superfluous, are injurious. It is well known
that the ingestion of an over-supply of azotized matter does not occasion an
increased production of the fibrinous or gelatinous tissues ; and it may be
hence inferred that, as there is no means by which the superfluous amount
can be stored up in the system (in the mode that non-azotized matter is stored
up as Fat), it must be continually eliminated from the Blood. And there can
be no doubt that the Kidneys are the principal channel by which this is ef-
fected ; the amount of azote thrown oft' in a given time, in the various com-
pounds which they excrete, being equal to 10-1 Iths of the whole quantity
ingested. — The following are the results of the most satisfactory inquiries
that have yet been made, in regard to the influence of various kinds of Ali-
ment upon the amount of the solid matters in the Urine. These experiments
were performed by Dr. Lehmann of Leipsig, upon himself. In thejirsl series,
Dr. L. adopted an ordinary mixed diet ; but he took no more solid or liquid
aliment than was needed to appease hunger or thirst, and abstained from fer-
mented drinks. Every two hours he took exercise in the open air, but he
avoided immoderate exertion of every kind. The average result of the exa-
mination of the Urine passed under these circumstances, for fifteen days, is
given in the first line of the subsequent Table. — In a second series of experi-
ments, Dr. L. lived for twelve days on an exclusively Animal diet ; and for

SECRETION OF URINE. 645

the last six of these, it consisted solely of eggs. He took 32 eggs daily;
which contained 189'7 grammes of dry albumen, and 157'48 of fatty matters;
or about 228'75 grammes of carbon, and 30' 16 of azote. The amount of
Urea is shown, in the second line of the Table, to have undergone a very
large increase ; and it contained more than five-sixths of the whole azote in-
gested.— In a third series of experiments, Dr. L. lived for twelve days on a
Vegetable diet ; and its effect upon the solid matter of the Urine is shown in
the third line of the Table. — In a fourth, he lived for two days upon pure
farinaceous and oleaginous substances, without azotized food of any kind ;
and the azotized matter of the Urine must, therefore, have been solely the
result of the disintegration of the tissues. It is seen to undergo a very marked
diminution under this regimen, as is shown in the fourth line of the Table.
His health was so seriously affected, however, by this diet, that he was una-
ble to continue it longer.

Lactic Acid (?) Extractive
Solid Matters. Urea. Uric Acid, and Lactates. Matters.

I. Mixed diet . . 67-82 32-498 MS3 2'257 10-480

II. Animal diet . . . 87-44 53-198 1-478 2-167 5-145

III. Vegetable diet . . . 59-24 22-481 1-021 2-069 16-499

IV. Non-Azotized diet . . 41'68 15-408 0'735 5-276 11-854

850. The following inferences are drawn by Dr. Lehmann, from these
experiments : — " 1. Animal articles of diet augment the solid matters of the
Urine. Vegetable substances, and still more such as are deprived of azote,
on the contrary, diminish it. — 2, Although Azote be a product of decomposi-
tion of the organism, yet its proportions in the urine depend also on the food,
for we find a richly-azotized diet augmentvfconsiderably the quantity of Urea.
In the above experiments, the proportion of the Urea to the other solid mat-
ters was as 100 to 116 in a mixed diet; as 100 to 63 in an animal diet; as
100 to 156 in a vegetable diet; and as 100 to 170 in a non-azotized diet. — 3.
The quantity of Uric Acid depends less on the nature of the diet, than on
other circumstances ; the differences observed in it being too slight to warrant
us in ascribing them to the former cause. — 4. The combinations of Proteine,
and consequently the azote of the food, are absorbed in the intestinal canal ;
and what is not employed in the formation of the tissues, is thrown off by
the Kidneys in the form of Urea or Uric acid, — these organs being the chief
if not the sole, channel through which the system frees itself of its excess of
azote. — 5. The urine contains quantities of Sulphates and Phosphates pro-
portional to the azotized matters which have been absorbed ; and the -propor-
tion of these salts is sensibly increased under the use of a large amount of
those. — 6. In the same circumstances, the Extractive matters diminish, while
their quantity is increased by the use of vegetable diet, — a fact which proves
the influence of vegetable aliment over the production of these matters in the
urine. — 7. Under an animal diet, the quantity of Lactic acid diminishes ; but
the greater part of this acid is free. It is the reverse under a vegetable diet ;
there is more lactic acid, but it is united to bases. . The largest production of
lactic acid is under a non-azotized diet; and most of it is then combined with
ammonia. Therefore the lactic acid eliminated with the urine, is in great part
the product of non-azotized substances not entirely assimilated; but it results
also in part from the decomposition of the azotized substances entering into
the composition of the body and the food. — 8. The Kidneys not only sepa-
rate certain constituent parts of the organs, which have become inadequate for
the maintenance of life, but they also expel the superfluous nutritive matters
that may have been absorbed."* It must be remarked, with regard to these

* L'Experience, Dec. 7, 1843; andEdinb. Monthly Journal, March, 1844.

646 OF SECRETION.

inferences, that the statements concerning the amount of Lactic acid and the
Lactates, must be considered as invalidated by the discoveries of Liebig al-
ready referred to (§ 846). The most unequivocal facts determined by Dr.
Lehmann's inquiries, are those which relate to the influence of Diet on the
amount of Urea excreted. The experiments upon a purely non-azotized
diet were not continued long enough for a satisfactory result to be obtained ;
but it is evident that, so long as the ingesta contain no azote, the whole of
that element in the Urine must be attributed to the disintegration or waste of
the tissues, and may be fairly taken as a measure of its amount.

851. The fact of the pre-existence of the chief constituents of Urine in the
Blood, is important as explaining the facility with which the secreting function
appears to be transferred to other membranes, in some of the cases in which
the Kidney does not perform its function. Doubtless there has been much
error on this subject, arising out of deceptions practised by impostors ; but a
sufficient number of indubitably genuine cases are on record, to put it beyond
doubt that such transferences have taken place, — urinous fluid being secreted
from the stomach, mammae, umbilicus, nose, &c.* — On the other hand, the
Kidney may serve as the channel for the elimination of substances which
are usually drawn off by other organs. Thus, when the secreting action of
the Liver has been gradually impaired by structural disease, the Kidneys ap-
pear to have performed its function, in separating some (at least) of the ele-
ments of Bile. And a case has recently been mentioned, in which the urine
of a parturient female, who did not suckle her infant, was found to contain a
considerable amount of Butyric acid, during several days. The elimination
of Kiesteine by the Kidney during pregnancy will be presently noticed (§ 859).

852. The facility with which substances taken into the current of the
Circulation pass into the Urinary secretion, varies extremely ; and no general
law can be stated in regard to it. It appears from Wb'hler's elaborate re-
searches on this subject, that the salts which are most readily excreted are
those which excite the action of the kidneys.t The rapidity with which
absorption and elimination take place is often extremely remarkable; Prus-
siate of Potash having been detected in the urine, within two minutes after it
had been introduced into the stomach. The variations in this respect would
appear to depend chiefly on the degree of concentration of the saline solution,
which will affect the rapidity of its absorption, according to the laws of En-
dosmose; — its reception into the blood being more rapid, in proportion as its
density is lower, in comparison with that of the circulating fluid. Pure water,
or water containing but a small admixture of saline matter, is readily absorbed
into the blood-vessels of the Intestinal villi ; but it is as readily drawn off
through the Kidneys (by the agency, as it would seem, of the Malpighian
bodies, § 840) ; and consequently a large amount may be ingested in a short
time. But if the water contain an amount of saline matter equal to that of
the Serum, no absorption of it takes place; it remains in the intestinal tube;
and it is voided by the rectum. Further, if the quantity of saline matter in
the solution be greater than that of the Serum, not only will no absorption
take place, but there will be an endosmose of the water of the blood towards
the solution; so that a large quantity of fluid is discharged by the Intestinal
canal. This simple explanation, first offered by Liebig,:): accounts well for
the diuretic effect of most weak saline solutions, and the purgative qualities of
stronger ones. — For the transit of the peculiar principles of Vegetables, how-
ever, it appears that from one to two hours are usually required. The effect

* For a scientific explanation of this fact, see Princ. of Gen. and Comp. Phys., § 539.

+ See Miiller's Physiology, p. 589.

4! Chemistry applied to Agriculture and Physiology, Part ii.

MAMMARY GLANDS SECRETION OF MILK.

647

of Oil of Turpentine, and probably of other volatile agents, is produced much
rapidly; the characteristic odour of violets being perceptible in the

more

Urine passed but a few minutes after the vapour of the oil had been received
into the lungs.

4. — Mammary Glands. — Secretion of Milk.

853. We now come to those Glands, whose action is rather to elaborate
from the Blood certain products, which are destined for special uses in the
economy, than to eliminate matters, whose retention in the circulating current
would be injurious. Pre-eminent amongst these in size and importance, at
least during their period of activity, are the Mammary Glands ; which are
found only in the animals of the Class Mammalia, and which present them-
selves in an almost rudimentary state in some of the non-placental subdivisions
of the class (§ 44).

a. The structure of the Human Mammary Gland, which has been recently investigated
fully by Sir A. Cooper, is very simple, and easily described. It consists of a series of ducts
passing inwards from their termination in the nipple, and then ramifying like the roots of a
tree, their ultimate subdivisions terminating in minute follicles. The mamillary tubes are
usually about ten or twelve in number; they are straight ducts, of somewhat variable size;
and their orifices, which are situated in the centre of the nipple, and are usually concealed
by the overlapping of its sides, are narrower than the tubes themselves. At the base of the
nipple, these tubes dilate into reservoirs, which extend beneath the areola and to some dis-
tance into the gland, when the breast is in a state of lactation. These are much larger in
many of the lower Mammalia than they are in the Human female; their use is to supply
the immediate wants of the child when it is first applied to the breast, so that it shall not
be disappointed, but shall be induced to proceed with sucking until the draught be occasioned
(§ G'26). From each of these reservoirs commence five or six main branches of the lacti-
ferous tubes, each of which speedily subdivides into smaller ones; and these again divari-
cate, until their size is very much reduced, and their extent greatly increased. The propor-
tional size of the trunk and of its branches, appears to follow the same law which governs
that of the blood-vessels. The breast is not formed into regular lobes by the ramifications
of the ducts; because they ramify between, and intermix with each other so as to destroy

[Fig. 251.

\

The Mammary Gland after the removal of the
skin, as taken from ihe subject three days after
delivery ; 1, the surface of the chest ; 2, subcuta-
neous fat ; 3, the skin covering the gland ; 4, cir-
cumference of the gland; 5, its lobules separated
by fat; 6, the lactiferous ducts converging to unite
in the nipple; 7, the nipple slightly raised and
showing the openings of the tubes at its extremity.]

A vertical section of the Mammary Gland,
showing its thickness and the origins of the lacti-
ferous ducts ; 1, 2, 3 its pectoral surface ; 4, section
of the skin on the surface of the gland; 5, the thin
skin covering the nipple ; 6, the lobules and lobes
composing the gland ; 7, the lactiferous tubes com-
ing from the lobules; 8, the same tubes collected
in the nipple.]

648

Distribution of the milk-ducts in the Mamma of the Human female, during lactation; the ducts

injected with wax.

the simplicity and uniformity of their divisions. It is very rarely, however, that they inos-
culate. The mammary ducts are composed of a fibrous coat lined by a mucous membrane ;
the latter is highly vascular, and forms a secretion of its own, which sometimes collects in
considerable quantity when the milk ceases to be produced.

b. The gland itself is composed of the union of a number of glandules, which are con-
nected by means of the fibrous or fascial tissue of the gland ; it is between these, that the
mammary tubes may be observed to ramify; and from them their branches spring. When
the glandules arc rilled with injection, and for a long time macerated in water and un-
ravelled, they are found to be disposed in lobuli; and when a branch of mammary tube is
separated, with the glandules attached, the part appears like a bunch of fruit hanging by its
stalk. When the lactiferous tube proceeding from a glandule is minutely injected, the latter
will be found to be composed of numerous follicles, in which the ultimate ramifications of
the former terminate, or rather originate. Their size, in full lactation, is that of a holt-

Fig. 203.

Fig. 254.

Termination of portion of milk-
duct in a cluster of follicles ; from
a mercurial injection ; enlarged
four limes.

Uhirnate follicles of Mammary
gland, with their secreting cells,
a, a;—b, b, the nuclei.

MAMMARY GLANDS SECRETION OF MILK. 649

pricked in paper by the point of a very fine pin; so that the follicles are, when distended
\vitli quicksilver or milk, just visible to the naked eye. At other times, however, the follicles
do not admit of being injected, though the lactiferous tubes may have been completely filled.
They are lined by a continuation of the same membrane, with that which lines the ducts;
and this possesses a high vascularity. The arteries which supply the glandules with blood,
become very large during lactation; and their divisions spread themselves minutely on the
follicles. From the blood which they convey, the milk is secreted and poured into the
follicles, whence it flows into the ducts. From the researches of Mr. Goodsir it appears,
that, in common with other glandular structures, the inner surface of the milk-follicles is
covered with a layer of epithelium-cells; which, being seen to contain milk-globules, may
be without doubt regarded as the real agents in the secreting process. Absorbent vessels
are seen to arise in large numbers in the neighbourhood of the follicles; their function ap-
pears to be, to absorb the more watery part of the milk contained in the follicles and tubes,
so as to render it more nutrient than it is as first secreted ; and also to relieve the distention
which would occur, during the absence of the child, from the continuance of the secreting
process.

c. The Mammary gland may be dejected at an early period of fetal existence ; being
easily distinguishable from the surrounding parts, by the redness of its colour and its high
vascularity, especially when the whole is injected. At this period it presents no diiference
in the male and female ;% and it is not until near the period of puberty, that any striking
change manifests itself, — the gland continuing to grow, in each sex, in proportion to the
body at large. About the age of thirteen, however, the enlargement of the gland com-
mences in the Female; and by sixteen years, it is greatly evolved, and some of the lactife-
rous tubes can be injected. At about the age of twenty, the gland attains its full size
previous lo lactation ; but the milk follicles cannot even then be injected from the tubes.
During pregnancy, the mammas receive a greatly-increased quantity of blood. This deter-
mination often commences very early, and produces a feeling of tenderness and distention,
which is a valuable sign (where it exists in connection with others) of the commencement
of gestation. The Areola at this time becomes darker in its colour, and thicker in sub-
stance, and more extended; its papilla become more developed, and the secretion from its
follicles increased. The vascularity of the gland continues to increase during pregnancy;
and at the time of parturition, its tabulated character can be distinctly felt. The follicles
are not, however, developed sufficiently for injection, until lactation has commenced. After
the cessation of the catamenia from age, so that pregnancy is no longer possible, the lactife-
rous ducts continue open, but the milk follicles are incapable of receiving injection. The
substance of the glandules gradually disappears, so that in old age only portions of the ducts
remain, which are usually loaded with mucus; but the place of the glandules is commonly
filled up by adipose tissue, so that the form of the breast is preserved. Sir A. Cooper
notices a curious change, which he states to be almost invariable with age, — namely, the
ossification of the arteries of the breast, the large trunks as well as the branches ; so that
their calibre is greatly diminished, or even obliterated.

d. The Mammary gland of the Male is a sort of miniature picture of dial of the female.
It varies extremely in its magnitude, being in some persons of the size of a large pea ;
whilst in others it is an inch, or even two inches in diameter. In its structure it corre-
sponds exactly with that of the female, but is altogether on a smaller scale. It is composed
of lobules containing follicles, from which ducts arise; and these follicles and ducts are not
too minute to be injected, although with difficulty. The evolution of the gland goes on pan
passu with that of the body, not undergoing an increase at any particular period; it is some-
times of considerable size in old age. A fluid, which is probably mucus, may be pressed
from the nipple in many persons ; and this in the dead body, with even more facility than in
the living. That the essential character of the gland is the same in the male as in the female,
is shown by the instances, of which there are now several on record, in which infants have
been suckled by men. The following is given by Dr. Dunglison.* "Professor Hall, of the
University of Maryland, exhibited to his Obstetrical class, in the year 1837, a coloured man,
fifty-five years of age, who had large, soft, well-formed mammae, rather more conical than
those of the female, and projecting fully seven inches from the chest; with perfect and large
nipples. The glandular structure seemed to the touch to be exactly like that of the female.
This man had officiated as wet-nurse, for several years, in the family of his mistress ; and
he represented that the secretion of milk was induced by applying the children entrusted to
his care to the breasts during the night. When the milk was no longer required, great dif-

* Dunglison's Physiology, [sixth ed., vol. ii. p. 480.] See also the case described by the
Bishop of Cork, in the Philosophical Transactions, vol. xli. p. 813: one mentioned by Cap-
tain Franklin (Narrative of a Journey to the Polar Sea, p. 157); and one which fell under
the notice of the celebrated traveller Humboldt (Personal Narrative, vol. iii. p. 58).
55

650 OF SECRETION.

lieulty was experienced in arresting the secretion. His genital organs were fully deve
loped." — Corresponding facts are also recorded of the male of several of the lower animals

854. The secretion of Milk consists of Water holding in solution Sugar,
various Saline ingredients, and a peculiar albuminous substance termed
Caseine; and having Oleaginous particles suspended in it. The constitution
of this fluid is made evident by the ordinary processes, to which it is sub-
jected in domestic economy. If it be allowed to stand for some time, exposed
to the air, a large part of the oleaginous globules come to the surface, being
of less specific gravity than the fluid through which they are diffused. At
the same time there is reason to believe that they undergo a change which
will be presently described. The cream thus formed does not, however, con-
sist of oily particles alone; but includes a considerable amount of caseine,
with the sugar and salts of the milk. These are further separated by the
continued agitation of the cream ; which, by rupturing the envelopes of the
oil-globules, separates it into butter, formed by their aggregation, and butter-
milk, containing the caseine, sugar, &c. A considerable quantity of caseine,
however, is entangled with the oleaginous matter ; and this has a tendency to
decompose, so as to render the butter rancid. It may be separated by melting
the butter at the temperature of 180°; when the caseine will fall to the bot-
tom, leaving the butter pure, and much less liable to change. — The milk, after
the cream has been removed, still contains the greatest part of its caseine and
sugar. If it be kept long enough, spontaneous change takes place in its com-
position; the sugar is converted into lactic acid, and this coagulates the caseine,
precipitating it in small flakes. The same precipitation may be accomplished
at any time, by the addition of an acid; all the acids, however, which act
upon albumen, do not precipitate caseine, as will presently be pointed out in
detail; the most effectual is that contained in the dried stomach of a calf,
known as rennet. This exerts so powerful an influence over it, that, accord-
ing to the experiments of Berzelius, a piece of the membrane coagulated the
caseine of 1800 times its weight of milk, with the loss of only l'17th part of
its own weight; so that the active principle, dissolved from the rennet, must
have collected the caseine of about 30,000 times its weight of milk. The
whey left after the curd has been separated, contains a large proportion of the
saccharine and saline matter, entering into the original composition of the
milk. This may be readily separated by evaporation.*

a. When Milk is examined with the Microscope, it is seen to contain a large number of
particles of irregular size and form, suspended in a somewhat turbid iluid; these particles
(according to the measurement of Donnef) vary in size from about the 1-12, 700th to the
l-3040th of an inch; and they are termed milk-globules. They are not affected by the mere
contact of ether or alkalies; but if these reagents are shaken with them, an immediate solu-
tion is the result. The same effect happens, if they are first treated with acetic acid.
Hence it is evident, that the globules consist of oily matter, inclosed in an envelope of some
kind; and an extremely delicate pellicle may, in fact, be distinguished after the removal of
the oily matter by ether; or, after the globules have been ruptured, and their contents pressed
out, by rubbing a drop of milk between two plates of glass. No proof of the organization
of this pellicle has, however, been detected ; and it is probably to be regarded as the simple
result of the contact of oil with albuminous matter, which is known to give rise to a mem-
branous film. — Besides these milk-globules, other globules of much smaller >i/e are seen in
milk; and these present the peculiar movement, which is exhibited by molecules in gene-
ral. Most of them seem to consist of oily matter, not inclosed in an envelope, as they are
at once dissolved, when the fluid is treated with ether; but, according to the statements of
Donne, it would seem that, a portion of them are composed of caseine, suspended, not dis-
solved, in the fluid. It may be reasonably doubted, however, whether these were not in

* A considerable quantity is thus obtained for household purposes in Switzerland,
j- Cours de Microscopic, Douzieme Legon.

MAMMARY GLANDS SECRETION OF MILK. 651

a state of change ; whether from their own decomposition, or from incipient coagulation;
either of which might have taken place during the processes of filtration, &c., that were
required to determine their nature. In addition to the foregoing particles, there are found in
the Colostrum, or milk first secreted after delivery, large yellow granulated corpuscles, which
are described by Donne as composed of a multitude of small grains aggregated together, and
frequently including a true globule of milk in their centre: these are for the most part solu-
ble in ether; but traces of some adhesive matter, probably mucus, holding together the par-
ticles, are then seen. They are considered by some as exudation-corpuscles; to which they
certainly bear a close resemblance. Lamella? of epithelium are also found in the milk. —
All the larger globules may be removed by repeated filtration; and the fluid is then nearly
transparent. This, in fact, is the simplest way of separating the oleaginous from the other
constituents of the milk; as little caseine then adheres to the former. That the transparent
fluid which has passed through the filter contains nearly the whole amount of the caseine
of the milk, appears a sufficient proof that this is, for the most part, truly dissolved in the
fluid.

b. We shall now consider the chemical characters of each of the foregoing ingredients. —
The Oleaginous matter of milk principally consists, like fatty matter in general, of the two
substances, elaine and stearine; which are converted in the process of saponification into
the elaic, stearic, and margaric acids: but it also contains another substance peculiar to it,
which yields in saponification three volatile acids, of strong animal odour, to which Chev-
reul has given the names of butyric, caproic, and capric acids ; whilst the fatty substance
itself, to which the peculiar smell and taste of butter are due, is designated as butyrine. The
peculiar acids are not only formed when the butyrine is treated with alkalies; but are pro-
duced by the ordinary decomposition of this principle, which is favoured by time and mode-
rate warmth. — The Caseine or cheesy matter of milk, which is obtained with some slight
admixture of fatty matter in the production of cheese from skimmed milk, is chiefly distin-
guished from Albumen, by the peculiar readiness with which it is precipitated by feeble
organic acids, such as the lactic and acetic ; and by its non-coagulability by heat alone. The
Caseine of Human milk, however, is much less precipitable by acids, than is that of the
Cow; very commonly resisting the action of the mineral acids, and even that of the acetic;
but being always coagulated by rennet, though the curd is long in collecting. It is remarked
by Dr. G. 0. Rees,* that the caseine of human milk thus bears somewhat the same relation
to that of the cow, that the albumen of chyle bears to that of the blood. — The Sugar of milk,
which may be obtained by evaporating whey to the consistence of a syrup and then setting
it aside to crystallize, contains a large proportion (12 per cent.) of water, so that it may be
considered as really a hydrate of sugar; it is nearly identical in its composition with starch,
and may, like it, be converted into true sugar by the action of sulphuric acid ; and when in
contact with a ferment, or decomposing azotized compound, it is extremely prone to be con-
verted into lactic acid, by appropriating to itself the elements of water. It is, in fact, through
this process, that the coagulation of the caseine is effected, by means of rennet ; for as soon
as a very minute quantity of lactic acid is generated, it withdraws from the caseine the free
alkali which kept it in solution, and the caseine is consequently precipitated. The same
effect will be produced by incipient decomposition of the caseine itself; which will soon
occasion lactic acid to be generated from the sugar, in sufficient quantity to give to the rnilk
a distinctly acid reaction. — The Saline matter contained in milk, appears to be nearly iden-
tical with that of the blood; with a larger proportion of the phosphates of lime and mag-
nesia, which amount to 2 or 2j parts in 1000. These phosphates are held in solution chiefly
by the Caseine; which seems to have a power of combining with them, even greater than
that of Albumen: the presence of a minute proportion of free alkali, also, assists their solu-
tion. A small portion of iron in the state of phosphate, together with the chlorides of
potassium and sodium, may also be detected in milk.f

855. The proportion of these different constituents is liable to great varia-
tion, from several causes. Thus, the whole amount of the solid constituents
may vary from 86 to 138'6 parts in 1000; the difference being partly due to
individual constitution, but in great part, also, to the amount and character
of the ingesta. The average seems to be between 100 and 120 parts. The
following are the results of the analyses of Simon; the first column being
the average of fourteen observations upon the same woman ; the second giv-
ing the maximum of each ingredient; and the third the minimum: —

Art. MILK, in the Cyclopaedia of Anatomy and Physiology,
t Haidlen, in Annalen der Chemie und Pharmacie, xlv. p. 263.

652 OF SECRETION.

I. II. III.

Water SS3-G 914-0 861-4

Butter 25-3 54-0 8'0

Caseine 34-3 45"2 19'6

Sugar of Milk and Extractive Matters 48'2 G2-4 39'2

Fixed salts 2-3 2-7 1-G

It also appears from the analyses of Simon, that the proportion of the differ-
ent ingredients is liable to variation, according to the time which has elapsed
since parturition. The quanthy of Caseine is at its minimum at the com-
mencement of lactation, and then gradually rises until it attains a nearly fixed
proportion. The quantity of Sugar, on the contrary, is at its maximum at
first, and gradually diminishes. The amount of Butter (as appears from the
wide extremes shown in the above tables) is more variable than that of any
other constituent — .That some of the variations are due, moreover, to the
character of the ingesta, and others to the external temperature, amount of
exercise, and other circumstances affecting the individual, is proved by the
recent inquiries of Dr. Playfair upon the Milk of the Cow. He has shown
that the amount of butter depends in part upon the quantity of oily matter in
the food; and in part upon the amount of exercise which the animal takes,
and the warmth of the atmosphere in which it is kept. Exercise and cold,
by increasing the respiration, eliminate part of the oily matter in the form of
carbonic acid and water; whilst rest and warmth, by diminishing this drain,
favour its passage into the milk. — The proportion of Caseine, on the other
hand, is increased by exercise ; which would seem to show that this ingre-
dient is derived from the disintegration of Muscular tissue, — and thus adds
strength to the Author's view (§ 681) that of the matter thus set free, a part
only is destined to immediate excretion, and that a part may again be
subservient to the operations of Nutrition. Dr. Playfair's experience on this
head seems to correspond with the results of common observation in Swit-
zerland, where they pasture cattle in very exposed situations, and are obliged
to use a great deal of muscular exertion. The quantity of Butter yielded by
them is very small; whilst the Cheese is in unusually large proportion. But
these very cattle, when stall-fed, give a large quantity of Butter and very little
Cheese.

856. The change which naturally takes place, from the condition of Co-
lostrum to that of true Milk, during the first week of lactation, is a very im-
portant one. The Colostrum has a purgative effect upon the child, which is
very useful in clearing its bowels of the meconium that loads them at birth;
and thus the necessity of any other purgative is generally superseded. Oc-
casionally, however, the colostric character is retained by the milk, during
an abnormally long period; and the health of the infant is then severely af-
fected. It is important to know that this may occur, even though the milk
may present all the usual appearances of the healthy secretion ; but the mi-
croscope at once detects the difference.* The return to the character of the
early milk, which has been stated to take place after the expiration of about
twelve months, seems to indicate that Nature designs the secretion no longer
to be encouraged. The mother's milk cannot then be so nutritious to the
child as other food ;t and every medical man is familiar with the injurious
consequences, to which she renders herself liable by unduly prolonging lac-
tation.:):

* See Donne, "Du Lait, et en particulier oelui des Nourrices;" and Brit, and For. Med.
Review, vol. vi. p. 1S1.

f On the whole subject of Infant Nutrition, the Author would strongly recommend the
excellent little \vork of Dr. A. Combe, formerly referred to.

J One of these, which has particularly fallen under the Author's notice, is debility of the

MAMMARY GLANDS SECRETION OF MILK. 653

857. It is very interesting to observe that Milk contains the three classes
of principles which are required for human food, — the Albuminous, Oleagi-
nous, and Saccharine ; and it is the only secreted fluid, in which these all
exist in any considerable amount. It is, therefore, the food most perfectly
adapted for the young animal; and is the only single article supplied by na-
ture, in which such a combination exists. Our artificial combinations will be
suitable to replace it, just in proportion as they imitate its character; but in
none of them can we advantageously dispense with milk, under some form
or other. It should be remembered that the saline ingredients of Milk, espe-
cially the phosphates of lime, magnesia, and iron, have a very important
function in the nutrition of the infant, — affording the material for the consoli-
dation of its bones, and for the production of its red blood-corpuscles; and
any fluid substituted for milk, which does not contain these, is deficient in
essential constituents. It is very justly remarked by Dr. Rees, that of all
the secreted fluids, Milk is most nearly allied in its composition to blood.

858. The proportion of the different ingredients in the Milk of different
animals, is subject to considerable variation : and this fact is of much practi-
cal importance in guiding our selection, when good Human milk cannot be
conveniently obtained for the nourishment of an infant. The first point to
be inquired into, is the quantity of solid matter contained in each kind ; this
may be determined either by evaporation, or by the specific gravity of the
fluid. The Specific Gravity of Human milk is stated by Dr. Rees to vary
between 1030 and 1035; others, however, have estimated it much lower.
That of the Cow appears to be usually about the same ; that of the cream,
however, being 1024, and that of the skimmed milk about 1035. The varia-
tion will in part depend (as in the case of the urine) upon the quantity of fluid
ingested, and in part, it is probable, upon the manner in which the milk is
drawn ; for it is well known to milkers, that the last milk they obtain is much
richer than that with which the udder is distended at the commencement.
The quantity of solid matter, obtainable from Human and from Cow's Milk
by evaporation, seems, like the specific gravities of the fluids, to be nearly the
same. In the relative proportion of the ingredients, however, there is a con-
siderable difference ; there being much more sugar, and less caseine in Human
Milk than in that of the Cow. The following table exhibits the relative pro-
portion of the different ingredients, in the Milk of various animals, from which
it is commonly obtained: —

Cow. Goat. Sheep. Ass. Mare.

Water ..... 861-0 868-0 856-2 907-0 S96-3

Butter . ... 38-0 33-2 42-0 12-10 traces

Caseine . . 68'0 40'2 45-0 16-74 162

Sugar of Milk and Extractive Matters . 29-0 52-8 .00-0 )

Fixed Salts . . . .6-1 5-8 6-85

It appears from this, that, whilst the milk of the Cow, Goat, and Sheep do
not differ from each other in any very prominent degree, that of the Ass and
Mare is a fluid of very dissimilar character, containing a comparatively small
proportion of caseine and butter, and abounding in sugar. Hence it is, that
it is much more disposed to ferment than other milk ; indeed the sugar of
Mare's milk is so abundant, that the Tartars prepare from it a spirituous
liquor, to which they give the name of koumiss. It appears from these de-
tails that no milk more nearly approaches that of the Human female, than
that of the Sheep and Goat ; these both possess, however, a larger proportion
of caseine, which forms a peculiarly dense curd ; and the milk of the Goat

retina, sometimes proceeding to complete amaurosis ; this, if treated in time, is most commonly
relieved by discontinuance of lactation, generous diet, and quinine.

55*

654 OF SECRETION.

is tainted with the peculiar odour of the animal, which is more intense if the
individual be dark-coloured. The milk of the Cow will usually answer very
well for the food of the infant ; care being taken to dilute it properly, accord-
ing to the age of the child, and to add a little sugar. It is an interesting cir-
cumstance, lately ascertained, that the milk of Carnivorous Mammals, fed ex-
clusively on animal diet, contains scarcely a trace of sugar, whilst the caseine
and butter are abundant.

859. From what has been stated of the close correspondence between the
elements of the Blood and those of the Milk, it is evident that we can scarcely
expect to trace the existence of the latter, as such, in the circulating fluid.
To what degree the change, in which their elaboration consists, is accom-
plished in the Mammary gland, or during the course of the circulation, there
is no certain means of ascertaining. The recent discovery of the usual pre-
sence of the organic compound named kiesteine (which is nearly related to
caseine), in the urine of pregnant women, seems to indicate that the conversion
of albumen into caseine takes place in the blood, — this curious excretion being
the means of preventing its accumulation in the circulating fluid, previously
to the time when it is secreted by the mammae.* It is evident that this secre-
tion cannot serve as the channel for the deportation of any element, the accu-
mulation of which would be injurious to the system; since it does not occur
in the male at all; and is present in the female at particular times only. Yet
there is reason to believe that if, whilst the process is going on, it be suddenly
checked, the retention of the material in the blood, or the reabsorption of the
secreted fluid, is attended with injurious consequences. Thus if, when the
milk is first secreted, the child be not put to the breast, an accumulation takes
place, which, if not relieved, occasions great general disturbance of the system.
The narrowness of the orifice of the milk-tubes obstructs the spontaneous exit
of the fluid, especially in primiparse; the reservoirs and ducts become loaded;
further secretion is prevented ; and a state of congestion of the vessels of the
gland, tending to inflammation, is induced. The accompanying fever is partly
due, no doubt, to the local disturbance; but in part also, there seems reason
to believe, to the reabsorption of the milk into the blood; this cannot but be
injurious, since, although but little altered, the constitution of milk is essen-
tially different, especially in regard to the quantity of cry stall izable matter
(sugar) which it contains. The instances of the vicarious secretion of milk
are not numerous ; and in no instance is there any proof that the elements of
the fluid were pre-existent in the blood. Some of the most curious are those
in which it has been poured out from a gland in the groin ; but it is probable
that this was in consequence of the existence of a real repetition, in that
place, of the true mammary structure, — this being the situation of the mamma?
of many of the inferior animals, of which the analogues in Man are usually
undeveloped.

a. The following is a more unequivocal case of vicarious secretion ; and it is peculiarly
interesting us exhibiting the injurious effects of the re-absorption of the secretion, and the
relief which the system experienced when it was separated from the blood by the new
ehannel. "A l;i< ly of delicate constitution (with n predisposition to pneumonia) was pre-
vented from suckling her child, as she desired, by the following circumstance. Soon after
her delivery she had a severe fever, during which her breasts bceame very large and hard;
the nipples were swollen and firm; and there was evidently an abundant secretion of
milk; but neither the sucking of the infant, nor any artificial means, could draw a single
drop of llni 1 from the swollen glands. It was clear that the milk-tubes were closed; and as
the breasts continued to grow larger and more painful, purgatives and other means were
employed to cheek the secretion of milk. After three days the lever somewhat diminished,
and was replaced by a constant cough, which was at first dry, but soon after was followed

' See Dr. Golding Bird, in Guy's Ho?p. Rep., vol. v.

SALIVARY GLANDS AND PANCREAS. 655

by t.ho expectoration of simple mucus. After this, the cough diminished in severity, and the
expectoration became easy ; but the sputa were no longer mucous, but were composed of a
liquid, which had all the physical characters of genuine milk. This continued for fifteen
days; the quantity of milk expectorated amounting to three ounces or more in the twenty-
four hours. The breasts gradually diminished in size : and by the time that the expectoration
ceased, they had regained their natural dimensions. The same complete obstacle to the
flow of milk from the nipples recurred after the births of four children successively, with
the same sequela?. After the sixth, she had the same symptoms of fever, but this time
they were not followed by bronchitis or the expectoration of milk ; she had in their stead
copious sweatings, which, with other severe symptoms, reduced her to a cachectic state, and
terminated fatally in a fortnight."*

860. Of the quantity of Milk ordinarily secreted by a good Nurse, it is
impossible to gain any definite idea; as the amount which can be artificially
drawn, affords no criterion of that which is secreted at the time of the draught
(§ 626). The quantity which can be squeezed from either breast at any one
time, and which, therefore, must have been contained in its tubes and reser-
voirs, is about two ounces. The amount secreted is greatly influenced by
the mental and physical condition of the female, and also by the quantity and
character of the ingesta. In regard to the influence of the mental state upon
this secretion, ample details have already been given (Chap. ix.). With
respect to the physical state most favourable to the production of an ample
supply of this important fluid, it may be stated generally, that sound health,
a vigorous but not plethoric constitution, regular habits, moderate but not
fatiguing exercise, and an adequate but not excessive amount of nutritious
food, furnish the conditions most required. It is seldom that stimulating
liquors, which are so commonly indulged in, are anything but prejudicial ; but
the unmeasured condemnation of them in which some writers have indulged,
is certainly injudicious; as experience amply demonstrates the improvement
in the condition both of mother and infant, which occasionally results from the
moderate employment of them.

861. The influence of various Medicines upon the Milk, is another im-
portant question, which has not yet been sufficiently investigated. As a
general rule, it appears that the most soluble saline compounds pass into the
milk as into other secretions ; but there are many exceptions. Common salt,
the sesqui-carbonate of soda, sulphate of soda, iodide of potassium, oxide of
zinc, tris-nitrate of bismuth, and sesqui-oxide of iron, have been readily de-
tected in the milk, when these substances were experimentally administered
to an ass; and ordinary experience shows, that the human infant is affected
by many of these, when they are administered to the mother. The influence
of mercurial medicines taken by the mother, in removing from the infant a
syphilitic taint possessed by both, is also well known. The vegetable purga-
tives, especially castor oil, senna, and colocynth, have little efiect upon the
milk ; hence they are to be preferred to the saline aperients, when it is not
desired to act upon the bowels of the child.

5. — Salivary Glands and Pancreas.

862. The structure of the Salivary Glands and Pancreas in Man, bears
considerable resemblance to that of the Mammary glands. In some of the
lower tribes, however, they are much simpler. Thus, in the Echinodermata
and in Insects, the Salivary glands have the character of prolonged coeca,
more or less convoluted ; and the Pancreas of Fishes presents itself in the
form of a cluster of short cosca round the pyloric extremity of the stomach,
and opening into it by distinct orifices. The accompanying figure will give

* Bulletino delle Scienze Mediche. Apr. 1839; and Brit, and For. Mod. Review, Jan.
1840.

056

OF SECRETION.

Fig. 255.

Fig. 256.

Lobule of Parotid gland of a new-born infant
injected with mercury. Magnified 50 diam.

Distribution of Capillaries around the
follicles of Parotid Gland.

a sufficient idea of the structure of these glands in Man ; the follicles are

very minute, having a diameter only about
Fig. 257. three times greater than that of the capillary

blood-vessels. Their development commences
from a simple canal, sending oft" bud-like pro-
cesses, which opens from the mouth, and lies
amidst a cellular blastema. As development
proceeds, the canal becomes more and more
ramified, and communicates with the enlarged
parent-cells of the blastema, which remain as
the terminal follicles of the branches of the
gland-duct (§ 823).

863. The Salivary secretion is by no means
necessarily constant ; being almost or com-
pletely suspended by cessation of the move-
ment of the masticator muscles and tongue, if
unexcited by any nervous stimulus. Hence
it is, that the secretion is checked during sleep ;
so that, if the mouth be kept open, its surface
is almost dried up by the atmosphere. The
mode in which the secretion is excited through

the influence of the nervous system has already been considered (§§ 625, 626).
The quantity of Saliva formed during the twenty-four hours has been estimated
at about 15 or 20 ounces ; but on this point it is evidently impossible to speak
with certainty. The fluid obtained from the mouth is of a more viscous cha-
racter than the true saliva secreted by the glands ; being mingled with mucus.
The salivary fluid varies as to its chemical reaction ; being sometimes slightly
acid, and sometimes slightly alkaline ; but it is seldom precisely neutral.
According to Huenefeld, it will at the same time strike a blue colour with
reddened litmus-paper ; and turn blue litmus-paper red ; but the saliva ex-
amined directly before, and during, the act of eating, is always alkaline. It
seems probable that the acid reaction is due to the mucus of the mouth ;
which, at times when only a small amount of saliva is excreted, is not neu-
tralized by its alkali. The specific gravity of Saliva varies from 1'006 to
T009. It contains a small number of corpuscles, which seem to be partly
epithelium-cells from the mucous surface of the mouth, and partly the secret-
ing cells of the salivary vesicles. The solid matter contained in Saliva
amounts to from 10 to 13 parts in 1000. The animal principles of which

Rudimentary Pancreas from Cod : —
a, pyloric extremity of stomach; b, in-
testine.

LACHRYMAL GLAND THE TESTIS. 657

this is composed are Albumen, Mucus, and a peculiar substance termed Ptya-
lin, which is soluble in water, insoluble in alcohol, and yet is different either
from albumen or gelatin. A considerable proportion of saline and earthy
matter exists in the solid residue of saliva ; this is nearly of the same cha-
racter as that which the blood contains, being chiefly composed of the phos-
phate of lime and soda, the chlorides of sodium and potassium, and the lac-
tates of soda and potash. One remarkable property of the salivary secretion,
is its formation of a rust-red precipitate when mixed with a solution of per-
salt of iron. This is supposed to be due to the presence in it of the prin-
ciple termed sulpho-cyanogen. The tartar which collects on the human teeth
consists principally of the earthy phosphates, the particles of which are held
together by about 20 per cent, of animal matter ; and nearly the same may
be said of the salivary concretions which occasionally obstruct the ducts. — It
appears from various recent experiments, that the peculiar animal matter of
the Saliva has a decided effect in metamorphosing certain alimentary sub-
stances, and thus performs the first part of the digestive process. Starch may
be converted into sugar, and sugar into lactic acid, by its agency ; and if acidu-
lated, it has a solvent power for caseine, animal flesh, and other albuminous
substances (§ 669).

864. The Pancreatic Secretion of Man cannot, of course, be readily ob-
tained for analysis ; that which is procured from the lower animals, however,
probably gives a sufficiently correct idea of its character. It seems to be of
a nearly similar nature with saliva, but usually contains a much larger propor-
tion of solid matter; in that of the Dog as much as 87 parts in 1000 have
been found ; and in that of the Sheep, 40 parts. The probable offices of this
secretion in the digestive process, have been already noticed (§§ 669, 670).

6. — Lachrymal Gland.

865. The Lachrymal glands and their secretion may be next mentioned ;
but neither require any lengthened description. The gland in Man is formed
very much on the plan of the Parotid, being composed of branched canals
terminating in follicles, the ultimate ramifications of the several branches
forming lobules or divisions of the glands. The lachrymal fluid has not re-
cently undergone any accurate analysis ; and all that can be stated respecting
it is the general fact, that the quantity of solid matter in it is extremely small,
and that this consists chiefly of saline, and either mucous or albuminous
compounds. It seems probable that the secretion of the lachrymal gland
itself is very little else than the serum of the blood, deprived of a great part
of its albumen ; and that the mucus of the tears is secreted from the surface
of the conjunctival membrane. This secretion has a slightly alkaline reac-
tion. It is being constantly formed in moderate amount, for the purpose of
cleansing the surface of the eye from the impurities which would otherwise
rest upon it ^ and it is then absorbed by the open orifices of the nasal duct,
and carried into the nose, as fast as it is poured out. The cause of this ab-
sorption does not seem very clear. Capillary attraction is probably in part
concerned; and it has been thought that the momentary partial vacuum, oc-
casioned by the inspiratory effort in all the air-passages, will cause the empty-
ing of the nasal duct below, and a consequent in-draught above. The influ-
ence of the nervous system upon this secretion has been already adverted to
(§§ 625, 626).

7. — The Teslis. — Spermatic Fluid.

866. In the Testes we return to the tubular form of glandular structure,
which so remarkably distinguishes the Kidney from all the other glands

658

OF SECRETION.

hitherto mentioned. The external forms presented by these glands through-
out the Animal kingdom, are extremely various ; but their composition is for
the most part very uniform. The object is sometimes attained by a simple
but much elongated canal ; sometimes by shorter branched tubes ; and in
other instances, again, by numerous aggregated coeca, which are often rounded
into cells. In regard to this, as to many other glands, it may be stated that,
whilst its general form in Insects is that of prolonged tubes, the required ex-
tension of surface is given in the Mollusca by the multiplication of cells, so
that the structure has a compact spongy character. It is interesting to remark
that, in some of the lowest Fishes, this organ consists of a mass of vesicles
which have no efferent duct; and that the secretion formed within these
escapes by the rupture of the vesicles, allowing it to escape into the abdomi-
nal cavity, whence it passes by openings that lead directly to the exterior.
In these Fishes, the ova are discharged from the ovarium in a very similar man-
ner ; a modification of which plan is followed in all the higher Vertebrata, —
the ovum being in them also discharged, by the rupture of its containing vesi-
cle or ovisac, into the abdominal cavity, but being immediately received and
conveyed away by the funnel-shaped internal prolongation of the external ori-
fice, which is known as the fimbriated extremity of the Fallopian tube.*

a. The Testis in Man has in every respect, however, a distinctly glandular character. It
consists of several lobules, which are separated from each other by processes of the tunica
albuginea that pass down between them, and also by an extremely delicate membrane (de-
scribed by Sir A. Cooper under the name of tunica vasculosa) consisting of minute ramifica-
tions of the spermatic vessels united by areolar tissue. Each lobule is composed of a mass
of convoluted Tiibuli Seminiferi, throughout which blood-vessels are minutely distributed.

[Fig. 258.

[Fig. 259.

The Testicle injected with mercury; 1, tunica
albuginea ; 2, seminiferous tubes; 3, the rete vas-
culosum testis ; 4, a globule of mercury which has
ruptured the tubes ; 5, the vasa efferentia which
form the coni vasculosi, G, coui vasculosi forming
the head of the epididymis; 7, epididymis ; 8, glo-
bus minor of the epididymis; 9, vas dcferens.]

A view of the minute structure of the Testis ;
1, 1, tunica albuginea; :>. 0, corpus highmorianum;
3, 3, tubuli seininiferi convoluted into lobules; 4,
vasa recta ; 5, rete testis ; 6, vasa efferentia ; 7,
coni vasculosi constituting the globus major of
the epididymis; ;-, body of the epididymis; !>, its
globus minor; 10, vas deferens 11, vasculum
aberrans or blind duct.]

See Principles of General and Comparative Physiology, § G41.

THE TESTIS SPERMATIC FLUID.

659

The lobules (lifter greatly in size, some containing one, and others many of the tubuli ; the
total number of the lobules is estimated at about 450 in each testis, and that of the tubuli at
840. The convolutions of the tubuli arc so arranged, that each lobule forms a sort of cone,
the apex of which is directed towards the. Rcte Testis. It is difficult to trace the free ex-
tremities of the Seminiferous tubes, owing to the frequency of their anastomoses with each
other; in this respect, therefore, the structure of the testis accords closely with that of the

Fig. 260.

Human Testis, injected with mercury as completely as possible; 1, 1, lobules formed of the semini-
ferous tubes ; 2, rete testis ; 3, vasa efferentia ; 4, flexures of the efferent vessels passing into the head,
5, 5, of the epididymis ; 6, body of the epididymis ; 7, appendix ; 8, cauda ; 9, vas deferens.

Fig. 261.

Plan Of the structure of the Testis and Epididymis; a, a. seminiferous tubes; a*, a*: their anasto-
moses; the other references as in the last figure.

660 OF SECRETION.

Kidney. The diameter of the Tubuli is for the most part very uniform; in the natural con-
dition they seem to vary from about the l-195th to the l-10th of an inch; but when injected
with mercury they are distended to a size nearly double the smaller of these dimensions.
When they have reached to within a line or two of the Rete Testis, they cease to be con-
voluted, several unite together into tubes of larger diameter, and these enter the rete testis
under the name of tubuli recti. The rete teslis consists of from seven to thirteen vessels,
which run in a waving course, anastomose with each other, and again divide, being all
connected together. The vasa efferentia which pass to the head of the epididymis are at
first straight, but soon become convoluted, each forming a sort of cone, of which the apex is
directed towards the rete testis, the base to the head of the epididymis. The number of
these is stated to vary from nine to thirty ; and their length to be about eight inches. The
epididymis itself consists of a very convoluted canal, the length of which is about twenty-one
feet. Into its lower extremity, that is, the angle which it makes where it terminates in the
vas defcrcns, is poured the secretion of the vasculum aberrans or appendix ; which seems
like a testis in miniature, closely resembling a single lobule in its structure. Its special func-
tion is unknown.

b. The Testicles originate, in the Embryo, from the lower part of the Corpora Wolffiana
(§ 839, c) ; arising from their lower and inner sides, whilst the Kidneys spring from their
upper and outer parts. They make their first appearance in the Chick about the fourth day,
as delicate striae on the Wolffian bodies ; and at this period no difference can be detected be-
tween the Testes and the Ovaria, which originate in precisely the same manner. Like
the kidneys, the germ-preparing organs increase in proportion with the diminution in the
temporary structures , at first their efferent ducts open into those of the Wolffian bodies, but
they are subsequently separated by the formation of a partition, like that which separates
the rectum from the cloaca. In the Human embryo, the rudiments of the sexual organs, —
whether testes or ovaria, — first present themselves soon after the kidneys make their appear-
ance, that is, towards the end of the seventh week. They are at first much prolonged, and
seem to consist of a kind of soft, homogeneous blastema, in which the tubular structure subse-
quently developes itself. The Ovary at that period has the same aspect and texture; but its
subsequent course of development is different. The Testis gradually assumes its permanent
form ; the epididymis appears in the tenth week ; and the gubernaculum, (a membranous
process from the filamentous tissue of the scrotum, analogous to the round ligament arising
from the labium, and attached to the ovary, of the female,) which is originally attached to
the vas deferens, gradually fixes itself to the lower end'of the testis or epididymis. The
Testes begin to descend at about the middle period of pregnancy ; at the seventh month
they reach the inner ring ; in the eighth they enter the passage ; and in the ninth they usually
descend into the scrotum. The cause of this descent is not very clear. It can scarcely be
due merely, as some have supposed, to the contraction of the gubernaculum; since that does
not contain any fibrous structure, until after the lowering of the testes has commenced. It
is well known that the testes are not always found in the scrotum at the time of birth, even
at the full period. Upon an examination of 97 new-born infants, Wrisberg found both testes
in the scrotum in 67, — one or both in the canal in 17, — in 8 one testis in the abdomen, — and
in 3 both testes within the cavity. Sometimes one or both testes remain in the abdomen
during the whole of life ; but this circumstance does not seem to impair their function. This
condition is natural, indeed, in the Ram.

867. The fluid secreted by the Testes is thick, tenacious, and of a greyish
or yellowish colour. It is mingled, during or before emission, with ildid
secreted by the Prostate, Cowper's glands, &,c. ; and it cannot, therefore, be
obtained pure, but by drawing it from the testicle itself; hence no accurate
analysis can be made of it in the Human subject. The so-called Spermatozoa
and Seminal Granules, which form the most important and characteristic parts
of the Semen, are so intimately connected with the Reproductive Function,
that they will be more appropriately described under that head. It maybe here
remarked, however, that they correspond most exactly with other Secretions,
in their mode of production ; for, as will be shown hereafter, they are elaborated
by cells, which lie within the tubuli, and which rupture so as to set them free,
when they are mature (§ 902). The peculiar odour which the Semen pos-
sesses, does not appear to belong to the proper spermatic fluid; but is probably
derived from one or other of the secretions with which it is mingled. The
chemical analyses which have been made of this fluid are all defective, inas-
much as they do not distinguish the real secretion of the testes from the mucus,
prostatic fluid, &c., with which it is mingled. It may be stated, however, that

CUTANEOUS AND MUCOUS FOLLICLES.

661

it has an alkaline reaction, and contains albumen, with a peculiar animal prin-
ciple termed Spermatine ; and also saline matter, consisting chiefly of muriates
and phosphates, especially the latter, which form crystals when the fluid has
stood for some little time.

8. — Cutaneous and Mucous Follicles,

868. Having now described the structure F'1S- 262.

and functions of the principal Glands, which
are composed of aggregated masses of secret-
ing cells or tubes, we may proceed to those in
which the glandulse are more scattered, but
are still, in their aggregate amount, of sufficient
importance to claim particular notice. This
is especially the case in the Skin, and its in-
ternal prolongations, forming Mucous Mem-
branes. The Skin is the seat of various secre-
tions ; for each of which it is provided with
special organs. Of these the most important
is the Perspiration; which is formed in small
glandular organs seated just beneath the cutis,
and diffused over the whole surface of the
body. The efferent ducts of these Glandulse
open by minute pores in the Epidermis, which
are seen in elevated lines on the skin of the
palm of the hand and the sole of the foot ; they
penetrate the epidermis rather obliquely, so
that a sort of little valve is formed by it, which
is lifted up by the excreted fluid as it issues.
The ducts pass through the Epidermis and
Cutis in a spiral direction; and then enter the
glands, which consist of the convolutions of
the ducts, more or less subdivided, on which
blood-vessels are distributed. Where the
Epidermis is thin, the canal is straighter.— On
the palm of the hand, the sole of the foot, and
the extremities of the fingers, the apertures of
the perspiratory ducts are visible to the naked
eye ; being situated at regular distances along
the little ridges of sensory papillae, and giving
to the latter the appearance of being crossed
by transverse lines. According to Mr. Eras-
mus Wilson,* as many as 3528 of these
elandulae exist in a square inch of surface on

- , , . , Sudoriferous Gland from the palm ol

the palm of the hand ; and as every tube, when the hand) magnified 40 diameters; 1,1,
straightened out, is about a quarter of an inch contorted tubes, composing the gland.

in length, it follows that, in a Square inch Of and uniting into two excretory ducts, 2,

skin from the palm of the hand, there exists a 2, which unite into one spiral canal, that
length of tube equal to 883 inches, or 73g feet. Perforate^ the epide™is at 3, and open-

rr,, ^ on its surface at 4; the gland is imbedded

The number of glandule in other parts of the in fat-vesicles, which are seen at 5, 5.
skin, is sometimes greater, but generally less

than this ; and according to Mr. Wilson, about 2800 may be taken as the
average number of pores in each square inch throughout the body. Now the

56

Practical Treatise on Healtby Skin, p. 42.

662

OF SECRETION.

[Fig. 263.

[Fig. 265.

Vertical section of the skin
and sweat-glands of the axilla;
— a. Layer of glands with their
ducts traversing*, the cutis and
cuticle, c. Small hair, d, d.
Portions of larger hairs.—
Magn. one and a half diam.]

[Fig. 264,

f

Sweat-gland and the commencement of its
duct :— a. Venous radicles on the wall of the
cell in which the gland rests. This vein anas-
lomoses with others in the vicinity, b. Capilla-
ries of the gland separately represented, arising
from their arteries, which also anastomose.
The blood-vessels are all situated on the outside
or deep surface of the tube, in contact with the
basement-membrane. — Magn. 35 diam.]

a. Vertical section of the cuticle from the heel,
detached by maceration. The epithelium of the
sweat-duct, continuous with the cuticle, has been
drawn out of the tube of basement-membrane, as
far as the gland, where it begins to be contorted.
The cavity of the duct is seen dilating as it enters
the cuticle, and then stretching up to the surface
through the epidermic lamince. The deep surface
of the duct is continuous with the surface of the
cavities in which the papillae are lodged. — Magn.
35 diameters.

b. Duct at its entrance into the cuticle. — More
highly magnified.]

number of square inches of surface, in a man of ordinary stature, is about
2500; the total number of pores, therefore, may be about seven millions;
and the length of the perspiratory tubing would thus be 1,750,000 inches, or
145,833 feet, or 48,611 yards ; or nearly 28 miles.

869. The Secretion of fluid by these Glands is continually taking place ;
but this fluid, being usually carried off in the form of vapour as fast as it is
separated, does not accumulate and become sensible. If, however, from the
increased amount of the secretion, or from the* condition of the surrounding
air, the whole fluid thus poured out should not evaporate, it accumulates in

CUTANEOUS AND MUCOUS FOLLICLES. 663

minute drops upon the surface of the skin. Thus the Sudoriferous excretion
may take the form either of sensible or insensible transpiration ; the latter
being constant, the former occasional. It is difficult to obtain enough of this
secretion for analysis, free from the sebaceous and other matters which accu-
mulate on the surface of the skin ; and its character can only, therefore, be
stated approximately. It has usually an acid reaction, which seems due to
the presence of acetic acid ; and to this, or to lactic acid, we are probably to
attribute the sour smell which it has, especially in some disordered states of
the system. The proportion of solid matter, according to Anselmino, varies
between 5 and 12'5 parts in 1000. The greatest part of it consists of animal
matter, which is apparently a proteine-compound in a state of incipient decom-
position. The remainder consists of saline compounds ; of which the chlorides
of potassium and sodium appear to be pretty constantly present ; whilst the
muriate of ammonia, free acetic acid, and acetate of soda, have also been said
to occur in it. — The proportion of these ingredients would probably be found
larger in the fluid of the Sudoriferous glands, if we had the means of collecting
it separately ; for of the whole fluid which passes off" from the surface of the
skin, only a small proportion can be properly said to be secreted by the Sudo-
riferous glands ; the greater part, under ordinary circumstances, being the
product of simple Evaporation, by which, of course, nothing but pure watery
vapour is dissipated.

870. The entire amount of fluid which is insensibly lost from the Cutaneous
and Pulmonary surfaces, is estimated by Seguin at 18 grains per minute ; of
which 11 grains pass off by the skin, and 7 by the lungs. The maximum
loss by Exhalation, cutaneous and pulmonary, during twenty-four hours, (ex-
cept under very peculiar circumstances,) is 5 Ibs. ; the minimum 1§ Ib. It
varies greatly, according to the condition of the atmosphere, and that of the
body itself. The manner and degree in which it is influenced by atmospheric
conditions, will be better discussed under the head of. Animal Heat (§ 897);
since this influence has a most important effect in the regulation of the tem-
perature of the body. As already pointed out, the Urinary excretion is in
great degree vicarious with it, in regard to the amount of fluid discharged. —
the urine being more watery in proportion as the Cutaneous Exhalation is
diminished in amount, — and vice versa (§ 840). But we are also to look at
these two excretions as vicarious, in regard to the deportation (or getting rid)
of the products of the waste of the system. The share which the Skin has
in this office has probably been generally under-rated. There is reason to
believe that at least 100 grains of azotized matter are excreted from it daily;
and any cause which checks this excretion, must throw additional labour on
the kidneys, and will be likely to produce disorders of their function.

871. The Exhalant action of the Skin is influenced by general conditions of
the vascular and nervous systems; which are as yet ill understood. It is quite
certain, however, that through the influence of the latter the secretion may
be excited or suspended ; this is seen on the one hand in the state of syncope,
and the effects of depressing emotions, especially fear, and its more aggravated
condition, terror ; and on the other in the dry condition of the skin during
states of high nervous excitement. It is very probable that, in many forms of
fever, the suppression of the perspiration is a cause, rather than an effect, of
disordered vascular action ; for there are several morbid conditions of large
parts of the surface, in which the suppression of the transpiration appears to
be one of the chief sources of danger, having a tendency to produce congestion
and inflammation of internal organs. From the recent experiments of Dr.
Fourcault,* it appears that complete suppression of the Perspiration in animals.

* Comptes Rendus de 1'Academie, May, 1844; and Lancet, June 8, 1S44.

664

OF SECRETION.

by means of a varnish applied over the skin, gives rise to a state termed by
him Cutaneous Asphyxia ; which is marked by imperfect arterialization of the
blood, and considerable fall of temperature (§§ 768, 891); and which, as it
produces death in the lower animals, would probably do the same in Man.
A partial suppression by the same means gives rise to Febrile symptoms, and
to Albuminuria.

872. The Skin is likewise furnished with numerous Sebaceous glands, also
distributed more or less closely throughout the whole surface of the body. By
these an Adipose secretion is poured forth, which keeps, the skin from being
dried and cracked by the action of the sun and air. It is especially abundant
in the races which are formed to inhabit warm climates. Some of these glan-

[Fig. 266.

Sebaceous glands, showing their size and relation to the hair-follicles : — A and B from the nose ; c from
the beard. In the latter the cutis sends down an investment of the hair-follicle. — JMagn. IS diam.]

dulre are simple follicles lined with secreting cells, and contained in the sub-
stance of the Skin itself; whilst others are formed out of similar follicles, more
or less branched, elongated, and convoluted ; and others, again, seem to con-
sist of little else than clusters of Fat cells, from one part of which an excretory
duct arises: these last commonly open into the passage, by which the Hair
makes its way outwards. Besides these there are other glands situated in
particular parts of the body, and having special functions. Such are the Ceru-
minous glands situated beneath the skin of the auditory meatus ; these are
closely analogous in form to the sudoriferous glands, as the accompanying
figure shows ; but their secretion is very different, being nearly solid, and
having somewhat of a resinous character. — A peculiar series of glandular,
bearing a general resemblance to the sudoriferous glands, but of larger size,
have lately been discovered by Prof. Homer* and M. Robin to exist in the
human axillae ; where they probably serve to secrete the peculiar odorous
matter, characteristic of that part. In many of the lower animals, such glands
may be detected, having a structure of considerable complexity. The odorous
secretion would appear to be elaborated from the blood by a simple chemical
change ; for it may be made evident even in blood that has been dried up, by

* [Am. Journ. Mecl. Science, Jan. 1840, p:*13.]

CUTANEOUS AND MUCOUS FOLLICLES.

Fis. 267.

6C5

Cutaneous glands of external meatus auditorius.— 1. Section of the skin, magnified three diameter? :
2, 2, hairs ; 3, 3, superficial sebaceous glands ; 1, 1, larger and deeper-seated glands, by which the ceru-
men is secreted.— 2. A hair, perforating the epidermis at 3 ; 1,1, sebaceous glands, with their excretory
ducts 2,2; 4, base of the hair, in its double follicle 5,5. — 3. Cerumen-gland, formed by the contorted
tube, 1, 1, of the excretory duct, 2; 3, vascular trunk and ramifications.— The last two figures highly
magnified.

[Fig. 268.

Cutaneous Follicles or Glands of the Axilla, magnified one-third.— (Homer.)]

treating it with sulphuric acid. This aromatic principle differs sufficiently in
the blood of different animals, to enable a person with a delicate sense of
smell to determine from what animal any specimen has been procured ; and
this fact has been applied with success to juridical investigations. It has even

56*

066

OF SECRETION.

been stated that the blood of the human Male may be distinguished from that
of the Female, by its more powerful odour; but this does not appear to be
the case, — at least with sufficient certainty for medico-legal inquiries.*

873. Besides the crypts or follicles, which have been spoken of as gene-
rally existing in Mucous Membranes (§ 178), there exist, in that of the Intes-
tinal Canal, numerous glandulae in various parts, for the elaboration of par-
ticular secretions. In the Stomach, for example, a large number of these
secreting organs, some of them possessing rather a complex structure, are
included in the thickness of its walls, composing, indeed, the greater part of
the mucous membrane. If this be divided by a section perpendicular to its
surface, it is seen to be made up of a number of tubuli closely applied to each
other, their blind extremities being in contact with the submucous tissue, and
their open ends being directed towards the cavity of the stomach. In some
situations, these tubuli are short and straight ; in other parts they are longer,
and present an appearance of irregular dilatation or partial convolution. This,
indeed, is their usual character, especially towards the cardiac orifice of the

Fipr. 269.

Section of the coats of
the stomach, near the py-
lorus, showing the gastric
glands, 1, magnified three
times. 2, magnified twenty
limes.

[Fig. 270.

A

A. Horizontal section of a stomach-cell, a
little way within its orifice, a. Basement-
membrane, b. Columnar epithelium. All
but the centre of the cavity of the cell is oc-
cupied by transparent mucus, which seems
to have oozed from the open extremities of
the epithelial particles, c. Fibrous matrix
surrounding and supporting the basement-
membrane, d. Small blood-vessel.

B. Horizontal section of a set of stomach
tubes proceeding from a single cell. The
letters refer to corresponding- parts. The
epithelium is glandular; the nuclei very
delicate ; the cavity of the tubes very small,
and in some cases not visible.

From the dog, after twelve hours' fasting.
Magnified 200 diameters.]

* See Annales d'Hygiene, vol. i. pp. 207 and 548; vol. ii. p. 217; vol. x. p. 100, &c.

CUTANEOUS AND MUCOUS FOLLICLES.

667

stomach. On the other hand, towards the pyloric extremity, they have a
much more complex structure. Betweeen the tubuli, blood-vessels pass up
from the sub-mucous tissue, and form a vascular net-work on its surface.
From the examination of these horizontal sections of the mucous membrane
at various depths, Dr. Todd* has ascertained that the tubuli are arranged in
bundles or groups, surrounded and bound together by a fine areolar mem-
brane ; the size of the bundles, and the number of tubules contained in them,
vary considerably. The tubes do not, in general, open directly upon the
surface, but into the bottom of small depressions or pits, which may be seen
to cover the membrane. These pits are more or less circular in form, and
are separated from one another by partition-like elevations of the membrane,
which vary in depth ; and sometimes even by pointed processes, that have
been mistaken by some anatomists for villi. The diameter of these pits
varies from about l-100th to l-250th of an inch; it is always greatest near

[Fig. 271.

Fig. 272.

[Fig. 273.

Portion of the mucous
membrane of the stomach,
showing entrances to the
secreting tubes, in pits
upon its surface.

Vertical section of a stomach cell, with it§
tubes : A in the middle region, B in the pyloric
region, a a. Orifices of the cells on the inner
surface of the stomach, b b. Different depths at
which the columnar epithelium is exchanged
for glandular, c. Pyloric tube, or prolonged
stomach cell. d. Pyloric tubes, terminating
variously, and lined to their extremities with
sub-columnar epithelium.

From the dog, after twelve hours' fasting.
Magnified 200 diameters.]

A. Inner surface of the stomach, showing
the cells after the mucus has been washed
out. Magnified 25 diameters.

B. Columnar epithelium of the inner sur-
face and cells of the stomach : — a. Free
ends of the epithelial particles, seen on
looking down upon the membrane, b. Nu-
clei visible at a deeper level, c. The free
ends seen obliquely, d. Deep or attached
ends of the same. The oval nuclei are seen
near the deeper ends.

From the dog. Magnified 300 diameters.]

* Gulstonian Lectures on the Physiology of the Stomach, in Medical Gazette, 1839.
See also Dr. Sprott Boyd's Inaugural Dissertation on the Mucous Membrane of the Stomach,
in Edinb. Med. and Surg. Journal, vol. xlvi.

068

OF SECRETION.

[Fig. 274.

the pylorus. When the surface of the membrane, cleansed from mucus and
epithelium-scales, is examined with a sufficient magnifying power, it is seen
that from three to five perforations exist in the bottom of each pit ; and these
are the openings of the secreting tubes. The Gastric fluid, elaborated by this
apparatus, having been already made a subject of special consideration (§ 664)
need not be here described.

874. The whole Mucous sur-
face of the Intestinal canal is fur-
nished with glandular follicles of
a very similar character; of which
some approach those of the sto-
mach in complexity of structure;
whilst others evidently corre-
spond with the crypts of ordinary
Mucous Membrane. An innu-
merable multitude of pores are
easily seen, by the aid of a sim-
ple lens, to cover the whole in-
ternal surface of the large Intes-
tine ; and these are the entrances
to tubular follicles, closely resem-
bling those of the stomach, but
more simple in structure. Their
coecal extremities abut against the
sub-mucous tissue : towards the
end of the Rectum, however,
they are much prolonged, and
constitute a peculiar layer be-
tween the mucous and muscular
coats ; the tubes which are there
visible to the naked eye, being
erect, parallel, and densely crowd-
ed. These glands probably form
the peculiarly thick and tenacious
mucus of the large intestine. In
the small intestine, on the other
hand, the cceca are less deep and
their apertures are smaller. These
apertures are, for the most part,
situated around the bases of the
villi : in the fetus and newly-born child, they are so abundant as to be almost

A section of the Ileum, inverted so as to show the ap-
pearance and arrangement of the villi on an extended
surface, as well as the follicles of Lieberkiilm ; the whole
seen under the microscope. A close examination of this
cut will show a great number of black points in the
spaces between the projections of villi : these are the
follicles of Lieberkiihn.]

Fig. 275.

Fit:. 276.

One of the glandulrc majores sim-
plices, viewed from above at A, and
seen in section at B ; from the large
intestine.

Mucous coat of small intestines as
altered in fever; the follicles of Lie-
berktihn filled with tenacious white
secretion.

CUTANEOUS AND MUCOUS FOLLICLES.

669

[Fig. 277.

A section of Ihe small Intestine containing

in contact ; but in the adult, the intervals increase, so as to occupy more
space than the apertures. The glandulae of the small intestines have long
been known under the name of the follicles of Lieberkuhn ; they become
particularly evident (Fig. 275) when the mucous membrane is inflamed, being
then filled with an opaque whitish secre-
tion, which is absent in the healthy state.
— Besides the foregoing descriptions of
solitary glandulae, the Ccecum and the
lower part of the Rectum contain a num-
ber of simple and large follicles, which
produce slight rounded elevations on the
surface of the mucous membrane ; the
centre of each of these elevations is per-
forated by an aperture of the follicle ; and
around this are seen the orifices of the
tubular coeca, which closely envelope
the globular follicle (Fig. 270). These
seem most abundant where the largest
quantity of mucus is required. They
have been confounded with the glands of
Brunner ; but are rather analogous to the
solitary Peyerian glands, presently to be
noticed.

875. The true glands of Brunner are

chiefly situated in the Duodenum ; and some of the slands of Peyer' as shown under

they lie not in the mUCOUS but in the the '«°Pe- These glands appear to be
J . small lenticular excavations, containing, ac-

sub-mucous tissue, where they form a cording lo Boehm, a white, milky and rather

Continuous layer of white bodies SUr- thick fluid, with numerous round corpuscles of
rounding the whole intestine. Their various sizes, but mostly smaller than blood-
size, Unless diseased, is Scarcely that of Slobules- The meshes seen in the cut are the

a hemp-seed ; each consists of nume- ordinary tripe-like folds of the mucous coat,

V /. i • , and not the venous texture spoken ot under the

rous minute lobules, of which the ducts foiiicies.]
open into a common excretory tube ;

and in the lobules may be distinguished the minute ramifications of these
ducts, with clusters of follicles forming acini, of which about six hundred
are computed 'to exist in each. Hence these glands
are of complex structure, much resembling that of the
Salivary glands and Pancreas, and entirely differing
from all the other glandulse of the walls of the ali-
mentary canal. Of the peculiar nature of their secre-
tion nothing is known.

876. The so called Peyerian glands constitute,
when aggregated together, large patches on the mucous
membrane of the small intestine, where they are
known as the glandulse agminatse ; and it is to
these alone that Peyer's name is usually applied.
Similar bodies, however, known as the glandulse
solitarise, exist separately in the lower part of the

small intestines ; where they have been confounded with the glands of Brun-
ner, which do not extend beyond the commencement of the Jejunum. The
glands of Peyer, when examined in a healthy mucous membrane, present the
appearance of circular white slightly-raised spots, about a line in diameter,
over which the membrane is usually less set with villi, and very often entirely
free from them. Each of these white spots, of which a large number are
contained in the agminated glands, is surrounded by a zone of openings like

278.

Conglomerate gland of
Brunner, from commence-
ment of duodenum; mag-
nified a hundred limes.

670

OF SECRETION.

Fig. 279.

Portion of one of the patches of Peyer's glands,
from the end of the Ileum, highly magnified j the villi
are also displayed.

those of the follicles of Lieberkiihn, which lead (as do those) into tubular
co3ca. On rupturing the surface of one of the white bodies, there is found a

cavity, corresponding in extent with
the spot, and of considerable extent ;
but this cavity has usually no ex-
cretory opening, and the tubular fol-
licles by which it is surrounded,
have no connection with it. In its
interior is found a grayish-white
mucous matter, interspersed with
cells in various stages of develop-
ment. There is reason to believe
that, at a certain period of the ex-
istence of each of these glandulae,
an excretory orifice is formed, by a
sort of dehiscence in the wall of the
cavity ; and that, through this, the
product secreted by the contained
cells may be poured forth. Each
of them may be compared, on this
view, to one of the ultimate folli-
cles, which constitutes the secreting
portion of any one of the larger
glands (§ 823) ; the only difference being, that the latter are situated at the
extremities of the ramifying ducts, by which their product is collected and
conveyed away ; whilst the former pour their secretion at once into the
cavity of the intestine. — The membrane which covers in the cavity is ex-
tremely thin, and is very liable to be destroyed by ulceration ; hence it is, that,
after inflammation of the enteritic mucous membrane, the patches of Peyer
are often to be seen as a congeries of shallow open cells or follicles.

877. Although the particular use of each variety of the Intestinal glandulfe
cannot yet be determined, there seems little doubt that their general function
is, to eliminate from the Blood those putrescent matters which would other-
wise accumulate in it; whether as one of the results of the normal ivaste of
the system, or as produced by various morbific causes, Avhich act as ferments,
and thus occasion an unusual tendency to decomposition in the solids and
fluids of the body. That the putrescent elements of the feces are not imme-
diately derived from the food taken in, so much as from the excreting action
of the Intestinal Glandnlae, appears from this consideration, among others ; —
that faecal matter is still discharged, even in considerable quantities, long after
the intestinal tube has been completely emptied of its alimentary contents.
We see this in the course of many diseases, when food is not taken for many
days, during which time the bowels have been completely emptied of their
previous contents by repeated evacuations; and whatever then passes, in ad-
dition to the biliary and pancreatic fluids, must be derived from the intestinal
walls themselves. Sometimes a copious flux of putrescent matter continues
to take place spontaneously ; whilst it is often produced by the agency of
purgative medicine. The "colliquative diarrhrea," which frequently comes
on at the close of exhausting diseases, and which usually precedes death by
starvation, appears to depend, not so much upon a disordered state of the
intestinal glandulae themselves, as upon the general disintegration of the solids
of the body, which calls them into extraordinary activity for the purpose of
separating the decomposing matter.

GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 671

CHAPTER XVI.

GENERAL REVIEW OF THE NUTRITIVE PROCESSES. ANIMAL HEAT.

1.— Review of the Nutritive Processes, with Practical Applications.

878. THE detailed survey which has been now taken, of the different
Functional operations concerned in maintaining the life of the individual,
may suggest to us some general views that have important practical applica-
tions. In the first place, it has been shown, that the province of the Animal
is not to combine Inorganic elements into Organic compounds, fit to be ap-
plied to the purposes of Nutrition; but to use those which are prepared for
it by the Plant. The nutritive materials thus obtained may be divided into
two great classes, the azotized and the non-azotizecL The former have been
shown (§ 642) to be so nearly identical in composition with the proximate
principles of which the Animal body is composed, that no great amount of
chemical transformation can be required to prepare them for being appropri-
ated by it. The latter are altogether different in character; and whether or
not they can, by any process of transformation, be made subservient to the
nutrition of the Azotized tissues, it is unquestionable that their ordinary use
is to serve as the materials for the Respiratory process, and for the mainte-
nance of Animal heat. The demand for these several articles in the system
will depend, in regard to the former, upon the amount of Tissue which has
been disintegrated and needs repair; and with respect to the latter, upon the
amount of Heat which it is necessary to generate, to keep up the tempera-
ture of the body to its regular standard. Hence a highly-azotized diet is
most required when the greatest amount of muscular exertion is being used;
whilst a diet, in which non-azotized substances are predominant, will serve
to sustain the Animal Heat in a cold atmosphere. The adjustment of the
diet to the wants of the system, is a matter of the greatest importance for
the preservation of health. If too great an amount of azotized food be in-
gested, and the superfluity be thrown upon the Kidneys to eliminate (§ 850),
disorder of the Urinary Secretion is almost certain, sooner or later, to mani-
fest itself. The quantity of Lithic Acid, in particular, undergoes considerable
increase; and, by the removal of its bases through the increased production
of other acids, it is very likely to pass out in an insoluble state, giving rise to
Gravelly deposits. Or it may accumulate in the Blood, and there combine
with Soda; forming a salt which is deposited in various parts (especially in
the neighbourhood of the smaller joints), forming concretions, which are com-
monly known under the name of "chalk-stones." These deposits usually
take place, however, after severe attacks of a peculiar Inflammation, known
as Gout; and this inflammation seems to be connected with the accumulation
of Lithate of Soda in the Blood. — Over this disease a careful regulation of
the diet exercises a powerful control. A patient affected with the " Lithic
Acid diathesis," may palliate, if not altogether cure his disorder, by rigorously
abstaining from the use of any superfluous amount of azotized compounds
as food ; and by subsisting as much as possible upon those belonging to the
Farinaceous group. It is by no means every case, however, that is capable
of alleviation by treatment of this sort ; in fact, it can seldom be rigorously

672 GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

enforced, except in early life, or at any rate when the constitution is unbroken
by disease or intemperance. Not unfrequently it will be found, that the per-
sistence in a diet of this kind, occasions so much disorder of the stomach, as
to be quite out of the question. — On the other hand, in the " Strumous dia-
thesis," there would seem to be a low condition of those vital powers, which
are concerned in the conversion of the Albuminous materials prepared by
the Digestive process, into the Fibrinous matter which is ready for assimila-
tion; so that, by a perversion of the ordinary nutrient actions, Albuminous
Tubercle is deposited in the interstices of the tissues, instead of these tissues
being themselves regenerated by Organizable Fibrine ; and the same may
take place in a more rapid manner, in consequence of that disturbance of the
nutrient processes, which is known in healthy constitutions as Inflammation
(§ 802). It is obvious, then, that the treatment of the Strumous Diathesis
should be directed towards the invigoration of the general powers of the sys-
tem ; and although, when disease of the Chest has once established itself, a
warm moist atmosphere may be necessary as a preventive of inflammatory
affections, it is a great mistake to imagine that such a plan is applicable to
those in whom there is merely a Strumous predisposition ; for this should be
combated by such means as are calculated rather to brace than to relax the
system, — especially out-door exercise, a nutritious diet in which easily-digested
proteine-compounds should predominate, and a dry and well-ventilated habi-
tation. There can be no doubt that the Tuberculous Cachexia is encouraged,
and developed, by injudicious management during the early ages of life, in
many cases where it might have been avoided.*

879. Equally important is the regulation of the diet, in regard to its non-
azotized constituents. If these are in excess, the elimination of them from
the Blood falls especially upon the Liver (§ 836) ; and a continued excess
gives rise to disorders in its function, which a diminution in the quantity of
Farinaceous or Oleaginous matter ingested would prevent or cure. This is
especially liable to happen to Europeans proceeding to warm climates ; who
are not warned by their decrease of appetite, that there is no longer a necessity
for the same supply ; but force themselves to eat much more than they have
any real occasion for. — There is a very remarkable condition of the system,
in which there is a tendency to the presence of a large amount of Sugar within
the vessels ; either through the absence of power to convert that which has
been taken in ; or through the actual production of that compound, as a result
of the waste of the system. We have seen that Sugar may be detected in
the Serum of healthy blood, drawn soon after a meal; but that it soon becomes
untraceable, — probably in consequence of its being carried off by the respi-
ratory process (§ 697). In the disease termed Diabetes, or the " saccharine
diathesis," there is a much larger amount of Sugar in the Blood : and this
appears to be constantly present, as if, from some cause, its elimination by
the usual channel were retarded. The Sugar makes its appearance, also, in
the Urine ; the Kidneys taking-on the unusual office of separating this com-
pound, that it may not accumulate in the Blood. — Some late researches on
the exclusive employment of azotized principles as articles of diet, in the
treatment of the Saccharine diathesis, have given very favourable results. The
plan was long since proposed by Dr. Hollo ; and when the diseased condition
lias been uncomplicated by other maladies (as is not unfrequently the case),
the rigorous enforcement of such a diet has been attended with success in
numerous instances. One of the greatest difficulties in the application of the
system, however, has arisen from the longing which the patients experience

* Sec the excellent works of Sir James Clark, in which the importance of Hygienic treat-
ment is strongly insisted on.

GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 673

for Vegetable food ; since this tempts them to gratify their appetites, to the
complete prejudice of the remedial system, — a very small amount of farina-
ceous matter being sufficient to cause the re-appearance of the Sugar, after it
had seemed to be entirely got rid of. It has been proposed, however, by M.
Bouchardat to gratify this longing to a certain degree, by allowing the use of
bread made of wheaten flower, from which nearly all the Fecula has been
separated, — the Gluten only being left, with such a small amount of Fecula
as may serve to make it rise in fermentation ; so that it is as free from un-
azotized constituents, as the average of animal substances. This plan has
been very successfully practiced; having frequently kept the disease in com-
plete check, where, from the advanced period of life, the duration of the
morbid state, and other circumstances, a perfect cure could not be reasonably
expected.

880. From what has been stated in Chap. xii. respecting the nature of the
Function of Circulation, it is evident that primary disorders of that function
are not nearly so frequent as they are ordinarily supposed to be ; and that
the proximate cause of morbid phenomena is seldom to be found in them.
By the action of the Heart and Blood-vessels, the nutrient fluid, which has
been prepared from the alimentary materials submitted to the digestive appara-
tus, is conveyed to the tissues which it is to nourish ; but the true process of
Nutrition is independent of this, and may take place after the motion of the
fluid has ceased, just as it commences before any movement shows itself.
For the tissue which exists in the Embryo during the early period of its de-
velopment, and also in any newly-forming part, is destitute of vessels, consist-
ing only of cells ; and these grow and reproduce themselves at the expense
of the nutritive materials supplied to them from without, just as does the
whole mass of a Cellular Plant. Moreover it has been shown (§ 740), that
the activity of the nutrient processes has much to do with the movement of
the fluid through the smaller vessels, and is a cause rather than a consequence
of it. If the action of the Heart cease, the whole circulation must obviously
come to a stand ere long; but in many animals the Capillary movement may
continue for some time after the general circulation has been checked; and,
so long as blood is supplied to the parts, so long may their nutrition continue,
provided other circumstances be favourable. It is unquestionably true, that
the cessation of the Circulation is usually the immediate cause of Death; and
that, when the suspension is permanent, the loss of the vitality of the system,
considered both as a whole, and as made up of distinct parts, is a necessary
consequence. But still, we find that the cause of this cessation seldom origi-
nates in the Circulating apparatus itself; and in general, a disturbed state of
the Circulation is to be looked upon rather as a result, than as a cause, of
diseased action. An extreme case of such a disturbance, which, when suffi-
ciently prolonged, is attended with fatal results, is to be found in Asphyxia ;
in which the cessation of the action of the Lungs induces a stagnation of the
Blood in their capillaries ; and as, in warm-blooded animals, the whole cur-
rent of Blood has to pass through the Lungs, before proceeding again to the
system, a total suspension of the Circulation necessarily results from this inter-
ruption (§§ 738 and 779). Now if we take this (which it appears reasonable
to do) as a type of a great number of morbid conditions of different organs,
we are led to see why a serious disturbance of the movement in any one part
should affect the entire circulating apparatus, and should thus influence its
flow through almost every other organ. There are no other organs, however,
in which a stagnation can be so serious as in the Lungs; since there are none
through which the whole current flows. The Liver ranks next in importance,
since all the venous blood collected from the Chylopoietic viscera passes
through it ; and every practical man is aware how frequently derangement of
57

674 GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

the circulation through the Liver, originating in an unhealthy state of the gland
itself, is a cause of serious disorders in the abdominal viscera. — Minor irregu-
larities in the Circulation, in various parts, not unfrequently become causes of
serious inconvenience. Thus, few conditions are more common, especially
amongst persons of active minds but inert habits, than undue determination of
blood to the Head, conjoined with torpor of the circulation through the Skin,
especially that of the extremities, which are ordinarily cold. The obvious
indication here is, to endeavour to restore the balance of the Circulation ; and
excitement of the flow of blood through the Skin, by frictions, moderately-
stimulating applications, exercise, &c., will commonly prove of great utility.

881. There are many disorders commonly regarded as affections of the
Circulation, which evidently consist in reality of a morbid alteration in the
Nutritive processes : among these there can be little doubt that we are to rank
local Determinations and Congestions, which result from an exalted or dimi-
nished activity of the formative actions ; and Inflammation, in which these
actions are perverted. Much has been said and written, to very little purpose,
respecting the essential nature of this process ; it has been attributed by some
to disordered action of the vessels, and by others to an injurious impression
on the nerves, — the fact, that Inflammation may occur in tissues which con-
tain neither vessels nor nerves, having been entirely overlooked. The only
view of the character of Inflammation that seems likely to account for its
phenomena, is that which regards it as essentially consisting in a disturbance
of the due relation between the living Tissue and the nutrient materials
contained in the Blood ; in other words, as an abnormal form of the ordinary
nutritive process (§§ 802 — 806). A similar remark may be made, in regard
to those productions formerly termed "Heterologous transformations" of
tissue ; which are rather to be regarded as new growths, that have appro-
priated the nutriment designed for the support of the proper tissues, and have
therefore become developed at the expense of these. It is quite as absurd
to attempt to account for the growth of Scirrhus, Carcinoma, &c., by any
peculiar action of the vessels of the part, as it would be to attribute the secre-
tion of fatty matter by the cells of one tissue, or of phosphate of lime by
those of another, to the peculiar distribution of their vessels. The progress
of research obviously leads to the conclusion, that in every part of the living
body there is an inherent and independent vitality, which enables it to grow
and maintain its normal structure and constitution, so long as it is supplied
with the requisite materials; and that changes in the character of the tissue
can be referred to nothing else than to alterations in its properties, resulting
from external agencies, or to alterations in the materials supplied for its
renewal. Of these two morbific causes, the latter is undoubtedly the most
frequent ; and the tendency which is now gaining ground, to seek in the Blood
for indications of pathological changes, when there is no obvious general dis-
turbance of the system, will probably lead to a greatly-increased knowledge
of the real nature of diseased states ; in spite of the opposition which any
return to the Humoral Pathology is sure to excite, in the minds of those who
reirurd it as an exploded and pernicious system.

882. The Sympathy between different parts of the system, which espe-
cially manifests itself in the tendency to simultaneous affection with the same
Disease, affords an excellent illustration of this principle. Of those Sympa-
thetic actions, which result from the Nervous connections of the various
organs, this is not the place to speak ; since we are at present concerned
with those perversions of the Nutritive processes, which give rise to Inflam-
matory and other diseases. Where a certain tissue, throughout the body, is
similarly affected, there is strong reason to presume that the morbific cause
is conveyed to it in the Blood ; this is the case, for example, with regard to

GENERAL REVIEW OF THE NUTRITIVE PROCESSES. 675

the Mucous membranes, which all manifest a tendency to Inflammation, when
Arsenic has been received into the system : and certain forms of the disease
commonly termed Influenza, are marked by a similar disposition. The same
may be said in regard to Inflammation of the Fibrous membranes, Areolar
tissue, Serous membranes, and other structures. It has been considered a
sufficient account of these consentaneous affections, to say that they result
from Sympathy, — a mere verbal quibble, which explains nothing. If, on the
other hand, we regard the disease as a perversion of the ordinary processes
of Nutrition, Secretion, &c., and as dependent upon an abnormal condition of
the Blood (such as is induced by the introduction of a poison into it), the
rationale of the sympathetic disturbance becomes apparent; — since all the
tissues of the same kind will of necessity be similarly affected, although some
local cause may occasion one to suffer more severely than another. In the
ingenious paper by Dr. W. Budd, already referred to (§ 785), the perfect cor-
respondence, which not unfrequently manifests itself between the diseased
actions on the two sides of the body, is adduced in support of the same view,
to which it is made to afford very striking confirmation. The fact that this
kind of Sympathy not unfrequently manifests itself between tissues having
an analogous structure, but very different function, is another argument in
favour of the same view ; of this fact, the sympathy of which every practical
man is aware, between the Skin and Mucous Membranes, is a very good
example. The sympathy of the different tissues forming any individual organ,
by which disease in one becomes a cause of disorder in the rest, is, however,
to be very differently explained. We have examples of this in Inflammatory
affections of the Mucous membranes, which usually extend themselves to the
remaining constituents of the organs of which they form a part; and in those
of the Serous membranes, which almost always follow inflammation of the
organs they invest. Here the local disturbance of one part appears sufficient
to account for the extension of it to another, that is closely connected with it
by vessels and nerves; this has been termed the Sympathy of Contiguity.
The Fibrous membranes are less liable to be affected in this manner, than are
most other tissues; and the reason appears simply this, — that there is usually
less vascular connection between them and the adjacent parts, than there is
in the case of the Serous membranes. Hence the Fibrous membranes fre-
quently act as insulators, preventing the spread of disease to adjacent parts.
883. The general characters of the processes of Nutrition and Secretion
are so nearly allied, that what has been stated of the Pathological states of the
former, is nearly as applicable to those of the latter. Although it is unques-
tionable that disordered Secretion may result from a purely local cause, acting
on the solid tissue of the part affected, yet there is also increasing reason to
believe, that in a large number of cases, the abnormal character of the pro-
duct is in reality a result of the abnormal state of the Blood from which it
is separated; and that the organ itself is still performing a healthy function,
in separating from the blood that which would be injurious to it. This
leads us to refer such disorders to causes much more remote than those
which were formerly supposed to operate ; but they are undoubtedly nearer
the true ones. Such a view has been prosecuted by Dr. Prout in regard to
the abnormal conditions of the Urine, with great success; and there can be
little doubt that it is also applicable to the Biliary secretion, on the true
chemical nature of which there is scarcely yet an agreement among Chemists,
and whose pathological conditions, therefore, are, and must long remain,
comparatively obscure. It is obvious that, if the Assimilation of Nutritive
matter be in any respect wrongly performed, the products of the Decomposi-
tion of the Tissues (in which these excretions probably originate, § 819), must
also be different; and our remedial measures must often be directed, therefore,
not so much to the Secreting organ, as towards the previous operations.

676 GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

884. These considerations are of the highest importance in the treatment
of Disease ; the success of which will greatly depend upon the degree in
which the Physician follows the indications of Nature, instead of putting him-
self in antagonism to her course of operation. If we pay but a slight attention
to those phenomena which result from the introduction of poisons into the
system, we perceive that there is almost invariably an increased excretion of
some kind, which tends to eliminate them from the blood. Even where there
is no other obvious means for their removal, we can have little doubt that the
Respiratory function gives important aid in their separation ; when we keep
in view that from five to eight ounces of solid carbon, to say nothing of the
hydrogen, are thrown off from the lungs in the course of every twenty-four
hours. It is important to bear this circumstance in mind ; since it enables us
to understand how, if time be given, the system frees itself from such noxious
substances; and it points out the duty of the medical attendant to be rather
that of supporting the powers of the body by judiciously-devised means, and
of aiding in the elimination of the noxious matter by a copious supply of pure
air, than of interfering more actively to promote that which Nature is already
effecting in the most advantageous manner. We see the results of this ope-
ration in the case of Narcotic poisoning ; in which, if the Respiratory process
can be artificially kept up for a sufficient length of time, the powers of the
nervous system are gradually restored, even after what seemed to be their
complete and final cessation. — There can be no doubt that, in like manner,
the system makes an effort to rid itself of other noxious substances, the pre-
sence of which in the blood results from morbid processes going on in the
body itself, and which, if retained, would produce the most serious conse-
quences. Thus a copious discharge of Lithic acid by the Urine will frequently
avert or curtail an attack of Gout. The copious acid perspirations, which
occur in certain forms of Rheumatism, are the means by which the Lactic acid
(which seems to be the materies morbi of this disease) is separated from the
blood. And there can be no doubt that an attack of Diarrho?a often prevents
more serious disease, by removing an unusual accumulation of the elements
of bile, or by eliminating an undue amount of putrescent matter, the continued
presence of which in the circulating fluid would induce the most serious dis-
orders in the nervous system. — There can be no doubt that a due regulation
of the Excreting processes is one of the most important means, by which the
Physician can counteract the results of disordered actions in the system. They
may frequently require to be gently stimulated, in order to remove some mor-
bific elements from the blood. But it will be seldom that it will be desirable
to check them, even when apparently excessive, unless there be strong reason
to believe, that the excess proceeds from a disordered state of the organ itself,
produced by local causes only.

2. — Animal Heat.

885. All the vital actions that have been considered in the preceding pages,
require a certain amount of Heat as a condition of their performance ; and in
the more elevated tribes of animals, in which (for the very purposes of their
creation) a high degree of constancy and regularity is required in these actions,
there is a provision within themselves for the maintenance of their temperature
at'a certain standard. We shall inquire, in the first place, into the amount of
Heat thus generated by Man ; and then into the sources of its production.

880. Our present knowledge of the Temperature of the Human body under
different circumstances, is chiefly due to the investigations of Dr. J. Davy.
Much additional information may be expected, however, from inquiries which

ANIMAL HEAT. 677

are at present in progress. Dr. Davy's observations* have included 114 in-
dividuals of both sexes, of different ages, and among various races, in different
latitudes, and under various temperatures; the external temperature, however,
was in no instance very low, and the variations were by no means extreme.
The mean of the ages of all the individuals was 27 years. The following is
a general statement of the results, the temperature of the body being ascer-
tained by a thermometer placed under the tongue.

Temperature of the air 60° Average temperature of the body 91-28°

69° 98-15°

78° " " " " QS'S5°

79-5° " " 99-21°

" 80° 99-67°

82° 99-9°

Mean of all the experiments 74° Mean of all the experiments 100°

Highest temperature of air 82° Highest temperature of body 102°

Lowest temperature of air 00° Lowest temperature of body 96-5°

From this we see that the variations noted by Dr. Davy, which were evidently
in part the consequence of variations in external temperature, but which were
also partly attributable to individual peculiarities, amounted to 5§ degrees ; the
lower extreme would probably undergo still further depression, if the inquiries
were carried on in very cold climates. — The Temperature of the body may
be affected by internal as well as by external causes ; thus in diseases which
involve an accelerated pulse and an augmented respiration, the temperature is
generally higher than usual, even though a large portion of the lung may be
unfit for its function. This is often remarkably seen in the last stages of
Phthisis, when the inspirations are extremely rapid, and the pulse so quick as
scarcely to admit of being counted ; the skin, in such cases, often becomes
almost painfully hot. On the other hand, in diseases of the contrary character,
such as Asthma and the Asiatic Cholera, the temperature of the body falls,
sometimes, to the extent of 20 degrees. The following observations have been
made on this subject by M. Donne ;t it is much to be desired, however, that
fuller data could be collected on the subject. In a case of Puerperal Fever,
the pulse being 168, and the respiration 48 per minute, the temperature was
104°. In a case of Hypertrophy of the Heart, the pulse being 150 and the
respirations 34, the temperature was 103°. In a case of Typhoid Fever, the
pulse being 136, and the respirations 50, the temperature was 104°. And in
a case of Phthisis, the pulse being 140, and the respirations 62, the tempera-
ture was 102°. On the other hand, in a case of Jaundice, in which the pulse
was but 52, the temperature was only 96'40° ; but the same temperature was
observed in a case of Diabetes, in which the pulse was 84. The limited re-
sults of Mons. D.'s experiments, whilst they clearly indicate that a general
relation exists between the temperature of the body and the rapidity of the
pulse, also show that this relation is by no means invariable, but that it is
liable to be affected by several causes, of which our knowledge is as yet very
limited. Dr. Dunglison speaks of having frequently seen the thermometer at
106° in Scarlatina and Typhus ; and Dr. Edwards mentions a case of Tetanus,
in which it rose to HOf 4

* Phil. Trans., 1814; republished in Anatomical and Physiological Researches.

t Archives Generates, Oct. 1835 ; and Brit, and For. Med. Rev., vol. ii. p. 248.

J [An extensive series of observations has been made by M. Roger* on the temperature
of children in health and various diseases.

In nine examinations of infants from one to twenty minutes after birth, the temperature
(observed in these and in all the other cases, in the axilla), was from 99 95 to 95'45. Im-

* Arch. Gen. de Medecine, Juillet, Aout, &c., 1844.
57*

678 GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

887. Although there appears to be, for all species of animals, a distinct
limit to the variations of bodily temperature, under which their vital opera-
tions can be carried on, this limitation does not prevent animals from existing
in the midst of great diversities of external conditions ; since they have within
themselves the power of compensating for these, in a very extraordinary de-
gree. This power seems to exist in Man to a higher amount than in most
other animals; since he can not only support, but enjoy, life under extremes,
either of which would be fatal to many. In many parts of the tropical zone,
the thermometer rises every day through a large portion of the year to 110°;
and in British India it is said to be seen occasionally at 130°. On the other
hand, the degree of cold frequently sustained by Arctic voyagers, and quite
endurable under proper precautions, appears much more astonishing; by
Capt. Parry, the thermometer has been seen as low as — 55°, or 87° below
the freezing point ; by Capt. Franklin at — 58°, or 90° below the freezing
point ; and by Capt. Back at — 70°, or 102° below the freezing point. In both
cases, the effect of the atmospheric temperature on the body is greatly influ-
enced by the condition of the air as to motion or rest; thus, every one has
heard of the almost unbearable oppressiveness of the sirocco or hot wind of
Sicily and Italy, the actual temperature of which is not higher than has often
been experienced without any great discomfort, when the air is calm : and, on
the other side, it may be mentioned that, in the experience of many Arctic voya-
gers, a temperature of — 50° may be sustained, when the air is perfectly still,
with less inconvenience than is caused by air in motion at a temperature fifty
degrees higher. This is quite conformable to what might be anticipated on
physical principles.

888. Again, the degree of moisture contained in a heated atmosphere, makes
a great difference in the degree of elevation of temperature, which may be sus-

mediately after birth the temperature was at the highest; but it quickly fell to near the
lowest of those above stated; but, by the next day, it •was again completely or nearly what
it was before. The rapidity of the pulse and of respiration appeared to have no certain re-
lation to the temperature.

In thirty-three infants of from one to seven days old, the most frequent temperature was
98'6; the average was 98-75; the maximum (in one case only) 102'2; the minimum (also
observed only once) 96°'S. All the infants were healthy. The frequency of respiration
had no evident or constant relation to the temperature. A few of the infants were of a
weakly habit; their average was 97-7 : the others were strong, and their average tempera-
ture was 99°-534. The age of the infant (in this short period) had no influence on its
temperature ; neither had its sex, nor its state of sleep or waking, nor the period after
suckling.

In twenty-four children, chiefly boys, from four months to fourteen years old, the most fre-
quent temperature was above 98°'G ; the average was 98°'978, the minimum was98°'15;
the maximum 990-95. The average temperature of those six years old or under, was
98°-798 ; of those above six years old, 99°-158. The average number of pulsations in the
minute was in those under six years old 102; in those above that age 77; yet the tempera-
ture of the latter was higher than that of the former, or of younger infants. There was no
evident relation between the temperature and the frequency of respiration ; nor in a few
examinations, was the temperature affected in a regular way, by active exercise for a short
time, or by the stage of digestion.

As already said, in all the examinations from which these results were obtained, the
thermometer was held in the axilla; comparative examinations proved that the tempera-
ture of the axilla (though lower than that of internal organs), was higher than that of any
cither part of tho surface of the skin. Of the other parts examined, the warmest was the
abdomen, then in succession, the cavity of the mouth, the bend of the arm, the hands, the
feet; of which last, the average temperature, in four examinations, was only S7°'35. (These
results correspond sufficiently with those obtained by Dr. John Davy.)

In diseased states, (to the illustration of which the greater part of the memoir is devoted.)
the temperature of the skin in children may descend to 74°'3, and may ascend to 108°'5.
Its range of variation is therefore much greater than in adults, in whom M. Andral found it
to vary indifferent diseases not more than from 95° to 1U7°-G. — M. C.]

ANIMAL HEAT. 679

tained without inconvenience. Many instances are on record, of a heat of
from 250° to 280° being endured in dry air for a considerable length of time,
even by persons unaccustomed to a particularly high temperature ; and per-
sons whose occupations are such as to require it, can sustain a much higher
degree of heat, though not perhaps for any long period. The workmen of
the late Sir F. Chantrey have been accustomed to enter a furnace in which
his moulds were dried, whilst the floor was red-hot, and a thermometer in the
air stood at 350° ; and Chabert, the " Fire-king," was in the habit of entering
an oven, whose temperature was from 400° to 600°. It is possible that these
feats might be easily matched by many workmen who are habitually exposed
to high temperatures; such as those employed in Iron-foundries, Glass-
houses, and Gas-works. In all these instances, the dryness of the air facili-
tates the rapidity of the vaporization of the fluid, of which the heat occasions
the secretion by the Cutaneous glands; and the large amount of caloric which
becomes latent in the process, is for the most part withdrawn from the body,
the temperature of which is thus kept down. Exposure to a very elevated
temperature, however, if continued for a sufficient length of time, does pro-
duce a certain elevation of that of the body ; as might be expected from the
statements already made in regard to the variation in the heat of the body
with changes in atmospheric temperature (§ 886). In the experiments of
MM. Berger and Delaroche, it was found that, after the body had been ex-
posed to air of 120° during 17 minutes, a thermometer placed in the mouth
rose nearly 6 degrees above the ordinary temperature; it may be remarked,
however, that as the body was immersed in a close box, from which the head
projected (in order to avoid the direct influence of the heated air on the tem-
perature of the mouth), the air had probably become charged with the vapour
exhaled from the surface, and had therefore somewhat of the effects of a moist
atmosphere. At any rate, the temperature of the body does not appear to
rise, under any circumstances, to a degree very much greater than this. In
one of the experiments of Drs. Fordyce and Blagden, the temperature of a
Dog, that had been shut up for half-an-hour in a chamber of which the tem-
perature was between 220° and 236°, was found to have risen from 101° to
about 108°. MM. Delaroche and Berger tried several experiments on differ-
ent species of animals, in order to ascertain the highest temperature to which
the body could be raised without the destruction of life, by inclosing them in
air heated from 122° to 201°, until they died: the result was very uniform,
the temperature of the body at the end of the experiment only varying
in the different species between 11° and 13° above their natural standard:
whence it may be inferred, that an elevation to this degree must be fatal.
This elevation would be attained comparatively soon in a moist atmo-
sphere ; partly because of the greater conducting power of the medium ;
but principally on account of the check which is put upon the vapor-
ization of the fluid secreted by the skin. Even here, however, custom
and acquired constitution have a very striking influence ; for whilst the in-
habitants of this country are unable to sustain, during more than 10 or 12
minutes, immersion in a vapour-bath of the temperature of 110° or 120°, the
Finnish peasantry remain for half-an-hour or more in a vapour-bath, the tem-
perature of which finally rises even to 158° or 167°. — Accurate experiments
are yet wanting, to determine the influence of humidity on the effects of cold
air. From experiments on young Birds incapable of maintaining their own
temperature, of which some were placed in cold dry air, and others in cold air
charged with moisture, it was found by Dr. Edwards that the loss of heat was
in both instances the same; the effect of the evaporation from the surface in
the former case, being counter-balanced in the latter by the depressing influ-
ence of the cold moisture. This influence, the existence of which is a mat-

680 GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

ter of ordinary experience, is probably exerted directly upon the nervous
system.

889. Having thus considered the general facts which indicate the faculty
possessed by the living system, in the higher Animals, of keeping up its tem-
perature to an elevated standard, and of preventing it from being raised much
beyond it by any degree of external heat, we have next to inquire to what
this faculty is due. We shall be more likely to arrive at accurate results in
such an inquiry, the more comprehensive is our survey of the phenomena to
which it relates.*

a. The most recent experiments on the temperature of Plants (those made by MM. Bec-
querel and Breschet with the thermo-multiplier) have demonstrated, that in those parts in
which the vital processes are taking place with activity, a sensible amount of caloric is being
constantly evolved. The amount of this evolution of heat is generally very low, not more,
in fact, than a single degree (Fahr.) ; and as it does not more than counterbalance the effect
of the evaporation, which is continually taking place from the surface, there is no sensible
difference between the temperature of the plant and that of the surrounding air. At the
time of Flowering, however, a much greater degree of heat is generated in many plants,
especially in those in which a large number of flowers are crowded together, as in the case
of the Arum tribe: thus a thermometer placed in the midst of twelve spadixes has been
seen to rise to 121°, whilst the temperature of the air was only 06°. During the Germina-
tion of seeds, again, a considerable development of heat takes place; this, which is soon
carried off from a single seed, becomes very sensible when a large number are heaped toge-
ther, as in malting; the thermometer plunged into a heap of germinating barley having been
seen to rise to 110°.

b. These facts are of more importance than might appear at first sight ; for they indicate
unequivocally, that the source of the heat is to be looked for in the Organic functions, not in
those of Animal life. The evolution of Caloric has been attributed by many physiologists
to the Nervous system ; the influence which this system evidently possesses over the func-
tion, being mistaken for the efficient cause of it. As has been remarked on several former
occasions, however, — the fact that any change takes place in Vegetables, to the same degree
(under certain conditions,) with that in which it ever presents itself in Animals, is a suffi-
cient proof that it cannot be dependent upon nervous agency, although it may be influenced by
it. Moreover, it may be remarked that the production of Heat is an operation of an entirely
physical character, and that it may be referred to physical causes; whilst the operations in
which the Nervous system is concerned, are such as we cannot liken in any degree to physical
phenomena, and are of a purely vital character. — In our inquiry into the sources of the Heat
evolved by living beings, we are limited, therefore, to those which can operate in the Vege-
table kingdom ; and on examining into the phenomena which present any relation to this,
we are at once struck with the fact, that an absorption of Oxygen from the air, with an ex-
trication of Carlxmic acid, is continually taking place (constituting the true Respiratory pro-
cess of Plants, § 750); and that these changes occur with excessive activity, at the very
periods at which the evolution of Heat is most remarkable, — those, namely, of germination
and flowering. The quantity of Oxygen consumed by flowers is enormous — those of the
Arum Italicum having been found to convert 40 times their own bulk of that gas into Carbonic
acid, between the periods of their first appearance and their final decay ; and of this, the far
larger proportion is consumed by the sexual apparatus, which has been found to consume 132
times its own bulk of Oxygen in 24 hours. That this change is a condition necessary for the
production of Heat, is fully proved by the fact, that no caloric is evolved when the flowers
are excluded from the contact of Oxygen ; whilst the substitution of pure oxygen for atmo-
spheric air occasions the elevation of temperature to be more rapid and considerable than
usual."|" The same may be said of the heat liberated by seeds in the act of Germination : a
large amount of oxygen is absorbed, and of carbonic acid given out, during this process; and
the evolution of Heat may be easily shown to be as dependent upon this change, as in the
instance just quoted.

c. When the phenomena of Calorification in Animals are carefully examined, they are
found to harmonize completely with this view. Throughout the whole kingdom, an exact
conformity may be perceived between the amount of Oxygen consumed and of Carbonic

•acid given off, and the degree of Heat liberated. In the cold-blooded animals, whose tcm-

* This subject is more fully treated in the Author's Principles of General and Compara-
tive Physiology, §§ 548 — 567.

"j" See the very interesting experiments of MM. Vrolik and Vriese, in the Ann. des Sci.
Nat., N. S. Botan., torn, xi., p. 551.

DEVELOPMENT OF HEAT. 681

perature is almost entirely dependent upon that of the surrounding element, the respiration
is feeble, being carried on, for the most part, through the medium of water. In the warm-
blooded Verti-brata, however, which have the power of keeping up the heat of their bodies to
an elevated standard, even when that of the surrounding air is far beneath it, the quantity of
oxygen consumed is very large; and that required by Birds is more, in proportion to their size,
than that employed by Mammalia; as we should expect from the more elevated tempera-
ture of the former. In the class of Insects, we have a very remarkable illustration of the
same general fact. It appears, from the researches of Mr. Newport, that Insects, during
their larva and pupa states, and even in their perfect condition when at rest, are to be re-
garded as truly cold-blooded animals ; their temperature rising and falling with that of the
surrounding medium, and being at no time more than a degree or two above it. In a state
of activity, however, the temperature of the body attains a considerable elevation, — fre-
quently as much as 10° or 15° above that of the air. It must be remembered that, owing
to their larger extent of surface in proportion to their bulk, small animals are cooled much
more rapidly than large ones; and the temperature of Insects would probably rise much
higher, if it were not for the loss they are thus continually experiencing, which is greatly
increased by the action of the wings. In one of Mr. N.'s experiments, a single Humble-bee,
in a state of violent excitement, communicated to three cubic inches of air as much as 4°
of heat within five minutes; its own temperature being raised 7° in the same time. When
several individuals in a state of excitement, however, are clustered together, so that the loss
of heat is prevented, the elevation of temperature is much more considerable; thus a ther-
mometer introduced among seven "Nursing-Bees" stood at 92$°, whilst the external air
was only 70° ; and the temperature of a hive was raised by disturbing it, during winter,
from 4S^° to 102°, the temperature of the air being only 34 J at the time! In all these
instances, the amount of Oxygen consumed bears an exact proportion to that of the Heat
evolved.

890. In the higher animals, as in the lower, exercise has a considerable
effect in producing an elevation of temperature ; and, that this is not merely
due to the acceleration of the circulation, is shown by the very curious fact,
that the exercise of a particular muscle will cause an increase in the heat
liberated from it, as shown by needles plunged in its substance, and connected
with the thermo-multiplier.* It may, indeed, be stated as a general proposi-
tion, applicable as well to different parts of the same being, as to different
individuals, that the development of Heat is proportional to the activity of the
molecular processes which constitute the functions of Nutrition, Secretion,
&c. ; increasing with their activity, and diminishing with their torpor. It is
very easy to explain, on this principle, the known influence of the Nervous
system on the calorific function : since, although the molecular changes in the
organized fabric are not dependent upon the agency of that system, they are
very much influenced by it; and thus we can readily understand how a state
of nervous excitement may produce an elevation of temperature, whilst a de-
pression of nervous power occasions a cooling of the body. The experi-
ments of Sir B. Brodie, Chossat, and others, — in which a greater or less
portion of the nervous centres was removed, and the animal cooled notwith-
standing the maintenance of the circulation, — by no means prove that the
Nervous system is directly concerned in the production of heat; since in all
such experiments, there is a gradual loss of those other vital powers, which
are concerned in the function of calorification. From the experiments of Dr.
W. Philip and Dr. Hastings, it appears that an animal whose nervous centres
have been removed, cools much faster when left to itself, than when Artifi-
cial Respiration is practised; and that, if the cooling have made much pro-
gress before the artificial respiration is caused to commence, the temperature
may be raised ; — and this, too, in spite of the very imperfect manner in which
natural Respiration is replaced by movements artificially effected.

891. That the maintenance of Animal Heat is due in part to those molecu-
lar changes, to which the Cutaneous Respiration is subservient, appears from

torn. vi.

See the experiments of MM. Becquerel and Breschet, in Ann. des Sci. Nat. N. S. Zool.,

682 GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

the following experiments recently performed by MM. Becquerel and Bres-
chet. The hair of Rabbits was shaved off, and a composition of glue, suet,
and resin, forming a coating through which air could not pass, was applied
over the whole surface. It might seem natural to suppose that, by preventing
the evaporation of the sweat, the temperature of the tissues would be very
sensibly increased ; and that, by this increase of the temperature of the whole
body, a high state of fever would be engendered, with the symptoms of which
the animal would at last die. But the contrary occurred. In the first Rabbit,
which had a temperature of 100° before being shaved and plastered, it had
fallen to 891° by the time the material spread over him was dry. An hour
after, the thermometer placed in the same parts (the muscles of the thigh and
chest) had descended to 76°. In another Rabbit, prepared with more care,
by the time that the plaster was dry, the temperature of the body was not
more than 5|° above that of the surrounding medium, which was at that time
69^°; and in an hour after this, the animal died. These experiments place
in a very striking point of view the importance of the Cutaneous surface as a
respiratory organ, even in the higher animals : and they enable us to under-
stand how, when the secreting power of the Lungs is nearly destroyed by
disease, the heat of the body is kept up to its natural standard by the action
of the Skin. A valuable therapeutic indication, also, is derivable from the
knowledge which we thus gain, of the importance of the Cutaneous Respira-
tion; for it leads us to perceive the desirableness of keeping the skin moist,
in those febrile diseases in which there are great heat and dryness of the sur-
face, since secretion cannot properly take place through a dry membrane. Of
the relief afforded by cold or tepid sponging in such cases, experience has
given ample evidence.

892. All the foregoing facts point to the formation of Carbonic Acid, by the
union of the Oxygen absorbed from the air with Carbon set free from the
body, as the main source of the evolution of Heat within the Animal sys-
tem. The precise mode in which this union is accomplished, is not yet
known; but it is certain that, in whatever manner the combination may take
place, a certain measure of caloric must be generated. The combustion of
from 5 to 10 oz. of Carbon per day, however, would be by no means suffi-
cient to keep up the temperature of the Human body to its proper standard ;
for it has been experimentally ascertained, that the amount of Caloric set free
by a warm-blooded animal in a given time is more than can be thus accounted
for. It does not hence follow, however, that we are to look to any other than
Chemical processes, for the explanation of this most important function; since
there can be no doubt that there are many other changes of composition, con-
tinually taking place in the living body, which have their share in the pro-
duction of the effect. These take place, for the most part, at the expense of
the surplus of Oxygen absorbed over that which is given out in the form of
Carbonic Acid; this surplus amounting to as much as 15 per cent, of the
whole (§ 766). Of the manner in which this surplus is employed, no precise
account can be given; but there can be little doubt that part of it is expended
in uniting with Hydrogen, to form a portion of the watery vapour which is
exhaled from the lungs; and that another part unites with the Phosphorus
and Sulphur which are taken in as food (forming part of the proteine-com-
pounds (§ 114), to be excreted as Phosphates and Sulphates (§ 847). These
and other changes, in which the absorbed Oxygen participates, will be attended
with the evolution of Caloric; and thus we are probably to account for the
excess of Heat generated by a warm-blooded animal in a given time, above
that which would be produced by the combustion of the amount of Carbon
exhaled by it during the same period; as shown in the experiments of Dulong

DEVELOPMENT OF HEAT. 683

and Despretz.* Although, therefore, the Chemical doctrine of Calorification
cannot be regarded as yet perfected as to its details, there can be no reasonable
doubt that it is altogether sufficient to account for the phenomena in question.
And it may be stated as a general fact, that the production of Animal Heat is
due to the various changes in Chemical composition, that are continually
taking place within the system; of which changes, the absorption of Oxygen,
and the disengagement of Carbonic Acid, are the two chief external manifesta-
tions:— and that the degree of Caloric liberated bears a close relation to the
activity of these changes, either in regard to the body at large, or to any
portion of it.

893. The researches of Dr. Edwards upon Animal Heat have brought to
light some very interesting facts, regarding the diversity which exists as to
the power of generating heat, in the same species of animal, at different ages,
and at different periods of the year.

a. It appears to be a general fact, that the younger the animal, the less is its independent
calorifying power. The development of the embryo of oviparous animals is entirely de-
pendent upon the amount of external warmth supplied to it; and there are many kinds of
Birds, which, at the time they issue from the egg, are so deficient in the power of generating
heat, that their temperature rapidly falls, when they are removed from the nest and placed
in a cold atmosphere. It was shown by collateral experiments, that the loss of heat was
not to be attributed to the absence of feathers, nor to the extent of surface exposed in com-
parison with the bulk of the body; and that nothing but an absolute deficiency in the power
of generating it, would account for the fall of temperature. This is quite conformable to
facts well ascertained in regard to Mammalia. The fetus, during intra-uterine life, has
little power of keeping up its own temperature; and in many cases it is much dependent
on external warmth, for some time after birth. The degree of this dependence, however,
differs greatly in the various species of Mammalia, as among Birds: being less, in propor-
tion as the general development is advanced. Thus, young Guinea pigs, which can run
about and pick up food for themselves almost as soon as they are born, are from the first
independent of parental warmth ; whilst, on the other hand, the young of Dogs, Cats, Rab-
bits, &c., which are born blind, and which do not, for a fortnight or more, acquire the same
development with the preceding, rapidly lose their heat when withdrawn from contact with
the body of the mother.

b. In the Human species it is well known, that external warmth is necessary for the
Infant; but the fact is too often neglected (under the erroneous idea of hardening the con-
stitution) during the early years of childhood. It is to be carefully remembered, that the
development of Man is slower than that of any other animal; and that his calorifying
power is closely connected with his general bodily vigour. In the case of children born
very prematurely, the greatest attention must be given to the sustenance of the heat of the
body (§ 932) ; and though the infant becomes more independent of it as development
advances, it is many years before the standard can be maintained without assistance,
throughout the ordinary vicissitudes of external temperature. The calorifying power,
which is fully possessed by adults, decreases again in advanced age. Old people complain
that their " blood is chill;" and they suffer greatly from exposure to cold, the temperature of
their whole body being lowered by it.

c. Tbese facts have a very interesting connection with the results of statistical inquiries,
as to the average number of deaths at different seasons, recorded by M. Quetelet.j-

* It has been recently shown by Liebig, that the discrepancy between the actual amount
of heat generated, and the amount which was calculated to have been produced by the
union of Carbon and Hydrogen with Oxygen, to form the Carbonic Acid and Water exhaled,
in these experiments, may be nearly reconciled by adopting a more correct estimate of the
heat generated by combustion of given quantities of Carbon and Hydrogen respectively. But
all tlrese calculations proceed upon the supposition, that the whole amount of Oxygen ab-
sorbed, which is not exhaled as Carbonic acid, is exhaled in combination with Hydrogen, as
Water; and thus no account is taken of other combustion-processes going on in the body, by
which a greater amount of heat may be generated, than by the combustion of Hydrogen.
We have no means whatever of ascertaining how much of the watery vapour thrown off
by the lungs and skin is actually formed within the body, and how much is the mere super-
fluity of the liquid ingested.

| Essai de Physique Sociale, torn. i. p. 197.

684

GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

First
Month.

2—3
Years.

8—12
Years.

25—30
Years.

50—65
Years.

90 Years
arid above.

January

1-39

1-22

1-08

1-05

1-30

1-58

February

1-28

1-13

1-06

1-04

122

1-48

March

1-21

1-30

1-27

Ml

Ml

1-25

April

1-02

1-27

1-34

1-06

1-02

0-96

May

0-93

1-12

1-21

1-02

0-93

0-84

June

0-83

0-94

0-99

1-02

0-85

0'75

July

0-78

0-82

0-88

. 0-91

0-77

0-64

August

0-79

0-73

0-82

0-96

0-85

0-66

September

0-86

0-76

0-81

0-95

0-89

0-76

October

0-91

0-78

0-76

0-93

0'90

0-74

November

093

091

0-80

0-97

1-00

1-03

December

107

1-01

0-90

0'97

1-15

1-29

We see from this table that, during the first month of infant life, the external temperature
has a very marked influence; for the average mortality during each of the three summer
months being 80, that of January is nearly 140, and the average of February and March is
125. This is confirmed by the result obtained by MM. Villerrne and Milne-Edwards, in
their researches on the mortality of the children conveyed to the Foundling Hospitals in
the different towns in France ; for they not only ascertained that the mortality is much the
greatest during the first three months in the year, but also that it varies in different parts of
ilie kingdom, according to the relative severity of the winter. As childhood advances, how-
ever, the winter mortality diminishes, whilst that of the spring undergoes an increase; this
is probably due to the greater prevalence of certain epidemics at the latter season ; for the
same condition is observed, in a still more remarkable degree, between the ages of S and 12
years, — the time when children are most severely affected by such epidemics. As the con-
stitution acquires greater vigour, and the bodily structure attains its full development, the
influence of the season upon mortality becomes less apparent; so that at the age of from
25 to 30 years, the difference between the summer and winter mortality is very slight. This
difference reappears, however, in a very marked degree, at a later period, when the general
vigour, and the calorifying power, undergo a gradual diminution. Between the ages of 50
and 65 it is nearly as great as in early infancy ; and it gradually becomes more striking,
until, at the age of 90 and upwards, the deaths in January are 158, for every 04 in July (a
proportion of 2^ to ]); and the average of the three winter months is 145, whilst that of
the three summer months is only 68, or less than one-half.

894. Not only does the same individual possess different degrees of calori-
fying power, at different periods of his life, but also at different seasons of
the year.

a. Dr. Edwards found that Sparrows, when exposed for some time to a temperature of
32° during the summer, rapidly lost heat, the refrigeration during 3 hours being from 6 to
21 degrees ; but that, when they were placed in the same circumstances during winter (after
having been accustomed to a warm temperature) the refrigeration was much less, not being
in any instance more than 2° in 3 hours. Although it would be difficult to prove the fact
experimentally in regard to Man, there can be little doubt that he shares with the other
Mammalia in this variation. It is well known that the general vigour of the system is less
in summer than in winter; in hot climates than in moderately cold. Moreover, we con-
tinually experience the great discomforts of a eold day in summer; when, our system not
being prepared for it, we can less readily maintain our temperature at its normal standard.
The practical inference, — that we should bo much on our guard against exposure to low
temperatures during summer, — is one of much importance'; and its value has been fully
confirmed by experience. The same principle may also be applied to the explanation of
the well-known fact, that those who have been long resident in warm climates fuel the cold
acutely; whilst those who have been inured to cold are able to resist it much better, than
those who arc' exposed to it for the first time. The former have a continued summer con-
stitution; and their system not being called upon by its external conditions to produce much
heat, the power is after a time partially lost. On the other hand, those who live in cold
climates have a perpetual iriiilrr constitution (as it were) established; and the amount of
heat generated by them is much greater. It will be obvious that this must be the case, if
Man's capability of living under the greatest varieties of climate be sufficiently considered.
From Dr. E.'s experiments it appears, that every month makes an evident difference in the

DEVELOPMENT OF HEAT. 685

seasonal degree ; the heat lost by Sparrows in August being much less than that lost by
birds of the same species in July.

895. Our knowledge of the dependence of all the vital processes in warm-
blooded animals, upon the Heat of their bodies, — and of the dependence of
their Calorifying power upon the due supply of material for the Chemical
changes which generate Heat, — has lately received some very remarkable
additions from the experiments of M. Chossat.* He found that Birds, when
totally deprived of food and drink, suffered a progressive, though slight, daily
diminution of temperature. This diminution was not so much shown by a
fall of their maximum heat, as by an increase in the diurnal variation, which
he ascertained to occur even in the normal state. The amount of this varia-
tion, in Birds properly supplied with food, is about l£° Fahr. daily; the
maximum being about noon, and the minimum at midnight. In the in-
anitiated state, however, the average variation was about 6°, gradually
increasing as the animal became weaker: moreover, the gradual rise of tem-
perature, which should have taken place between midnight and noon, was
retarded; whilst the fall subsequently to noon commenced much earlier than
in the healthy state; so that the average of the whole day was lowered by
about 4^° between the first and tine penultimate days of this condition. On
the last day, the production of Heat diminished very rapidly, and the ther-
mometer fell from hour to hour, until death supervened; the whole loss on
that day being about 25° Fahr., making the total depression about 29£°.
This depression appears, from the considerations to be presently stated, to be
the immediate cause of Death. — On examining the amount of loss sustained
by the different organs of the body, it was found that 93 per cent, of the Fat
had disappeared, — all, in fact, which could be removed; whilst the Nervous
Centres scarcely exhibited any diminution in weight. The loss of weight of
the whole body averaged about 40 per cent.; and that of the various other
component tissues was very much what might have been anticipated. From
the constant coincidence between the entire consumption of the Fat, and the
depression of Temperature, — joined to the fact that the duration of life under
the inanitiating process evidently varied (other things being equal) with the
amount of Fat previously accumulated in the body, — the inference seems
irresistible, that the Calorifying power depended chiefly, if not entirely, on
the materials supplied by this substance. The maintenance of the normal
amount of matter in the Nervous centres, is a very remarkable fact; and
seems to countenance the idea, that the substances peculiar to Nervous tissue
may be formed from Fatty matter, rather than from a Proteine-compound
(§ 249).

896. Whenever, therefore, the store of combustible matter in the system was
exhausted, — whether by the Respiratory process alone, or by this in conjunc-
tion with the conversion of Adipose matter into the materials for the Nervous
or other tissues, — the inanitiated animals died, by the cooling of their bodies
consequent upon the loss of Calorifying power. That this is the real expla-
nation of the fact, is shown by the results of a series of very remarkable ex-
periments performed by M. Chossat, with a view of testing the correctness
of this view. When inanitiated animals whose death seemed impending (in
several instances death actually took place, whilst the preliminary processes
of weighing, the application of the thermometer, &c., were being performed),
were subjected to artificial heat, they were almost uniformly restored from a
state of insensibility and want of muscular power to a condition of compara-
tive activity; their temperature rose, their muscular power returned, they flew

* Recherches Experimentales sur 1'Inanition, Paris, 1843. See, also, the Brit, and For.
Med. Rev. for April, 1844.

58

686 GENERAL REVIEW OF THE NUTRITIVE PROCESSES.

about the room and took food when it was presented to them ; and, if the ar-
tificial assistance was sufficiently prolonged, and they were not again subjected
to the starving process, most of them recovered. If they were left to them-
selves too early, however, the digestive process was not performed, and they
ultimately died. Up to the time when they began to take food, their weight
continued to diminish ; the secretions being renewed, under the influence of
artificial heat, sometimes to a considerable amount. It was not until Diges-
tion had actually taken place (which, owing to the weakened functional power,
was commonly many hours subsequently to the ingestion of the food), that
the animal regained its power of generating heat ; so that, if the external
source of heat was withdrawn, the body at once cooled : and it was not until
the quantity of food actually digested was sufficient to support the wants of
the body, that its independent power of Calorification returned. It is to be
remembered that, in such cases, the resources of the body are on the point of
being completely exhausted, when the attempt at re-animation is made ; con-
sequently it has nothing whatever to fall back upon ; and the leaving it to itself
at any time until fresh resources have been provided for it, is consequently
as certain a cause of death, as it would have been in the first instance. — It
can scarcely be questioned, from the similarity of the phenomena, that Inani-
tion, with its consequent depression of temperature, is the immediate cause
of death in various Diseases of Exhaustion; and it seems probable that there
are many cases, in which the depressing cause is of -a temporary nature, and
in which a judicious and timely application of artificial Heat might prolong
life until it has passed off, — just as artificial Respiration is serviceable in cases
of Narcotic Poisoning (§ 885). It is especially, perhaps, in those forms of
Febrile disease, in which no decided lesion can be discovered after death, that
this view has the strongest claim to reception ; but many other cases will
occur to the intelligent Practitioner.*

897. Having thus considered the means, by which the degree of Heat ne-
cessary for the performance of the functions of the Human system is gene-
rated, we have to inquire how its temperature is prevented from being raised
too high ; in other words, what Frigorifying means there are, to counter-
balance the influence of causes, which in excess would otherwise be fatal, by
raising the heat of the body to an undue degree. How is it, for example,
that, when a person enters a room whose atmosphere is heated to one or
two hundred degrees above his body, the latter does not partake of the eleva-
tion, even though exposed to the heat for some time ? Or, since the inhabitants
of a climate where the thermometer averages 100° for many weeks together,
are continually generating additional heat in their own bodies, how is it that
this does not accumulate, and raise them to an undue elevation ? The means
provided by Nature for cooling the body when necessary, are of the simplest
possible character. From the whole of its soft moist surface, simple Evapo-
ration will take place at all times, as from an inorganic body in the same cir-
cumstances ; and the amount of this will be regulated merely by the condi-
tion of the atmosphere as to' warmth and dryness. The more readily watery
vapour can be dissolved in atmospheric air, the more will be lost from the

* The beneficial result of the administnition of Alcohol in such conditions, and the large
amount in which it may be given with impunity, may probably be accounted for on this
principle. That ii i< a ^p'viiie stimulus to the Nervous system, cannot be doubted from its
eil'eets on the healthy body; but that it serves as a fuel to keep up the Calorifying process,
appears equally certain. Now its ^ivat ellieaey in such cases seems to depend upon the
readiness \vith which it will be taken into the Circulation, by a simple act of Endosmotic
Imbibition, when the special Absorbent process dependent upon the peculiar powers of the
cells of the villi (§ 181), is in abeyance. There is no other combustible fluid, whose density,
relatively to that of the Blood, will permit of its rapid Absorption by the simple physical
process adverted to.

OF REPRODUCTION. 687

surface of the body in this manner. In cold weather, very little is thus carried
oft", even though the air be dry : and a warm atmosphere, already charged
with dampness, will be nearly as ineffectual. But simple evaporation is not
the chief means by which the temperature of the body is regulated. The
Skin, as already mentioned (§ 868), contains a large number of glandular, the
office of which is to secrete an aqueous fluid ; and the amount of this Exha-
lation appears to depend solely or chiefly upon the temperature of the sur-
rounding air. Thus, when the external heat is very great, a considerable
amount of fluid is transuded from the skin ; and this, in evaporating, converts
into latent heat a large quantity of the free caloric, which would otherwise
raise the temperature of the body. If the atmosphere be hot and dry, and
also be in motion, both Exhalation and Evaporation go on with great rapidity.
If it be cold, both are checked, — the former almost entirely so ; but if it be
dry, some evaporation still continues. On the other hand, in a hot atmosphere,
saturated with moisture, Exhalation continues, though Evaporation is almost
entirely checked; and the fluid poured out by the exhalant glands accumulates
on the skin. There is reason to believe that the secretion continues, even
when the body is immersed in water, provided its temperature be high. — We
learn from these facts the great importance of not suddenly checking Exhala-
tion, by exposure of the surface to cold, when the secretion is being actively
performed ; since a great disturbance of the circulation will be likely to ensue,
similar to that which has been already mentioned, as occurring when other
important secretions are suddenly suspended.

CHAPTER XVII.

OF REPRODUCTION.

1. — General Character of the Function.

898. THE Function of Reproduction has been commonly regarded as so
entirely different in character from the ordinary Nutritive processes, that no
analogy can be drawn between them. The results of late inquiries, however,
leave no doubt that the difference between them is extremely small, — having,
in fact, a relation rather to the object of the action, than to the mode in which
it is performed. In the ordinary function of Nutrition, there is a continual
regeneration or reproduction of the tissues and organs of the body; but the
new parts are destined still to constitute the same whole. On the other hand,
in Reproduction, the newly-formed parts are destined from the first to be cast
off from the parent structure, and to become new individuals. Still, their ori-
gin is essentially the same in both instances ; as appears from the mode in
which the multiplication of the lower Plants and Animals takes place. Thus
in the simplest Cryptogamia, such as the Yeast Fungus,* every single cell
may be regarded as a distinct individual ; since it is capable of living by itself,
and of generating new cells ; and thus the production of a new cell, in con-
nection with the original one, may be regarded as alike an act of Nutrition
and of Reproduction. So again, in the Hydra and other Polypes, the remark-
able power of reparation which is manifested in their Nutritive operations,

* See Principles of General and Comparative Physiology, § 98.

688 OF REPRODUCTION.

may be employed in generating new individuals ; since, when the body is
divided into numerous parts, each one of these has the power of developing
all the rest of the structure, and thus of becoming a complete animal (§ 9).
Still we find in most Plants, and in all Animals, some portion of the structure
specially designed to form and to set free germs, which are destined to become
new individuals; and it is in the liberation and development of these, that the
function of Reproduction essentially consists.

899. In Plants it is very evident that these germs differ but little from
those which elsewhere produce new cells (§ 122) ; and that the first aspect
of the new being is neither more nor less than a single cell, in which all the
other cells of the structure subsequently originate. In the Cryptogamia, the
cell-germs are contained in what is termed the spore; and, when liberated
from the parent, they are developed into cells without any further assistance
than that which they derive from the air, moisture, &c., that surround them.
In Flowering Plants, on the other hand, the cell-germs are conveyed into a
new set of organs, in which they are supplied with nutriment previously ela-
borated for them by the parent ; and, in this manner, they are enabled to attain
an ultimate development which is much higher than that of the Cryptogamia.
It is now well established, that the pollen-grain of Phanerogamia is analogous
to the spore of Cryptogamia; since it contains the reproductive granules, which
are the germs of the first cells of the new individual. When the pollen-grains
are cast upon the stigmatic surface, they project one or more long tubes, which
insinuate themselves down the soft loose tissue of the style, and reach the
ovarium. Into these tubes, the granules which the pollen-grain contained are
seen to pass; and they are thus conveyed into the ovules, the foramina of
which are penetrated by the extremities of the pollen-tubes. The ovules
previously contained nothing but starchy matter; but from the time that the
pollen-tubes have thus implanted (as it were) their contents in their cavity,
they may be considered as fecundated. The subsequent growth of the embryo
from the first-formed cells, takes place according to the principles already
stated, under the head of Nutrition ; and thus it is seen, that the mysterious
process of Reproduction evidently consists, in Flowering Plants, of nothing
else than the implantation of a cell-germ prepared by the mule organs, in a
nidus or receptacle adapted to aid its early development, which nidus consti-
tutes the essential part of the female system.

900. There is now good reason to believe that, in no Animals, is the Re-
productive apparatus less simple than it is in the higher Plants ; — that is to
say, in every instance, two sets of organs, a germ-preparing, and a germ-
nourishing, are present. These organs differ much in form and complexity
of structure in the various tribes of Animals ; but. their essential function is
the same in all. Those which are termed Male organs prepare and set free
certain bodies, which, having an inherent power of motion, have been sup-
posed to be independent Animalcules, and have been termed Spermatozoa ;
there is but little reason, however, to regard them in this light, since ciliated
epithelium-cells may exhibit as much activity ; and there is no evidence that
their function is any higher than that of the pollen-tube of Plants, which con-
veys into the ovulum the germs of the first cells of the embryo. This view of
the character of the Spermatozoa rests alike upon the nature of their move-
ments, and the mode of their production.* Dr. Barry's observations on the
history of the Ovum, and on the nature of the act of Fecundation (which will
be presently given in some detail) have left scarcely any doubt, that this act
consists in the introduction of some new element into the Ovule, through the
medium of the Spermatozoa ; the arrival of which at the surface of the ovary

* See Principles of General and Comparative Physiology, § GOG.

ACTION OF THE MALE. 689

had been more than once previously seen, and the penetration of which to the
Ovum there was good reason to suspect: and these have been confirmed by
the observations of Dr. A. Farre on the Ovum of the Earth-worm, which he
has distinctly seen to be penetrated by Spermatozoa. The act of Fecunda-
tion is evidently analogous, therefore, in Animals, to the process which has
been described as taking place in the Flowering Plants. In many of the
lower tribes of Animals, the spermatic fluid effused by an individual of one
sex, comes into direct contact with the ova previously deposited by the other;
but in all the higher tribes, as in Man, the act of fecundation is performed be-
fore, or shortly after the ova quit the ovarium. With these general views, we
shall now be prepared to consider the share which each sex has in the Function
of Reproduction.

2. Action of the Mule.

901. The Spermatic fluid secreted by the Testes of the Male (§ 867), differs
from all other secretions, in containing a large number of very minute bodies,
only discernible with a high power of the Microscope ; and these, in ordinary
cases, remain in active motion for some time after they have quitted the living
body. The Human Spermatozoon (of which representations are given in
Plate I., Fig. 18), consists of a little oval flattened body from the l-600th to
the l-800th of a line in length, from which proceeds a long filiform tail gradu-
ally tapering to the finest point, of l-50th or at most l-40th of a line in length.
The whole is perfectly transparent ; and nothing that can be termed structure
can be satisfactorily distinguished within it.* The movements are principally
executed by the tail, which has a kind of vibratile undulating motion. They
may continue for many hours after the emission of the fluid ; and they are not
checked by its admixture with other secretions, such as the urine and the
prostatic fluid. Thus, in cases of nocturnal emission, the Spermatozoa may
not unfrequently be found actively moving through the \irine in the morning;
and those contained in the seminal fluid collected from females that have just
copulated, are frequently found to live many days. Their presence may be
readily detected by a Microscope of sufficient power, even when they have
long ceased to move, and are broken into fragments ; and the Physician and
the Medical Jurist will frequently derive much assistance from an examination
of this kind. Thus, cases are of no uncommon occurrence, especially among
those who have been too much addicted to sexual indulgence, in which seminal
emissions take place unconsciously and frequently, and produce great general
derangement of the health; and the true nature of the complaint is obscure,
until the fact has been detected by ocular examination. Again, in charges of
rape, in which evidence of actual emission is required, a microscopic exami-
nation of the stiffened spots left on the linen will seldom fail in obtaining proof,
if the act have been completed: in such cases, however, we must not expect
to meet with more than fragments of Spermatozoa; but these are so unlike
anything else, that little doubt need be entertained regarding them. It has
been proposed to employ the same test, in juridical inquiries respecting doubt-
ful cases of death by suspension : seminal emissions being not unfrequent
results of this kind of violence: but there are many obvious objections which
should prevent much confidence being placed in it.t

* It has been asserted that distinct oral and anal orifices, with appearances of internal
organs, have been seen in the Spermatozoa of certain Mammalia ; but these observations
have not been confirmed ; and they are not borne out by the attentive examination of the
larger Spermatozoa of other animals.

f See the Author's Article "Asphyxia," in the Library of Practical Medicine, and the
authorities there referred to.

58*

690 OF REPRODUCTION.

902. The mode of Evolution of Spermatozoa, which has been recently
discovered by Wagner, is so different from the ordinary method of produc-
tion amongst Animalcules, as of itself to indicate that the former cannot be
referred to the same category with the latter. It may be best studied in those
animals which only have a periodical fertility ; and the Passerine Birds are
among the most convenient subjects for the purpose. During the winter, the
testes are small and almost bloodless, and no trace of Spermatozoa can be
detected within them ; on the return of spring, however, they undergo great
enlargement and become almost gorged with blood, and the gradual steps of
the evolution of the Spermatozoa may be easily observed. The fluid drawn
from them is first seen to contain a number of granular corpuscles, resembling
those known as the Seminal Granules in the human semen (delineated at «,
Fig. 18, Plate I.); and in a short time there are seen, in addition to these,
numerous rounded transparent vesicles, at first having but one nucleus, and
afterwards presenting several. These nuclei bear a close resemblance to the
granular corpuscles just mentioned ; and it is probable that the former are to
be regarded as cytoblasts, from which the Spermatoferous cells (shown, as
existing in the human. semen, in Fig. 19, Plate I.) are evolved. The nuclei
seem afterwards to resolve themselves into a fine granular matter, which is
diffused through the whole vesicle or "cyst of evolution;" and in this, a linear
arrangement soon becomes perceptible. The lines become more and more
distinct, and are at last seen to be evidently produced by the arrangement of
the Spermatozoa, which lie side by side within the vesicle; and the form of
this changes from a sphere to a long oval. After a time they break forth,
but still adhere to each other for a short period, forming bundles, such as may
often be met with in the human semen, when taken directly from the testis
(Fig. 20, Plate I.).* That the Spermatozoa are the essential elements of the
spermatic fluid, has been reasonably inferred from several circumstances, such
as their absence or imperfect development in hybrid animals, which are nearly
or entirely sterile : and the fact that Fecundation essentially consists in the
direct communication of one of them with a certain point in the Ovum, ap-
pears too well established to admit of further doubt. Regarding the uses of
the other constituents of the Semen, no sufficient account can be given.

903. The power of procreation does not usually exist in the Human Male,
until the age of from 14 to 16 years; and it may be considered probable that
no Spermatozoa are produced until that period, although a fluid is secreted by
the testes. At this epoch, which is ordinarily designated as that of Puberty, a
considerable change takes place in the bodily constitution: the sexual organs
undergo a much-increased development; various parts of the surface, especially
the chin and the pubes, become covered with hair; the larynx enlarges, and
the voice becomes lower in pitch, as well as rougher and more powerful ; and
new feelings and desires are awakened in the mind. Instances, however, are
by no means rare, in which these changes take place at a much earlier
period; the full development of the generative organs, with manifestations of
the sexual passion, having been observed in children of but a few years old.
The procreative power may last, if not abused, during a very prolonged
period. Undoubted instances of virility at the age of more than 100 years
are on record ; but in these cases, the general bodily vigour was preserved in
a very remarkable degree. The ordinary rule seems to be, that sexual power
is not retained by the male in any considerable degree, after the age of 60 or
(55 years. To the use of the sexual organs for the continuance of his race,

* For a fuller account, with illustrations, of the development of the Spermatozoa, and its
analogy with the formation of other tissues, see Princ. of Gen. and Comp. Phys., §§ 430

und 007.

ACTION OF THE MALE. 691

Man is prompted by a powerful Instinctive desire, which he shares with the
lower animals. This Instinct, like the others formerly alluded to (§ 428 —
430), is excited by sensations ; and these may either originate in the sexual
organs themselves, or may be excited through the organs of special sensation.
Thus in Man it is most powerfully aroused by impressions conveyed through
the sight or the touch: in many other animals, the auditory and olfactive organs
communicate impressions which have an equal power ; and it is not impro-
bable that, in certain morbidly-excited states of feeling, the same may be the
case in ourselves. That local impressions have also a very powerful effect in
exciting sexual desire, must have been within the experience of almost every
one ; the fact is most remarkable, however, in cases of Satyriasis, which dis-
ease is generally found to be connected with some obvious cause of irritation
of the generative system, such as pruritus, active congestion, &c. That some
part of the Encephalon is the seat of this as of other instinctive propensities,
appears from the considerations formerly adduced; but that the Cerebellum
is the part in which this function is specially located, cannot be regarded as
by any means sufficiently proved (§§ 466 — 470). The instinct, when once
aroused (even though very obscurely felt), acts upon the mental faculties and
moral feelings; and thus becomes the source, though almost unconsciously so
to the individual, of the tendency to form that kind of attachment towards one
of the opposite sex, which is known as love. This tendency cannot be re-
garded as a simple passion or emotion, since it is the result of the combined
operations of the reason, the imagination, and the moral feelings ; and it is in
the engraftment (so to speak) of the psychical attachment, upon the mere
corporeal instinct, that a difference exists between the sexual relations of Man
and those of the lower animals. In proportion as the Human being makes
the temporary gratification of the mere sexual appetite his chief object, and
overlooks the happiness arising from spiritual communion, which is not only
purer but more permanent, and of which a renewal may be anticipated in
another world, — does he degrade himself to the level of the brutes that perish.
Yet how lamentably frequent is this degradation !

904. When impelled by sexual excitement, the Male seeks intercourse with
the Female, the erectile tissue of the genital organs becomes turgid with blood
(§ 748), and the surface acquires a much-increased sensibility ; this is espe-
cially acute in the Glans penis. By the friction of the Glans against the rugous
walls of the Vagina, the excitement is increased ; and the impression which
is thus produced at last becomes so strong, that it produces, through the
medium of the Spinal Cord, a reflex contraction of the muscles which sur-
round the Vesiculae Seminales (§ 393). These receptacles discharge their
contents (partly consisting of semen and partly of a secretion of their own)
into the Urethra ; and from this they are expelled with some degree of force,
and with a kind of convulsive action, by its own Compressor muscles. Now
although the sensations concerned in this act are ordinarily most acutely plea-
surable, there appears sufficient evidence that they are by no means essential to
its performance ; and that the impression which is conveyed to the Spinal Cord
need not give rise to a sensation, in order to produce the reflex contraction of
the Ejaculator muscles (§ 372). The high degree of nervous excitement
which the act of coition involves, produces a subsequent depression of corre-
sponding amount; and the too frequent repetition of it is productive of conse-
quences very injurious to the general health. This is still more the case with
the solitary indulgence, which (it is to be feared) is practised by too many
youths ; for this, substituting an unnatural degree of one kind of excitement,
for that which is wanting in another, cannot but be still more trying to the
bodily powers. The secretion of seminal fluid being, like other secretions,
very much under the control of the nervous system, will be increased by the

692 OF REPRODUCTION.

continual direction of the mind towards objects which awaken the sexual pro-
pensity (§ 626, note) ; and thus, if intercourse be very frequent, a much larger
quantity will altogether be produced, although the amount emitted at each
period will be less. The formation of the secretion seems of itself to be a
much greater tax upon the corporeal powers, than might have been supposed
a priori: and it is a well-known fact, that the highest degree of bodily vigour
is inconsistent with more than a very moderate indulgence in sexual inter-
course ; whilst nothing is more certain to reduce the powers, both of body
and mind, than excess in this respect. These principles, which are of great
importance in the regulation of the health, are but results of the general law,
which prevails equally in the Vegetable and Animal kingdoms, — that the
Development of the Individual, and the Reproduction of the Species, stand
in an inverse ratio to each other.

3. — Jlction of the Female.

905. The essential part of the Female Generative system is that in which
the Ova are prepared ; the other organs are merely accessory, and 'are not to
be found in a large proportion of the Animal kingdom. In many of the lower
animals, the Ovaria and Testes are so extremely like each other, that the dif-
ference between them can scarcely be distinguished ; and the same has already
been stated, regarding the condition of these organs in Man, at an early period
of development (§ 866 6). The fact is one of no small interest. In the lower
animals, the Ovarium consists of a loose tissue containing many cells, in which
the Ova are formed, and from which they escape by the rupture of the cell-
walls ; in the higher animals, as in the Human female, the tissue of the Ova-
rium is more compact, forming what is known as the stroma; and the Ova,
except when they are approaching maturity, can only be distinguished in the
interstices of this, by the aid of a high magnifying power. We owe to Dr.
Barry the discovery of the earliest stages in the production of the Ovum and
its accessory parts, in Mammalia and other Vertebrata. In order to under-
stand his account, however, it will be necessary that the parts of which the
ovum consists should be previously understood. — Taking the Fowl's Egg as a
familiar illustration, it must be remarked, in the first place, that neither the
albumen which forms the white, nor the shell-membrane with its testaceous
covering, exist in the Ovarian Ovum ; these portions being added during its
passage along the oviduct. The parts which we have to analyze, are the
Yolk-membrane and its contents. Within the Yolk-membrane, we find in the
first place, the Yolk itself; a substance consisting in part of albuminous gran-
ules, and in part of oily globules. Towards the centre, the character of the
Yolk in some degree changes ; its colour being lighter, and the granules pre-
senting more the appearance of cells, with minuter globules in their interior.
The central portion is termed the discus vitellinus. Occupying the centre of
the yolk (in the immature ovulum) is a large cell, very distinct in aspect from
the rest, and having a well-marked nucleus upon its walls. This is termed
the germinal vesicle; and the nucleus, the germinal spot. — The Mammalian
Ovum contains exactly the same parts; but the yolk is much smaller in pro-
portion, and corresponds in character rather with the discus vitellinus, than
with the whole yolk of the Bird's egg. The Ovum in all Vertebrated animals
is produced within a capsule or bag, the exterior of which is in contact with
the stroma of the ovarium ; this has been termed in Mammalia, the Graafian
follicle, after the name of its first discoverer ; but the more general and ap-
propriate designation of Ovisac has been given to it by Dr. Barry, who has
shown that it exists in other classes of Vertebrata. Between the Ovum and
the Ovisac, in Oviparous animals, there is scarcely any interval ; but in the

ACTION OF THE FEMALE. 683

Mammalia, a large amount of granular matter is present ; and this arranges
itself into some peculiar structures discovered by Dr. Barry, and presently to
be described. The membrane which surrounds the yolk in Mammalia has
received, on account of its thickness and peculiar transparency, the designation
of zona pellucida. — The several parts of the Ovum now described are shown
in Fig. 5, Plate I.

906. From the researches of Dr. Barry on the early development of the
Ovum, it appears that the Germinal Vesicle is the part which can first be
distinctly traced. In Fig. 1 (Plate I.) is seen a representation of one of its
incipient stages in the Rabbit; there is nothing here visible, but a collection
of very transparent vesicles, surrounded by a mass of dark granules. In the
succeeding stage, represented in Fig. 2, some of the vesicles have enlarged,
and the granules immediately surrounding them have become developed into
cells. A more advanced condition is represented (on a smaller scale) in Fig.
3 ; in which a distinct spot (b] is seen on the central vesicle (a), marking it as
the Germinal Vesicle ; whilst many of the granules surrounding it have be-
come cells, and have taken-on a very regular arrangement. After a time, a
membrane forms around each cluster of granules, separating it from the stroma
of the ovarium ; this is the Ovisac. At a later period, a separation takes place
between the inner and outer portions of the mass of granular matter, included
between the ovisac and the germinal vesicle ; and the separation is completed
by the development of a membrane, which envelopes the inner stratum. This
stratum becomes the Yolk, and includes most of the oil-particles which pre-
viously existed within the ovisac ; whilst the portion of the granular mass,
exterior to this, gives origin in Mammalia to certain structures of a very pe-
culiar character, which seem to be concerned in the liberation of the ovum
from the Graafian follicle or Ovisac. The appearance of the Human Ovisac
and its contents is seen in Fig. 4. The granules immediately surrounding
the Ovum assume the appearance of cells ; and these unite to form a sort of
membrane, to which the name of tunica granulosa has been given. This is
seen at t g (Fig. 7). The granules lining the Ovisac also combine themselves
into a membranous structure ; to which Dr. Barry has given the designation
of membrana granulosa (g g, Fig. 6). These are connected by four band-
like extensions of the same cellulo-membranous structure, which seem to sus-
pend the ovum in its place ; and these are called retinacula (r r, Figs. 6" and
7). The space between the Tunica Granulosa and the Membrana Granulosa,
which is not occupied by the Retinacula, is filled with fluid, in which few or
no cells can be seen. The uses of this structure, so far as they are apparent,
will be described, when the processes by which the Ovum escapes from the
Ovary are detailed.

907. The Ovisac does not form the entire structure which has been described
as the Graafian follicle ; for this consists of two layers, of which the inner
one is the true Ovisac, whilst the outer results from a thickening and conden-
sation of the surrounding layer of the Stroma of the Ovarium. It is the outer
layer only which is vascular ; the inner presents no trace of structure ; and
the increase of the ovum must take place by simple imbibition, through it, of
the supply of nutritive matter brought into contact with its exterior. The
Ovarium may be seen, even in the fetal animal, to contain immature Ova ; in
which the several parts can be clearly distinguished. At a later period, how-
ever, the number of Ova greatly increases ; and the development of some ad-
vances, whilst others degenerate. According to the recent valuable inquiries
of Dr. Ritchie,* it appears that, even during the period of childhood, there is a
continual rupture of Ovisacs, and discharge of Ova, at. the surface of the

* London Medical Gazette, 1844.

694 OF REPRODUCTION.

Ovarium. The Ovaria are studded with numerous minute copper-coloured
maculae ; and their surface presents delicate vesicular elevations, which are
occasioned by the most matured ovisacs : the dehiscence of these takes place
by minute punctiform openings in the peritoneal coat ; and no cicatrix is left.
At the period of puberty, the stroma of the ovarium is crowded with Ovisacs;
which are still so minute, that in the Ox (according to Dr. Barry's computa-
tion) a cubic inch would contain 200 millions of them. The greatest advance
is seen in those which are situated nearest the surface of the Ovarium ; and
in these, the Graafian follicle with its two coats, may be distinctly traced. It
is curious that the outer wall (which is itself a part of the condensed stroma
of the ovarium) should contain an immense number of minute ovisacs ; so'
that this, in the adult animal, is the most convenient situation in which to
view them: these ovisacs have been termed by Dr. Barry " parasitic ovisacs."
In those animals whose aptitude for conception is periodical, the development
of the Ova, to such a degree that they become prepared for fecundation, is
periodical .also. This development becomes evident, when the parts are ex-
amined in an animal which is "in heat," by the projection of the Graafian
follicles from the surface ; and it consists not merely in an increase of size,
but in certain internal changes presently to be described.

908. In the Human female, the period of Puberty, or of commencing apti-
tude for procreation, is usually between the 13th and 16th year; it is earlier
in warm climates than in cold;* and in densely-populated manufacturing towns,
than in thinly peopled agricultural districts. The mental and bodily habits
of the individual have also a considerable influence upon the time of its
occurrence ; girls brought up in the midst of luxury or sensual indulgence,
undergoing this change earlier than those reared in hardihood and self-denial.
The changes in which Puberty consists, are for the most part connected with
the Reproductive system. The external and internal organs of generation

[*It has been stated, by almost all physiological writers, that women reach maturity, and
that menstruation commences much earlier in hot climates, particularly between the tropics,
than in temperate and very cold countries. Haller states that in the warm regions of Asia,
the catamenia appear from' the 8th to the 10th year; and in Switzerland, Britain, and other
temperate regions, at the age of 12 or 13, and later the farther we ascend towards the north.
The same view has been held by nearly all subsequent writers on the subject, and they infer
that animals, like plants, reach maturity sooner in hot than in cold climates. Dewees says
that menstruation occurs later in our northern than in our southern states. From many
elaborate and interesting papers which have been published within a few years, especially
from those of Mr. Roberton of Manchester, it would seem that the natural period of puberty
in women occurs in a much more extended range of ages, and is much more equally dis-
tributed through that range than others have alleged, and that, in other countries, the parallel
between plants and fruits does not hold good.

At Gottingen, Osiander ascertained the ages at which ] 37 women began to menstruate.
In 21 of these the catamenia appeared at 14; in 32 at 15 ; in 24 at 16 ; 9 at 12 ; and 1 not
before the 24th year. The Indian girls in Canada, and in our north-western states and ter-
ritories, begin to menstruate frequently at 12, 13 and 14. From the statement of Baron
Humboldt, the same is equally true of the Kowiacs, and the tribes of northern Asia, where
girls of ID years are sometimes found mothers. The notion that women in Lapland do not
menstruate till ~M, and then only during summer, is founded on a mistake in Linna?us's
Flora Lapponica. Tooke states that the Sclavonian, or native Russians, reach puberty at an
early age; and Dr. Robert Lee, who was in the Crimea, and all the Russian provinces along
the Black Sea, and in the Ukraine, and whose opportunities of observation were extensive,
says that his conviction is, that over the whole south of Russia the period of puberty is the
same as in Great Britain; and that women cease to bear children at the same age. The
same would appear to hold good in Java, and in all the islands of the Indian Archipelago, and
in Sierra Leone; and the difference said to exist in Arabia in this respect is due to the
early marriages, and universal hceiitioiisnrss and depravity of morals 'in thatcouiitry. It
would appear from observations made in the West India Islands, that menstruation occurs
there about the same period, and that the alleged difference in this respect between the
negress and tfie white female does not exist. — M. C.]

ACTION OF THE FEMALE. 695

undergo a considerable increase of size ; the mammary glands enlarge ; and a
deposition of fat takes place in the mamma? and on the pubes, as well as over
the whole surface of the body, — giving to the person that roundness and ful-
ness, which are so attractive to the opposite sex, at the period of commencing
Womanhood. The first appearance of the Catamenia usually occurs whilst
these changes are in progress, and is a decided indication of the arrival of the
period of Puberty ; but it is not unfrequently delayed much longer ; and its
absence is by no means to be regarded as a proof of the want of aptitude for
procreation, since many women have borne large families, without having ever
menstruated. The Catamenial discharge appears normally to consist of blood
deprived of its fibrine ; the fluid being composed of serum, in which red cor-
puscles are suspended, and being readily distinguishable from true blood by
its want of power to clot. When clots are found in it, therefore, a morbid
condition of the secreting surface must be inferred. The interval which usu-
ally elapses between the successive appearances of the secretion, is about four
weeks ; and the duration of the flow is from three to six days. There is,
however, great variety in this respect among the inhabitants of different cli-
mates, and among individuals ; in general, the appearance is more frequent,
and the duration of the flow greater, among the residents in warm countries,
and among individuals of luxurious habits and relaxed frame, than among the
inhabitants of colder climes, or among individuals inured to bodily exertion.
The first appearance of the discharge is usually preceded and accompanied by
considerable general disturbance of the system ; especially pain in the loins
and a sense of fatigue in the lower extremities ; and its periodical return is
usually attended with the same symptoms, which are more or less severe in
different individuals.

909. Much discussion has taken place respecting the causes and purposes
of the Menstrual flow ; and recent inquiries have thrown much light upon
them. The state of the Female Generative system, during its continuance,
appears to be analogous to the heat of the lower animals ; many of which
have a sero-sanguinolent discharge at that period. There is good reason to
believe that in Women the sexual feeling becomes stronger at that epoch ;
and it is quite certain that there is a greater aptitude for Conception, imme-
diately before and after Menstruation, than there is at any intermediate period.
Observations to this effect were made by Hippocrates, and were confirmed by
Boerhaave and Haller; indeed coitus immediately after menstruation appears
to have been frequently recommended as a cure for sterility, and to have
proved successful. It is well known that, among many of the lower animals,
the Ova are entirely extruded by the Female, before the Spermatic fluid of
the Male reaches them ; and that even in Birds, this occasionally takes place.
This question has been recently made the subject of special inquiry by M.
Raciborski ; who affirms that the exceptions to the rule — that Conception
occurs immediately before or after, or during, Menstruation — are not more
than 6 or 7 per cent. Indeed, in his latest work on this subject,* he gives the
details of 15 cases, in which the date of Conception could be accurately fixed,
and the time of the last appearance of the Catamenia was also known ; and in
all but one of them, the correspondence between the two periods was very
close. Even in the exceptional case, the Catamenia made their appearance
shortly after the Coitus ; which took place at about the middle of the interval
between the two regular periods. When Conception occurs immediately be-
fore the Menstrual period, the Catamenia sometimes appear, and sometimes
are absent ; if they appear, their duration is generally less than usual. The
fact that Conception often takes place immediately before the last appearance

* Sur la Ponte des Mammiferes. Paris, 1844.

696 OF REPRODUCTION.

of the Catamenia (and not after it, as commonly imagined), is one well known
to practical men. Numerous cases have been collected by Mr. Girdwood,
Dr. Robert Lee, MM. Gendrin, Negrier, Raciborski, and others, in which the
Menstrual period was evidently connected with the maturation and discharge
of Ova; but the most complete observations yet made upon this subject, are
those of Dr. Ritchie (loc. cit.) He states that about the period of Puberty a
marked change usually takes place in the mode in which the Ovisacs discharge
their contents ; but that this change does not necessarily occur simultaneously
with the first appearance of the Catamenia; as in some cases the conditions,
which obtain in the period before puberty, are extended into that of menstrua-
tion. The Ovaries now receive a much larger supply of blood ; and the Ovi-
sacs show a great increase in bulk and vascularity ; so that, when they appear
at the surface of the ovary, they present themselves as pisiform turgid eleva-
tions ; and the discharge of their contents leaves a much larger cicatrix, and
is accompanied by an effusion of blood into their cavity, with other subsequent
changes, to be presently described. It would appear, however, that although
such a discharge takes place most frequently at the Menstrual period, yet that
the two occurrences are not necessarily co-existent; for menstruation may
take place without any such rupture ; whilst, on the other hand, the matura-
tion and discharge of mature ova may occur in the intervals of Menstruation,
and even at periods of life when that function is not taking place. The
essential condition of Menstruation itself would appear to be the increased
turgescence of the vessels of the Uterus ; and the appearance, on its internal
surface, of a meshwork of deciduous villous vessels, which may remain for at
least two weeks. It is evident that this is a preparation for the formation of
the Decidua (§ 919).

910. The duration of the period of aptitude for procreation, as marked by
the persistence of the Catamenia, is more limited in Women than in Men;
usually terminating at about the 45th year; it is sometimes prolonged, how-
ever, for ten or even fifteen years longer ; but cases are rare in which women
above 50 years of age have borne children. There is usually no Menstrual
flow during Pregnancy and Lactation ; in fact, the cessation of the Catamenia
is generally one of the first signs, indicating that Conception has taken place.
But it is by no means uncommon for them to appear once or twice subse-
quently to Conception; and in some women, there is a regular monthly dis-
charge, though probably not of the usual secretion, through the whole period.
Some very anomalous cases are recorded, in which the Catamenia never
appeared at any other time than during Pregnancy ; and were then regular.
The absence of the Catamenia during Lactation is by no means constant,
especially if the period be prolonged; when the Menstrual discharge recurs,
it may be considered as indicating an aptitude for Conception ; and it is well
known that, although Pregnancy seldom recurs during the continuance of
Lactation, the rule is by no means invariable.

911. The function of the Female, during the coitus, is entirely of a passive
character. When the sexual feeling is strongly excited, there is a considera-
ble degree of turgescence in the erectile tissue surrounding the vagina, and
composing the greater part of the nymphac and the clitoris ; and there is also
an increased secretion from the mucous follicles.* But these changes are by

[* The glands of Duverney have been lately (1840) very accurately described by Profes-
sor Tiedemann, his attention having been directed to the.se organs by the late Dr. Fricke, of
Hamburg. These glands are situated at either side of the entrance of the vagina, beneath
the integument covering the inferior part of the vagina, as well as the superficial perinea!
fascia, and the constrictor vagina? muscle. The space they occupy lies between the lower
end of the vagina, the ascending ramus of the ischium, the crus clitoridis, and the erector
clitoridis muscle. Superiorly are the fibres of the levator ani which are attached to the

ACTION OF THE FEMALE. 697

no means necessary for effectual coition ; since it is a fact well established,
that fruitful intercourse may take place, when the female is in a state of nar-
cotism, of somnambulism, or even of profound ordinary sleep. It has been
supposed by some, that the os uteri dilates, by a kind of reflex action, to re-
ceive the semen ; but of this there is no evidence. The introduction of a
small quantity of the fluid just within the Vagina, appears to be all that is
absolutely necessary for conception ; for there are many cases on record, in
which pregnancy has occurred, in spite of the closure of the entrance to the
vagina by a strong membrane, in which but a very small aperture existed.
That the Spermatozoa make their way towards the Ovarium, and fecundate
the Ovum either before it entirely quits the Ovisac or very shortly afterwards,
appears to be the general rule in regard to the Mammalia ; and the question
naturally arises, — by what means do they arrive there. It has been supposed
that the action of the cilia, which line the Fallopian tubes, might account for
their transit; but the direction of this is from the Ovaria towards the Uterus,
and would therefore be opposed to it. A peristaltic action of the Fallopian
tubes themselves may generally be noticed in animals killed soon after sexual
intercourse ; and in those which have a two-horned membranous Uterus, such
as is evidently but a dilatation of the Fallopian tube, this partakes of the same
movement, as may be well seen in the Rabbit : in animals, however, which
have a single Uterus with thicker walls (as in the Human female), it must
evidently be unavailable. Among the tribes whose Ova are fertilized out of
the body, the power of movement inherent in the Spermatozoa is obviously
the means by which they are brought in contact with the Ova : and it does
not seem unreasonable to suppose, that the same is the case in regard to the
higher classes ; and that the transit of these curious particles, from the Va-
gina to the Ovaries, is effected by the same kind of action as that which
causes them to traverse the field of the microscope. — We shall now consider
the changes in the Ovum and its appendages, by which it is prepared for
fecundation.

912. Up to the period when the Ovum is nearly brought to maturity, it re-
mains in the centre of the Ovisac or inner layer of the Graafian follicle ; and
it is supported in its place by the Retinacula, which connect its Tunica
Granulosa with the Membrana Granulosa that lines the ovisac. (See Fig. 6,

ischium, and behind these are the transversi-perinei muscles. They are surrounded by very
loose cellular tissue. They are rounded, but somewhat elongated, being flat and bean-
shaped. Their long diameter is from 5 to 10 lines; their transverse diameter 2^ to 4j lines,
and they are from 2^- to 3 lines thick. The excretory duct is at the anterior edge of the
superior part of the gland, and runs beneath the constrictor vaginae, horizontally forwards
and inwards, to the inner face of the nympha, opening in front of the carunculas myrtiformes,
in the midst of a number of small mucous follicles. These glands were first discovered by
Duverney in the cow, about the middle of the seventeenth century. Bartholinns subse-
quently found them in the human female, and his observations were confirmed by Duver-
ney, Morgagni, Santorini, Peyer, &c. Haller denied their existence; and such structure
seems to have been forgotten until they were again described by Mr. Taylor (Dublin
Journal, vol. xiii. 1838). They are analogous to Cowper's glands in the male, according to
Tiedemann, and like them are sometimes wanting, and differ in size. In advanced age
they are said to diminish in size, and even disappear. They are present in the females of
all animals, where Cowper's glands exist in the males. They secrete a thick, tenacious,
grayish-white fluid, which is emitted in large quantities, at the termination of the sexual act,
most likely from the spasmodic contraction of the constrictor vaginae muscle, under which
they lie. Its admixture with the male semen is supposed to probably have some connection
with impregnation, and it has been suggested that it may be the vehicle of the fecundating
principle of the semen. These glands were probably known to the ancients, and it is doubt-
less their secretion which Hippocrates and others describe as the female semen. — (1843.)
These glands have lately been described by Huguier of Paris, in the Archives d'Jlnatomie.
His description corresponds in every respect with that given above. — (1847.) — M. C.J
59

698 OF REPRODUCTION.

Plate I.) The Ovum then begins to move towards the periphery of the
Graafian follicle; and always towards that point of it which is nearest the
surface of the Ovary. This movement appears to be due, in the first instance,
to the shortening of the Retinacula in that direction ; and whilst the Ovum
lies against the membrane of the Ovisac, a gradual thinning of the latter seems
to take place. At the same time an important change is occurring in the outer
Avail of the Graafian follicle, especially at the part most deeply imbedded in
the Ovary ; its vascularity is greatly increased, and its substance appears
thickened. This thickening is probably due to the deposition of blood in a
state ready to become more highly organized, upon the exterior of the Ovisac;
and the consequence of it is, that considerable pressure is made upon the con-
tents of the follicle, the effect of which is, of course, exerted most upon the
thinnest part of it. Thus, a sort of vis a tergo is exercised against the Ovum
and the Disc (consisting of the tunica granulosa and the central part of the
retinacula) in which it is imbedded ; and the whole is forced, by the rupture
of the Graafian follicle, into the funnel-shaped entrance of the Fallopian tube,
— the Retinacula being gradually detached from the Membrana Granulosa,
which is left behind. This action is represented in Fig. 8, Plate I. What
becomes of the Ovisac is not certain. Dr. Barry affirms that he has some-
times known it to be subsequently expelled from the ovary ; but it appears
more commonly to coalesce with the surrounding envelope, and to constitute,
together with it, the lining of the cavity, which is usually found in the Corpus
Luteum. The substance known under this name is found in the Ovary, after
the Ovum has escaped from it ; and the importance of the question, how far
its presence may be regarded as an indication that Conception has taken
place, requires that we should have clear ideas respecting its nature.

913. The term Corpus Luteum has been usually applied to a reddish-yel-
low substance, glandular in aspect, friable in consistence, and very vascular;
which occupies the part of the Ovary from which the germ has escaped, and
is larger or smaller according to the length of time that has elapsed since con-
ception. At first it is usually so large as to occasion a considerable projection
on the surface of the Ovary ; its form is oval, or resembles that of a bean.
"When cut across, its dimensions are usually found to be from 4 to 5-8ths of
an inch in its long diameter, and from 3 to 4-8ths in its short ; and it thus
occupies from a fourth to a half of the whole area of the ovarium ; but these
dimensions are not unfrequently exceeded. The centre of this substance is
hollow ; and by a proper acquaintance with this character, the true Corpus
Luteum may be distinguished from substances, bearing a general resemblance
to it, but very different in their character. The following is Dr. Mont-
gomery's account of it. " Its centre exhibits either a cavity, or a radiated or
branching white line, according to the period at which the examination is
made. If within the first three or four months after conception, we shall, I
believe, always find the cavity still existing, and of such a size as to be capable
of containing a grain of wheat at least, and very often of much greater dimen-
sions ; this cavity is surrounded by a strong white cyst ; and as gestation
proceeds, the opposite parts of this cyst approximate, and at length close to-
gether, by which the cavity is completely obliterated, and in its place there
remains an irregular white line, whose form is best expressed by calling it
radiated or stelliform. This is visible as long as any distinct trace of the
Corpus Luteum remains." The true Corpus Luteum is further distinguished
by its capability of being injected from the vessels of the Ovary ; which is
not the case with Tubercular deposits, or other substances which may stimu-
late it. After Delivery, the size of the Corpus Luteum rapidly diminishes;

* Signs of Pregnancy, p. 226.

ACTION OF THE FEMALE. 699

and in a few months it ceases to be recognizable as such. The cicatrix by
which the Ovum has escaped is visible for some time longer ; but this too,
according to the careful researches of Dr. Montgomery, cannot be distin-
guished at a subsequent period. Hence there is no correspondence between
the number of Corpora Lutea found in the ovaries of a woman, or of Cica-
trices on their surface, and the number of children she may have borne. The
number of Corpora Lutea must always be less, when there have been many
conceptions; but the number of Cicatrices maybe greater; for several causes,
such as the escape of unimpregnated ova, or the bursting of little abscesses,
may give rise to such appearances.

914. Much discussion has taken place amongst Embryologists, as to
whether the substance of the Corpus Luteum is deposited within the Graafian
follicle, externally to it, or betiveen its layers. The first is the opinion of
Baer, BischofF, and others ; who regarded it as a growth from the inner layer
of the Graafian follicle. The second is the opinion of Dr. R. Lee and Mr.
Wharton Jones. The third is the doctrine taught by Drs. Montgomery and
Barry; the former regarding it, however, as deposited between the two layers,
of which the cellulo-vascular layer of the Graafian follicle (which are both
derived from the condensed stroma of the ovarium) consist ; whilst the latter
maintains that the deposit takes place between the true Ovisac and its Ovarian
envelopes. The recent inquiries of Dr. Ritchie* throw great light on this
question ; by showing that a great variety of changes may take place, after the
discharge of the Ovum from the Ovisac ; amongst which may be included all
the appearances described by the several writers just quoted. The following
is an abstract of the results of Dr. R.'s researches.

a. The appearances presented by the Ovaries, Graafian follicles, and by the blood which
is contained in the latter subsequent to their rupture, vary according to the time at which
they are examined, and the absorbing power of the individual. — In cases of the recent dis-
charge of an Ovum, the Peritoneal coat of the Ovary is marked by a jagged slit or opening,
having a florid vascular areola ; in those of longer standing, the opening is covered over, —
with the exception of a minute circular foramen in the centre, (or where the slit has been of
great length) of two such openings, — with new tissue, surrounded by a claret-coloured mar-
gin ; and in those still more ancient, the whole is healed up into a cicatrix, which is more
or less superficial and free from discoloration, according to its age.

b. With respect to the Blood, which is generally contained in the ruptured follicles, it is
seen first as a florid coagulum; next, having only its centre scarlet-coloured, and its peri-
phery more or less black, and perhaps furrowed; frequently the clot has a gamboge colour
from the decomposition of its red corpuscles, or has become pale from their absorption ; and
lastly, the clot is found in different stages of absorption. But it sometimes also happens, —
and that indifferently in every variety of the uterine state, — that the ruptured follicles are
found empty, or containing only an aqueous fluid.

c. The coats of the ruptured Follicles have been found vn four different general conditions,
apparently dependent on their relative degree of organization ; and each class presenting,
also, modifications of their respective characteristics, proceeding in part from the same cause,
and in part also from changes connected with the period of their progress in which they
were examined.

i. The first class was distinguished by the attenuated state of the coats of the ruptured
Follicle; and by the total absence of any organic changes in these, different from their con-
dition previous to their discharge. The only alterations observable resulted from the me-
chanical dyeing of their coats of an inky-black, or of a yellow colour, proceeding from their
contact with decomposed blood. — The first class of appearance was found indifferently in
all ages and states, subsequent to puberty.

ir. The second general class of ruptured Follicles was characterized, in addition to the
appearances just described, by organic changes in their coats ; consisting, progressively, of
an increased vascularity, a thickening, a whitening of the colour, and finally, a corrugation
of their tissue. The white bodies thus formed, to which Dr. R. has given the designation of
Corpora Jllbida, may exist tinder two distinct forms: — 1. As soft bodies of a yellowish fatty
aspect having the outer coat much thickened, whilst their inner remains as a delicate dia-

Merlical Gazette, 1S44.

700 OF REPRODUCTION.

phanous pellicle ; these, after a lengthened period, present themselves as yellowish-white,
and generally globular bodies, more or less fissured from their contraction, and sometimes in
process of absorption, having a granular-looking structure, and seldom being divisible into
laminae by simple dissection: — and 2. As dense bodies of a whitish, shining, firm structure,
their inner coat being the seat of these changes, and their outer adhering loosely as a
transparent peculiar layer; the inner layer presents itself as a thick, opaque, deeply-
wrinkled or corrugated, and rocky cyst, or is sometimes partially diaphanous, and of a shin-
ing pearly aspect, and very white colour; and it sometimes contains a yellow, greenish,
transparent fluid, or a clot of blood, either unchanged, or converted into a yellow or black
pigment. This second variety appears to be the Corpus Luteum of Baer. — These white
bodies, or Corpora Albida, were found by Dr. R. in every variety of uterine condition, subse-
quent to the establishment of menstruation, but. never before it ; and the dense kind, espe-
cially, were persistent for a long period. They had no necessary connection with the gravid
condition; but they were occasionally (especially the dense variety) the only specialty ob-
servable in the ovaries of the puerperal female, some time after delivery.

in. The third class was characterized by the presence of an organized yellow-coloured
brain-like, granular matter; forming todies to which Dr. R. has given the name of Corpora
Cephaloidea. These differed, according as the cerebriform matter was deposited between
the layers of ruptured Follicles, having transparent pellicular walls, as in Class i., or having
either their inner or outer coat thickened, as in Class n. ; — or according as the cerebriform
matter was deposited externally to the two inner layers of the Follicle. — The former of those
varieties was found by Dr. Ritchie in menstruating females; also during the first months of
the gravid state; and sometimes even in the period of lactation. In some instances, only
one or two of the cerebriform bodies were found ; but in others, five or six. Their struc-
ture, especially in the more perfectly-organized specimens, presented a striking resemblance
to the convoluted reddish-yellow surface of the brain, covered by its inner membranes, and
painted with its scarlet-coloured and dark vessels. These cephaloid bodies undergo diminu-
tion in proportion to their age, and the absorbing power of the female. In those possessed
of only thin coats, or having the outer layer as the seat of the thickening, the inner walls of
the cysts speedily contracted and coalesced; so that their centres exhibited a delicate opaque
streak : or, in those better developed, a serrated, curved, and well-marked white line, ac-
cording as the cyst was of elliptical or of a globular form. This variety of cerebriform cyst
was met with in a recent state as well in immediate connection with the existence of men-
struation, as during the first seven months of pregnancy ; and in this latter case, by under-
going a conversion in its form presently to be noticed (iv), they constituted the Corpora
Lutea of Dr. Montgomery. — In the second variety of Cephaloid bodies, the two inner layers
of the Graafian Follicle were converted into a dense white body, surrounded by an envelope
of yellow matter. Such cysts (the Corpora Lutea of Dr. Lee) were never observed as an
effect of menstruation simply, but were met with exclusively in the gravid female ; although
two were seen (as were also the cephaloid bodies of the preceding order) to be present in
some cases of single conception. This form of Cephaloid bodies was generally distinguished
by large, persistent, white, glistening cavities. The granular cephaloid matter was some-
times found quite absorbed within a few days after parturition; but in other instances it
underwent the metamorphosis characteristic of the next class.

iv. The fourth general state of the ruptured Graafian follicle was peculiar to the impreg-
nated and lactating female, in the period between the 8th and 13th months after concep-
tion ; and appeared to be a conversion of the Corpora Cephaloidea already described, arising
out of a higher and more perfect organization. Down to the 7th month of pregnancy, the
cysts contained in the Ovaries did not differ in any respect from the cerebriform bodies
found in the unimpregnated state; except that they were sometimes plumper, more vascu-
lar, bettor developed, and had their inner layer more frequently thickened. A change in
the hue of the granular matter thefri commences, which becomes more decided as time
elapses; so that by the end of the 1st month after delivery, it becomes of a decided rose
colour, changing to a still more florid hue on exposure to air. Its cavity also contracts, so as
to leave but. a stellated pnint, nr a curved groove: and a fibrous appearance (probably de-
pendent on the triictiun thus exercised) is seen in the surrounding substance. Although
these bodies, termed by Dr. Ritchie Corpora rubra, are found exclusively in the later months
of pregnancy, or in the puerperal state, yet they are not always present in those conditions.

The number of cases examined by Dr. Ritchie is not, perhaps, sufficient to
enable us to found any positive statements upon the results of his examina-
tion of them ; but the following inductions appear highly probable : — 1. That
the presence of Corpora Rubra may be regarded as indicative, not only of
conception, but also of an advanced state of pregnancy, or of recent delivery;
but that their absence is not to be regarded as any proof to the contrary. — 2.

ACTION OF THE FEMALE. 701

That the presence of Corpora Cephaloidea of the second order is to be re-
garded as indicative of conception. — 3. That the presence of the Corpora
Cephaloidea of the first order, or of Corpora Mbida, cannot be regarded as
in the least degree indicative of Conception ; as they may result from the
simple discharge of an Ovum, in the ordinary course of those changes to
which the Ovarium is subject. — The excess of Corpora Albida above every
other appearance is due, not merely to their being an ordinary result of the
discharge of unimpregnated Ova ; but also to the frequency of their produc-
tion as degenerated forms (so to speak) of the Corpora Cephaloidea and Cor-
pora Rubra of the gravid female ; and also to their occasional existence as,
from the first, the only Ovarian change following upon Conception.

915. The object of the changes which have been already described, is to
bring the Ovum within reach of the fecundating influence ; and to convey it
into the Uterus after it has been fertilized. We have now to consider the
changes in the Ovnm itself, Avhich take place during the same epoch. At
about the same period that the Ovum moves towards the periphery of the
Graafian follicle, the Germinal Vesicle moves towards the periphery of the
yolk-bag ; and it always takes up its position at the precise point of the Zona
Pellucida which is nearest the Ovisac, and which is closest, therefore, to the
surface of the Ovary. Moreover, the Germinal Spot is always on that part
of the Germinal Vesicle, which is in closest contact with the Zona Pellucida.
(See a, Figs. 9 and 10, Plate I.) Thus, the Germinal Spot is very near the
exterior of the Ovary ; but is separated from it by the peritoneal coat of the
latter, by a thin layer of its stroma forming the external layer of the Graafian
follicle, by the ovisac forming its internal membrane, and by the zona pellu-
cida. We have already seen how the obstacle interposed by the three former
to the entrance of the Spermatozoon, is overcome ; we shall presently find
that the Zona Pellucida undergoes a similar change.

916. Whilst the Ovum is being prepared for fecundation, a series of very
important actions takes place in the Germinal Vesicle. The exterior or peri-
pheral portion of the Spot, which previously consisted of a collection of very
minute granules, begins to develope itself into a ring of new cells of extreme
delicacy (Fig. 9, «) ; these gradually enlarge, and a second ring of cells is
developed within it, pushing the first-formed cells further away from the cen-
tre. Many successive rings of cells are thus formed ; and at last the whole
Germinal Vesicle is filled with them, as shown at b, Fig. 10. Still there
remains a pellucid space in the centre of the Germinal Spot (resembling that
seen at a, Fig. 12) ; in which no cells are developed. The first-formed cells
that have been pushed outwards, are so much compressed by those subse-
quently formed, as frequently to undergo liquefaction ; and during the time
that the Ova are being matured for fertilization, there is a continual new pro-
duction of cells at the centre, and a degeneration at the circumference. — At
the same time, the Yolk undergoes changes somewhat analogous ; for it
ceases to contain separate oil-globules ; and large elliptical discs or cells are
seen in it, especially just beneath the Zona Pellucida (Fig. 9, c).* Here, too,
the formation of new cells takes place from the periphery towards the centre ;
the peripheral ones gradually undergo liquefaction, as is seen in the outer
layer of those in Fig. 10, which are becoming indistinct ; and they are replaced
by a new layer pushed outwards from the centre. The same process sub-
sequently continues in the Yolk, for some time after fecundation ; and this
not only in regard to the yolk as a whole, but in respect to its individual cells,

* It is to be remembered that the observations of Dr. Barry, here quoted, were made on
the Rabbit : and are, therefore, probably applicable equally to other Mammalia, but not to
Oviparous Animals.

59*

702 OF REPRODUCTION.

as is shown in Fig. 11, Avhere concentric rings of new cells are seen in each
of the parent vesicles. Even in the most advanced of these secondary cells,
another generation may be seen, and these are developed upon the same plan
with those of the Germinal Vesicle : thus in Fig. 12, the pellucid centre of
the original nucleus of the parent disc is seen at a, and is surrounded by seve-
ral concentric rings of cells, increasing in size from within outwards ; and at
b is represented the condition of the outer and older cells, in which the same
process is undergoing repetition. (Although the figure only represents one
secondary cell as in the act of producing others, the others of the same age
are alike engaged in the process of multiplication.) — The foregoing history is
equally applicable to the cells, from which the Embryo subsequently origi-
nates ; and it is probably the general mode in which the process takes place.

917. At the time when the interior of the Germinal Vesicle is being pre-
pared for the reception of the fecundating influence, the portion of the Zona
Pellucida against which it lies becomes attenuated ; and a chink then forms in
it, just above what was the pellucid centre of the Germinal Spot. Through
this chink, the Spermatozoon can reach the Germinal Vesicle; and that it does
so, we are now entitled to affirm, not only from analogy, but also from actual
observation (§ 900). What is the nature of the influence communicated by it
is less certain; but from the known character of the process of fecundation in
Plants, we shall have little difficulty in concluding, that it deposits in the
Germinal Vesicle the rudiments of the first cells, which are subsequently to
be developed into the Embryonic structure. It is certain that none of the
cells previously contained in the Germinal Vesicle subsequently form part of
it ; in fact, they all liquefy after a time, and disappear entirely. But in the
previously pellucid centre of what Avas the Germinal Spot, two new cells are
seen after fecundation ; these enlarge at the expense of the rest; and from
them, all the permanent structures originate. This pair of cells is seen at a,
Figs. 13 and 14; in the former some of the cells of the Germinal Vesicle are
still left ; in the latter, they have been all absorbed. The Germinal Vesicle
returns after fecundation to the centre of the Yolk, being at first entirely con-
cealed by its discs (Fig. 11); and the cleft in the Zona Pellucida soon closes,
so as to be no longer distinguishable. The two new cells and the other con-
tents of the Germinal Vesicle, undergo such a rapid increase in size, that they
soon fill the whole interior of the Zona Pellucida ; and the cells of the Yolk
being reduced by the pressure into a liquid form, their elements are absorbed
by the new cells of the Embryonic structure. This, at least, is the case in
the Mammalia; among which the Yolk performs but a very subordinate part,
having only to serve for the development of the Embryo during a very brief
period.— In each of the two primary Germ-cells (as they may be called) a
series of changes takes place, exactly conformable to that already described as
occurring in the Germinal Vesicle ; — that is to say, — a ring of new cells origi-
nates in the margin of its nucleus, — this increases in size, and is pushed out-
wards by another ring nearer the centre, this again by another, and so on, —
and at last, two cells appear in the pellucid central space, which are developed
at the expense of all the rest, and are to be regarded as the real permanent
offspring of the parent. These changes may be seen in progress in Figs. 13
and 14; in the former, the original cells of the Germinal Vesicle have not
quite disappeared, although their liquefaction is in progress ; in the latter, no
vestige of them is left, the whole cavity being occupied by the twin-cells.

918. These changes commence during the passage of the Ovum along the
Fallopian tube; and during its transit to the Uterus, it acquires a sort of gela-
tinous envelope, which is inclosed in a membrane of fibrous texture, termed
the Chorion. The gelatinous envelope is probably of an albuminous nature
in reality, corresponding with the white of the Bird's egg; whilst the fibrous

ACTION OF THE FEMALE. 703

texture of Chorion seems to be produced, like the membranous basis of the
egg-shell of the Bird (§ 118), by the exudation of Fibrine from the lining
membrane of the Fallopian tube or Oviduct. The outer layer of this en-
velope, in the egg of the Bird, is consolidated by the deposition of particles of
Carbonate of Lime in its areolrc ; but it undergoes no higher organization.
The Chorion of the Mammal, on the other hand, subsequently undergoes
changes of a much higher order; which adapt it for participating, to a most
important degree, in the nutrition of the included embryo. — The first of these
changes consists in the extension of the surface of the membrane into a num-
ber of villous prolongations, which give it a spongy or shaggy appearance.
These serve as absorbing radicles, and form the channel through which the
embryo is nourished by the fluids of the parent, until a more perfect commu-
nication is formed, in the manner to be presently explained.

919. We have now to speak of the changes in the Uterus, which take
place in consequence of Conception, and which prepare it to receive the
Ovum. Of these the most important is the formation of the Membrana De-
cidua, so called from its being cast off at each parturition. This membrane
has been usually supposed to be a new formation ; and has been described as
originating in coagulable lymph thrown out on the inner surface of the Uterus,
into which vessels are prolonged from the subjacent surface. It appears,
however, from the late researches of Dr. Sharpey and Prof. Weber,* that this
is not the true account of it; and that the Decidua is really composed of the
inner portion of the Mucous membrane itself, which undergoes a considerable
change in its character. The Mucous membrane of the Uterus had been ob-
served by Dr. J. Reid to possess, on its free surface, a tubular structure ; not
very unlike that which has been described as existing in the lining membrane
of the stomach (§ 873 and Fig. 269). This tubular portion becomes thickened
and increased in vascularity, within a short time after conception ; and when
the inner surface of a newly-impregnated Uterus is examined with a low
magnifying power, the orifices of its tubes (Plate I., Fig. 17, b, b) are very
distinctly seen, being lined with a white epithelium. The blood-vessels (c, c)
form a very minute net-work, which extends in loops from the subjacent
portion of the membrane. According to the recent observations of Mr. J.
Goodsir,t the interfollicular spaces (a, a, a) also are crowded with nucleated
particles ; and it is to the development of this interfollicular substance, as well
as to the enlargement of the follicles themselves, and the copious development
of epithelial cells in their interior, that the mucous membrane in this condition
owes its increased thickness. At a later period, the Decidua may be found
to consist of two distinct layers; the Decidua vera, lining the uterus; and the
Decidua reflexa, covering the exterior of the ovum. It was formerly supposed
that the latter is a portion of the former, which has been pushed before the
ovum at its entrance into the uterus ; but the two layers are so different in
texture, that they cannot be supposed to have the same origin. The difficulty
appears to be solved by the observations of Mr. Goodsir. " From what has
now been stated," he remarks, " it appears that the Decidua consists of two
distinct elements; the mucous membrane of the uterus, thickened by a pecu-
liar development ; and a non-vascular cellular substance, the product of the
uterine follicles. The former constitutes, at a later period, the greater part of
the decidua vera; the latter, the decidua reflexa. This view of the consti-
tution of the Decidua clears up the doubts which were entertained regarding
the arrangement of these membranes at the os uteri and entrances of the Fallo-
pian tubes. It is evident that these orifices will be open or closed, just as the

* Miiller's Physiology, pp. 1574-1580.

f Anatomical and Pathological Observations, Chap. ix.

704 OF REPRODUCTION.

cellular secretion is more or less plentiful, or in a state of more or less vigor-
ous development." — " When the ovum enters the cavity of the uterus, the
cellular decidua surrounds it, and becomes what has been named the decidua
reflexa, by a continuation of the same action, by which it had been increasing
in quantity before the arrival of the ovum. The cellular decidua grows around
the ovum by the formation of new cells, the product of those in whose vicinity
the ovum happens to be situated."

920. When the Ovum has arrived in the Uterus, therefore, and the villous
tufts of the Chorion are developed, these come into contact, in the first in-
stance, with the layer of cellular decidua, which intervenes between them
and the vascular decidua. Through this cellular membrane, therefore, the
ovum must derive its nutriment from the vascular surface; and it cannot be
deemed improbable, that the office of its component cells is to draw from the
subjacent vessels the materials which are to serve for the nutrition of the
ovum, and to present it to the villous tufts of the chorion. Each of these is
composed (according to the observations of Mr. J. Goodsir) of an assemblage
of nucleated cells, which are found in various stages of development ; and
these are always inclosed within a layer of basement-membrane, which
seems to be itself composed of flattened cells united by their edges. At the
free extremity of each villus, is a bulbous expansion, the cells composing
which are arranged round a central spot ; and it is at this point that the most
active processes of growth take place, the villus elongating by the develop-
ment of new cells from its germinal spot, and (like the spongiole of the plant)
drawing in. nutriment from the soil in which it is imbedded. — In its earliest
grade of development, the chorion and its villi contain no vessels ; and the
fluid drawn in by the tufts is communicated to the embryo, by the absorbing
powers of the germinal membrane of the latter. But when the tufts are pe-
netrated by blood-vessels; and their communication with the embryo becomes
more direct, the means by which they communicate with the parent are found
to be still essentially the same ; — namely, a double layer of nucleated cells,
one layer belonging to the foetal tuft, and the other to the vascular maternal
surface. It is from these elements that the Placenta is formed, in the manner
next to be described.

921. The first stage in this process consists in the extension of the foetal
vessels into the villi of the Chorion over its entire surface, in the manner here-
after to be detailed (§ 941) ; so that the nutriment which these villi imbibe,
instead of being merely added to the albuminous fluid surrounding the yolk-
bag, is now conveyed directly to the embryo. This, — the earliest and simplest
mode by which the Foetus effects a new connection with the parent, — is the
only one in which it ever takes place in the lower Mammalia, which are hence
properly designated as " non-placental," rather than as ovo-viviparous (§ 44).
In the higher Mammalia, however, there soon occurs a great extension of the
vascular tufts of the foetal Chorion, at certain points ; and a corresponding
adaptation, on the part of the Uterine structure, to afford them an increased
supply of nutritious fluid. These specially-prolonged portions are scattered,
in the Ruminantia and some other Mammalia, over the whole surface of the
Chorion, forming what are termed the Cotyledons ; but in the higher orders,
and in Man, they are concentrated in one spot, forming the Placenta. In
some of the lower tribes, the maternal and the foetal portions of the Placenta
may be very easily separated ; the former consisting of the thickened Decidua;
and the latter being composed of the prolonged and ramifying vascular tufts
of the Chorion, dipping down into it. But in the Human Placenta, the two
elements are mingled together through its whole substance.

922. On looking at the Postal surface of the Human Placenta, we perceive
that the umbilical vessels diverge in every direction from the point at which

ACTION OF THE FEMALE.

705

they enter it; and their subdivisions ramify very minutely, forming a large
part of its substance. The terminal ramifications are represented by Dr. J.
Reid* as having the digitated aspect represented in Fig. 23, (Plate I.) ; but
this is one of the more complex forms. In its simplest character, each
villus is cylindrical or nearly so ; and the digitated villi are only solitary villi
grouped together at the extremity of a primary branch. Each villus contains
a capillary vessel, which forms a series of loops, communicating with an
artery on one side and with a vein on the other; but the same capillary may
pass into several villi, before re-entering a larger vessel. The vessels of the
villi are covered, as in the Chorion, by a layer of cells (Fig. 280y), inclosed

Fig. 280.

Fig. 281.

Portion of the external membrane,
with the external cells, of a placental
villus:— a. cells seen through the mem-
brane ; 6, cells seen from within the
villus; e, cells seen in profile along the
edge of the villus.

Extremity of a placental villus :— a, exter-
nal membrane of the villus, continuous with
the lining- membrane of the vascular system
of the mother ; 6, external cells of the villus,
belonging to the placental decidua ; c, c, ger-
minal centres of the external cells ; d, the
space between the maternal and fetal por-
tions of the villus; e, the internal membrane of
the villus, continuous with the external mem-
braneof the chorion;/, the internal cellsof'he
villus, belonging to the chorion ; g, the loop of
umbilical vessels.

in basement-membrane (e) ; but the fo3tal tuft thus formed is inclosed in a se-
cond series of envelopes (a, b, c), derived from the maternal portion of the
Placenta, — a space (d) being left, however, between the two, at the extremity
of the tuft.

923. Whilst the foetal portion of the Placenta is thus being generated by
the extension of the vascular tufts of the Chorion, the Maternal portion is
formed by the enlargement of the vessels of the decidua, between which they
dip down. " These vessels assume the character of sinuses ; and at last swell
out (so to speak) around and between the villi ; so that finally the villi are
completely bound up or covered by the membrane which constitutes the walls
of the vessels, this membrane following the contour of all the villi, and even
passing to a certain extent over the branches and stems of the tufts. Between
this membrane, or wall of the enlarged decidual vessels, and the internal mem-
brane of the villi, there still remains a layer of the cells of the decidua. "t In
this manner is formed the Maternal portion of the Placenta, which may be re-
garded in its adult state (as was well pointed out by Dr. J. Reid) in the light
of a large sac formed by a prolongation of the inner coat of the Uterine vessels ;
against the fcetal surface of which sac, the tufts just described may be said to
push themselves, so as to clip down into it, carrying before them a portion of
its thin wall, which constitutes a sheath to each tuft. Now as every extension

* Edinb. Med. and Surg. Journal, Jan. 1841.

•j- Goodsir's Anatomical and Pathological Observations, p. 60.

706

OF REPRODUCTION.

of the uterine vessels carries the decidua before it, every one of the vascular
tufts that dips down into it will be covered with a layer of the cellular struc-
ture of the latter; and the foetal portion of each tuft will thus be inclosed in a
layer of maternal cells and basement-membrane (Fig. 280, «, 6, c ; and Fig.

281, a, b, e). In this manner, the whole interior of the placental cavity is in-
tersected by numerous tufts of foetal vessels, disposed in fringes, and bound
down by reflections of the delicate membrane that forms its proper wall ; just
as the intestines are held in their places by reflections of the peritoneum that
covers them. This view was suggested to Dr. R. by the very interesting fact,
that the tufts of foetal vessels not unfrequently extend beyond the uterine sur-
face of the Placenta, and dip down into the uterine sinuses ; Avhere they are
still covered, and held in their places, by reflections of the same membrane
(Plate I., Fig. 24). All the bands which connect and tie down the tufts (Fig.

282, g), are formed of the same elements as the envelopes of the tufts them-
selves ; namely, a fold of the lining membrane of the decidual sinuses, and a
layer of the cellular decidua.

Fig. 282.

Diagram illustrating1 the arrangement of the placental decidua :— a, decidua in contact with the interior
of the uterus; ft, venous sinus passing obliquely through it by a valvular opening; c, a curling artery
passing in the same direction ; cl, the lining membrane of the maternal vascular system, passing in from
the artery and vein, lining the bag of the placenta, and covering e, e, the fcctal tufts, passing on to them
from their stems from the foetal side of the cavity, also by the terminal decidual bars/./, from the uterine
side, and from one tuft to the other by the lateral bar, g ; h, h, separated fcetal tufts, showing the internal
membrane and cells, which, with the loops of umbilical vessels, constitute the true foetal portion of the

tufts.

•

924. The blood is conveyed into the Placental cavity by the "curling
arteries" of the Uterus ; and is returned from it by the large veins, that are
commonly designated as sinuses. The foetal vessels, being bathed in this
blood, as the branchiae of aquatic animals are in the water that surrounds them,
not only enable the foetal blood to exchange its venous character for the arte-
rial, by parting with its carbonic acid to the maternal blood, and receiving
oxygen from it; but they also serve as rootlets, by which certain nutritious
elements of the maternal blood (probably those composing the liquor sanguinis)
are taken into the system of the Foetus. In this they closely correspond with
the villi of the Intestinal canal; and there is this further very striking analogy,
— that the nutrient material is selected and prepared by two sets of cells, one
of which (the maternal) transmits it to the other (the fcctal), in the same man-
ner as the epithelial cells of the intestinal villi seem to take up and prepare
the nutrient matter, which is destined to be still further assimilated by the
special absorbing cells of their interior (§ 672). There is no more direct
communication between the Mother and Foetus than this; all the observations
which have been supposed to prove the existence of real vascular continuity,

ACTION OF THE FEMALE. 707

having been falsified by the extravasation of fluid, consequent upon the force
used in injecting the vessels. Moreover, the different size of the blood-corpus-
cles in the Foetus and in the Parent (§ 149) shows the non-existence of any
such communication.

925. The formation of the Placenta, in the manner just described, com-
mences in the latter part of the second month ; during the third, it acquires
its proper character; and it subsequently goes on increasing, in accordance
with the growth of the ovum. Towards the end of the term of gestation,
however, it becomes more dense and less vascular; owing, it would seem, to
the obliteration of several of the minuter vessels, which are converted into
hard fibrous filaments. The vessels of the Uterus undergo great enlargement
throughout, but especially at the part to which the Placenta is attached; and
the blood in moving through them produces a peculiar murmur, which is
usually distinctly audible at an early period of Pregnancy, and may be regarded
(when due care is taken to avoid sources of fallacy), as one of its most unequi-
vocal positive signs. The Placental bruit is thus described by Dr. Mont-
gomery.* " The characters of this phenomenon are, a low murmuring or
somewhat cooing sound, resembling that made by blowing gently over the lip
of a wide-mouthed phial, and accompanied by a slight rushing noise, but with-
out any sensation of impulse. The sound is, in its return, exactly synchronous
with the pulse of the mother at the time of examination ; and varies in the
frequency of its repetitions, with any accidental variation which may occur
in the maternal circulation. Its situation does not vary during the course of
the same pregnancy ; but in whatever region of the uterus it is first heard, it
will in future be found, if recognized at all, — for it is liable to intermissions, —
at least we shall occasionally be unable to hear it where we have already
heard it a short time before, and where we shall shortly again recognize it.
According to my experience, it will be most frequently heard about the situa-
tion of the Fallopian tube of the right side ; but it may be detected in any of
the lateral or anterior parts of the uterus." That the cause of this sound
exists in the Uterus itself, is distinctly proved by the fact, that it has been
heard when that organ was so completely anteverted, that the fundus hung
down between the patient's thighs. A sound so much resembling this, as to
be scarcely distinguishable from it, may be occasioned, however, by a cause
of a very different nature, — namely, an abdominal tumour, pressing upon the
aorta, iliac arteries, or enlarged vessels of its own; and, in doubtful cases, it
is necessary to give full weight to the possibility of such an explanation. The
sound may be imitated at any time, by pressing the stethoscope on the iliac
arteries. The Placental bruit has been not unfrequently heard in the llth
week ; but it cannot generally be detected before the fourth month, when the
fundus uteri rises above the anterior wall of the pelvis.

926. The amount of the peculiar tissue of the Uterus (§ 234) greatly
increases during pregnancy. At the same time, the Mammary gland and its
appendages undergo a fuller development; and from this a valuable, but not
unequivocal, indication of pregnancy may be drawn. Occasional shooting
pains in the Mammae are not unfrequently experienced within a short period
after conception ; and more continued tenderness is also not unusual. A sense
of distension is very commonly experienced at about the end of the second
month; and from that time a distinct " knottiness" usually begins to present
itself, increasing with the advance of Pregnancy. In many instances, how-
ever, these mammary sympathies are entirely absent; and they may be simu-
lated by changes that take place in consequence of various affections pf the
Uterus. A change of colour in the areola is a very common, but not an

* Op. cit., p. 121.

708 OF REPRODUCTION.

invariable, occurrence in the early months of pregnancy ; but another sign is
afforded by the areola and nipple, which is of more value because more con-
stant,— namely, a puffy turgescence, and an increased development of the
little glandular follicles, or tubercles, which commonly secrete a dewy mois-
ture.— The presence or absence of kiesteine in the Urine (§ 859) also may
probably be regarded as a valuable diagnostic sign. This substance appears
on the surface of the fluid, after it has stood for two or three days, in the form
of a thin pellicle of a somewhat fatty aspect; it is preceded by a sediment
which has very much the appearance of cotton wool; and it disappears when
the urine is decomposing, at the same time emitting an odour like that of
putrid cheese.* — Many other changes in the constitution take place during
Pregnancy ; indicated by the buffmess of the blood, the irritability of the sto-
mach, and the increased excitability of the mind. All these, however, are
discussed with sufficient amplification, in works on Obstetric Medicine.

927. The act of Conception, being one of a purely organic nature, is not
attended with any consciousness on the part of the mother ; but there are
some women, in whom it is attended with certain sympathetic affections, such
as faintness, vertigo, &c., that enable them to fix upon the particular time at
which it has taken place. From that period, however, the Mother has no
direct consciousness of the change going on in the Uterus (save by the effects
of its increasing pressure on other parts), until the occurrence of what is
termed " Quickening." This is generally described as a kind of fluttering
movement, attended with some degree of syncope or vertigo. After it has
once occurred, and has strongly excited attention, it is occasionally renewed
once or twice, and then gives place to the ordinary movements of the foetus.
Not unfrequently, however, no movement whatever is felt, until near the end
of the term of gestation, or even through the whole of it. As to the cause of
the sensation, Obstetricians are much divided; and no satisfactory account
has been given of it. It has been vulgarly supposed to be due to the first
movement of the Fo3tus, which was imagined then to become possessed of an
independent life: and the English law recognizes the truth of this doctrine,
in varying the punishment of an attempt to procure Abortion, according to
whether the woman be " quick with child" or not; and in delaying execution
when a woman can be proved to be so, though it is made to proceed if she is
not, even if she be unquestionably pregnant. Whether or not the first sensible
motions of the Foetus are the cause of the peculiar feeling in question, there
can be no doubt that the Embryo has as much independent vitality before, as
after, the quickening. From the time that the Ovum quits the Ovary, it ceases
to be a part of the Parent, and is dependent on it only for a due supply of
nourishment, which it converts, by its own inherent powers, into its proper
fabric. This dependence cannot be said to cease at the moment of quicken-
ing; for the connection must be prolonged during several weeks, before the
Foetus can be said to be capable of living without such assistance. The earliest
period at which this may occur, will be presently considered (§ 932).

928. At the conclusion of about nine (solar) months from the period of con-
ception, the time of Parturition arrives. The Uterus, by its own efforts, and
by the assistance of the muscles of Expiration, expels its contents ; and the
membranes of the Ovum being usually ruptured before it is entirely dis-
charged, the Foetus comes at once into the world. Although there can be no
doubt that, as already stated (§ 393), the contractile fibres of the Uterus may
be called into effectual action without Nervous influence, yet it is equally cer-
tain that Uterine contractions may be induced through the Spinal system of

* [See an excellent paper on this subject in Am. Journ. of Med. Sci., vol. iv., N. S., by
Elisha Kane, M. P.— M. C.]

ACTION OF THE FEMALE. 709

nerves. For in no other way can we account for many phenomena which
are obviously of a reflex character; such as the sudden contraction of the Ute-
rus, previously distended and inactive, when cold is applied to the external
surface of the body, or- when the child is applied to the nipple. In the first
stage of labour, the Uterine contractions appear to be alone concerned; and
it is not until the head of the child is passing through the Os Uteri, and is
entering the Vagina, that the assistance of the Expiratory muscles is called
in. The excitor fibres, which convey to the Spinal Cord the stimulus that
calls them into action, must originate, therefore, rather in the Vagina than in
the Uterus itself. Whilst the fibres of the fundus and body of the Uterus are
in powerful contraction, those of the Cervix Uteri and Vagina must be in a
state of dilatation ; and this dilatation appears to be in some respects different
from the mere yielding to the pressure of the child's head. A slow contrac-
tion of the fibres of the fundus and body of the Uterus, and a yielding of
those of the cervix, usually take place during some days previous to Par-
turition ; so that the child lies lower, and the size of the abdomen diminishes.*

929. As to the reason why the period of Parturition should be just nine
months after that of Conception, we know nothing more than we do of that
of similar facts in the physical history of Man — such as the periodical return
of the Catamenia, — the renewal of the Teeth, — the recurrence of the tend-
ency to Sleep, &c. That it is immediately dependent upon some state of the
constitution, rather than upon the condition of the Uterus, appears from the
fact that, in cases of Extra-uterine pregnancy, contractions resembling those
of labour take place in its walls. Moreover, various states of the constitu-
tion, especially that which is designated as irritability, may induce the occur-
rence of the parturient efforts at an earlier period ; and this constitutes Abor-
tion, or Premature delivery, according to the viability of the child. There
are some women, in whom this regularly happens at a certain month, so that it
seems to be an action natural to them ; but it is always to be prevented, if pos-
sible, being injurious alike to the mother and child ; and this prevention is to
be attempted by rest and tranquillity of mind and body, and by a careful avoid-
ance of all the exciting causes, which may produce Uterine contractions by
their operation on the Nervous system. For it is to be remembered that,
although the muscular fibres of the Uterus are capable, like those of the ali-
mentary canal, of an independent action, they are likely to be excited to ope-
ration through the Nervous system, and especially through the Sympathetic
(§ 393). The same action which expels the Foetus, also detaches the Pla-
centa ; and if the Uterus contract with sufficient force after this has been
thrown off, the orifices of the vessels which communicated with it are so
effectually closed, that little or no hemorrhage takes place. If, however, the
Uterus does not contract, or relaxes after having contracted, a large amount
of blood may be lost in a short time from the open orifices. For some little
time after Parturition, a sero-sanguineous discharge, termed the Lochia, is
poured out from the Uterus ; and this commonly contains shreds of the De-
ciduous membrane, which had not been previously detached. Within a few
weeks after delivery, the Uterus regains (at least in a healthy subject) its pre-
vious condition; and it is probable that the portion of its mucous Membrane,
which had been thrown off" as Decidua, is very early reproduced.

930. Although the duration of Pregnancy is commonly stated at nine
solar months, it would be more correct to fix the period at 40 weeks, or 280
days ; which exceeds nine months by from 5 to 7 days, according to the
months included. This, at least, is the average result of observation, in cases

* See some interesting Papers on the Physiology of Parturition, by Dr. W. Tyler Smith,
in the Lancet, July 6 and 13, 1844.

60

710 OF REPRODUCTION.

in which the period of Conception could be fixed from peculiar circumstances,
with something like certainty. The mode of reckoning customary among
women, is to date from the middle of the month after the last appearance of
the Catamenia; but it is certain that Conception is much more likely to take
place soon after they have ceased to flow, or even before their access, than at
a later period (§ 909) ; so that, in most instances, it would be most correct to
expect Labour at forty weeks and a few days after the last recurrence of the
Menses. The period of Quickening may be relied on in some women, in
whom it occurs with great regularity in a certain week of Pregnancy; but
there is in general great latitude as to the time of its occurrence. The usual
•or average time is probably about the 18th week.

931. The question of the extreme limits of Gestation, is one of great import-
ance both to the Practitioner and to the Medical Jurist ; but it is one which
cannot yet be regarded as satisfactorily decided. Many persons, whose expe-
rience should give much weight to their opinion, maintain that the regular
period of 40 weeks is never extended for more than two or three days ; whilst,
on the other hand, there are numerous cases on record, which, if testimony is
to be believed at all, (and in many of these, the character and circumstances
of the parties placed them above suspicion,) furnish ample evidence that Ges-
tation may be prolonged for at least three weeks beyond the regular term.*
The English law fixes no precise limit ; and the decisions which have been
given in our courts, when questions of this kind have been raised, have been
mostly formed upon the collateral circumstances. The law of France pro-
vides that the legitimacy of a child born within 300 days after the death or
departure of the husband, shall not be questioned ; and a child born after more
than 300 days is not declared a bastard, but its legitimacy may be contested.
By the Scotch law, a child is not declared a bastard, unless born after the
tenth month from the death or departure of the husband.

a. The analogical evidence drawn from observations on the lower animals is extremely
strong. The observations of Tessier, which were continued during a period of forty years,
with every precaution against inaccuracy, have furnished a body of results, which seems
quite decisive. In the Cow, the ordinary period of gestation is about the same as in the
Human female; but out of 577 individuals, no less than 20 calved beyond the 298th day, and
of these, some went on to the 321st, making an excess of nearly six weeks. Of 447 Mares,
whose natural period of gestation is about 335 days, 42 foaled between the 359th and the 419th
day, the greatest protraction being thus 84 days, or just one-fourth of the usual term. Of 912
Sheep, whose natural period is about 151 days, 96 yeaned beyond the 153d day; and of
these, 7 \vent on until the 157th day, making an excess of 6 days. Of 161 Rabbits, whose
natural period is about 30 days, no fewer than 25 littered between the 32d and 35th; the
greatest protraction was here one-sixth of the whole period, and the proportion in which
there was a manifest prolongation was also nearly one-sixth of the total number of indi-
viduals. In the incubation of the common Hen, Tessier found that there was not unfre-
quently a prolongation to the amount of three days, or one-seventh of the whole period.

b. In regard to Cows, the observations of Tessier have been recently confirmed by those
of Earl Silencer, who has publishedf a table of the period of gestation as observed in 764
individuals; lie considers the average period to be 284 or 285 days: but no fewer than 310
calved after the 285th day: and of these, 3 went on to the 300th day, and 1 to the 313th.
It is curious that, among the calves born between the 290th and 300th days, there was a
decided preponderance of males, — these being 74, to 32 females; whilst all of those born
after the 300th day were fc'inales.

c. It appears, however, from some recent statements published on the authority of Earl
Spencer, that the Male parent may exert an important influence on Ihe period of gestation.
Of 75 Cows in calf by a particular bull, the average period was 288^ days, or four days
more than the usual period. Ol'ihe 764 cows previously mentioned, 185 (nearly one-fourth)
went less than 281 days; whilst not one of the cows in calf to this bull did so. On the

* A good collection of such cases will be found in Dr. Montgomery's excellent work on
the Signs of Pregnancy.

f Journal of the English Agricultural Society, 1S39.

ACTION OF THE FEMALE. 711

other hand, of the 764 cows first mentioned, 111 (rather more than one-seventh) went above
289 days; while, of the cows in calf by this bull, 29 out of 75 (nearly two-fifths) went above
289 days.*

d. Another series of observations has recently been published by Mr. C. N. Bement of
Albany, U. S.,f who has recorded the period of gestation of 62 Cows. The longest period
was 336 days; the shortest, 213 days. The average period for male calves was 288 days;
and for females, 2 82 days.

These variations are probably to be regarded as due, not so much to a pro-
longation of the period of (7/ero-gestation, as to various circumstances which
may have a retarding influence on the process of Fecundation, and on the
transmission of the Ovum through the Fallopian tube. These have been well
pointed out by Dr. Montgomery.:): It may be added that, in Dr. Barry's ob-
servations on the early changes that take place in the Ovum of Rabbits, he
has noticed several irregularities of this description. — On the whole, it may
be considered that, in regard to the Human female, the French law is a very
reasonable one. It is probable, from the circumstances alluded to in the pre-
ceding paragraph, that Gestation is protracted to the extent of a week, ten
days, or a fortnight, much more frequently than is commonly supposed. In
several of the cases in which the protraction appeared indubitable, the Infant
•was unusually large and vigorous.

932. In regard to the shortest period at which Gestation may terminate,
consistently with the viability of the Child, there is a still greater degree of
uncertainty. Most practitioners are of opinion, that it is next to impossible
for a Child to live and grow to maturity, which has not nearly completed its
seventh month ; but it is almost unquestionable that Infants, which have been
born at a much earlier period, have lived for some months. It is rare in such
cases, however, that the date of Conception can be fixed with sufficient pre-
cision to enable a definite statement to be given. Of the importance of the
question, a case which recently occurred in Scotland affords sufficient proof.
A vast amount of contradictory evidence was adduced on this trial ; but, on
the general rule of accepting positive in preference to negative testimony, it
seems that we ought to consider it possible, that a child may live for some
months, which has been born at the conclusion of 24 weeks of gestation. In
the case in question, the Presbytery decided in favour of the legitimacy of an
Infant born alive within 25 weeks after marriage. §

a. A very interesting case is on record, || in which the mother (who had borne five chil-
dren) was confident that her period of gestation was less than 19 weeks; the facts stated
respecting the development of the child are necessarily very imperfect, as it was important
to avoid exposing his body, in order that his temperature might be kept up ; but at the age
of three weeks, he was only 13 inches in length, and his weight was no more than 29 oz.
At that time, he might be regarded, according to the calculation of the mother, as correspond-
ing with an infant of 22 weeks or 5^ months; but the length and weight were greater than
is usual at that period, and he must have been probably born at about the 25th week. It is
an interesting feature in this case, that the calorific power of the Infant was so low, that
artificial heat was constantly needed to sustain it; but that, under the influence of the heat
of the fire, he evidently became weaker, whilst the warmth of a person in bed rendered
him lively and comparatively strong. During the first week, it was extremely difficult to
get him to swallow ; and it was nearly a month before he could suck. At the time of the
report, he was four months old, and his health appeared very good.

b. Another case of very early viability has been more recently put on record by Mr.
Dodd:1T in this, as in the former instance, the determination of the child's age rests chiefly
on the opinion of the mother ; but there appears no reason for suspecting any fallacy. The

> Dr. J. C. Hall, in Medical Gazette, May 6, 1842.

t American Journal of the Medical Sciences, October, 1845. J Op. cit., p. 272.

§ Report of Proceedings against the Rev. Fergus Jardine, Edin., 1839.
|| Edinb.'Med. and Surg. Journal, vol. xi.
1T Provincial Medical and Surgical Journal, vol. ii. p. 474.

712 OF REPRODUCTION.

child seems to have been born at the 26th or 27th week of gestation ; and having been
placed under judicious management, it has thriven well.

c. One of the most satisfactory cases on record, is that detailed by Dr. Outrepont (Professor
of Obstetrics at Wurtzburgh), and stated by Dr. Clmstison in his evidence on the case just
alluded to. The evidence is as complete as it is possible to be in any case of the kind ; being
derived not only from the date assigned by the Mother to her Conception, but also from the
structure and history of the Child. The Gestation could have only lasted 27 weeks, and was
very probably less. The length of the child was 13^ inches, and its weight was 24 oz. Its
development was altogether slow; and at the age of eleven years, the child seemed no more
advanced in body or mind, than most other lads of seven years old. In this last point, there
is a very striking correspondence with the results of other observations upon very prema-
ture children, made at an earlier age : and these all harmonize with the general principle
already more than once alluded to, — that the shorter the period during which the early de-
velopment of the embryo takes place at the expense of nourishment supplied by the parent,
the lower is the degree of development it will ultimately attain (§ 45).

d. To these may be added another case of recent occurrence in America : in which a
woman, who believed herself to be in the sixth month of pregnancy, was prematurely de-
livered in consequence of a fall. The child seemed barely alive, showing scarcely any
motion, and being too feeble to cry. It had no nails on its hands or feet, nor hair on the scalp ;
and the cranium was imperfectly ossified. At the end of seven weeks it was weighed for
the first time, and found to weigh only 26 oz. When ten months old, it was playful, lively,
and healthy; and weighed 10^ Ibs. The reporter of this case regrets that he did not take
more particular notice of the state of the Child at birth, which he was prevented from
doing by the daily expectation of its death.*

933. There is another question regarding the Function of the Female in
the Reproductive act, which is of great interest in a scientific point of view,
and which may become of importance in Juridical inquiries; — namely, the
possibility of Stiperfcetation, that is, of two distinct conceptions at an interval
of greater or less duration ; so that two fetuses of different ages, the offspring
perhaps of different parents, may exist in the Uterus at the same time. — The
simplest case of Su perforation, the frequent occurrence of which places it be-
yond reasonable doubt, is that in which a female has intercourse on the same
day with two Males of different complexions, and bears twins at the full time;
the ,two infants resembling the two parents respectively. Thus, in the slave-
states of America, it is not uncommon for a black woman to bear at the same
time a black and a mulatto child; the former being the offspring of her black
husband, and the latter of her white-paramour. The converse has occasionally
though less frequently, occurred ; a white woman bearing at the same time a
white and a mulatto child. There is no difficulty in accounting for such
facts, when it is remembered that nothing has occurred to prevent the Uterus
and Ovaria from being as ready for the second conception as for the first ; since
the orifice of the former is not yet closed up ; and, at the time when one ovum
is matured for fecundation, there are usually more in the same condition.
But it is not easy thus to account for the birth of two children, each appa-
rently mature, at an interval of five or six months ; since it might have been
supposed that the uterus was so completely occupied with the first Ovum, as
not to allow of the transmission of the seminal fluid, necessary for the fecun-
dation of the second. In cases where two children have been produced at
the same time, one of which was fully-formed, whilst the other was small and
seemingly premature, there is no occasion whatever to imagine that the two
were conceived at different periods ; since the smaller fetus may have been
" blighted," and its development retarded, as not unfrequently happens in other
cases. Nor is it necessary to infer the occurrence of Superfetation in every
case, in which a living child has been produced a month or two after the birth
of another; since the latter may have been premature, whilst the former has
been carried to the full term. But such a difference can scarcely be, at the

* American Journal of the Medical Sciences, April 1843.

DEVELOPMENT OF THE EMBRYO. 713

most, more than 2| or three months ; and there are several cases now on re-
cord, in which the interval was from 110 to 170 days, whilst neither of the
children was premature in appearance; so that the possibility of a second
Conception, when the Uterus already contains an Ovum of several months,
can scarcely be denied, however improbable it may seem.

4. — Development of the Embryo.

934. Under this head it is intended to state, not so much the details of the
process of Development, as those leading facts, the knowledge of which is
desirable in itself, as well as essential to the due comprehension of the former.
It is difficult to see what practical benefit can result from a minute acquaint-
ance with all the steps of the evolution of the Embryo, however interesting
these may be in a scientific point of view; and the time of the ordinary Stu-
dent, on which there are so many pressing calls, may be much better occupied
than in committing them to memory. In the following sketch, little will be
said respecting the latter stages of the process, or the development of particular
organs, since these have been already noticed under their severally distinct
heads. Our attention will first be given to the formation of the Embryonic
mass, and of the membranes surrounding the Yolk-bag; and then to the ori-
gin of the Vertebral column, Digestive organs, and Circulating apparatus.

935. The Ovum, when it quits the Ovarium, has been stated to contain
within the Germinal Vesicle, two cells which did not exist there previously
to fecundation; and from each of these, two new cells are subsequently pro-
duced, which in their turn give birth to eight others (§ 917). In this manner,
the number of vesicles originating in the twin-cells of the Germ is continually
increased, until at last they become too numerous to be counted, and form a
cluster resembling a Mulberry in appearance ; this mulberry-like structure
may be conveniently termed the Germinal Mass (Plate I., Fig. 15, «). In the
centre of this mass there is found a peculiar Cell, differing from the rest in its
greater size, and in possessing a very well-defined annular nucleus, with a
pellucid cavity in its centre (Fig. 16, a, b}. From this peculiar Cell, all the
parts which enter permanently into the composition of the Embryo are de-
veloped ; the vesicles forming the exterior of the germinal mass being sub-
servient to a merely temporary purpose. This central or Embryonic Cell is
gradually brought to the surface of the Germinal Mass, by the formation of a
cavity c in the interior of the latter; for the layer of cells within which this
cavity is formed, progressively extends itself, until it comes into contact with
the inner surface of the Yolk-bag, having absorbed the yolk into the hollow
thus left. Thus out of the periphery of the Mulberry-mass, appears to be
formed the exterior layer of what is termed the Germinal Membrane: this
membrane is first seen as an epithelium-like layer of cells, covering the Yolk;
but beneath this layer, which is afterwards known as the serous lamina of the
Germinal membrane, two others are subsequently produced from the central
portion of the Germinal mass. Now it is highly interesting to observe, that
this Germinal Membrane, which in the higher animals is a mere temporary
structure, subservient only to a temporary function, forms, in the lower tribes,
the greater part of the permanent fabric of the body. Thus, in the Polypes,
the cavity in which the Yolk is inclosed becomes a Stomach ; the external
layer of the Germinal Membrane becomes the integument; whilst the internal
forms the lining of the Digestive cavity, of which the mouth is formed by
absorption of its wall at one point. Here the Yolk is directly absorbed and
assimilated by the surrounding membrane. In the higher Oviparous animals,
the Germinal Membrane serves to absorb nutritious matter from the Yolk,
and to prepare it for the use of the Embryo itself, by converting it into Blood

60*

714 OF REPRODUCTION.

(§ 938) ; but, after the Yolk has been exhausted, the Yolk-bag is taken into
the body, and is gradually removed by absorption. In Mammalia, these
structures are of less importance. The store of Yolk, laid up for the nutrition
of the Embryo, is comparatively inconsiderable; being only destined to serve
for the short time that elapses, before the Ovum forms its new connection
with the Parent, through the medium of the Chorion ; and the Yolk-bag is
ultimately separated from the Embryo, and thrown off as useless. Still the
early processes are the same in Mammiferous, as they are in Oviparous ani-
mals ; and the Development of Man, of a Bird, of a Reptile, or of a Fish,
takes place, up to a certain point, upon the same general plan.

936. The Embryonic Cell, and the cluster of cells that surrounds it, hav-
ing arrived on the surface of the Yolk by the movement just described, con-
stitute what is known in the Bird's egg under the name of the Cicatricula.
This is a semi-opaque disc, composed of numerous flattened cells; and in the
midst of it is seen a round transparent space, termed the Area Pellucida,
which is nothing else than the place occupied by the large Embryonic Cell,
now become flattened, and still retaining its clearness. In the centre of this
is seen a very faint line, which is termed the Primitive Trace; and this is
the large annular Nucleus (Plate I., Fig. 16, b) of the Embryonic Cell, now
become elongated, and itself beginning to be developed into cells. The same
process then takes place within the Embryonic Cell, which has been described
as occurring within the Germinal Vesicle (§ 916); the granules forming the
periphery of the nucleus are first developed into cells, and these are pushed
outwards by a new series subsequently generated near the centre. From the
mass of cells thus formed, a hollow process passes down into the Yolk; and
this gradually extends itself in the same manner as did that formed from the
Mulberry-mass, until it includes the whole Yolk, and comes into contact with
the inner surface of the layer of cells already mentioned as forming the serous
or external lamina of the Germinal Membrane. This second layer of cells
is probably that which forms the vascular lamina of the Germinal Membrane.
A third process seems to be afterwards sent down, from a part of the nucleus
somewhat interior to that from \vhich the last proceeded: and this becomes
the mucous or internal lamina of the Germinal Membrane.

937. The cell-germs forming the periphery of the Nucleus having been thus
developed, those nearer the centre then begin to exhibit a corresponding acti-
vity. Their evolution follows exactly the same plan as that which has been
described in regard to the contents of the Germinal Vesicle (§ 916); with
the exception that these are arranged in an elongated and not in a circular
form. The shape of the nucleus at this time may be compared to that of a
pear; the large end marking the situation of the Head ; whilst the prolonged
portion is the rudiment of the body. On the median line is seen a groove,
occupying the situation in which the Nervous Centres are to be subsequently
evolved (Fig. 25, Plate II.). These, when first developed, are surrounded by
a tubular structure, which has but a temporary existence in the higher Verte-
brata, but which is permanent in the lower Fishes : this structure, termed the
Chorda JJoraalis, is found, wherever it exists, to be entirely composed of
nucleated cells. From the cells which are exterior to these, is produced the
Vertebral Column ; and the mode in which this originates is somewhat as
follows. The cells on cither side of the central ^pace (in which the elements
of the nervous system are not yet developed) rise up in a ridge, so that the
central space becomes a groove ; these two ridges gradually rise up and ap-
proach one another, and they are then observed to contain, in what subse-
quently becomes the thoracic region, a few pairs of small opaque plates.
The ridges (termed plicifi dorsalcs,or dorsal lamina?) continue inclining towards
each other, until they coalesce, so that a complete tube is formed ; and in this

DEVELOPMENT OF THE EMBRYO. 715

tube an indication is soon perceived of a division into vertebrae, of which the
plates just mentioned are the incipient arches (Fig. 26, Plate II.). Towards
the anterior extremity, however, the dorsal lamina? do not at once close in ;
and the large cells, in which the great divisions of the Encephalon originate
(§ 358), may be seen between them. From the Dorsal Lamina on either side,
a prolongation passes outwards and then downwards, forming what is known
as the ventral lamina; in this are developed the Ribs and the transverse pro-
cesses of the Vertebrae ; and the two have the same tendency to meet on the
median line, and thus to close in the abdominal cavity, which the dorsal
lamina? have to inclose the spinal cord. At the same time the layers of the
Germinal Membrane, which lie beyond the extremities of the Embryo, are
folded in, so as to make a depression on the yolk ; and their folded margins
gradually approach one another under the abdomen. In these two modes, a
cavity is formed beneath the Embryonic mass, which is separated from the
general cavity of the Yolk by the folds just described; but these still leave a
passage which, in the Bird, remains of considerable size until a much later
period, but which, in the Mammiferous Ovum, is soon obliterated. For the
sac which contains the yolk, and from which the abdominal cavity is pinched
off (as it were) at a very early period, is destined, in the Mammiferous ani-
mal, to be entirely cast away ; the purpose which it has to serve being one of
a very temporary character.

938. Whilst these new structures are being produced, a very remarkable
change is taking place in that part of the Serous lamina, which surrounds the
Area Pellucida. This rises up on either side in two folds ; and these gradually
approach one another, at last meeting in the space between the general en-
velope and the embryo, and thus forming an additional investment to the
latter. As each fold contains two layers of membrane, a double envelope
is thus formed ; of this, the outer lamina adheres to the general envelope ;
whilst the inner remains as a distinct sac, to which the name of Amnion is
given. (See Figs. 284, 285, and 286.) This takes place during the third
day in the Chick ; the period at which it occurs in the Human Ovum is diffi-
cult to be ascertained, owing to the small number of normal specimens which
have come under observation at a sufficiently early stage. — During the same

Fig. 283. Fig. 284.

Plan of early uterine Ovum. Within the Diagram of ovum at later stage ; the digestive ca-

external ring, or zona pellucida, are the serous vny beginning to be separated from the yolk-sac,

lamina, a; the yolk, b; and the incipient em- and the ainnion beginning to be formed; a, chorion;

bryo, c. b, yolk-sac ; c, embryo ; d, and e, folds of the serous

layer rising up to form the Amnion.

period, a very important provision for the future support of the Embryo begins
to be made; by the development of Blood-vessels and the formation of Blood.
Hitherto, the Embryonic structure has been nourished by direct absorption of

716 OF REPRODUCTION.

the alimentary materials supplied to it by the Yolk; in the same manner as
the simplest Cellular plant is developed at the expense of the carbonic acid,
moisture, &c., which it obtains for itself from the surrounding elements. But
its increasing size, and the necessity for a more free communication between
its parts than any structure consisting of cells alone can permit, call for the
development of Vessels, through which the nutritious fluid may be conveyed.
These vessels are first seen in that part of the Vascular lamina of the Germinal
Membrane, which immediately surrounds the embryo ; and they form a net-
work, bounded by a circular channel, which is known under the name of the
Vascular Jlrea (Fig. 27, Plate II.). This gradually extends itself, until the
vessels spread over the whole of the membrane containing the yolk. The
first blood-discs appear to be formed from the nuclei of the cells, whose
cavities have become continuous with each other to form the vessels (§ 222) ;
and from these, all subsequent blood-discs are probably generated. This net-
work of blood-vessels serves the purposes of absorbing the nutritious matter
of the Yolk, and of conveying it towards the embryonic structures, which are
now in process of rapid development. The first movement of the fluid is
towards the embryo ; and this can be witnessed before any distinct heart is
evolved. The same process of absorption from the Yolk, and of conversion
into Blood, probably continues as long as there is any alimentary material left
in the sac.

939. The Yolk-sac is early separated in the Mammalia, by a constriction
of the portion which is continuous with the abdomen of the Embryo; and it
is known from that time under the name of the Umbilical Vesicle. The com-
munication, however, remains open for a time through the constricted portion,
which is termed the Vitelline Duct ; and even after this has been cut off, the
trunks which connected the circulating system of the Embryo with that of the
Vascular Area, are still discernible; these are called Omphalo-Mesenteric,
Meseraic, or Vitelline vessels. It was formerly believed, that the nutrient
matter of the yolk passes directly through the Vitelline duct, into the (future)
digestive cavity of the Embryo, and is from it absorbed into its structure; but
there can now be little doubt, that the Vitelline vessels are the real agents of
its absorption, and that they convey it to the tissues in process of formation.
They do, in fact, correspond to the Mesenteric veins of Invertebrated animals,
which are the sole agents in the absorption of nutriment from their digestive
cavity (§ 674) ; and the yolk-bag, as already remarked, is the temporary sto-
mach of the Embryo, — remaining as the permanent stomach in the Radiated
tribes. Previously to the ninth day of incubation (in the Fowl's egg), a series
of folds are formed by the lining membrane of the yolk-bag, which project
into its cavity; these become gradually deeper and more crowded, as the bag
diminishes in size by the absorption of its contents. The Vitelline vessels,
that ramify upon the yolk-bag, send into these folds (or valvulse conniventes)
a series of inosculating loops, which immensely increase the extent of this
absorbing apparatus. But these minute vessels are not in immediate contact
with the yolk; for there intervenes between them a layer of nucleated cells,
which is easily washed away. It was from the colour of these, communicated
to the vessels beneath, that Haller termed the latter vasa lutea; when the
layer is removed, the vessels present their usual colour. There seems good
reason to believe, that these cells, like those of the Intestinal Villi in the adult
(§ 672), are the real agents in the process of absorbing and assimilating the
nutritive matter of the yolk ; and that they deliver this up to the vessels, by
themselves undergoing rupture or dissolution, being replaced by new layers.

940. The formation of the Heart takes place in the Vascular layer, beneath
the upper part of the Spinal Column; it at first appears as a mere cavity in its
substance, surrounded only by cells ; but its walls gradually acquire firmness

DEVELOPMENT OF THE EMBRYO.

717

and distinctness, and become sufficiently powerful to propel the blood through
the vessels of the Embryo and those of the Vascular Area. The first ap-
pearance of the Heart in the Chick is at about the 27th hour ; the time of its
formation in Mammalia has not been distinctly ascertained. In its earliest
form, it has the same simple character, which is presented by the central im-
pelling cavity of the lower Invertebrata ; being a mere prolonged canal, which
at its posterior extremity receives the veins, and at its anterior sends forth the
arteries. After a short time, however, it becomes bent upon itself (Plate II.,
Fig. 27, d] ; and it is soon subdivided into three cavities, which exist in all
Vertebrata, — a simple auricle or receiving cavity, a simple ventricle or pro-
pelling cavity, and a bulbus arteriosus at the origin of the aorta. The circu-
lation is at first carried on exactly upon the plan, which is permanently
exhibited by Fishes. The Aorta subdivides into four or five arches on either
side of the neck ; and these are separated by slits or fissures, much resem-
bling those which form the entrances to the gill-cavities of Cartilaginous
Fishes. These arches reunite to form the descending aorta, which transmits
branches to all parts of the body. Such is the first phase or aspect of the
Circulating Apparatus, which is common to all Vertebrata during the earliest
period of their development, and which may, therefore, be considered as its
most general form. It remains permanent in the class of Fishes; and in them
the vascular system undergoes further development on the same type, a num-
ber of minute tufts being sent forth from each of the arches, which enter the
filaments of the gills, and serve for the aeration of the blood. In higher
Vertebrata, however, the plan of the circulation is afterwards entirely changed,
by the formation of new cavities in the heart, and by the production of new
vessels ; these changes will be presently described. It is incorrect, therefore,
to speak of the vascular arches in their necks as branchial arches ; since no
branchiae or gills are ever developed from them. The clefts between them
may be very distinctly seen in the Human Foetus towards the end of the first
month ; during the second, they usually close up and disappear.

941. With the evolution of a Circulating apparatus, adapted to absorb
nourishment from the store prepared for the use of the Embryo, and to con-
vey it to its different tissues, it becomes necessary that a respiratory apparatus

Fig. 285.

Fig. 286.

.-•*

The Amnion in process of formation, by the
arching over of the serous lamina; a, the
chorion ; 6, the yolk-bag, surrounded by se-
rous and vascular lamina ; e, the embryo ;
d, «, and/, external and internal folds of the
serous layer, forming the amnion ; g, incipi-
ent allantois.

Diagram representing a Human Ovum in'
second month; a. I, smooth portion of cho-
rion ; a. 2, villous porlion'of chorion ; k, k,
elongated villi, beginning to collect into Pla
centa; 6, yolk-sac or umbilical vesicle; c, em
bryo ;/, amnion (inner layer); g-, allantois;
h, outer layer of amnion, coalescing with
chorion.

718

OF REPRODUCTION.

should also be provided, for unloading the blood of the carbonic acid with
which it becomes charged during the course of its circulation. The tempo-
rary Respiratory apparatus now to be described, bears a strong resemblance
in its own character, and especially in its vascular connections, with the gills
of the Mollusca; which are prolongations of the external surface (usually
near the termination of the intestinal canal), and which almost invariably
receive their vessels from that part of the system. This apparatus is termed
the Jlllantois. It consists at first of a kind of diverticulum or prolongation of
the lower part of the Digestive cavity, the formation of which has been already
described. This is at first seen as a single vesicle, of no great size (Fig.
285, g] ; and in the Foetus of Mammalia, which is soon provided with other
means of aerating its blood, it seldom attains any considerable dimensions.
In Birds, however, it becomes so large as to extend itself around the whole
Yolk-sac, intervening between it and the membrane of the shell ; and through
the latter it comes into relation with the external air. The preceding diagram
(Fig. 286) will serve to explain its origin and position in the Human ovum.
The chief office of the Allantois in Mammalia is to convey the vessels of the

c

Diagram of Human Ovum, at the time of formation of Placenta; a, rnuco-gelattnous substance, block-
ing up os uteri ; 6, 6, Fallopian tubes; c, c, Decidua vera, prolonged at c'2. inio Fallopian tube ; rf, cavity
of uterus, almost completely occupied by ovum; e, e, angles at which Decidua vera is reflected ;./", De-
cidua serotina ; g, allanlois; h, umbilical vesicle ; i, amnion ; k, chorion, lined with outer fold of serous
tunic.

DEVELOPMENT OF THE EMBRYO. 719

embryo to the Chorion; and its extent bears a pretty close correspondence
with the extent of surface, through which the Chorion comes into vascular
connection with the Decidua. Thus, in the Carnivora, whose Placenta ex-
tends like a band around the whole Ovum, the Allantois also lines the whole
inner surface of the Chorion, except where the Umbilical Vesicle comes in
contact with it. On the other hand, in Man and the Quadrumana, whose
Placenta is restricted to one spot, the Allantois is small, and conveys the
foetal vessels to one portion only of the Chorion. When these vessels have
reached the Chorion, they ramify in its substance, and send filaments into its
villi; and in proportion as these villi form that connection with the uterine
structure, which has been already described, do the vessels increase in size.
They then pass directly from the Fo3tus to the Chorion; and the Allantois,
being no longer of any use, shrivels up, and remains as a minute vesicle, only
to be detected by careful examination. The same thing happens in regard to
the Umbilical vesicle, from which the entire contents have been by this time
exhausted; and from henceforth the Fcetus is completely dependent for the
materials of its growth, upon the supply it receives through the Placenta,
which is conducted to it by the vessels of the Umbilical Cord. This state of
things is represented in the preceding diagram. — The Allantois has a corre-
spondence in situation with the Urinary Bladder ; but it is only the lower
part of it, pinched off, as it were, from the rest, that remains as such. The
duct by which it is connected with the abdomen gradually shrivels; and a
vestige of this is permanent, forming the Urachus or suspensory ligament of
the Bladder, by which it is connected with the Umbilicus. Before this takes
place, however, the Allantois is the receptacle for the secretion of the Corpora
Wolffiana, and of the true Kidneys, when they are formed.

942. It will be seen from the preceding diagram, that the Umbilical Cord
receives an investment from the Amnion, which forms a kind of tubular
sheath around it ; it is continuous at the Umbilicus with the integument of
the fetus; and at the point where the cord enters the Placenta, it is reflected
over its internal or foetal surface. The Amnion (which thus forms a shut
sac, like that of the Pleura, Arachnoid, &c.) contains a fluid known as the
liquor amnii; this consists of water holding in solution a small quantity of
albumen and saline matter, and resembling, therefore, very diluted serum.
During the first two months of gestation, the Amnion and the inner surface
of the Chorion (which is really the reflected layer of the Amnion, just as the
lining of the abdominal cavity is formed by the peritoneum) are separated by a
gelatinous-looking substance ; which may perhaps be considered as represent-
ing the white of the egg in Birds; and which probably aids in the nutrition
of the Embryo, previously to the formation of the Placenta (§ 918). This
is absorbed during the second month; and the Amnion is then found imme-
diately beneath the Chorion. — In the Umbilical Cord, when it is completely
formed, the following parts may be traced. 1. The tubular sheath afforded
by the Amnion. 2. The Umbilical Vesicle, with its pedicle, or Omphalo-
Enteric duct. 2. The Vasa Omphalo-Meseraica, or mesenteric vessels of
the Embryo, by which the Yolk was absorbed into the body of the Fcetus;
these accompany the pedicle. 4. The Urachus, and remains of the Allantois.
5. The Vasa Umbilicalia, which, in the later period of gestation, constitute
the chief part of the Cord. These last vessels consist in Man of two Arte-
ries and one Vein. The Arteries are the main branches of the Hypogastric;
and they convey to the Placenta the blood which has to be aerated and other-
wise revivified, by being brought into relation with that of the Mother. The
Vein returns this to the Foetus, and discharges a part of it into the Vena
Porta3, and a part directly through the Ductus Venosus into the Aorta.

720 OF REPRODUCTION.

943. A change in the type of the Circulating system of the foetus, from
that at first presented by it (§ 940), takes place at a very early period. At
about the 4th week, in the Human Embryo, a septum begins to be formed in
the Ventricle; and by the end of the 8th week it is complete. The Septum
Auriculorum is formed at a somewhat later period, and it remains incomplete
during the whole of foetal life ; it is partly closed by the valvular fold cover-
ing the Foramen Ovale, which fold is developed during the third month.
During the same period, a transformation takes place in the arrangement of
the large vessels proceeding from the Heart; which ends in their assumption
of the form they present until the end of Foetal life; and this undergoes but
a slight alteration, when the plan of the circulation is changed at the moment
of the first inspiration. The number of Aortic arches on each side, which
was five at first, soon becomes reduced in the Mammalia to three, by the
obliteration of the two highest pairs. The Bulbus Arteriosus is subdivided,
by the adhesion of its walls at opposite points, into two tubes, of which one
becomes the Aorta and the other the Pulmonary Artery ; and of the three
pairs of (branchial) arches, the highest, being connected with the Aortic trunk,
contributes to the formation of the Subclavian and Carotid arteries ; whilst of
the middle pair, the arch on the right side is obliterated, the other becoming
the Arch of the Aorta. The lowest pair arises from the Pulmonary trunk,
and forms the Pulmonary artery on each side ; that on the left side, however,
goes on to join the descending Aorta as before, and thus constitutes the Ductus
Arteriosus.

944. The following is the course of the circulation of the blood in the
Foetus. The fluid brought from the Placenta by the Umbilical Vein is partly
conveyed at once to the Vena Cava ascendens, by means of the Ductus
Venosus, and partly flows through the Vena Portae into the Liver, whence it
reaches the ascending Cava by the Hepatic Vein. Having thus been trans-
mitted through the two great depurating organs, the Placenta and the foetal
Liver, it is in the condition of arterial blood ; but, being mixed in the vessels
with that which has been returned from the trunk and lower extremities, it
loses this character in some degree by the time that it arrives in the Heart.
In the right Auricle, which it then enters, it would be also mixed with the
venous blood conveyed by the descending Cava; were it not that a very curi-
ous provision exists, to prevent (in great degree, if not entirely) any such fur-
ther dilution. The Eustachian valve has been found, by the experiments of
Dr. J. Reid,* to serve the purpose of directing the arterial blood, which flows
upwards from the ascending Cava, through the Foramen Ovale, into the left
Auricle, whence it passes into the Ventricle ; whilst it also directs the Venous
blood, that has been returned by the descending Cava into the right Ven-
tricle. When the Ventricles contract, the Arterial blood which the left con-
tains is propelled into the ascending Aorta, and supplies the branches that
proceed to the head and upper extremities, before it undergoes any admix-
ture ; whilst the Venous blood, contained in the right Ventricle, is forced
through the Pulmonary artery and Ductus Arteriosus into the descending
Aorta, mingling with the arterial current which that vessel previously con-
veyed, and passing thus to the trunk and lower extremities. Hence the Head
and superior extremities, whose development is required to be in advance of
that of the lower, are supplied with blood nearly as pure as that which returns
from the Placenta : whilst the rest of the body receives a mixture of this,
with what has previously circulated through the system ; and of this mixture
a portion is transmitted to the Placenta, to be renovated by coming into rela-
tion with the maternal fluid. At birth, the course of the current is entirely

* Eclinb. Med. and Surg. Journal, vol. xliii.

DEVELOPMENT OF THE EMBRYO.

[Fig. 288.

«.Ul *l I 11 '

721

U U

The Fcetal Circulation ; 1, the umbilical cord, consisting of the umbilical vein and two umbilical
arteries; proceeding from the placenta (2) ; 3, the umbilical vein dividing into three branches; two (4, 4)
to be distributed to the liver; and one (5), the ductus venosus, which eaters the inferior vena cava (G);
7, the portal vein, returning the blood from the intestines, and uniting with the right hepatic branch; 8,
the right auricle; the course of the blood is denoted by the arrow, proceeding from 8 to 9, the left auricle;
10, the left ventricle ; the blood following the arrow to the arch of the aorta (tl), to be distributed through
the branches given off by the arch to the head and upper extremities. The arrows, 12 and 13, represent
the return of the blood from the head and upper extremities through the jugular and subclavian veins,
to the superior vena cava (14), to the right auricle (8), and in the course of the arrow through the right
ventricle (15), to the pulmonary artery (16) ; 17, the ductus arteriosus, which appears to be a proper con-
tinuation of the pulmonary artery— the offsets at each side are the right and left pulmonary artery cut
off; these are of extremely small size as compared with the ductus arleriosus. The ductus arteriosus
joins the descending aorta (IS, 18), which divides into the common iliacs, and these into the internal
iliacs, which become the umbilical arteries (19), and return the blood along the umbilical cord to the
placenta; while the other divisions, the external iliacs (20), are continued into the lower extremities.
The arrows at the termination of these vessels mark the return of the venous blood by the veins to the
inferior cava.]

changed by its diversion into the Lungs ; which takes place immediately on
the first inspiration. The Ductus Venosus and Ductus Arteriosus soon shrivel
into ligaments ; the Foramen Ovale becomes closed by its valve ; and the
circulation, which was before carried on upon the plan of that of the higher
Reptiles, now becomes that of the complete Bird or Mammal. It is by no
means unfrequent, however, for some arrest of development to prevent the
61

722 OF REPRODUCTION.

completion of these changes; and various malformations, involving an imper-
fect discharge of the function, may hence result.*

945. The Alimentary Canal has been shown to have its origin in the Yolk-
sac or Umbilical Vesicle ; being a portion pinched off (as it were) from that
part of it, which is just beneath the Spinal Column of the Embryo (§ 937).
At first it is merely a long narrow tube, nearly straight, and communicating
with the Umbilical Vesicle at about the middle of its length ; thus it may be
regarded as composed of the union of two, an upper and a lower division.
At first, neither Mouth nor Anns exists ; but these are formed early in the
second month, if not before. The tube gradually manifests a distinction into
its special parts, (Esophagus, Stomach, Small Intestine, and Large Intestine ;
and the first change in its position occurs in the Stomach, which, from being
disposed in the line of the body, takes an oblique direction. The curves of
the large and small intestines present themselves at a later period. It is at the
lower part of the small Intestine, near its termination in the large, that the
entrance of the Omphalo-Enteric duct exists ; and a remnant of this canal is
not unfrequently preserved throughout life, in the form of a small pouch or
diverticulum from that part of the intestine. The various Glandular structures
connected with the alimentary canal, originate in diverticula from its walls, in
the manner already described in regard to the Liver (§ 826, g}. The Lungs
and Respiratory apparatus a*re formed in like manner, as diverticula from the
(Esophagus (§ 757, b, c).

946, The mode in which the chief organs of the Human embryo originate
having been thus described, and sufficient particulars in regard to their subse-
quent development having been already given under distinct heads, it is un-
necessary here to add more on this very interesting but complex subject; be-
cause for practical purposes there is little or no advantage to be gained from
the most perfect aquaintance with it. The most important of all the facts that
have come under our review, is that which has been stated as in the highest
degree probable, if not yet absolutely proved, in regard to the relative offices
of the Male and Female in this hitherto mysterious process. According to
the view here given, the Male furnishes the germ; and the Female supplies
it with Nutriment, during the whole period of its early development. There
is no difficulty in reconciling such a doctrine with the well-known fact, that
the offspring commonly bears a resemblance to both parents (of which the
production of a hybrid between distinct species is the most striking example) ;
since numerous phenomena prove that, in this earliest and simplest condition
of the organism, the form it will ultimately assume very much depends upon
circumstances external to it ; among which circumstances, the kind of nutri-
ment supplied will be one of the most important.t Upon the same principle
we may account for the influence of the mental condition of the Mother upon
her Offspring^ during a later period of pregnancy. That such influence may
occur, there can be no reasonable doubt. " We have demonstrative evidence,"
says Dr. A. Combe,J " that a fit of passion in a nurse vitiates the quality of
the milk to such a degree, as to cause colic and indigestion [or even death]
in the suckling infant. If, in the child already born, and in so far independent
of its parent, the relation between the two is thus strong, is it unreasonable to
suppose that it should be yet stronger, when the infant lies in its mother's
womb, is nourished indirectly by its mother's blood, and is, to all intents and
purposes, a part of her own body? If a sudden and powerful emotion of her
own mind exerts such an influence upon her stomach as to excite immediate

* See Principles of General and Comparative Physiology, Chap. vi.
•f Sec Principles <il' (Icnenil and Comparative Physiology, § (305.
j On the Management of Infancy, p. 7G.

DEVELOPMENT OF THE EMBRYO. 723

vomiting, and upon her heart as almost to arrest its motion and induce fainting,
can we believe that it will have no effect on her womb and the fragile being
contained within it ? Facts and reason, then, alike demonstrate the reality of
the influence: and much practical advantage would result to both parent and
child, were the conditions and extent of its operations better understood."
Among facts of this class, there is, perhaps, none more striking than that
quoted by the same Author from Baron Percy, as having occurred after the
siege of Landau in 1793. In addition to a violent cannonading, which kept
the women for some time in a constant state of alarm, the arsenal blew up
with a terrific explosion, which few could hear with unshaken nerves. Out
of 92 children born in that district within a few months afterwards, Baron
Percy states that 16 died at the instant of birth ; 33 languished for from 8 to
10 months, and then died ; 8 became idiotic, and died before the age of 5 years ;
and 2 came into the world with numerous fractures of the bones of the limbs,
caused by the cannonading and explosion. Here, then, is a total of 59 chil-
dren out of 92, or within a trifle of 2 out of every 3, actually killed through the
medium of the Mother's alarm and the natural consequences upon her own
organization, — an experiment (for such it is to the Physiologist) upon too large
a scale for its results to be set down as mere " coincidences." No soundly-
judging Physiologist of the present day is likely to fall into the popular error,
of supposing that marks upon the Infant are to b.e referred to some transient
though strong impression upon the imagination of the Mother; but there ap-
pear to be a sufficient number of facts on record, to prove that habitual mental
conditions on the part of the Mother may have influence enough, at an early
period of gestation, to produce evident bodily deformity, or peculiar tendencies
of the mind. But whatever be the nature and degree of the influence thus
transmitted, it must be such as can act by modifying the character of the nu-
tritive materials supplied by the Mother to the Fretus ; since there is no other
channel by which any influence can be propagated. The absurdity of the
vulgar notion just alluded to, is sufficiently evident from this fact alone ; as it
is impossible to suppose that a sudden fright, speedily forgotten, can exert
such a continued influence on the nutrition of the Embryo, as to occasion any
personal peculiarity.* The view here stated is one which ought to have great
weight, in making manifest the importance of careful management of the health
of the Mother, both corporeal and mental, during the period of pregnancy ;
since the constitution of the offspring so much depends upon the impressions
then made upon its most impressible structure.

947. It is frequently of great importance, both to the Practitioner and to
the Medical Jurist, to be able to determine the age of a Foetus, from the physi-
cal characters which it presents ; and the following table has been framed by
Devergiet in order to facilitate such determination. It is to be remarked, how-
ever, that the absolute Length and Weight of the Embryo are much less safe
criteria, than its degree of Development, — as indicated by the relative evolution
of the several parts, which make their appearance successively. Thus it is
very possible for one child, born at the full time, to weigh less than another.
born at 8 or even at 7 months ; its length, too, may be no greater ; but the
position of the middle point of the body will usually afford sufficient ground

* For some valuable observations on this subject, see Montgomery on the Signs of Preg-
nancy. Numerous cases have been recorded, during the last few years (especially in the
Lancet and Provincial Medical Journal) in which malformations in the Infant appeared
distinctly traceable to strong impressions made on the mind of the Mother, some months
previously to parturition ; these impressions having been persistent during the remaining
period of pregnancy, and giving rise to a full expectation on the part of the Mother, that the
child would be affected in the particular manner which actually occurred.

f Medecine Legale, vol. i. p. 495.

724 OF REPRODUCTION.

for the determination ; since, during the two latter months of pregnancy, the
increasing development of the lower extremities throws it lower down.

Embryo 3 to 4 weeks. — It has the form of a serpent ; — its length from three to five lines ;
its head indicated by a swelling ; its caudal extremity (in which is seen a white line, indi-
cating the continuation of the medulla spinalis), slender, and terminating in the umbilical
cord; — the mouth indicated by a cleft; — the eyes by two black points; the members begin
to appear as nipple-like protuberances ; — the liver occupies the whole abdomen ; — the bladder
is very large. The chorion is villous, but its villosities are still diffused over the whole surface.

Embryo of 6 weeks. — Its length from 7 to 10 lines; — its weight from 40 to 75 grains; —
face distinct from cranium ; — aperture of nose, mouth, eyes, and ears perceptible : — head
distinct from thorax ; — hands and fore-arms in the middle of the length, fingers distinct; —
legs and feet situated near the anus ; — clavicle and maxillary bone present a point of ossifi-
cation ; — distinct umbilicus for attachment of cord, which at that time consists of the om-
phalo-meseraic vessels, of a portion of the urachus, of a part of the intestinal tube, and of
filaments which represent the umbilical vessels. The placenta begins to be formed; — the
chorion still separated from the amnion; — the umbilical vesicle very large.

Embryo of 2 months. — Length from 16 to 19 lines; weight from 150 to 300 grains; the
elbows and arms detached from the trunk ; — heels and knees also isolated ; — rudiments of
the nose and of the lips; — palpebral circle beginning to showjtself; — clitoris or penis ap-
parent ; anus marked by a dark spot ; rudiments of lungs, spleen, and supra-renal capsules ;
— ccecum placed behind the umbilicus; — digestive canal withdrawn into the abdomen; —
urachus visible ; — osseous points in the frontal bone and in the ribs. — Chorion commencing
to touch the amnion at the point opposite the insertion of the placenta; placenta begins to
assume its regular form; — umbilical vessels commence twisting.

Embryo of 3 months. — Length from 2 to 2^ inches; — weight from 1 oz. to 1^ oz. (Troy);
— head voluminous; — eyelids in contact by their free margin: membrana pupillaris visible;
— mouth closed; — fingers completely separated; — inferior extremities of greater length than
rudimentary tail ; — clitoris and penis very long; — thymus as well as supra-renal capsules
present ; — ccecum placed below the umbilicus ; — cerebrum 5 lines, cerebellum 4 lines, me-
dulla oblongata 1^ line, and medulla spinalis J of a line, in diameter; — two ventricles of
heart distinct. — The decidua reflexa and decidua uterina in contact: — funis contains umbili-
cal vessels and a little of the gelatine of Warthon ; — placenta completely isolated ; — umbilical
vesicle, allantois, and omphalo-mesenteric vessels have disappeared.

Fatus of 4 months. — Length 5 to 6 inches; — weight 2^ to 3 oz. ; — skin rosy, tolerably
dense; — mouth very large and open; — membrana pupillaris very evident ; nails begin to
appear: — genital organ and sex distinct ; — ccecum placed near the right kidney; — gall-bladder
appearing; — meconium in duodenum; coecal valve visible; umbilicus placed near pubis ; —
ossicula auditoria ossified; — points of ossification in superior part of sacrum; — membrane
forming at point of insertion of placenta on uterus; — complete contact of chorion with
amnion.

Fcetus of 5 montJis. — Length 6 to 7 inches ; weight 5 to 7 oz. ; — volume of head still com-
paratively great; — nails very distinct; — hair beginning to appear; — 'skin without sebaceous
covering; — white substance in cerebellum; heart and kidneys very voluminous ; — ccecum
situated at inferior part of right kidney ; — gall-bladder distinct ; — germs of permanent teeth
appear ; — points of ossification in pubis and calcaneum ; — meconium has a yellowish-green
tint, and occupies commencement of large intestine.

Foetus of 6 months. — Length 9 to 10 inches: — weight 1 Ib. ; — skin presents some appear-
ance of fibrous structure; — eyelids still agglutinated, and membrana pupillaris remains; —
sacculi begin to appear in colon; — funis inserted a little above pubis; — face of a purplish
red; — hair white or silvery; — sebaceous covering begins to present itself; — meconium in
large intestines; — liver of dark red; — gall-bladder contains serous fluid destitute of bitter-
ness;— testes near kidneys ; — points of ossification in four divisions of sternum ; — middle
point at lower end of sternum.

F(Etus o/7 months. — Length 13 to 15 inches; weight 3 to 4 Ibs. ; — skin of rosy hue, thick,
and fibrous ; — sebaceous covering begins to appear ; — nails do not yet reach extremities of
fingers; — eyelids no longer adherent; — membrana pupillaris disappearing; — a point of ossi-
fication in the astragalus ; — meconium occupies nearly the whole of large intestine ; — valvular
conniventes beginning to appear; — ccecum placed in right iliac fossa; — left lobe of liver
almost as large as right; — gall-bladder contains bile; — brain possesses more consistency; —
testicles more distant from kidneys ; — middle point at a little below end of sternum.

Foetus of 8 months. — Length 14 to 16 inches; — weight 4 or 5 Ibs. ; — skin covered with
well-marked sebaceous envelope; nails reach extremities of fingers; — membrana pupillaris
becomes invisible- during this month; — a point of ossification in last vertebra of sacrum; —
cartilage of inferior extremity of femur presents no centre of ossification ; — brain has some

PROPORTION OF SEXES. 725

indications of convolutions ; — testicles descend into internal ring ; — middle point nearer the
umbilicus than the sternum.

Fcctus of 9 months, I he full term. — Length from 17 to 21 inches: — weight from 5 to 9 Ibs.,
the average probably about 6^ Ibs.; — head covered with hair in greater or less quantity, of
from 9 to 12 lines in length; — skin covered with sebaceous matter, especially at bends of
joints ; — membrana pupillaris no longer exists ; — external auditory meatus still cartilaginous ;
— four portions of occipital bone remain distinct ; — os hyoides not yet ossified ; point of ossi-
fication in the centre of cartilage at lower extremity of femur ; — white and grey substances
of brain become distinct; — liver descends to umbilicus;- — testes have passed inguinal ring,
and are frequently found in scrotum; — meconium at termination of large intestine; — middle
point of body at umbilicus, or a little below it.

948. Even at Birth, there is a manifest difference in the physical conditions
of Infants of different sexes ; for, in the average of a large number, there is a
decided preponderance on the side of the Males, both as to the Length and
the Weight of the body.

a. The Length of the body in fifteen new-born infants of each sex, as ascertained by Qne-
telet,* was as follows : —

Males. Females. Total.

From 16 to 17 inchest (French) . . 2 4 6

17 to 18 8 19 27

- 18 to 19 28 18 46

19 to 20 12 8 20

- 20 to 21 0 1 1

From these observations, the mean and the extremes of the Lengths of the Male and Female
respectively, were calculated to be, —

Males. Females.

Minimum . . 16 inches, 2 lines 16 inches, 2 lines

Mean IS 6 18 lj

Maximum 19 8 20 6

Notwithstanding that the maximum is here on the side of the Female (this being an acci-
dental result, which would probably have been otherwise, had a larger number been ex-
amined), the average shows a difference of 4J lines in favour of the Male.

b. The inequality in the Weight of the two is even more remarkable; the observations of
M. QueteletJ were made upon 63 male and 56 female infants.

Infants weighing from Males. Females. Total.

1 to 1^ kilog.§ 0 1 1

Ii to 2 0 1 1

2 to 2£ 3 7 10

2J to 3 13 14 27

3 to 3£ 28 23 51

3£ to 4 14 7 21

4 to 4£ 5 3 8

The extremes and means were as follows : —

Males. Females.

Minimum . . . 2-34 kilog. 1-12

Mean .... 3-20 2-91

Maximum . . . 4-50 4-25

c. The average weight of infants of both sexes, as determined by these inquiries, is 3-05
kilog. or 6'7 Ibs. ; and this corresponds almost exactly with the statement of Chaussier, whose
observations were made upon more than 20,000 infants. The mean obtained by him, with-
out reference to distinction of sex, was 6'75 Ibs. ; the maximum being 11-3 Ibs., and the mini-
mum 3'2 lbs.|| The average in this country is probably rather higher; according to Dr.
Joseph Clarke,1T whose inquiries were made on 60 males and 60 females, the average of

* Sur L'Homme, torn. ii. p. 8.

t The French inch is about one-fifteenth more than the English.
j Op. cit, torn. ii. p. 35.

§ The kilogramme is equal to 2^ Ibs. avoirdupois.

|| These numbers have been erroneously stated in many Physiological works ; owing to
the difference between the French and English pound not having been allowed for.
IT Philosophical Transactions, vol. Ixxvi.

61*

726 OF REPRODUCTION.

Male children is 7 3 Ibs.: and that of Females 6-f Ibs. He adds that children which at the
full time •weigh less than 5 Ibs. rarely thrive ; being generally feeble in their actions, and
dying within a short time. Several instances are on record, of infants whose weight at birth
exceeded 15 Ibs. It appears that healthy females, living in the country, and engaged in
active but not over-fatiguing occupations, have generally the largest children ; and this is
what might be expected d priori from the superior activity of their nutritive functions.

949. Notwithstanding that, in any ordinary population, there is a decided
preponderance in the number of Females, the number of Male births is con-
siderably greater than that of females. Taking the average of the whole of
Europe, the proportion is about 106 Males to 100 Females. It is curious,
however, that this proportion is considerably different for legitimate and for
illegitimate births; the average of the latter being only 102£ to 100, in the
places where that of the former was 105| to 100. This is probably to be
accounted for by the fact, which is one of the most remarkable contributions
that have yet been made by Statistics to Physiology, that the Sex of the off-
spring is influenced by the relative ages of the parents. The following table
expresses the average results obtained by M. Hofacker* in Germany, and by
Mr. Sadlert in Britain; between which it will be seen that there is a manifest
correspondence, although both were drawn from a too limited series of observa-
tions. The numbers indicate the proportion of Male births to 100 Females,
under the several conditions mentioned in the first column.

Hofacker. Sadler.

Father younger than Mother . . 9O6 Father younger than Mother . . 86-5

Father and Mother of equal age . 9OO Father and Mother of equal age . 94' 8

Father older by 1 to G years . . 103-4 Father older by 1 to 6 years . . 103-7

6 to 9 . . . 124-7 . . 6 to 11 . . . 126-7

9 to 18 . . . 143-7 . . 11 to 10 . . . 147-7

18 and more . . 200-0 . . 16 and more . . 163-2

From this it appears, that the more advanced age of the Male parent has a
very decided influence in occasioning a preponderance in the number of Male
infants ; and as the state of society generally involves a condition of this kind
in regard to marriages, whilst in the case of illegitimate children the same
does not hold good, the difference in the proportional number of male births
is accounted for. We are not likely to obtain data equally satisfactory in
regard to the influence of more advanced age on the part of the Female parent ;
as a difference of 10 or 15 years on that side is not so common. If it exist
to the same extent, it is probable that the same law would be found to prevail
in regard to Female children born under such circumstances, as has been
stated with respect to the Male; — namely, that the mortality is greater during
embryonic life and early infancy, so that the preponderance is reduced.

950. There appears to be, from the first, a difference in the viability (or
probability of life) of Male and Female children ; for, out of the total number
born dead, there are 3 Males to 2 Females : this proportion gradually lessens,
however, during early infancy ; being about 4 to 3 during the first two months,
and about 4 to 5 during the next three months; after which time the deaths
are nearly in proportion to the numbers, of the two sexes respectively, until
the age of puberty. The viability of the two sexes continues to increase
during childhood ; and attains its maximum between the 13th and 14th years.
For a short time after this epoch has been passed, the rate of mortality is
higher in Females than in Males ; but from about the age of 18 to 28, the
mortality is much greater in Males, being at its maximum at 25, when the
viability is only half what it is at puberty. This fact is a very striking one ;
and shows most forcibly that the indulgence of the passions not only weakens
the health, but in a great number of instances is the cause of a very premature

* Annales d'Hygiene, Oct. 1S29. f Law of Population, vol. ii. p. 343.

PROPORTION OF SEXES.

727

death. From the age of 28 to that of 50, the mortality is greater, and the
viability less, on the side of the Female ; this is what would be anticipated
from the increased risk, to which she is liable during the parturient period.
After the age of 50, the mortality is nearly the same for both.

a. These facts have been expressed by Quetelet in a form which brings them prominently
before the eye (Fig. 289). The relative viability of the Male at different ages is represented
by a curved line; the elevation of which indicates its degree, at the respective periods
marked along the base line. The dotted line which follows a different curve, represents
the viability of the Female. Starting from a, the period of birth, we arrive at the maxi-
mum of viability for both at b ; from this point, the Female curve steadily descends towards

Fig. 2S9.

Diagram representing the comparative Viability of the Male and Female at different Ages.

n, at first very rapidly, but afterwards more gradually; whilst the Male curve does not de-
scend quite so soon, but afterwards falls much lower, its minimum being c, which corresponds
with the age of 25 years. It afterwards ascends to d, which is the maximum of viability
subsequently to the age of puberty; this point is attained at the age of 30 years, from which
period, up to 50, the probability of life is greater in the Male than in the Female. In the
decline of life there seems little difference for the two sexes.

951. Similar diagrams have been constructed by Quetelet, to indicate the
relative Heights and Weights of the two sexes (Fig. 290).

a. In regard to Height it may be observed, that the increase is most rapid in the first
year, and that it afterwards diminishes gradually; between the ages of 5 and 16 years, the
annual increase is very regular. The difference between the Height of the Male and Fe-
male, which has been already stated to present itself at birth, continues to increase during
infancy and youth; it is not very decided, however, until about the 15th year, after which
the growth of the Female proceeds at a much diminished rate, whilst that of the Male con-
tinues in nearly the same degree, until about the age of 19 years. It appears, then, that the
Female comes to her full development in regard to Height, earlier than does the Male. It
seems probable, from the observations of Quetelet, that the full height of the Male is not

728

OF REPRODUCTION.

generally attained until the age of 25 years. At about the age of 50, both Male and Female
undergo a diminution of their stature, which continues during the latter part of life.

b. The proportional Weight of the two sexes at different periods, corresponds pretty
closely with their height. Starting from birth, the predominance then exhibited by the Male
gradually increases during the first few years ; but towards the period of puberty, the pro-
portional weight of the Female increases; and at the age of 12 years, there is no difference
between the two sexes in this respect. The weight of the Male, however, then increases
much more rapidly than that of the Female, especially between the ages of 15 and 2U
years ; after the latter period, there is no considerable increase on the side of the Male,
though his maximum is not attained until the age of 40; and there is an absolute diminu-
tion on the part of the Female, whose weight remains less during nearly the whole period of
child-bearing. After the termination of the parturient period, the weight of the Female again
undergoes an increase, and its maximum is attained about 50. In old age, the weight of
both sexes undergoes a diminution in nearly the same degree. The average Weights of _the
Male and Female, that have attained their full development, are twenty times those of the
new-born Infant of the two sexes respectively. The Height, on the other hand, is about 85-
times as much.

Fig. 290.

70 13

952. The chief differences in the Constitution of the two sexes manifest
themselves during the period, when the Generative function of each is in the
greatest vigour. Many of these distinctions have been already alluded to ;
but there are others of too great importance to be overlooked ; and these
chiefly relate to the Nervous System and its functions. There is no obvious
structural difference in the Nervous System of the two sexes (putting aside
the local peculiarities of its distribution to the organs of generation) ; save the
inferior size of the Cerebral Hemispheres in the Female. This difference,
which is not observed in other parts of the Encephalon, is readily accounted
for on the principles formerly stated ; when we compare the physical charac-
ter of Woman, with that of Man. For there can be no doubt that — putting
aside the exceptional cases which now and then occur — the intellectual pow-
ers of Woman are inferior to those of Man. Although her perceptive facul-
ties are more acute, her capability of sustained mental exertion is much less ;
and though her views are often peculiarly distinguished by clearness and deci-
sion, they are generally deficient in that comprehensiveness which is neces-
sary for their stability. With less of the volitional powers than Man pos-
sesses, she has the emotional and instinctive in a much stronger degree. The
emotions therefore predominate; and more frequently become the leading

PROPORTION OF SEXES. 729

springs of action, than they are in Man. By their direct influence upon the
bodily frame, they produce changes in the organic functions, which far sur-
pass in degree anything of the same kind that we ordinarily witness in Man;
and they thus not unfrequently occasion symptoms of an anomalous kind,
which are very perplexing to the Medical practitioner, but very interesting to
the Physiological observer. But they also act as powerful motives to the
Will; and, when strongly called forth, produce a degree of vigour and deter-
mination, which is very surprising to those who have usually seen the indi-
vidual under a different aspect. But this vigour, being due to the strong
excitement of the Feelings, and not to any inherent strength of Intellect, is
only sustained during the persistence of the motive, and fails as soon as it
subsides. The feelings of Woman, being frequently called forth by the
occurrences she witnesses around her, are naturally more disinterested than
those of Man; his energy is more concentrated upon one object; and to this
his intellect is directed with an earnestness that too frequently either blunts
his feelings, or carries them along in the same channel, — thus rendering them
selfish. The intuitive powers of Woman are certainly greater than those
of Man. Her perceptions are more acute, her apprehension quicker ; and
she has a remarkable power of interpreting the feelings of others, which
gives to her, not only a much more ready sympathy with these, but that
power of guiding her actions so as to be in accordance with them, which we
call tact. This tact bears a close correspondence with the adaptiveness to
particular ends, which we see in Instinctive actions. In regard to the infe-
rior development of her Intellectual powers, therefore, and in the predomi-
nance of the Instinctive, Woman must be considered as ranking below Man;
but in the superior purity and elevation of her Feelings, she is as highly
raised above him. Her whole character, Psychical as well as Corporeal, is
beautifully adapted to supply what is deficient in Man; and to elevate and
refine those powers, which might otherwise be directed to low and selfish
objects.

APPENDIX.

I.— ON PHRENOLOGY.

WITHOUT entering into a general discussion of the merits of the system of Phrenology at
present in vogue, which would be misplaced in a Treatise like the present, the Author feels
it desirable to express the opinion, which a recent careful examination of the chief questions
at issue between Phrenologists and their opponents have led him to entertain.

That the different portions of the Cerebral mass should have different parts to perform in
that wonderful series of operations, by which the Brain as a whole becomes the instrument
of the Mind, does not seem to him in the least improbable. Nor, if we duly consider the
general plan of construction of the nervous centres in Vertebrated animals, is it a legitimate
objection to such a view, that there is no mechanical distinction of "organs" either upon
the surface or in the interior of the Cerebrum ; for in the Spinal Cord and Medulla Oblon-
gata, there is a continuous tract of grey matter, which is really made up of an assemblage of
ganglia having dissimilar functions, although there are no external indications of the dis-
tinctness of these ganglia. Further, it appears to be quite legitimate to judge of the com-
parative powers of different parts of the Cerebrum, or of the same portions in different in-
dividuals, by their comparative sizes; due allowance being made for other circumstances of
difference. And if the development of a particular part of the Cerebrum were constantly
found to be in harmony with the manifestation of a certain feature of psychical character,
there would be strong ground for regarding such a part as the instrument of the mental
operation in question. The attempt to establish a system of Cerebral Physiology by com-
parative observations of this nature, appears to the Author, therefore, a most legitimate one ;
and his objections to the present system of Phrenology are based only on the very imperfect
manner in which it has been constructed ; the foundations on which it rests being (in his
opinion) of a veiy insecure character; and the superstructure having been built up of the
slightest possible materials. The following are the chief points on which he feels called
upon to express his dissent.

1. The present system of Phrenology is founded only on comparative observation of the
psychical character and cerebral conformation in different individuals of the Human species
alone; evidence derived from Comparative Anatomy being admitted only so far as it corre-
sponds with the system thus constructed. When the fundamental importance of the study
of Comparative Anatomy in the determination of the functions of all other organs, and of
other parts of the Nervous System itself, is duly considered, the Author cannot regard any
system of Cerebral Physiology as having a claim to a place in a scientific treatise, which is
not founded on this basis.

2. The present system of Phrenology is altogether inconsistent with well-ascertained facts,
regarding the Comparative Anatomy and Embryological Development of the Cerebrum. It
is clearly established by anatomical research, that the posterior lobes of the Cerebrum are
relatively much smaller in the Quadrumana than they are in Man, and that they disappear
altogether in the Carnivora, not a vestige of them being discoverable in any of the lower
Mammalia ; and that the middle lobes, though they may be traced in the lowest of the Mam-
malian Class, are altogether wanting in Birds, Reptiles, and Fishes. The Cerebrum of these
animals, therefore, is the rudiment of the anterior lobe only of that of Mammalia. — Further,
it has been lately shown by Prof. Retzius (whose researches on this head are confirmatory
of those of Tiedemann, at the same time being more full and precise), that the development
of the Cerebrum of the Human Embryo takes place on the same plan. In the first period,
which corresponds with the second and third months, only the anterior lobes form ; in the
second period which is comprised in the end of the third month, in the fourth, and in a
small portion of the fifth, the two middle lobes appear; and it is not until the latter part of
the fifth month, that the development of the posterior lobes properly commences. They
sprout, as it were, from the posterior extremity of the middle lobes; from which they are
divided, on the brain of the mature foetus, as well as, occasionally in that of adults, by a dis-
tinct furrow. — The exact mutual confirmation afforded by these two sources of knowledge,

732 APPENDIX.

proves the complete inadmissibility of the ordinary Phrenological interpretation cf the in-
creased development of the posterior lobes in Man, — namely, that they are present in all
Vertebrata, but that they are pushed backwards in the higher forms by the increased de-
velopment of the anterior portion of the Cerebrum. Now as the Instincts and Propensities
are located, according to the present system of Phrenology, in the posterior and middle lobes
of the Cerebrum, which are altogether wanting in the Oviparous Classes in which these In-
stincts and Propensities most strongly manifest themselves, it would appear that some funda-
mental error must exist in the allocation.

3. The present system of Phrenology takes no account whatever of the series of ganglionic
masses, which lie at the base of the Cerebrum in Man, and which are thrown into the shade
(as it were) by its excessive development; but which increase in relative size and import-
ance as we descend the scale, until, in the lower Fishes and Invertebrata generally, they
come to constitute the whole Brain. We have seen that, in the Cod, the rudiment of the
Cerebrum is much smaller than a single pair of these ganglia, — the Optic ; and as this rudi-
ment does not possess a ventricle (which is present in the Sharks, &c., dividing the rudiment
of the hemisphere which arches over it, from the corpus striatum which lies at its base), it
is probably to be regarded as not really analogous to any part of the Cerebrum strictly so
called, but to the Corpus Striatum, which (with the Thalamus) constitutes an independent
organ. Thus we have the Cerebrum entirely disappearing in the Osseous Fishes ; and the
whole Brain made up of the Sensory Ganglia and the Cerebellum. — In the Invertebrata, not
the rudiment of a Cerebrum can be discovered ; the cephalic masses of nervous matter being
made up of ganglia in immediate connection with the organs of sense and motion. It is
obvious, therefore, that these organs must be 'of primary importance as centres of nervous
action ; and that the functions of the Cerebrum, whatever be their nature, must be of a super-
added, and of a non-essential character. — The view which the Author takes of these pheno-
mena will be found at large in the Text. He regards the Sensory Ganglia as the seat of
Sensation (each kind of sensation being communicated through its own ganglion) and of
the simple feelings of pleasure and pain connected with those sensations ; and also as the
instrument of those consensual movements, which follow immediately and necessarily upon
sensations. To this category he would refer the purely Instinctive actions, which are imme-
diately prompted by sensations, which seem to involve no idea of the purpose towards which
they are directed, and which cannot be said (the idea of the object being deficient) to spring
from a desire or propensity. Probably all or nearly all the actions of Invertebrata and of
the lower Fishes are of this class. The emotions and propensities of Man and of the higher
Mammalia, which form the chief springs of action in them, may be regarded as involving
the combined operation of the Sensory Ganglia and the Cerebrum; the latter affording the
ideas, whilst the former invest these ideas with the pleasure or pain, which gives them the
form of passions, desires, or propensities, and which causes them to become the moving
springs of a great part of the intellectual operations, which are purely Cerebral. The action
of the Cerebrum in the passions, emotions, &c., is limited, therefore, on this view of their
nature, to its instrumentality in furnishing the several classes of ideas to which those emotions
respectively relate. If the Phrenological system be thus modified, there will no longer be
the same difficulty in reconciling it with the facts of Comparative Anatomy ; since in those
animals which are unpossessed of the posterior lobes, the actions, which in Man and the
higher Mammalia result from desires or propensities involving a distinct idea or conception
of the object, may be purely instinctive, and may thus be performed through the medium of
the Sensory Ganglia alone, without the participation of the Cerebrum.

4. The present system of Phrenology leaves undetermined a very large proportion of the
Cerebral surface in Man, — probably not less than one-half; namely the whole series of
convolutions covering the opposing median surfaces of the hemispheres, the convolutions of
nearly the whole of the base of the Cerebrum, and those of the fissure of Sylvius. Yet
not the slightest ground can be adduced for the supposition that these unappropriated por-
tions have any less participation in the operations of the intellect, the exercise of the moral
feelings, or the influence of the animal propensities, than have the external and superior
portions of the respective lobes. No admission of the imperfection of the present system
of Phrenology can be a sufficient explanation of this fact, which would seem to indicate
some fundamental error in the method employed ; since one of the great claims which is set
up in behalf of that system is the completeness of the system of Psychical philosophy which
it presents ; so that, if there were every facility for observing the relative development of the
parts of the Cerebral surface in question, there would seem to be no "organs" left to distri-
bute over it.

5. If it be urged, however, that none of these objections are sufficient to overthrow the
position, now established by a long course of observation, that a constant correspondence
exists in Man between the development of certain parts of the Cerebrum, and particular
Psychical characteristics, and that the present system must consequently be true, in spite of
its inconsistency with the facts of Comparative Anatomy, it becomes necessary to inquire in

APPENDIX. 733

more detail into the character of the evidence adduced in its behalf. — The following objec-
tions may be urged upon this subject. The greater part of the observations upon which the
present system of Phrenology rests, have been made upon crania alone, or upon casts of
crania; not upon the cerebrum itself. In this method of observation there are many falla-
cies; especially those arising from the indisputable fact, that the cerebrum may be moulded
in such a manner as to undergo considerable alteration in form, without any change in its
internal structure or in the relative development of its several parts. And an extensive
comparison of the crania of different nations shows that their differences of form have in
many instances no relation whatever to their psychical character. That the form of the cra-
nium is to a certain extent independent of that of the brain, and may impress itself upon its
contents, appears further from a comparison between the cerebral and cranial conformations
of different species of animals. It is found that, even when closely-allied species are com-
pared together, similar projections of the cranium may cover different convolutions ; the
general form of the cranium being modified by its instrumentality in other functions, espe-
cially in mastication, and by its position upon the trunk and its mode of muscular connection
with it. There is a peculiar uncertainty attending all estimates of the comparative size of
the Cerebellum, from inspection of the exterior of the cranium ; for the observations of Prof.
Retzius upon the varieties of form which the cranium presents in different races, have in-
dicated this fact among others, — that the position of the cerebellum may vary considerably,
being much more horizontal in one case and more vertical in another; so that cerebella of
the same size may exist in crania having very different amounts of occipital protuberance;
and vice vei-sa. — Further, after dismissing the sources of error already mentioned, there yet
remain many, arising from want of precision in the cranioscopical observations, and want of
opportunity of forming a correct estimate of the characters of the individuals whose " deve-
lopments" have been examined. The difficulty of precisely estimating the relative sizes of
different organs by any system of measurement, which has been acknowledged and regretted
by candid phrenologists, often leads to the formation of very different inferences from the
same data, as the Author can vouch from his own knowledge. And when the estimate of
the character has been formed from craniological indications, there are many difficulties in
the way of a faithful comparison with the real character of the individual, of which the
manifestation in his ostensible conduct can generally reveal but a small part. Now there
can be little doubt, that the habit of attending-to and of recording coincidences between cere-
bral developments and psychical manifestations, without due regard to the cases in which
there is no coincidence, has been far too prevalent amongst professed phrenologists. Unless
the failures are duly chronicled with the successes, no value can be attached to any series
of observations, however numerous and satisfactory. Many such failures, upon points in.
regard to which there could be no misapprehension or evasion, have come under the Author's
knowledge; and have tended to prevent his reception of the present phrenological system;
but they find no place in formal treatises on Phrenology, which lead their readers to suppose
that the coincidences are invariable. The connection of the Sexual propensity with the
Cerebellum has been usually regarded by Phrenologists as one of the best-ascertained of its
whole series of dogmata ; and yet we have seen how little this determination can stand the
test of a careful scrutiny.

Those who are desirous of studying the Phrenological system at present in vogue, as ex-
pounded by an intelligent and unfettered partisan, may be referred to Mr. Noble's recent
treatise, entitled "The Brain and its Physiology;" whilst the objections summed up in this
Appendix are Stated more at large in a critique on that work in the British and Foreign Me-
dical Review, forOctober, 1846.

II._ON ARTIFICIAL SOMNAMBULISM AND MESMERISM.

It appears to the Author that the time has now come, when a tolerably definite opinion
may be formed regarding a large number of the phenomena commonly included in the term
"Mesmerism." Notwithstanding the exposures of various pretenders, which have taken
place from time to time, there remains a considerable mass of phenomena, which cannot
be so readily disposed of, and which appear to him to have as just a title to the attention of
the scientific Physiologist, as that which is possessed by any other class of well-ascertained
facts.

Passing over, for the present, the inquiry into the manner in which these effects may be
induced, the Author may briefly enumerate the principal phenomena which he regards as
having been veritably presented in a sufficient number of instances, to entitle them to be
considered as genuine and regular manifestations of the peculiar bodily and mental condition
under discussion.

1. A state of complete Coma or perfect insensibility, analogous in its mode of access and
departure to that which is known as the "Hysteric Coma," and (like it) usually distin-
62

734 APPENDIX.

guishable from the Coma of Cerebral oppression by a constant twinkling movement of the
eyelids. In this condition, severe surgical operations may be performed, without any con-
sciousness on the part of the patient ; and it is not unfrequently found that the state of tor-
por extends from the Cerebrum and Sensory Ganglia to the Medulla Oblongata, so that the
respiratory movements become seriously interfered with, and a state of partial asphyxia
supervenes.

2. A state of Somnambulism or Sleep-waking, which may present all the varieties of the
natural Somnambulism, from a very limited awakening of the mental powers, to the state
of complete double Consciousness (§ 500), in which the individual manifests all the ordi-
nary powers of his mind, but remembers nothing of what has passed when restored to bis
natural waking state. This state of Somnambulism, in the form which it commonly takes,
is characterized by the facility with which the thoughts are directed into any channel which
the observer may desire, by the principle of " suggestion ;" and by the want of power, on
the part of the Somnambulist, to apply the teachings of ordinary experience to the correction
of the erroneous ideas which are thus made to occupy the mind. In these particulars, this
condition closely corresponds with that of Dreaming; and differs from it chiefly in the
readiness with which ideas are excited through the ordinary channels of sensation, and with
•which the bodily powers are called into action to give effect to the ideas thus aroused. The
emotional states are more easily brought into play, than the purely intellectual operations.
It is a peculiar characteristic of this condition, that the whole attention maybe so completely
fixed upon one object, that there is an insensibility to all impressions unconnected with it,
although every thing which bears upon it is fully appreciated. In this respect there is a
complete correspondence with the phenomena of ordinary somnambulism ; but there is this
difference, — that, from the greater subjection of the mind to external influences, it may be
more readily played upon, (so to speak) by the observer, and may thus be exclusively fixed
upon any object which he may direct. In this manner, a state of insensibility to pain may
be brought about, nearly as complete as that which occurs in the comatose state, by causing
the mind to be strongly and exclusively directed towards another object. This condition
rinds its parallel in that of Reverie ; in which strong impressions upon the body may be
unfelt, so long as the mind is engrossed upon some different train of thought.

3. A frequent phenomenon of this condition, and one which has its parallel in Natural
Somnambulism, is a remarkable exaltation of one or more of the Senses, so that the indi-
vidual becomes susceptible of influences, which, in his natural condition, would not be in
the least perceived. The Author has referred to a case (§ 532, note) in which such an
exaltation of the sense of Smell was manifested ; and in the same case, as in many others,
there was a similar exaltation of the sense of Temperature. The exaltation of the Muscular
Sense, by which various actions that ordinarily require the guidance of vision, are directed
independently of it, is a common phenomenon of the Mesmeric or Artificial, as of the
Natural, Somnambulism.

4. The Muscular system may also be excited to action in unusual modes, and with
unusual energy. Notwithstanding the fallacy of many of the cases of Cataleptic rigidity
which have been publicly exhibited, the Author is satisfied, from investigations privately
made, of the possibility of artificially inducing this condition. A slight irritation of the
muscles themselves, or of the skin which covers them, — as by drawing the points of the
ringers over them, or even wafting currents of air over the surface, — is sufficient to excite
the tonic muscular contraction, which may continue in sufficient force to suspend a con-
siderable weight, for a longer period than it could be kept up by any conceivable effort of
voluntary power. Further, by directing the attention exclusively to any sef *of muscles, and
by impressing the mind of the Somnambulist with the facility of the action to be performed,
a very extraordinary degree of muscular power may be called forth, even in very feeble
individuals. Thus the Author has seen a man of extremely low muscular development and
small stature, not only lift up a 28 Ib. weight upon his little finger, but even swing it round
his head with the greatest apparent facility, — having been previously assured that it was as
light as a feather. Upon taking up the same weight upon their own little fingers, the
Author and his friends were very glad to lay it down after raising it a foot from the ground ;
and the subject of the experiment (a respectable middle-aged man, who was not a regular
"exhibitor," and upon whom no suspicion of any kind rested) declined, when in his waking
state, even attempting to lift the weight, on the ground that it would strain him too much.

These are the principal phenomena of Artificial Somnambulism, in regard to which the
Author feels his mind made up. He does not see why any discredit should be attached to
them, since they correspond in all essential particulars with those of states, which naturally
or spontaneously occur in many individuals, and which he has had opportunities of per-
sonally observing, in cases in which the well-known characters of the parties placed them
above suspicion. When the facility with which the mind of the Somnambulist is played on
by suggestions conveyed either in language or by other sensations which excite associated
ideas, and the absence of the corrective power ordinarily supplied by past experience, are

APPENDIX. 735

duly kept in view, many of the supposed " higher phenomena" of Mesmerism may be
accounted for, without regarding the patient on the one hand as possessed of extraordinary
powers of divination, or on the other as practising a deception. Thus, hearing in mind
that Somnambulism is an acted dream, the course of which is governed by external impres-
sions, it is easy to understand how the subject of it may be directed by leading questions to
enter buildings which he has never seen, and to describe scenes which he has never wit-
nessed, without any intentional deceit. The love of the marvellous so strongly possessed
by many of the witnesses of such exhibitions, prompts them to grasp at and to exaggerate
the coincidences in all such performances, and to neglect the failures ; and hence reports
are given to the public, which, when the real truth of them is known, prove to have been
the results of a series of guesses, the correctness of which is in direct relation to the amount
of guidance afforded by the questions themselves. In like manner the manifestations of the
excitement of the " phrenological organs" seem to depend upon the conveyance of a sug-
gestion to the patient, either through his knowledge of their supposed seat, or through the
anticipations expressed by the by-standers. Many instances are recorded, in which the
intention has been stated of exciting one organ, whilst the finger has been placed upon or
pointed at another ; and the resulting manifestation has always been that which would flow
from the former. It does not hence follow that intentional deception is being practised by
the Somnambulist; since the condition of mind already referred to, causes it to respond to
the suggestion which is most strongly conveyed to it. Many of the emotional states are
readily excitable, by placing the muscles in the position which naturally expresses them ;
thus the combative tendency may be called forth by gently flexing the fingers, so as to
double the fist ; a cheerful hilarious mood may be induced by drawing outwards the cor-
ners of the mouth as in laughter ; and this may be exchanged for the reverse state of gloom
and ill-temper, by drawing the eyebrows downwards and towards each other, as in frown-
ing. In like manner, on putting the hand upon the vertex, the Somnambulist draws him-
self up, and shows the manifestation of self-esteem ; whilst the depression of the head into
the position of humility calls forth the corresponding emotion. Those who have carefully
observed the habits of infants and young children, must perceive the accordance of these
phenomena with those which continually present themselves at that early period of life,
when the condition of the mind is so completely under the government of suggestions re-
ceived from without.

In regard to the alleged powers, which are said to be possessed by many Somnambulists,
of reading with the eyes completely covered, or of discerning words enclosed in opaque
boxes, the Author need only here express his complete conviction that no case of this de-
scription has ever stood the test of a searching investigation.

The modes in which the Artificial Somnambulism may be induced, are extremely vari-
ous. The experiments of Mr. Braid have shown, that one of the most effectual is the con-
tinued convergence of the eyes upon a bright object, held at a small distance above and in
front of them, and gradually approximated towards them. The mere steady direction of the
eyes towards a distant object, in persons who have often practised the former method, fre-
quently serves to induce the state. All the phenomena described in the preceding para-
graphs, have been witnessed by the Author in individuals thus " hypnotized ;" and he
considers that this curious class of observations cannot be better prosecuted than by the em-
ployment of that method. He is not yet satisfied that, in the ordinary " Mesmeric " process,
any other influence than this is really exerted; but the patient is sent to sleep with the
dominant idea that some special influence is exerted by the Mesmerizer, and this idea affects
all the subsequent phenomena, — producing, for example, in some cases, insensibility to every-
thing but what is said by the mesmerizer or by an individual placed by him en rapport with
the Somnambulist. It will generally be found, that the degree of this supposed connection,
depends upon the notions of it previously formed by the individual Mesmerized. In the
hypnotic state, there is an entire absence of any such peculiar influence ; the Somnambulist
being equally conscious of what is said or done by every bystander.

The Author may refer to an Article in the British and Foreign Medical Review for April, "
1845, as on the whole expressing (although not written by himself) his opinions upon this
curious and interesting subject.

INDEX.

The Numbers refer to the Paragraphs.

ABERRATION, spherical, 535; chromatic, 535

Abnormal forms of nutritive process, 802 — S09

Abortion, 929

Abscess, 804

Absorbent cells, 181, 182

vessels, see Lacteals, and Lympha-
tics

ABSORPTION

Nutritive, general account of, 107, 271 ; by
intestinal surface, 672 — 675; by lacteals,
672,674; by blood-vessels, 673, 675; by
general surface, 676 — 681 ; by skin, 676 —
679 ; by lungs, 678, 775, 776
Interstitial, by lymphatics, 680, 681 ; by veins,

681 b
Of gases and vapours by lungs, 775, 776

Abstinence, cases of, 653

Actinia, nervous system of, 312, 313

Activity, varying, of nutritive processes, 786 —
791

Adapt! veness of movements, no proof of sensa-
tion, 306

Addison, Mr., his observations on blood-cor-
puscles referred to, 151, 158, 159; on fibril-
lation of liquor sanguinis, 136 ; on blood-ves-
sels of lungs, 758 ; on pus, 806

Adhesion, 793, 794

Adipose tissue, see Fat-cells

Aeration, 107 ; see Respiration

Afferent nerves, 289, 344

Age, influence of, on pulse, 727 a ; on excretion
of carbonic acid, 767 b ; on excretion of urea,
844; on activity of nutritive processes, 786,
812; on power of calorification, 893

Air, influence of respiration on, 765 — 768

Air-cells of lungs, 757, 758

Albinoism. 80

Albumen, 112; composition of, 114; properties
of, 113 — 115 ; conversion of into fibrine, 1 14,
117, 153 — 158; proportion of in blood, 697,
706; purposes of, 698; diminution of in blood,
707 d; predominance of in tubercular depo-
sits, 878

Albuminous principles of food, 640, 857 ; ap-
plication of in the animal body, 642

Albuminuria, 707 d

Alcock, Dr., his experiments on nerves of taste,
407

Alcohol, use of in supporting heat, 896 note

AJfourous, 105

Aliment, causes of demand for, 629 — 635; see
Food

Alimentary materials, 640 ; see Food

Allantoin, 845 c

Allantois, origin and uses of, 839 c

Allen and Pepys, their researches on respira-
tion, 765

American nations, 101

Amphibia, 31

Amphioxus, 110, 180; nervous centres of, 425

Anosmia, 707 c

Andral, M., on amount of carbonic acid excret-
ed, 767; on pathological changes in blood,
706, 707

Animal Heat, see Heat

Animal kingdom, primary subdivisions of, 5

Animal magnetism, Appendix II.

Animals, distinguished from Plants, 1 — 4
early development of, 3

Anselmino, on solid matters of cutaneous ex-
halation, 869

Aplastic deposits, 804, 807

Aplysia, 12, 15 ; nervous system of, 321

Apoplexy, decrease of fibrine in, 707 c ; death
by, 814

Arabian nations, 94

Arciform fibres of medulla oblongata, 353

Area pellucida, 936

Areolar tissue, 138, 139

Areas, comparative, of arteries, 710

Arnott, Dr., on stammering, 619; on the ven-
ous circulation, 7446

Arteries, distribution of, 710; area of, 710;
structure and properties of, 728 — 732 ; elas-
ticity of, 729 ; their contractility, proofs of,
730 ; its influence in regulating the circula-
tion, 732; their tonicity, 731; influence of
nerves upon, 623, 732

Articulata, 5, 16 — 19; segmental division of,
16 ; animal powers of, 17 ; nutrition of, 18 ;
bi-lateral sympathy of, 16 ; respiration and
heat of, 18 ; nervous system of, 324 — 334

Articulate sounds, 612 — 619; vowels, 613 —
615; consonants, 616, 617

Articulation, movements of, guided by sensa-
tion, 611, 617

Asphyxia, nature of, 778; phenomena of, 779;
780 ; referred to, 738, 740, 814, 820

Assimilation in Plants, 107; in Animals, 271,
781

Asthma, spasmodic, 504, 759

Atrophy, 789—791

62*

738

INDEX.

The Numbers refer to the. Paragraphs.

Attention, effects of, on sensations, 519 — 521
Auditory ganglia, in Fishes, 357 ; in Man, 422
Auditory nerve, 446 ; terminations of, in ear,

559
Auricles of heart, action of, 718, 719 ; capacity

of, 723 b

Automatic actions, 438 a
Azote, absorption and exhalation of, 766; ex-
cretion of, in urine, 819, 842 — 850 ; respira-
tion in, 769, 780

B.

BAKEY, Dr. M., his researches on the blood-
corpuscles referred to, 148 ; his embryologi-
cal researches referred to, 130, 900—918

Barry, Sir D., his experiments on the venous
circulation, 744 b

Basement-membrane, 135

Bat, peculiar sensibility of, 526

Batrachia, 31, 32; metamorphosis of, 32

Beaumont, Dr., his experiments and observa-
tions on digestion, 637, 649, 657—660, 664—
666

Becquerel on the heat of Plants, 889 a ; on the
heat of Animals, 891 ; on the heat of Muscle,
890

Bee, perfection of instinct of, 336; construction
of hexagonal cell by, 336 note ; uneducability
of, 429 b ; temperature of, 889 c

Bell, Sir C., his discoveries referred to, 344,
349,351,376,377,433

Bell, Mr. T., on the development of the teeth,
217 i ; on secretion after death, 624

Bellinger!, on the Spinal Cord, 349

Berger and Delaroche, their experiments on
Animal Heat, 888

Berber race, 94

Bernard, M. Ch., his researches on digestion,
658 b, 664 b, 669

Bibra, Von, his analyses of Bone, 196 ; of Teeth,
212

Bile, secretion of, 831 — 837; composition of,
833; amount of, 834 ; formed from venous
blood, 831 ; partly an excrementitious fluid,
836; effects of non-elimination of, 836;
sources of, 836 ; purposes of, in digestive
process, 660, 670, 671, 835

Birds, 33 — 41 ; skeleton of, 37, 38 ; respiration
and heat of, 33, 757, 889 c ; covering of, 36 ;
instinctive powers and intelligence of, 39,
479, nutritive system in, 40; bi-lateral sym-
metry in, 40; development of young in, 41 ;
blood-corpuscles of, 146 b, 149 ; brain of, 361

Bischofl', his experiments on respiration, 768

Bladder, contraction of, 390

Blake, Mr., his experiments on the Circulation,
725

Blind persons, acuteness of touch in, 525

Blondlot, M., his researches on digestion, 658
b, 664 b

BLOOD,

Physical and vital properties of, 69G — 70S ;
composed of liquor sanguinis and cor-
puscles, 696; proportion of components
of, in health, 697 ; purposes of, 698 ; total
amount of in body, 724

Structure of Red Corpuscles, 143, 144; form
of corpuscles, 145, 146 ; size of corpuscles,

146; chemical constitution of corpuscles,
147 ; origin of, from each other, 148 ; first
production of, in embryo, 149 ; purposes
of, in animal economy, 150
Colourless corpuscles, 151, 152; their uses

in the economy, 153 — 159
Serum, composition of, 697 ; milky, 697 e
Coagulation of, 699 — 705 ; due to fibrine
alone, 117, 118, 699; an act of vitality,
118, 700, 701 ; causes influencing, 701, 702;
proportions of serum and clot, 703; buffy
coat, causes of, 704, 705 ; composition of,
116 a; artificially producible, by retarding
coagulation, 699

Pathological changes in, 706 — 70S ; normal
proportion of chief constituents, 706 ; in-
fluence of abstinence and hemorrhage,
707 ; increase of fibrine in inflammation,
158, 707 a, 802; deficiency of fibrine in
fever and hemorrhagic diseases, 7076; in-
crease of corpuscles in plethora, 707 c;
diminution in chlorosis, anaemia, &c., 707
c ; decrease of albumen in Bright's disease,
707 d ; general depravation of, 70S ; imper-
fect elaboration of, in tuberculous cachexia,
.807

Changes produced in, by respiration, 769 —
772 ; difference of arterial and venous
blood, 769; excretion of carbonic acid from,
769 ; absorption of oxygen by, 766 ; gases
extracted from, 770 ; change of colour,
causes of, 771, 772 ; aeration of, by gene-
ral surface, 768
Organization of, 118, 700, 796
Movement of through vessels, see Circulation
Blood-discs, see Corpuscles
Blood-vessels, see Arteries, Capillaries, and

Veins

Bone, 192—207; structure of, 192 — 196; form-
ation of, in membrane, 197 ; in cartilage,
198 — 200 ; chemical composition of, 196 ;
growth of, 201 — 203; regeneration of, 204
—207
Bouchardat, M., his researches on digestion,

670

Bovista giganteum, 153 a
Bourgery, M., his observations on air-cells of

lungs, 757 a

Bowman, Mr., his observations on muscular

fibre, 226, 228, 231, 232, 590 a ; on mucous

membrane, 176; on structure of the kidney,

839—841 ; on fatty liver, 929

Brain, see Encephalon, Cerebrum, Cerebellum,

&c.
Brewster, Sir D., his law of visible direction,

543

Bright's disease of the Kidney, 707 d
Brodie, Sir B., his experiments on the Par Va-

gum, 414, a; on animal heat, 890
Bronchial tubes, contractility of, 410, 759
Brunner's glands, 875

Buchanan, Dr., his researches on the blood re-
ferred to, 697 e

Budd, Dr. W., his cases of reflex action re-
ferred to, 365 — 369 ; his observations on
symmetrical diseases referred to, 785, 882
Buffy coat, 704, 705
Bulbus arteriosus, 940, 943
Bushmen, 70

INDEX.

739

The Numbers refer to the Paragraphs.

C.

CACOPLASTIC deposits, S07
Callus, formation of, 206
Cancer, 809, 881
Capacity of respiration, 764
Capillary vessels, distribution and size of, 219,
220 ; origin of, 221, 222 ; properties of their
walls, 739 ; absent in some tissues, 220 ; in-
dependent movement of blood in, 733 ;
proofs of, 734—739

Capillary circulation, 733 — 742 ; phenomena
of, 734; continues after cessation of heart's
action, 735; in acardiac foetus, 736; stagna-
tion of, in Asphyxia, &c., 738 ; influence of
local excitement on, 737 ; laws regulating,
739 — 741 ; connection of, with nervous in-
fluence, 742

Carbonic acid, excretion of, 749; sources of,
750 — 754 ; amount of, 765 — 767; made sub-
servient to introduction of oxygen, 766 ;
effected through the skin, 768 ; contained
in venous blood, 770; expiration of, in hy-
drogen, 769 ; influence of on colour of blood,
771, 772; effects of its retention in the sys-
tem, 778—780

, absorption of, by lungs, 776

Carnivorous animals, nutrition of, 644
Cartilage, structure of, 187 — 191 ; composition
of, 177, a ; nutrition of, 188, 191 ; ulceration
and reparation of, 191 ; ossification of, 198
—200

Catamenia, 908, 909
Caucasian race, 93

Cells, the types of Organization, 259 ; compose
bulk of fabric of Vegetables, 106—109 ;
origin of, 122 — 124; transformations of,
120, 121

Origin of animal structures in, 110; indi-
vidual growth of, in animals, 126, 127;
history of development of, 128 — 131 ;
transformations of, 132, 133, 223; indi-
vidual life of, 126, 811; continual death
of, in living body, 108, 261, 811 ; varying
duration of, 811, 812

Functions of, general, 110, 126, 132,259;
in Absorption, 181, 182, 271, 672; in As-
similation, 153, 154, 271 ; in Secretion,
174, 179, 278, 821—823; in Reproduc-
tion, 174,281, 902

Persistence of, in animal tissues, 180 ; in
pigment, 163, 164; in fat, 184; in shell,
192 ; in epidermis and epithelium, 160 —
174 ; in cartilage, 187 ; in muscle, 230 ;
in nerve, 245

Replacement of by Fibres, 134, 136
Cellular Plants, 106
Cellular tissue, see Areolar tissue
Cellulose, Vegetable, 4, 111
Cementum of teeth, structure of, 208, 211;

composition of, 212; development of, 216
Centipede, nervous system and actions of, 326

—329

Cerebellum, 340, 457—470 ; of Fishes, 357 ; of
Reptiles, 360; of Birds, 361 ; of Mammalia,
362 ; of Human embryo, 358, 359, 361; re-
lative dimensions of, 457, 458, 461 ; experi-
ments on, 459, 460, 463 ; observations on
size of, in castrated animals, 468, 469 ; con-
nection of, with motor power, 459 — 465 ;

with sexual instinct, 466 — 470; pathological
changes in, 464, 465, 467 ; phrenological ac-
count of, 470

Cerebro-spinal fluid, 476, 477
Cerebrum, 340, 471 — 495; general structure
of, 472—474 ; of Fishes, 357 ; of Reptiles,
360 ; of Birds, 361 ; of Mammalia, 362; of
Human embryo, 358, 359, 361 ; general
functions of, 478 — 480; relative dimensions
of, 481 — 484 ; experiments on, 485 ; patholo-
gical changes in, 486 ; connection of, with
intelligence, 485 — 495; with the will, 487,
494 ; distinct functions of several parts of,
Appendix I. ; peculiar conditions of, in sleep,
somnambulism, &c., 499, 500, Appendix II.
Ceruminous glands, 872
Chstodon rostratus, 490
Change, involved in idea of life, 254
Cheselden's case of cataract, 541
Chimpanzee, 51 — 59
Chlorosis, 707 c
Chondrine, composition and properties of, 141,

187 a

Chorda dorsalis, ISO, 937
Chorda? vocales, 603, 605, 607
Chorea, 504 note
Chorion, production of, 918; subsequent changes

in, 918, 920—923
Chossat,his experiments on inanition, 652, 895,

896

Chyle, 674 ; formation of, in intestines, 660 ; ab-
sorption of, 181, 672 ; analysis of, 691; aspect
of, 692 ; changes of, in progress through
lacteals, 692, 693 ; globules contained in,
their nature and source, 155, 693 ; their
destination, 154 — 159, 693 ; chyle from tho-
racic duct, 693, 695; relative constitution
of, 691

Chyme, formed by digestive process, 657 — 660
Chymification, 663 — 669; a chemical action,

667

Cicatricula, 936
Cilia, 171—173
Cineritious matter, 246
CIRCULATION

General account of, 272 ; objects of, 709 ;
course of, in Man, 710 ; arterial trunks,
710; capillaries, 219, 710; veins, 710
In Plants, 712 — 714; in lower Animals, 715,

716

Action of Heart, 719 — 727; connection of,
with nervous system, 416, 576, 580,
717; rhythmical movements of, 717 — 719;
sounds of, 720, 721 ; course of blood in,
722; differences of two sides, 723 ; quan-
tity of blood impelled by, 724, 725; force
of contractions, 726 ; number of contrac-
tions, 727

Action of Arteries, 728—732; their elas-
ticity and contractility, 728 ; influence of
their elasticity, 729 ; proofs of their con-
tractility, 730; their tonicity, 731 ; influ-
ence of their contractility, 732
Independent motion in capillaries, 733 —
742; proofs of, 734—738; stagnation in,
738, 740; influence of capillaries in regu-
lating amount of flow, 740 ; contractility of
capillaries, 739; general principles of their
action, 751 ; influence of nerves on capil-
lary circulation, 742

740

INDEX.

The Numbers refer to the Paragraphs.

Motion of Blood in Veins, 743 — 745 ; struc-
ture and properties of veins, 743 ; causes
of flow of blood through, 744 ; influence
of gravity upon, 745

Peculiarities of circulation, in lungs, 746 ; in
portal system, 6S5, 746 ; in cranium, 476,
747; in erectile tissue, 748; in foetus,
early state of, 938—940 ; subsequent con-
dition of, 943—944
Disorders of circulation, SSI

Civilization, influence of, on development of
human body, 87 — 90

Clot, of Blood, see Crassamentum

, organization of, 118, 119, 700,

796

Coagulable lymph, see Liquor Sanguinis

Coagulation, of blood, 699 — 705; due to fibrine
alone, 117, 118, 699; an act of vitality, 118,
700, 701 ; circumstances influencing, 701,
702 ; proportion of serum and clot, 703 ; of
chyle, 117, 693; of lymph, 694; of fibrine,
117—119

Coathupe, Mr., his experiments on respiration,
764; on products of combustion of charcoal,
776 note

Coccochloris, 125

Cochlea, 566

Cockchafer, 19

Ccecilia, 31

Coition, act of, in Male, 904 ; in Female, 911

Cold, degree of, endurable by Man, 987 ; death
by, 814, 895, 896 ; means of producing, in
the living body, 897; influence of, on young
animals, 893, 894

Collard de Martigny, his experiments on re-
spiration, 769, 774

Colostrum, 854 a, 856

Colour of Skin, 79 — 81 (see Pigment-cells)

Colourless corpuscles in blood, 151 — 158

Colours, impressions made by, 552 ; comple-
mentary, 552; deficiency of power of distin-
guishing, 553

Combe, Dr. A., quoted from, 658 a, 666, 671

Commissures of Brain, 474 ; deficiency of,
474 a

Complementary colours, 552

Conception, aptitude for, 909; act of, 911,
927

Conchifera, nervous system in, 317, 318

Concussion of brain, effects of, 580, 625

Consciousness, double, 500

Consensual movements, 335; of Articulata,
336; ofVertebrata, 337, 430— 436; of Eye-
balls, 450—456

Consonants, 616

Contractility of Muscle, 573; two forms of,
574 ; of arteries, 730, 731 ; of Capillaries,
739 ; of bronchial tubes, 410, 759 (see Irri-
tability)

Contraction of Muscle, mode of, 230, 575,
576 ; causes of, 575, 576 ; alternating with
relaxation, 575,577; after death, 578, 595 —
597 ; dependent on arterial blood, 583, 584 ;
power of, the same at different degrees of
extension, 592 ; energy of, in Man, 598 ; in
Insects, 599; rapidity of, 600

Convolutions of Brain, 472

Convulsive diseases, 502 — 504

Cooling power of cutaneous exhalation, 897

Cooper, Sir A., his experiments on circulation

on

ney,

through cranium, 290 ; his researches
mammary gland and its secretion, 853

Coral, 6

Corallines, 4

Cornaro, his diet, 653

Cornea, structure and nutrition of, 189

Corpora Albida, 914

Cephaloidea, 914

Lutea, 912-914

Malpighiana, of Spleen, 683; of Kid-

8396

Olivaria, 352, 353

Pyramidalia, 352, 353

Quadrigemina, 422, 436

Restiformia, 352, 353

Rubra, 914

Striata, 423, 424

Wolffiana, 26, 839 c

Corpus Callosum, 474

Corpuscles, Red, of Blood, 143 — 150; struc-
ture of, 143, 144; form of, 145, 146; size of,
in Mammalia, 146a; in Birds, 1466; in Rep-
tiles, 146 c; in Fishes, 146 d; chemical con-
stitution of, 147; origin of, 148; production
of in embryo, 149; large in foetus, 149; uses
of, in animal economy, 150, 698; proportion
of in Blood, 697; increase of, in plethora,
707 c; diminution of, in chlorosis, 707 c

Colourless, of Blood, 151—159 ;

characters of, 151; movement of, 152; uses

of, 153— 159

of Chyle, 155

of Lymph, 155

of Spleen, 684 b

of Supra-Renal Capsules, 686

Cortical Substance, of Brain, 472

, of Kidney, S39 a

Convulsive diseases, 501 — 504

Cotyledons of Ruminants, 921

Coughing, act of, 381

Cranium, circulation in, 476, 747; forms of in
different races of Men, 81 — 87

Crassamentum of Blood, 696

Crowing inspiration of infants, 504

Crusta petrosa of teeth, 208, 211, 212, 216

Cruveilhier, M., his observations on heart, 718
— 722; on purulent deposits, 837 a

Crying, act of, 380

Cryptogamia, reproduction in, 899

Crystalline lens, 190

Currie, Dr., case of dysphagia related by, 677

Cutaneous follicles, perspiratory, 868 — 870;
sebaceous, 872

Cuttle-fish, nerves of arms in, 322, 323; ejec-
tion of ink by, 438

Cutis anserina, 234

Cyclostome Fishes, 22

Cylinder-epithelium, 170

D.

DAB.TOS, contractility of, 234

Davy, Dr. J., his researches on animal heat,
886

Death, somatic and molecular, 813 — 816,880;
death of individual cells, 811, 812 ; by as-
phyxia, 814; by cold, 814, 895; by syncope,
814; by necramia, 814; by retention of se-
cretions, 278, 832, 842

INDEX.

741

The Numbers refer to the Paragraphs.

Decay, constant in Animal body, 268, 632, 633,

750 (see Disintegration)
Decidua, formation of, 919
Decomposition, continual, in living beings, 268,

632, 633 (see Disintegration)
Decussation, of optic nerves, 445
Defecation, movements concerned in, 391, 392
Degeneration, of nervous structure, 263, 292 —
296; of muscular fibre, 239, 263, 586; of ele-
ments of blood into pus, SOO, 805 ; into tu-
bercle, 807. SOS

Deglutition, 382—386; a reflex action, 382,
383 ; nerves concerned in, 384, 385; actions
preceding, 386 a-c; in Polypes, 382
Delaroche and Berger, their experiments on

Animal Heat, S8S
Dental groove, 217
Dentine, 208; structure of, 210; composition

of, 212; development of, 213, 214
Dermo-skeleton, 20
Despretz, M., his researches on animal heat,

S92
Devergie, M., his table of development of foetus

at different ages, 947
Diabetes, 879

Diaphragm, movements of, 761
Diathesis, gouty, S7S, S84; saccharine, 879;

tubercular, 878
Diet-scale, see Food
DIGESTION,

General account of, 270; in lower Animals,
655; alimentary materials, 641 ; their re-
spective destinations, 642 — 647; inorganic
substances, 648; relative digestibility of
different kinds of food, 666; importance of
bulk, 666

Processes of, 656 — 662 ; mastication and
insalivation, 656; deglutition, 656; con-
dition of stomach in, during health, 657 ;
disorder of, 658 ; entrance of food into
stomach, 659 ; movements of stomach,
659; expulsion into duodenum, 660; pas-
sage along intestines, 661 ; discharge of
faeces, 662

Chemical phenomena of, 663 — 671 ; compo-
sition and properties of gastric juice, 664;
its chemical action, 665, 667 ; artificial so-
lution of food , 668 ; Wasmann's researches
on pepsin, 668 ; Bernard and Barreswill's
researches, 669 ; conversion of saccharine
and oleaginous principles, 670, 671
Influence of nerves upon, 387, 413 — 415
Interstitial, according to Dr. Prout, 681
Digestive cavity in lower animals, 655 ; origin

and formation of, 937, 945
Direction, law of visible, 543
Discs, of Blood, see Corpuscles
Disintegration of Muscular tissue, 239, 263,

586 ; of Nervous tissue, 263, 292—296
Distance, adaptation of eye to, 536 ; estimate

of, 548

Diving animals, 77S
Dobson, Mr., his experiments on the Spleen,

f*c* "

6So

Domesticability of Animals, 39, 42
Donne, M., his observations on Milk, 854 a,

856 ; on temperature in disease, 886
Doris, gills of, 755
Dormant Vitality, 255
Dorsal vessel of Articulata, 18

Double consciousness, 500

Draper, Professor, on Capillary Circulation 713,

741

Dreaming, 499
Dugong, heart of, 710
Dulong, M., his researches on animal heat,

892

Dumas, his analysis of fibrine, 114
Duration of life in individual parts, 810 — 812
Dytiscus, experiments on, 328
Dzondi, on deglutition, 656

E.

EAR, general action of, 556; comparative struc-
ture of, 557, 558; distribution of auditory
nerve in, 559 ; uses of membrana tympani,
563; of tympanic cavity, 564; of labyrinth,
565, 566 ; of external ear and meatus, 567,
568

Echinodermata, 7 — 10; shell of, 192

Educability, of Birds, 39, 479 ; of Mammalia,
42, 480 ; of Man, 60

Edwards, Dr., his experiments on respiration,.
769; on animal heat, 888, 893, 894

Efferent nerves, 289, 344

Egg, see Ovum

Egg-shell, Membrane of, 118

Ehrenberg, on limits of vision, 540

Eighth Pair of Nerves, see Glosso-pharyngeal,
Par Vagum, and Spinal Accessory

Ejaculatio seminis, 372, 393, 904

Elaboration of fibrine, 116, 154 — 159

Elasticity of arterial walls, 728, 729

Elastic tissues, 138, 139

Electricity, not identical with nervous power,
297

Embryo, early development of, 915—917, 934
— 945 ; formation of germinal mass, 935 ; of
germinal membrane, 935, 936 ; of vertebral
column, 937; of amnion, 938 ; of vascular
area and umbilical vessels, 938, 939 ; of
heart and branchial arches, 940 ; of allan-
tois, 941; of umbilical cord, 941, 942; later
circulation in, 943, 944 ; influence of mo-
ther on, 946 ; table of development, 947;
size and weight of at birth, 948; proportion
of males and females, 949 ; relative viability
of, 950

Embryonic cell, 935, 936

Embryonic development, of brain, 358, 359,
361 ; of cephalic nerves, 420, 421 ; of lungs,
757 b, c ; of blood-corpuscles, 149 ; of liver,
826 g; of kidney, 839 c ; of heart, 940 ; of
circulating apparatus, 940, 943, 944; of di-
gestive cavity, 945

Emissio seminis, 372, 393

Emotions, influence of on Intelligence and
Will, 440; on nutrition and secretion, 625 —
628 '

Emotional actions, 437 — 440

Enamel, 208; structure of, 209 ; composition
of, 212; development of, 215

Endosmose, 271, 675

Encephalon, 356 ; comparative anatomy of, 357
— 362 ; weight of, in proportion to entire
body, 475 ; proportions of different parts,
in Fishes, 357 — 359 ; in Reptiles, 360 ; in
Birds, 361; in Mammalia, 362; in Human

742

INDEX.

The Numbers refer to the Paragraphs.

embryo, 358, 359, 361 ; supply of blood to,
476, 477

Epidermic tissues, 160 — 174; epidermis, 161,
162 ; hair, 166—168 ; nails, 162, 165 ; epithe-
lium, 169—174; nutrition of, 135, 161, 174;
functions of, 162, 174

Epilepsy, 503

Epithelium, 169 — 174; the real secreting struc-
ture, 174; cylindrical, 170; tesselated, 170;
ciliated, 171—173

Erect vision, 543

Erectile tissue, 748

Ethiopian nations, 97 — 99

Eustachian tube, uses of, 564

Eustachian valve, uses of, 944

Evans, Dr. Julian on the structure of the Spleen,
6S3, 684

EXCRETION,
Objects of, 275; of carbon, 275, 833 ; of ni-
trogen, 276, 842; result of decomposition,
275, 819; elements of, previously in blood,
820, 832, 842

Excretions, outlets of, guarded by spinal cord,
391

Exhalation, in Plants, 107 ; by lungs, 773, 774 ;
influenced by mental state, 774 ; from skin,
870, 871

Experiments on nerves, fallacies of, 302 — 306

Expiration, act of, 761

External Ear, uses of, 567

Exudation corpuscles, 800, 805

Eye, general action of, 536 ; an optical instru-
ment, 536; adaptation of, to distance, 536,
537 ; defects of, 538 ; optical powers of, 540;
consensual movements of, 450 — 456

F.

FACIAL nerve, 406

Fasces, composition of, 662

Fallopian tubes, passage of Spermatozoa
through, 911; passage of ova along, 911,
918; contractions of, produced by nervous
agency, 393

Falsetto notes, how produced, 609

Faraday, Mr., optical illusion discovered by,
551

Farre, Dr. A., discovery of Spermatozoa in
Ovum, 900

Fat-cells, 184; contents of, 185; uses of, 186;
formation of, 186

Fatty livers, 829

Feathers, 166

Fecundation in Plants, 899; in Animals, 900

Fever, state of blood in, 707 b

Fenestra ovalis, 557, 558

rotunda, 558

Fenwick, Mr., his experiments on absorption,
673

Ferments, action of, in digestion, 669; in
blood, 70S, 877

Ferneley, Mr., on areas of arteries, 710 a

Fibres, origin of, 118, 119, 136; white, 138,
140; yellow, 138, 142; mixture of in areolar
tissue, 138; in serous and synovial mem-
branes, 175; in mucous membrane and skin,
176, 177

of Muscle and Nerve, see Muscular

Fibre, and Nervous tissue

Fibrillae, ultimate of Muscle, cellular nature
of, 230

Fibrine, composition of, 114; properties of,
114, 115; coagulation of, 117—119; elabo-
ration of, 117, 158, 159; in chyle, 693; in
blood, 696 — 705; increase of, in inflamma-
tion, 158, 707 a, 802; diminution of, in fever
and hemorrhagic diseases, 707 b ; imperfect
elaboration of, in strumous diathesis, 807,
878; formed at expense of albumen, 114 —
117; effusion of, 803 ; organization of, 119,
700, 795, 796

Fibro-cartilage, 187

Fibrous tissues, simple, 138 — 142; origin of,
118, 119, 136

Fifth Pair of nerves, 403, 404 ; lingual branch
of, 404, 407; development of, 421; influ-
ence of, on organic processes, 625

Fishes, 26, 27; skeleton of, 26 ; respiration of,
27, 755; air-bladder of, 27, 755; kidneys
of, 838, 839 c; encephalon of, 357, 358;
circulation in, 27, 716; blood-corpuscles of,
146, d

Flourens, M., his experiments on the nervous
system, 432, 435, 436, 459

Fluids, absorption of, by intestinal surface,
674, 675 ; by general surface, 676, 677 ; by
veins, 675, 676; by lacteals, 674,675; by
lymphatics, 679

Fly-catcher, incubation of, 41

Foetus, table of development of, 947; circula-
tion in, 940, 943, 944; brain of, compared
with that of lower animals, 358, 359, 361 ;
see Embryo

Follicles of Lieberkuhn, 874

Food, causes of demand for, 629 — 635 ; differ-
ent kinds of, 640, 648 ; relative amount of
azote in each, 647; destination of, 641 —
646; desire for, 636 — 639; relative digesti-
bility of different kinds of, 666; mechanical
reduction of, 656 ; action of stomach upon,
657 — 659 ; passage of, into intestine, 660 ;
passage of, through intestinal canal, 661 ;
ejection of insoluble portion of, 662; mode
of solution of, 663 — 671 ; smallest quantity
of, on which life can be supported, 653;
greatest quantity that can be devoured, 654;
supply of, required by Man, 650, 651 ; suf-
ficiency of, indicated by satiety, 649 ; allow-
ance of, in Navy, 650; in Milbank Peniten-
tiary, 651 ; in Edinburgh House of Refuge,
651 ; in Convict-ship, 651 ; effects of insuf-
ficient supply of, 651, 652

Form, mode of acquiring knowledge of, by
touch, 523 ; by sight, 541, 542, 546, 547

Fourth pair of nerves, 405

Fourth ventricle, 346, 355

Foville, Dr., his observations on brain, 486

Freckles, 164

Fremy, M., his analysis of Nervous matter,
249

Frog, metamorphoses of, 31; excitable state
of spinal cord in, 401 a

Functions, 260 ; division of, into organic and
animal, 261, 262; connection of, 263 — 267;
of Animal life, 283—288 ; of Organic life,
268—282

Fungous growths, 809

INDEX.

743

The Numbers refer to the Paragraphs.

G.

GALL, Dr., his statements respecting the Cere-
bellum, 468

Gall-bladder, 825 e,f

Ganglia, structure of, 252, 245 — 247

of Special sense in Vertebrata, 422 —

425

of Sympathetic, 314, 342

Gangrene, 804

Gases, contained in blood, 770; absorption of,
by lungs, 775 — 777

Gasteropoda, Nervous System of, 319 — 321

Gastric fluid, composition and properties of,
664; action of, 665; secretion of, propor-
tional to wants of the system, 657 ; not de-
pendent on nervous influence, 414, 415 ; but
affected by it, 626, 637

Gelatine, composition of, 141

, of cartilage, 187 a; of bone, 196

Gelatinous principles of food, 640; application
of, in the animal body, 642

Gerber, Prof., referred to, 693 a

Germinal mass, 935

membrane, 935; serous layer, 936;

mucous and vascular layers, 936

spot, 905, 915

vesicle, 905, 906, 915—917

Gestation, signs of, 926; ordinary duration of,
928 — 930 ; protracted, 931 ; shortest period
of, 932

Gills, respiration by, 755

Glands, general structure of, 821 — 823

, lymphatic, 682

, vascular, 683 — 690

Globules, see Corpuscles

Globuline, composition of, 147

Glosso-pharyngeal nerve, functions of, 384,
407 ; development of, 420, 421

Glycerine, composition and properties of, 185 a

Glycicoll, 141 c

Goodsir, Mr., his observations on primary
membrane, 135; on the Teeth, 217; on
Bone, 194; on ulceration of Cartilage, 191 ;
on Absorption, 181, 672; on Vascular
Glands, 6S3; on Secretion, 822, 823; on
Milk-cells, 853 b; on formation of Decidua,
919; on structure of Placenta, 921 — 923

Gouty diathesis, 878, 884

Graafian follicle, 905, 912—914

Grainger, Mr., referred to, 345, 367

Granulation, process of, 799 — 801

Gravity, influence of on Circulation, 745

Greenhow, Dr., his plan of treating burns,
798

Grey matter of Nervous system, 245, 246; of
Brain, 472

Gryllotalpa, nervous system of, 332

Gulliver, Mr., his observations on blood-cor-
puscles referred to, 146, 149, 151, 156, 158;
on reparation of bone, 206 ; on chyle, 692

Guy, Dr., his researches on the Pulse, 727

H.

HABITUAL movements, 438

Hzmatine, 147

Hsmatococcus, 125

Hair, characters of, in different human races,

82; structure, growth, and composition of,
166—168

Hales, Dr., his experiments on the circulation,
726

Hall, Dr. M., his discoveries on the Nervous
system, 307, 345, 363, 365, 374, 375, 383,
386, 392, 394, 398, 400, 505 ; his views on
muscular irritability, 585, 589 6

Haller, his doctrine of muscular irritability,
591

Hastings, Dr., his experiments on capillary
circulation, 717 a; on animal heat, 890

Haversian canals, 193; formation of, 197, 199,
201

Hearing, sense of, 556 — 572 ; physical condi-
tions of, 557, 560 — 562; use of tympanum,
563 ; tympanic cavity and Eustachian tube,
564; chain of bones, 565; labyrinth, 566;
external ear, 567 ; auditory nerve, 559 ;
tones produced by succession of sounds,
569 ; estimate of degree, direction, and dis-
tance of sounds, 570; rapidity of perception
by, compared with sight, 571 ; uses of, in
regulating voice, 572, 611

Heart, 717; muscular fibre of, 234; inherent
contractility of, 717; rhythmical movements
of, 717 — 719; influence of nerves on, 416,
576,717 a-c; sounds of, 720, 721; course
of blood through, 722; differences of struc-
ture in two sides of, 723 ; difference of
valves, 723 c ; quantity of blood propelled
by, 724, 725 ; force of contraction of, 726 ;
number of contractions of, 727 ; various
causes influencing, 727 a-e ; origin of, 940 ;
subsequent development of, 943

Heat, Animal, amount of, developed by Man,
885, 886; in disease, 886; dependence of
on formation of carbonic acid, 889 — 892 ;
development of, in Plants, 889 a, b; in
lower animals, 889, c; effect of exercise on,
890 ; partly maintained by artificial respira-
tion, 896; dependent in part on cutaneous
respiration, 891 ; chemical theory of, 892;
heat of young animals, 893 ; variations in
power of generating, at different seasons,
894; loss of, during inanition, 895, 896 ; pro-
visions against excess, 897

Heat, external, influence of, on incubation of
Birds, 41 ; influence of, on vital actions in
general, 885; extremes of, endurable by
Man, 887, 888; power of resisting, 887,
888, 897

Heat, sexual, 909

Helmholtz, his observations on composition of
muscle, 238 b, 586

Hemiopia, 545 note

Hepatic artery, 826 d

cells, 183, S26/

duct, 826 c

vein, 826 a, e

Herbivorous animals, nutrition of, 645

Hering, experiments of, on circulation, 724

Heterologous growths, 809, 881

Hiccup, act of, 380.

Hippuric acid, 845 a

Holland, Dr., referred to, 521

Horny matter, composition of, 162

Horses, cerebella of, 468.

Hottentots, 100

Houston, Dr., on acardiac fffitus, 736

744

INDEX.

The Numbers refer to the Paragraphs.

Hunger, sense of, 412, 636—638

Hunter, John, on muscular tonicity, 593, 594;
on functions of lymphatics, 6S1 a, c ; on con-
tractility of arteries, 731 ; on union by ad-
hesion, 794

Hutchison, Mr., on capacity of respiration, 764

Hydra, 9; movements of, 313; reproduction
of parts in, 9, 792

Hydrophobia, 502.

Hymenoptera, nerves of wings of, 298 ; in-
stincts of, 336, 429

Hypertrophy, 787, 788

Hypoglossal nerve, functions of, 418, 419 ; de-
velopment of, 420, 421

Hysteria, 503 ; remarkable abstinence in, 653

I.

IDEAS, formation of, 488.

Idiots, actions of, 428, 474, 478, 484 .

Improvability of Man, 60

Inanition, Chossat's experiments on, 895, 896

Incontinence of urine, 401, 504

Indo-European nations, 95

Indian nations, 95

Infants, inferior calorifying power of, 893, 932 a

Inflammation, increase of fibrine of blood in,
707 a, 802 ; diminished vitality of the tissues
in, 803 ; results of, 804 — 806 ; generally un-
favourable to reparation, 793, 799 — 801 ;
prevention of, after injuries, 798; how far
concerned in deposition of tubercle, 808

Ingestion of food, actions concerned in, 382,
656

Insalivation, 656

Insects, Muscular apparatus of, 19 ; strength of,
599; instincts of, 17, 429,479; heat deve-
loped by, 889 c ; nervous system of, 325 —
336 ; reflex actions of, 328, 329 ; consensual
actions of, 336; circulation in, 715; respira-
tion in, 755

Inspiration, act of, 761

Instinctive actions, characters of, 428

Instincts, of Articulata, 17, 336,429,479; of
Birds, 479; of Mammalia, 42, 480; of Man,
428, 437—440, 484 ; of Cuttlefish, 438 ; of In-
fants and Idiots, 428, 484

Intelligence, of Vertebrata, 23, 482 ; of Birds,
479 ; of Mammalia, 480 ; of Man, 484 ; gene-
ral absence of, in Invertebrata, 429 ; seat of,
in the Cerebrum, 478

Intercellular passages, 218

Intervertebral nerves, 421

Intestines, peristaltic movements of, 388, 389;
passage of food through, 660, 661 ; glandular
of, 661, 874—876 ; secretions of, 66], 877

Intuitive perceptions, 490

Invertebrata, general absence of red corpus-
cles in, 150 ; character of blood of, 155

Iron, contained in food, 648 ; in blood-discs,
147; administration of, in chlorosis, 707 c

Irritability, of muscular fibre, see Muscle

lulus, nervous system arid actions of, 326, 329

J.

JENNINGS, Mr., on artificial insufflation of lungs,
760 a

Jewish nation, 80, 94

Jones, Dr. Bence, his observations on phos-
phatic deposits, 295 note

Jones, Mr. Wharton, his observations on blood-
corpuscles, 152, 159 a; on effects of inflam-
mation, 704 ; on capillary circulation, 780

K.

KELLIE, Dr., his experiments on circulation in
cranium, 747

Kidneys, general function of, 276, 819 ; struc-
ture of, 838, 839 ; cortical and medullary sub-
stances, 839 a ; tubuli uriniferi, 839 a; Mal-
pighian bodies in, 839 6; circulation in, 840;
embryological development of, 839 cj see
Urine.

Kiernan, Mr., on the liver, 826, 827

Kiesteine, in urine of pregnant women, 859,
926

Knight, Mr., observation on incubation of Fly-
catcher, 41

Kronenberg, Dr., on roots of spinal nerves, 304,
344

L.

LACHRYMAL gland, 865

secretion, 865; influence of nerv-

ous system on, 625, 626

Lacteals, origin and distribution of, 672 ; func-
tions of, 674, 675

Lactic acid, present in stomach during diges-
tion, 664 b ; not a constituent of urine, 846

Lacunae of bone, 193, 194

Lamina spiralis, 559

Lamprey, 22

Lane, Mr., his investigations on chyle, 693 a

Language, indication of affinity of races, 95 a

Laryngeal nerves, 378

Larynx, structure of, 602 — 604; action of, 604
— 611 ; muscles of, 604, 605

Laughing, act of, 380

Lecanu, M., his analysis of blood, 697 a; his
observations on urine, 844

Lehmann, his experiments on composition of
urine, 844, 849, 850

Letellier, M., his researches on respiration.
767 a

Leuret, M., his observations on Cerebellum,
468, 469

Liebig, Prof., on digestive process, 669 ; on
red corpuscles of blood, 150 a ; on compo-
sition of urine, 845 — 848; on uric acid, 845

Life, idea of, involves change, 254, 255 ; dura-
tion of, in individual parts, 259, 810 — 812

Ligaments, structure of, 140; vocal, 140

Ligamentum nucha:, 140

Light, laws of refraction of, 533 — 535 ; rapidity
of perception of, compared with sound, 571 ;
inlluence of, on metamorphosis, 32; effect
of, on pupil, 395, 443; influence of, on pig-
ment-cells, 164

Lime, an element of animal structures, 648

Lingual branch of fifth pair, 407

Lintott, Mr., his observations on the teeth,
217 c

Liquor sanguinis, 696 ; organization of, 117 —
119,795,796

INDEX.

745

Tlic Numbers refer to the Paragraphs.

Liver, general function of, 275, 819 ; univer-
sally present in Animal Kingdom, 825; size
and form of, in Vertebrata, 825 c, d ; gene-
ral structure of, 826 ; component cells of,
183, 826 /; distribution of portal vessels,
826 b ; of hepatic artery, 826 d ; of hepatic
vein, 826 a, e ; of hepatic ducts, 826 c ; con-
gestion of, 827; cirrhosis of, 828 ; embryo-
nic development of, 826 g; proportional
size of, before and after birth, 826 g, 830;
secretion of bile by, S31 — 836, see Bile;
other depurating actions of, 837
Lizards, 29

Locomotive actions, 397
Looped terminations of Nerves, 240, 248
Lungs, structure of, in lower Vertebrata, 756 ;
in Man, 737 ; development of, 757 a-c ; ac-
tion of, in respiration, 760 ; capacity of, 764;
chemical changes in, 765 — 767; exhalation
by, 773, 774 ; absorption by, 775, 776
Lymph, composition of, 691 ; elaboration of,
682; globules in, 155, 694 ; purposes of, 154
—159

Lymph, coagulable, see Liquor Sanguinis
Lymphatic glands, structure of, 682
Lymphatics, distribution of, through the body,
676 ; function of, 679, 680 ; specially con-
cerned in nutritive absorption, 680, 681

M.

MACARTNEY, Dr., his views on the reparative
processes, 793 — SOI

Macleod, Dr., on first production of blood-cor-
puscles, 149 a

Madden, Dr., his experiments upon absorption,
677, 775

Madder, effect of, on bones, 202 ; on teeth, 210

Magnetism, Animal, Appendix II.

Magnus, his experiments on the blood, 770

Malayo-Polynesian race, 103

Malignant growths, 809, 881

Mammalia, 42 — 50 ; sub-classes of, 44 ; skele-
ton of, 46 ; respiration and heat of, 47, 757 ;
subdivisions of, 48 ; brain of, 362 ; intelli-
gence of, 42, 485 ; blood-corpuscles of, 146 a

Mammary gland, 853; structure of glandule,
853, a, 6 ; development of, 853, c ; structure
of in male, 853 d ; secretion of, 854 — 861 ;
see Milk

Man, characteristics of, 51 — 61 ; erect attitude
of, 51 — 57 ; hand of, 57 ; other distinctive
characters of, 58 ; sensibility and locomotive
power of, 59 ; intelligence of, 60 ; soul of,
61; psychical operations in, 283 — 286; sub-
division of into races, 62, 63, 78 — 105; com-
mon origin of, 91 ; extremes of variation
amongst races of, 72 ; proper food of, 646

Mantis, nervous system of, 328

Margarine, composition and properties of, 185 a

Mastication, 656

Matteucci, his experiments on Electricity, 297

Mayer, Prof., his experiments on the Spleen,
685

Median nations, 95

Medulla Oblongata, 350 ; structure and connec-
tions of, 351 — 355 ; ganglionic character of,
355; general functions of, 370, 374, 384;

63

centre of respiratory movements, 374; cen-
tre of acts of deglutition, 384, 385

Medullary matter of nervous system, structure
of, 243, 246 ; functions of, 248

Melolontha vulgaris, 1!)

Membrana granulosa, 906, 912

Membrana tympani, uses of, 563

Membrane, basement or primary, 135 ; fibrous,
140; mucous, 176 — 179; serous and syno-
vial, 175

Membrane, development of bone in, 197

Memory, 491

Menstruation, 90S, 909

Metamorphosis of Batrachia, &c., 32, 630 a

Milk, peculiarity of as alimentary substance,
642, 647 ; general composition of, 854, 857 ;
microscopic characters of, 854 a ; constitu-
ents of, 854 b ; proportion of constituents in
human milk, 855 ; in milk of different ani-
mals, 858 ; quantity of, 860 ; change in cha-
racter of, during nursing, 856 ; consequences
of retention of, 859 ; transference of secre-
tion, 859 a; foreign substances entering,
861 ; influence of emotions on, 627 ; secre-
tion of, in male, 853 c

Milky aspect of Chyle, 692

serum, 697 e

Milbank Penitentiary, 651

Mind, elementary operations of, 487 — 495 ; in-
fluence of, on nutrition and secretion, 625 —
628

Mineral ingredients of Food, 648

Mitchell, James, case of, 532

Modelling process, 797, 798

Molecular base of Chyle, 692

Molecular death, 813, 815, 816

Mollusca, 5, 1 1 — 15; deficiency of symmetry
in, 11 — 13; organs of locomotion in, 13;
organs of nutrition in, 14 ; blood and respira-
tion of, 15 ; shells of, 192 ; nervous system
in, 315 — 322 ; circulation in, 715 ; respiration
in, 755

Mongolian nations, 96

Montgomery, Dr., on Corpus luteum, 913, 914;
on placental bruit, 925

Mother, influence of, on foetus, 946

Motions of Plants, 1, 230

Motor influence, laws of propagation of, 299

Motor linguae, 418, 419
oculi, 405

nerves, determination of, 300 — 303

tract of Sir C. Bell, 351

Mucous layer of germinal membrane, 936

Mucous Membrane, 176 — 179; of stomach,
appearance of, in health, 657 ; in disease,
658; intestinal, structure of, 661 ; glandular
of, in stomach, 873; in intestines, 874 — 877

Mucus, properties of, 179

Mulder, his analysis of albumen and fibrine,
114; of proteine and its oxides, 116; of
gelatine, 141 a

Muller, Prof., his researches on vision referred
to, 519,537,543, 552; on hearing, 561,562,
564; on blood, 699; on voice, 606— 610; on
respiration, 769; on cancer, 809

Muscular Fibre, 223 — 240 ; chemical composi-
tion of, 238

Structure of, 224, 225; in muscles of Animal
life, 225 — 233 ; arrangement of, in fasci-

746

INDEX.

The Numbers refer to the Paragraphs.

culi,226; composed of fibrillje, 226 ; en-
veloped in sheath, 227 ; form and com-
parative dimensions of, 228, 229 ; structure
of ultimate fibrillae, 230; state of, in con-
traction, 231, 233; origin of, 235, 236;
reparation of, 237; supply of blood-vessels
to, 239; supply of nerves to, 240; struc-
ture of, in Muscles of Organic life, 234;
development of, 235, 236; disintegration
of, from use, 239, 263, 586
Contractility of, 573, 574 ; irritability of, 575 ;
contraction alternating with relaxation,
576, 577; persistence of after death, 578 ;
depressed by sedatives, 579; by violent
nervous impressions, 580, 581; increased
by stimuli, 582; dependent on arterialized
blood, 583 — 585; increased by habitual
employment of particular muscles, 587;
diminished by want of action, 588 ; in-
fluence of nerves on, 589 — 591 ; loss of,
from section of nerves, 589 b, c ; restored
after exhaustion, 589 d; an independent
endowment, 591 ; difference of, on two
sides of heart, 585; the same at different
degrees of contraction, 592 ; power gene-
rated by, in Man, 598; in Insects, 599
Tonicity of, 593—597 ; effect of heat and

cold upon, 593, 594
Contraction of, after death, 595 — 597

Muscular Contraction, influence of, on Circu-
lation, 744 c

Muscular Sense, 433, 434

Tension, maintained through Spinal

Cord, 398, 399

Musk-deer, blood-corpuscles of, 146 a, 151 ;
hair of, 166

Myolemma, 227, 235

Myopia, 538

Myxinoid fishes, 180

Myriapoda, nervous system of, 326; develop-
ment of head of, 426 a

N.

NAILS, 162, 165

Necrsmia, 70S

Negro races, 97—99

Nerves, origin of, in ganglia, 246, 247; termi-
nations of, in muscles, 239 ; in skin and
sensory organs, 248 ; mode of determining
functions of, 300—306

Nervous agency, hypothesis on its nature, 297;
laws of its transmission, 298, 299; not es-
sential to Nutrition and Secretion, 620, 624 ;
influence of, on organic functions, 625 — 628

Nervous circle, 433

Nervous System, general functions of, 289, 307 ;
elementary structure of, 241 — 253; fibrous
matter of, 242 — 244 ; vesicular matter of, 245,

246 ; arrangement of fibres in ganglia, 246,

247 ; afferent and efferrnt fibres of, 289, 344 ;
use of plexuses in, 298; isolated course of
single fibres, 298; general purposes of, 307
— 309; dependence of its activity upon supply
of blood, 290, 291 ; functional activity of, in-
volves disintegration, 292 — 296; nature of
changes in, 297; existence of in lowest Ani-
mals, 311, 312; general recapitulation of

functions, 496 — 498; peculiar conditions of,
499 — 501 ; pathological states of, 501 — 505
Nervous system of Radiata, 313, 314; of Mol-
lusca, 315 — 323; of Articulata, 324 — 336; of
Vertebrata, 337—362

Nervous tissue, 241 — 253; fibrous element of,
242 — 244; cellular element of, 245, 246; re-
lation of two structures in, 246 — 248; com-
position of, 249; nutrition of, 250, 251; first
development of, 252; regeneration of, 253;
disintegration of, with use, 292 — 296; decay
of, when not employed, 442
Neuro-skeleton, 20

Newport, Mr., his observations on the blood-
corpuscles of Insects, 156; on their nervous
system, 325—330; on their temperature,
889 c ; on development of head of Myria-
poda, 426 a

Nitrogen, proportion of, in different articles of
food, 647; exhalation and absorption of,
766; respiration in, 769, 780; amount of, in
blood, 770
Nostoc, 125

Nucleus, 124; its offices and metamorphosis,
in Plants, 124, 125; in Animals, 128 — 133
Nucleus-filaments, 138
NUTRITION,

General account of, 273, 274, 781 ; connec-
tion of, with nervous system, 279; not de-
pendent upon nervous agency, 624; but
influenced by it, 624, 625
Essential nature of, 782; a continuous pro-
cess of cell development, 782, 783; select-
ing power of individual parts, 784, 785
Varying activity of, 786 — 791 ; affected by
age, 786 ; hypertrophy, 787, 788 ; atrophy,
789—791

Reparative processes, 792 — 801 ; reproduc-
tion of parts in lower Animals, 792; union
by first intention, 793, 794; organization
of liquor sanguinis, 119, 795; organization
of blood, 700, 796; modelling process of
Dr. Macartney, 797 ; circumstances favour-
able to, 798; granulation, 799 — 801
Abnormal forms of Nutritive processes, 802
— 809; inflammation, 802 — 804; suppura-
tion, 805, 806; tubercular deposit, 807.
808 ; cancerous growths, 809
Varying duration of different parts, 810 —
812; limited term of existence of cells,
811; variation of, with period of life, 812
Death, or Cessation of Nutrition, 813 — 816;
somatic and molecular, 813; somatic, by
Syncope, 814 ; by Asphyxia, 814; by Cold,
814 ; Molecular, consequent upon somatic,
815; dependent on local change, 816

O.

OBLIQUE muscles of orbit, 451
Oceanic races, 102
Octopus, nerves of, 298
Odoriferous glandule, 872
Odorous matter in blood, 872
Odours, sensibility to, 531, 532
(Esophagus, descent of food through, 386,656
Oleaginous principles of food, 640, 641 ; de-
stination of, in Animal body, 643 — 646, 671

INDEX.

747

The Numbers refer to the Paragraphs.

Oleine, composition and properties of, 185 a

Olfactory lobes, in Fishes, 357 — 359; in Rep-
tiles, 360; in Birds, 361; in Mammalia,
362; in Man, 422

Olfactive nerves, functions of, 331

Olivary bodies, 350—354

Omphalo-Meseraic vessels, 939

Optic lobes, in Fishes, 357 — 359 ; in Reptiles,
360; in Birds, 361 ; in Mammalia, 362; in
Human embryo, 358, 359, 361 ; in Man,
422 ; functions of, 436

Optic Nerve, 442 — 445 ; an excitor of motion,
443; decussation of, 445; termination of, in
retina, 539

Optic Thalami, 423, 424

Orang Outan compared with Man, 50 — 60

Orbicularis muscle, reflex action of, 394

Orbit, motor nerves of, 405; muscles of, 450,
451

Organic fibres of Nervous System, 244, 247,
341

Organization, connection of, with vital proper-
ties, 781 ; incipient in liquor sanguinis, 117
— 119 ; in coagulable lymph, 1 17, 795

Organs of Sense, their mode of operation, see
Ear, Eye, &c.

Ornithorrhyncus, 44; mammary gland of, 821

Ossification, in membrane, 197, 201 ; in carti-
lage, 198—201

Ostrich, incubation of, 41

Otter-breed, origination of, 70

Ovarium, origin of ova in, 905 — 907 ; corpus
luteum in, 913, 914

Ovisac, 907, 908

Ovum, component parts of, 905; origin of, 906,
907; maturation of, 909; arrival of sperma-
tozoa at, 900, 911 ; discharge of, from ovary,
912; first changes in, 915—918; later
changes in, 934 — 947

Owen, Mr., on blood-corpuscles of Siren, 145
note; on structure of dentine, 210 ; on forma-
tion of dentine, 213, 214 ; on formation of
enamel, 215 ; on formation of crusta petrosa,
216

Oxygen, introduction of, in respiration, 766;
presence of, in arterial blood, 770, 771 ; in-
fluence of, on colour of blood, 771, 772 ;
effect of respiration of, 777

P.

PAGET, Mr. J., on areas of arteries, 710 6 ; on
concentric hypertrophy of heart, 597 ; on
absence of corpus callosum, 474 o; on ac-
tion of heart, 717

Pancreas, structure of, 862 ; secretion of, 669,
670, 863

Papillae, of skin, 522 ; of tongue, 527

Papuans, 104

Paralysis agitans, 381 note

Paraplegia, cases of, showing reflex action,
366—369

Parturition, 393, 928, 929

Par Vagum, 408; the excitor of respiratory
movements, 374, 375; influence of, on pha-
rynx, 385 ; on cBSOphagus, 386 ; on stomach,
387 ; chief excitor of sense of hunger, 412,

637; effects of section of. on lungs, 409 —
411 ; on digestion, 412 — 415; on heart, 416

Pelagian-Negro races, 104

Pelvis, various forms of in different races of
Men, 88

Pepsin, 668, 669

Perception, 488—490

Perenni-branchiate Batrachia, 32

Peristaltic movements of intestines, 388, 575,
660; independent of nervous agency, 388;
influenced by spinal cord through sympa-
thetic, 388, 389

Peyerian glands, 874, 876

Philip, Dr. Wilson, his experiments on the Par
Vagum, 414, 415; on connection of Nervous
System with heart, 717 a; with Capillaries,
742 ; on animal heat, 890

Phosphorus, an element of food, 648 ; in pro-
teine-compounds, 113, 114; oxidation of, in
system, 847

Photophobia, 431

Phrenological doctrines regarding Cerebellum,
466—470

Phrenology, observations on, Appendix I.

Physiology, objects of the science, and mode
of pursuing it, Introduction,

Pigment-cells, 163, 164

Piementum nigrum, 164

Placenta, 44 ; formation and structure of, 920
—924

Placental souffle, 925

Plants, see Vegetables

Playfair, Dr., his observations on Milk, 855

Plethora, increase of blood-corpuscles in,
708 c

Plexus of nerves, use of, 298

Plica Polonica, 168

Plicae dorsales, 937

Pneumogastric nerve, see Par Vagum

Poisseuille, M., his experiments on the circu-
lation, 726, 729, 730

Polli, Dr., his observations on blood, 701, 702

Polydesmus, nervous system of, 326

Polynesian races, 103

Polypes, 6 — 10 ; circulation in, 715 ; reproduc-
tion of parts in, 9, 792; movements of, 313

Porrigo favosa, 809 a

Portal circulation, 685, 746; in liver, 826,
827 ; in kidneys, 839 b— 841

Portio dura, 406

Posterior roots of spinal nerves, 344

Pregnancy, signs of, 926 ; see Gestation

Presbyopia, 538

Prichard, Dr., his ethnographical researches
referred to, 63 note, 77, 92

Primitive trace, 936

Protecting agency of Spinal Cord, 394 — 396

Proteine, composition and properties of, 116

Proteus, 32; blood-corpuscles of, 146 c, 151

Prout, Dr., his classification of alimentary sub-
stances, 640 ; his observations on secondary
digestion, 681 ; on amount of carbonic acid
excreted, 767 ; on watery exhalation from
the lungs, 773; on urine, 845 d; on general
disorders of secretion, 883

Puberty, in Male, 903; in Female, 90S

Pulsation of heart, 717

of arteries, 729

Pulse, average frequency of, at different ages,

748

INDEX.

The Numbers refer to the Paragraphs.

727; variations of, under different circum-
stances, 727 a-e ; proportion of to respira-
tory movements, 762
Pulse, respiratory, 744 b

venous, 723 c

Pupil, action of, 395
Purkinje, optical experiment of, 555
Pus, production of of, 779, 800, 805, 806
Pyramids, anterior and posterior, 350 — 354

Q.

QUADRUMANA, 50

Quekett, Mr. J.,, his observations on bone re-
ferred to, 194 a

Quetelet, M., his researches on relative mor-
tality at different seasons, 699 c ; on length
and weight of infants at birth, 948 ; on rela-
tive viability of males and females, 950 ; on
comparative heights of males and females,
951

Quickening, 927

R.

RACIBORSKI, his researches on Conception, 909
Radiata, 5 — 10; general structure of, 5; affi-
nity with vegetables, 6, 7 ; symmetry in, S ;
reproduction of parts in, 9; nutritive organs
in, 10; nervous system in, 311 — 314
Rainey, Mr., his researches on structure of

lungs, 757

Recti muscles of orbit, 450
Red Corpuscles of Blood, see Corpuscles, Red
Reeds, vibrating, laws of, 606 c
Rees, Dr. G. O., his observations on blood-cor-
puscles referred to, 143, 144, 148; on com-
position of Chyle and Lymph, 691 ; on Saline
matter of Blood, 697 d
Reflex action, 313, 363 ; in Mollusca, 316, 317,
322; in Articulata, 327—329,335; in Ver-
tebrata, 337, 364—373
, cases of in Man, without sensa-
tion, 365—370

Regeneration of parts, in lower Animals, 9
792; of bone, 204—207, 792; of nervous
substance, 253
Reid, Dr. J., his researches on respiratory
movements, 374, 375 ; on movements o
deglutition, 384 — 386; on movements of sto-
mach, 3!S7 ; on glosso-pharyngeal nerve, 407
on pneurnogastric, 408 — 416 ; on laryngea
nerves, 378, 379 ; on spinal accessory, 417
on muscular contractility, 589; on irritabi
lity of heart, 717; on Asphyxia, 723 c
780 ; on capillary circulation, 740 ; on mu
cous membrane of uterus, 919 ; on structure
of placenta, 922
Reid, Dr. D. B., his researches on respiration

765

Reinforcement, fibres of, 326
Reparativc processes, 792 — 801 ; Dr. Macart
ney's views of, 793 — SOI ; union by first in
tention, 794; process of organization o
liijuor sanguinis, 119, 795; organization o
blood, 700, 796; modelling process, 797

causes favourable to, 798 ; granulation, 799
—801

lepetition of parts in Radiata, 6 — 9 ; in Ar-
ticulata, 324, 330
IEPRODUCTION,
General account of, 281, 282,898; in Plants,

109, 898, 899 ; in Animals, 900
History of, in Male, 901 — 904; spermatic
fluid, 867, 901 ; evolution of spermatozoa,
902 ; power of, 903 ; coitus, 904
History of, in Female, 905—933; general
account of ovum, 905; first development
of, 906, 907; menstruation, 908, 909;
aptitude for conception, 909, 910 ; coitus,
911 ; escape of ovum, 912 ; corpus luteum,
913, 914; first changes in ovum, 915 —
917; addition of chorion, 918 ; formation
of decidua, 919 ; formation and structure
of placenta, 920 — 924; sound of, 925 ; in-
crease of tissue of uterus, 926; quicken-
ing, 927 ; parturition, 928, 929; ordinary
duration of gestation, 930; protracted ges-
tation, 931 ; shortest term of gestation,
932 ; superfffitation, 933
Development of embryo, see Embryo
Reproduction of lost parts, 9, 792
Reptiles, 28 — 32; respiration and circulation
in, 28, 756; different orders of, 29, 30;
connected with Fishes by Batrachia, 31,
32; brain of, 360; blood-corpuscles of,
145, 146 c ; lungs of, 756
Resistance, sense of, 514
RESPIRATION,

General purposes of, 749—754; necessity
for, 749 ; in Plants, 750 ; in Animals,
generally, 751 ; in warm-blooded Verte-
brata, 752 ; variation in degree of, 753,
754

Structure and action of Respiratory organs,
in Invertebrata, 755 ; in lower Vertebrata,
756 ; structure and development of lungs
in Man, 757 ; arrangement of their blood-
vessels, 758 ; contractility of bronchial
tubes, 758 ; movements concerned in ex-
change of air, 760, 761 ; number and ex-
tent of, 762, 763 ; capacity of lungs, 764
Chemical phenomena, 765 — 768; carbonic
acid exhaled, 765; proportional amount
of oxygen absorbed, 766; absolute quan-
tity of carbon set free, 767 ; variations in,
767 a-i ; azote absorbed and exhaled,
766; cutaneous respiration, 768
Effects on the blood, 769 — 772; carbonic
acid in venous blood, 769, 770; exhala-
tion of, in hydrogen and azote, 769 ; com-
parative analysis of free gases in arterial
and venous blood, 770; causes of change
of colour, 771,772

To be regarded as an Excretion, 275, 749 ;
consequences of retention of carbonic
acid, 778 — 780 ; phenomena of Asphyxia,
779 ; its immediate causes, 780
Movements of, 760 — 763 ; dependent on
Nervous agency, 374, 375 ; centre of, in
Medulla oblongata, 376 ; nerves concerned
in, 374 — 376 ; independent of will and of
consciousness, 377 ; guard to entrances of
lungs, 378, 379; modifications of, 379 —
381 ; influence of pain on, 431, 763 ; num-

INDEX.

749

The Numbers refer to the Paragraphs.

ber of, 76.2, 763; share of lungs and air-
passages in, 759, 760; various influences
affecting, 763

Respiratory Circulation, 710 ; peculiarity of,
746

Respiratory pulse, 744 6

Restiform bodies, 350 — 354

Rete mucosum, 161

Retina, structure of, 539 ; the recipient of
visual impressions, 536; inversion of pic-
tures upon, 543; persistence of impressions
on, 551, 552 ; vanishing of images on, 554 ;
visual representation of, 555

Retinacula, 906, 912

Rigor Mortis, 232, 595—597

Ritchie, Dr., his researches on development
of ova, 907 ; on Menstruation, 909 ; on the
Corpus luteum, 914

Robinson, Mr., on effusion of fibrine, 803

S.

SACCHARINE principles of food, 640 ; destina-
tion of, 641, 643, 645, 670

Saliva, properties of, 656, 668, 863 ; incorpo-
ration of with food, 656

Salivary glands, structure of, 862 ; secretion
of, 863 ; influence of nervous system on,
625, 626

Saunders, Mr. E., his researches upon the
teeth, 217 k-m

Savart, M., his researches upon sound, 469 a

Scharling, Prof., his researches on respiration
767

Schleiden, his researches on the development
of cells in Plants, 124

Schwann, his experiments on muscular con-
traction, 592 ; his observations on cellular
origin of Animal structures, 135

Seasons, influence of on Calorification, 894

Sebaceous glands, 872

SECRETION, general nature of, 275—278, 817 ;
structures adapted for, 821 — 823 ; essen-
tially composed of cells, 821 — 823 ; disor-
ders of, connected with nutritive processes,
882 ; not dependent on nervous agency, 620,
624 ; influence of nervous system on, 625 —
628

Secretions, amount of, 818; sources of, 819
elements of, pre-existing in the blood, 820
some of them used in the system, 820 ; see
Bile, Urine, Milk, &c.

Seguin, on cutaneous exhalation, 870
Selecting power, of individual parts, 782 — 785
Semicircular canals, 366
Seminal secretion, 867, 901, 904; influencec

by state of feeling, 626 note
SENSATION, 307, 308 ; characteristic of Ani
mals, 283, 284; why associated with reflea
actions, 371, 372; dependent on Capillarj
Circulation, 290, 507, 508 ; the originator o
consensual movements, 430 — 432; the guide
of voluntary movements, 433
Sensations, nature of, 506 ; different kinds of,

507 ; dependence of on supply of blood,

508 ; pain or pleasure connected with, 509 ;
influence of habit on, 510 — 513 ; special,

514, 518 ; common, 514, 515 ; subjective
and objective, 516, 518, 521 ; transference
of, 517 ; influence of attention on, 519 — 521 ;
knowledge gained from, 487 — 490
Sense, Muscular, 433, 434
Sensibility in different parts, 507, 508
Sensitive Plant, movements of, 1
Sensorium, 435

ensory ganglia, 422 — 427 ; functions of, 428
—440

nerves, 441 — 449 ; terminations of, 248

tract of Sir C. Bell, 351

Serous membranes, 175

Serpents, 29

Serres, his measurements of Cerebellum, 457 ;

of Cerebrum, 481
Serum of blood, 696; composition of, 697;

proportion of, to clot, 703; milky, 697 e
Seventh pair, portio mollis of, 446 ; portio

dura of, 406
Sexual instinct, 903, 909 ; its supposed loca-
tion in the Cerebellum, 466 — 470
Sharpey, Dr., his observations on development
of bone, 197 — 201 ; on muscular fibrillae,
230, note ; on nerves of Cuttlefish, 322; on
decidua, 919
Shell, structure of, in Echinodermata, 192 ; in

Mollusca, 192
Siege of Landau, 946
Sighing, act of, 380
Sight, sense of, see Vision
Simon, Mr., on Thymus and Thyroid Glands,

687, 688

Single vision with two eyes, 545 — 547
Siren, 32 ; blood-corpuscles of, 145 note
Sixth pair of nerves, 405
Size, mode of estimating by vision, 549
Skin, structure of, 176, 177 ; contractility of,
234 ; absorbing power of, 676 — 679 ; respi-
ratory power of, 768 ; exhaling apparatus
in, S6S ; transpiration from, 869—871 ; seba-
ceous and ceruminous glands in, 872 ; exu-
dation from, increased by heat, 897
Skull, forms of, in different races of Men, 83

—87

Sleep, 499

Smell, sense of, 531, 532 ; seat of, 531 ; con-
ditions of, 531; acuteness of, in some Ani-
mals and Men, 532
Sneezing, act of, 381, 531
Sobbing, act of, 380
Solen, nervous system of, 317, 318
Somatic death, 813, 814
Somnambulism, 500, Appendix II.
Sound, laws of propagation of, 560 — 562; suc-
cessive pulses of, 569 ; mode of estimating
direction, distance, and intensity of, 570 ;
rapidity of perception of, compared with
that of light, 571 ; use of in regulating voice,
572,611
Sounds, articulate, 612—619

, of heart, 720, 721 ; of placenta, 925

Spasmodic diseases, '501 — 504
Species, discrimination of, 64 — 67; variation
within limits of, 68—73; distinguished by
physiological and psychological characters,

74 77

Spencer, Earl, on the duration of gestation in
Cattle, 931

750

INDEX.

The Numbers refer to the Paragraphs.

Spermatic fluid, 867

Spermatozoa, 900, 901 ; function of, 900, 911,
917; development of, 902

Sphincters, action of, 391, 392

Sphinx ligustri, Nervous system of, 325

Spinal accessory nerve, 411

Spinal Cord of Vertebrata, 346—350 ; its com-
parative anatomy, 346 ; its divisions, 346,

347 ; its connections with the nerves, 347,

348 ; functions of several parts of, 349, 350;
general functions of, 363' — 373 ; absence of
proper sensibility in, 365 ; protecting agency
of, 394 — 396; maintenance of muscular ten-
sion through, 398, 399 ; influence of, on
heart, 717 a; power of sustaining locomo-
tive actions, 397 ; pathological conditions of,
400,401,501—504

Spinal nerves, double roots of, 344
Spinal system, nerves of, 402 — 421
Spleen, structure of, 683 ; functions of, 684,

685

Sponges, 1, 7
Spongioles of Plants, 107
Stammering, causes of, 617, 618; treatment

of, 619
Star-fish, structure of, 8 — 10; nervous system

of, 312, 314

Stark, Dr., his analysis of Bone, 196 b
Stearine, composition and properties of, 185 a
Stereoscope, 546, 547
Stilling, Dr., his researches on the Spinal

Cord, 347

Stomach, presence of, characteristic of Ani-
mals, 2 ; general characters of, 655 ; state
of, in health, 657; in disease, 758 ; sense of
hunger referred to, 637 ; movements of, 387,
413, 659; influenced by nerves, 387, 413 ;
secretions of, 665, 873 ; influence of nerves
on, 414, 415 ; effects of blows on, 580, 625
Stomato-gastric system, of Mollusca, 319, 320 ;

of Articulata, 332—334
Strabismus, 454 a-d
Strangury, 504

Strings, vibrating, laws of, 606 a
Strumous diathesis, 878 (see Tubercle)
Subjective sensations, 516, 518, 521
Suction, act of, 386 c
Sudoriferous glandulse, 868 ; their secretion,

869, 870

Sulphur, contained in food, 648 ; in proteine-
compounds, 113, 114; oxidation of, in sys-
tem, 847

Superfo3tation, 933
Suppuration, 799 — 801
Supra-renal capsules, 686
Swimming-bladder, 27
Symmetrical diseases, 784, 785
Symmetry, radiate, 8 ; bilateral, of Articulata
18; of Vertebrata, 25; deficiency of, in
Mollusca, 12
Sympathetic System, peculiar fibres of, 244 ,
general structure of, 338, 341, 342; influ-
ence of, on movements of intestinal canal
388, 389 ; on ureter and muscular coat o
bladder, 390 ; on uterus and fallopian tubes
393; on heart and vessels, 416, 623, 717 b
730, 732 ; on ductus choledochus, 825 /
on processes of organic life, 620 — 628
Sympathies, motor, 620 — 623 ; organic, 625 —
628

Syncope, 580, 814
Synovial Membranes, 175
Syro-Arabian nations, 94

T.

TALIACOTIAN operation, 253

Taste, nerves of, 407, 447

Taste, sense of, 527 — 530 ; nerves concerned
in, 407, 447; conditions of, 528 : partly de-
pendent on smell, 529 ; educability of, 530 ;
purposes of, 529

Teeth, 208 — 217 ; component tissues of, 208
— 216; development of, in Human infant,
217, a-i ; a test of age, 217 k, I, m

Temperature, sense of, 514, 524 ; ordinary, of
the human body, 886 ; extremes of sustain-
able by Man, 887, 888 ; (see Heat)

Tendons, structure of, 140 ; attachment of to
muscle, 233

Tenesmus, 504

Tension of Muscles, 398, 399

Tetanus, 401, 502

Testis, structure of, 866 ; development of, 866
b ; secretion of, 867

Tessier's experiments on duration of gestation,
931

Thackrah, Mr., his observations on coagula-
tion of blood, 703

Thalami Optici, 423, 424

Thaumatrope, 551

Third pair of Cranial Nerves, 405
ventricle of Brain, 358, 359

Thirst, sense of, 639

Thorax, movements of, in respiration, 760,
761

Thymus gland, 687,688

Thyroid gland, 689

Tiedemann, his researches on absorption, 675

Tissues, elementary, classification of, 137

Todd, Dr., on mucous membrane, 873

Tomes, Mr., his observations on bone referred
to, 196, 203, 207

Tongue, papilla of, 527 ; movements of, 418,
419

Tonicity of muscles, 593 — 597 ; of arteries,
731 ; effects of deficiency of, 745

Tortoises, 29

Touch, nerves of, 448

Touch, sense of, 522 — 826 ; varying acuteness
of, indifferent parts, 522; ideas derived from,
514,523; peculiarities of, 524 ; improvability
of, 525 ; modifications of, in different ani-
mals, 526 ; connection of, with vision, 541,
542

Toynbee, Mr., his researches on non-vascular
tissues, 187—190

Trainers' diet, 654

Transudation, 824

Travers, Mr., his observations on formation of
new vessels, 222; on production of new tis-
sue, 795

Trifacial nerve, 403, 404

Tubercula Quadrigemina, 422, 436

Tubercular matter, 807, 808 ; tendency in the
system to deposit, 878

Tubular tissues, simple, 218 — 222; compound,
223—253

INDEX.

751

The Numbers refer to the Paragraphs.

Tunica granulosa, 906, 912

Turkish race, 96

Tunicata, nervous system and actions of, 316

Tympanum, membrane of, 563 ; cavity of, 564

U.

UMBILICAL cord, 941, 942

vesicle, 939, 941

Unguiculated Mammalia, 48, 49

Ungulated Mammalia, 48, 49

Unity, specific, of human races, 91

Urea, composition of, S44 ; increase of by ex-
ercise, 844

Uric acid, composition of, 845; pathological
changes in, 845 a-d

Urine, nature and purposes of its secretion, 842
— 852; effects of its retention, 842; com-
position of, in health, 843; amount of urea
contained in, 844; uric acid in, 845; hippu-
ric acid in, 845 a ; no lactic acid in, 846;
saline compounds in, 847; alkaline or acid
reaction of, 848 ; amount of azotized matter
in, 849 ; influence of diet on, 849, 850 ; trans-
ference of secretion, 851 ; excretion of saline
matter with, 852

Uterus, changes of, preparatory to gestation,
919; increase in substance during gestation,
926 ; contractions of, how far dependent on
nervous agency, 393, 928

V.

VAGUS nerve, see Par Vagum

Valentin, his researches on Spinal Cord, 349;
on movements of Stomach, 387 ; on the Sym-
pathetic, 388, 390, 393, 730 ; on Olfactory
nerve, 441 ; on Optic nerve, 442 ; on Portio
Dura, 406 ; on Par Vagum, 408, 416 ; on Spi-
nal Accessory, 417; on Hypoglossal, 418;
on quantity of blood in system, 724

Valves of heart, actions of, 722, 723 c; sounds
produced by, 720, 721

Vapour, exhalation of, from lungs, 773, 774

Variation, extremes of in species, 68 — 71 ; in
Man, 72, 73

Varicose nerve-tubes, 243

Vasa lutea, 939

Vascular area, 938

lamina of Germinal Membrane, 936,

938, 940

Vegetable proximate principles, 111

Vegetables, distinguished from Animals, 1 — 4;
food of, 2 ; movements of, 1, 283 ; early de-
velopment of, 3; formation of cells in, 106 —
109, 120—125; general functions of, 107,
261; circulation in, 712 — 714; respiration
in, 750 ; reproduction in, 899
Veins, distribution of, 710; structure of, 743;
movement of blood in, 744; causes of con-
gestion in, 745; pulsation in, 723 c

Ventricles of heart, contraction of, 718 — 721 ;

force of, 726 ; thickness of, 723 ; capacity of,

724

Ventricles of brain, third, 358; fourth, 346,

358
Vertebra, 21 ; origin of, 937

Verfebral column in Fishes, 26

Vertebrata, 5, 20—25 ; skeleton of, 21, 22; ex-
tremities of, 22; predominance of nervous
system in, 20, 23 ; organs of animal and vege-
tative life in, 25; symmetry in, 25; intelli-
gence of, 23 ; nervous system of, 339 — 362

Vesicles of Brain in Embryo, 358

Vessels, formation of, in Plants, 218 ; in Ani-
mals, 221, 222

Viability of Infant, earliest period of, 932

Vierordt, his researches on respiration, 765,
767

Villi of Mucous Membrane, 178, 472, 473

Visceral system of nerves, see Sympathetic

Visible direction, law of, 543

Vision, sense of, 533 — 555; optical conditions
of, 534—537; defective, 538; limits of, 540;
mental conditions of, 541 ; connection of,
with touch, 541, 542; erect, 543; single, 544,
545; appreciation of form by, 546, 547; of
distance, 548 ; of size, 549 ; persistence of
impressions, 551 ; complementary colours,
552 ; want of power to distinguish colours,
553; vanishing of images, 554; visual per-
ception of retina, 555

Vital Action involves change, 254

dependence of, on external stimuli,

255, 258

Vital Actions, classifications of, into Functions,
260

Vital forces, 256

Vitality, duration of in individual parts, 810 —
812; dormant, 255

of general system, destroyed by sudden

shock, 580, 735, 742

Vital properties, 256, 258 ; retention of, 259

Vitelline vessels, 939

Vitreous humour, 190

Voice, 602 — 619 ; conformation of larynx, 603
— 605; sounds resembling produced by
strings, 606 a ; by flute-pipes, 606 b ; by reeds,
606 c ; action of chordae vocales, 607; arti-
ficial larynx, 607 ; pitch, how regulated, 608 ;
falsetto notes, how produced, 609 ; influence
of air-passages on, 610 ; movements concern-
ed in, how directed, 611

Volkmann, his experiments on Muscular con-
traction, 576

Voluntary actions, distinguished from automa-
tic, 483 ; originate in Cerebrum, 483, 495

Vomiting, 505

Vowel sounds, 614, 615

W.

WAGNER, his observations on blood-corpuscles,
148, 155, 157, 159 a ; his account of develop-
ment of Spermatozoa, 902
Wasmann, his researches on pepsin 668
Waste of Animal tissues, see Decay, and Dis-
integration

Weber, Prof., his researches on sensation, 522 ;
on absorption, 672; on movements of heart,
717 a

Whale, Spermaceti, peculiar sensibility of, 526
Wheatstone, Prof., his Stereoscope, 546, 547
White corpuscles of blood, 151 — 159
White fibrous tissue, 138—141

752

INDEX.

The Numbers refer to the Paragraphs.

White matter of nervous system, 242, 243 '

Williams, Dr., on contractility of bronchi, 759;
on Necrcemia, 708; on Inflammation, 158;
on causes of Venous Congestion, 745

Willis, Mr., his researches on the Voice, 604 —
608

Wilson, Mr. Erasmus, on cutaneous follicles,
868

Wings of Insects, interlacement of nerves sup-
plying, 298; rapidity of motion of, 600

Wollaston, Dr., his observations upon sound,
569 a ; upon hemiopia, 545 note

Y.

YAWNING, act of, 390
Yellow fibrous tissue, 138—142
Yolk, 905, 935, 939
Yolk-bag, 905, 935, 939

Young animals, lowcalorifying power of, 893,
932 a ; influence of cold upon, 893 c

Z.

ZONA pellucida, 905,917

Zwicky, Dr., on organization of thrombus, 700

THE END.

,